Synthesis, characterization, and reactivity of terminal titanium imido complexes incorporating constrained-geometry carboranyl ligands

Article abstract of DOI:10.1021/om050312g

Reaction of [Me₂C(C₅H₄)(C ₂B₁₀H₁₀)]Li₂ with Ti(=NR)Cl ₂(Py)₃ afforded the corresponding titanium imido complexes [η⁵:σ-Me₂C(C₅H₄)(C ₂B₁₀H₁₀)]Ti(=NR)(Py) (R = ^tBu (1), 2,6-Me₂C₆H₃ (2), 2,6-ⁱPr ₂C₆H₃ (3)). Complexes 2 and 3 were also prepared by an imido exchange reaction of 1 with RNH₂ (R = 2,6-Me₂C₆H₃, 2,6-ⁱPr ₂C₆H₃). Similarly, [η⁵:σ- Me₂C(C₉H₆)(C₂B₁₀H ₁₀)]Ti-(=N^tBu)(Py) (4) was prepared from the reaction of [Me₂C(C₉H₆)(C₂B₁₀H ₁₀)]Li₂ with Ti-(=N^tBu)Cl₂(Py) ₃3. The reactivity of 1 toward a series of unsaturated organic compounds was examined. Complex 1 underwent imido/oxo exchange reactions with carbonyl compounds such as Ph₂CO, PhCHO, and PhNCO to generate the corresponding imines or carbodiimide and oxotitanium oligomers. The resulting insoluble oxotitanium oligomer was trapped by Me₃SiCl, resulting in the formation of a chloride complex, [η⁵:σ-Me ₂C(C₅H₄)(C₂B₁₀H ₁₀)]Ti-(OSiMe₃)Cl (5). Interaction of 1 with CS ₂ gave ^tBuN=C=N^tBu and ^tBuN=C=S with a molar ratio of 1:3 as well as an insoluble sulfidotitanium complex. 1 was able to catalyze the hydroamination of phenyl acetylene with amines to afford both Markovnikov and antiMarkovnikov products. The product ratio was dependent upon the steric hindrance of the amines used. High regioselectivity was observed for sterically demanding amines such as t-BuNH₂. The anti-Markovnikov [2+2] cycloaddition intermediate [η⁵:σ- Me₂C(C₅H₄)(C₂B₁₀H ₁₀)]-Ti(η³-N^tBuCH=CPh) (6) was successfully isolated from a stoichiometric reaction of 1 with phenyl acetylene in toluene. The molecular structures of 3-6 were further confirmed by single-crystal X-ray analyses.

Full text of DOI:10.1021/om050312g

3772
Organometallics 2005, 24, 3772-3779
Synthesis, Characterization, and Reactivity of Terminal
Titanium Imido Complexes Incorporating
Constrained-Geometry Carboranyl Ligands
Hong Wang,† Hoi-Shan Chan,† and Zuowei Xie*,†,‡
Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories,
Hong Kong, People’s Republic of China, and State Key Laboratory of Elemento-Organic
Chemistry, Nankai University, Tianjin, People’s Republic of China
Received April 20, 2005
Reaction of [Me2C(C5H4)(C2B10H10)]Li2 with Ti(dNR)Cl2(Py)3 afforded the corresponding
titanium imido complexes [η5:σ-Me2C(C5H4)(C2B10H10)]Ti(dNR)(Py) (R ) tBu (1), 2,6-Me2C6H3
(2), 2,6-iPr2C6H3 (3)). Complexes 2 and 3 were also prepared by an imido exchange reaction
of 1 with RNH2 (R ) 2,6-Me2C6H3, 2,6-iPr2C6H3). Similarly, [η5:σ-Me2C(C9H6)(C2B10H10)]Ti-
(dNtBu)(Py) (4) was prepared from the reaction of [Me2C(C9H6)(C2B10H10)]Li2 with Ti-
(dNtBu)Cl2(Py)3. The reactivity of 1 toward a series of unsaturated organic compounds was
examined. Complex 1 underwent imido/oxo exchange reactions with carbonyl compounds
such as Ph2CO, PhCHO, and PhNCO to generate the corresponding imines or carbodiimide
and oxotitanium oligomers. The resulting insoluble oxotitanium oligomer was trapped by
Me3SiCl, resulting in the formation of a chloride complex, [η5:σ-Me2C(C5H4)(C2B10H10)]Ti-
(OSiMe3)Cl (5). Interaction of 1 with CS2 gave tBuNdCdNtBu and tBuNdCdS with a molar
ratio of 1:3 as well as an insoluble sulfidotitanium complex. 1 was able to catalyze the
hydroamination of phenyl acetylene with amines to afford both Markovnikov and anti-
Markovnikov products. The product ratio was dependent upon the steric hindrance of the
amines used. High regioselectivity was observed for sterically demanding amines such as
t-BuNH2. The anti-Markovnikov [2+2] cycloaddition intermediate [η5:σ-Me2C(C5H4)(C2B10H10)]-
Ti(η3-NtBuCHdCPh) (6) was successfully isolated from a stoichiometric reaction of 1 with
phenyl acetylene in toluene. The molecular structures of 3-6 were further confirmed by
single-crystal X-ray analyses.
Introduction
complexes very high activities in the copolymerization
of R-olefins due to the increased electron deficiency and
more open coordination environment of the central
metal ions.6 They may also provide metal imido com-
plexes with some interesting properties since the iden-
tity of the ancilliary ligands has a large effect on the
reactivity of the resulting imido complexes.1-5
Group 4 metal imido complexes have attracted con-
siderable interest in the past decade.1 These complexes
are finding many applications in C-H activation,2 [2+2]
cycloadditions,3 catalytic hydroamination of alkynes,4
and NR group transfer reactions.5 A wide range of
ancilliary ligands has been used to support the MdNR
unit. However, group 4 metal imido complexes with
constrained-geometry ligands have not been reported
in the literature.1e It has been well documented that the
constrained-geometry ligands can offer group 4 metal
In view of the role of the carboranyl moiety of group
4 metal complexes bearing [Me2A(C5H4)(C2B10H10)]2-
,
[Me2A(C9H6)(C2B10H10)]2- (A)C,Si),7 and[iPr2NB(C9H6)-
(C2B10H10)]2- 8 in the polymerization/insertion reactions
and the impact of the supporting ligands on the reactiv-
ity of metal imido complexes, we have incorporated the
above constrained-geometry carboranyl ligands into
group 4 metal imido complexes. Herein we report the
* To whom correspondence should be addressed. Fax:
(852)26035057. Tel: (852)26096269. E-mail: zxie@cuhk.edu.hk.
† The Chinese University of Hong Kong.
‡ Nankai University.
(1) For reviews, see: (a) Wigley, D. E. Prog. Inorg. Chem. 1994, 42,
239. (b) Mountford, P. Chem. Commun. 1997, 2127. (c) Gade, L. H.;
Mountford, P. Coord. Chem. Rev. 2001, 216-217, 65. (d) Okuda, J.;
Eberle, T. In Metallocenes: Synthesis, Reactivity, Applications; Togni,
A., Halterman, R. L., Eds.; Wiley-VCH: New York, 1998; Vol. 1, p 415.
(e) Smith, S. B.; Stephan, D. W. In Comprehensive Coordination
Chemistry II; McCleverty, J. A.; Meyer, T. J., Eds.; Pergamon: New
York, 2004; Vol. 4, p 38.
(2) (a) Hoyt, H. M.; Michael, F. E.; Bergman, R. G. J. Am. Chem.
Soc. 2004, 126, 1018. (b) Cundari, T. R.; Klinckman, T. R.; Wolczanski,
P. T. J. Am. Chem. Soc. 2002, 124, 1481. (c) Bennett, J. L.; Wolczanski,
P. T. J. Am. Chem. Soc. 1997, 119, 10696. (d) Lee, S. Y.; Bergman, R.
G. J. Am. Chem. Soc. 1995, 117, 5877. (e) Bennett, P. T.; Wolczanski,
P. T. J. Am. Chem. Soc. 1994, 116, 2179. (f) de With, J.; Horton, A. D.
Angew. Chem., Int. Ed. 1993, 32, 903. (h) Arney, D. J.; Bruck, M. A.;
Huber, S. R.; Wigly, D. E. Inorg, Chem. 1992, 31, 3749.
(3) (a) Dubberley, S. R.; Friedrich, A.; Willman, D. V.; Mountford,
P. Chem. Eur. J. 2003, 9, 3634. (b) Guiducci, A. E.; Coeley, A. R.;
Skinner, M. E.; Mountford, P. J. Chem. Soc., Dalton. Trans. 2001, 1392.
(c) Sweeney, Z. K.; Salsman, J. L.; Anderson, R. A.; Bergman, R. G.
Angew. Chem., Int. Ed. 2000, 39, 2339. (d) Harlan, C. J.; Tunge, J. A.;
Bridgewater, B. M.; Norton, J. R. Organometallics 2000, 19, 2365.
(e) Thorman, J. L.; Guzei, I. A.; Young, V. G.; Woo. L. K. Inorg, Chem.
2000, 39, 2344. (f) Blake, A. J.; McInnes, J. M.; Mountford, P.; Nikonov,
G. I.; Swallow, D.; Watkin, D. J. J. Chem. Soc., Dalton Trans. 1999,
379. (g) Meyer, K. E.; Walsh, P. J.; Bergman, R. G. J. Am. Chem. Soc.
1995, 117, 974. (h) Meyer, K. E.; Walsh, P. J.; Bergman, R. G. J. Am.
Chem. Soc. 1994, 116, 2669. (i) Walsh, P. J.; Hollander, F. J.; Bergman,
R. G. Organometallics 1993, 12, 3705. (j) de With, J.; Horton, A. D.
Organometallics 1993, 12, 1493. (k) Hill, J. E.; Fanwick, P. E.;
Rothwell, I. P. Inorg, Chem. 1991, 30, 1143.
10.1021/om050312g CCC: $30.25 © 2005 American Chemical Society
Publication on Web 06/22/2005

Terminal Titanium Imido Complexes
Organometallics, Vol. 24, No. 15, 2005 3773
139.8, 124.5 (C5H5N), 149.8, 110.2, 108.3, 107.9, 104.7 (C5H4),
103.0, 101.7 (cage C), 68.0 ((CH3)3C), 42,1, 32.6, 31.4 ((CH3)2C),
32.0 ((CH3)3C). 11B NMR (benzene-d6): δ -3.2 (3B), -8.5 (2B),
-10.9 (2B), -13.5 (3B). IR (KBr, cm-1): ν 3060 (w), 2962 (s),
2589 (vs), 1602 (s), 1442 (m), 1219 (s), 1183 (s), 1042 (m), 801
(s), 702 (m), 618 (w). Anal. Calcd for C19H34B10N2Ti: C, 51.11;
H, 7.68; N, 6.27. Found: C, 51.38; H, 7.70; N, 6.03.
synthesis and structural characterization of several
terminal titanium imido complexes bearing [Me2C(C5H4)-
(C2B10H10)]2- and [Me2C(C9H6)(C2B10H10)]2- ligands and
their reactivities toward unsaturated organic molecules
such as CS2, PhNCO, ketone, aldehyde, and alkyne.
Preparation
of
[η5:σ-Me2C(C5H4)(C2B10H10)]Ti-
Experimental Section
(dNC6H3Me2-2,6)(Py) (2). A toluene solution (10 mL) of
2,6-dimethylaniline (62 mg, 0.5 mmol) was added to a toluene
solution (15 mL) of 1 (223 mg, 0.5 mmol) with stirring at room
temperature, and the mixture was stirred overnight. The color
of the solution turned from orange to dark brown. After
removal of the solvent, the residue was extracted with a mixed
solvent of toluene/n-hexane (5:1, 10 × 2 mL). The organic
solutions were combined and concentrated to about 10 mL.
Complex 2 was isolated as a dark red solid after this solution
stood at room temperature for 3 days (129 mg, 52%). 1H NMR
(benzene-d6): δ 8.59 (d, J ) 5.1 Hz, 2H, C5H5N), 7.27 (dd, J )
7.5 Hz, 1H, C6H3(CH3)2), 7.09 (d, J ) 7.5 Hz, 2H, C6H3(CH3)2),
6.86 (dd, J ) 5.1 Hz, 2H, C5H5N), 6.67 (m, 1H, C5H4), 6.50
(dd, J ) 5.1 Hz, 1H, C5H5N), 6.37 (m, 1H, C5H4), 5.63 (m, 1H,
C5H4), 5.25 (m, 1H, C5H4), 2.45 (s, 6H, C6H3(CH3)2), 1.56
(s, 3H, (CH3)2C), 1.54 (s, 3H, (CH3)2C). 13C NMR (benzene-d6):
δ 152.5, 140.3, 124.7 (C5H5N), 159.4, 137.8, 132.5, 129.2, 125.6,
121.7 (C6H3(CH3)2), 149.3, 111.5, 111.3, 109.3, 109.0 (C5H4),
104.6, 102.8 (cage C), 42.1, 32.2, 31.5 ((CH3)2C), 20.2, 20.1
(C6H3(CH3)2). 11B NMR (benzene-d6): δ -2.5 (3B), -4.7 (2B),
-6.8 (2B), -9.4 (3B). IR (KBr, cm-1): ν 3015 (w), 2973 (m),
2923 (m), 2579 (vs), 1608 (m), 1459 (s), 1280 (m), 1050 (m),
803 (vs), 512 (w). Anal. Calcd for C20.5H31.5B10N1.5Ti (2 -
0.5Py): C, 54.12; H, 6.98; N, 4.62. Found: C, 53.88; H, 7.27;
N, 4.50.
General Procedures. All experiments were performed
under an atmosphere of dry dinitrogen with the rigid exclusion
of air and moisture using standard Schlenk or cannula
techniques, or in a glovebox. All organic solvents were freshly
distilled from sodium benzophenone ketyl immediately prior
t
to use. Ti(NR)Cl2(Py)3 (Py ) pyridine; R ) Bu, 2,6-Me2C6H3,
2,6-iPr2C6H3),9 Me2C(C5H5)(C2B10H11),7,10 and Me2C(C9H7)-
(C2B10H11)11 were prepared according to the literature methods.
All other chemicals were purchased from Aldrich Chemical Co.
and used as received unless otherwise noted. Infrared spectra
were obtained from KBr pellets prepared in the glovebox on a
Perkin-Elmer 1600 Fourier transform spectrometer. 1H and
13C NMR spectra were recorded on a Bruker DPX 300
spectrometer at 300.13 and 75.47 MHz, respectively. 11B NMR
spectra were recorded on a Varian Inova 400 spectrometer at
128.32 MHz. All chemical shifts were reported in δ units with
reference to the residual protons of the deuterated solvents
for proton and carbon chemical shifts, and to external
BF3‚OEt2 (0.00 ppm) for boron chemical shifts. Elemental
analyses were performed by MEDAC Ltd., U.K. or Shanghai
Institute of Organic Chemistry, CAS, China.
Preparation of [η5:σ-Me2C(C5H4)(C2B10H10)]Ti(dNtBu)-
(Py) (1). A 1.6 M solution of n-BuLi in hexane (0.63 mL,
1.0 mmol) was added dropwise to a THF solution (20 mL) of
Me2C(C5H5)(C2B10H11) (125 mg, 0.5 mmol) at 0 °C, and the
mixture was stirred at room temperature overnight. After
removal of the solvent, toluene (25 mL) was added to the
resulting solid. To this toluene suspension was slowly added
Ti(dNtBu)Cl2(Py)3 (213 mg, 0.5 mmol) at room temperature,
and the reaction mixture was then refluxed overnight. After
removal the precipitate, the clear red solution was concen-
trated to about 10 mL. Complex 1 was isolated as a dark red
crystalline solid after this solution stood at room temperature
for 3 days (156 mg, 70%). 1H NMR (benzene-d6): δ 8.59
(d, J ) 5.1 Hz, 2H, C5H5N), 6.88 (m, 2H, C5H5N + C5H4), 6.50
(m, 3H, C5H5N + C5H4), 5.44 (d, J ) 2.4 Hz, 1H, C5H4), 5.02
(d, J ) 2.4 Hz, 1H, C5H4), 1.49 (s, 3H, (CH3)2C), 1.48 (s, 3H,
(CH3)2C), 1.20 (s, 9H, (CH3)3C). 13C NMR (benzene-d6): δ 153.2,
This complex was also prepared in 50% yield via the reaction
of the [Me2C(C5H4)(C2B10H11)]Li2 (prepared in situ from Me2C-
(C5H5)(C2B10H11) (125 mg, 0.5 mmol) and n-BuLi (0.7 mL,
1.0 mmol) in THF) with Ti(dNC6H3Me2-2,6)Cl2(Py)3 (237 mg,
0.5 mmol) in toluene using the same procedure reported
for 1.
Preparation
of
[η5:σ-Me2C(C5H4)(C2B10H10)]Ti-
i
(dNC6H3 Pr2-2,6)(Py)‚C6H5CH3 (3‚C6H5CH3). A toluene so-
lution (10 mL) of 2,6-diisopropylaniline (89 mg, 0.5 mmol) was
slowly added to a toluene solution (10 mL) of 1 (233 mg,
0.5 mmol) with stirring at room temperature, followed by the
identical procedure reported for 2 to give 3‚C6H5CH3 as dark
1
red crystals (161 mg, 50%). H NMR (benzene-d6): δ 8.51 (d,
J ) 5.1 Hz, 2H, C5H5N), 7.13 (dd, J ) 7.2 Hz, 1H, C6H3Pri2),
7.04-6.91 (m, 7H, C6H3Pri2 + C6H5CH3), 6.74 (m, 1H, C5H4),
6.72 (dd, J ) 5.4 Hz, 2H, C5H5N), 6.45 (m, 1H, C5H4), 6.38
(dd, J ) 5.1 Hz, 1H, C5H5N), 5.58 (m, 1H, C5H4), 5.29 (m, 1H,
C5H4), 3.69 (m, 2H, CH(CH3)2), 2.11 (s, 3H, C6H5CH3), 1.49
(s, 3H, (CH3)2C), 1.45 (s, 3H, (CH3)2C), 1.26 (d, J ) 6.9 Hz,
6H, CH(CH3)2), 1.13 (d, J ) 6.9 Hz, 6H, CH(CH3)2). 13C NMR
(benzene-d6): δ 152.9, 140.3, 123.0 (C5H5N), 156.3, 143.9,
137.9, 129.3, 125.7, 124.7 (C6H3Pri2 + C6H5CH3), 149.6, 111.5,
110.4, 109.3 (C5H4), 103.2 (cage C), 42.1, 31.9, 27.9, 25.8, 24.3,
23.0 (CH(CH3)2 + (CH3)2C), 21.4 (C6H5CH3). 11B NMR (benzene-
d6): δ -6.4 (3B), -8.7(2B), -10.5 (2B), -12.8 (3B). IR (KBr,
cm-1): ν 3020 (w), 2954 (s), 2583 (vs), 1614 (s), 1450 (s), 1369
(m), 1265 (m), 1051 (s), 806 (vs), 521 (m). Anal. Calcd for
(4) (a) Lorber, C.; Choukroun, R.; Vendier, L. Organometallics 2004,
23, 1845. (b) Ruck, R. T.; Zuckerman, R. L.; Krska, S. W.; Bergman,
R. G. Angew. Chem., Int. Ed. 2004, 43, 5372. (c) Tillack, A.; Jiao, H.;
Castro, I. G. Hartung, C. G.; Beller, M. Chem. Eur. J. 2004, 10, 2409.
(d) Tillack, A.; Castro, I. G.; Hartung, C. G.; Beller, M. Angew. Chem.,
Int. Ed. 2002, 41, 2541. (e) Pohlki, F.; Doye, S. Angew. Chem., Int. Ed.
2001, 40, 2305. (f) Straub, B. F.; Bergman, R. G. Angew. Chem., Int.
Ed. 2001, 40, 4632. (g) Bytschkov, I. Doye, S. Eur. J. Org. Chem. 2001,
4411. (h) Johnson, J. S.; Bergman, R. G. J. Am. Chem. Soc. 2001, 123,
2923. (i) Haak, E.; Bytschkov, I.; Doye, S. Angew. Chem., Int. Ed. 1999,
38, 3389. (j) Baranger, A. M.; Walsh, P. J.; Bergman, R. G. J. Am.
Chem. Soc. 1995, 115, 2753. (k) Walsh, P. J.; Baranger, A. M.;
Bergman, R. G. J. Am. Chem. Soc. 1992, 114, 1708. (l) Heutling, A.;
Pohlki, F.; Bytschkov, I.; Doye, S. Angew. Chem., Int. Ed. 2005, 44,
2951.
(5) (a) Blum, S. A.; Walsh, P. J.; Bergman, R. G. J. Am. Chem. Soc.
2003, 125, 14276. (b) Lee, S. Y.; Bergman, R. G. J. Am. Chem. Soc.
1996, 118, 6396.
C
25.5H41B10NTi (3 + 0.5 toluene - Py): C, 59.17; H, 7.98; N,
2.71. Found: C, 58.78; H, 7.88; N, 3.08.
This complex was also obtained in 40% yield via the reaction
of [Me2C(C5H4)(C2B10H10)]Li2 (prepared in situ from Me2C-
(C5H5)(C2B10H11) (125 mg, 0.5 mmol) and n-BuLi (0.7 mL,
(6) (a) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem.,
Int. Ed. 1999, 38, 428. (b) Hultzsch, K. L.; Spaniol, T. P.; Okuda, J.
Angew. Chem., Int. Ed. 1999, 38, 227. (c) Siemeling, U. Chem. Rev.
2000, 100, 1495. (d) Park, J.; Yoon, S. C.; Bae, B.-J.; Seo, W. S.; Suh,
I.-H.; Han, T. K.; Park, J. R. Organometallics 2000, 19, 1269.
(7) (a) Wang, H.; Wang, Y.; Li, H.-W.; Xie, Z.Organometallics 2001,
20, 5110. (b) Wang, H.; Li, H.-W.; Xie, Z. Organometallics 2003, 22,
4522. (c) Hong, E.; Kim, Y.; Do, Y. Organometallics 1998, 17, 2933.
(d) Han, Y.; Hong, E.; Kim, Y.; Lee, M. H.; Kim, J.; Hwang, J.-W.; Do,
Y. J. Orgamomet. Chem. 2003, 679, 48.
i
1.0 mmol) in THF) with Ti(dNC6H3Pr2 -2,6)Cl2(Py)3 (266 mg,
0.5 mmol) in toluene using the same procedure reported for
1.
Preparation of [η5:σ-Me2C(C9H6)(C2B10H10)]Ti(dNtBu)-
(Py) (4). A 1.6 M solution of n-BuLi in hexane (0.63 mL,
1.0 mmol) was added dropwise to a THF solution (20 mL) of
(8) Zi, G.; Li, H.-W.; Xie, Z. Organometallics 2002, 21, 1136.

3774 Organometallics, Vol. 24, No. 15, 2005
Wang et al.
Me2C(C9H7)(C2B10H11) (150 mg, 0.5 mmol) at 0 °C. The reaction
mixture was stirred overnight at room temperature. After
removal of the solvent and addition of toluene (25 mL), Ti(d
NtBu)Cl2(Py)3 (213 mg, 0.5 mmol) was slowly added to this
suspension at room temperature, followed by the same pro-
cedure reported for 1 to give 4 as dark red crystals (104 mg,
42%). 1H NMR (benzene-d6): δ 8.71 (d, J ) 5.1 Hz, 2H, C5H5N),
7.92 (d, J ) 8.7 Hz, 1H, indenyl), 7.57 (dd, J ) 5.1 Hz, 2H,
C5H5N), 7.52 (d, J ) 3.3 Hz, 1H, indenyl), 7.20 (dd, J )
5.1 Hz, 1H, C5H5N), 7.17 (d, J ) 3.3 Hz, 1H, indenyl), 7.12 (d,
J ) 8.7 Hz, 1H, indenyl), 6.93 (t, J ) 8.7 Hz, 1H, indenyl),
6.48 (t, J ) 8.7 Hz, 1H, indenyl), 1.90 (s, 3H, (CH3)2C), 1.76
(s, 3H, (CH3)2C), 1.25 (s, 9H, (CH3)3C). 13C NMR (benzene-d6):
δ 150.6, 136.1, 123.1 (C5H5N), 128.7, 127.9, 125.2, 124.3, 123.4,
120.7, 115.9, 104.7, 103.7 (indenyl), 93.0 (cage C), 69.7
((CH3)3C), 44.2, 33.3, 32.1 ((CH3)2C), 31.1 ((CH3)3C). 11B NMR
(benzene-d6): δ -3.4 (3B), -5.4 (2B), -6.5 (2B), -9.5 (3B). IR
(KBr, cm-1): ν 3050 (w), 2956 (s), 2563 (vs), 1603 (w), 1451
(m), 1366 (m), 1121 (vs), 1043 (m), 802 (m), 744 (s). Anal. Calcd
for C23H36B10N2Ti: C, 55.64; H, 7.31; N, 5.64. Found: C, 55.42;
H, 7.17; N, 5.69.
identical with those of the authentic sample. The solid-state
IR spectrum of the resulting yellow solid showed a character-
istic B-H absorption at 2570 cm-1
.
Preparation of [η5:σ-Me2C(C5H4)(C2B10H10)]Ti(OSiMe3)-
Cl (5). A THF solution (10 mL) of PhNCO (119 mg, 1.0 mmol)
was slowly added to a THF solution (15 mL) of 1 (466 mg,
1.0 mmol) at room temperature, and the mixture was stirred
for 5 h. The yellow precipitate was collected by filtration and
washed with THF (5 mL × 2). A THF solution (10 mL) of Me3-
SiCl (163 mg, 1.5 mmol) was then added to a THF (10 mL)
suspension of the above resulting solid (oligomeric oxoti-
tanium) at room temperature. The reaction mixture was
stirred overnight to afford an orange solution. After removal
of the solvent, the residue was extracted with a mixed solvent
of toluene/n-hexane (2:1, 10 mL × 2). The organic solutions
were combined and concentrated to about 5 mL, from which 5
was isolated as red crystals after this solution stood at room
temperature for 3 days (285 mg, 68%). 1H NMR (benzene-d6):
6.09 (m, 1H, C5H4), 5.86 (d, J ) 2.4 Hz, 1H, C5H4), 5.74
(m, 1H, C5H4), 5.39 (d, J ) 2.4 Hz, 1H, C5H4), 1.32 (s, 3H,
(CH3)2C), 1.22 (s, 3H, (CH3)2C), 0.11 (s, 9H, Si(CH3)3). 13C NMR
(benzene-d6): δ 156.4, 118.8, 108.3, 117.1, 112.3 (C5H4), 106.9,
103.8 (cage C), 42.6, 31.2, 31.1 ((CH3)2C), 1.18 (Si(CH3)3).
11B NMR (benzene-d6): -1.9 (2B), -5.8 (4B), -8.9 (2B), -11.6
(2B). IR (KBr, cm-1): ν 3010 (w), 2956 (m), 2596 (vs), 1469
(w), 1380 (w), 1253 (s), 1093 (m), 1053 (s), 945 (vs), 835 (vs),
756 (s). Anal. Calcd for C13H29B10ClOSiTi: C, 37.10; H, 6.94.
Found: C, 37.28; H, 7.15.
Reaction of 1 with CS2. An NMR tube was loaded with 1
(12.0 mg, 2.7 × 10-2 mmol) and C6D6 (0.5 mL). CS2 (2.3 mg,
3.0 × 10-2 mmol) was added to this solution at room temper-
ature in the glovebox. The color of the solution turned from
orange to lime green after the reaction mixture was heated at
50 °C overnight. A yellow solid [{η5:σ-Me2C(C5H4)(C2B10H10)}-
TiS]n was produced (8.4 mg, 95%). There was no 11B NMR
signal in the solution. The 1H NMR spectrum indicated the
formation of 1,3-di-tert-butylcarbodiimide (tBuNdCdNtBu) and
tert-butyl isothiocyanate (tBuNdCdS) with a molar ratio of
1:3. The 1H NMR spectrum and GC/MS of tBuNdCdNtBu and
tBuNdCdS were identical to those of authentic samples. The
solid-state IR spectrum of the resulting yellow solid showed a
Preparation
of
[η5:σ-Me2C(C5H4)(C2B10H10)]Ti(η3-
NtBuCHdCPh) (6). Phenyl acetylene (61 mg, 0.6 mmol) was
added to a toluene (15 mL) solution of 1 (233 mg, 0.5 mmol)
at room temperature, and the reaction mixture was heated at
90 °C overnight. The color of the solution turned from orange
to dark red. After removal of the solvent, the residue was
extracted with a mixed solvent of THF/toluene (1:5, 10 mL ×
2). The organic solutions were combined and concentrated to
about 10 mL, from which 6 was isolated as dark red crystals
after this solution stood at -30 °C for 2 days (70 mg, 30%).
1H NMR (benzene-d6): δ 10.6 (s, 1H, PhCdCNH), 7.17-7.08
(m, 5H, C6H5), 6.52 (m, 1H, C5H4), 5.89 (m, 1H, C5H4), 5.21
(d, J ) 3.0 Hz, 1H, C5H4), 4.53 (d, J ) 3.0 Hz, 1H, C5H4), 1.44
(s, 3H, (CH3)2C), 1.41 (s, 3H, (CH3)2C), 0.96 (s, 9H, (CH3)3C).
13C NMR (benzene-d6): δ 221.8, 146.9 (PhCdCNH), 142.1,
128.8, 128.4, 127.1 (C6H5), 150.6, 112.9, 111.9, 110.0, 103.6
(C5H4), 102.4, 100.2 (cage C), 61.5 ((CH3)3C), 42.7, 31.8, 31.6
((CH3)2C), 31.0 ((CH3)3C). 11B NMR (benzene-d6): δ -4.2 (2B),
-7.0 (2B), -10.3 (4B), -13.3 (2B). IR (KBr, cm-1): ν 3075 (w),
2967 (m), 2572 (vs), 1616 (w), 1463 (s), 1380 (s), 1267 (m), 1198
(m), 1038 (s), 812 (s), 693 (m), 501 (s). Anal. Calcd for C22H35B10-
NTi: C, 56.28; H, 7.51; N, 2.98. Found: C, 56.11; H, 7.25; N,
3.18.
characteristic B-H absorption at 2570 cm-1
.
Reactions of 1 with Organic Carbonyls. An NMR tube
was charged with 1 (14.0 mg, 3.0 × 10-2 mmol) and C6D6
(0.5 mL). Benzophenone (5.5 mg, 3.0 × 10-2 mmol) was added
to this solution at room temperature. A pale yellow solid,
[{η5:σ-Me2C(C5H4)(C2B10H10)}TiO]n, was produced upon mixing
the reagents (8.9 mg, 95%). There was no 11B NMR signal in
1
the solution. The H NMR spectrum showed the formation of
Ph2CdNtBu by comparison with literature data.12 The solid-
state IR spectrum of the resulting pale yellow solid showed a
characteristic B-H absorption at about 2570 cm-1
.
Treatment of 1 (14.0 mg, 3.0 × 10-2 mmol) with phenyl
aldehyde (3.2 mg, 3.0 × 10-2 mmol) in C6D6 in an NMR tube
resulted in the immediate formation of the corresponding
imine (PhCHdNtBu) and a pale yellow solid, [{η5:σ-Me2C-
(C5H4)(C2B10H10)}TiO]n (9.0 mg, 96%). The imine was identified
by comparison of its 1H NMR spectrum with the literature
one.5b The solid-state IR spectrum of the resulting pale yellow
solid showed a characteristic B-H absorption at about
General Procedure for Hydroamination Reaction. All
manipulations were done in the glovebox. A screw cap flask
was loaded with 1 (23.0 mg, 5.1 × 10-2 mmol) as the catalyst,
amine (1.5 mmol), phenyl acetylene (102 mg, 1.0 mmol), and
10 mL of toluene. The flask was heated with stirring at 90 °C
for 2 days. The yields and the ratios of anti-Marlovnikov to
Marlovnikov products were determined by GC-MS in compari-
son with authentic samples after hydrolysis with 5% HCl and
for ketone/aldehyde.
X-ray Structure Determination. All single crystals were
immersed in Paraton-N oil and sealed under N2 in thin-walled
glass capillaries. Data were collected at 293 K on a Bruker
SMART 1000 CCD diffractometer using Mo KR radiation. An
empirical absorption correction was applied using the SADABS
program.13 All structures were solved by direct methods and
subsequent Fourier difference techniques and refined aniso-
2570 cm-1
.
Reaction of 1 with Phenyl Isocyanate. An NMR tube
was charged with 1 (12.0 mg, 2.7 × 10-2 mmol) and C6D6
(0.5 mL). The phenyl isocyanate (3.6 mg, 3.0 × 10-2 mmol)
was added to this solution at room temperature, and the
reaction mixture was put in an ultrasonic bath for 8 h,
whereupon the color of the solution turned from orange to dark
red. A yellow solid, [{η5:σ-Me2C(C5H4)(C2B10H10)}TiO]n, was
formed (8.9 mg, 95%). There was no 11B NMR signal in the
solution. The1H NMR spectrum indicated the formation of
1
tBuNdCdNPh. Its H NMR spectrum and GC-MS data were
(9) Blake, A. J.; Collier, P. E.; Dunn, S. C.; Li, W.-S.; Mountford, P.;
Shishkin, O. V. J. Chem. Soc., Dalton Trans. 1997, 1549.
(10) (a) Xie, Z. Acc. Chem. Res. 2003, 36, 1. (b) Xie, Z.; Chui, K.;
Yang, Q.; Mak, T. C. W. Organometallics 1999, 18, 3947.
(11) Wang, S.; Yang, Q.; Mak, T. C. W.; Xie, Z. Organometallics 2000,
19, 334.
(13) Sheldrick, G. M. SADABS: Program for Empirical Absorption
Correction of Area Detector Data; University of Go¨ttingen: Germany,
1996.
(12) Moretti, I.; Torre, G. Synthesis 1970, 141.

Terminal Titanium Imido Complexes
Organometallics, Vol. 24, No. 15, 2005 3775
Table 1. Crystal Data and Summary of Data Collection and Refinement for 3-6
3‚toluene
34H50B10N2Ti
4
5
6
formula
cryst size, mm
fw
C
C23H36B10N2Ti
0.50 × 0.40 × 0.30
496.5
C13H29B10ClOSiTi
0.30 × 0.20 × 0.10
420.9
C22H35B10NTi
0.30 × 0.20 × 0.10
469.5
0.40 × 0.30 × 0.20
642.8
cryst syst
space group
a, Å
triclinic
P(-1)
monoclinic
P21/c
14.710(3)
10.463(2)
17.836(4)
90
94.98(3)
90
2734.9(9)
4
1.206
monoclinic
P21
7.380(1)
15.544(1)
10.070(1)
90
102.28(1)
90
1128.7(1)
2
1.238
monoclinic
P21/n
13.172(1)
14.591(1)
13.973(1)
90
105.39(1)
90
2589.1(3)
4
1.204
9.561(2)
10.511(2)
20.781(2)
97.47(1)
91.46(1)
115.18(1)
1866.4(4)
2
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
Dcalcd, Mg/m3
radiation (λ), Å
2θ range, deg
µ, mm-1
F(000)
1.144
Mo KR (0.71073)
2.0 to 50.0
0.256
Mo KR (0.71073)
2.8 to 51.0
0.329
Mo KR (0.71073)
4.1 to 50.0
0.552
Mo KR (0.71073)
3.8 to 50.0
0.343
680
1040
436
984
no. of obsd reflns
no. of params refnd
goodness of fit
R1
3965
4812
3856
3385
409
325
245
307
1.140
1.105
0.994
1.081
0.106
0.045
0.052
0.069
wR2
0.253
0.122
0.114
0.167
Table 2. Selected Structural Data for 3-6a
Scheme 1
3
4
5
6
Ti-C(ring)
2.340(9)
2.398(8)
2.404(2) 2.378(4) 2.331(5)
2.532(2) 2.328(5) 2.372(4)
2.342(10) 2.473(2) 2.292(5) 2.311(5)
2.356(9)
2.408(9)
2.332(2) 2.327(5) 2.330(6)
2.331(2) 2.365(5) 2.385(5)
av Ti-C(ring)
Ti-C(cage)
Ti-C(cycle)
2.369(10) 2.414(2) 2.338(5) 2.346(6)
2.224(8)
2.233(2) 2.156(4) 2.172(5)
1.969(5)
2.182(5)
2.174(2)
Ti-N(py)
Ti-N(imido)
Ti-O
Ti-Cl
Ti-N(imido)-C
2.163(7)
1.713(7)
1.704(2)
1.887(4)
1.755(3)
2.340(2)
168.1(6)
Cent-Ti-C(cage) 105.9
166.5(2)
106.0
104.8
105.7
a Distances are in Å and angles are in deg; Cent ) the centroid
of the five-membered ring of Cp or indenyl.
tropically for all non-hydrogen atoms by full-matrix least-
squares calculations on F2 using the SHELXTL program
package.14a For noncentrosymmetric structure 5, the appropri-
ate enantiomorph was chosen by refining Flack’s parameter x
toward zero.14b Most of the carborane hydrogen atoms were
located from difference Fourier syntheses. All other hydrogen
atoms were geometrically fixed using the riding model. Crystal
data and details of data collection and structure refinements
are given in Table 1. Selected bond distances and angles are
compiled in Table 2. Further details are included in the
Supporting Information.
ligands through simple metathesis reactions. Treatment
of Ti(dNR)Cl2(Py)3 (R ) tBu, 2,6-Me2C6H3, 2,6-iPr2C6H3)
with 1 equiv of dilithium salt of the carbon-bridged
ligand [Me2C(C5H4)(C2B10H10)]Li2 gave new constrained-
geometry titanium imido complexes [η5:σ-Me2C(C5H4)-
t
(C2B10H10)]Ti(dNR)(Py) (R ) Bu (1), 2,6-Me2C6H3 (2),
2,6-iPr2C6H3 (3)) in 50-70% isolated yields. Complexes
2 and 3 were also prepared by the imido exchange
reaction. Addition of 1 equiv of 2,6-dimethylaniline or
2,6-diisopropylaniline into a toluene solution of 1 at
room temperature resulted in the rapid formation of 2
and 3 in about 50% isolated yield, respectively. The
above synthetic routes were summarized in Scheme 1.
Complexes 1-3 represent the first examples of group 4
metal imido complexes supported by constrained-
geometry (Cp-D) ligands.
Results and Discussion
Synthesis and Characterization. Titanium imido
compound Ti(dNtBu)Cl2(Py)3 was reported to be a very
useful synthon to a series of titanium imido com-
plexes,1b,15 in which the two chloro groups offer a
valuable entry point to introduce various kinds of
(14) (a) Sheldrick, G. M. SHELXTL 5.10 for windows NT: Structure
Determination Software Programs; Bruker Analytical X-ray Systems,
Inc.: Madison, WI, 1997. (b) Flack, H. D. Acta Crystallogr. 1983, A39,
876.
(15) (a) Dunn, S. C.; Batsanov, A. S.; Mountford, P. J. Chem. Soc.,
Chem. Commun. 1994, 2007. (b) Collier, P. E.; Dunn, S. C.; Mountford,
P.; Shishkin, O. V.; Swallow, D. J. Chem. Soc., Dalton Trans. 1995,
3743. (c) Dunn, S. C.; Mountford, P.; Shishkin, O. V. Inorg. Chem. 1996,
35, 1006.
Complexes 1-3 were air- and moisture-sensitive, very
soluble in toluene, and even slightly soluble in n-hexane.
1
The H NMR spectra of 1-3 showed four multiplets of
the cyclopentadienyl ring protons and two singlets in
the region 1.49-1.55 ppm attributable to the bridging
Me2C unit. In addition, one singlet at 1.20 ppm assign-

3776 Organometallics, Vol. 24, No. 15, 2005
Wang et al.
Figure 2. Molecular structure of [η5:σ-Me2C(C9H6)-
(C2B10H10)]Ti(dNtBu)(Py) (4).
Figure 1. Molecular structure of [η5:σ-Me2C(C5H4)-
i
(C2B10H10)]Ti(dNC6H3Pr2 -2,6)(Py) (3).
Scheme 2
able to the methyl protons of the C(CH3)3 unit was
observed in the 1H NMR spectrum of 1; the resonances
at 68.0 and 32.0 ppm corresponding to the tert-butyl
imido group (dNC(CH3)3) were also found in its 13C
NMR spectrum. For 2 and 3, the 1H NMR spectra
showed one singlet (δ ) 2.45 ppm) of the (CH3)2C6H3
methyl protons and two doublets (δ ) 1.26 and 1.13
ppm) with equal intensity for the isopropyl methyl
protons, respectively. The 11B NMR spectra exhibited a
3:2:2:3 splitting pattern for 1-3.
Figure 3. Molecular structure of [η5:σ-Me2C(C5H4)-
(C2B10H10)]Ti(OSiMe3)Cl (5).
Reactivity. Metal imido complexes are useful for
imido group transfer in catalytic processes as well as
in organic syntheses. It is interesting to know if the
constrained-geometry carboranyl ligand has any effects
on the reactivity of the resulting metal imido complexes.
Complex 1 underwent imido/oxo exchange reactions
with Ph2CdO, PhCHO, and PhNdCdO to generate the
corresponding imine or carbodiimide and oxotitanium
oligomer as a pale yellow solid. These reactions occurred
spontaneously and quantitatively at room temperature
as shown in Scheme 3. The resulting solids from the
above reactions had identical solid-state IR spectra and
showed a characteristic absorption at about 2570 cm-1
for B-H. The resulting imines or carbodiimide was
identified by GC-MS and by comparison with authentic
samples and literature data.5b,12 These reactions may
involve initial dissociation of pyridine, followed by
overall [2+2] cycloaddition between the CdO and the
TidN moiety, to give oxoazametallacyclobutanes. Re-
version of these metallacycles would generate an oxo-
titanium oligomer with the concurrent extrusion of
Ph2CdNBut, PhCHdNBut, or PhNdCdNBut.
The indenyl analogue [η5:σ-Me2C(C9H6)(C2B10H10)]Ti-
(dNtBu)(Py) (4) was prepared in 42% isolated yield from
the reaction of Ti(dNtBu)Cl2(Py)3 with [Me2C(C9H6)-
(C2B10H10)]Li2 in a molar ratio of 1:1 in toluene (Scheme
2). In addition to the aromatic protons, two singlets
(δ ) 1.90 and 1.76 ppm) assignable to the Me2C protons
t
and one singlet at 1.25 ppm attributable to the Bu
protons were also observed in the 1H NMR spectrum of
4. Like complexes 1-3, the 11B NMR spectrum showed
a 3:2:2:3 splitting pattern.
The solid-state structures of 3 and 4 as derived from
single-crystal X-ray diffraction studies confirmed that
the geometry around the titanium atom in 3 and 4 is
best described as a distorted tetrahedron. Figures 1 and
2 show the molecular structures of 3 and 4, respectively.
Key structural data are compiled in Table 2. The Ti-
C(cage) and Ti-C(ring) distances as well as the C(Cent)-
Ti-C(cage) angles in 3 and 4 are very comparable to
Extremely poor solubility of the resulting oxotitanium
oligomer {[η5:σ-Me2C(C5H4)(C2B10H10)]TiO}n in all stan-
dard solvents made its characterization by NMR tech-
niques impossible. It has been reported that group 4
oxometallocenes can be trapped by reacting with a
number of reagents, resulting in addition across the Md
O bonds.18 Treatment of {[η5:σ-Me2C(C5H4)(C2B10H10)]-
7a
those found in [η5:σ-Me2C(C5H4)(C2B10H10)]Ti(NMe2)2
and [η5:σ-Me2C(C9H6)(C2B10H10)]Ti(NMe2)2.7a The Ti-
N(imido) bond distances of 1.713(7) Å in 3 and
1.704(2) Å in 4 fall in the range of the TidNR bond
lengths (1.672(7)-1.723(4) Å) for a wide variety of
ancillary ligand enviroments.9,15a,16,17 The Ti-N(imi-
do)-C angles of 168.1(6)° in 3 and 166.5(2)° in 4 are
very comparable to the C-NdTi angles observed in
titanium imido complexes.9,15a,16,17
(16) Stewart, P. J.; Blake, A. J.; Mountford, P. Inorg. Chem. 1997,
36, 3616.
(17) Dunn, S. C.; Mountford, P.; Robson, D. A. J. Chem. Soc., Dalton
Trans. 1997, 293.

Terminal Titanium Imido Complexes
Organometallics, Vol. 24, No. 15, 2005 3777
Scheme 3
TiO}n with excess Me3SiCl in THF gave the expected
addition product [η5:σ-Me2C(C5H4)(C2B10H10)]Ti(OSiMe3)-
Cl (5) in 68% isolated yield. In addition to four multi-
plets of the Cp protons, its 1H NMR spectrum exhibited
two singlets with an equal intensity at δ ) 1.32 and
1.22 ppm assignable to the (CH3)2C protons and a
singlet at δ ) 0.11 ppm attributable to the methyl
protons of the Si(CH3)3 unit. The formation of 5 was also
supported by the 13C NMR spectrum. The 11B NMR
spectrum showed a 2:4:2:2 splitting pattern. The suc-
cessful isolation of 5 further confirmed the formation
of the oxotitanium oligomer in the above imido/oxo
exchange reactions.
The molecular structure of 5 is shown in Figure 3.
The Ti atom is η5-bound to the five-membered ring of
the cyclopentadienyl and σ-bound to the cage carbon
atom of the carboranyl, a chlorine atom, and an oxygen
atom in a distorted-tetrahedral geometry. The average
Ti-C(ring) distance of 2.339(5) Å, Ti-C(cage) distance
of 2.157(4) Å, and Ti-Cl distance of 2.234(2) Å are close
to the corresponding values of 2.341(2), 2.179(2), and
2.277(1) Å found in [η5:σ-Me2C(C5H4)(C2B10H10)]TiCl-
(NMe2)2,7a respectively. The Ti-O distance of 1.755(3)
Å and the Ti-O-Si angle of 169.2(2)° are compared
with the corresponding values of 1.806(2) Å and 174.5-
(1)° observed in [η5-(Me3Si)2C5H3]Ti(OSiPh3)(CH2Ph).19
The linearity of the Ti-O-Si angle suggests the pres-
ence of O(pπ)-Si(dπ) and O(pπ)-Ti(dπ) interactions.19
Complex 1 also reacted with CS2, but the reaction
proceeded very slowly, taking 3 days at room temper-
ature for the complete consumption of 1. The reaction
rate increased rapidly at higher temperatures. After
treatment of 1 with a slight excess of CS2 in C6D6 at
50 °C overnight, the 1H NMR spectrum showed the
formation of BuNdCdNtBu and BuNdCdS with a
molar ratio of 1:3. The resulting pale yellow precipitate
was presumably {[η5:σ-Me2C(C5H4)(C2B10H10)]TiS}n. The
formation of the symmetrical carbodimide tBuNdCdNt-
Bu was the result of the consecutive reaction of 1 with
the newly formed tBuNdCdS.20 The slower reaction of
1 with CS2 in comparison with the above carbonyl
compounds might be attributed to the lower electrophi-
licity of the carbon atom in CS2 and the soft nature of
sulfur, which makes CS2 disfavor the coordination to
the hard titanium center.
t
t
The crucial reaction step in the hydroamination
reactions catalyzed by group 4 metal imido complexes
is believed to be the formal [2+2] cycloaddition of a Ct
(18) (a) Hanna, T. A.; Baranger, A. M.; Bergman, R. G. J. Org. Chem.
1996, 61, 4532. (b) Blum, S. A.; Bergman, R. G. Organometallics 2004,
23, 4003.
(19) Duchateau, R.; Cremer, U.; Harmsen, R. J.; Mohamud, S. I.;
Abbenhuis, H. C. L.; van Santen, R. A.; Meetsma, A.; Thiele, S. K.-H.;
van Tol, M. F. H.; Kranenburg, M. Organometallics 1999, 18, 5447.

3778 Organometallics, Vol. 24, No. 15, 2005
Wang et al.
Scheme 4
Figure 4. Molecular structure of [η5:σ-Me2C(C5H4)-
(C2B10H10)]Ti(η3-NtBuCHdCPh) (6).
Ti(1)-N(1) distance of 1.887(4) Å is much shorter than
the corresponding values of 2.059(2) Å in A and
2.087(3) Å in B. The Ti(1)-C(26) distance of 1.969(5) Å
is also shorter than the corresponding values of 2.060-
(2) Å in A and 2.031(4) Å in B. The Ti(1)-C(25) distance
of 2.182(5) Å is 0.213 Å longer than that of Ti(1)-C(26),
but is significantly shorter than the corresponding
values of 2.428(2) Å in A and 2.428(3) Å in B. As a
consequent result, the C(26)-C(25)-N(1) angle of
121.1(4)° in 6 is much greater than the 115.8(2)°
observed in A and the 115.8(3)° found in B. In addition,
the measured Ti(1)-C(25) distance of 2.182(5) Å is much
shorter than the average Ti(1)-C(ring) distance of
2.346(6) Å. All these data suggest that the C6H5CdCH-
NBut moiety is best described as a η3 rather than η2 π
ligand. Such bonding interactions may result from the
highly electron-deficient titanium center.
Hydroamination. The successful isolation of the key
intermediate 6 prompts us to examine the catalytic
activity of 1 in hydroamination of alkynes which have
received considerably current interest.4 The catalytic
reactions were carried out at 90 °C in toluene for 20 h
with a 2:3 molar ratio of phenylacetylene and amines
(tert-butylamine and 2,6-dimethylaniline) in the pres-
ence of 5% 1 as catalyst. Phenylacetylene was com-
pletely consumed after 20 h, as indicated by GC. Due
to the potential susceptibility of the resulting imines to
hydrolysis, the hydroamination products were directly
detected by a hydrolytic workup (Scheme 4). The two
amines employed in the reactions revealed an interest-
ing regioselectivity for catalyst 1. The reaction of tert-
butylamine with phenylacetylene gave, after hydrolytic
workup, the anti-Markovnikov addition product (PhCH2-
CHO) and Markovnikov product (PhCOCH3) with a
molar ratio of 4:1. When 2,6-dimethylaniline was used
for the reaction, the ratio of anti-Markovnikov to Mark-
ovnikov products changed to 5:4. It was clear that steric
factors of the amines play a key role in the hydroami-
nation of phenylacetylene. These results were consistent
with those derived from the 1H NMR spectra discussed
previously in this paper. It was noted that complex 6
was also able to catalyze the hydroamination of phenyl-
acetylene with a reactivity very similar to that of 1.
C bond to the MdNR bond to form a metallacyclic
complex. Many attempts to isolate such a metallacyclic
intermediate have been made,21,22 and the first isolation
and structural characterization of the metallacyclic
intermediate in an anti-Markovnikov hydroamination
of terminal alkynes were reported in 2004.21 The
1H NMR spectrum indicated that 1 reacted with PhCt
CH in C6D6 at 80 °C to give two [2+2] cycloaddition
products with a molar ratio of 9.5:0.5. Under the same
reaction conditions, or even at room temperature,
interaction of 2 with 1 equiv of PhCtCH afforded two
products in a 1:1 molar ratio. No reactions were
observed even at 80 °C between 1 or 2 and Me3SiCt
CSiMe3 in C6D6. These results suggested that [2+2]
cycloaddition reactions were very sensitive to the sub-
strates, and a pure addition product was likely isolated
from the reaction of 1 with PhCtCH. Treatment of 1
with 1 equiv of phenyl acetylene in toluene at 90 °C
gave, after workup, a metallacycle, [η5:σ-Me2C(C5H4)-
(C2B10H10)]Ti(η3-NtBuCHdCPh) (6), in 30% isolated
1
yield. In the H NMR spectrum, the metallacycle me-
thine proton was observed as a singlet with a rather
downfield chemical shift of δ ) 10.6 ppm. The reso-
nances at δ ) 221.8 and 146.9 ppm observed in the
13C NMR spectrum were assignable to the carbons of
the metallacycle in 6. Its 11B NMR spectrum showed a
1:1:2:1 splitting pattern.
Single-crystal X-ray analyses confirmed that 6 is one
of the very rare examples of a metallacyclic intermediate
in an anti-Markovnikov hydroamination of a terminal
alkyne, shown in Figure 4. The structural features of
the [η5:σ-Me2C(C5H4)(C2B10H10)]Ti moiety are very simi-
lar to those observed in 3 and 5, as judged by bond
distances and angles (Table 2). The metallacycle ring
is planar and the phenyl group on the C(26) is turned
slightly out of the metallacycle plane. Similar structure
features are also observed in (η5-C5Me5)2Ti[N(Ph)CHd
CH] (A)22b and LTi[N(C6H3Pri-2,6)CHdC(C6H5Me-4)]
(L ) MeC(C5H4N)(CH2NSiMe3)2) (B).21 But the bond
distances and angles within the metallacyclic ring in 6
are quite different from those observed in A and B. The
(20) Zuckerman, R. L.; Bergman, R. G. Organometallics 2000, 19,
4795.
(21) Ward, B. D.; Maisse-Francois, A.; Mountford, P.; Gade, L. H.
Chem. Commun. 2004, 704.
Conclusion
(22) (a) Walsh, P. J.; Baranger, A. M.; Bergman, R. G.J. Am. Chem.
Soc. 1992, 114, 1708. (b) Polse, J. L.; Andersen, R. A.; Bergman, R. G.
J. Am. Chem. Soc. 1998, 120, 13405.
Several new titanium imido complexes containing the
constrained-geometry carboranyl ligand [Me2C(C5H4)-

Terminal Titanium Imido Complexes
Organometallics, Vol. 24, No. 15, 2005 3779
(C2B10H10)]2- or [Me2C(C9H6)(C2B10H10)]2- were pre-
pared by either salt metathesis or imido exchange
reactions. Reactions of [η5:σ-Me2C(C5H4)(C2B10H10)]
Ti(dNtBu)(Py) (1) with various unsaturated molecules
such as PhCHO, Ph2CO, PhNCO, and CS2 gave either
N/O or N/S exchange products in addition to the
formation of titanium oxo/sulfido oligomers, a reactivity
pattern that is similar to that observed in other tita-
nium imido complexes. The [2+2] cycloaddition of a Ct
C to the TidN bond led to the isolation and structural
characterization of the metallacyclic intermediate
[η5:σ-Me2C(C5H4)(C2B10H10)]Ti(η3-NtBuCHdCPh) (6) with
unique structural features, which offers an opportunity
to study the key step in hydroamination reactions.
Complex 1 also catalyzed the hydroamination of phenyl
acetylene with amines to give both Markovnikov and
anti-Markovnikov products. The product ratio was de-
pendent upon the steric hindrance of the amines used.
Acknowledgment. This work was supported by
grants from the Research Grants Council of The Hong
Kong Special Administration Region (Project No.
CUHK4026/02P), Direct Grant (2060274), and State
Key Laboratory of Elemento-Organic Chemistry, Nan-
kai University (Project No. 0314).
Supporting Information Available: Tables of crystal-
lographic data and data collection details, atomic coordinates,
bond distances and angles, anisotropic thermal parameters,
and hydrogen atom coordinates for complexes 3-6. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM050312G