Steric control of coordination geometry in titanium-lmido complexes of n,n-bis(arylimino)acenaphthylene ligands

Article abstract of DOI:10.1021/ic902101z

Titanium complexes of N,N-bis(arylimino)acenaphthylene (BIAN) α-diimine ligands with varied steric profiles have been prepared. Coordination of the BIAN ligand derivatives to TiCl₄ afforded the adducts (dpp-BIAN)TiCl₄ (1a), (tmp-BIAN)TiCl₄ (1b), and (dmp-BIAN)TiCl₄ (1c) (dpp = 2,6-diisopropylphenyl; tmp = 2,4,6-trimethylphenyl; dmp = 3,5-dimethylphenyi). While the least sterically crowded complex 1c is robust toward loss of the diimine ligand, the dpp-BIAN and tmp-BIAN ligands are readily displaced by pyridine from the more crowded derivatives 1 a and 1b, respectively. The crowded profiles engendered by the tmp-BIAN and dpp-BIAN ligands result in the formation of five-coordinate titanium-imide complexes, (dpp-BIAN)TiCl₂(=NBu) (2a) and (tmp-BIAN)TiCl₂(=NBu) (2b), upon addition of BuNH₂ to solutions of 1 a or 1 b, respectively. Single-crystal X-ray diffraction studies reveal a square pyramidal coordination environment with an apical imide ligand and a short Ti-N distance, consistent with a Ti-N triple bond. Conversely, the less crowded dmp-BIAN ligand affords a six-coordinate titanium imido complex, (dmpBIAN)TiCl₂(=NBu)(NH₂Bu) (4), upon treatment of 1c with BuNH₂. Surprisingly the imido ligand is coordinated trans to one arm of the diimine. This six coordinate species is fluxional in solution, and exchange and variable temperature ¹H NMR experiments suggest dissociation of the coordinated BuNH₂ ligand to generate a five-coordinate imido intermediate analogous to 2a and 2b. 2010 American Chemical Society.

Full text of DOI:10.1021/ic902101z

2222 Inorg. Chem. 2010, 49, 2222–2231
DOI: 10.1021/ic902101z
Steric Control of Coordination Geometry in Titanium-Imido Complexes of
N,N0-bis(arylimino)acenaphthylene Ligands
Kensha Marie Clark, Joseph W. Ziller, and Alan F. Heyduk*
Department of Chemistry, University of California, Irvine, California 92697
Received October 23, 2009
Titanium complexes of N,N0-bis(arylimino)acenaphthylene (BIAN) R-diimine ligands with varied steric profiles have
been prepared. Coordination of the BIAN ligand derivatives to TiCl4 afforded the adducts (dpp-BIAN)TiCl4 (1a), (tmp-BIAN)-
TiCl4 (1b), and (dmp-BIAN)TiCl4 (1c) (dpp = 2,6-diisopropylphenyl; tmp = 2,4,6-trimethylphenyl; dmp = 3,5-dimethylphenyl).
While the least sterically crowded complex 1c is robust toward loss of the diimine ligand, the dpp-BIAN and tmp-BIAN ligands are
readily displaced by pyridine from the more crowded derivatives 1a and 1b, respectively. The crowded profiles engendered by the
tmp-BIAN and dpp-BIAN ligands result in the formation of five-coordinate titanium-imide complexes, (dpp-BIAN)TiCl2(dNtBu)
(2a) and (tmp-BIAN)TiCl2(dNtBu) (2b), upon addition of tBuNH2 to solutions of 1a or 1b, respectively. Single-crystal X-ray diffrac-
tion studies reveal a square pyramidal coordination environment with an apical imide ligand and a short Ti-N distance, consistent
with a Ti-N triple bond. Conversely, the less crowded dmp-BIAN ligand affords a six-coordinate titanium imido complex, (dmp-
BIAN)TiCl2(dNtBu)(NH2tBu) (4), upon treatment of 1c with tBuNH2. Surprisingly the imido ligand is coordinated trans to one arm
of the diimine. This six coordinate species is fluxional in solution, and exchange and variable temperature 1H NMR experiments
suggest dissociation of the coordinated tBuNH2 ligand to generate a five-coordinate imido intermediate analogous to 2a and 2b.
Introduction
including H-atom abstraction, [2 þ 2] cycloaddition, and
insertion.4-28 There are also many transition metal com-
plexes in which a terminal imido ligand acts as a robust
spectator ligand while reactions such as metathesis occur at
a more reactive alkylidene or alkylidyne functionality
within the complex.14,29-33 In the case of the early transi-
tion metal imido complexes, especially of the Group IV
Transition metal complexes with terminal imido ligands
have attracted interest owing to their varied reactivity.1-3
In mid- and late transition metal complexes, terminal
imido ligands can access many reactivity pathways,
*To whom correspondence should be addressed. E-mail: aheyduk@
uci.edu.
(1) Dehnicke, K.; Strahle, J. Angew. Chem., Int. Ed. 1981, 20, 413.
(2) Nugent, W. A.; Haymore, B. L. Coord. Chem. Rev. 1980, 31, 123.
(3) Wigley, D. E. Prog. Inorg. Chem. 1994, 42, 239.
(4) Ashley-Smith, J.; Green, M.; Stone, F. G. A. J. Chem. Soc., Dalton
Trans. 1972, 1805.
(5) Au, S. M.; Huang, J. S.; Yu, W. Y.; Fung, W. H.; Che, C. M. J. Am.
Chem. Soc. 1999, 121, 9120.
(6) Brown, S. D.; Betley, T. A.; Peters, J. C. J. Am. Chem. Soc. 2003, 125,
322.
(18) Li, Z.; Quan, R. W.; Jacobsen, E. N. J. Am. Chem. Soc. 1995, 117,
5889.
(19) Evans, D. A.; Woerpel, K. A.; Hinman, M. M.; Faul, M. M. J. Am.
Chem. Soc. 1991, 113, 726.
(20) Mansuy, D.; Mahy, J. P.; Dureault, A.; Bedi, G.; Battioni, P.
J. Chem. Soc., Chem. Commun. 1984, 1161.
(21) Hu, X.; Meyer, K. J. Am. Chem. Soc. 2004, 126, 16322.
(22) Michelman, R. I.; Andersen, R. A.; Bergman, R. G. J. Am. Chem.
Soc. 1991, 113, 5100.
(7) Burrell, A. K.; Steedman, A. J. Organometallics 1997, 16, 1203.
(8) Chong, A. O.; Oshima, K.; Sharpless, K. B. J. Am. Chem. Soc. 1977,
99, 3420.
(9) Chao, Y. W.; Wexler, P. A.; Wigley, D. E. Inorg. Chem. 1990, 29, 4592.
(10) Dewith, J.; Horton, A. D.; Orpen, A. G. Organometallics 1993, 12,
1493.
(23) Michelman, R. I.; Ball, G. E.; Bergman, R. G.; Andersen, R. A.
Organometallics 1994, 13, 869.
(24) Mindiola, D. J.; Hillhouse, G. L. J. Am. Chem. Soc. 2001, 123, 4623.
(25) Mindiola, D. J.; Hillhouse, G. L. Chem. Commun. 2002, 1840.
(26) Spencer, L. P.; Yang, P.; Scott, B. L.; Batista, E. R.; Boncella, J. M.
J. Am. Chem. Soc. 2008, 130, 2930.
(11) Dewith, J.; Horton, A. D. Angew. Chem., Int. Ed. 1993, 32, 903.
(12) DuBois, J.; Tomooka, C. S.; Hong, J.; Carreira, E. M. Acc. Chem.
Res. 1997, 30, 364.
(13) Glueck, D. S.; Wu, J. X.; Hollander, F. J.; Bergman, R. G. J. Am.
Chem. Soc. 1991, 113, 2041.
(14) Green, M. L. H.; Hogarth, G.; Konidaris, P. C.; Mountford, P.
J. Organomet. Chem. 1990, 394, C9.
(15) Groves, J. T.; Takahashi, T. J. Am. Chem. Soc. 1983, 105, 2073.
(16) Kee, T. P.; Park, L. Y.; Robbins, J.; Schrock, R. R. J. Chem. Soc.,
Chem. Commun. 1991, 121.
(27) Verma, A. K.; Nazif, T. N.; Achim, C.; Lee, S. C. J. Am. Chem. Soc.
2000, 122, 11013.
(28) Waterman, R.; Hillhouse, G. L. J. Am. Chem. Soc. 2003, 125, 13350.
(29) Bazan, G. C.; Khosravi, E.; Schrock, R. R.; Feast, W. J.; Gibson,
V. C.; Oregan, M. B.; Thomas, J. K.; Davis, W. M. J. Am. Chem. Soc. 1990,
112, 8378.
(30) Fox, H. H.; Schrock, R. R.; Odell, R. Organometallics 1994, 13, 635.
(31) Grubbs, R. H.; Chang, S. Tetrahedron 1998, 54, 4413.
(32) Schaverien, C. J.; Dewan, J. C.; Schrock, R. R. J. Am. Chem. Soc.
1986, 108, 2771.
(17) Kogut, E.; Wiencko, H. L.; Zhang, L. B.; Cordeau, D. E.; Warren,
T. H. J. Am. Chem. Soc. 2005, 127, 11248.
(33) Schrock, R. R.; Krouse, S. A.; Knoll, K.; Feldman, J.; Murdzek,
J. S.; Yang, D. C. J. Mol. Catal. 1988, 46, 243.
r
pubs.acs.org/IC
Published on Web 02/03/2010
2010 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 5, 2010 2223
metals titanium and zirconium, the imido ligand dominates
complex has been shown to play a pivotal role in controlling
the selectivity of these reactions.41,53,74-79
the reactivity of the complex. Facile room-temperature C-H
bond activation of hydrocarbons by (silox)2Ti(=NSitBu3)
Owing to the dependence of imido reactivity on the sterics
and electronics of auxiliary ligand platforms, the synthesis
and structural characterization of Group IV imido com-
plexes with new supporting ligands continues to be of inter-
est. The synthon, TiIV(=NtBu)Cl2(py)n (n = 2, 3), has been
used to prepare a variety of new titanium imido complexes,
including anilido derivatives and complexes with multiden-
tate nitrogen donor ligands such as amidinates,80 pyridyla-
mines,81 and tetraazamacrocycles.82 Formally reduced,
titanium(II) complexes react with azobenzene, resulting in
the transfer of a nitrene and formation of TiIV=NPh com-
plexes with simple alkoxide or halide ligands.38,69 More
recently, one-electron oxidation and deprotonation of a
titanium(III) diamido complex have been employed to pre-
pare an imidotitanium(IV) complex supported β-diketimi-
nate ligand.48,83-85 An attractive feature of the latter system
is that the steric profile of β-diketiminate ligand can be easily
modified; however, the ligand backbone itself is prone to
nucleophilic attack and often reacts with metal-ligand
multiple-bond functionalities.84-86
This paper reports recent efforts to support the titanium
imido functionality with R-diimine ligands containing an
acenaphthylene backbone. The coordination chemistry of
N,N0-bis(arylimino)acenaphthylene (BIAN) ligands with
mid- and late transition metals is well established, and the
ligand is noted for its stability, particularly in supporting
electrophilic catalysts for olefin polymerization.87-96 More-
over, the ligand is prepared by a condensation reaction from
acenaphthenequinone and virtually any aniline derivative, so
the steric profile of the ligand can be tailored to control the
metal coordination environment. Three different BIAN
derivatives, shown in Chart 1, were used herein to prepare
-
(silox=tBu3SiO-) and Cp*2Ti(=NtBu) (Cp* = C5Me5
)
intermediates highlight the enhanced reactivity of the
MIV=NR fragment (M = Ti or Zr) deriving from strong
polarization of the metal-nitrogen multiple bond.34-38
Examples of the reactivity of Group IV imidos with unsatu-
rated substrates are legion, including stoichiometric and
catalytic imine metathesis, and 1,2-addition reactions like
hydroamination.38-73 Manipulation of the coordination
geometry and steric and electronic environment of the metal
(34) Bennett, J. L.; Wolczanski, P. T. J. Am. Chem. Soc. 1994, 116, 2179.
(35) Bennett, J. L.; Wolczanski, P. T. J. Am. Chem. Soc. 1997, 119, 10696.
(36) Cundari, T. R. J. Am. Chem. Soc. 1992, 114, 10557.
(37) Cummins, C. C.; Schaller, C. P.; Vanduyne, G. D.; Wolczanski, P. T.;
Chan, A. W. E.; Hoffmann, R. J. Am. Chem. Soc. 1991, 113, 2985.
(38) Polse, J. L.; Andersen, R. A.; Bergman, R. G. J. Am. Chem. Soc.
1998, 120, 13405.
(39) Nielson, A. J.; Glenny, M. W.; Rickard, C. E. F. J. Chem. Soc.,
Dalton Trans. 2001, 232.
(40) Ruck, R. T.; Zuckerman, R. L.; Krska, S. W.; Bergman, R. G.
Angew. Chem., Int. Ed. 2004, 43, 5372.
(41) Ong, T. G.; Yap, G. P. A.; Richeson, D. S. Chem. Commun. 2003,
2612.
(42) Pohlki, F.; Doye, S. Chem. Soc. Rev. 2003, 32, 104.
(43) Bytschkov, T.; Doye, S. Tetrahedron Lett. 2002, 43, 3715.
(44) Blake, A. J.; McInnes, J. M.; Mountford, P.; Nikonov, G. I.;
Swallow, D.; Watkin, D. J. J. Chem. Soc., Dalton Trans. 1999, 379.
(45) Park, J. T.; Yoon, S. C.; Bae, B. J.; Seo, W. S.; Suh, I. H.; Han, T. K.;
Park, J. R. Organometallics 2000, 19, 1269.
(46) Zhang, Z.; Leitch, D. C.; Lu, M.; Patrick, B. O.; Schafer, L. L.
Chem.;Eur. J 2007, 13, 2012.
(47) Blum, S. A.; Walsh, P. J.; Bergman, R. G. J. Am. Chem. Soc. 2003,
125, 14276.
(48) Basuli, F.; Aneetha, H.; Huffman, J. C.; Mindiola, D. J. J. Am.
Chem. Soc. 2005, 127, 17992.
(49) Ong, T. G.; Yap, G. P. A.; Richeson, D. S. J. Am. Chem. Soc. 2003,
125, 8100.
(50) Hill, J. E.; Fanwick, P. E.; Rothwell, I. P. Inorg. Chem. 1991, 30, 1143.
(51) Walsh, P. J.; Hollander, F. J.; Bergman, R. G. J. Am. Chem. Soc.
1988, 110, 8729.
(52) Bytschkov, I.; Doye, S. Eur. J. Org. Chem. 2003, 935.
(53) Cao, C. S.; Ciszewski, J. T.; Odom, A. L. Organometallics 2001, 20,
5011.
(54) Lorber, C.; Choukroun, R.; Vendier, L. Organometallics 2004, 23,
1845.
(55) Vujkovic, N.; Ward, B. D.; Maisse-Francois, A.; Wadepohl, H.;
Mountford, P.; Gade, L. H. Organometallics 2007, 26, 5522.
(56) Johnson, J. S.; Bergman, R. G. J. Am. Chem. Soc. 2001, 123, 2923.
(57) Mcgrane, P. L.; Jensen, M.; Livinghouse, T. J. Am. Chem. Soc. 1992,
114, 5459.
(58) Lee, S. Y.; Bergman, R. G. Tetrahedron 1995, 51, 4255.
(59) Meyer, K. E.; Walsh, P. J.; Bergman, R. G. J. Am. Chem. Soc. 1995,
117, 974.
(74) Ward, B. D.; Maisse-Francois, A.; Mountford, P.; Gade, L. H.
Chem. Commun. 2004, 704.
(75) Li, C. Y.; Thomson, R. K.; Gillon, B.; Patrick, B. O.; Schafer, L. L.
Chem. Commun. 2003, 2462.
(76) Heutling, A.; Pohlki, F.; Doye, S. Chem.;Eur. J. 2004, 10, 3059.
(77) Ackermann, L.; Bergman, R. G. Org. Lett. 2002, 4, 1475.
(78) Cao, C. S.; Shi, Y. H.; Odom, A. L. Org. Lett. 2002, 4, 2853.
(79) Zhang, Z.; Schafer, L. L. Org. Lett. 2003, 5, 4733.
(80) Blake, A. J.; Collier, P. E.; Dunn, S. C.; Li, W. S.; Mountford, P.;
Shishkin, O. V. J. Chem. Soc., Dalton Trans. 1997, 1549.
(81) Li, Y.; Banerjee, S.; Odom, A. L. Organometallics 2005, 24, 3272.
(82) Hayday, G. J.; Wang, C.; Rees, N. H.; Mountford, P. Dalton Trans.
2008, 3301.
(60) Muller, T. E.; Beller, M. Chem. Rev. 1998, 98, 675.
(61) Odom, A. L. Dalton Trans. 2005, 225.
(62) Guiducci, A. E.; Cowley, A. R.; Skinner, M. E. G.; Mountford, P.
J. Chem. Soc., Dalton Trans. 2001, 1392.
(83) Mindiola, D. J. Acc. Chem. Res. 2006, 39, 813.
(84) Hamaki, H.; Takeda, N.; Tokitoh, N. Inorg. Chem. 2007, 46, 1795.
(85) Basuli, F.; Huffman, J. C.; Mindiola, D. J. Inorg. Chem. 2003, 42,
8003.
(63) Hazari, N.; Mountford, P. Acc. Chem. Res. 2005, 38, 839.
(64) Fairfax, D.; Stein, M.; Livinghouse, T.; Jensen, M. Organometallics
1997, 16, 1523.
(65) Duncan, A. P.; Bergman, R. G. Chem. Rec. 2002, 2, 431.
(66) Doxsee, K. M.; Farahi, J. B.; Hope, H. J. Am. Chem. Soc. 1991, 113,
8889.
(86) Bourget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. Rev. 2002,
102, 3031.
(87) van Asselt, R.; Elsevier, C. J. Organometallics 1994, 13, 1972.
(88) van Asselt, R.; Elsevier, C. J. Tetrahedron 1994, 50, 323.
(89) van Asselt, R.; Elsevier, C. J.; Amatore, C.; Jutand, A. Organome-
tallics 1997, 16, 317.
(67) Profilet, R. D.; Zambrano, C. H.; Fanwick, P. E.; Nash, J. J.;
Rothwell, I. P. Inorg. Chem. 1990, 29, 4363.
(68) Sweeney, Z. K.; Salsman, J. L.; Andersen, R. A.; Bergman, R. G.
Angew. Chem., Int. Ed. 2000, 39, 2339.
(90) van Asselt, R.; Elsevier, C. J.; Smeets, W. J. J.; Spek, A. L. Inorg.
Chem. 1994, 33, 1521.
(91) van Asselt, R.; Elsevier, C. J.; Smeets, W. J. J.; Spek, A. L.; Benedix,
R. Recl. Trav. Chim. Pays-Bas. 1994, 113, 88.
(69) Hill, J. E.; Profilet, R. D.; Fanwick, P. E.; Rothwell, I. P. Angew.
Chem., Int. Ed. 1990, 29, 664.
(70) Mcgrane, P. L.; Livinghouse, T. J. Org. Chem. 1992, 57, 1323.
(71) Cao, C. S.; Shi, Y. H.; Odom, A. L. J. Am. Chem. Soc. 2003, 125,
2880.
(72) Meyer, K. E.; Walsh, P. J.; Bergman, R. G. J. Am. Chem. Soc. 1994,
116, 2669.
(73) Harlan, C. J.; Tunge, J. A.; Bridgewater, B. M.; Norton, J. R.
Organometallics 2000, 19, 2365.
(92) van Asselt, R.; Gielens, E. E. C. G.; Rulke, R. E.; Vrieze, K.; Elsevier,
C. J. J. Am. Chem. Soc. 1994, 116, 977.
(93) van Asselt, R.; Rijnberg, E.; Elsevier, C. J. Organometallics 1994, 13,
706.
(94) van Asselt, R.; Vrieze, K.; Elsevier, C. J. J. Organomet. Chem. 1994,
480, 27.
(95) El-Ayaan, U.; Murata, F.; El-Derby, S.; Fukuda, Y. J. Mol. Struct.
2004, 692, 209.
(96) Svejda, S. A.; Brookhart, M. Organometallics 1999, 18, 65.

2224 Inorganic Chemistry, Vol. 49, No. 5, 2010
Clark et al.
Chart 1
7.4 Hz, aryl-H, 2H), 7.43 (d, 3J = 7.7 Hz, aryl-H, 4H), 7.53 (t,
3J = 6.5, aryl-H, 4H), 8.12 (d, 3J = 8.3, aryl-H, 2H). 13C NMR
(CDCl3, 125.7 MHz) δ/ppm: 25.11 (CH(CH3)2), 25.12
(CH(CH3)2, 29.3 (CH(CH3)2), 125. Seven (aryl-C), 126.0
(aryl-C), 127.8 (aryl-C), 128.7 (aryl-C), 129.1 (aryl-C),
130.9 (aryl-C), 132.9 (aryl-C), 140.4 (aryl-C), 145. One
(aryl-C), 170.8 (aryl-C). IR (KBr) ν/cm-1: 3061(w), 2964 (s),
1615(s), 1579 (s), 1290 (m), 1179 (m), 936 (m br), 780 (m).
Synthesis of (tmp-BIAN)TiCl4 (1b). Using the same condi-
tions reported for 1a, tmp-BIAN derivative 1b was isolated as a
brick-red solid in 98% yield from 5.0 g of tmp-BIAN (8.2 mmol)
and 1.7 g of TiCl4 (9.0 mmol). Anal. Calcd for C30H28N2-
new titanium imido complexes. Whereas BIAN ligands with
sterically demanding substituents afford five-coordinate
complexes with apical imido ligands, the BIAN ligand with
the smallest aryl substituent affords an unusual six-coordi-
nate complex with an imido ligand cis to a primary amine
ligand. This paper reports the synthesis and characterization
in solution and the solid state of titanium imido complexes
supported by chelating BIAN ligands.
Cl4Ti 1/2CH2Cl2: C 56.47%, H 4.51%, N 4.32%. Found: C
3
56.83%, H 4.77%, N 4.38%. 1H NMR (CDCl3, 500 MHz)
δ/ppm: 2.42 (s, p-CH3, 6H), 2.52 (s, o-CH3, 12H), 6.12 (d, 3J =
3
7.3 Hz, aryl-H, 2H), 7.09 (s, aryl-H, 4H), 7.58 (t, J = 7.5,
aryl-H, 2H), 8.14 (d, 3J = 8.3, aryl-H, 2H). 13C NMR (CDCl3,
125.7 MHz) δ/ppm: 14.1 (CH3), 20.9 (CH3), 126.0 (aryl-C),
126.2 (aryl-C), 129.4(aryl-C), 129.5 (aryl-C), 130.5 (aryl-C),
131.0, 132.6 (aryl-C), 138.0 (aryl-C), 145.0 (aryl-C), 146.7
(aryl-C), 169.5 (aryl-C). IR (KBr) ν/cm-1: 2961 (s), 2917(s),
1619 (m), 1582 (s), 1436 (w), 1295 (s), 1198 (w), 854 (s), 833 (s),
778 (s).
Experimental Section
General Procedures. The complexes described below are air-
and moisture-sensitive necessitating that manipulations be car-
ried out under an inert atmosphere of argon or nitrogen gas
using standard Schlenk, vacuum-line, and glovebox techniques.
Hydrocarbon solvents were sparged with argon, then deoxyge-
nated and dried by passage through Q5 and activated alumina
columns, respectively. Ethereal and halogenated solvents were
sparged with argon and then dried by passage through two
activated alumina columns. To test for effective oxygen and
water removal, non-chlorinated solvents were treated with a few
drops of a purple solution of sodium benzophenone ketyl in
tetrahydrofuran (THF). The metal salt TiCl4 was purchased
Synthesis of (dmp-BIAN)TiCl4 (1c). Using the same condi-
tions reported for 1a, dmp-BIAN derivative 1c was isolated as
an orange solid in 84% yield from 3.0 g of tmp-BIAN (6.2 mmol)
and 1.3 g of TiCl4 (6.8 mmol). Anal. Calcd for C28H24N2Cl4Ti: C
58.16%, H 4.18%, N 4.85%. Found: C 58.16%, H 4.24%, N
1
4.87%. H NMR (CDCl3, 500 MHz) δ/ppm: 2.46 (s, m-CH3,
12H), 6.82 (d, 3J = 7.3 Hz, aryl-H, 2H), 7.16 (s, aryl-H, 2H),
3
7.22 (s, aryl-H, 4H), 7.57 (t, J = 8.4, aryl-H, 2H), 8.13 (d,
3J = 8.4, aryl-H, 2H). 13C NMR (CDCl3, 125.7 MHz) δ/ppm:
21.5 (CH3), 118.3 (aryl-C), 125.2 (aryl-C), 126.7 (aryl-C),
128.9 (aryl-C), 130.1 (aryl-C), 131.1 (aryl-C), 132.4 (aryl-C),
139.9 (aryl-C), 145.7 (aryl-C), 150.1 (aryl-C), 167.9 (aryl-C).
IR (KBr) ν/cm-1: 2926(s), 1608 (m), 1298 (s), 848 (m), 830 (m),
777 (s), 669(m).
t
from Alfa-Aesar and used as received. BuNH2 and pyridine
(Aldrich) were dried by refluxing over CaH2 and distilling under
argon. The ligands N,N0-bis(2,6-diisopropylphenylimino)acen-
aphthylene (dpp-BIAN), N,N0-bis(2,4,6-trimethylphenylimino)-
acenaphthylene (tmp-BIAN), and N,N0-bis(3,5-dimethylpheny-
limino)acenaphthylene (dmp-BIAN) were prepared according to
published procedures.95,97,98
Synthesis of (dpp-BIAN)TiCl2(=NtBu) (2a). In a typical
experiment, 1.0 g of 1a (1.5 mmol, 1 equiv) was added to 50 mL
of CH2Cl2 and then frozen in a liquid nitrogen cold well. Upon
thawing, tBuNH2 (318 mg, 1.47 mmol, 3.0 equiv) was added to
the mixture portion-wise over 30 min. The reaction mixture
was allowed to warm slowly to 25 °C with constant stirring,
which was continued overnight. The reaction mixture was fil-
tered, and the solvent was removed under reduced pressure to
yield 970 mg of pure 2a as an orange solid (71% yield). Anal.
Calcdfor C40H49N3Cl2Ti:C69.57%, H 7.15%, N 6.08%. Found:
Physical Measurements. NMR spectra were collected on
Bruker Avance 500 MHz spectrometers in dry, degassed chloro-
1
form-d1 at 298 K. H NMR spectra were referenced to TMS
using the residual proteo impurities of the solvent; 13C NMR
spectra were referenced to TMS using the natural abundance
13C impurities of the solvent. All chemical shifts are reported
using the standard notation in parts-per-million; positive che-
mical shifts are to a higher frequency from the given reference.
Infrared spectra were recorded as KBr pellets with a PerkinEl-
mer Spectrum One FTIR spectrophotometer.
1
C 69.84%, H 6.79%, N 5.60%. H NMR (CDCl3, 500 MHz)
δ/ppm: 0.80 (d, 3J = 6.8 Hz, CH(CH3)2, 12H), 1.22 (s, C(CH3)3,
9H), 1.41 (d, 3J = 6.6 Hz, CH(CH3)2, 12H), 3.40 (m, CH(CH3)2,
3
3
4H), 6.27 (d, J = 7.3 Hz, aryl-H, 2H), 7.41 (d, J = 7.8 Hz,
aryl-H, 4H), 7.51 (m, aryl-H, 4H), 8.08 (d, 3J = 8.2, aryl-H,
2H). 13C NMR (CDCl3, 125.7 MHz) δ/ppm: 24.0 (CH(CH3)2),
24.9 (CH(CH3)2), 29.3 (CH(CH3)2), 30.5 (C(CH3)3), 73.4
(C(CH3)3), 123.5 (aryl-C), 124.9 (aryl-C), 127.2 (aryl-C),
128.2 (aryl-C), 128.4 (aryl-C), 128.7 (aryl-C), 132.2
(aryl-C), 135.4 (aryl-C), 138.9 (aryl-C), 169.7(aryl-C). IR
(KBr) ν/cm-1: 2806 (m), 1964 (s), 1622 (s), 1232 (s), 836 (s), 798
(m), 783 (s), 757 (s), 610 (w), 504 (m).
Synthesis of (dpp-BIAN)TiCl4 (1a). In a typical preparation,
5.0 g of dpp-BIAN (10.0 mmol, 1 equiv) was added to 75 mL of
CH2Cl2 and frozen in a liquid nitrogen cold well. Upon thawing
the mixture, neat TiCl4 (1.9 g, 10.0 mmol, 1 equiv) was added, and
the mixture was allowed to warm slowly to 25 °C with constant
stirring. After 1 h, the solvent was removed under reduced
pressure, and the red-orange residue was washed several times
with pentane to afford 6.19 g of pure 1a (90% yield). Anal. Calcd
for C36H40N2Cl4Ti: C 62.63%, H 5.86%, N 4.06%. Found: C
62.89%, H 6.21%, N 3.86%. 1H NMR (CDCl3, 500 MHz)
Synthesis of (tmp-BIAN)TiCl2(=NtBu) (2b). Using the same
conditions reported for the preparation of 2a, tmp-BIAN
derivative 2b was isolated as a brick-red solid in 89% yield from
720 mg of tBuNH2 (9.8 mmol, 3 equiv) and 2.0 g of 1b (3.2 mmol,
3
3
δ/ppm: 0.81 (d, J = 6.8 Hz, CH(CH3)2, 12H), 1.43 (d, J =
6.6 Hz, CH(CH3)2, 12H), 3.90 (m, CH(CH3)2, 4H), 6.49 (d, 3J =
1 equiv). Anal. Calcd for C34H37N3Cl2Ti 1/2CH 2Cl2: C
3
63.86%, H 5.90%, N 6.48%. Found: C 64.28%, H 6.55%, N
6.34%. 1H NMR (CDCl3, 500 MHz) δ/ppm: 1.16 (s, C(CH3)3,
9H), 2.32 (s, o-C H3, 12H), 2.42 (s, p-CH3, 6H), 6.68 (d, 3J = 7.0
Hz, aryl-H, 2H), 7.09 (s, aryl-H, 4H), 7.59 (t, 3J = 7.4,
aryl-H, 2H), 8.19 (d, 3J = 8.3, aryl-H, 2H). 13C NMR
(97) Gasperini, M.; Ragaini, F.; Cenini, S. Organometallics 2002, 21,
2950.
(98) Paulovicova, A.; El-Ayaan, U.; Shibayama, K.; Morita, T.; Fukuda,
Y. Eur. J. Inorg. Chem. 2001, 2641.

Article
Inorganic Chemistry, Vol. 49, No. 5, 2010 2225
(CDCl3, 125.7 MHz) δ/ppm: 18.7 (aryl-CH3), 21.2 (aryl-CH3),
31.0 (C(CH3)3), 73.8 (C(CH3)3), 125.6 (aryl-C), 126.0 (aryl-C),
127.8 (aryl-C), 129.0 (aryl-C), 129.3 (aryl-C), 130.6 (aryl-C),
132.3 (aryl-C), 137.1 (aryl-C), 145.0 (aryl-C), 168.7 (aryl-C).
IR (KBr) ν/cm-1: 2967 (s), 2917 (s), 1624 (m), 1584 (s), 1470 (s),
1380 (m), 1223 (s), 1026 (m), 850(m), 829 (m), 775(s).
130.9 (aryl-C), 139.7 (aryl-C), 140.1 (aryl-C), 147.3 (aryl-C),
150.7 (aryl-C), 162.6 (aryl-C), 166.0 (aryl-C). IR (KBr)
ν/cm-1: 3283 (m), 3192 (m), 3107(w), 2960 (s), 1633 (s), 1591
(s), 1372 (m), 1247 (s), 1121 (s), 846 (s), 774 (s), 659 (s), 533 (m).
t
Synthesis of (dmp-BIAN)TiCl2[=N(2,6-C6H3Me2)](NH2 Bu)
(5). 2,6-Dimethylaniline (97 mg, 0.81 mmol, 1.5 equiv) was
added to a scintillation vial containing 400 mg of 4 (0.61 mmol,
1 equiv) in 20 mL of CH2Cl2. After 2.5 h at 25 °C the solvent was
removed from the mixture under reduced pressure. The residual
solid was redissolved in 20 mL of CH2Cl2, and an additional
97 mg of 2,6-dimethylaniline (0.81 mmol, 1.5 equiv) was added
to the solution. After stirring overnight at 25 °C, the solvent was
again removed from the mixture under reduced pressure. The
residual solid was washed with pentane to afford 300 mg of 5, as
Synthesis of (dpp-BIAN)TiCl2[=N(2,6-C6H3Me2)] (3a). 2,6-
Dimethylaniline (106 mg, 0.876 mmol, 1 equiv) was added
dropwise to a stirred solution of 2a (576 mg, 0.834 mmol, 1
equiv) in 20 mL of CH2Cl2. After 2 h the solvent was removed
under reduced pressure. The residue was recrystallized by
layering a CH2Cl2 solution with pentane for 250 mg of dark
green crystalline 3a (43% yield). Anal. Calcd for C44H49-
N3Cl2Ti 1/4CH2Cl2: C 69.94%, H 6.67%, N 5.53%. Found:
3
C 71.0%, H 6.60%, N 5.78%. 1H NMR (CDCl3, 500 MHz) δ/
ppm: 0.88 (d, 3J = 6.5 Hz, CH(CH3)2, 12H), 1.17 (d, 3J = 6.5
Hz, CH(CH3)2, 12H), 2.46 (s, aryl-C H3, 6H), 3.24 (m, CH-
(CH3)2, 4H), 6.54 (t, 3J = 7.4 Hz, aryl-H, 1H), 6.71 (t, 3J = 9.0
Hz, aryl-H, 2H), 7.36 (d, 3J = 8 Hz, aryl-H, 4H), 7.49 (t, 3J =
8 Hz, aryl-H, 2H), 7.60 (t, 3J = 7.5 Hz, aryl-H, 2H), 8.16 (d,
3J = 8, aryl-H, 2H). 13C NMR (CDCl3, 125.7 MHz) δ/ppm: 19.4
(aryl-CH3), 23.7 (CH(CH3)2, 24.4(CH(CH3)2, 29.6(CH(CH3)2),
121.1 (aryl-C), 123.5 (aryl-C), 124.8 (aryl-C), 126.0 (aryl-C),
126.7 (aryl-C), 126.9 (aryl-C), 128.3 (aryl-C), 128.4 (aryl-C),
128.5 (aryl-C), 128.9 (aryl-C), 129.0 (aryl-C), 132.7 (aryl-C),
a yellow solid (71% yield). Anal. Calcd for C40H44N4Cl2Ti
3
1/4CH2Cl2: C 67.07%, H 6.22%, N 7.77%. Found: C 67.33%,
H 6.13%, N 7.55%. 1H NMR (CDCl3, 500 MHz) δ/ppm: 1.24
(s, Ti-NH2C(CH3)3, 9H), 2.11 (s, m-CH3, 6H), 2.42 (s, TidN-
(C6H3(m-CH3)2), 6H), 2.55 (s, m-CH3, 6H), 2.87 (s, Ti-NH2-
C(CH3)3, 2H), 6.42 (t, 3J = 7.5, aryl-H, 1H), 6.56 (d, 3J = 7.5
Hz, aryl-H, 2H), 6.62 (s, aryl-H, 1H), 6.85 (d, aryl-H, 3J = 7.5
Hz, 1H), 7.05 (s, aryl-H, 1H), 7.08 (s, aryl-H, 2H), 7.13 (d,
3J = 7.5 Hz, aryl-H, 1H), 7.17 (s, aryl-H, 2H), 7.43 (t, 3J = 7.5,
aryl-H, 1H), 7.45 (t, 3J = 7.5, aryl-H, 1H), 7.96 (d, 3J = 8.5,
aryl-H, 1H), 8.00 (d, 3J = 8.5, aryl-H, 1H). 13C NMR (CDCl3,
125.7 MHz) δ/ppm: 20.0 (aryl-CH3), 20.5 (aryl-CH3), 21.0 (aryl-
CH3), 30.5 (C(CH3)3), 51.5 (Ti-NH2C(CH3)3), 116.7 (aryl-C),
117.6 (aryl-C), 120.3 (aryl-C), 124.2 (aryl-C), 125.6 (aryl-C),
125.7 (aryl-C), 126.0 (aryl-C), 126.1 (aryl-C), 127.7 (aryl-C),
127.8 (aryl-C), 128.0 (aryl-C), 129.8 (aryl-C), 130.4 (aryl-C),
130.8 (aryl-C), 136.4 (aryl-C), 138.3 (aryl-C), 139.4 (aryl-C),
144.0 (aryl-C), 146.3 (aryl-C), 147.6 (aryl-C), 156.9 (aryl-C),
161.7 (aryl-C), 164.6 (aryl-C). IR (KBr) ν/cm-1: 3302 (w),
3347 (w), 2956 (s), 2917(s), 1629 (s), 1585 (s), 1467 (s), 1371 (m),
1283 (s), 1207 (m), 1111(m), 845 (m), 773 (s), 661 (s).
138.9 (aryl-C), 145.1 (aryl-C), 145.8 (aryl-C). IR (KBr) ν/cm-1
:
3061(w), 2961 (s), 2926 (m), 1622 (s), 1582 (s), 1565 (m), 1437 (m),
1300 (s), 800 (m), 785 (m), 758 (m).
Synthesis of (tmp-BIAN)TiCl2[=N(2,6-C6H3Me2)] (3b).
Using the same conditions reported for the preparation of 3a,
tmp-BIAN derivative 3b was isolated as a green solid in 21%
yield from 31 mg of 2,6-dimethylaniline (0.25 mmol, 1.1 equiv)
and 140 mg of 2b (0.23 mmol, 1 equiv). Anal. Calcd for
C38H37N3Cl2Ti 1/4CH2Cl2: C 67.99%, H 5.59%, N 6.22%.
3
Found: C 67.93%, H 5.99%, N 6.25%. 1H NMR (CDCl3, 500
MHz) δ/ppm: 2.12 (s, Ar-CH3, 12H), 2.31(s, Ar-CH3, 6H),
2.33 (s, Ar-CH3, 6H), 6.43 (t, 3J = 7.5 Hz, Ar-H, 1H), 6.60 (d,
3J = 7.5 Hz, Ar-H, 2H), 6.62 (d, 3J = 7.5 Hz, Ar-H, 2H), 6.95 (s,
Ar-H, 4H), 7.48 (t, 3J = 7.5 Hz, Ar-H, 2H), 8.05 (d, 3J = 8.5 Hz,
Ar-H, 2H). 13C NMR (CDCl3, 125.7 MHz) δ/ppm: 18.8 (aryl-
CH3), 19.8 (aryl-CH3), 21.2 (aryl-CH3), 121.8 (aryl-C), 125.8
(aryl-C), 126.9 (aryl-C), 128.1 (aryl-C), 128.3 (aryl-C), 129.0
(aryl-C), 129.5 (aryl-C), 130.0 (aryl-C), 131.1 (aryl-C), 132.7
(aryl-C), 133.4 (aryl-C), 137.3 (aryl-C), 145.5(aryl-C), 161.5-
(aryl-C). IR (KBr) ν/cm-1: 2953 (s), 2896 (s), 1613 (s), 1577 (s),
1473 (s), 1280 (m), 1094 (m), 1029 (m), 850 (m), 772 (m), 736 (m).
VT NMR studies of 4. Variable-temperature 1H NMR spec-
troscopy (600 MHz) was used to extract activation parameters
for the fluxionality of 4 in both the presence and absence of
t
added BuNH2. An NMR tube fitted with a J. Young Teflon
valve was charged with 20 mg of 4. The sample was dissolved in
CDCl3 and subjected to three freeze-pump-thaw cycles.
1H NMR spectra were collected in the temperature range
328-380 K, allowing the sample to equilibrate for 5 min at each
temperature. The shape and position of the two methyl reso-
nances for the dmp-BIAN ligand were fitted using the Complete
Band Shapes Method to acquire the rate constants for exchange
at each temperature. Activation parameters were subsequently
calculated using an Eyring plot over the temperature range.
General Details of X-ray Data Collection and Reduction.
X-ray diffraction data were collected on a Bruker CCD platform
diffractometer equipped with a CCD detector. Measurements
t
Synthesis of (dmp-BIAN)TiCl2(=NtBu)(NH2 Bu) (4). A solu-
tion of 1.0 g of 1c (1.7 mmol, 1 equiv) dissolved in 50 mL of
CH2Cl2 was frozen in a liquid nitrogen cold well. Upon thawing,
tBuNH2 (760 mg, 10.4 mmol, 6 equiv) was added to the mixture
in aliquots over 30 min. The reaction mixture was allowed to
warm slowly to 25 °C with constant stirring, which was con-
tinued overnight. The reaction mixture was filtered, and the
solvent was removed under reduced pressure to yield 710 mg of
pure 3 as a golden solid (64% yield). Anal. Calcd for
˚
were carried out at 163 K using Mo KR (λ = 0.71073 A) radia-
tion, which was wavelength selected with a single-crystal gra-
phite monochromator. The SMART program package was used
to determine unit-cell parameters and for data collection. The
raw frame data were processed using SAINT and SADABS to
yield the reflection data files. Subsequent calculations were
carried out using the SHELXTL program suite. Analytical
scattering factors for neutral atoms were used throughout the
analyses. Thermal ellipsoid plots were generated using ORTEP-
3 for Windows. Diffraction data for 1b, 2b, 3b, and 4 are shown
in Table 1.
C36H44N4Cl2Ti 1/4CH2Cl2: C 64.72%, H 6.67%, N 8.33%.
3
Found: C 65.10%, H 7.06%, N 8.36%. 1H NMR (CDCl3, 500
MHz) δ/ppm: 0.64 (s, Ti=NC(CH3)3, 9H), 1.20 (s, Ti-NH2-
C(CH3)3, 9H), 2.37 (s, m-CH3, 6H), 2.42 (s, m-CH3, 6H), 2.82 (s,
Ti-NH2C(CH3)3, 2H), 6.65 (d, 3J = 7.2 Hz, aryl-H, 1H), 6.66(d,
3J = 7.8 Hz, aryl-H, 1H), 6.99 (s, aryl-H, 2H), 7.00 (s, aryl-H,
1H), 7.06 (s, aryl-H, 1H), 7.35 (s, aryl-H, 2H), 7.37 (t, 3J = 7.2,
aryl-H, 1H), 7.40 (t, 3J = 7.8, aryl-H, 1H), 7.91 (d, 3J = 8.4,
aryl-H, 1H), 7.96 (d, 3J = 7.8, aryl-H, 1H). 13C NMR (CDCl3,
125.7 MHz) δ/ppm: 21.4 (aryl-CH3), 30.1 (C(CH3)3), 31.1
(C(CH3)3), 51.4 (Ti-NH2C(CH3)3), 70.4 (TidNC(CH3)3),
116.8 (aryl-C), 118.4 (aryl-C), 124.7 (aryl-C), 126.2 (aryl-C),
126.7 (aryl-C), 126.9 (aryl-C), 128.0 (aryl-C), 128.2 (aryl-C),
128.25 (aryl-C), 128.3 (aryl-C), 130.1 (aryl-C), 130.7 (aryl-C),
Results and Discussion
Synthesis and Characterization of (BIAN)TiCl4 Com-
plexes. Lewis acidic TiCl4 readily coordinates neutral
BIAN donor ligands to afford six-coordinate adduct
complexes. The BIAN ligand derivatives that will be

2226 Inorganic Chemistry, Vol. 49, No. 5, 2010
Clark et al.
Table 1. X-ray Diffraction Data-Collection and Refinement Parameters for [tmp-BIAN]TiCl4 (1b), [tmp-BIAN]Ti(=NtBu)Cl2 (2b), (tmp-BIAN)TiCl2[=N(2,6-C6H3Me2)]
(3b), and [dmp-BIAN]Ti(=NtBu)Cl2(NH2tBu) (4)
1b CH2Cl2
3
2b 2CH2Cl2
3
3b 2CH2Cl2
3
4 CH2Cl2
3
empirical formula
formula weight
crystal system
space group
C31H30Cl6N2Ti
691.17
orthorhombic
Pna21
19.5926(16)
18.4456(15)
8.7253(7)
90
90
90
C36H41Cl6N3Ti
776.32
monoclinic
P21
10.7937(14)
12.3268(16)
15.0167(19)
90
105.631(2)
90
C40H41Cl6N3Ti
824.36
monoclinic
Cc
12.249(5)
21.633(8)
15.987(6)
90
110.581(5)
90
C37H46Cl4N4Ti
736.48
triclinic
P1
˚
a/A
12.1324(17)
13.1859(18)
13.2874(19)
104.719(3)
112.632(2)
92.344(3)
1874.6(5)
2
˚
b/A
˚
c/A
R/deg
β/deg
γ/deg
3
˚
V/A
Z
refl. collected
3153.3(4)
4
33904
1924.1(4)
2
11717
3966(3)
4
33004
16242
indep. refl. (Rint
R1 (I g 2σI)
wR2 (all data)
)
7786 (0.0276)
0.0290
0.0788
7061 (0.0303)
0.0557
0.1421
8846 (0.0325)
0.0364
0.0958
6398 (0.0262)
0.0588
0.1548
discussed here present substantially different steric pro-
files when coordinated to a metal center. As shown in
Chart 1, the most crowded metal environment is expected
for the dpp-BIAN ligand, which directs four iso-propyl
substituents above and below the metal binding site.
Conversely, dmp-BIAN should afford the least crowded
metal environment since the methyl groups of the 3,5-
dimethylphenyl substituents point away from the metal
binding site. The reactions of dpp-BIAN, tmp-BIAN, and
dmp-BIAN with TiCl4 proceeded smoothly, forming
the six coordinate adducts 1a-c in high overall yields
(1a, (dpp-BIAN)TiCl4, 90%; 1b, (tmp-BIAN)TiCl4,
98%; 1c, (dmp-BIAN)TiCl4, 84%;). Reaction progress
was indicated by darkening of the reaction solutions from
the orange color of the free BIAN ligands to the dark red
color of the titanium(IV) adducts. In the infrared spec-
trum, coordination of the BIAN ligands to titanium
resulted in small but characteristic red-shifts in the CdN
stretching frequencies (ca. 30 cm-1). Similarly, coordina-
tion of the BIAN ligands to titanium induces diagnostic
Figure 1. ORTEP for (tmp-BIAN)TiCl4 CH2Cl2 (1b CH2Cl2). Ellip-
3
3
soids are drawn at 50% probability. Solvent and hydrogen atoms have
been omitted for clarity.
tmp-BIAN ligand acting as a neutral diimine toward
titanium. This is further supported by the observed
N-C and C-C distances, which are normal for an
acenaphthylenediimine.91,95
1
shifts in the H NMR resonances of the acenaphthylene
ring. Downfield shifts of ∼0.17 and ∼0.27 ppm were
observed for the 3,30 and 4,40 resonances of the naphthyl
moiety, respectively, while an upfield shift of 0.26 ppm was
The addition of 2 equiv of pyridine to CH2Cl2 solutions
of 1a or 1b results in loss of BIAN ligand and precipita-
tion of the bis(pyridine) adduct, TiCl4(py)2. Similarly, the
addition of dpp-BIAN or tmp-BIAN to TiCl4(py)2 did
not result in the formation of 1a or 1b. In contrast,
complex 1c, with the smaller dmp-BIAN ligand, is stable
in the presence of pyridine, and 1c could be prepared by
the addition of dmp-BIAN to TiCl4(py)2. Since the three
BIAN ligands and pyridine all offer similar imine nitro-
gen donor atoms to the Lewis-acidic metal center, the
displacement of dpp-BIAN and tmp-BIAN from 1a and
1b, respectively, suggests that steric crowding around the
BIAN ligands overrides any stabilizing effect associated
with a chelate effect. This idea is supported further by the
stability of 1c to pyridine. While the displacement of
BIAN from 1a and 1b by pyridine is rapid and complete,
all three complexes, 1a-c, appear to be stable to weaker
donor ligand such as Et2O and THF.97
1
observed for the 5,50 resonances. Additionally, the H
NMR resonances in the aryl imine functionalities each
shifted downfield upon coordination to the titanium metal
center.
Single crystal X-ray diffraction studies were used to
probe the solid-state structure of 1b. Layering CH2Cl2
solutions of 1b with pentane resulted in the precipitation
of deep red crystals suitable for X-ray diffraction studies.
Figure 1 shows the molecular structure of the six-coordi-
nate titanium complex and Table 2 highlights metrical
data for the titanium coordination sphere. The titanium
center of 1b is best described as octahedral; however,
there is significant distortion resulting from the small bite
angle of the tmp-BIAN ligand (N(1)-Ti(1)-N(2)
73.53°). This small bite angle results in a strained five-
membered chelate ring, as evidenced by N-C-C bond
angles that are smaller in 1b (∼118°) than in free BIAN
ligands (∼133°).95 Titanium-chloride bond lengths vary
Synthesis and Characterization of Five-Coordinate
Alkyl- and Aryl-Imido Complexes. Titanium complexes
1a and 1b with sterically demanding dpp-BIAN and
˚
between 2.23 and 2.29 A, with the shorter distances
t
observed for chloride ligands located trans to the tmp-
BIAN ligand. Long Ti-N bonds are consistent with the
tmp-BIAN ligands readily react with BuNH2 to afford
five-coordinate titanium imido complexes. In a typical

Article
Inorganic Chemistry, Vol. 49, No. 5, 2010 2227
Table 2. Selected Bond Distances and Angles for [tmp-BIAN]TiCl4 (1b)
˚
Bond Distances/A
Ti-Cl(1)
Ti-Cl(2)
Ti-Cl(3)
Ti-Cl(4)
2.2280(6)
2.2430(6)
2.2875(6)
2.2986(6)
Ti-N(1)
Ti-N(2)
2.2654(16)
2.2717(16)
Bond Angles/deg
N(1)-Ti-Cl(1)
N(2)-Ti-Cl(1)
N(1)-Ti-Cl(2)
N(2)-Ti-Cl(2)
N(1)-Ti-Cl(3)
N(2)-Ti-Cl(3)
N(1)-Ti-Cl(4)
N(2)-Ti-Cl(4)
96.04(4)
169.60(4)
160.33(4)
86.80(4)
85.95(4)
88.61(4)
84.07(4)
85.62(4)
N(1)-Ti-N(2)
Cl(1)-Ti-Cl(2)
Cl(1)-Ti-Cl(3)
Cl(2)-Ti-Cl(3)
Cl(1)-Ti-Cl(4)
Cl(2)-Ti-Cl(4)
Cl(3)-Ti-Cl(4)
73.53(2)
103.59(2)
90.91(2)
90.91(2)
93.20(2)
94.18(2)
169.55(2)
Scheme 1
The coordination environments about the titanium-
(IV) centers of 2b and 3b were elucidated by single crystal
X-ray diffraction experiments. The molecular structure
of 2b is shown as a thermal ellipsoid plot in Figure 2a, and
selected metrical parameters can be found in Table 3. The
titanium center of 2b is square pyramidal with approx-
imate Cs symmetry. The apical position is occupied by
the tert-butyl-imido ligand. The imido displays a short
˚
Ti-N bond length of 1.69 A and a nearly linear Ti-N-C
bond angle of 167°. These metrical parameters fall in the
ranges normally assigned to TitN triple bonds.1 Simple
molecular-orbital and symmetry arguments suggest that
an apical imido ligand in a square pyramid can act as a
six-electron donor (σ2 þ π4) to a d0 TiIV center to form a
TitNR triple bond.3,100,101 The impact of this strong
NfTi π donation is noticeable in the bond lengths of the
chloride ligands as well, which are elongated by nearly
˚
0.1 A relative to the equatorial chloride ligands of 1b.
experiment, cold CH2Cl2 solutions of 1a or 1b were treated
portion-wise with 3 equiv of tBuNH2, resulting in an exo-
thermic reaction and the precipitation of 2 equiv of
tBuNH3Cl as a white solid. From the resulting dark red
solutions, the five-coordinate complexes (dpp-BIAN)TiCl2-
(=NtBu) (2a) and (tmp-BIAN)TiCl2(=NtBu) (2b), respec-
tively, could be obtained in high yields (Scheme 1). Crude
samples of 2a and 2b are always contaminated with some
free BIAN ligand, which could be removed by recrystalliza-
tion of the crude product from dichloromethane.
Since five-coordinate 2b should have less steric repulsion
than six-coordinate 1b, this elongation in Ti-Cl bond
lengths can be ascribed to a decrease in the ClfTi π
donation in 2b. In contrast to the lengthening of the
Ti-Cl bonds, the dpp-BIAN Ti-N bonds are slightly
shorter than the tmp-BIAN Ti-N bonds of 1b. Finally,
the titanium center of 2b is displaced from the basal plane
˚
of the square pyramid by 0.594 A, resulting in an average
angle of 104° between the apical and equatorial donor
atoms.
Alkyl-imido ligands coordinated to titanium(IV) ty-
pically are reactive toward imide exchange with ani-
lines.80,99 Despite a crowded coordination environment
at titanium, complexes 2a and 2b react with the hindered
aniline, 2,6-dimethylaniline, at room temperature to
afford (dpp-BIAN)TiCl2[=N(2,6-C6H3Me2)] (3a) and
(tmp-BIAN)TiCl2[=N(2,6-C6H3Me2)] (3b), respec-
tively. Reaction yields for these imide metathesis reac-
tions were lowered by competitive displacement of the
The solid-state structure for aryl imido complex 3b is
analogous to that of tert-butyl imido complex 2b. Dark
green crystals suitable for X-ray diffraction provided the
molecular structure shown in Figure 2b and the metrical
data presented in Table 3. The titanium center in 3b is
square pyramidal with the aryl imido ligand occupying
the apical position. As observed for 2b, a short Ti-N
˚
bond distance (1.718(2) A) and a nearly linear Ti-N-C
bond angle (165.27(19)°) are consistent with significant
TitN triple bond character in 3b. The aryl group of the
imido ligand is rotated into the mirror plane of the
approximately Cs-symmetric structure to minimize steric
interactions with the methyl groups of the tmp-BIAN
ligand. Other bond distances and angles are consistent
with those observed for 2b.
t
BIAN ligand with BuNH2, which is liberated during
the reaction. Attempts to increase the overall yield of 3a
and 3b by introducing the aniline as the anilinium
t
t
chloride (and trap the BuNH2 as BuNH3Cl) resulted
in lower yields of the desired aryl imido products and
more free BIAN ligand.
(99) Coles, M. P.; Dalby, C. I.; Gibson, V. C.; Clegg, W.; Elsegood,
M. R. J. Polyhedron 1995, 14, 2455.
(100) Cundari, T. R. J. Am. Chem. Soc. 1992, 114, 7879.
(101) Lin, Z. Y.; Hall, M. B. Coord. Chem. Rev. 1993, 123, 149.

2228 Inorganic Chemistry, Vol. 49, No. 5, 2010
Clark et al.
that any fluxional behavior in the titanium coordination
environment is significantly faster than the NMR time
scale. Conversion of tert-butylimido derivatives 2a-b to
arylimido derivatives 3a-b is readily observed in the 1H
NMR resonances for the ortho substituents of the
dpp-BIAN and tmp-BIAN ligands. In complex 3b, an
upfield shift of 0.1 ppm is observed for the ortho-methyl
resonances of the tmp-BIAN ligand. In the case of 3a,
the isopropyl methyl resonances shift closer together
by ∼0.3 ppm. The methine resonance shifts slightly,
from 3.37 ppm in 2a, to 3.25 ppm in complex 3a. This
methine resonance also is broadened, indicating hindered
rotation about the N-Cipso bond as a result of increased
steric constraints imposed by the 2,6-dimethylphenylimi-
do ligand.
Six-Coordinate Imido Amine Complexes. In contrast to
the reactions used to prepare 2a and 2b, complex 1c reacts
with tBuNH2 to afford an octahedral imido-amine com-
plex, (dmp-BIAN)TiCl2(=NtBu)(NH2 Bu) (4), as shown
t
in Scheme 2. As discussed above, the dmp-BIAN ligand is
expected to provide a more open coordination environ-
ment around the metal center since the methyl substitu-
ents of the N-aryl groups are oriented away from the
metal-binding pocket of the diimine. Using the same
reaction conditions employed for the preparation of 2a
and 2b (i.e., 3 equiv of tBuNH2), the conversion of 1c to an
imido complex was incomplete; however, the addition of
t
a fourth equivalent of BuNH2 afforded the six coordi-
nate complex, 4, as the major product. Further increasing
t
the quantity BuNH2 to 6 equiv produced high yields of
spectroscopically pure 4, without any contamination by
free dmp-BIAN ligand.
The solid-state structure of 4 differs substantially from
the structures of five-coordinate imido complexes 2b and
3b. Single-crystal X-ray diffraction studies were con-
ducted on brown crystals of 4 grown by layering a satu-
rated CH2Cl2 solution of 4 with heptane. The molecular
structure of 4 is shown in Figure 3, and selected metrical
parameters are given in Table 3. Crystals of 4 are triclinic
with P1 symmetry. The imido and amine ligands occupy
cis positions of a six-coordinate titanium center. These
two ligands were disordered so that the imido and amino
ligands had to be modeled at 50% occupancy for each
position (see Supporting Information). While reason-
Figure 2. ORTEP of (a) (tmp-BIAN)TiCl2(=NtBu) 2CH2Cl2 (2b 2-
CH2Cl2) and (b) (tmp-BIAN)TiCl2[=N(2,6-C6H3Me2)] 2CH2Cl2 (3b 2-
CH2Cl2) as determined by single crystal X-ray diffraction studies.
Thermal ellipsoids are shown at 50% probability. Hydrogen atoms and
solvent molecules are omitted for clarity.
3
3
3
3
˚
˚
ably accurate Ti-N (2.156(4) A) and TidN (1.787(4) A)
bond distances could be obtained for amino and imido
ligands, respectively, we could not observe asymmetry in
the binding of the titanium center to the dmp-BIAN
ligand. It is worth noting that the TidN bond distance
NMR spectroscopic data for 2a,b and 3a,b are consis-
tent with the observed solid-state X-ray structures. A
singlet 1H NMR resonance, attributable to the tert-butyl
imido ligand of complexes 2a and 2b, was observed at 1.22
and 1.16 ppm, respectively. The 1H and 13C NMR
signatures for the acenaphthylene backbone of 2a and
2b are consistent with Cs symmetric geometry. The N-aryl
groups also appeared symmetric in solution at room
temperature; notably, only one 1H NMR resonance was
observed for the ortho-methyl groups of the 2,4,6-tri-
methylphenyl groups of 2b, indicating fast rotation about
the N-Cipso bond. Similarly, in the case of 2a, only one
methine resonance and two isopropyl methyl resonances
(at 0.80 and 1.41 ppm) were observed. Variable tempera-
ture NMR studies of 2a,b did not reveal significant
changes to the 1H NMR spectra upon cooling, suggesting
˚
observed in 4 is elongated by 0.19 A relative to the
titanium-imido distance observed for 2b, consistent with
the imido ligand being trans to the BIAN ligand in 4.
While the Ti-N-C bond angle for the imido ligand of 4
is still close to linear (179.1(4)°), the longer TidN bond
length suggests an effective decrease in NfTi π dona-
tion, though the imido group can still be considered an
overall six-electron donor. The titanium coordination
sphere is completed by two trans chloride ligands that
˚
˚
bond at lengths of 2.4545(11) A and 2.3734(11) A. These
halide distances are considerably longer than the dis-
tances observed for the trans chloride ligands in 1b and
are comparable to the equatorial chloride ligand dis-
tances observed in 2b.

Article
Inorganic Chemistry, Vol. 49, No. 5, 2010 2229
Table 3. Selected Bond Distances and Angles for [tmp-BIAN]Ti(=NtBu)Cl2 (2b), (tmp-BIAN)TiCl2[=N(2,6-C6H3Me2)] (3b), and [dmp-BIAN]Ti(=NtBu)Cl2(NH2tBu) (4)
˚
Bond Distances/A
2b
3b
4
Ti-N(1)
Ti-N(2)
Ti-N(3)
Ti-N(4)
Ti-Cl(1)
Ti-Cl(2)
2.254(4)
2.259(4)
1.690(4)
2.257(2)
2.258(2)
1.718(2)
2.398(3)
2.288(3)
1.787(4)
2.156(4)
2.4545(11)
2.3734(11)
2.3208(14)
2.3360(13)
2.3366(9)
2.3241(10)
Bond Angles/deg
2b
3b
4
Ti-N(3)-C(31)
Ti-N(4)-C(33)
N(1)-Ti-N(2)
N(1)-Ti-Cl(1)
N(2)-Ti-Cl(1)
N(1)-Ti-Cl(2)
N(2)-Ti-Cl(2)
N(1)-Ti-N(3)
N(2)-Ti-N(3)
N(1)-Ti-N(4)
N(2)-Ti-N(4)
N(3)-Ti-Cl(1)
N(3)-Ti-Cl(2)
N(4)-Ti-Cl(1)
N(4)-Ti-Cl(2)
Cl(1)-Ti-Cl(2)
164.1(4)
165.27(19)
179.1(4)
132.2(3)
71.73(10)
80.39(7)
82.12(7)
73.30(12)
89.98(10)
145.38(10)
149.38(10)
85.01(9)
73.45(8)
85.50(6)
146.24(6)
148.82(6)
88.64(6)
101.75(9)
103.39(9)
84.48(7)
85.15(8)
100.03(16)
104.23(17)
168.16(16)
96.43(16)
90.36(13)
157.67(14)
98.64(17)
94.43(17)
81.79(13)
106.84(13)
162.66(4)
107.85(14)
106.19(14)
106.60(8)
107.21(8)
96.68(5)
96.90(3)
Scheme 2
NMR data suggest that the imido-amine functionalities
of 4 are preserved in solution. Unlike the spectra obtained
for five-coordinate imido complexes 2a and 2b, which
show only three 1H NMR resonances for the acenaphthy-
lenediimine backbone, six sharp 1H NMR resonances are
observed for the BIAN backbone of 4 in the room-
temperature spectrum. This data is consistent with the
molecular structure shown in Figure 3, which has the
imido ligand trans to one nitrogen donor of the BIAN
ligand and the amino ligand trans to the other nitrogen
donor of the BIAN ligand. The proton signatures for the
tert-butyl groups of the imido and amino ligands are well
resolved as singlets at 0.64 and 1.20 ppm, respectively,
indicating that these ligands do not exchange on the
Figure 3. ORTEP of (dmp-BIAN)TiCl2(=NtBu)(NH2 Bu) CH2Cl2
t
3
(4 CH2Cl2) as determined by single crystal X-ray diffraction studies.
3
Thermal ellipsoids are shown at 50% probability. Hydrogen atoms and
the solvent molecule are omitted for clarity.
room temperature. The 1H NMR spectrum of 4 in CDCl3
containing one equiv of BuNH2 showed separate sharp
t
resonances for free and coordinated amine ligand at 1.18
and 1.20 ppm, respectively. The chemical shift of the tert-
butyl imido resonance is well upfield of the chemical
shift for the tert-butyl imido resonances observed for 2a
and 2b, consistent with decreased NfTi π donation.
Two singlets were observed for the 3,5-dimethylaryl
substituents of the dmp-BIAN in the 1H NMR spectrum,
consistent with the arylimine arms of the dmp-BIAN
ligand being located trans to different groups. Complex
t
NMR time scale. Moreover, the coordinated BuNH2
ligand does not exchange rapidly with free BuNH2 at
t

2230 Inorganic Chemistry, Vol. 49, No. 5, 2010
Clark et al.
Figure 5. Eyring plot of the rate constants for the isomerization of 4 in
CDCl3 (328-378 K).
analogous reactions to form 3a and 3b, the formation of 5
must be driven to completion by the removal of free
tBuNH2 liberated during the reaction. Hence the forma-
Figure 4. Partial 1H NMR spectra (600 MHz) in CDCl3 of 4 in the
temperature range 328-380 K showing the dmp-BIAN methyl reso-
nances (2.4 ppm), the tert-butylamino resonance (1.2 ppm), and the tert-
butylimido resonance (0.65 ppm).
t
tion of 5 is in equilibrium as long as free BuNH2 is
present, and NMR-scale reactions provided an estimate
for Keq of ∼0.37 at 298 K.
Changes in the 1H NMR spectrum of 5 relative to
complex 4 are consistent with the formation of the six-
coordinate arylimido-amine complex. Namely, the dis-
appearance of the tert-butylimido resonance at 0.65 ppm,
and the appearance of the arylimido ortho-methyl resonance
at 2.43 ppm were observed. The downfield shift of the ortho-
methyl substituents from those found in free 2,6-dimethyl-
aniline (2.16 ppm), which is consistent with the chemical
shifts observed for complexes 3a and 3b, is indicative of the
delocalization of electron density about the titanium-imido
bond and the aryl moiety. As observed for 4 the backbone
of the dmp-BIAN ligand in 5 is asymmetric showing six
resonances, while two resonances are observed for the
dimethylaryl groups on the imine nitrogens. These spectro-
scopic signatures are consistent with 5 having Cs symmetry
with trans chloride ligands and cis imido and amino ligands.
4 maintains overall Cs symmetry in solution at room
temperature.
Variable-temperature 1H NMR experiments on 4 in the
presence and absence of added BuNH2 suggest that the
t
coordinated amine ligand does dissociate at elevated temp-
eratures to access a fluxional five-coordinate species. Moni-
toring samples of pure 4 in CDCl3 by H NMR spectro-
1
scopy at elevated temperatures revealed broadening of the
two methyl resonances at 2.37 and 2.42 ppm for the dmp-
BIAN ligand, eventually coalescing into a singlet at
2.42 ppm at approximately 362 K as shown in Figure 4.
Similarly, the six unique BIAN resonances in the aryl
1
region of the H NMR spectrum of 4 coalesced to three
resonances at elevated temperatures. These observations
are consistent with the two sides of the dmp-BIAN ligand
of 4 becoming equivalent on the NMR time scale at
elevated temperatures. Rate constants were estimated in
the temperature range 328-380 K for the process that
exchanges the two methyl environments in 4 (trans to
amino and trans to imido ligands, respectively). Figure 5
shows the Eyring plot used to extract activation para-
meters of ΔHq = 19.7 ( 1.1 kcal mol-1 and ΔSq = 1.0 (
4.8 eu. Similar VT NMR experiments carried out in the
Conclusions
Steric profiles of the BIAN ligands examined herein have an
impact on the observed coordination geometry and stability
of titanium halide and titanium imido complexes. In the case
of the (BIAN)TiCl4 derivatives, the smallest BIAN ligand,
dmp-BIAN, stays coordinated to the titanium center in the
presence of excess pyridine. Furthermore, dmp-BIAN dis-
places pyridine from TiCl4(py)2 to form (dmp-BIAN)-
TiCl4, indicating that the stability of the titanium complex
with the smallest BIAN ligand is not derived from a kinetic
barrier but rather from thermodynamic preference. On the
other hand, the larger BIAN derivatives, tmp-BIAN and
dpp-BIAN, which have 2,6-disubstituted arylimine donors,
were readily displaced by pyridine from (tmp-BIAN)TiCl4
and (dpp-BIAN)TiCl4, respectively. The instability of these
two complexes relative to TiCl4(py)2 indicates that unfavor-
able steric interactions between the BIAN substituents and
the chloride ligands must offset the thermodynamic prefer-
ence for chelating a ligand to the titanium center.63,80,82
In the case of the titanium imido complexes, increased
BIAN ligand sterics enforce low-coordinate and more reactive
t
presence of 1 equiv of BuNH2 showed the same coale-
scence behavior for the dmp-BIAN 1H NMR resonances.
In this experiment, the 1H NMR resonances for the
coordinated and free BuNH2, which are separate and
t
sharp at 298 K, broaden and merge into a singlet with a
coalescence temperature of 360 K. These exchange data
and activation parameters are consistent with the disso-
t
ciation of the neutral BuNH2 ligand from 4 at elevated
temperature to afford a five-coordinate intermediate. By
analogy to the five-coordinate geometries of 2a and 2b,
this putative intermediate is likely a square-pyramidal
(dmp-BIAN)TiCl2(=NtBu) species.
The tert-butyl imido ligand could be exchanged with
2,6-dimethylaniline to form a six-coordinate arylimido-
amine complex, 5, as shown in Scheme 2. Unlike the

Article
Inorganic Chemistry, Vol. 49, No. 5, 2010 2231
geometries at the metal center. The smallest dmp-BIAN ligand
affords pseudo-octahedral titanium imido complexes that
retain a neutral amine donor ligand in the sixth coordination
site. The imido and amine ligands orient themselves trans to the
BIAN imine donors leaving the chloride ligands in mutually
has implications for future ligand and molecule designs. To
exploit the full reactivity of early transition metal imido
complexes, low-coordinate environments must be generated
for the metal center.34-38 While the larger steric profiles of
tmp-BIAN and dpp-BIAN did afford lower coordinate
titanium-imido complexes, these steric parameters also turn
on a decomposition pathway that expels the BIAN ligand
from the metal coordination sphere. Thus, future efforts to
design low-coordinate titanium imido complexes with steri-
cally demanding, chelating ligands must avoid this type of
decomposition. One strategy to avoid this path would be to
keep the sterically demanding groups on formally anionic
ligands, so that ligand loss is inhibited by both covalent and
ionic bonding contributions.
t
trans positions. While the neutral BuNH2 ligand does dis-
sociate from 4 to give access to a more reactive five-coordinate
intermediate, even in thermodynamically favorable aryl-for-
alkyl imide aminolysis reactions, binding of the alkylamine to
the metal center strongly inhibits the reaction. In contrast, the
larger tmp-BIAN and dmp-BIAN ligands enforce five-coordi-
nate geometries by precluding the binding of a neutral amine
ligand, and as such the aminolysis reaction proceeds readily.
While the neutral tBuNH2 ligand does dissociate from 4 to give
access to a more reactive five-coordinate intermediate, even in
thermodynamically favorable aryl-for-alkyl imide aminolysis
reactions, binding of the alkylamine to the metal center
strongly inhibits the reaction. In contrast, the larger tmp-BIAN
and dmp-BIAN ligands enforce five-coordinate geometries by
precluding the binding of a neutral amine ligand, and as such
the aminolysis reaction proceeds readily.
Acknowledgment. The authors thank NSF-CAREER
for supporting this work. A.F.H. is an Alfred P. Sloan
Foundation Fellow and a Camille Dreyfus Teacher-
Scholar.
Supporting Information Available: X-ray crystallographic
data in CIF format. This material is available free of charge
via the Internet at http://pubs.acs.org.
The strong impact of BIAN ligand sterics on the coordina-
tion geometry and the stability of titanium imido complexes