Organometallics 1996,14, 3014-3029
3014
C2B3 and C2B4 Carborane Ligands as Cyclopentadienyl Analogues: Early Transition Metal Complexes1 Kenneth E. Stockman, Karl L. Houseknecht, Eric A. Boring, Michal Sabat, M. G. Finn,* and Russell N. Grimes* Department of Chemistry, University of Virginia, Charlottesville, Virginia 22901 Received February 27, 1995@ This paper reports the directed synthesis, characterization, and reactivity of a series of tantalum, niobium, and zirconium sandwich complexes incorporating small carborane or cobaltacarborane ligands, centered on the development of suitable families of reagents for eventual application to organic synthesis. Complexes of the types (R12C2B4H4)MC12Cp'and (Et2C2B4H4)ZrCl*THFCp' (R1 = Et, SiMe3, or Me; Cp' = C5H5 or CsMes; M = Ta, Nb) were prepared from Cp'MC1, reagents (M = Ta, Nb, Zr) and the R12C2B4H5- monoanion in THF. Similar treatment of the Cp*Co(EtzCzB3H4)- cobaltacarborane anion (Cp* = CsMe5) afforded the bent triple-decker sandwich complexes [ C ~ * C O ( E ~ ~ C ~ B ~ H ~(M ) I= MTa, C ~N~b) C.~Both ' families of compounds were obtained generally in high yield as air-stable crystalline solids t h a t are readily soluble in organic solvents. In the Ta and Nb species, replacement of one or both chlorines with a variety of alkyl groups was effected via reactions with alkylating agents to generate (R12C2B4H4)Ta(L)C1Cp' or (R12C2B4H4)ML2Cp' (M = Ta, Nb), and the corresponding alkylated triple-deckers [Cp*Co(EbC2B3&)1Ta(L)ClCp' and [Cp*Co(EbCzB3H3)1TaL2Cp' (L = Me, Et, Ph, CHzPh, CH2CMe3, or OPh). Yields of the mono- and dialkyl derivatives ranged from moderate to quantitative. The new complexes were characterized via lH, 13C,and llB NMR, mass spectrometry, and elemental analysis supplemented by FTIR and W-visible spectroscopic data for many compounds, electrochemical studies on selected species, and crystal structure determinations on seven products. Exploratory studies of the reactivities of these complexes revealed significant differences from those of standard organometallic species such as Cp2TiCl2 or CpzZrR2. Thus, tantalum and niobium C2B4 dichloro complexes on treatment with Al2Me6 gave dimethyl derivatives rather than methylidene compounds. The reaction of (EtzCzB4H4)TaMe2Cp with excess HBF4 in acetonitrile formed a single isolable product identified as a difluoro derivative, (EbC2B&)TaF2Cp. X-ray crystal structures were obtained for KMe3SikC2B4HdTaClzCp (lb),(EbC2Bfi)TaC12Cp*Co(EbC2B3&)TaMe2Cp* (IC),[Cp*Co(EbC2B3HdlTaC12Cp(4a),(EbC2B&)TaPhzCp (6d), ( C Hand ~ P(EbCzB4H4)NbMezCp ~)C~C~ (8a). Crystal data Cp (7b),C ~ * C O ( E ~ Z C ~ B ~ H ~ ) T ~(7c), for lb: space group P21Ia; 2 = 4; a = 14.292(4) b = 9.008(2) c = 17.899(7) ,8 = 112.61(2)";R = 0.043 for 2854 independent reflections. For IC: space group P21Ic; 2 = 4; a = 8.650(2) b = 12.3626) c = 18.601(7)8,p = 90.10(3)"*R = 0.038 for 1831independent reflections. For 4a: space group P21In; 2 = 4; a = 8.874(2) b = 14.303(4) c = 18.585(6) p = 91.53(2)";R = 0.036 for 3033 independent reflections. For 6d: space group Pi; 2 = 2; a = 8.943(1) b = 15.726(2) c = 7.843(2) a = 90.58(2)";,b = 102.78(2)"; y = 103.53(1)"; R = 0.024 for 3376 independent reflections. For 7b: space group P21In; 2 = 4; a = 8.998(2) b = 14.374(2) c = 18.508(3)A, p = 92.98(2)"; R = 0.027 for 3169 independent reflections. For 7c: space group P21In; Z = 4; a = 12.780(2) b = 16.084(2) c = 13.442(2) /?= 104.16(1)";R = 0.030 for 3684 independent reflections. For 8a: space group P21Ic; 2 = 4; a = 14.148(3) b = 7.781(5) c = 15.315(2) ,8 = 116.32(1)"; R = 0.031 for 2297 independent reflections.
A,
A,
A, A,
A, A, A,
A,
A,
A,
A,
The small carborane ligands nido-[RRC2B4H4I2-and arachno-[RRC2B3H512- (R, R' = H, alkyl, SiMe3) are sixelectron donors that form stable $ complexes with a variety of metal and metalloid fragments.2 These groups are isoelectronic with C5H5-, as are other boroncontaining ligands including nido-[RR'C2BgH9l2- (diAbstract published in Advance ACS Abstracts, June 1, 1995. (1)Organotransition-Metal Metallacarboranes. 38. (a) Part 37: Stephan, M.; Muller, P.; Zenneck, U.; Pritzkow, H.; Siebert, W.; Grimes, R. N. Inorg. Chem. 1996,34,2058. (b) Reported in part at the Fourth Boron U.S.A. Workshop, Syracuse, NY,July 1994; see Abstracts 9 and 68. Taken in part from: Stockman, K. E. Ph.D. Thesis, University of Virginia, 1995. (2) Recent reviews: (a) Grimes, R. N. Chem. Rev. 1992,92, 251. (b) Saxena, A. K.; Hosmane, N. S. Chem. Reu. 1993,93, 1081. @
A,
A,
A,
A,
A, A,
A,
A,
carbollide),%C4BR (borolyl), and R3C3B2R2 (diborolyl). The latter two ligand types,3 along with the bridgedeprotonated planar carborane unit [RRC2B3H3I4-, have a special property that adds a further dimension to metal coordination chemistry: they readily bind in v5 fashion to metals on opposite sides of the ring plane, generating extended families of stable multidecker sandwich c o m p l e ~ e s . l ~ ,Carborane-bridged ~~,~-~ systems of this type include triple-decker,2at e t r a d e ~ k e r ,and ~~,~ (3)(a) Siebert, W. Adu. Organomet. Chem. 1993, 35, 187. (b) Herberich, G. E.; Carstensen, T.; Koeffer, D. P. J.; Klaff, N.; Boese, R.; Hyla-Krypsin, I.; Gleiter, R.; Stephan, M.; Meth, H.; Zenneck, U. Organometallics 1994, 13, 619 and references therein.
0276-7333/95/2314-3014$09.00/0 0 1995 American Chemical Society
Carborane Ligands as Cyclopentadienyl Analogues
Organometallics, Vol. 14, No. 6, 1995 3015
Scheme 1
--
MCI, RZ
R1
I4
MCI, -
-
R' -
l o TaCIz 1b TaCI2
TaCI,, NbC14, ZrCI3 H, Me Me, Et, SiMeJ
IC
H H Me H H H Me
TaCIz
I d TaCI,
2
NbClz
30 ZrCI*THF 3b ZrCbTHF
Et SiMes Et Me Et Et
Et
RZ
CpToC14. Cp*TaCI,, or CpNbCI,
+
+
E.+tE
40 M 4b M 4c M
--
To, RZ To, R2 Nb. R2
-
H Me
H
(very recently) hexadeckelffCcomplexes as well as linked(12- 13-vertex) metallacarborane complexes of these sandwich oligomer^.^ Moreover, the carborane ligands elements were first reported by Hawthorne,8 but this have a well-documented ability to stabilize many transiarea has been reignited by the recent work of J ~ r d a n , ~ tion metal organometallic systems whose C5H5 or C5Bercaw,loand extensive studies by Stone.ll In the small Me5 counterparts are nonexistent or unstable, such as metallacarborane area, (17s-CsH8)M(Et2C2B4H4)(M = Ti, Fe(II1)- and Ru(II1)-arene complexes.6 While there V) and (17'-C7H7)Cr(EtzCzB4H4) were characterized in are exceptions, most metallacarboranes are resistant to our laboratories a decade ago,12and Hosmane et al. have air, heat, and moisture, and survive a far wider range prepared a number of Ti, Cr, Y, Zr, and Hf complexes of conditions (including multiple metal oxidation states) incorporating C2B4 l i g a n d ~ . ~Motivated ~J~ by the pothan do typical metal-hydrocarbon systems. tential for developmentfor new, stable catalytic systems Extensive studies of the synthesis, structures, and involving the early transition elements, we have initiated a study of the synthesis and characterization of a reactivity of small carborane metal complexes in one of family of Nb, Ta, and Zr complexes of C2B3 and C2B4 our laboratories have included the development of methods for placing a variety of organic and inorganic substituents at specific boron and carbon l o ~ a t i o n s . ~ ~ , ~ (8) (a) Lo, F. Y.; Strouse, C. E.; Callahan, K. P.; Knobler, C. B.; Hawthorne, M. F. J . A m . C h e h . SOC.1975,97, 428. (b) Salentine, C. This relatively facile tailorability enhances the utility G.; Hawthorne, M. F. Inorg. Chem. 1976,15,2872. of the carborane ligands as synthons, affording them a (9)(a)Crowther, D. J.; Baenziger, N. C.; Jordan, R. F. J . Am. Chem. range of steric and electronic properties that is unSOC. 1991,113,1455. (b) Uhrhammer, R.;Crowther, D. J.; Olson, J. D.; Swenson, D. C.; Jordan, R. F. Organometallics 1992,11,3098.(c) matched by cyclopentadienyl or any single family of Crowther, D. J.; Jordan, R. F. Makromol. Chem., Macromol. Symp. cyclopentadienyl analogues. An aspect of small carbo1993,66,121.(d) Uhrhammer, R.;Su, Y.-X.; Swenson, D. C.; Jordan, R. F. Inorg. Chem. 1994,33,4398. Fane chemistry that has been little explored is their (10)(a)Bazan, G. C.; Schaefer, W. P.; Bercaw, J. E. Organometallics complexation with early transition metals.2b Large 1993,12,2126.(b) Marsh, R.E.; Schaefer,W. P.; Bazan, G. C.; Bercaw, (4)(a)Piepgrass, K.W.; Holscher, M.; Meng, X.; Sabat, M.; Grimes, R. N. Inorg. Chem. 1992,31, 5202. (b) Pipal, J. R.; Grimes, R. N. Organometallics 1993,12,4452 and 4459. (c) Wang, X.;Sabat, M.; Grimes, R. N. J . A m . Chem. SOC.1994,116,2687. ( 5 ) Meng, X.; Sabat, M.; Grimes, R. N. J . A m . Chem. SOC.1993,115, 6143. (6)(a) Merkert, J. M.; Geiger, W. E.; Attwood, M. D.; Grimes, R. N. Organometallics 1991,10, 3545. (b) Stephan, M.; Davis, J. H., Jr.; Meng, X.; Chase, K. P.; Hauss, J.; Zenneck, U.; Pritzkow, H.; Siebert, W.; Grimes, R. N. J . A m . Chem. SOC.1992,114,5214. (7)(a) Piepgrass, K.W.; Grimes, R. N. Organometallics 1992,11, 2397. (b) Piepgrass, K.W.; Stockman, K. E.; Sabat, M.; Grimes, R. N. Organometallics 1992,11,2404. ( c )Benvenuto, M. A,; Grimes, R. N. Inorg. Chem. 1992,31,3897.(d) Benvenuto, M. A.; Sabat, M.; Grimes, R. N. Inorg. Chem. 1992,31,3904.
J . E. Acta Crystallogr. 1992,C48,1416. (11)(a) Stone, F.G. A. Adu. Organometal. Chem. 1990,31,53 and references therein. (b) Brew, S. A.; Stone, F. G. A. Adu. Organomet.
Chem. 1993,35,135. (12)Swisher, R.G.;Sinn, E.; Grimes, R. N. Organometallics 1984, 3,599. (13)(a) Siriwardane, U.; Zhang, H.; Hosmane, N. S. J . A m . Chem. SOC.1990, 112, 9637. (b) Oki, A. R.; Zhang, H.; Hosmane, N. S. Organometallics 1991, 10,3964. ( c )Oki, A. R.; Zhang, H.; Maguire, J. A.; Hosmane, N. S.; Ro, H.; Hatfield, W. E. Organometallics 1991, 10,2996. (d) Oki, A. R.; Zhang, H.; Maguire, J. A.; Hosmane, N. S.; Ro, H.; Hatfield, W. E.; Moscherosch, M.; Kaim, W. Organometallics 1992,11,4202.(e)Zhang, H.; Jia, L.; Hosmane, N. S. Acta Crystallogr. 1993,C49,453.(0 Hosmane, N.S.; Wang, Y.; Zhang, H.; Maguire, J. A.; Waldhoer, E.; a i m , W.; Binder, H.; Kremer, R. K. Organometallics 1994,13,4156.
Stockman et al.
3016 Organometallics, Vol. 14,No.6,1995
c9
c4
SI2
C6
d\ E5
ClR2
ClRl
/
ClR9A
\ ClR5
Figure 1. Molecular structure of [(Me3Si)zCzB4H4]TaClzCp (lb).
Figure 2. Molecular structure of (EtzCzB4H4)TaClzCp* (IC).
ligands that bear halide, alkyl, and/or hydride units on the metals. Results and Discussion Synthesis and Structure of (Ligand)M(Cadand (Ligand)M(CzBs)CoCp*Complexes. Carboranylcyclopentadienyl complexes of tantalum, niobium, and zirconium were prepared via disproportionation reactions between 2 equiv of [R12C2B4H& nido-carborane monoanions and CpTaCl4, Cp*TaC14, CpNbClr, or CpZrCls, forming the species la-d, 2, and 3a,btogether with neutral R12C2B4H4, which was recovered (Scheme 1). Compounds la-d and their derivatives (vide infra) are the only known tantalacarboranes other than the TaCZB9 icosahedral clusters reported earlier by Jordan et al.9 and a benzyne complex we reported recently (vide infra), while 2 is the first repokted niobium carborane complex of any type. As shown in Scheme 1 (bottom), analogous reactions of the nido-[Cp*Co(Et2CzB3HdImonoanion gave the bent triple-decker complexes 4ac. This method proved to be far more efficient than an earlier approach involving reactions of metal dihalides with the carborane dianions.14 All new complexes were characterized by lH, 13C,and llB NMR, mass spectrometry, and elemental analysis, supported in many cases by FTIR and W-visible spectroscopic data. X-ray crystal structures were obtained for lb,c and 4a, the molecular geometries of which are depicted in Figures 1-3. Data collection parameters and crystal data are presented in Table 1, bond distances and bond angles are listed in Tables 2-4, and tables of positional parameters as well as mean (14)Davis, J. H.,Jr.; Sinn, E.;Grimes, R. N. J. Am. Chem. SOC. 1989,111,4776.
CL2
ClRl
'W
C3E
C2R6
C2R9
Figure 3. Molecular structure of [Cp*Co(Et&B3H3)1TaClzCp (4a). plane calculations are included in the supporting information. The principal structural features in all three complexes, several of which are summarized in Table 5, are typical of metallocene dihalides and include normal metal-Cp, metal-carborane, and metal-Cl bond distances and Cp-M-C1 and C1-M-C1 bond angles. In
Organometallics, Vol. 14, No. 6,1995 3017
Carborane Ligands as Cyclopentadienyl Analogues
Table 2. Bond Distances and Selected Bond Angles for [(MesSi)&B&ITaCl&p (lb)
i
Ta-Cl( 1) Ta-Cl(2) Ta-C(2) Ta-C(3) Ta-C(lR1) Ta-C(lR2) Ta-C(lR3) Ta-C(lR4) Ta- C(1R5) Ta-B(4) Ta-B(5) Ta-B(6) Si(l)-C(2) Si(l)-C(4) Si(l)-C(B) Si(l)-C(6) Si(2)-C(3) Si(2)-C(7)
2
m
m
m
$ 2
Cl(l)-Ta-C1(2) Cl(l)-Ta-C(2) Ta-C(P)-Si(l) Ta-C(2)-C(3) Ta-C(2)-B(6) Ta-C(2)-B(7) Si(l)-C(2)-C(3) Si(l)-C(2)-B(6) Si(l)-C(2)-B(7) C(3)-C(2)-B(6) C(3)-C(2)-B(7) B(6)-C(2)-B(7) Ta-C(3)-Si(2) Ta-(C3)-C(2) Ta-C(3)-B(4) Ta-C(3)-B(7) Si(2)-C(3)-C(2) Si(2)-C(3)-B(4) Si(2)-C(3)-B(7)
Bond Distances, A 2.364(2) Si(2)-C(8) 2.354(2) Si(2)-C(9) 2.427(9) C(2)-C(3) 2.427(9) C(2)-B(6) 2.42(1) C(2)-B(7) 2.41(1) C(3)-B(4) 2.44(1) C(3)-B(7) C(lRl)-C(lR2) 2.44(1) 2.38(1) C(lRl)-C(lR5) C(lR2)-C(lR3) 2.41(1) 2.42(1) C(lR3)-C(lR4) C(lR4)-C(lR5) 2.42(1) 1.88(1) B(4)-B(5) 1.88 1) B(4)-B(7) 1.85(1) B(5)-B(6) 1.86(1) B(5)-B(7) 1.90(1) B(6)-B(7) 1.86(1) B(6)-B(7) Selected Bond Angles, deg 95.50(9) C(2)-C(3)-B(4) 85.4(2) C(2)-C(3)-B(7) 135.0(5) B(4)-C(3)-B(7) 71.9(5) B(4)-B(5)-B(6) 71.2(5) C(3)-B(4)-B(5) 95.8(6) C(2)-B(6)-B(5) 127.8(7) C(2)-Si(l)-C(4) 118.8(7) C(2)-Si(l)-C(5) 128.9(6) C(2)-Si(l)-C(6) 112.1(8) C(4)-Si(l)-C(5) 64.1(6) C(4)-Si(l)-C(6) 65.5(7) C(5)-Si(l)-C(6) 133.8(5) C(3)-Si(2)-C(7) 71.9(5) C(3)-Si(2)-C(8) 70.5(5) C(3)-Si(2)-C(9) 95.9(6) C(7)-Si(2)-C(8) 131.9(7) C(7)-Si(2)-C(9) 116.0(7) C(8)-Si(2)-C(9) 129.1(7)
1.84(1) 1.88(1) 1.51(1) 1.55(1) 1.74(1) 1.57(1) 1.73(1) 1.42(1) 1.41(1) 1.39(1) 1.40(1) 1.40(2) 1.71(2) 1.77(2) 1.66(2) 1.79(2) 1.79(2) 1.79(2) 110.9(8) 64.4(6) 64.6(7) 104.1(9) 105.7(8) 107.2(9) 113.2(4) 108.5(5) 110.3(5) 106.4(5) 112.2(6) 105.9(5) 117.0(5) 107.9(5) 105.8(5) 107.4(5) 110.4(6) 107.9(6)
Y
r
$ 9,
-
C
D
2
fix
each case, the carborane ligand is oriented with the sterically more demanding R1-C-C-R1 array on the "open" side of the complex. The dihedral (bending) angle subtended by the Cg and CzB3 ring planes is closely similar (50-54") in the three structures, and is significantly larger than the corresponding angle (ca. 48")in the bent-sandwich (SiMes)zCzB4H4-titanium complexes reported by Hosmane et al.13f This small but significant difference can be accounted for by steric interaction between the Cp and carborane ligands in the titanium complex, which limits the degree of bending; in the tantalum species, this limitation is less severe owing t o the larger metal center, allowing a slightly more bent geometry. The Cp* and C2B3 planes in 4a, on the other hand, are nearly parallel with a dihedral angle of only 8.4", typical of Cp*-metal-CzBs arrays (as discussed in earlier papers4). In the absence of other ligands on cobalt that could give rise to steric effects, this slight observed tilt is clearly of electronic origin and is related to the interaction between the bonding orbitals on cobalt and the available bonding MOs on the heterocyclic carborane ligand.4 Comparison of the structures of the CzB4Ta complexes l b and ICreveals close similarity in the bending angle, defined as above, and in other relevant parameters (Table 5). An exception, however, is seen in the carborane C-C bond distance which is significantly longer in l b than in IC (or in any of the other structures reported in this paper). This finding correlates with the
Stockman et al.
3018 Organometallics, Vol. 14,No. 6, 1995 Table 3. Bond Distances and Selected Bond Andes for (Et&B&)TaC12Cp* (IC) Ta-CK1) Ta-CK2) Ta-C(2) Ta-C(3) Ta-C(lR1A) Ta-C(lR1B) Ta-C(lR2A) Ta-C(lR2B) Ta -C(1R3A) Ta-C(lR3B) Ta-C( 1R4B) Ta-C(lR4A) Ta-C(lR5B) Ta-C(lR5A) Ta-B(4) Ta-B(5) Ta-B(6) C(2M)-C(2) C(2M)-C(2E) C(2)-C(3) C(2)-B(6) C(2)-B(7) C(3)-C(3M) C(3)-B(4) C(3)-B(7) C(3M)-C(3E)
Bond Distances, A C(1RlAI-U 1R2A) 2.343(4) C(lRlA)-C( 1R5A) 2.355(4) C(lRlA)-C(lRGA) 2.42(2) C(lRlB)-C(lRBB) 2.47(2) C(lRlB)-C(lR5B) 2.44(3) C(lRlB)-C(lRGB) 2.43(4) C(1R2A)-C( 1R3A) 2.52(3) C(1R2A)- C(1R7A) 2.40(3) C(lRBB)-C(lR3B) 2.46(2) C(lR2B)-C(lR7B) 2.37(3) C(1R3A)-C(1R4A) 2.37(3) C(1R3A)-C( 1R8A) 2.51(3) C(lRSB)-C(lR4B) 2.39(3) C(lR3B)-C(lR8B) 2.49(3) C(1R4B)-C( 1R5B) 2.39(2) C(lR4B)-C(lRSB) 2.42(2) C( 1R4A)-C( 1R5A) 2.42(2) C(1R4A)-C(1R9A) 1.59(2) C(lRSB)-C(lRlOB) 1.61(4) C( 1R5A)-C( 1R1OA) 1.40(2) 1.53(2) B(4)-B(5) 1.76(2) B(4)-B(7) 1.51(3) B(5)-B(6) B(5)-B(7) 1.50(3) 1.73(2) B(6)-B(7) 1.23(4) Selected Bond Agles, deg 95.0(2) Ta-C(3)-B(4)
1.33(5) 1.46(4) 1.51(4) 1.41(5) 1.41(4) 1.57(5) 1.42(4) 1.63(5) 1.40(4) 1.62(5) 1.37(4) 1.50(4) 1.32(5) 1.41(4) 1.49(4) 1.64(4) 1.49(4) 1.57(4) 1.54(4) 1.52(4) 1.77(2) 1.78(2) 1.65(2) 1.77(3) 1.76(3)
69(1) 96(1) 116(2) 114(1) 68(U 129(2) 127(2) 66(1) 113(2) 123(3) 105(1)
Table 4. Bond Distances and Selected Bond Andes for [CP*CO(E~ZCZB~H~)~T~C~ZCP (4a) Ta-Cl( 1) Ta-Cl(2) Ta-C(2) Ta-C(3) Ta-C(lR1) Ta-C( 1R2) Ta-C(lR3) Ta-C(lR4) Ta-C(lR5) Ta-B(4) Ta-B(5) Ta-B(6) Co-C(2) co-c(3) Co-C(2Rl) Co-C(2R2) Co-C(2R3) Co-C(2R4) Co-C(2R5) CO-B(4) CO-B(5) Co-B(6) C(2M)-C(2)
Bond Distances, A 2.376(2) C(2M)-C(2E) 2.391(2) C(2)-C(3) 2.469(8) C(2)-B(6) 2.442(8) C(3M)-C(3) 2.40(1) C(3M)-C(3E) 2.38(1) C(3)-B(4) 2.42(1) C(lRl)-C(lR2) 2.45(1) C(lRl)-C(lR5) 2.39(1) C(lR2)-C(lR3) 2.44(1) C(lR3)-C(lR4) 2.366(9) C(lR4)-C(lR5) 2.39(1) C(2Rl)-C(2R2) 2.030(8) C(2Rl)-C(2R5) 2.046(8) C(2Rl)-C(2R6) 2.043(8) C(2R2)-C(2R3) 2.037(8) C(2R2)-C(2R7) 2.067(8) C(2R3)-C(2R4) 2.067(9) C(2R3)-C(2R8) 2.068(8) C(2R4)-C(2R5) 2.09(1) C(2R4)-C(2R9) 2.06(1) C(2R5)-C(2R10) 2.055(9) B(4)-B(5) 1.51(1) B(5)-B(6) Selected Bond Angles, deg 32.3(1) C(2)-C(3)-C(3M)
Co-C(2)-B(6) C(2M)-C(2)-C(3) C(2M)-C(2)-B(6) C(3)-C(2)-B(6) Ta-C(S)-Co Ta-C(3)-C(2)
68.5(4) 121.5(7) 127.0(7) 111.4(7) 103.5(3) 73.5(5)
C(2)-C(2M)-C(2E) C(3)-C(3M)-C(3E) C(3)-B(4)-B(5) B(4)-B(5)-B(6) C(2)-B(6)-B(5)
1.53(1) 1.48(1) 1.55(1) 1.52(1) 1.53(1) 1.57(1) 1.39(1) 1.41(1) 1.40(2) 1.40(2) 1.36(1) 1.43(1) 1.43(1) 1.48(1) 1.40(1) 1.51(1)
1.44(1) 1.48(1) 1.40(1) 1.52(1) 1.51(1) 1.69(1) 1.73(1) 118.6(7) 114.6(7) 126.7(7) 127.1(6) 71.3(5) 68.1(4) 129.3(6) 69.1(5) 114.6(7) 113.9(7) 104.4(7) 104.0(7) 105.6(7)
lOO(1)
107(1)
release of electron density by the SiMea groups on lb, which would tend to mitigate the electron-deficiency in the region of the cage carbon atoms and hence reduce the multiple-bond character14 of the C-C interaction in the C2B4 ligand. All of the isolated metal dihalide complexes are significantly more stable than their bis(cyc1opentadienyl) counterparts. Thus, the tantalum compounds lad and 4a,b are air-stable solids, and the niobium complexes 2 and 4c are only mildly reactive with atmospheric moisture and can be handled on the benchtop. However, the zirconium species 3a and 3b form colorless precipitates (presumably oxygen-bridged polymers) on exposure to air in solution or in the solid state. The zirconium cyclopentadienyl complex 3a was isolated with 1 equiv of THF as solvent of crystallization. In this compound, the appearance of diastereotopic signals for the carboranyl ethyl groups indicates a comparatively slow process for ligand exchange. The permethylcyclopentadienyl complex 3b was isolated with 2-3 equiv of THF; in contrast to 3a, its carboranyl ethyl lH NMR signals were not split in a diastereotopic pattern, suggesting a more rapid ligand exchange process. This is consistent with the more hindered nature of the metal center, which is expected to enhance the rate of THF dissociation. Ligand Substitution Reactions: Synthesis of Alkyl, Aryl, and Phenoxide Complexes, The re-
placement of halide ligands by alkyl and aryl groups was found to be facile in most cases using standard alkylating reagents. Schemes 2 and 3 summarize the mono- and disubstitution reactions, respectively, for the dichlorotantalum carborane substrates. In general, the first chloride proved t o be substantially more reactive than the second. Thus, monoalkyl complexes were selectively obtained when relatively mild alkylating agents were used in excess (Scheme 2): Al2Me6 for short reaction times (5a,b),dialkylzinc reagents (5a-c, 5eg), and dialkylmagnesiums (5h,i). It is notable that, while dineopentylmagnesium generated complex 5h from l a in 58% yield, dineopentylzinc was unreactive with la.15 Disubstitution was achieved with more powerful nucleophiles (Scheme 31, as shown in the preparation of 6a-k in good yield via treatment of the dichloro species with Grignard reagents.16J7 The sterically hindered dineopentyl complexes 6h-j were obtained in yields of 90, 68, and 68%, respectively, on treatment (15) One exception has been noted: the monoethyl complex 6d was obtained with EtMgC1. (16)We have recently found that the reaction of la with dimethylzinc in THF instead of toluene produces the dimethyl complex 6a in good yield. (17) The proton NMR spectra for both the dihalide and the dialkyl complexes exhibit dramatic solvent effects for the cyclopentadienyl resonances. For example, la shows a shift of 0.83 ppm, from 6 5.60 in CsDs to 6 6.43 CDC13. The dimethyl complex 6a is similar, with signals at 6 5.37 in C6D6 and 6 6.02 CDC13. Interestingly, the Cp resonances for these species in CD3CN and CDzClz solvents are within 0.06 ppm of those recorded in CDC13.
Carborane Ligands as Cyclopentadienyl Analogues
Organometallics, Vol. 14, No. 6,1995 3019
Table 5. Comparison of Structural Parameters Cp(Cp*)-CzB3 dihedral angle, deg Co-Ta distance, A carborane C2-C3 distance, A Ta-CzB3 distance, Aa Co-CzB3 distance, Aa Ta-Cp(Cp*) distance, Ac Co-Cp(Cp*) distance, AC X-Ta-X (X = C1, Me, Ph) angle, deg
lb 53.10
50.42
1.51(1) 2.001
1.40(2) 2.018
2.098
2.165
95.50(9)
95.0
IC
4a
54.00,8.38 3.531 1.48(1) 1.995 1.536 2.096 1.664 92.3
6d 51.10 1.460(8) 2.019 2.100 110.2b
7b
7c
51.98,8.81 3.559 1.483(8) 2.011 1.548 2.115 1.666 91.4(2F
51.56,8.56 3.560 1.470(8) 2.019 1.541 2.098 1.672 91.5(2)d
Sa
48.92 1.463(5) 2.024e 2.114f 97.0(1F
Metal-ring plane distance. ClO-Ta-C4 (Ph-Ta-Ph) angle. C11-Ta-C12 (Me-Ta .-Me) angle. C11-Ta-C1 (phenyl-Ta-C1) angle. e Nb-CZB3 distance. f Nb-Cp distance. g C4-Nb-C5 (Me-Nb-Me) angle. a
Scheme 2 C2E
C3E C2M
C3M
C7
la
-
n
50
I C R'
50
L
be
H SiMeJ H Et Me
5d
Et
H
Me Et
Et
H
CH2Ph
51 SiMe3 H 5g E t Me bh 5i
Et
H
Et
Me
5j
olk. a g e n t
1; } {
R2
Et
5b
-
n
CHzPh CHzPh
'
)
Me2Zn EtMgCl C l
Zn(CH2Ph)z
Scheme 3 C13
la
-
60
I C
R'
60 E t 6b SiMe3
R'
L
:: )
Et Et
H H Me H
Et
H
CH2Ph
6g 6h
Et
Me
CHzPh
Et
H
CHztBu
63 6k
Et
Me
CH,IBu
Et
H
OPh
6c
6d 60
Me Ph
-
6k
olk. a g e n t
CH3MgBr PhLi
PhONo
with 2.5-3 equiv of neopentyllithium. The displacement of both chloro ligands on la by sodium phenoxide also proceeds smoothly to form 6k in nearly quantitative yield. Similar patterns were observed in the alkylation of the Cp*Co analogue 4a, depicted in Scheme 4 (top),
Figure 4. Molecular structure of (EtzCzB4H4)TaPhzCp (6d). which afforded the mono- and dialkylated derivatives 7a-f. The isolated yields of compounds 7a-d were quantitative, while those of the neopentyl species 7e and 7f were 80% and 58%, respectively. With two exceptions, all alkyl-, aryl-, and phenoxytantalum carborane complexes described here are airstable in the solid state for weeks and for at least 1day in solution. Decomposition under these conditions appears to consist mostly of slow hydrolysis to form oxo-bridged species (to be described in a subsequent paper).18 In contrast, the EtzCzB4-bis(neopentyl) complexes 6h-j are unstable, decomposing into uncharacterized products while standing in solution under N2 for several hours. However, the reddish-purple Cp*CoCzBs neopentyl analogues 7e and 7f are quite robust compounds. Complexes 6d and 7b,c were characterized by X-ray crystallography, with the structures depicted in Figures 4-6 and the relevant information listed in Tables 1,5, and 6-8. Comparison of the parameters in these molecules with the corresponding values in the dichloro species lb,c and 4a, which are very similar (Table 51, suggests that replacement of C1 by organic moieties in (18)When stored in CDCls, the chloroalkyl complexes Sa and 6d decompose on standing to the parent dichloride la. The process requires about 1 week for the methyl complex but only 2 days for the ethyl complex under similar conditions.
Stockman et al.
3020 Organometallics, Vol. 14,No. 6, 1995
C3E
CPAlO
(7b). Figure 5. Molecular structure of Cp*Co(EtzC~BsHdTaMezCp
Scheme 4 L'
L2
7b
Me Me
CI Me
7C
CH2Ph CI
Zn( C H Z P ~ ) ~
7d 7S
CHzPh CHzPh CHztEu CI
PhCHzMgBr Np2Mg*dioxone
71
CHztBu CHztBu NpLi
70 alkylating
olk. ogent Me2Zn or AIMeJ MeLi or MeMgBr
40
LMgBr
la
L = Me
Et.
n
2 6d, and 7b,c has little effect on the structures. Thus, the bend (dihedral) angle of the ring ligands on tantalum is 51.1"-52.0" for these structures, nearly identical with those observed in the analogous dichloro compounds. As is the case in the CoTa species 4a, the Cp* and C2B3 ring planes in the bent triple-deckers 7b and 7c are only slightly tilted, with dihedral angles of 8.8" and 8.6") respectively.
The dialkylation of the niobium dichloro complex 2 was accomplished in analogous fashion to the tantalum system, generating the dialkyle 8a and 8b on treatment with Grignard reagents (Scheme 4, bottom). An X-ray structure determination on 8a (Table 9 and Figure 7) provided the first structural characterization of a niobium carborane complex and revealed general similarity with the corresponding TaC2B4 species lb,c and 6d
Carborane Ligands as Cyclopentadienyl Analogues
Organometallics, Vol. 14, No. 6, 1995 3021
Table 7. Bond Distances and Selected Bond Angles for Cp+Co(Et&2BsHs)TaMe&p (7b)
C16 C14
ClR2
64
65 C2M
C2E C2R9
1
C2R6
Figure 6. Molecular structure of Cp*Co(Et&zB3H3)Ta(CHzPh)ClCp (7c). Table 6. Bond Distances and Selected Bond Angles for (EtzCzB&dTaPhzCp (6d) Ta-C(2) Ta-C(3) Ta-C(4) Ta-C(10) Ta-C(lR1) Ta-C(lR2) Ta-C( 1R3 Ta-C( 1R4) Ta-C(lR5) Ta-B(4) Ta-B(5) Ta-B(6) C(2)-C(2M) C(2)-C(3) C(2)-B(6) C(2)-B(7) C(2M)-C(2E) C(3)-C(3M) C(3)-B(4) C(3)-B(7) C(3M)-C(3E) C(4)-C(5)
Bond Distances, A 2.466(5) C(4)-C(9) 2.462(5) C(5)-C(6) 2.237(5) C(6)-C(7) 2.213(6) C(7)-C(8) 2.429(5) C(8)-C(9) 2.434(5) c(lO)-C(ll) 2.403(5) C(lO)-C(15) 2.423(5) C(lRl)-C(lRB) 2.414(5) C(lRl)-C(lR5) 2.453(6) C(ll)-C(12) 2.395(6) C(lR2)-C(lR3) 2.395(6) C(12)-C(13) 1.516(7) C(13)-C(14) 1.460(8) C(lR3)-C(lR4) 1.558(7) C(14)-C(15) 1.731(7) C(1R4)- C(1R5) 1.501(8) B(4)-B(5) 1.501(7) B(4)-B(7) 1.558(8) B(5)-B(6) 1.738(7) B(5)-B(7) 1.536(7) B(6)-B(7) 1.407(7) Selected Bond Angles, deg 110.2(2) C(2)-C(3)-C(3M) 137.4(3) C(2)-C(3)-B(4) 72.6(3) C(2)-C(3)-B(7) 68.8(3) C(3M)-C(3)-B(4) 95.3(3) C(3M)-C(3)-B(7) 120.0(4) B(4)-C(3)-B(7) 126.5(5) Ta-C(3)-C(2) 127.2(4) Ta-C(3)-C(3M) 112.1(5) C(2)-C(2M)-C(2E) 65.4(3) C(3)-C(3M)-C(3E) 65.2(3) C(3)-B(4)-B(5) 71.2(3) C(2)-B(6)-B(5) 95.3(3) B(4)-B(5)-B(6)
1.395(8) 1.397(7) 1.395(8) 1.397(8) 1.381(7) 1.395(7) 1.409(8) 1.380(9) 1.43l(8) 1.38(1) 1.436(8) 1.383(9) 1.383(9) 1.42(1) 1.407(8) 1.417(8) 1.696(9) 1.793(9) 1.693(9) 1.757(8) 1.778(8)
122.8(5) 114.0(5) 64.9(4) 121.9(5) 129.8(4) 65.6(4) 72.9(3) 134.9(3) 115.1(4) 113.5(4) 104.1(5) 105.3(5) 104.5(4)
(Table 5). A notable difference, however, is found in the reduced Cp-CzB3 dihedral angle in 8a (48.9”)which is
Ta-C(2) Ta-C(3) Ta-C(lR1) Ta-C(l1) Ta-C(lR2) Ta-C(12) Ta-C(lR3) Ta-C(lR4) Ta-C(lR5) Ta-B(4) Ta-B(5) Ta-B(6) Co-C(2) co-c(3) Co-C(2Rl) Co-C(2R2) Co-C(2R3) Co-C(2R4) Co-C(2R5) Co-B(4) Co-B(5) Co-B(6) C(2)-C(2M) C(ll)-Ta-C(12) Ta-C(2)-Co Ta-C(2)-C(2M) Ta-C(2)-C(3) Ta-C(2)-B(6) Co-C(2)-C(2M) Co-C(2)-C(3) Co-C(2)-B(6) C(2M)-C(2)-C(3) C(2M)-C(2)-B(6) C(3)-C(2)-B(6) Ta-C(3)-Co Ta-C(3)-C(2)
Bond Distances, A 2.484(6) C(2)-C(3) 2.499(6) C(2)-B(6) 2.428(8) C(2M)-C(2E) 2.321(6) C(3)-C(3M) 2.419(8) C(3)-B(4) 2.202(7) C(3M)-C(3E) 2.397(8) C(lRl)-C(lR2) 2.413(7) C(lRl)-C(lR5) 2.417(7) C(lR2)-C(lR3) 2.449(7) C(lR3)-C(lR4) 2.354(7) C(lR4)-C(lR5) 2.378(7) C(2Rl)-C(2R2) 2.032(6) C(2Rl)-C(2R5) 2.056(6) C(2Rl)-C(2R6) 2.039(6) C(2R2)-C(2R3) 2.036(6) C(2R2)-C(2R7) 2.065(6) C(2R3)-C(2R4) 2.095(6) C(2R3)-C(2R8) 2.066(6) C(2R4)-C(2R5) 2.087(7) C(2R4)-C(2R9) 2.061(7) C(2R5)-C(2R10) 2.055(6) B(4)-B(5) 1.523(7) B(5)-B(6) Selected Bond Angles, deg 91.4(2) Ta-C(3)-C(3M) 103.7(2) Ta-C(3)-B(4) 129.7(4) Co-C(3)-C(2) 73.2(3) Co-C(3)-C(3M) 67.8(3) Co-C(3)-B(4) 126.5(4) C(2)-C(3)-C(3M) 69.6(3) C(2)-C(3)-B(4) 68.5(3) C(3M)-C(3)-B(4) 120.5(5) C(2)-C(2M)-C(2E) 127.5(5) C(3)-C(3M)-C(3E) 111.9(5) C(3)-B(4)-B(5) 102.5(2) B(4)-B(5)-B(6) 72.1(3) C(2)-B(6)-B(5)
1.483(8) 1.547(8) 1.523(8) 1.515(8) 1.556(8) 1.526(8) 1.37(1) 1.39(1) 1.40(2) 1.35(1)
1.34(1) 1.426(9) 1.431(8) 1.501(9) 1.42(1) 1.509(9) 1.42(1) 1.49(1) 1.42(1) 1.51(1)
1.50(1) 1.673(9) 1.71(1) 130.4(4) 69.9(3) 67.9(3) 126.9(4) 69.0(3) 119.6(5) 112.8(5) 127.4(5) 113.7(5) 114.2(5) 105.8(5) 103.9(5) 105.7(5)
attributed to the slightly smaller covalent radius of Nb(VI relative to Ta(V), forcing closer Cp-carborane interaction in 8a than in the tantalum species (an effect previously mentioned). Electrochemistry. “ransition metal-carborane complexes exhibit reversible multielectron redox chemistry, thereby defining the metallacarborane fragment as an “electron r e s e r v ~ i r ” . ~ ~ The > ~ C2B4 ~ J ~ tantalum complexes la-c undergo quasireversible reduction at - 1.40, -1.35, and -1.65 V vs Fc/Fc+, respectively, and no oxidation is observed. In contrast, the CoCp*-capped tantalum complex 4a exhibits quasireversible oxidation ( f 0 . 6 7 V vs Fc/Fc+) and reduction (-1.65 V) waves in the cyclic voltammogram a t all scan rates (20-500 mV/ sec). However, the Cp*Co niobium compound 4c exhibits no oxidation wave within the solvent window and quasireversible reduction a t - 1.11 V. Reactions. Alkyl and aryl complexes bearing carborane ligands reported here proved to be less reactive than their isoelectronic Cp2 analogues toward a variety of reagents and conditions, as follows. (1)The treatment of complexes la and 2 with AleMes, in an effort to prepare Tebbe-type reagents suitable as catalysts for ring-opening metathesis polymerization (19)(a) Geiger, W. E., Jr. In Metal Interactions with Boron Clusters; Grimes, R. N., Ed.; Plenum Press: New York, 1982; Chapter 6, pp 239-268. (b) Merkert, J. M.; Geiger, W. E.; Davis, J. H., Jr.; Attwood, M. D.; Grimes, R. N. Organometallics 1989, 8, 1580. ( c ) Merkert, J. M.; Geiger, W. E.; Attwood, M. D.; Grimes, R. N. Organometallics 1991, 10, 3545. (d) Merkert, J.; Davis, J. H., Jr.; Geiger, W.; Grimes, R. N. J. Am. Chem. SOC.1992, 114,9846.
Stockman et al.
3022 Organometallics, Vol. 14,No. 6,1995
Table 9. Bond Distances and Selected Bond Table 8. Bond Distances and Selected Bond Angles for (Et&zB&)NbMe&p (8a) Andes for C D * C O ( E ~ Z C Z B ~ L ~ T ~ ( C H ~(7c) P~)C~CD Ta-Cl Ta-C(2) Ta-C(3) Ta-C(11) Ta-C(lR1) Ta-C(lR2) Ta-C(lR3) Ta-C(lR4) Ta-C(lR5) Ta-B(4) Ta-B(5) Ta-B(6) Co-C(2) cO-c(3) Co-C(2Rl) Co-C(2R2) Co-C(2R3) Co-C(2R4) Co-C(2R5) Co-B(4) CO-B(5) Co-B(6) C(2)-C(2M) C(2)-C(3) C(2)-B(6) C(2M)-C(2E) C(3M)-C(3) Cl-Ta-C(11) Ta-C(11)-C(12) Ta-C(L)-Co Ta-C(2)-C(2M) Ta-C(2)-C(3) Ta-C(2)-B(6) Co-C(2)-C(2M) Co-C(2)-C(3) Co-C(2)-B(6) C(2M)-C(2)-C(3) C(2M)-C(2)-B(6) C(3)-C(2)-B(6) Ta-C(3)-Co Ta-C(3)-C(2)
Bond Distances. A 2.394(1) 2.508(6) 2.481(6) 2.277(6) 2.406(7) 2.429(6) 2.423(7) 2.428(6) 2.388(6) 2.381(6) 2.373(6) 2.463(7) 2.043(6) 2.039(6) 2.049(6) 2.100(6) 2.099(6) 2.046(6) 2.031(5) 2.056(7) 2.055(7) 2.087(7) 1.527(8) 1.470(8) 1.56(1) 1.531(9) 1.520(8) Selected Bon 91.5(2) 120.1(4) 102.6(2) 128.7(4) 71.9(3) 70.1(3) 128.5(4) 68.7(3) 69.3(3) 119.3(5) 127.0(5) 113.6(5) 103.7(2) 73.9(3)
1.520(9) 1.565(8) 1.509(8) 1.41(1) 1.41(1) 1.40(1) 1.398(9) 1.374(9) 1.398(9) 1.39(1)
1.41(1) 1.39(1) 1.37(1) 1.40(1) 1.426(8) 1.418(8) 1.503(8) 1.427(8) 1.501(8) 1.420(8) 1.485(9) 1.428(8) 1.516(8)
Nb-C(2) Nb-C(3) Nb-C(4) Nb-C(5) Nb-C(lR1) Nb-C( 1R2) Nb-C(lR3) Nb-C( 1R4) Nb-C( 1R5) Nb-B(4) Nb-B(5) Nb-B(6) C(2M)-C(2) C(2M)-C(2E) C(2)-C(3) C(2)-B(6)
Bond Distances, A 2.433(3) C(2)-B(7) 2.459(4) C(3)-C(3M) 2.226(4) C(3)-B(4) 2.222(4) C(3)-B(7) 2.412(4) C(3M)-C(3E) 2.427(4) C(lRl)-C(lR2) 2.430(4) C(lRl)-C(lR5) 2.449(4) C(lR2)-C(lR3) 2.423(4) C(lR3)-C(lR4) 2.456(4) C(lR4)-C(lR5) 2.410(4) B(4)-B(5) 2.414(4) B(4)-B(7) 1.521(5) B(5)-B(6) 1.512(6) B(5)-B(7) 1.463(5) B(6)-B(7) 1.545(6)
71.3(2) 96.1(2) 120.4(3) 113.1(3) 65.2(2) 125.6(3) 129.8(3) 65.9(3) 112.9(3) 114.9(3) 104.1(3) 105.4(3) 104.9(3)
1.511(8)
1.717(9) 1.68(1)
130.6(4) 67.8(3) 69.0(3) 125.7(4) 68.1(3) 120.8(5) 111.6(5) 127.3(5) 114.1(5) 113.6(5) 105.4(5) 103.9(5) 105.4(5)
(ROMP),20afforded only the dimethyl compounds 6a and 8a,respectively, in slow reactions, rather than Ta or Nb methylidene complexes. These observations thus stand in contrast to the preparation of Tebbe's reagent from Cp2TiC12.21 In addition, unlike the isoelectronic bis(Cp) complexes of group 4 metals, thermolysis of dialkyl (EtzCzB4H4)TaRR'Cp complexes in the presence or absence of PMe3 leads to uncharacterized decomposition rather than to metal alkylidene compounds. (2) While CpzZrRz (R = Me or benzyl) undergoes rapid reactions with Cp'zFePh4B (Cp' = Cp or CsH4Me) to form cationic species,22 treatment of the dimethyl complex 6a or the dibenzyl species 6e with these reagents did not lead to the formation of the desired Ta-R cation (R = Me or benzyl). Instead, the ferrocenium salt decomposed and the tantalum complex was recovered. Similarly, insertion and elimination processes that are facile for bis(cyclopentadieny1)complexes (20)Gilliom, L. R.; Grubbs, R. H. J.A m . Chem. SOC.1986,108,733. (2l)(a)Tebbe, F. N.; Parshall, G. W.; Reddy, G. S. J.A m . Chem. SOC.1978,100, 3611. (b) Canizzo, L. F.; Grubbs, R. H. J. Org. Chem. 1985,50,2386. (22)(a) Jordan, R. F.; LaPointe, R. E.; Bradley, P. K.; Baenziger, N. Organometallics 1989, 8, 2892. (b) Alelyunas, Y. W.; Jordan, R. F.; Echols, S. F.; Borkowsky, S. L.; Bradley, P. K. Organometallics 1991, 10, 1406.
1.740(5) 1.524(5) 1.568(6) 1.738(6) 1.502(6) 1.402(7) 1.405(6) 1.409(6) 1.392(5) 1.411(6) 1.669(7) 1.805(6) 1.688(6) 1.760(6) 1.772(6)
C3E
ClR2
Figure 7. Molecular structure of (EtzCzB4H4)NbMezCp @a). of group 4 metals22b,23 appear to require irradiation in the isoelectronic CpTa(carborane1 series. Thus, while all attempts at inducing thermal insertion reactions of alkynes and nitriles have failed with the carborane (23)(a)Horton, A. D.; Orpen, A. G. Organometallics 1991,10,3910. (b)Ambrose, D. M.; Lee, R. A.; Petersen, J. L. Organometallics 1991, 10,2191. (c) Guram, A. S.;Jordan, R. F. J.Org. Chem. 1993,58,5595.
Organometallics, Vol. 14, No. 6, 1995 3023
Carborane Ligands as CyclopentadienylAnalogues Scheme 5
c
1
MeCN,
2+ 2BF4-
MeCNHTa E$+n n J
L
60
90
dialkyl species reported here, these processes are stimulated by p h o t ~ l y s i s .Another ~~ example is provided by the diphenyl complex 6d, which decomposes on heating in toluene to form an intractable mixture but on irradiation produces biphenyl in quantitative yield. (3) The dimethyl complex 6a was found to react rapidly with 2 or more equiv of HBF4 in CH3CN or CD3CN to give a single carborane-containing product with properties consistent with the four-coordinate dicationic species 9b (Scheme 5). The identity of 9b is supported by its elemental analysis and its lH, llB, and 13C NMR spectra, all of which are consistent with a symmetric structure indicating disubstitution. Significantly, the Ta-Me resonance of 6a has been completely replaced by a coordinated acetonitrile singlet at 6 2.01 that integrates for two CH3CN units. This signal appears both in spectra of the reaction mixture in CH3CN solvent and in the spectrum of the product obtained (in CDC13) afier removal of the volatile reaction components followed by overnight drying in vacuo, suggesting that loss of the bound acetonitrile is slow. Consistent with this observation is the absence of insertion or polymerization reactivity when 6a is protonated in the presence of a large excess of ethylene or propylene. Preliminary data suggest that monoprotonation of 6a to give a methyl monocationic complex proceeds cleanly. When protonation was attempted with 3,5-[(CF3)2CsH334B[ H ( O E ~ Z ,gas ~ I ,evolution ~~ was accompanied by decomposition of the carborane complex. Complex 9b may be compared with the analogous five-coordinate bis(cyclopentadieny1)zirconium complex [Cp2Zr(CH&N)3I[BPh& reported by Jordan and EcholsF6 Consistent with the greater degree of electron donation, enhanced complex stabilization, and greater steric demand to be expected from carborane ligands relative to v5-C5H5,complex 9b has shown no propensity to bind a third CH3CN donor, is stable t o air for brief periods, and does not abstract fluoride from the BF4- counterion. Summary. Early transition metal carborane sandwich complexes incorporating small carborane or cobaltacarborane ligands present a wide array of possibilities for exploitation in the design of reagents for organic synthesis, tailored via choice of metals and selective substitution on the cage or at the metal centers. In this paper we have described efficient routes to several classes of such compounds. However, the proper development of this area will require detailed exploration of their reactivity, and investigations of several aspects (24) Curtis, M. A,; Houseknecht, K. E.; Finn, M. G.; Grimes, R. N. Studies in progress. (25) Brookhart, M.; Grant, B.; Volpe, A. F., Jr. Organometallics 1992, 11, 3920. (26) Jordan, R. F.; Echols, S. F. Inorg. Chem. 1987,26, 383.
9b of this chemistry are well under way in our laboratories. These include (i)preparation of metal hydride complexes via hydride transfer reactions, and their reactions with alkynes; (ii)introduction of chiral functional groups; (iii) photochemical reactions; (iv) alkyVary1 eliminations and rearrangements; and (v) synthesis and reactions of cationic Cp(carborane)MR+and (carborane)MRz+comp l e x e ~ . As ~ ~ an example of (iv), we have recently reported2* the conversion of the diphenyl complex 6d t o a strikingly robust benzyne complex, Cp(PMe3)(v2&H4)Ta(Et2C2BdH4), via refluxing in toluene in the presence of excess PMe3. In contrast to benzyne-metal complexes in general, this compound is stable in methanol solvent and can be purified by silica gel chromatography in air.28Subsequent papers will describe in detail our findings in these and related aspects of this chemistry. Experimental Section Instrumentation. lH (300 and 500 MHz), llB (115.8 MHz), and 13C (75.5 and 125.3 MHz) NMR spectra were acquired on Nicolet NT-360, GE QE-300, or GE Omega-500 spectrometers. In the proton NMR spectra of new compounds, all ethyl CH2 signals were observed as doublets of quartets with coupling constants ( J values) of 7.5 and 15 Hz, and ethyl CH3 resonances appeared as triplets with J = 7.5 Hz, unless otherwise stated. Visible-ultraviolet spectra were recorded on a HewlettPackard 8452A diode array with a HP Vectra computer interface. Unit resolution mass spectra were obtained on a Finnegan MAT 4600 GCMS spectrometer using perfluorotributylamine (FC43) as a calibration standard. In all cases, strong parent envelopes were observed, and the observed and calculated unit-resolution spectral patterns were in close agreement. Elemental analyses were obtained in this department on a Perkin-Elmer 2400 CHN Analyzer using 2,4dinitrophenylhydrazone as a standard. Infrared spectra were recorded as thin films on a Mattson Cygnus FTIR spectrometer. Electrochemistry. Cyclic voltammetry was conducted in a one-compartment cell with a Pt disk (3 mm diameter) working electrode, a saturated Ag/AgCl reference electrode, and a platinum wire as the auxiliary electrode, using a Bioanalytical Systems CV27 voltammograph. Scan rates from 20 mV/sec t o 1 Vhec were employed; values reported were obtained a t 200 mV/sec. The solvent was dimethoxyethane (DME), which was purified by twice distilling from CaH2; the (27) Insertion reactions of the isolectronic CpzZrR+family of complexes are the basis for extensive work in olefin polymerization processes. For examples, see ref 22 and (a) Jordan, R. F. Adu. Organomet. Chem. 1991, 32, 325. (b) Jordan, R. F.; Bajgur, C. S.; Willett, R.; Scott, B. J.A m . Chem. SOC.1986,108,7410. ( c ) Bochmann, M.; Lancaster, S. J. Organometallics 1993,12,633. (d) Bierwagen, E. P.; Bercaw, J . E.; Goddard, W. A. J . A m . Chem. SOC.1994,116, 1481 and references cited therein. (28)Houseknecht, K. L.; Stockman, K. E.; Sabat, M.; Finn, M. G.; Grimes, R. N. J.A m . Chem. SOC.1995, 117, 1163.
3024 Organometallics, Vol. 14, No. 6, 1995 supporting electrolyte was 0.5 M Bu4NPF6, used as received and stored in the dry box. Potentials were measured against internal Cp~Fe/CpzFe+(f0.55 V vs NHE) and are reported vs NHE. Materials. The starting compounds Me3CCH~M&dioxane),~ ( P ~ C H Z ) ~and Z ~M, ~ ~ C C H were Z L ~prepared ~~ by literature methods. Complexes CpTaCl4, CpZrCla, and CpNbCl4 were synthesized via reactions of C5H5SiMe3 with the corresponding metal halides.31 C5H5SiMe3 was prepared via treatment of NaCp with SiMesCl in ether.29 CpNa was obtained from the reaction of NaH with freshly cracked dicyclopentadiene. NaH (80% in mineral oil) was washed with petroleum ether and dried prior to use. Cp*TaC14 (Strem), Cp'ZrCl4 (Strem), HBF4, MeMgBr, PhCHzMgBr, AlMe3, PhLi, BuLi, PhOH, and Me2Zn were purchased from commercial sources and used as received. The carborane EtzC2B4Hs was synthesized on a multigram scale via the reaction of B5H9 and diethylacetylene in diethyl ether solution, employing a recent major modificat i ~ ofn the ~ ~literature method.33 The disilyl carborane (Me3S ~ ) Z C ~ and B ~ the H ~ complex ~ ~ C ~ * C O ( E ~ ~ C Z Bwere ~ H ~ob)'~ tained as described elsewhere. Petroleum ether was used as received, and methylene chloride was distilled from CaH2. THF was distilled from N d K alloy-benzophenone immediately prior to use. Column chromatography was performed on silica gel 60 (Merck). All reactions were conducted under a n inert atmosphere unless otherwise indicated. Workup of products was generally carried out in air using benchtop procedures. Syntheses. (EtzCzB4Hd)TaClzCp (la). A 250 mL flask was charged with NaH (1.00 g, 42.0 mmol) and 125 mL of THF. At room temperature, Et2C2B4Hs (2.75 g, 20.6 mmol) was added dropwise via syringe over a 45 min period, carefully avoiding excessive H2 evolution, after which the mixture was stirred for 1 h. The NaEtzCzB4H5 solution was allowed to settle, and the supernatant was transferred by cannula into a 250 mL flask containing a suspension of CpTaC14 (4.00 g, 10.3 mmol) in 50 mL of THF. The yellow-brown solution was stirred for 4 h, after which the solvent was removed in vacuo to another flask to collect the neutral E ~ ~ C Z Bwhich ~ H ~ was , subsequently used in another reaction. The dark yellow residue left in the reaction flask was filtered twice through a pad of Celite with CHzC12. The resulting sticky yellow solid was washed with cold petroleum ether ( 3 x 5 mL) to give la (3.97 g, 8.76 mmol, 85%) as a yellow powder. 'H NMR (6, CDC13): 6.43 (C5H5, S, 5H), 3.14 (CHz, dq, 2H), 2.70 (CHz, dq, 2H), 1.23 (CH3, t, 6H). 'H NMR (6, C&): 5.60 (C5H5, S, 5H), 3.12 (CHz, dq, 2H), 2.48 (CHz, dq, 2H), 1.17 (CH3, t, 6H). NMR (6, CDC13): 126.7 (C&, br), 114.6 (C5H5), 23.1 (CH2), 14.6 (CH3). I'B NMR (6, CHzClz): 33.1 (lB, d, J = 137 Hz), 25.5 (2B, d, J = 162 Hz), 1.1(lB, d, J = 157 Hz). FTIR (cm-'): 3215 m, 2970 m, 2934 m, 2914 m, 2876 w, 2571 s, 2361 w, 2341 w. UV-vis (nm, in CH2Clz): 328 (45%), 248 (100%). MS mlz 447 (molecular ion envelope). Anal. Calcd for CllH19B4Cl~Ta:C, 29.60; H, 4.29. Found: C, 29.88; H, 4.40. [(Me3Si)&zB4H4]TaClzCp (lb). The same procedure was followed employing NaH (1.00 g, 42.0 mmol), (Me3Si)&zB4H6 (3.60 g, 16.4 mmol), and CpTaC14 (3.2 g, 8.2 mmol). Following the addition to CpTaC4, the orange brown solution was stirred overnight. In this case, the solvent was removed by rotary evaporation and the orange-brown solid was filtered through Celite. Column chromatography (4:l petroleum ether-CHzCld yielded a single orange band, which upon evaporation gave (29) Schrock, R. R.; Fellman, J. D. J. A m . Chem. SOC.1978,100, 3359. (30) Schrock, R. R. J . Organomet. Chem. 1976,22, 209. (31) Cardoso, A. M.; Clark, R. J. H.; Moorhouse, S. J . Chem. SOC.,
Dalton Trans. 1980, 1156. (32)(a) Stockman, K. E., Ph.D. Dissertation, University of Virginia, 1995. (b) Stockman, K. E.; Muller, P. M.; Curtis, M. A,; Grimes, R. N. Manuscript in preparation. (33) Maynard, R. B.;Borodinsky, L.; Grimes, R. Inorg. Synth. 1983, 22, 211. (34) Hosmane, N. S.; Sirmokadam, N. N.; Mollenhauer, M. N. J. Organomet. Chem. 1986,279,359.
Stockman et al. red orange crystals of l b (3.0 g, 5.6 mmol, 68%). The neutral carborane byproduct was lost on the silica gel. 'H NMR (6, CDC13): 6.36 (C5H5, s, 5H), 0.42 (SiMe3, s, 18H). I3NMR (6, CDC13): 127.1 (C&, br), 114.6 (C5H5),3.2 (SiMe3). llB NMR (6, CHzC12): 34.3 (lB, d, J = 153 Hz), 30.9 (2B, d, J = 158 Hz), -2.6 (lB, d, J = 160 Hz). FTIR (cm-I): 3126 m, 2968 m, 2962 m, 2899 w, 2588 s, 2575 s, 2552 s, 2389 w, 2341 w. UVvis (nm, in CHzC12): 334 (38%), 246 (100%). MS mlz 534 (molecular ion envelope), 519 (- Me), 499 (- Cl). Anal. Calcd for C13H27B4C12Si~Ta:C, 29.21; H, 4.99. Found: C, 29.15; H, 4.86. (Et~Cdl~HdTaClzCp* (IC). The same procedure was followed using NaH (0.50 g, 21 mmol), Et2CzB4H6 (0.520 g, 3.93 mmol), and Cp*TaC14 (0.900 g, 1.97 mmol). The reaction mixture was stirred overnight followed by workup as above. Washing twice with cold petroleum ether yielded yellow crystalline IC (0.687 g, 1.33 mmol, 68%). 'H NMR (6, CDC13): 3.09 (CH2, dq, 2H), 2.57 (CHz, dq, 2H), 1.78 (CbMe5, s, 15H), NMR (6, CDC13): 94.6 (C*sMes), 17.2 2.55 (CH3, t, 6H). (CHz), 13.2 (CHZ),9.6 (CsMe*5). I'B NMR (6, CH2Clz): 34.8 (lB, d, J = 116 Hz), 25.7 (2B, d, J = 152 Hz), -0.9 (lB, d, J = 185 Hz). W - v i s (nm, in CH2Clz): 364 (33%), 246 (100%). MS mlz 516 (molecular ion envelope). Anal. Calcd for C1&&4Cl2Ta: C, 37.21; H, 5.66. Found: C, 37.38; H, 5.98. (MezCzB&)TaClzCp (Id). The same procedure was followed employing NaH (0.50 g, 20.8 mmol), M ~ z C ~ B(0.50 ~H~ g, 4.8 mmol), and CpTaCl4 (0.90 g, 2.4 "01). The yellowbrown solution (total volume 225 mL) was stirred for 4 h and distilled in vacuo to another flask to collect the EtzCzB4H4 product. The remaining dark yellow-brown residue was filtered twice through Celite in CH2C12, yielding Id as bright yellow crystals (230 mg, 0.55 mmol, 23%). 'H NMR (6, CDC13): 6.44 (C5H5, S, 5H), 2.55 (CH3, S, 6H). I3C NMR (6, CDCl3): 123.1 (C&, br), 114.6 (C5H5), 17.2 (CH3). "B NMR (6, CH2C12): 33.9 (lB, d, J = 144 Hz), 26.0 (2B, d, J = 153 Hz), 3.1 (lB, d, J = 164 Hz). FTIR (cm-'): 3225 m, 3120 m, 3110 m, 3084 w, 2962 m, 2929 w, 2871 w, 2568 s, 2561 s, 2532 m, 2340 w, 2327 w. UV-vis (nm, in CHzC12): 374 (20%), 248 (100%). MS mlz 418 (molecular ion envelope), 382 (- Cl). Anal. Calcd for CgHlsB4ClzTa: C, 25.84; H, 3.61. Found: C, 26.04; H, 4.01. (Et&&H4)NbClzCp (2). The same procedure was followed with NaH (0.800 g, 33.3 mmol), EtzC&Hs (0.885 g, 6.71 mmol), and CpNbCl4 (1.00 g, 3.36 mmol). The red-brown solution (total volume 125 mL) was stirred for 4 h, followed by evaporation in vacuo to another flask to collect the neutral EtzCzB4He. The dark red residue left in the reaction flask was filtered twice through Celite with CH2C12 to yield 2 as a bright red crystalline solid (0.878 g, 2.45 mmol, 73%). 'H NMR (6, CDC13): 6.51 (C5H5, S, 5H), 3.12 (CH2, dq, 2H), 2.59 (CH2, dq, NMR (6, CDC13): 130.9 (C2B4, br), 2H), 1.25 (CH3, t, 6H). 113.6 (C5H5), 23.6 (CHz), 14.2 (CH3). "B NMR (6, CHzC12): 31.7 (lB, d, J = 146 Hz), 18.0 (2B, d, J = 158 Hz), -1.2 (lB, d, J = 165 Hz). FTIR (cm-'): 3215 m, 3124 m, 3115 m, 3088 w, 2968 m, 2935 w, 2877 w, 2575 s, 2561 s, 2538 m, 2361 w, 2343 w. W - v i s (nm, in CH2Clz): 370 (20%), 250 (100%).MS mlz 358 (parent ion envelope), 322 (- Cl). Anal. Calcd for CllH19B4Cl~Nb:C , 36.87; H, 5.34. Found: C , 37.06; H, 5.61. (EtZC&HdZrClCpTHF (3a). A 250 mL flask was charged with NaH (0.500 g, 20.8 mmol) and 125 mL of THF. At room temperature Et2CzB4H6 (1.22 g, 9.26 mmol) was added dropwise via syringe over a 15 min period, and the mixture was stirred for 1 h. The excess NaH was allowed to settle, and the supernatant was transferred by cannula to a 250 mL flask containing a suspension of CpZrCla (1.45 g, 4.63 mmol) in 50 mL of THF. The yellow solution was stirred for 2 h, and then the solvent was removed in vacuo to another flask to collect the neutral E ~ ~ C Z B The ~ H ~yellow . residue was dissolved in CHzClz and filtered through Celite under a dry nitrogen atmosphere to yield 3a as a moisture- and air-sensitive yellow solid (1.78 g, 3.84 mmol, 83%). 'H NMR ( 6 , CDC13): 6.37 (C5H5, s, 5H), 4.10 (THF, m, 2H),3.93 (THF, m, 2H), 3.06 (CHz,
Carborane Ligands as Cyclopentadienyl Analogues dq, lH), 2.68 (CHz, m, 2H), 2.24 (CH2, dq, lH), 2.09 (THF, m, 2H), 1.24 (CH3, t, 3H), 1.09 (CH3, t, 3H). 13C NMR (6, CDCl3): 129.5 (C&, br), 128.0 (C&, br), 113.7 (C5H5),23.6 (CH2), 14.2 (CH3). IIB NMR (6, CH2C12): 33.9 (lB, d, J = 130 Hz), 25.2 (2B, d, J = 146 Hz), 2.1 (lB, d, J = 157 Hz). (Et&2B4H4)ZrC1Cp*.THF(3b). The same procedure was followed using NaH (200 mg, 8.30 mmol), E ~ ~ C Z (199 B~H mg, ~ 1.51 mmol), and Cp*ZrC13 (250 mg, 0.75 mmol). The yellow solution was stirred for 4 h. The solvent and carborane were removed as before, and yellow residue was filtered through Celite with CHzClZ, and the volatiles were removed to yield 3b as a n adduct containing approximately 3 equiv of THF (258 mg, 0.425 mmol, 58% based on 3 equiv of THF). IH NMR (6, CDC13): 3.83 (THF, m, 16H), 2.78 (CHZ,dq, 2H), 2.39 (CHz, dq, 2H), 2.00 (C5Me5,s, 15H), 1.92 (THF, m, 16H), 1.14 (CH3, t, 3H). 13CNMR (6, CDC13): 130.1 (C&, br), 128.5 (CzB4, br), 112.0 (C5H5), 23.6 (CH2), 14.2 (CH3). "B NMR (6, CH2C12): 33.9 ( l B , d, J = 130 Hz), 25.2 (2B, d, J = 146 Hz), 2.1 (lB, d, J = 157 Hz). [Cp*Co(Et&&&)lTaCl&p (4a). (EtzCzB3H&oCp* (1.00 g, 3.15 mmol) was dissolved in 50 mL of THF, and to this solution was added a n equimolar amount of tert-butyllithium (1.74 mL, 1.8 M in hexane, 3.15 mmol) a t room temperature, resulting in a red-orange solution. After 30 min the solution was added to a flask containing CpTaCl4 (0.61 g, 1.57 mmol) in 25 mL of THF, resulting in a n immediate color change to deep green and then green-black. After the solution was stirred for 4 h, the solvent was removed by rotary evaporation and the residue was purified by column chromatography on silica in 4:l petroleum ether-CHzCl2 to afford two bands. The first band was recovered (EtzCzBsH&oCp* (0.20 g, 0.64 mmol), and the second was dark green 4a (0.40 g, 0.64 mmol, 40% based on recovered starting material). 'H NMR (6, CDC13): 6.10 (C5H5, S, 5H), 3.09 (CHz, dq, 2H), 2.69 (CHz, dq, 2H), 1.68 (C5Me5, s, 15H), 1.36 (CH3, t, 6H). 13C NMR (6, CDC13): 112.5 (C5H5), 111.3 (C2B3, br), 91.9 (C*5Me5), 23.1 (CHz), 14.7 (CH3), 10.2 (CsMe*5). IlB NMR (6, CH2C12): 62.4 (lB, d, J = 108 Hz), 36.6 (2B, d, J = 123 Hz). FTIR (cm-I): 3215 m, 3113 w,3099 w,2967 m, 2918 m, 2501 s,2362 m, 2342 m. UV-vis (nm, in CH2C12): 602 (lo%), 308 (loo%), 252 (52%). MS mlz 628 (parent ion envelope), 592 (- Cl). Anal. Calcd for C21H33B3ClzTaCo: C, 40.12; H, 5.29. Found: C, 40.18; H, 5.52. [Cp*Co(Et2C2BsH3)]TaCl&p*(4b). The same procedure was followed employing tert-butyllithium (0.87 mL, 1.8 M in hexane, 1.57 mmol), (EtzCzB3H&oCp* (0.500 g, 1.57 mmol) and Cp*TaC14 (0.61 g, 0.78 mmol). After stirring for 4 h, the solvent was removed by rotary evaporation and the residue was purified by column chromatographed in 4:l petroleum ether-CHzClz to afford two bands. The first was recovered neutral (EtzC2B3H&oCp* (102 mg, 0.64 mmol), and the second was dark green 4b (187 mg, 0.64 mmol, 42% based on recovered starting material). IH NMR (6, CDC13): 3.05 (CHZ, dq, 2H), 2.69 (CH2, dq, 2H), 2.08 (CsMes, s, 15H), 1.70 (C5Me5, CDC13): 110.1 (C2B3, S, 15H), 1.33 (CH3, t, 6H). 13C NMR (6, br), 122.6 (C5MeY5-Ta),91.3 (C*bMe&o), 23.7 (CHz), 14.3 (CH3), 13.4 (CbMe*5), 10.3 (C5Me*5). 'lB NMR (6,CH2C12): 63.4 (lB, d, J = 110 Hz), 33.1 (2B, d, J = 133 Hz). FTIR (cm-I): 3210 m, 3101 w, 2977 m, 2510 s, 2363 m, 2339 m. UV-vis (nm, in CHZC12): 615 (19%), 312 (loo%), 245 (45%). MS mlz 698 (molecular ion), 622 (- Cl). Anal. Calcd for C26H43B3C12TaCo: C, 44.69; H, 6.20. Found: C, 44.31; H, 6.11. [Cp*Co(EtzCgB3H3)]NbClzCp(4c). The same procedure was followed using tert-butyllithium (0.87 mL, 1.8 M in hexane, 1.57 mmol), (EtzCzB3H5)CoCp* (0.500 g, 1.57 mmol), and CpNbC14 (0.238 g, 0.785 mmol). After the solution was stirred for 4 h, the solvent was removed by rotary evaporation and the residue was purified by column chromatographed in 4:l petroleum ether-CHzClz to afford two bands, the first of which was recovered neutral (EtzCzB3H&oCp* (104 mg, 0.64 mmol). The second band was dark green 4c (163 mg, 0.30 mmol, 38% based on recovered starting material). 'H NMR
Organometallics, Vol. 14,No.6,1995 3025 (6 CDC13): 6.12 (C5H5, S, 5H), 2.98 (CHz, dq, 2H), 2.61 (CH2, dq, 2H), 1.71 (C5Me5, s, E H ) , 1.32 (CH3, t, 6H). 13C NMR (6, CDC13): 112.2 (C5H5), 110.5 (C2B3, br), 92.1 (C*sMes), 23.4 (CHd, 14.2 (CH3), 9.4 (C*sMes). IlB NMR (6, CHzC12): 63.0 (lB, d, J = 128 Hz), 31.7 (2B, d, J = 122 Hz). FTIR (cm-1): 3217 m,3115 m,3012 m,2978 m,2923 w,2504 s , 2 3 5 1 m, 2333 m. MS mlz 539 (parent ion envelope), 504 (- Cl). Anal. Calcd for C21H33B3C12NbCo: C, 46.65; H, 6.15. Found: C, 47.00; H, 6.23. (EtzC&4&)1TaClMeCp (5a). A 2.0 M solution of AlMe3 (1.75 mL, 2.35 mmol, 2.1 equiv) in toluene was added dropwise via syringe to la (0.500 g, 1.12 mmol) in 25 mL of THF. The mixture was stirred for 0.5 h, and the solvent was removed by rotary evaporation. The yellow solid was taken up in CH2Clz and filtered through Celite to yield 5a as lemon yellow crystals (405 mg, 0.95 mmol, 85%). Alternatively, 2.0 equiv of 1.0 M dimethylzinc can be used as a monomethylating agent to obtain 5a (83%). 'H NMR (6,C6D6): 5.45 (C5H5, s, 5H), 3.08 (CHz, dq, lH), 2.88 (CH2, dq, lH), 2.72 (CH2, dq, lH), 2.36 (CH2, dq, l H ) , 1.36 (CH3, t, 3H), 1.10 (CH3, t, 3H), 0.76 (TaCH3, S, 3H). 'H NMR (6, CDC13): 6.18 (C5H5,t, 2H), 3.12 (CH2, dq, lH), 3.00-2.71 (CH2, m, 2H), 2.51 (CHZ,dq, lH), 1.42 (CH3, d, 3H), 1.13 (CH3, d, 3H), 1.13 (Ta-CH3, s, 3H). 13C NMR (6, CDC13): 110.4 (C5H5), 41.8 (Ta-CHs), 23.2 (CH2), 23.1 (CHz), 15.0 (CHs), 14.5 (CH3). "B NMR (6,CH2C12): 37.1 (lB, d, J = 140 Hz), 26.7 (lB, d, J = 148 Hz), 17.5 (lB, d, J = 149 Hz), 0.1 (lB, d, J = 162 Hz). FTIR (cm-'): 3211 m, 2970 m, 2934 w, 2874 w, 2575 s, 2544 s, 2361 w. MS I z 425 (molecular ion), 410 (-CH3). Anal. Calcd for ClzHzzB4ClTa: C, 33.84; H, 5.21. Found: C, 33.96; H, 5.28. [(Me3Si)&B4&1TaClMeCp (5b). The above procedure was followed using AlMe3 (0.983 mL of a 2.0 M solution, 1.87 mmol, 2.1 equiv) in toluene and l b (0.500 g, 0.936 mmol) in 25 mL of THF. The yellow solid was taken up in CH& and filtered through Celite to yield 5b as lemon yellow crystals (433 mg, 0.84 mmol, 90%). IH NMR (6,CDC13): 6.14 (C5H5, s, 5H), 0.81 (Ta-CH3, s, 6H), 0.51 (SiMe3, s, 9H), 0.33 (SiMe3, s, 9H). 13C NMR (6, CDC13) 111.2 (C5H5), 44.9 (Ta-CH31, 3.0 (SiMes), 2.8 (SiMe3). IlB NMR (6,CH2Clz): 40.3 (lB, d, J = 144 Hz), 32.1 (lB, d, J = 150 Hz), 27.5 ( l B , d, J = 157 Hz), -2.3 (lB, d, J = 162 Hz). MS mlz 515 (molecular ion), 500 (CH3). Anal. Calcd for C14H30B4Si2TaCl: C, 36.49; H, 6.94. Found: C, 36.79; H, 7.35. (EtzCzB4H4)TaClMeCp*(512). The preceding procedure was followed employing AlMe3 (0.20 mL, 2.0 M in toluene, 0.40 mmol, 2.1 equiv) and IC (100 mg, 0.19 mmol), affording 5c as yellow crystals (86 mg, 0.17 mmol, 88%). Alternatively, use of diethylzinc gave 5c in 83% yield. 'H NMR (6,CDCl3): 3.10 (CH2, dq, lH), 2.91 (CH2, dq, lH), 2.77 (CH2, dq, lH), 2.55 (CH2, dq, 2H), 2.09 (C5Me5, s, 15H), 1.43 (CH3, t, 3H), 1.13 (CH3, t, 3H), 0.32 (Ta-CH3, s, 3H). 13CNMR (6, CDC13): 120.2 (C*sMes), 46.7 (Ta-CH3), 23.1 (CH2), 23.0 (CHZ),15.2 (CH3), 14.7 (CH3), 12.9 (CsMe*5). IlB NMR (6,CH2C12): 36.5 (lB, d, J = 142 Hz), 25.5 (lB, d, J = 142 Hz), 18.9 (lB, d, J = 147 Hz), 0.9 ( l B , d, J = 160 Hz). FTIR (cm-I): 3113 m, 2969 s, 2890 w, 2571 s, 2545 6,2266 w, 1986 m, 1575 m, 1567 m. MS mlz 498 (molecular ion), 483 (- CH3). Anal. Calcd for C17H32B4ClTa: C, 41.16; H, 6.50. Found: C, 40.95; H, 6.58. (EtzCzB4&)TaClEtCp (5d). A 2.0 M solution of ethylmagnesium chloride (1.75 mL, 2.35 mmol, 2.1 equiv) in toluene was added dropwise via syringe to la (0.500 g, 1.12 mmol) in 25 mL of THF. The mixture was stirred for 0.5 h, and the solvent was removed by rotary evaporation. The yellow solid was taken up in CHzCl2 and filtered through Celite to yield 5d as yellow crystals (192 mg, 0.44 mmol, 78%). 'H NMR (6, CDC13): 6.17 (C5H5, S, 5H), 3.15 (CH2, dq, l H ) , 2.85 (CHz, dq, 2H), 2.46 (Ta-CH*zCH3, m, 2H), 2.36 (Ta-CH&H*s, t, 3H), 1.84 (CH3, t, 3H), 1.43 (CH3, t, 3H). 13C NMR (6, CDC13): 111.0 (C5H5),55.1 (Ta-C*HzCHs), 23.2 (CHd, 23.0 (CHZ),20.4 (TaCH2C*H3), 15.5 (CH3), 14.7 (CHs). I'B NMR (6, CH2C12): 35.1 ( l B , d , J = 132Hz),24.5 (lB, d , J = 146Hz), 13.9(1B, d , J = 161 Hz), 0.1 (lB, d, J = 161 Hz). FTIR (cm-'1: 2918 m, 2872
3026 Organometallics, Vol.14,No. 6,1995 s, 2359 w, 2341 w, 1458 m, 1379 w. UV (nm): 368 (loo), 332
(83.4), 298 (60.4). MS mlz 439 (molecular ion), 410 (CH2CH3). (Et2CzB4H4)Ta(CHzPh)ClCp(5e). A sample of la (300 mg, 0.67 mmol) was dissolved in THF, and solid dibenzylzinc (180 mg, 0.84 mmol, 2.5 equiv of benzyl) was added under inert gas. The mixture was stirred for 2 h, following which the solvent was removed in vacuo. The residue was filtered through 3 cm of silica gel with CH2C12, and the solvent was removed to yield 5e (335 mg, 0.67 mmol, quantitative) as a red-orange solid. 'H NMR (6, CDC13): 7.23 (Ph, t, 2H), 6.91 (Ph, t, 1H), 6.81 (Ph d, 2H), 5.90 (CjH5, S, 5H), 3.29 (CH2, dq, lH), 3.20 (CH*2Ph,d, lH), 3.04-2.90 (CH2, m, 2H), 2.60 (CH2, dq, lH), 2.22 (CH*2Ph, d, l H ) , 1.46 (CH2, t, 3H), 1.14 (CHz, t, 3H). 13C NMR (6, CDC13): 149.0 (ipso CS), 129.5 (Ph), 128.1 (Ph), 123.3 (Ph), 114.8 (C5H5),72.1 (CH*2Ph), 24.5 (CH2),24.3 (CHz), 14.1 (CH3), 13.0 (CH3). "B NMR (6, CH2C12): 36.4 (lB, d, J = 140 Hz), 25.7 (lB, d, J = 145 Hz), 17.0 (lB, d, J = 141 Hz), -0.3 (lB, d, J = 160 Hz). FTIR (cm-'1: 3200 m, 2996 m, 2918 s, 2895 m, 2568 s, 2549 s, 2367 m, 1980 m, 1568 m. MS m/z 502 (molecular ion). Anal. Calcd for CleHzd34TaCl: 43.06; H, 5.22. Found: C, 43.70; H, 5.56. [(MesSi)&B4H4]Ta(CH2Ph)C1Cp (50. A sample of l b (300 mg, 0.56 mmol) was dissolved in THF, and solid dibenzylzinc (180 mg, 0.70 mmol, 2.5 equiv of benzyl) was added under inert gas. The mixture was stirred for 2 h, following which the solvent was removed in vacuo. The residue was filtered through 3 cm of silica gel with CHzC12, and the solvent was removed to yield 5f (320 mg, 0.54, 96%) as a red orange solid. IH NMR (6, CDCl3): 7.26 (Ph, t, J = 7.8 Hz, 2H), 6.91 (Ph,t,J=7.2Hz,lH),6.76(Ph,d, J=7.5H~,2H),5.84(C5H5, S, 5H), 3.58 (CH*2Ph, d, J = 13.8 Hz, lH), 1.83(CH*2Ph, d, J = 13.8 Hz, lH), 0.57 (SiMe3, s, 9H), 0.35 (SiMe3, s, 9H). 13C NMR (6, CDC13): 149.2 (ipso CS), 129.6 (Ph), 128.2 (Ph), 124.6 (Ph),111.8 (C5H5),70.5 (CHzPh), 3.4 (SiMes), 3.0 (SiMes). *lB NMR (6, CH2C12): 41.1 ( l B , d, J = 141 Hz), 31.1 (lB, d, J = 145 Hz), 27.1 (lB, d, J = 155 Hz), -2.9 (lB, d, J = 165 Hz). FTIR (cm-'): 3102 m, 2957 s, 2939 m, 2891 m, 2569 s, 2548 s, 2250 m, 1886 m. MS mlz 590 (molecular ion). Anal. Calcd for C20H34B4SizTaCl C, 40.69; H, 5.81. Found: C, 41.01; H, 6.02. (Et2C2B&)Ta(CH2Ph)ClCp* (5g). The same procedure was followed employing IC (200 mg, 0.39 mmol) and dibenzylzinc (120 mg, 0.48 mmol, 2.5 equiv of benzyl). Removal of the solvent yielded 5g as a n orange solid (194 mg, 0.34 mmol, 87%). 'H NMR (6, CDC13): 7.13 (Ph, t, 2H), 6.95 (Ph, t, lH), 6.85 (Ph, d, 2H), 3.18 (CH2, dq, lH), 3.15 (C*H2Ph, d, lH), 3.00-2.85 (CH2, m, lH), 2.60 (CH2, dq, lH), 2.28 (CH*2Ph, d, lH), 1.67 (C5Me5, s, 15H), 1.48 (CH2, t, 3H), 1.11(CH2, t, 3H). 13C NMR (6, CDC13): 149.9 (ipso CS), 129.1 (Ph), 128.0 (Ph), 124.3 (Ph), 94.2 (C*sMej), 71.3 (C*H2Ph), 24.3 (CH2), 24.0 (CH2),15.2 (CH31, 13.5 (CH31, 9.4 (C5Me"d. IlB NMR (6, CH2Cl2): 38.0 (lB, d, J = 139 Hz), 28.3 (lB, d, J = 144 Hz), 18.3 (lB, d, J = 150 Hz), -1.9 (lB, d, J = 162 Hz). MS mlz 572 (molecular ion). Anal. Calcd for C23H32B4ClTa: C, 48.62; H, 5.68, Found: C, 48.31; H, 5.15. ( E ~ ~ C ~ B ~ & ) T ~ ( C H Z C (5h). M ~ ~A) C sample ~ C ~ of l a (100 mg, 0.22 mmol) was dissolved in 25 mL of THF, and solid dineopentylmagnesium dioxane (70 mg, 0.27 mmol, 2.5 equiv of neopentyl) was added to the solution, producing a n instant color change from yellow to dark brown-black. The mixture was stirred for 2 h, after which the solvent was removed in vacuo and the residue was filtered through 3 cm of silica gel with CH2Clz; the solvent was then removed, and the residue was washed with 5 mL of cold petroleum ether to yield 5h (90 mg, 0.19 mmol, 86%) as a yellow oil. IH NMR (6, CDC13): 6.33 (C5H5, S, 5H), 3.22 (CH2, dq, lH), 2.94-2.83 (CHdC*H2tBu, m, 3H), 2.40 (CH2, dq, lH), 1.48 (CH3, t, 3H), 1.24 (C*HztBu*/ CH3, m, 13H). 13CNMR (6, CDCl3): 110.3 (C5H5), 83.2 (C*HztBu), 37.5 (C*Me3),36.2 (CMe*3),23.3 (CHz), 23.1 (CHz), 15.0 (CH31, 14.7 (CH3). "B NMR (6, CHzClz): 40.9 (lB, d, J = 146
Stockman et al. Hz), 33.2 (lB, d, J = 142 Hz), 28.0 (lB, d, J = 156 Hz), 0.3 (lB, d, J = 161 Hz). MS mlz 480 (molecular ion), 411 (-- CHZCMe3). (Et&&J&)Ta(CHzCMes)ClCp* (5i). The same procedure described for the synthesis of 5h was followed employing IC (100 mg, 0.19 mmol) and solid dineopentylmagnesium dioxane (61 mg, 0.24 mmol, 2.5 equiv of neopentyl). The mixture was stirred for 2h, with a gradual color change from yellow to dark yellow-brown, followed by workup as above to yield 5i (90 mg, 0.16 mmol, 86%) as a yellow oil. 'H NMR (6, CDC13): 3.34 (CH2,dq, lH), 2.83-2.70 (CH2 m, 2H), 2.51 (CH2, dq, lH), 2.25 (C*HztBu, d, J = 11.8 Hz, lH), 2.12 (CbMe5, s, 15H), 1.50 (CH3, t, 3H), 1.44 (CH3, t, 3H), 1.25 (tBu, S, 9H), 0.65 (C*HztBu, d, NMR (6, CDC13): 96.6 (CbMes), 81.1 J = 11.8 Hz, 1H). (C*HztBu), 36.1 (C*Me3), 32.4 (CMe*3), 24.5 (CH2),24.4 (CH21, 15.3 (CH31, 14.9 (CH31, 10.2 (C5Me*5). llB NMR (6, CH2C12): 39.2(1B,d,J= 140Hz),34.3(1B,d,J=147Hz),26.2(1B,d, J = 150 Hz), 1.2 (lB, d, J = 159 Hz). MS mlz 552 (molecular ion), 481 (- CH2CMe3). (EtzCzBdH4)TaMezCp (6a). A 1.4 M solution of methylmagnesium bromide (1.75 mL, 2.35 mmol, 2.1 equiv) in ether was added dropwise via syringe to la (0.500 g, 1.12 mmol) in 25 mL of THF. The mixture was stirred for 0.5 h, and the solvent was removed by rotary evaporation. The yellow solid was taken up in CHzClz and filtered through Celite to yield 6a as yellow fluffy crystals (413 mg, 1.02 mmol, 91%). Alternatively, 2.5 equiv of 1.4 MeLi in hexane can be used as a methylating agent to obtain approximately the same yield (87%). 'H NMR (6, CDC13): 6.02 (C5H5, S, 5H), 2.92-2.65 (CH2, m, 4H), 1.30 (CH3, t, 6H), -0.10 (Ta-CH3, s, 6H). 'H NMR (6, CDzClZ): 6.06 (CjH5, s, 5H), 2.88-2.60 (CH2, m, 4H), NMR (6, C&): 1.31 (Me, t, 6H), -0.08 (Ta-CH3, s, 6H). 5.37 (CjH5, S, 5H), 2.64 (CH2, dq, 2H), 2.49 (CHz, dq, 2H), 1.24 (CH3, t, 6H), -0.25 (Ta-CH3, s, 6H). 13C NMR (6, CDC13): 110.1 (CjHb), 50.4 (Ta-CH3), 23.0 (CH2), 15.3 (CH3). IlB NMR (6, CH2C12): 29.8 (lB, d, J = 134 Hz), 22.1 (2B, d, J = 145 Hz), -0.7 (lB, d, J = 160 Hz). FTIR (cm-'): 3115 m, 3051 w, 2967 m, 2931 m, 2876 m, 2538 s. UV-vis (nm, in CH2C12): 352 (loo%), 316 (85%), 248 (85%). MS mlz 405 (parent ion envelope), 390 (- CH3). Anal. Calcd for C I ~ H Z ~ BC, ~T 38.50; ~: H, 6.21. Found: C, 38.14; H, 6.59. [(MesSi)zCzB4H4ITaMe2Cp (6b). A 1.4 M solution of methylmagnesium bromide (2.0 mL, 2.8 mmol, 3 equiv) in ether was added dropwise via syringe to lb (0.500 g, 0.94 mmol) in 25 mL THF a t 0 "C. The mixture was stirred for 0.5 h a t 0 "C and then a t room temperature for 1 h. The solvent was removed by rotary evaporation, the yellow solid was taken up in CH2C12, filtered through Celite, and the solvent was removed to yield 6b as yellow crystals (460 mg, 0.93 mmol, 99%). IH NMR (6, CDC13): 5.97 (C5H5, s, 5H), 0.41 (SiMe3, s, 18H),0.01 (Ta-CH3, s, 6H). 13C NMR (6, CDC13): 109.2 (CjHg), 51.9 (Ta-CHs), 3.3 (SiMe3). IlB NMR (6, CDC13): 30.1 ( l B , d, J = 141 Hz), 24.7 (2B, d, J = 147 Hz), -0.9 (lB, d, J = 163 Hz). FTIR (cm-'1: 3207 m, 3115 w, 2965 m, 2955 m, 2899 w, 2563 s, 2557 s, 2521 s, 2361 w, 2343 w. UV-vis (nm, in CH2Cl2): 328 (38%),246 (100%). MS m/z 494 (molecular ion), 481 (- CH3). Anal. Calcd for C15H33BdSi2Ta: C, 36.49; H, 6.94. Found: C, 36.79; H, 7.35. (Et~Cd3~H~)TaMezCp* (612). A 1.4 M solution of methylmagnesium bromide (1.0 mL, 1.5 mmol, 3 equiv) in ether was added dropwise via syringe to IC (250 mg, 0.48 mmol) in 25 mL THF a t 0 "C. Purification as in the preceding syntheses afforded 6c as yellow fluffy crystals (225 mg, 0.46 mmol, 97%). IH NMR (6, CDC13): 2.82-2.61 (CH2, m, 4H), 1.98 (CjMe5, s, 15H), 1.29 (CH3, t, 6H), -0.53 (Ta-CH3, s, 6H). 13C NMR (6, CDC13): 117.7 (C*sMeb), 53.4 (Ta-CH3),22.9 (CHd, 15.3 (CH31, IlB NMR (6, CHzC12): 31.7 (lB, d, J = 136 Hz), 12.5 23.9 (lB, d, J = 138 Hz), -2.5 (lB, d, J = 158 Hz). FTIR (cm-I): 3225 m, 2954 s, 2943 m, 2554 s, 1965 s, 1876 m. UVvis (nm, in CH2C12): 370, (66%), 248 (100%). MS mlz 476 (parent ion envelope), 461 (- CH3). Anal. Calcd for C18H3bB4TaC, 45.45; H, 7.42. Found: C, 42.45; H, 7.70.
Carborane Ligands as Cyclopentadienyl Analogues (EtzCzB4HJTaPhzCp (6d). A 2 M solution of phenylmagnesium bromide in diethyl ether (11.2 mL, 33.6 mmol, 15 equiv) was added via syringe to a stirred solution of la (1.00 g, 2.24 mmol) in 20 mL of toluene under argon. The mixture was stirred for 1h, filtered in air, and the solvent was removed under vacuum. The yellow-brown residue was extracted with CHzClz and filtered through silica gel. The solvent was removed by rotary evaporation, and the solid residue was washed with pentane to afford 6d a s yellow crystals in quantitative yield (1.18 g, 2.24 mmol). 'H NMR ( 6 , CDC13): 7.29 (Ph, t, 4H), 7.19 (Ph, d, 4H), 7.06 (Ph, t, 2H), 6.01 (C5H5, S, 5H), 2.05 (CH2, dq, 2H), 1.97 (CHz, dq, 2H), 1.07 (CH3, dd, 6H). 13C NMR (6, CDC13): 194.4 (ipso Ph), 137.0 (Ph), 129.0 (Ph), 128.1 (Ph), 125.7 (Ph), 123.6 (Ph), 121 (CzBs, br), 110.8 (C5H5),24.4 (CH2), 14.6 (CH2). "B NMR (6, CH2C12): 34.1 (lB, d, J = 122 Hz), 22.1 (2B, d, J = 109 Hz), 2.9 ( l B , d, J = 136 Hz). MS mlz 529 (molecular ion). (EtzCzB4H4)Ta(CHzPh)zCp(6e). A 2 M solution of benzylmagnesium chloride (0.67 mL, 1.35 mmol, 3 equiv) in ether was added dropwise via syringe to la (200 mg, 0.45 mmol) in 25 mL of THF. Over the course of the addition the color slowly changed from yellow to red-orange. The mixture was stirred for 0.5 h, and the solvent was removed in vacuo. The red residue was taken up in CH2C12, filtered through Celite, and chromatographed with 4:l petroleum ether-CHzClz. One major orange band was eluted, which yielded 6e as a n orange oil (241 mg, 0.43 mmol, 96%). 'H NMR (6, CDC13): 7.18 (Ph, t, J = 7.2 Hz, 2H), 6.96-6.89 (Ph, m, 3H), 5.57 (C5H5, s, 5H), 3.01 (CH2, dq, 2H), 2.89-2.75 (CHdCH*zPh, m, 3H), 1.42 (CH3, t, 6H), 0.73 (CH*2Ph, d, J = 11.4 Hz, 1H). 13C NMR (6, CDC13): 150.4 (ipso c6), 128.9 (Ph), 128.4 (Ph), 124.5 (Ph), 119.7 (CsHs), 77.3 (CH*ZPh),22.9 (CHz), 15.1(CH3). "B NMR ( 6 , CH2C12): 31.6 (lB, d, J = 122 Hz), 22.8 (2B, d, J = 109 Hz), -0.2 (lB, d, J = 136 Hz). MS mlz 557 (parent ion envelope), 466 (- CH2Ph). Anal. Calcd for C25H33B4Ta: C, 53.84; H, 5.96. Found: C, 54.02, H, 6.10. [(MesSi)zC~B4~1Ta(CHzPh)zCp (SO. The same procedure was followed employing benzylmagnesium chloride (0.67 mL, 1.35 mmol) and l b (200 mg, 0.37 mmol) in 15 mL of THF. Over the course of the addition the color slowly changed from yellow to brown-orange. Workup as before yielded 6f (224 mg, 0.35 mmol, 96%) as a n orange-red viscous oil. 'H NMR (6, CDC13): 7.18 (Ph, t, 2H), 6.90-6.89 (Ph, t, 3H), 2.92 (CH*2Ph, d, 2H), 1.13 (CH*2Ph, d, l H ) , 0.24 (SiMe3, s, 18H). 13C NMR (6, CDC13): 148.2 (ipso CS), 130.9 (Ph), 127.7 (Ph), 124.5 (Ph), 119.7 (C5H5), 80.0 (CHZPh), 22.6 (CHz), 15.6 (CH3); "B NMR (6, CH2C12): 32.5 (lB, d, J = 129 Hz), 23.0 (2B, d, J = 115 Hz), -1.4 (lB, d, J = 146 Hz). MS mlz 645 (molecular ion), 554 (- CH2Ph). ( E ~ Z C Z B ~ H ~ ) T ~ ( C H(6g). ~ P ~A ) ~2.0 C ~M * solution of benzylmagnesium chloride (0.58 mL, 1.14 mmol, 3 equiv) in ether was added dropwise via syringe to IC (200 mg, 0.39 mmol) in 15 mL of THF. Over the course of the addition the color slowly changed from yellow to red-orange. The mixture was stirred for 0.5 h, and the solvent was removed in vacuo. The orange-red residue was taken up in CH2C12, filtered through Celite, and chromatographed with 4:l petroleum ether-CHzClz. One major orange band was eluted, which yielded 6g as a n orange oil (228 mg, 0.36 mmol, 94%). 'H NMR (6, CDC13): 7.23 (Ph, t, J = 7.2 Hz, 2H), 6.98-6.80 (Ph, m, 3H), 2.55-2.30 (CH2, m, 4H), 2.14 (CH*2Ph, d, J = 11.4 Hz, 1H) 1.97 (CsMe6, s, E H ) , 1.14 (CH*2Ph, d, J = 11.4 Hz, NMR ( 6 , CDC13): 149.5 (ipso CS), lH), 1.05 (CH3, t, 6H). 130.4 (Ph), 127.2 (Ph), 125.2 (Ph), 95.7 (C*sMes), 80.1 (C*H2Ph), 24.1 (CHz), 14.1 (CH3), 10.9 (CsMe*5). llB NMR ( 6 , CH2Cl2): 32.0 ( l B , d, J = 127 Hz), 22.4 (2B, d, J = 118 Hz), -1.2 ( l B , d, J = 145 Hz). MS mlz 628 (parent ion envelope), 535 (- CH2Ph). Anal. Calcd for C30H43B4Ta: C, 57.84; H, 6.90. Found: C, 58.80; H, 7.12. ( E ~ Z C ~ B ~ H ~ ) T ~ ( C H(6h). ~CA Msample ~ ~ ) ~ of C la ~ (100 mg, 0.22 mmol) was dissolved in 25 mL of THF, and solid neopentyllithium (44 mg, 0.56 mmol, 2.5 equiv) was added to
Organometallics, Vol. 14, No. 6, 1995 3027 the solution, producing a n instant color change from yellow to dark brown. The mixture was stirred for 0.5 h, following which the solvent was removed in vacuo. The residue was filtered through 3 cm of silica gel with CH2C12, and the solvent was removed, after which the residue was washed with 5 mL of cold petroleum ether to yield 6h (102 mg, 0.20 mmol, 90%) as a yellow oil which decomposed overnight, under inert gas, generating a n uncharacterizable brown residue. 'H NMR (6, CDCl3): 6.13 (C5H5, S, 5H), 2.73 (CHz, dq, 2H), 2.51 (CH2, dq, 2H), 1.29 (CH3, t 6H), 1.24 (CH*ztBu, d, 2H), 1.00 (tBu, S, 18H), -0.34 (CH*ztBu, d, 2H). 13C NMR (6, CDC13): 120 (CzBs), 106.6 (C5H5), 90.2 (C*HztBu), 38.4 (C*Me3), 35.2 (CMe*3), 22.6 (CH2), 15.1(CH3). "B NMR (6, CHzC12): 31.5 (lB, d, J = 135 Hz), 24.5 (2B, d, J = 119 Hz), -2.6 (lB, d, J = 137 Hz). MS mlz 517 (molecular ion), 446 (- CH2CMe3). [ ( M ~ ~ S ~ ) ~ C ~ B ~ H ~ ] T ~ (6i). ( C HThe ZCM preceding ~~)ZC~ procedure was followed employing neopentyllithium (37 mg, 0.48 mmol) and l b (100 mg, 0.19 mmol), which produced a red-orange solution on addition of the latter reagent. The solution was stirred for 30 min, after which solvent was removed, and the orange-brown solid was filtered through silica gel and chromatographed on silica to give a single yellow band that afforded 6i (78 mg, 0.13 mmol, 68%) as a yellow oil. lH NMR (6, CDC13): 6.14 (C5H5, s, 5H), 1.14 (CH*2CMe3, d, 2H), 1.02 (CMe3, s, 18H), 0.43 (SiMe3, s, 18H), 0.81 (CH3-Ta, s, 3H), -0.37 (CH*2CMe3, d, 2H). 13C NMR (6, CDC13): 105.8 (C5H5), 92.1 (C2B3), 35.2 (CMe*3), 31.6 (C*Me3), 29.6 (CHz), 3.6 (SiMe3). llB NMR (6, CH2C12): 40.0 (lB, d, J = 150 Hz), 25.2 (2B, d, J = 145 Hz), 0.9 (lB, d, J = 155 Hz). MS mlz 605 (molecular ion), 534 (- CH2CMe3). (Et&zB&)Ta(CHzCMes)2Cp* (6.9. The same procedure was followed employing neopentyllithium (30 mg, 36.0 mmol) and IC(50 mg, 0.09 mmol). Filtration through silica gel gave 6j as a yellow solid (39 mg, 0.06 mmol, 75%). As with 6h, this product decomposed overnight under inert gas. 'H NMR (6, CDC13): 2.69 (CH*2, dq, 2H), 2.49 (CH*2, dq, 2H), 2.02 (C5Me5, s, E H ) , 1.19 (CH*2CMe3, d, 2H), 1.07 (CH3, t, 6H), 0.88 (CMe3, s, 18H), -0.30 (CH*2CMe3, d, 2H). NMR ( 6 , CDC13): 122 (C2B3), 96.4 (C*sMed, 91.0 (C*HzCMe3), 39.1 (CMe*3), 35.4 (CMe*3), 22.5 (CHZ),15.0 (CH3), 9.6 (CsMe*5). MS mlz 587 (molecular ion), 516 (- CH2CMe3). (EtzCzBJ&)Ta(OPh)&p(6k). Phenol (126 mg, 1.3mmol) was added dropwise to a suspension of NaH (100 mg, 4.1 mmol) in 15 mL of THF. The PhONa solution was allowed to settle and then was decanted to a solution of l a (200 mg, 0.45 mmol) in 10 mL of THF. The solution was stirred for 2 h, the solvent was removed, and the residue was taken up in CH2Clz and filtered through 3 cm of silica gel to give 6k (245 mg, 0.44 mmol, 97%) as a n opaque yellow oil. 'H NMR (6, CDCl3): 7.35 (Ph, t, J = 7.8 Hz, 2H), 6.98 (Ph, t, J = 7.2 Hz, lH), 6.73 (Ph, d, J = 8.1 Hz, 2H), 6.26 (CsH5, S, 5H), 2.92 (CHz, dq, 2H), 2.51 (CH2, dq, 2H), 1.25 (CH3, t, 6H). 13C NMR (6, CDCl3): 165.0 (ipso CS), 129.9 (Ph), 126.1 (C2B3, br), 121.6 (Ph), 118.3 (Ph), 112.2 (C5H5), 23.0 (CH2), 14.9 (CH3). "B NMR (6, CH2C12): 20.7 (3B, unresolved coupling), -9.8 ( l B , d, J = 150 Hz). FTIR (cm-I): 3132 w, 3063 w, 3030 w, 2967 m, 2931 m, 2874 w, 2561 s, 2343 w, 1587 s, 1481 s, 1248 s, 1161 m, 891 m, 869 m, 839 m. UV-vis (nm, in CH2C12): 344 (40%), 296 (loo%), 260 (83%). Anal. Calcd for C~3H29B402Ta:C, 49.18; H, 5.20. Found: C, 49.45; H, 5.24. Cp*Co(Et&sBSHs)TaMeClCp (7a). A 1.0 M solution of dimethylzinc (1.0 mL, 0.96 mmol, 1equiv) in ether was added dropwise via syringe to 4a (204 mg, 0.32 mmol) in 25 mL of THF at room temperature causing a color change from dark green to dark red. The mixture was stirred for 0.5 h, after which the solvent was removed by rotary evaporation. The red-black solid was chromatographed in 3:l petroleum etherCH2C12 affording red-black 7a (190 mg, 0.32 mmol, quantitative). 'H NMR (6, CDC13): 5.78 (C5H5, S, 5H), 2.98 (CH2, dq, lH), 2.79 (CH2, m, 2H), 2.61 (CHZ,dq, 1H), 1.80 (CH3, t, 3H), 1.75 (C5Me5, s, E H ) , 1.61 (CH3, t, 3H), 0.58 (Ta-CH3, s, 3H). 13C NMR (6, CDC13): 109.1 (C5H51, 104.0 (C2B3, br), 102.5
3028 Organometallics, Vol. 14, No. 6, 1995
Stockman et al.
was stirred for 2 h, following which the solvent was removed (C2B3, br), 91.3 (C5Me5),40.7 (Ta-CH3),23.1 (CHz), 22.8 (CHz), in vacuo. The residue was filtered through 3 cm of silica gel 15.1(CH3), 14.4 (CH3),9.9 (CsMeb). llB NMR (6, CHzClZ): 65.7 with CHzC12, and the solvent was removed, after which the (lB, d, J = 110 Hz), 30.8 (lB, d, J = 101 Hz), 22.4 (lB, d, J = residue was washed with 5 mL of cold petroleum ether to yield 98 Hz). UV-vis (nm, in CHzC12): 322 (loo%), 243 (51%). MS 7e (80 mg, 0.13 mmol, 80%) as a reddish solid. 'H NMR (6, mlz 608 (molecular ion), 594 (- CH3). Anal. Calcd for CDCl3): 5.95 (C5H5, S, 5H), 3.03 (CH2, dq, lH), 2.85 (CH2, dq, C~2H36B3CoTaCl:C, 43.44; H, 5.97. Found: C, 44.01; H, 5.51. 2H), 2.38 (CHz, dq, lH), 2.08 (CHztBu, d, J = 12 Hz, lH), 1.75 Cp*Co(Et2CzB3H3)TaMezCp(a).A 1.4 M solution of (CH3, t, 3H), 1.69 (C5Me5, s, E H ) , 1.18 (CHztBu, d, J = 12 methylmagnesium bromide (0.86 mL, 1.2 mmol, 3 equiv) in Hz, lH), 1.04 (CMe3, t, 9H), 1.01 (CH3, t, 3H). I3C NMR ( 6 , ether was added dropwise via syringe to 4a (251 mg, 0.40 CDC13): 108.3 (C5H5), 84.5 (CHztBu), 91.5 (CbMes), 36.4 mmol) in 25 mL of THF at room temperature causing a color (CMe3), 35.1 (CMe3), 22.1 (CHZ),22.5 (CH2), 15.1 (CH31, 13.4 change from dark green to dark red. The mixture was stirred (CH3), 10.2 (C5Me*5). MS mlz 665 (molecular ion). llB NMR for 0.5 h, after which solvent was removed by rotary evapora(6, CHzC12): 65.4 (lB, d, J = 140 Hz), 30.4 (lB, unresolved), tion. The red-black solid was chromatographed in 3:l petro23.5 (lB, unresolved). leum ether-CHzClz affording red-black 7b (233 mg, 0.40 Cp*Co(Et&zB3H3)Ta(CHzCMes)zCp(70. A sample of 4a mmol, quantitative). 'H NMR ( 6 , CDC13): 5.73 (C5H5, s, 5H), (100 mg, 0.16 mmol) was dissolved in 25 mL of THF, and solid 2.85-2.65 (CH2, m, 4H), 1.70 (CsMes, s, 15H), 1.35 (CH3, t, neopentyllithium (31 mg, 0.40 mmol, 2.5 equiv of neopentyl) 6H), -0.44 (Ta-CH3,s, 6H). I3C NMR (6, CDC13): 108.5 (C5H51, was added to the solution causing a color change from dark 104.2 (C&, br), 90.4 (CsMes), 52.1 (Ta-CH31, 23.0 (CH2), 15.3 green t o dark red over 1 h. The mixture was stirred for 2 h, (CH3), 10.4 (C5Me5). IIB NMR (6, CH2C12): 17.7 (lB, d, J = following which the solvent was removed in vacuo. The 103 Hz), 27.8 (2B, d, J = 102 Hz). FTIR (cm-I): 3214 m, 3112 residue was filtered through 3 cm of silica gel with CHzC12, w, 3095 w, 2977 m, 2928 m, 2505 s, 2352 m, 2341 m. UV-vis and the solvent was removed, after which the residue was (nm, in CH2C12): 312 (loo%), 246 (33%). MS mlz 586 (molecwith 5 mL of cold petroleum ether to yield 7f (65 mg, ular ion), 571 (- CH3). Anal. Calcd for C Z ~ H ~ ~ B ~ C, C O T ~ washed : 0.09 mmol, 58%) as a reddish solid. 'H NMR (6, CDC13): 5.84 46.99; H, 6.69. Found: C, 49.39; H, 6.43. (C5H5, 9, 5H), 2.69 (CH2, dq, 2H), 2.54 (CH2, dq, 2H), 1.70 (C5Cp*Co(Et2CzBsHs)Ta(CH2Ph)ClCp(7c). A sample of 4a Me5, s, 15H), 1.65 (CH2, d, 2H), 1.34 (CH3, t, 3H), 0.93 (CMe3, (180 mg, 0.29 mmol) was dissolved in 25 mL of THF and solid S, 18H), -0.26 (CH2, d, J = 12 Hz, 2H). I3C NMR (6, CDC13): dibenzylzinc (214 mg, 0.87 mmol) was added to the solution 106.3 (C5H51, 104.2 (CZB3, br), 90.9 (CH21, 90.1 (C*5Me5), 37.4 causing a gradual color change from dark green to dark red (C*Me3),35.3 (CMe*3),22.1 (CHz), 15.0 (CH3), 10.4 (CbMe*s). over 1 h. The mixture was stirred for 2 h, following which "B NMR (6, CH2Clz): 60.1 ( l B , d, J = 145 Hz), 27.3 (2B, d, J the solvent was removed in vacuo. The residue was filtered = 131 Hz). MS mlz 700 (molecular ion), 628 (- CH2CMe3). through 3 cm of silica gel with CHzC12, and the solvent was (Et2CzB4K)NbMezCp (8a). A 1.4 M solution of methylremoved, after which the residue was washed with 5 mL of magnesium bromide (4.9 mL, 6.9 mmol, 10 equiv) in ether was cold petroleum ether to yield 7c (191 mg, 0.28 mmol, quantitaadded dropwise via syringe to (EtzCzB4H4)NbClzCp (250 mg, tive) as a dark red solid. 'H NMR (6, CDC13): 7.16 (Ph, t, J = 0.69 mmol) in 25 mL of THF at 0 "C. The mixture was stirred 7.8 Hz, 2H), 6.85 (Ph, d, J = 7.8 Hz, 2H), 6.80 (Ph, d, J = 7.2 for 0.5 h a t 0 "C and then a t room temperature for 1 h. The Hz, lH), 5.60 (C5H5,s, 5H), 3.20 (CHZ,dq, lH), 3.01 (CH2, m, solvent was removed by rotary evaporation, the yellow solid 2H), 2.68 (CH*2Ph, d, J = 12.6 Hz, l H ) , 2.53 (CH2, dq, lH), was taken up in CHzClz and filtered through Celite, and the 2.25 (CH*ZPh, d, J = 12.6 Hz, lH), 1.74 (CH3, t, 3H), 1.72 (C5solvent was removed to yield 8a as yellow crystals (206 mg, Me5, s, 15H) 1.01 (CH3, t, 3H). I3C NMR (6, CDC13): 151 (ipso 0.65 mmol, 95%). 'H NMR (6, CDC13): 6.01 (C5H5, s, 5H), 2.75 CS),129.5 (Ph), 127.8 (Ph), 123.4 (Ph), 110.4 (C5H5), 91.4 (c*5(CH2, m, 4H), 1.33 (CH3, t, 6H), 0.23 (Ta-CH3,s, 6H). I3C NMR Me5), 67.8 (C*H2Ph), 23.8 (CH2), 22.1 (CH2), 15.2 (CH3), 15.1 (6, CDC13): 108.8 (C5H5), 44.4 (Nb-CH3),23.5(CHz), 15.2 (CH3). (CH3), 10.4 (C5Me*5). IIB NMR (6, CHzC12): 65.9 (lB, d, J = "B NMR (6, CH2C12): 34.1 (lB, d, J = 130 Hz), 23.6 (lB, d, J 137 Hz), 31.3 (lB, d, J = 125 Hz), 24.2 ( l B , d, J = 139 Hz). = 138 Hz), -3.1 (lB, d, J = 161 Hz). FTIR (cm-'1: 2937 s, UV-vis (nm, in CH2C12): 250 (58%), 310 (loo%), 548 (lo%), 2874 m, 2361 s, 1458 m, 1379 m. W - v i s (nm, in CH2C12): MS mlz 685 (molecular ion). Anal. Calcd for C28H40B3372 (25%), 236 (100%). MS mlz 315 (parent ion envelope), 302 CoTaC1: C, 49.14; H, 5.89. Found: C, 48.94; H, 5.60. (-- Me). Anal. Calcd for C13H25B4Nb: C, 49.18; H, 7.94. Cp*Co(EtzCzB3H3)Ta(CHzPh)zCp(7d). A 2 M solution Found: C, 48.44; H, 7.58. of benzylmagnesium chloride (0.60 mL, 1.20 mmol, 3 equiv) (EtzCzB4K)Nb(CHzPh)2Cp (8b). A 2.0 M solution of in ether was added dropwise via syringe to a sample of 4a benzylmagnesium chloride (0.84 mL, 1.35 mmol) in ether was (250 mg, 0.16 mmol) in 25 mL of THF causing a gradual color added dropwise via syringe to 2 (200 mg, 0.55 mmol) in 15 change from dark green to dark red over 1 h. The mixture mL of THF. Over the course of the addition the color slowly was stirred for 2 h, following which the solvent was removed changed from red-orange to brown-orange. The mixture was in vacuo. The residue was filtered through 3 cm of silica gel stirred for 0.5 h, and the solvent was removed in vacuo. The with CHzClZ, and the solvent was removed, after which the brown residue was taken up in CH2C12, filtered through Celite, residue was washed with 5 mL of cold petroleum ether to yield and chromatographed with 4:l petroleum ether-CH~Cl2. One 7d (294 mg, 0.16 mmol, quantitative) as a reddish purple solid. major orange band was eluted, which yielded 8d as a yellow 'H NMR (6, CDC13): 7.14 (Ph, t, 2H), 6.80 (Ph, t, J = 7.2 Hz, solid (241 mg, 0.43 mmol, 96%). IH NMR (6, CDC13): 7.19 lH), 6.74 (Ph, d, 2H), 5.26 (C5H5, s, 5H), 3.00-2.80 (CH2, m, (Ph, t, 2H), 6.95 (Ph, t, lH), 6.72 (Ph, d, J = 2H), 5.46 (C5H5, 4H), 2.35 (CH*2Ph, d, J = 11.4 Hz, 2H), 1.75 (CsMe5, s, 15H), S, 5H), 3.53 (CH*zPh, d, 2H), 2.97 (CHz, dq, 2H), 2.79 (CHz, 1.48 (CH3, t, 6H), 0.84 (CH*2Ph, d, J = 11.4 Hz, 2H). I3C NMR dq, 2H), 1.43 (CH3, t, 6H), 0.62 (CH*zPh, d, 1H). I3C NMR (6, (6, CDC13): 153.4 (ipso CS), 128.2 (Ph), 127.9 (Ph), 123.2 (Ph), CDC13): 150.5 (ipso CS), 128.4 (Ph), 128.2 (Ph), 124.3 (Ph), 110.0 (C5H5), 105.5 (C&), 90.8 (C5Me5), 76.9 (C*HZPh), 22.2 110.3 (C5H5), 121 (C2B4, br), 75.6 (C*H2Ph), 22.9 (CHz), 15.4 (CH2), 15.4 (CH3), 10.4 (CsMe5). 'lB NMR (6, CH2C12): 63.0 (lB, d, J = 157 Hz), 28.2 (lB, d, J = 145 Hz). UV-vis (nm, in (CHd. "B NMR (6, CH2C12): 32.5 (lB, d, J = 129 Hz), 23.8 (2B, d, J = 124 Hz), 2.0 ( l B , d, J = 139 Hz). MS mlz 469 CH2Clz): 250 (58%), 310 (loo%), 548 (lo%), MS mlz 741 (parent ion envelope), 378 (- CH2Ph). (molecular ion). Anal. Calcd for C23H36B3CoTa: C, 56.80; H, 6.40. Found: C, 57.06; H, 6.61. Reaction of 6a with HBF4 i n Acetonitrile. A 50 mg sample (0.12 mmol) of 6a was dissolved in 5 mL of CH3CN in Cp*Co(Et2C2BsH3)Ta(CH2CMe3)ClCp(7e). A sample of a scintillation vial, following which 912 mg of HBF4.OEt2 in 7a (100 mg, 0.16 mmol) was dissolved in 25 mL of THF, and 9.5 g of CH3CN was added. Slight gas evolution was observed solid dineopentylmagnesium dioxane (50 mg, 0.20 mmol, 2.5 during the addition, but there was no color change. The equiv of neopentyl) was added to the solution producing a color solution was allowed to stand a t room temperature for 4 h, change from dark green to dark red over 1 h. The mixture
Organometallics, Vol. 14,No. 6, 1995 3029
Carborane Ligands as Cyclopentadienyl Analogues
maps, and those of the remaining compounds by direct after which the solvent was removed in vacuo t o yield methods using the SIR88 program.36 The structures were (EtzC2B4H4)Ta(NCMe)2Cp(Sb) as a yellow solid which was refined using full-matrix least-squares calculations with anisoinsoluble in nonpolar solvents, slightly soluble in CH2C12, and tropic thermal displacement parameters for all non-hydrogen readily soluble in polar solvents (CHsCN, THF). 'H NMR (6, atoms except the carbon atoms of the Cp* group in IC. In the CDC13): 6.45 (C5H5, S, 5H), 2.82 (CHz, dq, 2H), 2.52 (CHz, dq, latter case, the ring was found t o be disordered between two 2H), 2.01 (CH&N, S, 6H), 1.22 (CH3, t, 6H). 'H NMR (6, CD3orientations related by a ca. 20" rotation around an axis CN): 6.57 (C5H5, S, 5H), 2.74 (CH2, dq, 2H), 2.51 (CHz, dq, perpendicular to the plane of the ring. The carbon atoms 2H), 2.01 (CHsCN, S, 6H), 1.16 (CH3, t, 6H). 'H NMR (6, belonging to the two orientations were refined with the (CD&C=O): 6.59 (C5H5, S, 5H), 2.70 (CHz, dq, 2H), 2.50 (CH2, population parameters of 0.5 and isotropic thermal paramdq, 2H), 2.01 (CH3CN, S, 6H), 1.18 (CH3, t, 6H). 'H NMR (6, eters. The final difference Fourier maps were essentially CDzC12): 6.46 (C5H5, S, 5H), 4.20 (9, EtzO), 2.89 (CH2, dq, 2H), featureless except that for l b which showed a peak ca. 2.5 2.49 (CH2, dq, 2H), 2.03 (CH3CN, s), 1.40 (t, EtzO), 1.22 (CH3, efA3 high located in the vicinity of the Ta atom. t, 6H). "B NMR (6, CH3CN): 25.7 (lB, d, J = 162 Hz), 23.3 (lB, d, J = 157 Hz), -0.8 ( l B , s), -9.6 (lB, d, J = 166 Hz). MS mlz 414 (molecular ion). Anal. Calcd for C ~ ~ H ~ S B ~ N Z F B -Acknowledgment. This work was supported in part Ta: C, 28.54; H, 3.99; N, 4.44. Found: C, 29.51; H, 4.40; N, by the National Science Foundation, Grant No. DHE4.27.
X-ray Data Collection and Structure Determination. All measurements were conducted on a Rigaku AFC6S diffractometer either a t -100 "C (lb, 4a, and 7b,c) or at -120 "C (IC,6d, and 8a) using Mo K a radiation (A = 0.710 69 A). Details of the measurement and structure analysis procedures are summarized in Table 1. For each crystal, the intensities of three standard reflections were monitored, showing no significant variation. Empirical absorption corrections were applied following W scanning of several reflections with the x angle close t o 90" (transmission factors are reported in Table 1). All calculations were performed on a VAX station 3520 computer employing the TEXSAN 5.0 crystallographic software package.35 The structures of IC,6d, and 8a were solved by heavy atom techniques applying Patterson and Fourier
9322490 to R.N.G., and by the American Cancer Society (Junior Faculty Research Award No. C-66910) to M.G.F. Supplementary Material Available: Tables of thermal parameters, atom coordinates, and calculated least-squares planes (24 pages). Ordering information is given on any current masthead page. OM950160X
(35) TEXSAN 5.0: Single-Crystal Structure Analysis Software; Molecular Structure Corporation: The Woodlands, TX 77381, 1989. (36) SIR88; Burla, M. C.; Camalli, M.; Cascarano, G.; Giacovazzo, C.; Polidori, G.; Spagna, R.; Viterbo, D. J . Appl. Crystallogr. 1989,22, 389.
