Group 4 Metal Mono-Dicarbollide Piano Stool Complexes. Synthesis

Jun 15, 1995 - Daniel E. Bowen and Richard F. Jordan*. Department of Chemistry, University of Iowa, Iowa City, Iowa 52242. Robin D. Rogers. Department...
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Organometallics 1996, 14, 3630-3635

3630

Articles Group 4 Metal Mono-Dicarbollide Piano Stool Complexes. Synthesis, Structure, and Reactivity of (96-C2BsH11)M(NR2)2(NHR2) (M = Zr, R = Et; M = Ti, R = Me, Et) Daniel E. Bowen and Richard F. Jordan* Department of Chemistry, University of Iowa, Iowa City, Iowa 52242

Robin D. Rogers Department of Chemistry, Northern Illinois University, DeKalb, Illinois 60115 Received March 13, 1995@ The amine elimination reaction of C2B9H13 and Zr(NEtd4 yields the mono-dicarbollide complex (r5-C2B9H11)Zr(NEtz)z(NHEt2) (l),which has been shown to adopt a three-legged piano stool structure by X-ray crystallogra hy. Crystal data for 1: space group P21/c, a = 10.704(4)A, b = 11.066(3)A, c = 20.382(8) ,/?= 99.20(3)", V = 2383(1) Hi3, 2 = 4. Complex 1 undergoes facile ligand substitution by THF and 4-picoline, yielding (r5-C2BgH11)Zr(NEt2)2(THF) (2) and (1;15-C2BgH11)Zr(NEt~)~(4-picoline)2 (3). Compound 3 exists as the fourcoordinate species (y5-C2BgH11)Zr(NEt2)2(4-picoline)in CH2Cl2 solution. Complex 1 reacts (4). Similarly, selectively with 2 equiv of [NHzEt21Cl, yielding (r5-C2BgH11)ZrC12(NHEt2)2 the reaction of C2BgH13 and T i ( N R 2 1 4 yields (r5-C2BgHll)Ti(NR2)~(NHR~) (5, R = Me; 6, R = Et). Compounds 1-6 are potential precursors to group 4 metal (r5-C2B~H11)MR2L,alkyl species.

8:

Introduction Group 4 metal bent-metallocene y5-dicarbollidespecies of general type (r5-C2BgHll)(CsR5)M(R)and (q5C2BgHll)(C5R5)M(R)(L)(M = Ti, Zr, Hf; L = labile ligand) undergo a variety of ligand exchange, insertion (alkenes, alkynes, etc.), and ligand C-H activation reactions characteristics of electrophilic metal The combination of an electron deficient, Lewis acidic metal center (do,14-electron),a reactive M-R bond, and the presence of vacant coordination sites cis to the M-R bond promotes the coordination and activation of substrates by these complexes. These species are related t o (CsR&M(R)+ (M = group 4, a ~ t i n i d eand ) ~ (C5R&M(R) (M = group 3, lanthanide)4 complexes by formal replacement of a Cp- ligand by the isolobal C2BgH1l2ligand, and t o Cp2M(R)X species (M = group 4) by replacement of a Cp- and an X- ligand by CzBgH1l2-. A variety of other early transition metal bent-metal@Abstractpublished in Advance ACS Abstracts, June 15, 1995. (1)M = Zr, Hf: (a)Crowther, D. J.; Baenziger, N. C.; Jordan, R. F. J . Am. Chem. SOC.1991,113,1455.(b)Jordan, R. F. Makromol. Chem., Macromol. Symp. 1993,66,121.(c) Jordan, R. F. New Organometallic Models for Ziegler-Natta Catalysts. In Proceedings of the World Metallocene Conference; Catalyst Consultants Inc.: 1993;pp 89-96. (2)M = Ti: Kreuder, C.; Zhang, H.; Jordan, R. F. Organometallics, in press. (3)Reviews: (a) Jordan, R. F. Adv. Organomet. Chem. 1991,32,325. (b) Marks, T. J. Acc. Chem. Res. 1992,25,57. (4)Reviews and leading references (a) Watson, P. L.; Parshall, G. W. Acc. Chem. Res. 1985,18,51. (b) Thompson, M. E.; Bercaw, J. E. Pure Appl. Chem. 1984,56,1. (c) Schumann, H. Angew. Chem., Int. Ed. Engl. 1984,23,474.(d) Evans, W. J . Adu. Organomet. Chem. 1985, 24,131. (e) Burger, B. J.; Thompson, M. E.; Cotter, D.; Bercaw, J . E. J . A m . Chem. SOC. 1990, 112, 1566. (0 Schaverien, C. J. Adu. Organomet. Chem. 1994,36,283.

0276-7333/95/2314-3630$09.00/0

locene systems containing $-carboranyl ligands have been ~ r e p a r e d . ~ , ~ Group 4 metal mono-dicarbollide piano stool complexes of general type ($-C2BgH1l)MX2Ln (L = labile ligand, n = 0-3) are of interest because of the possibility of achieving higher levels of metal unsaturation and concomitant higher reactivity than in the bent-metallocene systems. For example, a do ($-C~BSH~I)M(R)~ or (v5-C2BgH11)M(R)Xcomplex is isolobal with group 4 metal (CsRs)M(R)z+and (C5R4SiRzNR)M(R)+specie^,^,^ which have been shown t o coordinate arenes, undergo (5)Group 3: (a) Bazan, G. C.; Schaefer, W. P.; Bercaw, J . E. Organometallics 1993,12,2126. (b) Marsh, R. E.; Schaefer, W. P.; Bazan, G. C.; Bercaw, J. E. Acta Crystallogr. 1992,C48, 1416. (c) Oki, A. R.; Zhang, H.; Hosmane, N. S. Organometallics 1991,10, 3964. Group 4: (d) Siriwardane, U.;Zhang, H.; Hosmane, N. S. J . A m . Chem. SOC.1990, 112, 9637. (e) Hosmane, N. S.; Wang, Y.; Zhang, H.; Maguire, J. A,; Waldhoer, E.; Kaim, W.; Binder, H.; Kremer, R. K. Organometallics 1994,13,4156. (0 Jia, L.;Zhang, H.; Hosmane, N. S. Acta Crystallogr. 1993,C49, 453. Group 5: (g) Uhrhammer, R.; Crowther, D. J.; Olson, J . D.; Swenson, D. C.; Jordan, R. F. Organometallics 1992,1I,3098. (h) Uhrhammer, R.; Su, Y.; Swenson, D. C.; Jordan, R. F. Inorg. Chem. 1994,33,4398. (i) Houseknecht, K.L.; Stockman, K. E.; Sabat, M.; Finn, M. G.; Grimes, R. N. J . A m . Chem. SOC.1995,117,1163. f-Element: (j) Fronczek, F. R.; Halstead, G. W.; Raymond, K. N. J . A m . Chem. SOC.1977,99,1769. (k) Manning, M. J.; Knobler, C. B.; Khattar, R.; Hawthorne, M. F. Inorg. Chem. 1991, 30, 2009. (6)For a recent review see: Saxena, A. K.; Hosmane, N. S. Chem. Reu. 1993,93,1081. (7)(a) Pellecchia, C.; Immirzi, A.; Pappalardo, D.; Pelusa, A. Organometallics 1994, 13, 3773. (b) Pellecchia, C.; Immirzi, A.; Zambelli, A. J . Organomet. Chem. 1994,479,C9. (c) Pellecchia, C.; Immirzi, A,; Grassi, A.; Zambelli, A. Organometallics 1993,12,4473. (d) Quyoum, R.; Wang, Q.; Tudoret, M.-J.; Baird, M. C.; Gillis, D. J. J . Am. Chem. SOC.1994,116,6435.(e)Gillis, D.J.; Tudoret, M.-J.; Baird, M. C. J . A m . Chem. SOC.1993,115,2543.(DCrowther, D.J.;Jordan, R. F.; Baenziger, N. C. Organometallics 1990,9,2574.

0 1995 American Chemical Society

Group 4 Metal Mono-Dicarbollide Piano Stool Complexes

C2B9H13

-

Organometallics, Vol. 14,No. 8,1995 3631

Scheme 1

Zr(NEf214 toluene, 23 OC

- NHEt2

I

THF ___t

,Zh NHEt2 Et2N L NEt2 1

Ti(N R2)4 toluene 23 OC

- NHR2 2 (NH2Et21CI

t

- 3 NHEt2

I

(C2BgH1 )Zr(NEt2)2(4-pi~~li ne)2

3 4-picoline

- 4-picoline

4

5,R=Me 6, R = Et

1 2-

I

clean olefin insertion reactions, and catalyze olefin polymerization, and with group 3 and lanthanide metal (CsRs)M(R)2 and (CsR5)M(R)(OR) specie^.^ However, early metal piano stool complexes based on q5-dicarbollide or related dianionic q5-carboranylligands are rare, being restricted to several group 5 and lanthanide species, e.g., (q5-C2BgH11)TG (X = C1, Me),Q (q5C2BgH11)M(THF)4 (M = Sm, Yb), and (q5-C2B~H11)Yb(DMF)4.5k Here we report that amine elimination reactions provide a convenient entry to group 4 metal mono-dicarbollide complexes. Results and Discussion Synthesis of (q5-C2BsH11)Zr(NEt2)2(~t2)(1). The new chemistry we have developed is summarized in Scheme 1. The amine elimination reaction of C2BgH13 and Zr(NEt2)4 proceeds readily in toluene at 23 ‘C, yielding (q5-C2BgH11)Zr(NEt2)2(NHEt2) (1)and 1equiv of NHEt2. Compound 1 is soluble and reasonably stable in CH2C12,1° but is only sparingly soluble in toluene or hexane despite the presence of six ethyl groups. Accordingly, 1 is isolated as a yellow solid by recrystallization from CH2C12/toluene. The llB NMR spectrum of ~~~~

(8) Representative patent literature concerning use of (C5R4SiRzNR)M(R)+species as olefin polymerization catalysts: (a) Canich, J. M. Eur. Pat. Appl. 420 436, 1991, (b) Canich, J. M.; Hlatky, G . G.; Turner, H. W. U.S. Patent 542 236,1990. (c) Stevens, J. C.; Timmers, F. J.; Wilson, D. R.; Schmidt, G. F.; Nickias, P. N.; Rosen, R. K; Knight, G. W.; Lai, S. Eur. Pat. 416 815,1990. (d) Campbell, R. E. U.S. Patent 5 066 741,1991. (e) LaPointe, R. E.; Rosen, R. K.; Nickias, P. N. Eur. Pat. 495 375, 1992. (9) (a) van der Heijden, H.; Schaverien, C. J.; Orpen, A. G. Organometallics 1989,8,255. (b) van der Heijden, H.; Pasman, P.; de Boer, E. J. M.; Schaverien, C. J.; Orpen, A. G. Organometallics 1989,8,1459. (c) Schaverien, C. J. J. Mol. Catal. 1994,90, 177. (d) Schaverien, C. J. Organometallics 1994, 13, 69. (10) Complex 1 decomposes slowly (ca. 20% after 48 h at 23 “C) in CHzClz to a species tentatively identified as (r5-CzBsHll)Zr(C1)(NEt2)(NHEt2).

1 contains five resonances in a 1/2/2/3/1 intensity ratio which are in the range observed for other early metal q5-dicarbollidecomplexes and are shifted downfield from the resonances for C2BgH13 and C2BgH12- or C2BsH112salts.ll The lH NMR spectrum contains a singlet for the dicarbollide C-H hydrogens, which confirms the C, symmetry implied by the llB spectrum, and appropriate resonances for one NHEt2 ligand (shifted from the free amine resonances) and two -NEt2 ligands. Two multiplets are observed for the NH(CH2CH3)2 methylene hydrogens, consistent with the expected diastereotopicity resulting from coordination of the amine to Zr. Collectively, these data are consistent with a threelegged piano stool structure for 1. There is no evidence for exchange of the N-H proton between Zr-NEt2 groups. Structure and Bonding in 1. The molecular structure of 1 was determined by single-crystal X-ray diffraction (Figure 1, Tables 1-3). Compound 1 adopts a monomeric three-legged piano stool structure containing an q5-dicarbollideligand with amide and amine ligands in the basal positions. One amide group (N2) adopts a “perpendicular” orientation in which the C -N-C plane is roughly perpendicular to the dicarbollide bonding face and parallel to the N2-Zr-centroid plane (angle between C7-N2-C9 and N2-Zr-centroid planes, 10.9”). The other amide (N3) lies in a “parallel”orientation such that the C-N-C plane is rotated ca. 75’ from the perpendicular orientation (angle between Cll-N3-C13 and N3-Zr-centroid planes, 75.4’). The amine ligand adopts a rotational conformation which minimizes steric interactions with the remaining ligands. There is a (11) (a) Siedle, A. R.; Bodner, G. M.; Todd, L. J. J. Organomet. Chem. 1971, 33, 137. (b) Jutzi, P.; Galow, P.; Abu-Orabi, S.; Arif, A. M.; Cowley, A. H.; Norman, N. C. Organometallics 1987, 6, 1024. (c) Buchanan, J.; Hamilton, E. J. M.; Reed, D.; Welch, A. J. J. Chem. SOC., Dalton Trans. 1990, 677.

Bowen et al.

3632 Organometallics, Vol. 14, No. 8,1995

Table 2. Atomic Coordinates (x104) and Equivalent Displacement Parameters (A2x lo3) for 1 atom

Figure 1. Molecular structure of (r5-C2B~H11)Zr(NEt2)2(NHEt2) (1).

compd colorlshape empirical formula fw temp cryst syst space group unit cell dimens (25 reflns, 14" 8

(v5-C2B9H1I )Zr(NEtddHNEtd (1) colorlesslfragment C14H42BgN3Zr 441.02 291(2) K monoclinic P2 IlC a = 10.704(4) 8,b = 11.066(3) 8, 25") c = 20.382(8) A, a = go", /3 = 99.20(3)", y = 90" V 2383.2(14) A3 z 4 1.229 Mg m-3 density (calcd) 0.466 mm-l abs coeff Enraf-Nonius CAD-4/0-28 diffractometerlscan radiatiodwavelength Mo Ka (graphite-monochromated)l 0.710 73 8, 928 F(OO0) 0.40 x 0.25 x 0.20 mm cryst size 1.93"-24.99" 8 range for data collection 01h112,Orkrl3, index ranges -24 I1 I23 no. of standardsldecay 312% 4424 no. of reflns colld no. indep reflns 4195 (Rint = 0.0560) full-matrix least-squares on F refinement method computing SHELXS-85, SHELX-93 datdrestraintslparams 4 176101244 goodness-of-fit on F 1.012 0.0387, 0.3539 SHELX-93 wt params final R indices [I > 28(1)1 R1 = 0.0386, wR2 = 0.0900 R1 = 0.1088, wR2 = 0.1179 R indices (all data) largest diff peak and hole 0.307 and -0.347 e A-3

slight asymmetry to the Zr-carborane bonding; Le., the Zr-B2 and Zr-B3 bonds are slightly shorter than the remaining Zr-cage bonds. This may be ascribed to steric effects. The slight tipping of the cage (i.e., the lengthening of the Zr-Cl,Zr-C2, and Zr-B1 bonds vs the Zr-B2 and Zr-B3 bonds) relieves steric interactions between the dicarbollide C-H units and the N2 amide group which lies directly beneath the Cl-C2 bond, and between the B1-H unit and the amine ligand which lies directly beneath the B1-H bond. The steric interactions between the dicarbollide and N2 amide ligands are also manifested by the disparity in the angles at N2

a

xla

YJb

zlc

2908(1) 49 15(3 2043(4) 2283(3) 3239(4) 1878(4) 4925(5) 5146(7) 5769(4) 7154(5) 1623(5) 2302(6) 1765(4) 388(5) 973(4) 822(6) 2909(5) 2239(5) 4341(5) 3541(5) 1934(5) 2684(5) 1571(5) 2426(5) 4036(5) 42 17(4) 2994(5)

2589(1) 2557(3) 1255(3) 42") 897(4) 1453(4) 24 1O(5 1144(5) 3561(4) 3288(5) -7(4) -935(5) 1679(4) 1592(5) 4353(4) 4983(5) 5367(4) 6186(4) 1940(4) 3284(4) 2922(4) 3061(4) 1888(5) 549(5) 887(4) 2446(5) 1577(5)

670(1) 1345(2) 1130(2) 940(2) -187(2) -375(2) 2080(2) 2301(3) 1206(2) 1413(3) 1005(2) 1473(3) 1777(2) 1877(3) 1052(2) 1689(3 860(2) 323(3) -174(2) -417(2) -519(2) -1230(3) -1186(3) -957(2) -841(2) -1013(2) -1496(3)

U(eqIa

U(eq) is defined as one-third of the trace of the orthogonalized

Vu tensor. Table 3. Selected Bond Lengths (A) and Angles (deg)for Compound 1 Zr-Centa Zr-N(2) Zr-B(3) Zr-C(2) Zr-C(l) C-Bb N( 1)-Zr-Cent N(3)-Zr-Cent N(3)-Zr-N(1) C(5)-N( 1)-C(3) C(3)-N( 1)-Zr C(9)-N(2)-Zr C(l3)-N(3)-C(ll) C( 11)-N( 3)-Zr

2.128(2) 2.047(3) 2.507(5) 2.566(4) 2.623(4) 1.69(3) 112.6 123.5 99.4(1) 111.3(3) 116.3(3) 110.6(3) 113.4(4) 119.9(3)

Zr -N(3) Zr-N(l) Zr-B(2) Zr-B(l) C(l)-C(2) B-Bb N(2)-Zr-Cent N(3)-Zr-N(2) N(2)-Zr-N(1) C(5)-N(l)-Zr C(9)-N(2)-C(7) C(7)-N(2)-Zr C( 13)-N(3)-Zr

2.029(3) 2.360(3) 2.538(5) 2.584(5) 1.571(6) 1.77(1) 110.3 108.9(2) 99.1(1) 113.9(3) 110.8(3) 138.7(3) 124.5(3)

a "Cent" denotes the centroid of the v5-face of the dicarbollide ligand. Average bond length.

(C7-N2-Zr, 138.7(3)'; C9-N2-Zr, 110.6(3)') and by several close H-H contacts.12 The Zr-centroid distance (2.128(2)A) is ca. 0.1 A longer than the corresponding distance in the bent-metallocene (q5-C2BgH11)(Cp*)ZrCMe=CMe2 (2.04 A) but com arable to that in {($C~B~H~~)(CP*)Z~)(LC-CH~) (2.09 ).l The structural data clearly indicate that strong Namide-Zr n-donation is present in 1. The amides are flat (sum of angles around N2 = 360.1", N3 = 357.8'1, and the Zr-Namide distances (2.04 A,average) are at the short end of the range observed for other unsaturated Zr(IV) amide complexes in which N-Zr n-donation is present (ca. 2.04-2.17 A).13 In particular, these Zr-N bond distances are comparable to those in the piano stool complexes Cp*Zr(NiPr2)C12 (2.00 A),14 meso-{p-

H

(12)There are several close H-H contacts: H1A-H'IA, 2.17 H2A-H7A, 2.20 A; HI-HlN1, 2.28 A.

A;

Group 4 Metal Mono-Dicarbollide Piano Stool Complexes

Organometallics, Vol. 14, No. 8,1995 3633 (d~)Zr(NEt~)~(NtiEt~) 1

(dc)Zr(NEt2)2(THF) M031 LUMO -10.3 eV

M032 LUMO+l -10.1 eV

M033 LUM0+2 -10.0 eV

Figure 2. Key frontier orbitals of the model compound (r5-C2BsH11)ZrH2(NH3)as determined by an extended Huckel molecular orbital analysis.

y5,y5-Me2Si( indenylla}{Zr(NMe2)3}2 (2.03-2.05 A), and, after correction for the difference in ionic radii of Ti(IV) vs Zr(IV),16Cp*Ti(NMe2)3 (1.92 A).17 The orientations of the amide ligands are also consistent with the presence of strong N-Zr n-bonding. As noted above, the N2 amide group adopts a sterically unfavorable perpendicular orientation which directs one ethyl group directly toward the dicarbollide cage, while the N3 amide is rotated ca. 75” from this orientation. Qualitative inspection of space-filling models indicates that rotation of the perpendicular amide to relieve amide/dicarbollide steric interactions would not cause severe amide/amine or amidelamide steric interactions, and suggests that this orientational preference has an electronic origin. To identify the n-acceptor orbitals in (q5-C2B9H11)ZrX2L piano stool species (X and L = anionic and neutral a-donor ligands), we carried out an extended Huckel analysis of the model compound ($C2B9H11)ZrH2(NH3).ls As expected by analogy to CpML3 piano stool this species has three lowlying empty Zr d orbitals (Figure 2). The LUMO (M031, Figure 2) has n-symmetry with respect to the Ha site, with lobes suitable for overlap with the p orbital of an amide in the parallel orientation, and d-symmetrywith respect to the Hb site. A second orbital (M033, LTJMO 2) has n-symmetry with respect to both H sites, with lobes oriented for n-bonding with an amide in the

2

I

(dc)Zr(NEt2)2(picoline).picoline

3

I I I,

I

, I ,

4

(dc)Ti(NMe2)2(NHMe2) 5

A L L

(dc)Ti(NEt2)2(NHEf2)

6

15

10

5

0

-5

-10 -15 -20 -25

Figure 3. Schematic diagram of llB NMR spectra of 1-6. The abbreviation “dc” indicates r5-C2BgH11. The chemical shift scale is in ppm. perpendicular orientation. The third frontier orbital, (M032, LUMO l), has n-symmetry with respect to the Hb site, with lobes oriented for n-bonding with a parallel amide, but is expected to be less effective in n-bonding due to poorer overlap. This orbital has d-symmetry with respect to the Ha site. Thus, in an species, one amide analogous (r15-C2BgHll>Zr(NR2)2(NR3) (13) Representative Zr(1V) amide complexes and average Zr-N should adopt a parallel orientation in which n-donation distances. (a) Zr(NMe&, 2.07 A (electron diffraction): Hagen, K.; to M031 is maximized, while the other should adopt a Holwill, C. J.; Rice, D. A.; Runnacles, J. D. Inorg. Chem. 1988, 27, near perpendicular orientation to allow n-donation to 2032. (b) (Me2N)sZr(~1-NMe2)2Zr(NMe2)3, terminal Zr-N, 2.045(3)2.108(3) A: Chisholm, M. H.; Hammond, C. E.; Huffman, J. C. M033 and to a lesser extent, M032. This is what is Polyhedron 1988, 7, 2515. (c) (Me2N)2Zr(iu-NtBu)2Z~NMe2)2, 2.06 A: observed in the solid state for 1. Nugent, W. A.; Harlow, R. L. Inorg. Chem. 1979, 18, 2030. (d) racReactivity of 1. Complex 1 may be converted to Ethylenebis(indenyl)Zr(NMez)n, 2.06 A: Diamond, G. M.; Petersen, J. L.; Jordan, R. F. Unpublished results. (e) Cp2Zr(NC4H4)2,2.17 A: other mono-dicarbollide Zr(IV) complexes via ligand Bynum, R. V.; Hunter, W. E.; Rogers, R. D.; Atwood, J. L. Inorg. Chem. substitution and protonolysis reactions. Compound 1 1980,19,2368. (14) Coalter, J. N.; Gunnoe, B.; Pupi, R. M.; Petersen, J. L. reacts with neat THF to yield (r15-C2BgH11)Zr(NEt2)2Unpublished results. (THF) (2) and with excess 4-picoline to yield ($(15)Christopher, J. N.; Diamond, G. M.; Jordan, R. F.; Petersen, J. C2BgH11)Zr(NEt2)2(4-picoline)2(3). The physical propL. Manuscript in preparation. (16)The ionic radius of Zr(IV) is ca. 0.1 A larger than that of Ti(IV) erties of 2 and 3 are similar to those of 1, and both in comparable coordination environments. Shannon, R. D. Acta derivatives are isolated as yellow solids by recrystalliCrystallogr. 1976, A32, 751. zation from CH2C12/toluene. The llB NMR spectrum of (17) Martin, A.; Mena, M.; Yelamos, C.; Serrano, R.; Raithby, P. R. J . Organomet. Chem. 1994,467, 79. 2 is almost identical to that of 1 (Figure 3), consistent (18)The model compound (35-C2BgHll)ZrH2(NH3)was constructed with a similar three-legged piano stool structure. The from 1 by replacement of the amide ligands by hydrides (Zr-H distance, 1.90 A) and replacement of the amine ethyl groups by lH and 13C NMR spectra of 2 contain THF resonances hydrogens (N-H distance, 0.90 A). The bond angles and other atoms/ which are significantly shifted from those of free THF. distances are unchanged from 1. Extended Huckel MO calculations The lH NMR and analytical data indicate that isolated were carried out on a CAChe system (CAChe Scientific Inc.), using H contains ~) the Alverez parameter set. The HOMO of ( I ~ ~ - C ~ B S H ~ ~ ) Zis~aH ~ ( N3 2 equiv of 4-picoline per Zr. However, as carborane-based orbital. illustrated in Figure 3, the llB NMR spectrum of 3 (CD2(19)(a) Albright, T. A.; Burdett, J. K.; Whangbo, M. H. Orbital Cl2) is almost identical to those of 1 and 2 and distinctly Interactions in Chemistry;John Wilely and Sons: New York, NY,1985; pp 384-387. (b) Bursten, B. E.; Clayton, R. H. Organometallics 1987, different from that of the five-coordinate complex (r56, 2004. (c) Legzdins, P.; Rettig, S. J.; Sanchez, L.; Bursten, B. E.; C2BgH11)ZrC12(NHEt2)2(4, vide infra).Additionally, the Gatter, M. G. J.Am. Chem. SOC.1985,107, 1411. (d) Lichtenberger, D. L.; Fenske, R. F. J . Am. Chem. SOC.1976, 98, 50. lH and 13C chemical shifts for the dicarbollide C-H

+

+

3634 Organometallics, Vol. 14,No.8,1995 units of 3 are very similar t o those of 1 and 2 and quite different from those of 4. The lH NMR spectrum of 3 (CD2C12) contains one set of 4-picoline resonances which are only slightly shifted from those of free 4-picoline and do not shift significantly or broaden when the temperature is lowered to 205 K.20 Addition of 1 equiv of 4-picoline to this solution causes the 4-picoline resonances to shift back toward the free picoline values, but only a single set of 4-picoline resonances is observed down to 205 K. Collectively these observationsestablish that 3 undergoes nearly complete dissociation of one 4-picoline ligand in CDzCl2 solution and that exchange of free and coordinated 4-picoline is very rapid on the NMR time scale. Complex 1 reacts with excess NHMe2 to yield a mixture of unidentified products21but does not react with Et2O. The reaction of 1 with 2 equiv of [NH2Et21Cl results in selective protonolysis of the Zr-amide bonds and formation of (y5-C2BgH11)ZrC12(NHEt2)2 (4), which is isolated as a yellow solid by recrystallization from CH2Cldtoluene. The llB NMR spectrum of 4 contains six resonances in a ll2l2l2llll intensity ratio which are shifted t o somewhat lower field from the resonances of 1-3 and are consistent with an y5-dicarbollide ligand in a C,-symmetric structure. The lH NMR spectrum of 4 contains two multiplets for the amine methylene hydrogens, and the 13C spectrum contains a single amine methylene carbon resonance. Collectively, these data are most consistent with a trans four-legged piano stool structure; in contrast, a cis structure would give rise to four 'H and two 13C ZrNH(CH2CH3)2 NMR resonances.22 Complex 4 does not undergo ligand substitution by THF. Synthesis of (q5-C2B9H11)Ti(NR2)2(NHRZ) Complexes. The amine elimination approach also provides access to mono-dicarbollide Ti(IV) complexes. Thus the reaction of C2BgH13 with Ti(NR2)d in toluene at 23 "C (5, R = Me; 6, R = yields (y5-C2BgH11)Ti(NR2)2(NHR2) Et). Compounds 5 and 6 are isolated as analytically pure red solids via simple removal of volatiles and hexane washing. The NMR properties of 5 and 6 are similar to those of 1 and are consistent with three-legged piano stool structures and the presence of a single amine ligand. Summary. Amine elimination reactions of C2BgH13 and M(NR& compounds provide convenient access to (y5-CzBgHll)M(NR2)2(NHR2) complexes which adopt three-legged piano stool structures and can be converted to a variety of derivatives via ligand substitution or protonolysis reactions. We are currently attempting to exploit this chemistry in the synthesis of (y5-C2B9HdM(RkL, alkyl complexes. (20) 1H NMR spectrum of free 4-picoline in CDzClz: 6 8.42 (d, J = 4 Hz, 2H), 7.09 (d, J = 4 Hz, 2H), 2.32 (s, 3H). (21) The IlB NMR spectrum of this mixture contains high-field resonances characteristic of C2BgH12- species, suggesting that the amine elimination is reversible. Similarly, 1 undergoes hydrolysis, yielding C2BgH12- and other unidentified products. (22) (a) These data are also accommodated by a cis structure which undergoes a dynamic process that collapses the expected four amine methylene resonances to two resonances, e.g., rapid interconversion with the trans isomer. This possibility is unlikely because the 'HNMR spectrum of 4 does not change significantly when the temperature is lowered to 205 K. Note that fast reversible amine dissociation would collapse the diastereotopic amine resonances of 4 to a single resonance; this is not observed at or below 295 K. (b) The spectrum of4 containing free NHEt2 ( 2 equiv) exhibits resonances for free and coordinated NHEt2.

Bowen et al. Experimental Section General Procedures. All manipulations were performed on a high-vacuum line or in a Vacuum Atmospheres glovebox under a purified N2 atmosphere. Solvents were distilled from appropriate drying agents and stored under N2 or vacuum: hexane (Nahenzophenone), toluene (Na), THF (Nahenzophenone), CHzCl2 (CaHz), CDzCl2 (CaHz), 4-picoline (activated 3 a molecular sieves). C2BgH13 was prepared by the literature procedure,23 and Zr(NEtz14, Ti(NMed4, and Ti(NEtd4 were prepared by a modificationz4of the literature p r o ~ e d u r e s . l ~ ~ J ~ NMR spectra were collected on a Bruker AMX-360 spectrometer in flame-sealed or Teflon-valved tubes. 'H and I3C chemical shifts are reported versus Me4Si and were determined by reference to the residual solvent peaks. The 'H NMR spectra contain broad B-H resonances in the range 6 0-3 which are not listed. llB{'H} NMR spectra were referenced to external BFyEt20 (6 0, CsDs). Elemental analyses were performed by E R Microanalytical Laboratory, Inc. (?s-C2BeH11)Zr(NEt2)2(NHEt2) (1). A solution of CzBgH13 (1.78 g, 13.2 mmol) in toluene (25 mL) was added to a solution of Zr(NEt2)4 (5.01 g, 13.2 mmol) in toluene (40 mL), dropwise over a period of 10 min with vigorous stirring at 23 "C. The reaction mixture was stirred for 2 h, concentrated to ca. 20 mL under vacuum, and filtered, yielding a pale yellow solid and an orange filtrate. The solid was dried under vacuum overnight (4.06 g, 69.6%). Compound 1 was recrystallized from a concentrated CHzClz solution layered with toluene at -40 "C:mp 142-144 "C. Anal. Calcd for C14H42BgN3Zr: Z, 38.13; H, 9.60; N, 9.53. Found: C, 37.96; H, 9.42; N, 9.39. 'H NMR (CDzC12): 6 3.59 (m, 8H, NCHz), 3.48 (br s, lH, NH), 3.27 (dqd, J = 14, 7, 3 Hz, 2H, HNCH2), 3.00 (dqd, J = 14, 8, 7 Hz, 2H, HNCHz), 2.68 (br s, 2H, dicarbollide CH), 1.32 (t, J = 7 Hz, 6H, HNCH&H3),1.09 (t, J = 7 Hz, 12H, NCHzCH3). "B{'H} NMR (CDzClz): 6 3.2 (lB), -4.1 (2B), -7.7 (ZB), -12.9 (3B), -20.8 (1B). 13C{'H} NMR (CDzC12): 6 48.9 (CzBgHii), 44.1 (HNCHz), 42.5 (NCHz), 14.2 (HNCHZCH~), 13.8 (NCHzCH3). (tl6-C2BeH11)Zr(NEt2)2(THF) (2). A yellow solution of 1 (0.350 g, 0.790 mmol) in THF (15 mL) was stirred for 30 min a t 23 "C. The volatiles were removed under vacuum, yielding a pale yellow solid which was left under vacuum for 1h. The solid was dissolved in THF (15 mL), and the volatiles were immediately removed under vacuum. The pale yellow solid was dried under vacuum for 3.5 h (0.280 g, 80.2%). Compound 5 was recrystallized from a concentrated CHzClz solution layered with toluene at -40 "C: mp 150 "C. Anal. Calcd for C~H39BgN20Zr:C, 38.22; H, 8.94; N, 6.37. Found: C, 38.07; H, 8.97; N, 6.18. 'H NMR (CD2Clz): 6 4.31 (m, 4H, THF), 3.63 (9, J = 7 Hz, 8H, NCHz), 2.67 (br s, 2H, dicarbollide CH),2.13 (m, 4H, THF), 1.09 (t, J = 7 Hz, 12H, NCHzCH3). IIB{lH} NMR (CD2Clz): 6 2.7 (lB), -4.0 (2B), -7.0 (2B), -12.9 (3B), -21.3 (1B). I3C NMR (CD2C12): 6 76.1 (t, J = 151 Hz, THF), 49.1 (d, J = 159 Hz, CzBgHii), 42.7 (t, J = 131 Hz, NCHz), 26.0 (t, J = 134 Hz, THF), 14.5 (q, J = 124 Hz, NCH2CH3). (~S-C2BeH~~)Zr(NEt2)~(4-picoline)~ (3). A 1:l mixture of 4-picoline/CH&lz (8 mL total, ca. 40 mmol of 4-picoline) was added to a solution of 1 (0.500 g, 1.13 mmol) in CHzClz (10 mL) with vigorous stirring at 23 "C. The resulting yellow solution was stirred for 45 min. All volatiles were removed, and the resulting yellow solid was dried under vacuum for 1 h (0.585 g, 93.1%). Compound 6 was recrystallized from a concentrated CHzClz solution layered with toluene at -40 "C: mp 145 "C. Anal. Calcd for Cz2H4~BgN4Zr:C, 47.68; H, 8.19; N, 10.11. Found: C, 47.54; H, 8.09; N, 9.94. 'H NMR (CD2Cld: 6 8.49 (d, J = 6 Hz, 4H, 0-4-picoline), 7.27 (d, J = 6 Hz,

+

(23) See reference 5g and (a)Wiesboeck, R. A.; Hawthorne, M. F. J . Am. Chem. SOC.1964, 86, 1642. (b) Plesek, J.; Hermanek, S.; Stibr, B. Znorg. Synth. 1083,22, 231. (24) Diamond, G. M.; Rodewald, S.; Jordan, R. F. Organometallics 1996, 14, 5. (25)(a) Bradley, D. C.; Thomas, I. M. J. Chem. SOC.1960, 3857. (b) Bradley, D. C.; Thomas, I. M. Proc. Chem. SOC.London 1959,225.

Organometallics, Vol. 14, No. 8, 1995 3635

Group 4 Metal Mono-Dicarbollide Piano Stool Complexes 4H, m-4-picoline), 3.66 (9, J = 7 Hz, 8H, NCHz), 2.56 (br s, 2H, dicarbollide CH), 2.42 (s, 6H, methyl, 4-picoline), 1.07 (t, J = 7 Hz, 12H, NCHzCH3). llB{ 'H) NMR (CDZClz): 6 2.5 (lB), -4.0 (2B), -6.5 (2B), -13.0 (3B), -21.2 (1B). 13C{'H} NMR (CDzC12): 6 150.9 (p-C, 4-picoline), 149.8 (OX, 4-picoline), 125.9 (m-C,4-picoline1, 49.4 (CzBgHll), 42.7 (NCHz), 21.4 (methyl, 4-picoline), 13.9 (NCHzCH3). (rl5-CzBgHll)ZrC1z(NHEt2)2(4). Solid [H~NEt&1(1.00 g, 9.15 mmol) was added to a solution of 1 (2.03 g, 4.61 mmol) in CHzClz (25 mL) with vigorous stirring at 23 "C. The pale yellow solution was stirred for 2 h. The volatiles were removed under vacuum, and the resulting pale yellow solid was dried under vacuum for 1 h (2.02 g, 99.0%). Compound 4 was recrystallized from a concentrated CHzClz solution layered with toluene at -40 "C. Compound 4 is quite stable in air in CHzClz solution: mp 157-159 "C. Anal. Calcd for C10H3bB9NzC1zZr: C, 27.12; H, 7.97; N, 6.33. Found: C, 27.27; H, 7.84; N, 6.22. lH NMR (CDzClz): 6 3.40-3.45 (br m, 6H, dicarbollide CH, NCHz), 3.04 (br s, 4H, NCHz), 2.86 (br s, 2H, HN), 1.32 (t,J = 7 Hz, 12H, NCHZCH~), llB{lH} NMR (CDzClz): B 10.1 (lB), 1.8 (2B), -2.3 (2B), -7.8 (2B), -9.4 (lB), -14.7 (1B). 13C(lH} NMR (CDzC12): 6 59.0 (br s, CzBgHll), 48.0 (s,NCHz), 15.0 (9, NCHzCHs). (rl5-CzB9H11)Ti(NMez)2(NHMe2) (5). A solution of CzBgH13 (1.20 g, 8.91 mmol) in toluene (25 mL) was added dropwise to a solution of Ti(NMezI4(1.99 g, 8.90 mmol) in toluene (40 mL) over 30 min a t 23 "C. The reaction mixture was stirred vigorously for 2.5 h, during which time a vacuum was periodically applied. The volatiles were moved under vacuum, and the maroon residue was triturated with hexane (50 mL). The hexane was removed under vacuum, and the resulting powder was heated under vacuum at 75 "C overnight, yielding a pale brick-red powder (2.72 g, 97.5%): mp 164-166 "C. Anal. Calcd for CeH30BgN3Ti: C, 30.64; H, 9.64; N, 13.40. Found: C, 30.48; H, 9.76; N, 13.20. 'H NMR (CDzClZ): 6 3.89 (br s, lH, HN), 3.43 (s, 12H, NCH3), 2.90 (br s, 2H, dicarbollide CH), 2.68 (d, J = 6 Hz, 6H, HNCH3). "B{lH} NMR (CDzClz): 6 9.5 (lB), -3.1 (4B), -12.3 (3B), -17.9 (1B). 13CNMR (CD2Clz): 6 53.9 (d, J = 168 Hz, CzBgHii), 49.3 (qq, J = 135, 6 Hz, NCHs), 41.8 (qp, J = 138, 5 Hz, NHCH3). (rle-CzBgH11)Ti(NEtz)2(NHEt2) (6). A solution of C2BgH13 (0.804 g, 5.98 mmol) in toluene (50 mL) was added to a solution of Ti(NEtz)4 (2.01 g, 5.97 mmol) in toluene (30 mL), dropwise over 25 min a t 23 "C with vigorous stirring. The deep maroon

reaction mixture was stirred overnight while a stream of N2 was bubbled through it. The volatiles were removed under vacuum, and the resulting pale brick red solid was triturated with hexane (50 mL) and dried under vacuum (1.96 g, 82.5%): mp 118-123 "C. Anal. Calcd for C14H42B9N3Ti: C, 42.28; H, 10.65; N, 10.57. Found: C, 42.05; H, 10.49; N, 10.36. IH NMR (CDzClz): 6 4.02 (m, 8H, NCHz), 3.37 (m, 2H, NHCHz), 3.17 (m, lH, HN), 2.90 (m, 2H, HNCHZ),2.87 (br s, 2H, dicarbollide CH), 1.31 (t,J = 7 Hz, 6H, HNCHzCHs), 1.10 (t,J = 7 Hz, 12H, NCHzCH3). llB{'H} NMR (CD2Clz): 6 9.1 (lB), -3.3 (4B), -12.5 (3B), -17.9 (1B). 13C NMR (CDzClz): 6 52.9 (d, J = 169 Hz, CzBgHii),47.9 (tq, J = 134,4 Hz, NCHz), 47.5 (t,J = 138 Hz, HNCHz), 15.9 (qq, J = 126 Hz, J = 3 Hz, 13.1(qt, J = 126, 3 Hz, NCHzCH3). HNCHZCH~), X-ray Diffraction Study of 1. Transparent colorless block-shaped crystals were obtained from a concentrated CH2Clz solution of 1 layered with toluene at -40 "C. A single crystal was mounted in a thin-walled glass capillary under Ar and transferred to the goniometer. The space group was determined to be P21k from the systematic absences. A summary of data collection and refinement parameters is given in Table 1. Least-squares refinement with isotropic thermal parameters led to R = 0.070. The geometrically constrained hydrogen atoms were placed in calculated positions (C-H = 0.95 A, B-H = 1.10 A, N-H = 0.90 A) and allowed to ride on the bonded atom with B = 1.2U,. The methyl hydrogen atoms were included as a rigid group with rotational freedom at the bonded carbon atom (C-H = 0.95 A, B = 1.2Ueq(C)).The C1, C2, and B1-B3 hydrogen atoms were located from a difference Fourier map and allowed to ride on the bonded atom with B = 1.2Ue,. Refinement of non-hydrogen atoms was carried out with anisotropic temperature factors. The final values of the positional parameters are given in Table 2.

Acknowledgment. This work was supported by the Department of Energy (DOE DE-GG02-88-ER13935). Supporting InformationAvailable: Tables of complete bond distances and angles, anisotropic displacement parameters, and hydrogen atom coordinates and an alternate view of 1 (7 pages). Ordering information is given on any current masthead page. OM9501900