Organometallics 1995,14, 2993-3001
2993
Early Metal Carborane Chemistry. Generation and Reactivity of (CsMe5)(?5-C2B9H11)TiMe Carsten Kreuder and Richard F. Jordan" Department of Chemistry, University of Iowa, Iowa City, Iowa 52242
Hongming Zhang Department of Chemistry, Southern Methodist University, Dallas, Texas 75275 Received March 21, 1995@ The methane elimination reaction of Cp"TiMe3 (Cp* = CsMes) and C2BgH13 yields the thermally sensitive titanacarborane (Cp*)(q5-C2BgH11)TiMe(4),which has been characterized by lH, 13C,and llB NMR spectroscopy. Complex 4 decomposes at 23 "C to the Mvene complex (q6-C5Me4CH2)(q5-CzBgH1l)T (5,30% isolated) and forms labile adducts with PMe3 and THF. (7), which loses Complex 4 inserts CH3CN, yielding (Cp*)(q5-C2BgH11)Ti(N=CMe~)(MeCN) MeCN upon recrystallization from toluene to afford (Cp*)(q5-CzBgHll)(Ti(N=CMe2)(8). X-ray diffraction analyses establish that 7 and 8 adopt monomeric bent metallocene structures with q5-CzB9Hll ligands. Data for 7: space group Pi,a = 9.588(6) A b = 9.940(4) A, c = 13.034(5) 8,a = 96.69(3)", j3 = 97.13(4)", y = 96.70(4)", V = 1213(1) 2 = 2, R = 0.081, R, = 0.091. Data for 8: space oup C2/c, a = 23.058(7) A, b = 13.042(6) A, c = 15.411(6) A, j3 = 118.66(3)", V = 4179(3) 3, 2 = 8, R = 0.088, R, = 0.088. Complex 4 also inserts 2-butyne, yielding (Cp*)(q5-C2BgH11)Ti(CMe=CMe2) (9). The reaction of 4 with ethylene yields propene and (Cp*)(q5-C2B9H11)TiEt(lo),which adopts a j3-agostic structure. The llB NMR spectra of 4-10 are similar and indicate that all of these compounds have bent metallocene structures analogous to those established crystallographically for 7 and 8. Complex 10 catalyzes the slow dimerization of ethylene to 1-butene; this contrasts with the ethylene polymerization catalysis observed for the analogous do metallocenes Cp*zScR and
x
Introduction We recently described the synthesis and reactivity of a new class of zirconium and hafnium carborane com(la,M plexes of stoichiometry [(Cp*)(C2BgHll)M(Me)I~ = Zr; lb, M = Hf; Cp* = q5-C5Me5) which contain C Z B ~ H(dicarbollide) ~~~1igands.l These species insert 2-butyne, yielding (Cp*)(qW!zBgHll)M(CMe=CMe2) alkenyl complexes (2a,b),and undergo thermal elimination of methane, yielding bridged methylene complexes [(Cp*)(q5-C2BgHll)M12~-CH2) (3a,b). Zirconium complexes 2a and 3a have been shown by X-ray crystallography to adopt bent-metallocene structures in which the dicarbollide ligands bind in an v5-manner. Thus, these compounds are isostructural and isolobal with (CsR&M(R) (M = group 3, lanthanide)2 and (C5R&M(R)+ (M = group 4, actinide) species3 and provide an opportunity t o probe the influence of metal charge on reactivity. The structures of la,b have not yet been @Abstractpublished in Advance ACS Abstracts, June 1, 1995. (1) (a) Crowther, D. J.; Baenziger, N. C.; Jordan, R. F. J . Am. Chem. SOC. 1991, 113, 1455. (b) Crowther, D. J.; 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.: Spring House, PA, 1993; pp 89-96. (2) 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) Jeske, G.; Lauke, H.; Mauermann, H.; Sweptson, P. N.; Schumann, H.; Marks, T. J. J . Am. Chem. SOC.1985, 107, 8091. (d) Booij, M.; Deelman, B. J.; Duchateae, R.; Postma, D. S.; Meetsma, A.; Teuben, J . H. Organometallics 1993, 12, 3531. (e) Schumann, H. Angew. Chem., Int. Ed. Engl. 1984, 23, 474. (0 Evans, W. J. Adv. Organomet. Chem. 1985, 24, 131. (g) Schaverien, C. J. Adv. Organomet. Chem. 1994,36, 283.
AS,
fully e l ~ c i d a t e d . ~ Several other early metal and felement carborane complexes with bent-metallocene structures have also been ~ r e p a r e d . ~ , ~ We are interested in extending our studies of the (Cp*)(C2BgH11)M(X) system t o titanium dicarbollide because the smaller species (CP*)(~~~-C~BSH~~)T~(R), metal radius should favor monomeric structures which may simplify the chemistry. Additionally, it is of interest to compare the reactivity of (Cp*)(C2BgHll)Ti(R) species to that of related do first-row metal complexes, i.e., ( C ~ R ~ ) ~ S Cand ( R (C5R&Ti(R)+.s~g )~~,~ Here we describe the generation and reactivity of the simplest (3) (a) Jordan, R. F. Adv. Organomet. Chem. 1991, 32, 325. (b) 1989, Hlatky, G. G.; Turner, H. W.; Eckman, R. R. J . Am. Chem. SOC. 111, 2728. ( c ) Hlatky, G. G.; Eckman, R. R.; Turner, H. W. Organometallics 1992, 11, 1413. (d) Marks, T. J . Acc. Chem. Res. 1992, 25, 57. (4)NMR data indicate that l a , b adopt unsymmetrical dimeric , structures. (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. Group 5: ( c ) Uhrhammer, R.; Crowther, D. J.; Olson, J. D.; Swenson, D. C.; Jordan, R. F. Organometallics 1992, 11, 3098. (d) Uhrhammer, R.; Su, Y.; Swenson, D. C.; Jordan, R. F. Inorg. Chem. 1994,33, 4398. f Elements: (e) Fronczek, F. R.; Halstead, G. W.; Raymond, K. N. J . Am. Chem. SOC. 1977, 99, 1769. (0 Manning, M. J.; Knobler, C. B.; Khattar, R.; Hawthorne, M. F. Inorg. Chem. 1991,30,2009. See also: (g)Oki, A. R.; Zhang, H.; Hosmane, N. S. Organometallics 1991, 10, 3964. (h) Siriwardane, U.; Zhang, H.; Hosmane, N. S. J.Am. Chem. SOC.1990, 112, 9637. (i) Zhang, H.; Jia, L.; Hosmane, N. S. Acta Crystallogr. 1993, C49,453. fj)Houseknecht, K. L.; Stockman, K. E.; Sabat, M.; Finn, M. G.; Grimes, R. N. J . Am. Chem. SOC.1995, 117, 1163. ~ ~ . . (6) For a recent review see: Saxena, A. K.; Hosmane, N. S. Chem. Rev. 1993, 93, 1081.
0276-733319512314-2993$09.00/0 0 1995 American Chemical Society
2994 Organometallics, Vol. 14, No. 6,1995
Kreuder et al. Scheme 1
= C2B9H11
Cp'TiMe3
+ C2B9H13
-
6
toluene
-2 CH4
Ti -CH3
%
4
8
7
9
member of this series, (Cp*)(y5-C2BgH11)Ti(Me). Earlier, Hawthorne and co-workers described the synthesis of several classes of titanacarboranes which adopt sandwich structures, including Ti(y6-R2C2Bl~Hl~)22(R = H, Me), CpTi(y6-R2C2B1oHlo)-(R = H, Me), and (ys-C8H& Ti(y5-C2BgH11)"- ( n = 0, 1).l0Grimes and co-workers prepared a related sandwich complex (ys-C8H8)Ti(y5Et2C2B4H4) and several iodinated derivatives.ll Recently Hosmane described the synthesis of several benttitanocene species incorporating the C2B4(SiMe3)~H4~ligand.12 The reactivity of these systems has not been extensively investigated. (7) (a) Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B. J.; Nolan, M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J. E. J. Am. Chem. SOC.1987,109,203. (b) Burger, B. J.; Thompson, M. E.; Cotter, W. D.; Bercaw, J. E. J . Am. Chem. SOC.1990,112, 1566. ( 8 )(a) Eisch, J. J.; Pombrik, S. I.; Zheng, G. Organometallics 1993, 12, 3856. (b) Eisch, J. J.; Caldwell, K. R.; Werner, S.; Kruger, C. Organometallics 1991, 10, 3417. ( c ) Eisch, J. J.; Piotrowski, A. M.; Brownstein, S. K.; Gabe, E. J.; Lee, F. L. J . Am. Chem. SOC.1985, 107, 7219. (d) Taube, R.; Krukowka, L. J . Organomet. Chem. 1988, 347, C9. (e) Bochmann, M.; Jaggar, A. J. J . Organomet. Chem. 1992, 424, C5. (0 Bochmann, M.; Jaggar, A. J.; Wilson, L. M.; Hursthouse, M. B.; Motevalli, M. Polyhedron 1989, 8, 1838. (g) Bochmann, M.; Lancaster, S. J. J . Organomet. Chem. 1992,434, C1. (h) Bochmann, M.; Wilson, L. M.; Hursthouse, M. B.; Motevalli, M. Organometallics 1988, 7, 1148. (i) Bochmann, M.; Wilson, L. M.; Hursthouse, M. B.; Short, R. L. Organometallics 1987, 6, 2556. (j> Amorose, D. M.; Lee, R. A.; Petersen, J. L. Organometallics 1991,10,2191. (k) Bochmann, M.; Jaggar, A. J.; Nicholls, J. C. Angew. Chem., Int. Ed. Engl. 1990, 29, 780. (1) Borkowsky, S. L.; Baenziger, N. C.; Jordan, R. F. Organometallics 1993, 12, 486. (m) Eshuis, J. J. W.; Tan, Y. Y.; Teuben, J. H. J . Mol. Catal. 1990, 62, 277. (9) See also: (a) Tritto, I.; Sacchi, M. C.; Li, S. Makromol. Chem., Rapid Commun. 1994, 15, 217. (b) Tritto, I.; Li, S.; Sacchi, M. C.; Zannoni, G. Macromolecules 1993, 26, 7111. ( c ) Dyachkovskii, F. S. In Catalyst Design for Tailor-Made Polyolefins; Soga, K., Terano, M., Eds.; Elsevier: New York, 1994; p 201. (10) (a)Salentine, C. G.; Hawthorne, M. F. Inorg. Chem. 1976,15, 2872. (b) Lo, F. Y.; Strouse, C. E.; Callahan, K. P.; Knobler, C. B.; Hawthorne, M. F. J . Am. Chem. SOC.1975,97,428. (11)Swisher, R. G.; Sinn, E.; Grimes, R. N. Organometallics 1984, 13, 599.
Results
Synthesis and Fate of (Cp*)(q5-C2BgH11)Ti(Me) (4). The reaction of equimolar amounts of Cp*TiMe3 and C2BgH13 in benzene or toluene (23 "C, minutes) results in rapid methane elimination and the formation of (Cp*)(y5-C2BgH11)Ti(Me)(4, Scheme l).13 Complex 4 could not be isolated due to thermal decomposition (vide infra);however, NMR monitoring experiments using an internal standard establish that 1 is formed in greater than 85%yield. The NMR properties of 4 are consistent with a C,-symmetric bent-metallocene structure and are unchanged over the temperature range -80 to +25 "C. Singlets are observed for the dicarbollide CH units in both the lH and l3C(lH} spectra, and a 1:2:2:1:2:1 pattern is observed in the llB{lH} spectrum. The llB chemical shifts are similar to those observed for other group 4 and 5 metal y5-dicarbollide complexes and support the proposed y5-coordination.1$5This issue is addressed in more detail below. The thermal sensitivity of 4 precluded accurate solution molecular weight measurements. However, as the dimeric structures adopted by early metal metallocenes with a similar degree of steric crowding are usually unsymmetrical (e.g. Cp*2Lu@-CH3)Lu(Me)(Cp*),Cp*zY@-CH3)Y(Me)and as the NMR (Cp*), and C~*~LU@-C~)LU(C~)(C~*))~~ spectra of 4 are consistent with a symmetric structure even a t low temperatures, it is likely that 4 is monomeric in solution. Complex 4 decomposes a t 23 "C (t1/2 ca. 2 h) to a mixture of fulvene ("tuck-in") complex 5 (40% NMR vs (12) Hosmane, N. S.; Wang, Y.; Zhang, H.; Maguire, J. A.; Waldhoer, E.; Kaim, W.; Binder, H.; Kremer, R. K. Organometallics 1994, 13, 4156. (13) Attempted preparation of titanium dicarbollide complexes by halide displacement (e.g. Cp"TiCl3 + C2BgH112-) was unsuccessful.
Early Metal Carborane Chemistry
Organometallics, Vol. 14, No. 6, 1995 2995
internal standard, 30%isolated, Scheme l),unidentified dridic dicarbollide B-H bonds and the electrophilic insoluble organometallicproducW, methane, and ethane. metal centers are r e ~ p o n s i b l e . ~ ~ NMR monitoring experiments suggest that paramag€&actionsof 4 with Lewis Bases. The Lewis acid netic species also are formed. The NMR parameters for properties of 4 were probed by NMR monitoring of the dicarbollide and C5Me4CH2 groups of 5 are consisreactions with representative Lewis bases. Addition of tent with a C,-symmetric structure. The fulvene mePMe3 to 4 results in formation of (Cp*)(q5-C2BgH11)Tithylene 13C resonance appears at low field (6 = 81) and (Me)(PMes)(6, Scheme 1). The low-temperature (-30 the JCHvalue is large (155 Hz). These data are in the "C) 13Cand lH spectra of 6 each contain two dicarbollide range observed for monomeric early metal fulvene CH resonances, indicating that the sides of the dicarcomplexes including, for example, (Cp*)(q6-C5Me4CH2)bollide ligand are inequivalent, and the low-temperature Ti(Me)(6 = 73.9,JCH= 150 Hz),15(C5Me4H)(q6-CsMe3Hl3C(lH} spectrum contains a doublet for the Ti-Me (CHz))Ti(Me)(6 = 74.4, JCH = 150 Hz),16and (Cp*)(q7group (2Jcp = 15 Hz), indicating that a single PMe3 is C5Me3(CH&Ti (6 = 67.4, JCH= 160 Hz).17-19 The large coordinated. Above 0 "C, PMe3 exchange is rapid on the JCH values for these complexes result from the small NMR time scale. Addition of excess PMe3 a t 23 "C does C-C-M angles andor significant sp2 character a t the not shift the resonances for 6, indicating that coordinafulvene carbon.20 Several early metal complexes with tion of a second PMe3 ligand does not occur in solution. bridging q5,q1-C5Me&H2 ligands have been characterSimilarly, addition of THF to 4 causes extensive shifting ized by X-ray diffraction, including [(Cp*)Sc(p-q5,q1-C5of the NMR resonances. However, in this case, decomMe&H2)1221 and [(Cp*)TiI2(~-q~,q~-CgMe4CHd(p-O)2.~~ position occurs at 23 "C (tll2 ca. 1 h) and THF exchange In these cases, the fulvene carbons exhibit normal is rapid down to -70 "C, so discrete Cp*(q5-C2BgHll)tetrahedral (sp3)g e ~ m e t r i e s .While ~ ~ 13Cdata have not Ti(Me)(THF), species could not be ~ h a r a c t e r i z e d . ~ ~ been reported for these pu-C5Me4CH2species, lower 6 Reaction of 4 with Acetonitrile. The reactions of values and JCHvalues ( 6.0dF) no. of params refined GOF A@(", m i d , e/A3 R b Rwb
r5
137.4°;30 Cp*z"i(CH3)(THF)+,137.8°;8fCp*2Ti{v2(0,C)(=NCGH~~)C(=CH~)}, 140.8°),31as expected given the similar cone angles of ~~-CzBgH11~and C P * - . ~The ~ N(31)-Ti-N(35) angle (85.6") is ca. 10" smaller than the X-M-X angles normally observed in do CpzMXz species (94-100").33 This is a manifestation of the high degree of steric crowding in this system; a similar reduction in X-M-X angle was observed for Cp*2Ti(MeXTHF)+(0-Ti-Me angle 88.9")8f and (v5-C2BgH11)2(30) McKenzie, T. C.; Sanner, R. D.; Bercaw, J. E. J . Organomet. Chem. 1975, 102, 457. (31) Beckhaus, R.; Straws, I.; Wagner, T.; Kiprof, P.Angew. Chem., Int. Ed. Engl. 193,32, 264. (32) Hanusa, T . P. Polyhedron 1982,1, 661.
UeqP
a Equivalent isotropic U defined as one-third of the trace of the orthogonalized U, tensor.
TaMe2- (Me-Ta-Me angle 82.5°).5dThe Ti-(dicarbollide centroid) distance (2.02 A) in 7 is ca. 0.07 A shorter than the Ti-(Cp* centroid) distance (2.09 A). Complex 8 also adopts a monomeric bent-metallocene structure; however the centroid-Ti-centroid angle is 5.9" larger (33)(a)Prout, K.; Cameron, T. S.; Forder, R. A.; Crithcley, S. R.; Denton, B.; Rees, G. V. Acta Crystallogr. 1974, B30,2290. (b) Lauher, J. W.; Hoffmann, R. J.Am. Chem. SOC.1976,98,1729. (c) Cardin, D. J.; Lappert, M. F.; Raston, C. L. Chemistry of Organo-Zirconium and -Hafnium Compounds;John Wiley and Sons: New York, 1986; Chapter 4.
Early Metal Carborane Chemistry
Organometallics, Vol. 14, No. 6, 1995 2997
Table 3. Selected Bond Distances (A) and Angles (deg) for Cp*(qS-C2BgH11)Ti(N=CMe2)(NCMe)(NCMe) (7) and Cp*(?S-C2BgH1~)Ti(N=CMe2) (8)" Ti-Cnt(b1) Ti-Cb(2) Ti-Cb(4) Ti-B(6) Ti-C(22) Ti-C(24) Ti-N(3 1) N(35)-C(36) C(32)-C(33) av B-B Cnt(b1)-Ti-Cnt(c1) Cnt(bl)-Ti-N(35) Cnt(cl)-Ti-N(35) Ti-N(31)-C(32) N(31)-C(32)-C(34) N(35)-C(36)-C(37) Ti-Cnt(b2) Ti-C(2) Ti-B(4) Ti -B(6) Ti-C(22) Ti-C(24) Ti-N(3 1) N(31)-C(32) Cnt(bZ)-Ti-N(31) Cnt(ba)-Ti-Cnt(ca) Cnt(c2)-Ti-N(31) C(33)-C(32)-C(34)
Compound 7 2.02 Ti-Cnt(c1) 2.49(2) Ti-C(3) 2.48(1) Ti-B(5) 2.44(2) Ti-C(21) 2.36(2) Ti-C(23) 2.45(2) Ti-C(25) 1.85(1) Ti-N(35) L.12(2) N(31)-C(32) L.58(2) C(36)-C(37) 1.77 C(32)-C(34) 138.7 105.0 103.2 175(1) 126(2) 177(2)
Cnt(bl)-Ti-N(31) Cnt(cl)-Ti-N(31) N(31)-Ti-N(35) N(31)-C(32)-C(33) Ti-N(35)-C(36) C(33)-C(32)-C(34)
Compound 8 1.91 Ti-Cnt(c2) 2.39(2) Ti-C(3) 2.40(3) Ti-B(5) 2.40(2) Ti-C(21) 2.40(2) Ti-C(23) 2.36(3) Ti-C(25) 1.89(2) av C-B 1.22(3) av B-B 111.0 114.6 104.4 116(2)
N(31)-C(32)-C(33)1 Ti-N(31)-C(32) N(31)-C(32)-C(34)
2.09 2.47(2) 2.51(2) 2.43(2) 2.41(2) 2.45(2) 2.19(1) 1.27(2) 1.46(2) 1.52(3) 107.8 103.9 85.6(5) 119(2) 172(1) 115(2) 2.07 2.42(2) 2.43(2) 2.37(2) 2.44(3) 2.36(2) 1.70 1.78 122(2) 173(2) 122(2)
Cnt(b1) and Cnt(c1) are the centroids of the q5 faces of the CzBgHll and Cp* ligands for compound 7, and Cnt(b2) and Cnt(c2) are the corresponding centroids for 8. El121
331
@
C(301
Figure 1. Molecular structure of Cp*(q5-C2B9H11)Ti(N=CMeZ)(MeCN)(7). and the Ti-(dicarbollide centroid) distance 0.11 A shorter than the corresponding values for 7, due to the lower coordination number. The azomethine ligand in 8 occupies the central coordination site (Le. Ti, N(31), and the two centroids are coplanar to within 0.004 A). The azomethine ligands in both 7 and 8 are oriented such that the methyl groups lie in the equatorial plane between the two q5 ligands. This orientation minimizes
C(301
Figure 2. Molecular structure of Cp*(r5-C2B9H11)Ti(N=CMed (8). steric interactions between the methyl groups and the Cp* and dicarbollide ligands and maximizes Ti-N n-bonding. The metrical parameters for the azomethine ligands in 7 and 8 are similar to those for other do metallocene azomethine complexes (e.g. (indeny1)zTi(N-CMePhXPhCNF and Cp2Zr(N=CHPh)Cl).gh,26e The short Ti-Nazomethine distances (7, 1.85 A; 8, 1.89 A) are consistent with strong Ti-N n-bonding. Reaction of 4 with 2-Butyne. Complex 4 undergoes single insertion of 2-butyne, yielding the alkenyl (9, Scheme 11, complex Cp*(v5-CzBgH11)Ti(CMe=CMe2) which is isolated as a red-brown solid. The lH and 13C NMR spectra of 9 each contain two dicarbollide CH resonances, indicating that a symmetry plane is not present. Additionally, one of the alkenyl methyl 'H resonances appears a t unusually high field (6 = 0.05). These observations imply that the alkenyl ligand lies in the equatorial plane between the Cp* and dicarbollide ligands and that rotation about the Ti-alkenyl bond is slow on the NMR time scale, and suggest that the alkenyl a-Me group is close t o the metal center. X-ray diffraction studies established the presence of "in-plane" /3-agostic M-CMe=CMe2 ligands in Cp*(v5-C2BgH11)Zr(CMe=CMez) (2a)laand (CsH4Me)zZr(C(Me)=CMe2)(THF)+.34However, there is no definitive evidence for a /3-agostic interaction in 9.35 The lH NMR spectrum of 9 in THF-d8 is significantly perturbed from that in toluene-&; in particular, the high-field alkenyl methyl resonance shifts downfield to the normal range (6 = 0.86). This suggests that 9 forms a THF adduct; however 9 is isolated in base-free form by recrystallization from THFA~exane.~~ Reaction of 4 with Ethylene. Complex 4 reacts rapidly with ethylene (23 "C,minutes, 1-3 atm, Scheme 2) to yield propene and (Cp*)(r5-C2B~H11)Ti(CH~CH3) (lo),via ethylene insertion, /3-H elimination, and rapid (34) Jordan, R. F.; LaPointe, R. E.; Bradley, P. K.; Baenziger, N. C. Organometallics 1989,8, 2892. (35) The JCHvalues for the alkenyl methyl groups are normal (125 Hz). (36) 1H NMR of 9 (THF-ds): d 3.77 (br s, l H , dicarbollide CHI, 3.53 (br s, l H , dicarbollide CH),2.15 (s, 15H, C a e s ) ,1.78 (s, 3H, C=CMed, 1.22 ( s , 3H, C=CMe2), 0.86 ( 6 , 3H, TiC(Me)).
2998 Organometallics, Vol. 14, No. 6, 1995
Kreuder et al. Scheme 2
10 I
J I
\
Ti -C4H9
/
I
llB NMR Spectra and Structures of 4-10. The llB NMR spectra for 4-10 are schematically illustrated in Figure 3, in which compounds are grouped together by coordination number for clarity (i.e.: 4, 5, 8-10, 3-coordinate, counting the q5-C2BgHll and Cp* as uni10. dentate ligands and excluding agostic interactions; 6, 7,4-coordinate). The spectra of 3-coordinate species 4, NMR data establish that 10 adopts a P-H agostic 5, and 8-10 are similar. Each contains a low-field structure similar to those of Cp*2Sc(CH&H3) and in the range d 10-20 (1B) and a high-field (CS%)~Z~(CH~CH~R)(L)+ (L = PR3, RCN) c ~ m p l e x e s . ~ ~ , resonance ~~ resonance in the range 6 -14 to -18 (1B). These Key NMR data for 10 include a high-field P-CH3 lH resonances may be assigned to the unique boron on the resonance (6 = -0.8, characteristic of a M-H interacC2B3 face and the capping boron trans to Ti, respection), a large Jc,-H value (144 Hz, characteristic of an tively, on the basis of comparison with data for ($acute M-C-C angle), and a reduced Jc,-cP value (28.5 C2BgH11)2TaX2- compounds, for which assignments Hz, characteristic of acute M-C-C and Ca-Cp-Hbfidge were made from llB-llB COSY spectra.5d Additionally, angle~).3~ each spectrum contains a set of resonances between 6 Exchange of the terminal and bridging @-hydrogens +6 and -13 for the remaining borons. The similarity of 10 is rapid on the NMR time scale even at -90 0C.39 of these spectra indicate that 4,5, and 8-10 all adopt The lH and 13CNMR spectra (singlets for the dicarbolsimilar structures; i.e., these compounds all adopt bentlide CH units) and the llB spectrum (1,2,2,3,1 pattern) metallocene structures similar to that established crysimply that 10 maintains effective C, symmetry over the tallographically for 8. temperature range -90 to +23 "C. No exchange of the The spectra of 6 and 7 are also quite similar. Each a-and P-hydrogens is observed. As bridgekerminal P-H contains a low-field resonance assignable to the unique exchange via "in-place" methyl rotation would not boron on the C2B3 face and a collection of high-field render the sides of the dicarbollide ligand equivalent, resonances lying in a relatively narrow range of ca. 15 these observations imply that 10 is in equilibrium with ppm. The spectrum of 7 is shifted upfield by ca. 7 ppm a nonagostic species.40 The J c ~ - H value (124 Hz) is relative to the spectrum of 6. The similarity of these consistent with the expected average of one small (uspectra indicates that 6 and 7 adopt similar structures, H) and two large (terminal H) values.38 i.e., that both adopt bent-metallocene structures as Complex 10 undergoes thermal decomposition (t1/2 < established crystallographically for 7. Additionally, the 12 h at 23 "C) to insoluble product(s) and thus could IIB NMR spectrum of 4 in the presence of THF is very not be isolated.41 similar to that of 6. This suggests that 4 forms a monoTHF adduct; however as noted above, this could not be (37) Compound 4 does not react with propylene and higher a-olefins confirmed from the other NMR spectra. (toluene, 1 atm, 23 "C).
ethylene insertion of the resulting hydride (Cp*)(v5C2BgH11)Ti(H)(not observed).37 In a secondary process, ethylene is catalytically dimerized to l-butene (ca. 4 t.o./h at 2-3 atm, 23 "C) via an insertionlp-H elimination process. The catalyst resting state is ethyl complex
~~~~~
(38)(a) Guo, Z.; Swenson, D. C.; Jordan, R. F. Organometallics 1994, 13, 1424. (b)Alelyunas, Y. W.; Guo, Z.; LaPointe, R. E.; Jordan, R. F. Organometallics 1993, 12, 544. (c) Jordan, R. F.; Bradley, P. K.; Baenziger, N. C.; LaPointe, R. E. J.Am. Chem. SOC.1990,112, 1289. (39)Some broadening of the Ti-CHZCHs resonances of 10 is observed at -90 "C. Solubility limitations precluded NMR analysis a t lower temperatures. (40) (a) Green, M. L. H.; Wong, L.-L. J. Chem.SOC.,Chem. Commun. 1988,677. (b) Casey, C. P.; Yi, C. S. Organometallics 1991,10,33. (c) McNally, J. P.; Cooper, N. J. Organometallics 1988, 7, 1704. (d) Bercaw, J. E.; Burger, B. J.; Green, M. L. H.; Santarsiero, B. D.; Sella, A.; Trimmer, M. S.; Wong, L.-L. J.Chem. SOC.,Chem. Commun. 1989, 734.
Discussion Structure, Bonding, and Reactivity. The alkane elimination reaction of C2BgH13 and Cp*TiMe3 provides a simple route to the bent-metallocene complex (Cp*)(41)Attempts to isolate 10 yielded mixtures of 10 and unidentified organometallic product(s). The lH NMR of these contained ethylene resonances, indicating that 10 undergoes P-H elimination.
Early Metal Carborane Chemistry
Organometallics, Vol. 14,No. 6, 1995 2999
Co'f DclTif Me)
(CSMe,CH2)(Dc)Ti
5r-k7uA4 Cp'(Dc)Ti(N=CMe2) 0
I
I
1
'
1
I
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9
10 r
25
1
1
20
1
15
1
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-5
II I -10 -15 -20
Cp*(Dc)Ti(Me)(PMe,) 6 I
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Cp'(Dc)Ti(Me)(THF),
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Figure 3. Schematic representation of llB NMR data for 4-10. Three- and 4-coordinate compounds are grouped together for consistency with the discussion in the text."DC" denotes r5-C2BsHll. Cp*(Dc)Ti(Me)(THF),denotes the species formed upon reaction of 4 with THF. (r5-C2BgH11)Ti(Me)(4) in base-free form. Compound 4 is formally derived from the closo carborane C~BIOHE (0-carborane) by replacement of a "BH" vertex by a d2 "Cp*Ti(Me)"fragment, which provides two electrons for cluster bonding. Compound 4 is also related t o Cp*zTi(Me)+by replacement of a CsMes- ligand by an ($CzBgH11)2- ligand. EHMO calculations show that do (CsRs)(y5-C2BsHll)M(H)species contain two low-lying metal-centered empty orbitals similar to those of do (CsR&M(H)"+ species,lb and structural comparisons indicate that the steric properties of Cp* and (r5czBgH11)~-ligands are similar.32 Thus, 4 and other (Cp*)(r5-CzBgHl1)Ti(X) complexes are best considered as a 14-electron Ti(IV) species, analogous to Cp*zTi(Me)+ and Cp*2Sc(Me). Consistent with this picture, (Cp*)(r5-C~B9H11)Ti(X) species display structural features and reactivity patterns characteristic of electrophilic metal complexes (Schemes 1, 2) including agostic interactions (101, ligand coordination (6, 71,insertion (6, 9,101, and (intramolecular) C-H activation (5). (Cp*)(r5-C2B9HdTi(X) complexes appear not to form 18electron (Cp*)(r5-C2BgH11)Ti(X)(L)2 adducts, and 4 decomposes predominantly to mononuclear fulvene complex 5 rather than to binuclear ((Cp*)(r5-C2BgHll)Ti}~-CH~)
species analogous to Zr and Hf complexes 3a,b. These results manifest the high degree of steric crowding in (Cp*)(r5-CzBgH11)Ti(X) species. Ethylene Reactivity. Cp*2ScR and analogous group 3 and lanthanide compounds polymerize ethylene t o high molecular weight linear polyethylene with high a ~ t i v i t y Cationic . ~ ~ ~ ~(C5R&M(R)+ ~~ species (M = group 4, actinide) are also highly active ethylene polymerization catalysts; activities and polymer properties depend strongly on the steric and electronic properties of the (C5R5)zM framework, the presence or absence of Lewis bases, and counteriodcocatalyst proper tie^.^^ For example, (C5Me4'Pr)zTiCldMAO,in which the active species is almost certainly (CsMe4'Pr)zTi(R)+,catalyzes ethylene polymerization, though with much lower activity than less crowded Ti catalysts, e.g. C p 2 T i X W O (X = Ph, C1) or Cp(C5Me4iPr)TiClz/MA0.44-46 In contrast, (Cp*)($-CzBgH11)TiR catalyzes the slow dimerization of ethylene to butene (Scheme 2); evidently the unobserved intermediate (Cp*)(r5-C2BgHl1)Ti("BU)undergoes P-H elimination much faster than ethylene insertion. This observation is reminiscent of the reactivity of the Zr and Hf dicarbollide complexes 1 and 3. These species polymerize ethylene with activity comparable t o that of sterically similar (CsMes)zM(R)+ s p e ~ i e sbut ~ ~produce l ~ ~ polymer ~ ~ ~ ~of much lower molecular weight as a result of rapid P-H e l i m i n a t i ~ n . ~ ~ , ~ , ~ ~ The striking difference in the molecular weights of oligomers/polymers produced by group 4 (Cp*)(CzBgHdM(R) and Cp*2M(R)"+ catalysts may be due in part to bond strength effects. Thermochemical studies clearly establish that P-H elimination processes are endothermic for early metal alkyl complexes.49 Factors which increase the M-R bond strength relative to the M-H bond strength should tend to disfavor /3-H elimination (other factors being equal). There is strong theoretical and experimental evidence that +M-R bonds in cationic metal species are selectively strengthened relative to corresponding +M-H bonds, due to the higher polarizability and n-donor ability of alkyl ligands vs the hydride ligand, which stabilizes the metal charge.50This effect may disfavor P-H elimination in cationic olefin polymerization catalysts, resulting in higher molecular weight product. In contrast, this effect is absent in the neutral dicarbollide systems and lower molecular weights are observed.51 (42)(a)Watson, P. L. J . Am. Chem. SOC.1982,104,337.(b) Ballard,
D.G. H.; Courtis, A.; Holton, J.; McMeeking, J.; Pearce, R. J . Chem. SOC.,Chem. Commun. 1978,994. (c) Evans, W.J.; Chamberlain, L. R.; Ulibarri, T. A.; Ziller, J. W. J . Am. Chem. SOC.1988,110,6423.(d) den Haan, K. H.; Wielstra, Y.; Eshuis, J. J. W.; Teuben, J. H. J . Orgunomet. Chem. 1987,323,181. (43)For a recent review see: Mohring, P. C.; Coville, N. J. J . Orgunomet. Chem. 1994,479,1. (44)Mallin, D.T.; Rausch, M. D.; Mintz, E. A,; Rheingold, A. L. J . Orgunomet. Chem. 1990,381,35. (45)(a) Ewen, J. A. J . Am. Chem. SOC.1984,106, 6355. (b) Ewen, J. A. Stud. Surf.Sci. Cutul. 1986,25,271. (c) Giannetti, E.; Nicoletti, G . M.; Mazzocchi, R. J . Polym. Sci., Polym. Chem. E d . 1985,23,2117. (46)However, the discrete cationic systems [(C~Me~)nTi(Me)l[BPh41 and [(C~Me&Ti(Me)(tetrahydrothiophene)l[BPhd are reported to be inactive with ethylene.8eJ" (47)Kaminsky, W.;Kulper, K.; Niedoba, S. Makromol. Chem., Mucromol. Symp. 1986,3,377. 1993. (48)(a)Jordan, R. F.; Crowther, D. J. U.S. Patent 5,214,173, (b) Karol, F. J.; Kao, S.; Brady, R. C. U.S. Patent 5,162,466, 1993. (49)Schock, L.E.; Marks, T. J. J . Am. Chem. SOC.1988,110,7701. (50)(a)Ziegler, T.; Tschinke, V.; Becke, A. J . Am. Chem. SOC.1987, 109,1351. (b) Mandich, M. L.; Halle, L. F.; Beauchamp, J. L. J . Am. Chem. SOC.1984,106,4403.
3000 Organometallics, Vol. 14,No. 6,1995
Ethylene insertion of P-agostic Ti-Et species 10 is much slower than for --Me species 4. Previously, Bercaw found that the P-agostic ethyl complex Cp*zScEt inserts ethylene more slowly than do Cp"2ScMe or higher nonagostic Cp*2ScCH&H2R species.7b The P-agostic interactions in 10 and Cp*zScEt probably disfavors ethylene coordination by utilizing the coordination site required for ethylene binding and perhaps may need to be broken for insertion t o occur. Unresolved Issue. An unresolved issue in the J I ' ~ Xis the possible chemistry of the ( C ~ * ) ( C ~ B S H ~series role of paramagnetic species in the thermolysis and other reactions of 4 and 10. We previously observed that CpzTi(CHzPh)+species decompose via Ti-CH2Ph homolysis to TiL1'products.81 Similar processes may be important in the chemistry of 4 and 10. Our studies of this problem will be reported in due course.
Experimental Section General Procedures. All manipulations were performed by using vacuum-line or Schlenk techniques or in a glovebox under a purified Nz atmosphere. Solvents were distilled from appropriate dryingldeoxygenating agents and stored under Nz or vacuum prior to use: toluene, benzene, hexane, THF, Et20 (Nahenzophenone);MeCN (PzO5, molecular sieves), 2-butyne (molecular sieves), PMe3 (Na, molecular sieves). CzBgHi3 and Cp*TiMe3 were synthesized using literature procedure^.^^^^^ NMR spectra were recorded on a Bruker AMX-360 instrument in flame-sealed or Teflon-valved tubes at 25 "C, unless indicated otherwise. 'H and 13C chemical shifts are reported versus Me4Si and were determined by reference to the residual solvent peaks. "B{'H} NMR spectra were referenced to external BF3*Et20and 31P{1H}NMR spectra to external H3PO4. The lH NMR spectra of 4-10 contain broad BH resonances which are not listed. Elemental analyses were performed by E&R Microanalytical Laboratory, Inc. (Cp*)(r16-CzB~H11)Ti(Me) (4). NMR Scale. An NMR tube was charged with Cp*TiMes (12 mg, 0.052 mmol) and CzB9H13 (7.0 mg, 0.052 mmol), toluene-& (0.4 mL) was added under vacuum at -196 "C, and the tube was warmed to -78 "C. The solids dissolved with CH4 evolution, and the solution turned intensely yellow. The tube was warmed t o 0 "C, and CH4 evolution continued; within 5 min, the reaction mixture turned deep red-brown. The tube was warmed to 23 "C for 5 min, and NMR spectra were recorded. The 'H NMR spectrum of the deep red solution established the formation of 4 in '85% yield. 'H NMR (toluene-&): 6 3.74 (br s, 2H, dicarbollide CH), 2.17 (s, 3H, TiMe), 1.71 (s, 15H, C5Me5). NMR (toluene= 122, TiMe), &, -30 "C): 6 133.8 (s, CsMes), 81.0 (q, 'JCH 69.2 (br d, 'JCH= 170, CzBgHll), 13.3 (9, 'JCH = 128, CSMe5). "B{'H} NMR (&De): 6 20.0 (lB), 5.4 (2B), 2.5 (2B),-4.4 (lB), -6.0 (2B), -14.7 (1B). Preparative Scale. A solution of C2BsH13 (202 mg, 1.50 mmol) in toluene (40 mL) was added to a solution of Cp*TiMe3 (343 mg, 1.50 mmol) in toluene (50 mL) at -78 "C. The reaction mixture was warmed to 0 "C (30 min) and then to 23 "C (10min). Attempts to isolate pure solid 4 were thwarted by its thermal decomposition and yielded partially soluble mixtures of 4 and 5; therefore, solutions of 4 prepared in this manner were used for further reaction chemistry. (rls-CsMe4CH~)(r15-CzBeH11)Ti (5). A solution of Cp*(v5C2BSH11)Ti(Me)4 (484 mg, 1.46 mmol) in toluene (30 mL) was stirred for 18 h a t 23 "C. The dark reaction mixture was (51) The higher effective metal charge (Le. lower metal electronegativity) and lower degree of steric crowding in group Boanthanide (CsRdzMR complexes (vs group 4 (Cp*)(CZBgHdMR complexes) may promote olefin insertion relative to ,8-H elimination. (52) Mena, M.; Royo, P.; Serrano, R.; Pellinghelli, M. A,; Tiripicchio, A. Organometallics 1989,8 , 476.
Kreuder et al. filtered and the residue washed with toluene. The filtrate and wash were combined, concentrated to 15 mL, and cooled to -30 "C overnight. The solid was collected by filtration. The filtrate was concentrated to 7 mL and layered with hexane (5 mL) to obtain a second crop of product. Total yield: 140 mg (30%). 'H NMR (C&): 6 2.86 (br s, 2H, dicarbollide CH)), 2.43 (s, 2H, C5Me&H2), 1.54 (s, 6H, C ~ M ~ ~ C H 0.33 Z ) (s, , 6H, Cae4CHz). NMR (toluene-&): 6 138.2 (s, C ~ M ~ ~ C H Z ) , 134.9 (s, C5Me4CH2), 125.6 (s, C ~ M ~ ~ C H 92.5 Z )(t, , 'JCH = 154, = C~M~~CH 65.6 Z ) ,(br d, 'JCH= 166, CzBgHii), 11.2 (9, 'JCH 129, C&e4CH2), 11.1 (q, ~ J C = H 128, C&e4CHz). l'B{'H} NMR (C6Ds): 6 19.2 (lB), 5.3 (2B), -0.2 (2B), -4.9 (lB), -7.8 (2B), -17.7 (1B). IR (KBr, cm-'1: 3012 (w), 2959 (w), 2915 (w),2870 (sh), 2583 (vs, v(BH)),2535 (VS v(BH)),1449 (w), 1381 (m), 1081 (w), 1022 (m), 971 (w), 776 (w), 729 (m), 639 (w). Anal. Calcd for ClzHz5BsTi: C, 45.83; H, 8.01. Found: C, 45.61; H, 8.04. (Cp*)(v5-CzB9H11)Ti(Me)(PMes) (6). A solution of 4 (16 mg, 0.05 mmol) in toluene-& (0.4 mL) was prepared in an NMR tube, PMe3 (ca. 0.5 mmol) was added by vacuum transfer a t -78 "C, and the tube was warmed to 23 "C. The volatiles were removed under vacuum, and the residue was dried under vacuum for 1 h. 'H NMR (toluene-d8, -30 "C): 6 3.93 (br s, lH, dicarbollide CH)), 2.57 (br s, lH, dicarbollide CHI, 1.78 (s, 15H, C&e5), 0.48 (br s, 9H, PMe31, -0.13 (s, 3H, TiMe). I3C{lH} NMR (toluene-&, -30 "C): 6 122.0 (s, C5Me5), 70.2 (br d, V c p = 15, TiMe), 61.8 (s, CzBgHd, 59.6 (9, CzBsHii), 14.5 (d, 'Jcp = 18, PMe3), 13.9 (s, C&e5). llB{'H} NMR (toluene-&): 6 14.6 (lB), 0.4 (2B),-1.6 (2B), -10.1 (3B), -12.1 (1B). 31P{1H}NMR (toluene-&, -30 "C): 6 -7.8 (PMe3). (Cp*)(;r15-C2B~H11)Ti(N=CMe2)(MeCN) (7). A solution of acetonitrile (110mg, 2.7 mmol) in toluene (30 mL) was added t o a solution of 4 (0.500 g, 1.51 mmol) in toluene (90 mL) at -78 "C, and the reaction mixture was warmed to 23 "C and stirred for 15 h. The green-yellow microcrystalline precipitate was collected by filtration (75 mg). The filtrate was cooled to -30 "C for 48 h, and a second crop (180 mg) of the same material was isolated (combined yield 255 mg, 41%). Compound 7 is dichromic, appearing green to reflected light and orange to transmitted light. The following NMR spectra were recorded in the presence of excess acetonitrile (ca. 20 equiv), which was added to disfavor MeCN dissociation. 'H NMR (toluene-ds): 6 3.05 (br s, 2H, dicarbollide CHI, 1.88 (s, 15H, C&e5), 1.43 (s,6H, =CMeZ), 0.7 (br s, excess MeCN). 13CNMR (toluene-ds): 6 169.0 (s, =CMeZ), 123.5 (s, CsMes), 117 (br s, MeCN), 56.5 (br d, 'JCH= 169, CzBgHid, 24.1 (9, 'JCH= 128, =CMe2), 13.5 (4, 'JCH= 127, Cp*), -0.4 (br s, MeCN). 'lB{'H} NMR (toluene-ds): 6 7.3 (lB), -5.3 (2B), -6.5 (2B), -13.2 (2B), -16.4 (2B). IR (KBr, cm-'1: 2316 (v(CSN)), 2287 (v(C=N)), 1678 (v(C=N)). Anal. Calcd for C17H35BsNzTi: C, 49.48; H, 8.54. Found: C, 49.17; H, 8.67. (Cp*)(f15-CzBgH11)Ti(N~CMe~) (8). The filtrate obtained after isolation of the second crop of 7 above was concentrated to 20 mL under vacuum and cooled to -30 "C for 14 h. Redbrown crystals (140 mg, 25% based on 4) were collected by filtration. 'H NMR (toluene-&): 6 3.62 (br s, 2H, dicarbollide CH), 1.77 (9, 15H, C&e5), 1.23 (9, 6H, =CMeZ). "B{lH) NMR (toluene&): 6 11.9 (lB),2.3 (2B), -1.0 (2B), -12.0 (3B),-16.6 (1B).IR (KBr, cm-'1: 1678 (v(C=N)). (Cp*)(q5-CzB9H11)Ti(CMe=CMez) (9). Excess 2-butyne (ca. 0.9 mmol) was added to a solution of (Cp*)(v5-CzB9Hll)Ti(Me) (60 mg, 0.18 mmol) in CsDs (0.6 mL) in an NMR tube via vacuum transfer. The NMR tube was maintained at 23 "C and agitated for 5 min. The volatiles were removed under vacuum, and the residue was dissolved in THF (3 mL). The solution was layered with hexane (3 mL) and cooled to -30 "C. A red-brown solid was isolated by filtration (55 mg, 79%). 'H NMR (toluene-&): 6 3.84 (br s, lH, dicarbollide CH), 3.31 (br s, l H , dicarbollide CH), 1.74 (s, 15H, CSMed, 1.44 (s, 3H, C=CMeZ), 0.89 (s, 3H, C=CMez), 0.14 (5, 3H, TiC(Me)=). I3C NMR (toluene-ds): 6 131.3 (5, CsMes), 65.1 (br d, 'JCH = 174, = 126, CzBgHll), 64.6 (br d, 'JCH= 168, CzBgHii),24.0 (q, 'JCH
Organometallics, Vol. 14,No. 6, 1995 3001
Early Metal Carborane Chemistry C=CMeMe), 23.3 (9, 'JCH = 125, C=CMeMe), 19.8 (q, 'JCH = 125, TiC(Me)=), 13.5 (q, ~ J C =H 128, C&fe5), vinyl carbons not observed. 13C NMR (THF-da): 6 213.7 (s, TiC(Me)=), 132.0 (s, CsMes), 130.0 (s, =CMeZ), 65.1 (br d, partially obscured by solvent resonance, CzBgHll), 64.3 (br d, 'JCH = 165, CzBgHll), 24.2 (9, 'JCH= 126, C=CMeZ), 23.6 (9, 'JCH = 125, C=CMeZ), = 128, C5Me5). 19.8 (9, 'JCH= 125, TiC(Me)=), 13.7 (9, 'JCH "B('H} NMR (CsDs): 6 15.3, 5.1, 1.9, 0.7, -0.6, -6.4, -7.9, -11.2, -14.3 (each 1B). Anal. Calcd for Cl~H35BgTi:C, 53.08; H, 9.17. Found: C, 51.89; H, 8.89. (Cp*)(rl5-CzBeH11)Ti(CHzCHs) (10). An NMR tube containing a solution of (Cp*)(~5-CzBgH11)Ti(Me) (16 mg, 0.050 mmol) in toluene-& (0.4 mL) was charged with 2-3 atm of ethylene or doubly labeled 13CzH4at -196 "C. The tube was warmed to 23 "C for 5 min and stored at -30 "C prior t o NMR measurements. 'H NMR (toluene-&): 6 3.18 (br s, 2H, dicarbollide CH), 2.93 (q, 3 J =~7.9,~ 2H, CHzCHs), 1.65 (s, 15H, C a e s ) , -0.75 (t, 3 J =~7.8,~ 3H, CHzCH3). 13C NMR (doubly I3C-labeledcompound, toluene-&, -30 "C): 6 89.5 (td, 'JCH= 144, 'Jcc = 28.5, '3CHz'3CH3), 64.7 (br d, 'JCH= 169, CzBgHll), 26.1 (qd, 'JCH = 124, 'Jcc = 28.5, '3CHz'3CH3), 13.0 (q, ~ J C = 128, H C&fe5), Cp*(Cips,)not observed. "B(lH} NMR (toluene-&): 6 14.3 (lB), 3.2 (2B), -0.6 (2B), -10.1 (3B), -14.3 (1B). X-ray Crystallographic Analysis of 7. Crystals of 7 were grown from a cold toluene solution. An orange, plate-shaped crystal was mounted on a Siemens R3mN diffractometer under a low-temperature nitrogen stream. Key crystallographic data are summarized in Table 1. Final unit cell parameters were obtained from 25 accurately centered reflections (12" < 28 < 20"). Three standard reflections monitored after every 150 reflections did not show any significant change in intensity during the data collection. The data were corrected for Lorentz and polarization effects. The structure was solved by direct-methods and subsequent difference Fourier syntheses using the SHELXTL-Plus p a ~ k a g e . Full-matrix ~~,~~ refinement was performed. All non-H atoms were refined
anisotropically. The carborane cage is disordered between two orientations. In the major orientation (60%),Cb(2) is a C atom and Cb(4) is a B atom. In the minor orientation (40%),Cb(2) is a B atom and Cb(4) is a C atom. The carborane H atoms were located in difference Fourier maps, and the methyl H atoms were placed at idealized positions (C-H = 0.96 A). X-ray Crystallographic Analysis of 8. Crystals of 8 were grown from a cold toluene solution. A red, plate-shaped crystal was mounted on the diffractometer under a low-temperature nitrogen stream. Key crystallographic data are summarized in Table 1. Final unit cell parameters were obtained from 25 accurately centered reflections (10" < 28 < 18"). Three standard reflections monitored after every 150 reflections did not show any significant change in intensity during the data collection. The data were corrected for Lorentz and polarization effects. The structure was solved by direct-methods and subsequent difference Fourier syntheses using the SHELXTLPlus ~ a c k a g e . Full-matrix ~ ~ , ~ ~ refinement was performed. The Ti, N, and methyl C atoms were refined anisotropically; the remaining C .and B atoms were refined isotropically. The carborane H atoms were located in difference Fourier maps, and the methyl H atoms were placed at idealized positions (C-H = 0.96 A).
Acknowledgment. This work was supported by NSF Grant CHE-9413022. C.K. is grateful to the Deutsche Forschungsgemeinschaft for a fellowship. Supplementary Material Available: For 7 and 8, tables of complete bond distances and angles, anisotropic displacement coefficients,and hydrogen atom coordinates and isotropic displacement coefficients (8 pages). Ordering information is given on any current masthead page. OM950207E (53)Sheldrick, G. M. SHELXTL-PLUS; Siemens Analytical X-ray Instruments, Inc., 1990. (54)International Tables for X-ray Crystallography; Kynoch Press: Birmingham, England, 1994;Vol. IV.
