Imido and organometallic-amido titanium(IV) complexes of a chelating phenanthrenediamide ligand

Article abstract of DOI:10.1021/om0701219

New titanium(IV) complexes of the chelating ligand N,N′-bis(3,5- dimethylphenyl)-phenanthrene-9,10-diamide (pada^2-) are described. Metalation of padaH₂ with TiCl₄ in the presence of base afforded the six-coordinate pyridin

Full text of DOI:10.1021/om0701219

5330
Organometallics 2007, 26, 5330-5338
Imido and Organometallic-Amido Titanium(IV) Complexes of a
Chelating Phenanthrenediamide Ligand
Nicole A. Ketterer, Joseph W. Ziller, Arnold L. Rheingold, and Alan F. Heyduk*
Department of Chemistry, 1102 Natural Sciences 2, UniVersity of California, IrVine, California 92697 and
the Department of Chemistry, UniVersity of California, San Diego, La Jolla, California 92093
ReceiVed February 6, 2007
New titanium(IV) complexes of the chelating ligand N,N′-bis(3,5-dimethylphenyl)-phenanthrene-
9,10-diamide (pada2-) are described. Metalation of padaH2 with TiCl4 in the presence of base afforded
the six-coordinate pyridine adduct (pada)TiCl2(py)2 (1), which was used as a starting point for all further
complexes presented in this work. Metathesis of 1 with LiN(SiMe3)2 afforded the four-coordinate complex
(pada)TiCl[N(SiMe3)2] (2), free of coordinating pyridine. Further elaboration of 2 with MeLi, PhLi, and
PhCH2MgCl provided the mixed alkyl-amido species (pada)TiR[N(SiMe3)2] (3a, R ) Me; 3b, R )
CH2Ph; 3c, R ) Ph), which are all stable in the solid state and in solution. Dichloride 1 reacts directly
with 2 equiv of PhCH2MgCl to give the five-coordinate complex (pada)Ti(CH2Ph)2(py) (4). The
corresponding dimethyl- and diphenyltitanium complexes could not be isolated; however, generation of
these species followed by in situ reaction with tBuNH2 afforded the new titanium imido complex (pada)-
Ti(dNtBu)(py)2 (6). The aryl imido derivative (pada)Ti[dN(2,6-C6H3Me2)](py)2 (7) was prepared by
transimination of 6 with 2,6-dimethylaniline. Imido complex 6 also reacted with benzaldehyde to give
the organic metathesis product benzadimine; however, more crowded ketone and imine substrates were
unreactive. Prolonged heating of 6 in the absence of reactive substrates led to irreversible dimerization,
forming [(pada)Ti(py)(µ-NtBu)]2 (8).
bond activation strategies27-29 have been devised to capitalize
on the reactive nature of Ti-C, Ti-N, and TidN bonds.
Mechanistic studies of alkene and alkyne hydroamination
suggest that the reactive intermediate is a Group IV imido
species generated from a bisamide metal precursor.30 While
titanium alkyl and amide complexes show enhanced hydroami-
nation reactivity,4 complexes with chelating η1-pyrrole-based
ligands have been found to be even more reactive thanks to
increased Lewis acidity at the titanium center.5,31 In imine
metathesis reactions steric and electronic parameters on both
the imine moiety as well as the imido group have a measurable
Introduction
Imido and organometallic-amido complexes of titanium are
of interest for a variety of catalytic and stoichiometric nitrogen-
group transfer reactions. Alkene and alkyne hydroamination,1-17
olefin polymerization,18-22 imine metathesis,23-26 and C-H
* To whom correspondence should be addressed. E-mail: aheyduk@
uci.edu.
(1) Ackermann, L.; Bergman, R. G.; Loy, R. N. J. Am. Chem. Soc. 2003,
125, 11956-11963.
(2) Tillack, A.; Castro, I. G.; Hartung, C. G.; Beller, M. Angew. Chem.,
Int. Ed. 2002, 41, 2541-2543.
(3) Ong, T. G.; Yap, G. P. A.; Richeson, D. S. Organometallics 2002,
21, 2839-2841.
(18) Adams, N.; Arts, H. J.; Bolton, P. D.; Cowell, D.; Dubberley, S.
R.; Friederichs, N.; Grant, C. M.; Kranenburg, M.; Sealey, A. J.; Wang,
B.; Wilson, P. J.; Zuideveld, M.; Blake, A. J.; Schroder, M.; Mountford, P.
Organometallics 2006, 25, 3888-3903.
(19) Bigmore, H. R.; Dubberley, S. R.; Kranenburg, M.; Lawrence, S.
C.; Sealey, A. J.; Selby, J. D.; Zuideveld, M. A.; Cowley, A. R.; Mountford,
P. Chem. Commun. 2006, 436-438.
(20) Groysman, S.; Tshuva, E. Y.; Goldberg, I.; Kol, M.; Goldschmidt,
Z.; Shuster, M. Organometallics 2004, 23, 5291-5299.
(21) Scollard, J. D.; McConville, D. H. J. Am. Chem. Soc. 1996, 118,
10008-10009.
(22) Tabernero, V.; Cuenca, T. Eur. J. Inorg. Chem. 2005, 338-346.
(23) McInnes, J. M.; Blake, A. J.; Mountford, P. J. Chem. Soc., Dalton
Trans. 1998, 3623-3628.
(24) McInnes, J. M.; Mountford, P. Chem. Commun. 1998, 1669-1670.
(25) Wang, H.; Chan, H.; Xie, Z. Organometallics 2005, 24, 3772-
3779.
(4) Haak, E.; Bytschkov, I.; Doye, S. Angew. Chem., Int. Ed. 1999, 38,
3389-3391.
(5) Shi, Y.; Ciszewski, J. T.; Odom, A. L. Organometallics 2001, 20,
3967-3969.
(6) Johnson, J. S.; Bergman, R. G. J. Am. Chem. Soc. 2001, 123, 2923-
2924.
(7) Ayinla, R. O.; Schafer, L. L. Inorg. Chim. Acta 2006, 359, 3097-
3102.
(8) Kaspar, L. T.; Fingerhut, B.; Ackermann, L. Angew. Chem., Int. Ed.
2005, 44, 5972-5974.
(9) Bexrud, J. A.; Beard, J. D.; Leitch, D. C.; Schafer, L. L. Org. Lett.
2005, 7, 1959-1962.
(10) Ackermann, L.; Bergman, R. G. Org. Lett. 2002, 4, 1475-1478.
(11) Tillack, A.; Khedkar, V.; Beller, M. Tetrahedron Lett. 2004, 45,
8875-8878.
(12) Esteruelas, M. A.; Lopez, A. M.; Mateo, A. C.; Onate, E.
Organometallics 2006, 25, 1448-1460.
(26) Guiducci, A. E.; Boyd, C. L.; Mountford, P. Organometallics 2006,
25, 1167-1187.
(13) Buil, M. L.; Esteruelas, M. A.; Lopez, A. M.; Mateo, A. C.
Organometallics 2006, 25, 4079-4089.
(27) Bashall, A.; Collier, P. E.; Gade, L. H.; McPartlin, M.; Mountford,
P.; Trosch, D. J. M. Chem. Commun. 1998, 2555-2556.
(28) Bennett, J. L.; Wolczanski, P. T. J. Am. Chem. Soc. 1994, 116,
2179-2180.
(14) Muller, C.; Loos, C.; Schulenberg, N.; Doye, S. Eur. J. Org. Chem.
2006, 2499-2503.
(15) Takaki, K.; Koizumi, S.; Yamamoto, Y.; Komeyama, K. Tetrahe-
dron Lett. 2006, 47, 7335-7337.
(29) Polse, J. L.; Andersen, R. A.; Bergman, R. G. J. Am. Chem. Soc.
1998, 120, 13405-13414.
(16) Zhang, Z.; Leitch, D. C.; Lu, M.; Patrick, B. O.; Schafer, L. L.
Chem. Eur. J. 2007, 13, 2012-2022.
(30) Walsh, P. J.; Baranger, A. M.; Bergman, R. G. J. Am. Chem. Soc.
1992, 114, 1708-1719.
(17) Hoover, J. M.; Petersen, J. R.; Pikul, J. H.; Johnson, A. R.
Organometallics 2004, 23, 4614-4620.
(31) Odom, A. L. Dalton 2005, 225-233.
10.1021/om0701219 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 09/28/2007

Imido and Organometallic-Amido Ti(IV) Complexes
Organometallics, Vol. 26, No. 22, 2007 5331
impact on reaction rates.24 C-H bond activations are perhaps
most sensitive to the titanium coordination environment. Access
to electronically and coordinatively unsaturated, three-coordi-
nate, titanium-imido complexes leads to facile activation of
the most robust C-H bonds by a 1,2-addition pathway;
however, addition of a fourth donor ligand stabilizes the
titanium-imido functionality, shutting down the C-H bond
activation chemistry completely.28,29,32
Synthetic efforts have focused on the preparation of titanium
complexes supported by new auxiliary ligands that control the
steric and electronic parameters governing reactivity at the
titanium metal center. While the soft coordination environment
of Cp-type ligands has permitted the synthesis of a variety of
titanium-imido and -amido complexes,33-41 the potential
reactivity of complexes supported by hard π-donor ligands has
made modular, sterically demanding nitrogen-donor ligands
attractive. Ligands with hard donor atoms such as N, O, and Cl
form strong M-L bonds to titanium42,43 and allowed the syn-
thesis of imido and organometallic-amido titanium com-
plexes.44-56 For example, titanium-imido complexes with
chelating amidinate ligands exhibit a range of insertion reactivity
with unsaturated substrates such as carbodiimides, CO2, COS,
and isocyanates.3,26,57,58 Likewise, titanium centers with chelating
Chart 1
â-diketiminate ligands support many metal-ligand multiple-
bond structures including imidos,55-57,59,60 alkylidenes,61-63 and
phosphinidenes.63-65 In these cases, the monoanionic, chelating
nitrogen ligand provides both strong electron donation and steric
protection to the electrophilic titanium center.
N,N′-Bis(aryl)phenanthrenediamine-derived ligands, shown in
Chart 1, are an attractive platform for studying the reactivity of
titanium imido and organometallic-amido complexes. In its
deprotonated form an N,N′-bis(aryl)phenanthrenediamide ligand
has two anionic π-donor nitrogen atoms, yet π donation is
moderated by conjugation of the nitrogen lone pair into the
phenanthrene ring system. The aromaticity of this ring system
also can protect the ligand backbone against the degradation
pathways observed for other unsaturated chelating ligands such
as â-diketiminate.62,66 A limited bite angle is enforced by the
rigid planarity of the phenanthrene ring system, providing a
uniform metal template for reactivity studies. Finally, steric
protection for the metal center can be installed via substituents
on the amide nitrogen donors, thus regulating access to the metal
center. Herein we report on the titanium coordination chem-
istry of N,N′-bis(3,5-dimethyphenyl)phenanthrene-9,10-diamide
(pada2-), including the synthesis and characterization of the first
imido and organometallic-amido complexes of a phenanthrene-
diamide ligand.
(32) Cummins, C. C.; Schaller, C. P.; Van Duyne, G. D.; Wolczanski,
P. T.; Chan, A. W. E.; Hoffmann, R. J. Am. Chem. Soc. 1991, 113, 2985-
2994.
(33) Dunn, S. C.; Hazari, N.; Cowley, A. R.; Green, J. C.; Mountford,
P. Organometallics 2006, 25, 1755-1770.
(34) Ciruelos, S.; Cuenca, T.; Gomez, R.; Gomez-Sal, P.; Manzanero,
A.; Royo, P. Organometallics 1996, 15, 5577-5585.
(35) Kissounko, D. A.; Guzei, I. A.; Gellman, S. H.; Stahl, S. S.
Organometallics 2005, 24, 5208-5210.
(36) Kunz, K.; Erker, G.; Doring, S.; Frohlich, R.; Kehr, G. J. Am. Chem.
Soc. 2001, 123, 6181-6182.
(37) Jin, J.; Chen, E. Y. Organometallics 2002, 21, 13-15.
(38) Hanna, T. E.; Keresztes, I.; Lobkovsky, E.; Bernskoetter, W. H.;
Chirik, P. J. Organometallics 2004, 23, 3448-3458.
(39) Owen, C. T.; Bolton, P. D.; Cowley, A. R.; Mountford, P.
Organometallics 2007, 26, 83-92.
(40) Bai, Y.; Roesky, W. H.; Noltmeyer, M. Z. Anorg. Allg. Chem. 1991,
595, 21-26.
(41) Martins, A. M.; Ascenso, J. R.; Azevedo, C. G.; Calhorda, M. J.;
Dias, A. R.; Rodrigues, S. S.; Toupet, L.; Leonardis, P.; Veiros, L. F. J.
Chem. Soc., Dalton Trans. 2000, 4332-4338.
(42) Wilkinson, G.; Stone, F. G. A.; Abel, E. W. ComprehensiVe
Organometallic Chemistry; Pergamon: Oxford, 1982; Vol. 3.
(43) Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M.
AdVanced Inorganic Chemistry, 6th ed.; Wiley: New York, 1999.
(44) Manzer, L. E. J. Am. Chem. Soc. 1977, 99, 276-277.
(45) Yelamos, C.; Heeg, M. J.; Winter, C. H. Organometallics 1999,
18, 1168-1176.
(46) Adams, N.; Arts, H. J.; Bolton, P. D.; Cowell, D.; Dubberley, S.
R.; Friederichs, N.; Grant, C. M.; Kranenburg, M.; Sealey, A. J.; Wang,
B.; Wilson, P. J.; Zuideveld, M.; Blake, A. J.; Schroder, M.; Mountford, P.
Organometallics 2006, 25, 3888-3903.
(47) Carmalt, C. J.; Newport, A. C.; O’Neill, S. A.; Parkin, I. P.; White,
A. J. P.; Williams, D. J. Inorg. Chem. 2005, 44, 615-619.
(48) Skinner, M. E. G.; Toupance, T.; Cowhig, D. A.; Tyrrell, B. R.;
Mountford, P. Organometallics 2005, 24, 5586-5603.
(49) Irigoyen, A. M.; Martin, A.; Mena, M.; Palacios, F.; Ye´lamos, C.
J. Organomet. Chem. 1995, 494, 255-259.
Results and Discussion
Synthesis and Metalation of padaH2. Transition-metal
complexes derived from 9,10-phenanthrenediamine are
known;67-69 yet the chemistry of N-aryl-substituted derivatives
is underdeveloped, perhaps for lack of an efficient ligand
synthesis. Scheme 1 shows our strategy for the preparation of
N,N′-bis(3,5-dimethylphenyl)phenantherene-9,10-diamine (padaH2)
via reductive cyclodehydrogenation of 1,2-bis(3,5-dimethylphen-
ylimino)-1,2-diphenylethane. Previous reports used lithium metal
and extended reaction times to achieve such cyclization
reactions;70-72 in our experience, KC8 produces good yields of
(58) Guiducci, A. E.; Cowley, A. R.; Skinner, M. E. G.; Mountford. P.
J. Chem. Soc., Dalton Trans. 2001, 1392-1394.
(59) Hazari, N.; Mountford, P. Acc. Chem. Res. 2005, 38, 839-849.
(60) Basuli, F.; Huffman, J. C.; Mindiola, D. J. Inorg. Chem. 2003, 42,
8003-8010.
(61) Basuli, F.; Bailey, B. C.; Huffman, J. C.; Mindiola, D. J. Chem.
Commun. 2003, 1554-1555.
(62) Basuli, F.; Bailey, B. C.; Huffman, J. C.; Mindiola, D. J. Organo-
metallics 2005, 24, 3321-3334.
(63) Mindiola, D. J. Acc. Chem. Res. 2006, 39, 813-821.
(64) Zhao, G.; Basuli, F.; Kilgore, U. J.; Fan, H.; Aneetha, H.; Huffman,
J. C.; Wu, G.; Mindiola, D. J. J. Am. Chem. Soc. 2006, 128, 13575-13585.
(65) Basuli, F.; Tomaszewski, J.; Huffman, J. C.; Mindiola, D. J. J. Am.
Chem. Soc. 2003, 125, 10170-10171.
(50) Li, Y.; Shi, Y.; Odom, A. L. J. Am. Chem. Soc. 2004, 126, 1794-
1803.
(51) Stewart, P. J.; Blake, A. J.; Mountford, P. Organometallics 1998,
17, 3271-3281.
(66) Basuli, F.; Bailey, B. C.; Watson, L. A.; Tomaszewski, J.; Huffman,
J. C.; Mindiola, D. J. Organometallics 2005, 24, 1886-1906.
(67) vanBelzen, R.; Hoffmann, H.; Elsevier, C. J. Angew. Chem., Int.
Ed. 1997, 36, 1743-1745.
(68) Andoseh, I. N.; Douglas, I.; Egharevba, G. O.; Megnamisi-Belombe,
M. Z. Z. Anorg. Allg. Chem. 1982, 484, 203-209.
(69) vanBelzen, R.; Klein, R. A.; Kooijman, H.; Veldman, N.; Spek, A.
L.; Elsevier, C. J. Organometallics 1998, 17, 1812-1825.
(70) Macpherson, E. J.; Smith, J. G. Tetrahedron 1971, 27, 2645-2649.
(71) MacPherson, E. J.; Smith, J. G. Chem. Commun. 1970, 1552-1553.
(72) vanBelzen, R.; Klein, R. A.; Smeets, W. J. J.; Spek, A. L.; Benedix,
R.; Elsevier, C. J. Recl. TraV. Chim. Pays-Bas 1996, 275-285.
(52) Bolton, P. D.; Adams, N.; Clot, E.; Cowley, A. R.; Wilson, P. J.;
Schroder, M.; Mountford, P. Organometallics 2006, 25, 5549-5565.
(53) Pietryga, J. M.; Jones, J. N.; Macdonald, C. L. B.; Moore, J. A.;
Cowley, A. H. Polyhedron 2006, 25, 259-265.
(54) Mountford, P. Chem. Commun. 1997, 2127-2134.
(55) Croft, A.; Charis, R.; Boyd, C. L.; Cowley, A. R.; Mountford, P. J.
Organomet. Chem. 2003, 683, 120-130.
(56) Bailey, B. C.; Basuli, F.; Huffman, J. C.; Mindiola, D. J. Organo-
metallics 2006, 25, 2725-2728.
(57) Ong, T. G.; Yap, G. P. A.; Richeson, D. S. J. Am. Chem. Soc. 2003,
125, 8100-8101.

5332 Organometallics, Vol. 26, No. 22, 2007
Ketterer et al.
Scheme 1
the desired phenanthrenediamine product under milder condi-
tions. Eight resonances are observed in the 1H NMR spectrum
of padaH2: four aryl resonances at 7.31, 7.38, 8.20, and 8.52
ppm, displaying the proper coupling patterns, are observed for
the phenanthrene backbone, while the 3,5-dimethylphenyl
substituents give rise to singlets at 1.97, 6.23, and 6.39 ppm.
The N-H resonance of the neutral diamine is visible as a sharp
singlet at 5.5 ppm in C6D6.
Figure 1. Molecular structure of (pada)TiCl2(py)2 (1) as determined
by X-ray diffraction. Hydrogen atoms and the solvent molecule
are omitted for clarity.
Scheme 2
The six-coordinate metal complex, (pada)TiCl2(py)2 (1), was
prepared in 96% yield by direct addition of padaH2 to TiCl4 in
the presence of base. Well-formed single crystals were obtained
from slow diffusion of pentane into a dichloromethane solution
of 1; however, crystals grown in this manner readily lose solvent,
resulting in poor-quality X-ray diffraction data. The molecular
connectivity of 1 shown in Figure 1 was obtained repeatedly
from data sets acquired using several different crystals. The
titanium coordination environment in 1 is pseudo-octahedral,
with nominal C2V symmetry. The two chloride ions occupy trans
positions with two cis pyridine ligands and the chelating pada2-
ligand adopting a puckered and bent conformation. Similar
distortions in metal complexes with unsaturated diamide ligands
have been attributed to an η4 interaction that allows donation
2
with sp2 hybridization. The nodal plane of these amide donors
is rotated by 48° relative to the equatorial plane of the titanium
center, which increases overlap between the amide lone electron
pair and the empty titanium dxy orbital.
of the CdC π electrons of the ligand into an empty metal dz
orbital.73-78 An alternative explanation, supported by recent
experimental and theoretical studies of d0 molybdenum and
tungsten complexes, suggests that this structural distortion serves
to increase π overlap between the nitrogen lone electron pairs
and the empty metal dxy orbital of the titanium center.79-81 In
the case of 1, the latter bonding model is supported by the
molecular structure. The six-coordinate geometry of 1 means
1
The solution H NMR spectrum of 1 is consistent with the
solid-state structure, though broadened resonances suggest a
fluxional coordination environment. Upon cooling the sample
to 275 K, all proton resonances sharpened and no new peaks
1
2
were observed. The H NMR spectrum with added pyridine
the dz orbital is strongly antibonding, which decreases its ability
displayed separate resonances for free and coordinated pyridine,
indicating that pyridine dissociation from 1 is slow on the NMR
time scale.
to participate in π bonding. Furthermore, the sum of angles
around each nitrogen atom of the pada2- ligand is consistent
(73) Pindado, G. J.; Thornton-Pett, M.; Bochmann, M. J. Chem. Soc.,
Dalton Trans. 1998, 393-400.
(74) Tom Dieck, H.; Rieger, H. J.; Fendesak, G. Inorg. Chim. Acta 1990,
177, 191-197.
Synthesis of Organometallic-Amido Titanium Com-
plexes. Complex 1 reacted readily with the lithium amide
reagent LiN(SiMe3)2 to afford (pada)TiCl[N(SiMe3)2] (2) as
shown in Scheme 2. Recrystallization of 2 from pentane at -35
°C gave medium-red blocks suitable for X-ray diffraction. The
molecular structure of 2 is shown in Figure 2, and selected bond
lengths and angles are shown in Table 1. The packing diagram
for 2 suggests an intermolecular π-stacked arrangement with a
long centroid-centroid distance of ∼3.6 Å (see Supporting
Information).82 The coordination environment about the titanium
center is distorted tetrahedral with a Cl(1)-Ti(1)-N(3) bond
angle of 114.50(5)° and ligand bite angle of 87.65(6)°. The Ti-
(75) Scholz, J.; Hadi, G. A.; Thiele, K.; Gorls, H.; Weimann, R.;
Schumann, H.; Sieler, J. J. Organomet. Chem. 2001, 626, 243-259.
(76) Chamberlain, L. R.; Durfee, L. D.; Fanwick, P. E.; Kobriger, L.
M.; Latesky, S. L.; McMullen, A. K.; Steffey, B. D.; Rothwell, I. P.; Foltin,
K.; Huffman, J. C. J. Am. Chem. Soc. 1987, 109, 6068-6076.
(77) Scholz, J.; Dlikan, M.; Strohl, D.; Dietrich, A.; Schuman, H.; Thiele,
K. Chem. Ber. 1990, 123, 2279-2285.
(78) Aoyagi, K.; Gantzel, P.; Kalai, K.; Tilley, T. D. Organometallics
1996, 15, 923-927.
(79) Ison, E. A.; Cameron, T. M.; Abboud, K. A.; Boncella, J. M.
Organometallics 2004, 23, 4070-4076.
(80) Galindo, A.; Ienco, A.; Mealli, C. Comm. Inorg. Chem. 2002, 23,
401-416.
(81) Wang, S. S.; Abboud, K. A.; Boncella, J. M. J. Am. Chem. Soc.
1997, 119, 11990-11991.
(82) Bu, X. H.; Tong, M. L.; Xie, Y. B.; Li, J. R.; Chang, H. C.;
Kitagawa, S.; Ribas, J. Inorg. Chem. 2005, 44, 9837-9846.

Imido and Organometallic-Amido Ti(IV) Complexes
Organometallics, Vol. 26, No. 22, 2007 5333
Scheme 3
Figure 2. Thermal ellipsoid plot of (pada)TiCl[N(SiMe3)2]‚C6H6
(2‚C6H6). Ellipsoids are shown at 50% probability, while hydrogen
atoms and the solvent molecule have been omitted for clarity.
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
SiCl extrusion occurs as shown in eq 1, the reverse 1,2-addition
reaction must be much faster than any other unimolecular or
bimolecular process to trap the putative three-coordinate imido
fragment.
(pada)TiCl[N(SiMe3)2]‚C6H6 (2‚C6H6)
bond lengths
bond angles
Ti(1)-N(1)
1.9131(15)
1.9033(15)
1.8905(15)
2.2686(6)
Cl(1)-Ti(1)-N(1)
106.43(5)
113.42(5)
114.50(5)
87.65(6)
Ti(1)-N(2)
Ti(1)-N(3)
Ti(1)-Cl(1)
Cl(1)-Ti(1)-N(2)
Cl(1)-Ti(1)-N(3)
N(1)-Ti(1)-N(2)
(1)-N(3) and Ti(1)-Cl(1) bond lengths are 1.8905(15) and
2.2686(6) Å, respectively. The Si(1)-N(3)-Ti(1)-Cl(1) torsion
angle of ∼5° forces one Me3Si group of the amide ligand to be
in close proximity to the chloride (∼3.72 Å).
Organometallic derivatives of 2 were prepared by metathesis
with the appropriate Grignard or organolithium reagents (Scheme
2). Methyl-, benzyl-, and phenylamide complexes 3a-c were
prepared in 73-94% yield, and all species were isolated as red-
orange amorphous solids. The distinguishing 1H NMR features
for 3a-c correspond to the hydrocarbon ligands. The 1H NMR
spectrum of methyl derivative 3a showed a singlet at 0.44 ppm,
while the benzylic protons of 3b were observed as a singlet at
2.35 ppm. Derivative 3c showed three aryl resonances for the
phenyl ligand, suggesting that rotation about the Ti-C bond is
fast in room-temperature solution. Other 1H NMR markers for
3a-c were diagnostic for the titanium-coordinated pada2-
ligand.
1
In solution, the room-temperature H NMR spectrum of 2
showed broad signals indicative of a coordination environment
that is fluxional on the NMR time scale. At 298 K, one broad
resonance was observed at 0.13 ppm for both trimethylsilyl
groups of the monodentate amide ligand. Similarly, a single
broad resonance at 2.26 ppm was observed for the four methyl
groups of the phenanthrenediamide ligand. Variable-temperature
1H NMR studies were used to investigate the fluxional processes
giving rise to the observed line broadening. Upon cooling the
sample to 238 K, the broad trimethylsilyl resonance at 2.26 ppm
splits into sharp singlets at 2.40 and 2.03 ppm. Similarly, the
broad methyl resonance at 0.13 ppm splits into sharp singlets
at -0.29 and 0.56 ppm. The exchange process was modeled
using the complete band shape method83 to afford rate constants
between 238 and 313 K; an Eyring analysis (see Supporting
Information) provided the activation parameters ∆Hq ) 23 (
2 kcal mol-1 and Sq ) 31 ( 5 eu.
Thermolysis of 2 was carried out in an attempt to eliminate
Me3SiCl and form a three-coordinate imido species (eq 1). The
orientation of the chloride and amide ligands in the solid-state
structure of 2 suggested that Me3SiCl elimination may be
possible. A similar Si-N-Ti-Cl arrangement was reported for
(nacnac)TiIIICl[N(SiMe3)2], which upon one-electron oxidation
eliminated Me3SiCl to form a titanium(IV) imido complex.56
The high activation enthalpy and large and positive activation
entropy measured for 2 are consistent with a dissociative
process, suggesting that Me3SiCl elimination may be operative
at room temperature. Heating benzene-d6 solutions of 2 to 140
°C resulted in no change over 48 h. Similarly, thermolysis
reactions carried out in the presence of diphenylacetylene or
benzophenone to trap the putative three-coordinate imido
showed no change after 12 h. These results suggest that if Me3-
Synthesis and Characterization of Bis(benzyl)titanium and
Imidotitanium Complexes. The bis(benzyl)titanium complex
(pada)Ti(CH2Ph)2(py) (4) was obtained by reaction of benzyl
Grignard with 1. While 4 was formed in high yields, it was
always contaminated with up to 20% bibenzyl.84 Recrystalli-
zation from pentane at -35 °C afforded higher purity material,
1
but the yield of 4 was reduced significantly. The H NMR
spectrum of 4 suggested that one pyridine molecule is coordi-
nated to the titanium center, but pyridine dissociation occurs
readily to form a four-coordinate species, (pada)Ti(CH2Ph)2.
The room-temperature 1H NMR spectrum of 4 with one added
equivalent of pyridine showed only one set of pyridine
resonances, consistent with fast exchange between free and
1
coordinated pyridine on the NMR time scale. The H NMR
resonances for the pada2- ligand and the two benzyl moieties
are symmetric, also consistent with rapid pyridine exchange via
a four-coordinate (pada)Ti(CH2Ph)2 intermediate.
Attempts to isolate dimethyl- or diphenyltitanium(IV) com-
plexes analogous to 4 were unsuccessful; however, these putative
species can be made and used in situ to prepare new titanium
imido complexes. Addition of MeLi or PhLi to 1 at low
(83) Sandstrom, J. Dynamic NMR Spectroscopy; Academic Press, Inc.:
New York, 1982.
(84) Axenov, K. V.; Kilpelainen, I.; Klinga, M.; Leskela, M.; Repo, T.
Organometallics 2006, 25, 463-471.

5334 Organometallics, Vol. 26, No. 22, 2007
Ketterer et al.
Figure 3. Thermal ellipsoid plot of (pada)Ti(dNtBu)(py)2‚OEt2
(6‚OEt2). Ellipsoids are shown at 50% probability, while hydrogen
atoms and the solvent molecule have been omitted for clarity.
Figure 4. Variable-temperature 1H NMR spectra (500 MHz,
CDCl3) for (pada)Ti(dNtBu)(py)2 (6) in the presence of 2 equiv
of free pyridine (fp ) free pyridine, cp ) coordinated pyridine).
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
(pada)Ti(dNtBu)(py)2‚OEt2 (6‚OEt2)
bond lengths
bond angles
Simple symmetry arguments dictate that both nitrogen lone pairs
can donate into empty titanium dxz and dyz orbitals to form the
TitN triple bond. The basal plane of 6 is occupied by two
pyridine molecules and the pada2- ligand. The N(1)-Ti(1)-
N(2) bite angle is again small at 82.63(13)°, and the phenan-
threne ring is bent away from the apical imido ligand and toward
the open coordination site of the Ti center.55,85 As observed for
1, the amide donors of the pada2- ligand in 6 are rotated to
maximize overlap between the filled amide pz orbital and the
empty titanium dxy orbital.
In solution, the five-coordinate titanium imido complex 6
undergoes fast, dissociative pyridine exchange. At 298 K, three
exchange-broadened pyridine peaks were observed at 7.15, 7.62,
and 8.57 ppm, and these resonances did not shift upon addition
of free pyridine. A broad singlet was observed at 2.12 ppm for
the methyl groups of the N-aryl substituents on the pada2-
ligand, while the neighboring ortho aryl protons were broadened
into the baseline of the spectrum.
Ti(1)-N(1)
2.012(3)
2.013(3)
2.252(3)
2.233(3)
1.699(3)
N(5)-Ti(1)-N(1)
112.49(14)
110.39(14)
97.92(13)
104.80(14)
82.63(13)
173.6(3)
Ti(1)-N(2)
Ti(1)-N(3)
Ti(1)-N(4)
Ti(1)-N(5)
N(5)-Ti(1)-N(2)
N(5)-Ti(1)-N(3)
N(5)-Ti(1)-N(4)
N(1)-Ti(1)-N(2)
Ti(1)-N(5)-C(41)
temperature resulted in precipitation of LiCl as a white solid
and development of a dark red solution, as observed during the
synthesis of bis(benzyl) derivative 4. While neither of these
putative complexes (pada)TiMe2(py) (5a) or (pada)TiPh2(py)
(5b) could be isolated, addition of tert-butylamine to cold
solutions of 5a or 5b resulted in formation of (pada)Ti(dNt-
Bu)(py)2 (6), as shown in Scheme 3. In this way, the new imido
complex 6 was prepared in 53% yield. Similarly, pure samples
of 4 treated with tert-butylamine formed 6 and two equivalents
of toluene.
X-ray diffraction studies of imido complex 6 revealed a square
pyramidal titanium center with an apical imido ligand. Yellow
crystals of 6 were obtained from diethyl ether at -35 °C; the
solid-state molecular structure of 6 is shown as a thermal
ellipsoid plot in Figure 3, and selected bond lengths and angles
are presented in Table 2. Five-coordinate titanium imido
complexes with apical imido ligands are well established, and
the stability of this structural motif has been attributed to the
strong trans effect of the imido ligand.85,86 The five-coordinate
geometry of 6 stands in contrast to related imidotitanium
complexes supported by neutral R-diimine ligands, which adopt
six-coordinate geometries.23 The apical imide ligand of 6 also
has a short Ti-N bond length (1.699(3) Å) relative to imido
complexes supported by R-diimine ligands (Ti-N 1.729(4) Å).
This short bond distance is consistent with a formal triple bond
between the N and Ti atoms,86-90 and this assignment is further
supported by a nearly linear Ti-N-C bond angle (173.6(3)°).
To examine the kinetics of pyridine exchange, CDCl3
solutions of 6 and two equivalents of free pyridine were
monitored by variable-temperature 1H NMR spectroscopy.
1
Representative portions of the H NMR spectra are shown in
Figure 4. At 318 K, three sharp resonances are observed for
pyridine protons at 8.58, 7.62, and 7.16 ppm. These resonances
integrated to four equivalents of pyridine per titanium center,
consistent with fast exchange between free and coordinated
pyridine molecules. Upon cooling, these three resonances
broaden and split into six resonances. At 219 K, six sharp
resonances are observed for the pyridine protons, corresponding
to two different pyridine environments. A doublet at 8.45 ppm
(3JHH ) 4.9 Hz), a triplet at 7.60 ppm (3JHH ) 7.6 Hz), and an
apparent triplet at 7.08 ppm can be assigned to pyridine
coordinated to the titanium center, whereas the resonances at
8.65, 7.72, and 7.34 ppm correspond to free pyridine in solution.
A one-to-one integration ratio for the coordinated and free
pyridine signals suggests that the ground-state titanium species
in solution is the five-coordinate complex observed in the solid
state. Though the free and coordinated pyridine resonances
overlap with the many other aryl resonances for 6, crude
(85) Blake, A. J.; Collier, P. E.; Unn, S. C.; Li, W.; Mountford, P.;
Shishkin, O. V. J. Chem. Soc., Dalton Trans. 1997, 1549-1558.
(86) Kaltsoyannis, N.; Mountford, P. J. Chem. Soc., Dalton Trans. 1999,
781-789.
(87) Lewkebandara, T. S.; Sheridan, P. H.; Heeg, M. J.; Rheingold, A.
L.; Winter, C. H. Inorg. Chem. 1994, 33, 5879-5889.
(88) Parsons, T. B.; Hazari, N.; Cowley, A. R.; Green, J. C.; Mountford,
P. Inorg. Chem. 2005, 44, 8442-8458.
(89) Shi, Y.; Cao, C.; Odom, A. L. Inorg. Chem. 2004, 43, 275-281.
(90) Cundari, T. R. J. Am. Chem. Soc. 1992, 114, 7879-7888.

Imido and Organometallic-Amido Ti(IV) Complexes
Organometallics, Vol. 26, No. 22, 2007 5335
Scheme 4
titanium center. Addition of free pyridine confirms that fast,
dissociative pyridine exchange occurs on the NMR time scale.
The strong similarity between the 1H NMR features of 6 and 7
suggest an analogous coordination environment around the
titanium arylimido fragment.
The well-known metathesis reactivity of Group IV imido
complexes prompted an investigation of the reactivity of 6 with
aldehydes, ketones, and imines (Scheme 4). The imine metath-
esis reaction has been used to convert aldehydes and ketones
into aldimines and ketimines, respectively, via a [2+2] cycload-
dition.92 Benzaldehyde reacted rapidly with 6 at room temper-
ature in C6D6 to afford N-tert-butylphenylimine, as determined
by GC-MS (m/z 161.20), which also showed complete con-
sumption of the benzaldehyde substrate. When the reaction was
1
followed by H NMR spectroscopy, complete conversion was
achieved in 3 h and a single (pada)titanium complex was
observed. While this complex could not be isolated from the
organic product, based on NMR data and literature precedent,
it seems likely to be a bridging oxo dimer, [(pada)Ti(py)(µ-
O)]2, though we cannot rule out a monomeric form analogous
to 6.
estimates for the exchange rate constants could be obtained
between 219 and 308 K; the activation parameters from an
Eyring plot (see Supporting Information) are ∆Hq ) 18 (
2 kcal mol-1 and ∆Sq ) 19 ( 7 eu. The positive entropy value
is indicative of dissociative ligand exchange to give a four-
coordinate titanium imido intermediate, as shown in eq 2. This
mechanistic assignment is further supported by concentration-
dependence rate studies at 298 K, which gave an observed rate
law that was independent of pyridine concentration. Further-
more, the activation parameters measured for 6 correspond well
to those measured for dissociation of one pyridine from [PhC-
(NSiMe3)2]TiCl[dN(2,6-C6H3Me2)](py)2 to afford the five-
coordinate monopyridine complex [PhC(NSiMe3)2]TiCl[dN(2,6-
C6H3Me2)](py).91
Preliminary studies suggest that complex 6 is unreactive with
ketone and imine substrates but instead decomposes to form a
dimeric complex. For example, a mixture of 6 and benzophe-
none in benzene-d6 did not react at room temperature. Upon
heating the solution to 80 °C, new 1H NMR resonances appeared
at the expense of the resonances for 6; however, no change was
observed for the benzophenone substrate. The transformation
went to completion over 4 h. Similar behavior was observed
when benzene-d6 solutions of 6 were heated to 80 °C in the
presence of N-2,6-dimethylphenylimine or in the absence of
substrate. In these reactions, simple thermolysis of 6 leads to
formation of a new titanium complex assigned as [(pada)Ti-
(py)(µ-NtBu)]2 (8), shown in Scheme 4. The room-temperature
1H NMR spectrum of 8 showed a new tBu peak shifted upfield
to 0.57 ppm, consistent with formation of a bridging imido
ligand. Integration of the 1H NMR spectrum gave a 1:1:1 ratio
for the imido, pada, and pyridine ligands, suggesting that
pyridine loss from 6 leads to formation of 8. A molar mass
determination for 8 gave 1300 ( 180 g mol-1, which is in
reasonable agreement with the expected value of 1225.30 g
mol-1 for the formulation of 8.93 APCI mass spectrometry gave
a m/z ) 1067.5 for 8, consistent with the [(pada)Ti(µ-Nt-
Bu)]2core of 8 formed upon loss of the coordinated pyridine
molecules during vaporization in the spectrometer.
Reactivity of Titanium Imido Complex 6. Transimination
reactivity has been observed between imido complex 6 and
derivatives of aniline. As shown in Scheme 4, 6 reacts with
2,6-dimethylaniline in dichloromethane to afford the aryl imido
complex (pada)Ti[dN(2,6-C6H3Me2)](py)2 (7) in 82% yield.
This type of reaction, which is driven by the greater basicity of
the alkylamine compared to the aniline, is well precedented for
Group IV metals.39,54,59,85 Conversion to 7 can be monitored
by 1H NMR spectroscopy. While free 2,6-dimethylaniline
dissolved in benzene-d6 has a methyl signal at 1.88 ppm, the
titanium-imido multiple-bond linkage induces a downfield shift
of this methyl resonance to 2.40 ppm in 7. This shift can be
attributed to decreased shielding of the methyl protons brought
about by strong N(π) f Ti(d) lone pair donation, which is
indicative of formation of the new Ti-N multiple bond.91 Other
1H NMR features for 7 were strikingly similar to the parent
complex 6. Notably, the phenanthrene backbone resonances of
7 were observed at the same chemical shift values as for 6.
Three exchange-broadened pyridine peaks, observed at 6.24,
6.68, and 8.48 ppm, integrate to two pyridine ligands per
Conclusion
The N,N′-bis(3,5-dimethylphenyl)phenanthrene-9,10-diamide
ligand provided a framework for the synthesis of thermally stable
and isolable titanium complexes with Ti-C, Ti-N, and TidN
bonds. The relatively unhindered 3,5-dimethylphenyl substitu-
ents afforded four-, five-, and six-coordinate complexes. Prepa-
ration of titanium imido complex 6 via organometallic inter-
mediates 4, 5a, and 5b, respectively, is noteworthy because it
involves a C-H bond 1,2-elimination. This process is related
to the reversible C-H bond activation sequence reported for
coordinatively unsaturated titanium imido complexes.28,94-96 In
order to realize such C-H bond activation reactivity, the imido
(92) Lee, S. Y.; Bergman, R. G. J. Am. Chem. Soc. 1996, 118, 6396-
6406.
(93) Burger, B. J.; Bercaw, J. E. In Vacuum Line Techniques for Handling
Air-SensitiVe Organometallic Compounds; Wayda, A. L., Darensbourg, M.
Y., Eds.; Experimental Organometallic Chemistry; American Chemical
Society: Washington, DC, 1987; pp 79-98.
(91) Stewart, P. J.; Blake, A. J.; Mountford, P. Inorg. Chem. 1997, 36,
3616-3622.

5336 Organometallics, Vol. 26, No. 22, 2007
Ketterer et al.
CH3), 6.17 (s, 4H, o-CH), 6.65 (s, 2H, p-CH), 7.38-7.46 (m, 6H,
Ar-H), 7.88 (d, 4H, o-Ar-H, 3JHH ) 7). 13C NMR (CDCl3, 125.7
MHz) δ/ppm: 21.30 (CH3), 118.31 (aryl-C), 126.47 (aryl-C), 128.37
(aryl-C), 128.73 (aryl-C), 131.12 (aryl-C), 137.81 (aryl-C), 137.92
(aryl-C), 149.38 (aryl-C-N), 164.10 (CdN). GC-MS m/z (%
relative intensity, ion): 416 (99, M), 339 (10, M - C6H5), 207
(85, M - C6H5 - CNC8H9).
functionality must be generated on a low-coordinate metal
center. Pyridine dissociation from 5a and 5b generates a four-
coordinate species in benzene solution, and this species reacts
with benzaldehyde. Unsaturated substrates with sterically de-
manding substituents, however, do not react with the (pada)-
Ti(dNR)(py) fragment, and instead, dimerization appears to be
the favored reaction path. This dimerization path also circum-
vents C-H bond reactivity, so future work will focus on
phenanthrenediamide ligands with more sterically demanding
substituents to block dimerization of low-coordinate imido
species.
Preparation of padaH2. Freshly cut potassium metal (5.599 g,
143.2 mmol, 6 equiv) and graphite (13.93 g, 116.0 mmol, 48 equiv)
were combined in a 500 mL Schlenk flask. The flask was evacuated
and heated gently to form KC8 as a bronze solid. The flask was
filled with argon gas, and THF (200 mL) was added to the KC8 by
cannula transfer. The KC8 slurry was cooled in an ice-water bath,
and a solution of bis(arylimino)bibenzyl (10.12 g, 24.05 mmol, 1
equiv) in 100 mL of THF was added by cannula transfer, resulting
in an immediate color change to dark maroon. The reaction was
stirred under argon for 12 h, at which time it was cooled again in
an ice-water bath. The reaction was quenched by dropwise addition
of 35 mL of MeOH. Upon warming to room temperature, the solid
byproducts were removed by suction filtration and washed with
100 mL of diethyl ether. The golden-yellow organic phases were
combined and extracted with 150 mL of water containing 10 g of
NH4Cl and then dried over MgSO4. Solvent removal yielded an
off-white bubbly solid. This residue was stirred with 20 mL of
MeCN for 2 h at which time the product precipitated as a white
solid (7.8 g, 78% yield). 1H NMR (C6D6, 500 MHz) δ/ppm: 1.97
(s, 12H, CH3), 5.51 (s, 2H, NH), 6.23 (s, 4H, o-Ar-H), 6.39 (s,
2H, p-Ar-H), 7.31 (dd, 2H, Ar-H), 7.38 (dd, 2H, Ar-H), 8.20
(d, 2H, Ar-H, 3JHH ) 8), 8.52 (d, 2H, Ar-H, 3JHH ) 8). 13C NMR
(125.7 MHz) δ/ppm: 21.0 (C-CH3), 113.2 (aryl-C), 121.5 (aryl-
C), 123.0 (aryl-C), 125.4 (aryl-C), 126.2 (aryl-C), 126.8 (aryl-C),
130.1 (aryl-C), 130.5 (aryl-C), 131.4 (aryl-C), 138.7 (CN), 146.9
(CN).
Experimental Section
General Procedures. The complexes described below are air
and moisture sensitive, necessitating that manipulations be carried
out under an inert atmosphere of argon or nitrogen gas using
standard Schlenk, vacuum-line, and glovebox techniques. Hydro-
carbon solvents were sparged with nitrogen and then deoxygenated
and dried by passage through Q5 and activated alumina columns,
respectively. Ethereal and halogenated solvents were sparged with
nitrogen 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 THF. Benzil, 3,5-
dimethylaniline, potassium, and MeLi were purchased from Alfa
Aesar and used as received. TiCl4, LiN(SiMe3)2, and PhCH2MgCl
were purchased from Aldrich and used as received. Graphite was
heated under dynamic vacuum overnight, pyridine was dried over
sodium benzophenone and vacuum distilled, and tBuNH2 and 2.6-
dimethylaniline were dried over refluxing CaH2 and distilled under
argon. PhLi was prepared according to literature procedures97 and
used as a solid. Elemental analyses were performed by Desert
Analytics. In most cases, satisfactory analyses were obtained;
however, in the case of complexes 6 and 8, low values for C and
Preparation of (pada)TiCl2(py)2 (1). In a nitrogen-filled glove-
box, padaH2 (2.83 g, 6.81 mmol, 1 equiv) was dissolved in
dichloromethane (40 mL), and the solution was frozen in a liquid
nitrogen cold well. In a separate vial, TiCl4 (1.29 g, 6.81 mmol, 1
equiv) was dissolved in dichloromethane (15 mL), and the solution
was frozen in a liquid nitrogen cold well. Both solutions were
thawed, and the TiCl4 solution was added to the solution containing
padaH2, resulting in an immediate color change to dark brown.
tBuNH2 (1.24 g, 17.0 mmol, 2.5 equiv) was added, and the reaction
mixture was stirred while being warmed to box temperature
(25.5 °C) for 2 h. Pyridine (2.47 g, 312 mmol, 4.5 equiv) was then
added, and the reaction mixture was stirred for an additional 12 h.
1
N were repeatedly obtained despite clean H NMR spectra (see
Supporting Information).
Physical Measurements. NMR spectra were collected on Bruker
Avance 400 and 500 MHz spectrometers in dry, degassed benzene-
d6, chloroform-d1, or THF-d8.1H 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 chemical shifts
are to a higher frequency from the given reference. Infrared spectra
were recorded as KBr pellets with a Perkin-Elmer Spectrum One
FTIR spectrophotometer. Electronic absorption spectra were re-
corded with a Perkin-Elmer Lambda 800 UV/vis spectrophotometer
Preparation of Bis(arylimino)bibenzyl. In a 3-neck round-
bottom flask fitted with a reflux condenser, benzil (23.97 g, 114.0
mmol, 1 equiv) was dissolved in 300 mL of dry toluene under argon.
3,5-Dimethylaniline (48.36 g, 399.1 mmol, 3.5 equiv), 3 Å sieves,
and 15 drops of HCl were then added to the round-bottom flask,
and the mixture was heated to reflux for 48 h. After cooling to
room temperature the sieves were removed by filtration and the
toluene was removed under reduced pressure to yield a yellow,
oily solid, which was dissolved in 200 mL of MeOH and stirred
for 2 h. The product, bis(arylimino)bibenzyl, precipitated as a bright
yellow solid that was collected by filtration and dried in vacuo (37.1
g, 78% yield). 1H NMR (CDCl3, 500 MHz) δ/ppm: 2.10 (s, 12H,
t
The reaction mixture was filtered to remove BuNH3Cl, and the
dichloromethane was removed in vacuo to provide 1, which was
pure by 1H NMR spectroscopy (4.5 g, 96% yield). Dark brownish
black, X-ray quality crystals were grown by dissolving the product
in dichloromethane and layering with pentane. Anal. Calcd for
C40H36N4Cl2Ti‚0.75CH2Cl2: C, 64.81; H, 5.00; N, 7.42. Found:
C, 64.91; H, 5.42; N, 7.08. IR (KBr) ν/cm-1: 699, 765, 832, 1038,
1207, 1312, 1441, 1600, 2914. UV/vis (CH2Cl2) λmax/nm (ꢀ/M-1
cm-1): 320 (13 717). 1H NMR (CDCl3, 500 MHz, 275 K) δ/ppm:
2.03 (s, 12H, CH3), 6.43 (s, 2H, p-Ar-H), 6.57 (t, 4H, m-py-H),
7.05 (br, o-Ar-H), 7.21 (dd, 2H, Ar-H), 7.25 (t, 2H, p-py-H),
7.46 (dd, 2H, Ar-H), 7.73 (d, 2H, Ar-H, 3JHH ) 8), 8.29 (m, 6H,
Ar-H, o-py-H). 13C NMR (125.7 MHz) δ/ppm: 21.4 (C-CH3),
113.1 (NC-CH), 116.5 (CH3C-CH), 121.4 (aryl-C), 122.5 (m-py-
CH), 123.4 (aryl-C), 125.1 (aryl-C), 126.8 (aryl-C), 127.8 (aryl-
C), 128.4 (p-py-CH), 137.7 (CN), 138.1 (C-CH3), 149.9 (o-py-CH),
153.3 ((CH)2-C-N).
(94) Latesky, S. L.; McMullen, A. K.; Rothwell, I. P.; Huffman, J. C. J.
Am. Chem. Soc. 1985, 107, 5981-5987.
(95) Bennett, J. L.; Wolczanski, P. T. J. Am. Chem. Soc. 1997, 119,
10696-10719.
Preparation of (pada)TiCl[N(SiMe3)2] (2). In a nitrogen-filled
glovebox, 1 (0.24 g, 0.35 mmol, 1 equiv) was dissolved in diethyl
ether (18 mL), and solid (Me3Si)2NLi (0.06 g, 0.35 mmol, 1 equiv)
was added to the reaction mixture. After 4 h, the solution was
filtered and the solvent removed in vacuo to afford 2 as a dark red
(96) Cundari, T. R.; Klinckman, T. R.; Wolczanski, P. T. J. Am. Chem.
Soc. 2002, 124, 1481-1487.
(97) Wehman, E.; Jastrzebski, J. T. B. H.; Ernsting, J.; Grove, D. M.;
van Koten, G. J. Organomet. Chem. 1988, 353, 133-143.

Imido and Organometallic-Amido Ti(IV) Complexes
Organometallics, Vol. 26, No. 22, 2007 5337
solid (0.22 g, 96% yield). Anal. Calcd for C36H44N3ClSi2Ti: C,
65.69; H, 6.74; N, 6.38. Found: C, 65.97; H, 6.81; N, 6.21. IR
(KBr) ν/cm-1: 762, 843, 925, 1040, 1174, 1249, 1327, 1447, 1599,
2955, 3366. UV/vis (Et2O) λmax/nm (ꢀ/M-1 cm-1): 413 (3839). 1H
NMR (C6D6, 500 MHz, 338 K) δ/ppm: 0.30 (br s, 18H, Si(CH3)3),
2.10 (br s, 12H, CH3), 6.54 (s, 2H, p-Ar-H), 7.03 (dd, 2H, Ar-
H), 7.24 (dd, 2H, Ar-H), 8.0 (d, 2H, Ar-H, 3JHH ) 5.5), 8.34 (d,
nitrogen cold well. In a separate vial, a 1 M diethyl ether solution
of PhCH2MgCl (0.620 mL, 0.620 mmol, 2 equiv) was frozen in a
liquid nitrogen cold well. Both solutions were allowed to thaw,
and the PhCH2MgCl solution was added dropwise to the cold
solution of 1. The reaction was stirred for 2 h at -35 °C, at which
time the solution became medium red with an off-white precipitate.
The solid was removed by filtration, and the solvent was removed
in vacuo to afford 4 as a medium red solid (0.1773 g, 89% yield).
3
2H, Ar-H, JHH ) 8). 13C NMR (125.7 MHz) δ/ppm: 4.91 (Si-
1H NMR (C6D6, 500 MHz) δ/ppm: 1.93 (s, 4H, CH2), 1.96 (s,
(CH3)3), 21.02 (CH3), 117.43 (aryl-C), 123.15 (aryl-C), 123.70 (aryl-
C), 126.04 (aryl-C), 126.16 (aryl-C), 126.89 (aryl-C), 133.36 (aryl-
C-N), 138.80 (aryl-C), 151.56 (aryl-C).
3
12H, CH3), 6.42 (s, 2H, p-Ar-H), 6.61 (d, 4H, o-Ar-H, JHH
)
7.5), 6.70-6.89 (m, 13H, CH2Ph-H and py-H), 7.17 (dd, 2H,
Ar-H), 7.25 (dd, 2H, Ar-H), 8.24 (d, 2H, Ar-H, 3JHH ) 8), 8.43
Preparation of (pada)TiMe[N(SiMe3)2] (3a). In a nitrogen-filled
glovebox, 2 (0.14 g, 0.21 mmol, 1 equiv) was dissolved in diethyl
ether (10 mL), and the solution was frozen in a liquid nitrogen
cold well. The solution was thawed, and MeLi (1.4 M, 0.15 mL,
0.22 mmol, 1 equiv) was added dropwise. The solution was allowed
to warm to glovebox temperature with stirring for 3 h. The solution
was filtered, and the solvent was removed in vacuo to afford 3a as
a reddish orange solid (0.13 g, 94% yield). Anal. Calcd for
C37H47N3Si2Ti: C, 69.67; H, 7.43; N, 6.59. Found: C, 69.99; H,
6.69; N, 6.49. IR (KBr) ν/cm-1: 762, 843, 925, 1040, 1174, 1249,
1327, 1447, 1599, 2955, 3366. UV/vis (toluene) λmax/nm (ꢀ/M-1
cm-1): 322 (15 079). 1H NMR (C6D6, 500 MHz) δ/ppm: 0.25 (br
s, 18H, Si(CH3)3), 0.44 (s, 3H, Ti-CH3), 2.10 (br s, 12H, CH3),
6.53 (s, 2H, p-Ar-H), 7.10 (dd, 2H, Ar-H), 7.28 (dd, 2H, Ar-
3
(d, 2H, Ar-H, JHH ) 8.5), 8.67 (br, 2H, o-py-H).
Preparation of (pada)Ti(dNtBu)(py)2 (6). In a nitrogen-filled
glovebox, 1 (3.175 g, 4.59 mmol, 1 equiv) and solid PhLi (0.790
g, 9.40 mmol, 2 equiv) were loaded into a 500 mL Schlenk flask.
The flask was removed from the glovebox and attached to a vacuum
line. Under argon, diethyl ether (200 mL) was added by cannula
transfer to the Schlenk flask, which was cooled in a dry ice acetone
bath. The reaction mixture was stirred for 2 h at -40 °C, during
t
which time it became dark brownish red. Dry, degassed BuNH2
(0.49 mL, 4.62 mmol, 1 equiv) and pyridine (0.23 mL, 2.31 mmol,
0.5 equiv) were added with a syringe to the cold solution. Stirring
was maintained for an additional 2 h while the reaction mixture
warmed to room temperature. The resulting medium red solution
was transferred to an air-free filter frit by cannula. Filtration and
solvent removal afforded 6 as a medium reddish orange solid
(1.6832 g, 53% yield). Crystals suitable for X-ray diffraction were
grown from a diethyl ether solution chilled to -35 °C. IR (KBr)
3
3
H), 8.17 (d, 2H, Ar-H, JHH ) 8.5), 8.44 (d, 2H, Ar-H, JHH
)
8.5). 13C NMR (125.7 MHz) δ/ppm: 4.56 (Si-(CH3)3), 21.10 (C-
CH3), 23.53 (Ti-CH3), 120.78 (aryl-C), 123.22 (aryl-C), 123.65
(aryl-C), 125.14 (aryl-C), 126.08 (aryl-C), 126.43 (aryl-C), 127.04
(aryl-C), 129.20 (aryl-C), 133.36 (aryl-C), 138.71 (aryl-C), 151.35
(aryl-CN).
ν/cm-1: 765, 828, 1040, 1190, 1339, 1599, 2958. UV/vis (toluene)
1
λ
max/nm (ꢀ/M-1 cm-1): 337 (12 837). H NMR (C6D6, 500 MHz)
t
δ/ppm: 1.49 (s, 9H, Bu), 2.18 (br s, 12H, CH3), 6.30 (br, 4H,
m-py-H), 6.48 (s, 2H, p-Ar-H), 6.65 (br, 2H, m-py-H), 7.11 (dd,
2H, Ar-H), 7.28 (dd, 2H, Ar-H), 8.07 (d, 2H, Ar-H, 3JHH ) 8),
Preparation of (pada)Ti(CH2Ph)[N(SiMe3)2] (3b). Complex
3b was prepared similarly to 3a from PhCH2MgCl (1 M, 0.418
mL, 0.418 mmol, 1 equiv) and 2 (0.2746 g, 0.417 mmol, 1 equiv)
to give the product as a reddish orange solid (0.2173 g, 73%
yield). Anal. Calcd for C43H51N3Ti: C, 72.34; H, 7.20; N, 5.89.
Found: C, 72.24; H, 6.87; N, 5.97. IR (KBr) ν/cm-1: 688, 843,
1029, 1261, 1324, 1448, 1594, 2960. UV/vis (toluene) λmax/nm
8.55 (br, 4H, o-py-H), 8.56 (d, 2H, Ar-H, JHH ) 8). 13C NMR
3
(125.7 MHz) δ/ppm: 21.11 (C-(CH3)3), 21.51 (C-CH3), 33.07
(C-(CH3)3), 119.92 (aryl-C), 123.30 (aryl-C), 123.42 (aryl-C),
124.39 (aryl-C), 125.45 (aryl-C), 125.81 (aryl-C), 126.66 (aryl-C),
130.83 (aryl-C), 130.96 (aryl-C), 137.15 (aryl-C), 149.78 (aryl-C),
154.74 (aryl-C).
1
(ꢀ/M-1 cm-1): 329 (18 322). H NMR (C6D6, 500 MHz, 340K)
δ/ppm: 0.24 (br s, 18H, Si(CH3)3), 2.09 (s, 12H, CH3), 2.35 (s,
2H, CH2), 6.10 (t, 1H, p-CH), 6.21-6.23 (m, 4H, PhCH2), 6.55 (s,
2H, p-Ar-H), 6.85 (s, 4H, o-Ar-H), 7.05 (dd, 2H, Ar-H), 7.29
(dd, 2H, Ar-H), 7.77 (d, 2H, Ar-H), 8.40 (d, 2H, Ar-H). 13C
NMR (125.7 MHz) δ/ppm: 5.11 (Si-(CH3)3), 21.43 (CH3), 120.80
(aryl-C), 121.53 (aryl-C), 123.69 (aryl-C), 124.73 (aryl-C), 125.58
(aryl-C), 125.78 (aryl-C), 126.29 (aryl-C), 126.90 (aryl-C), 127.41
(aryl-C), 129.15 (aryl-C), 133.83 (aryl-C), 138.94 (aryl-C), 151.51
(aryl-C).
Preparation of (pada)Ti(dN-2,6-C6H3Me2)(py)2 (7). In a
nitrogen-filled glovebox, 6 (0.1523 g, 0.220 mmol, 1 equiv) was
dissolved in 16 mL of dichloromethane. 2,6-Dimethylaniline (0.030
mL, 0.242 mmol, 1 equiv) was added to the solution, and the
mixture was stirred for 12 h. The solvent was removed in vacuo,
and the resulting red solid was washed with cold heptane to produce
pure 7 (0.1360 g, 82% yield). Anal. Calcd for C48H45N5Ti: C, 77.93;
H, 6.13; N, 9.47. Found: C, 78.10; H, 6.30; N, 9.25. IR (KBr)
ν/cm-1: 696, 757, 848, 1067, 1219, 1296, 1443, 1485, 1604. UV/
vis (toluene) λmax/nm (ꢀ/M-1 cm-1): 335 (6438). 1H NMR (C6D6,
500 MHz) δ/ppm: 2.03 (br s, 12H, m-CH3), 2.45 (s, 6H, o-CH3),
6.29 (br, 4H, m-py-H), 6.43 (s, 2H, p-Ar-H), 6.67 (br, 2H, p-py-
H), 6.76 (t, 1H, p-Ar-H), 7.05 (d, 2H, m-Ar-H, 3JHH ) 7.5), 7.12
Preparation of (pada)TiPh[N(SiMe3)2] (3c). Complex 3c was
prepared similarly to 3a from PhLi (0.067 g, 0.797 mmol, 1 equiv)
and 2 (0.5025 g, 0.763 mmol, 1 equiv) to give the product as a
reddish orange solid (0.5088 g, 95% yield). Anal. Calcd for
C42H49N3Ti: C, 72.07; H, 7.06; N, 6.00. Found: C, 71.88; H, 7.17;
N, 5.70. IR (KBr) ν/cm-1: 763, 840, 1190, 1249, 1466, 1600, 2955,
3
(dd, 2H, Ar-H), 7.30 (dd, 2H, Ar-H), 8.01 (d, 2H, Ar-H, JHH
) 8.5), 8.53 (m, 6H, Ar-H, o-py-H). 13C NMR (125.7 MHz)
δ/ppm: 19.62 (o-CH3), 21.39 (m-CH3), 118.70 (aryl-C), 120.74
(aryl-C), 123.41 (aryl-C), 123.82 (aryl-C), 124.59 (aryl-C), 124.93
(aryl-C), 125.60 (aryl-C), 127.20 (aryl-C), 127 26 (aryl-C), 130.72
(aryl-C), 131.26 (aryl-C), 131.82 (aryl-C), 137.60 (aryl-C), 149.97
(aryl-C), 153.95 (aryl-C), 160.44 (aryl-C).
1
3372. UV/vis (toluene) λmax/nm (ꢀ/M-1 cm-1): 320 (15 866). H
NMR (THF-d8, 500 MHz) δ/ppm: 0.00 (s, 18H, Si(CH3)3), 2.18
(br s, 12H, Me), 6.49 (br m, 2H, o-Ph-CH), 6.62 (s, 2H, p-Ar-
CH), 7.15 (dd, 2H, Ar-H), 7.20 (br m, 3H, Ph-H), 7.38 (dd, 2H,
3
3
Ar-H), 7.63 (d, 2H, Ar-H, JHH ) 8), 8.52 (d, 2H, Ar-H, JHH
) 8). 13C NMR (C6D6, 125.7 MHz) δ/ppm: 4.60 (Si-(CH3)3),
21.17 (C-CH3), 120.37 (aryl-C), 123.59 (aryl-C), 125.85 (aryl-
C), 126.03 (aryl-C), 126.29 (aryl-C), 126.86 (aryl-C), 127.16 (aryl-
C), 129.19 (aryl-C), 130.24 (aryl-C), 133.15 (aryl-C), 138.87 (aryl-
C), 151.69 (aryl-C).
Preparation of [(pada)Ti(py)(µ-NtBu)]2 (8). In a Strauss tube,
100 mg of 6 (0.14 mmol, 1 equiv) was dissolved in benzene, and
the solution was heated to 60 °C for 4 h, at which time the solution
became dark red. The volatiles were removed in vacuo to afford 8
as a dark red solid (0.08 g, 82% yield). IR (KBr) ν/cm-1: 761,
Preparation of (pada)Ti(CH2Ph)2py (4). In a nitrogen-filled
glovebox, 1 (0.2133 g, 0.308 mmol, 1 equiv) was dissolved in
diethyl ether (15 mL), and the solution was frozen in a liquid
1
829, 1039, 1336, 1448, 1598. H NMR (C6D6, 500 MHz) δ/ppm:
t
0.56 (s, 9H, Bu), 1.81 (br s, 6H, Me), 2.45 (br s, 6H, Me), 6.41

5338 Organometallics, Vol. 26, No. 22, 2007
Table 3. Crystal Data Collection and Refinement Parameters
Ketterer et al.
(pada)TiCl2(py)2 (1)
(pada)TiCl[N(SiMe3)2]‚C6H6 (2‚C6H6)
(pada)Ti(dNtBu)(py)2‚OEt2 (6‚OEt2)
empirical formula
fw
cryst syst
space group
a/Å
b/Å
c/Å
C41H38Cl4N4Ti
691.53
monoclinic
C2/c
34.856(7)
13.879(3)
15.984(3)
90
107.438(3)
90
7377(3)
8
C42H50ClN3Si2Ti
736.38
triclinic
P1h
11.3545(16)
12.0530(18)
16.572(2)
84.444(3)
72.678(3)
69.857(2)
2032.7(5)
2
C48H55N5OTi
765.87
monoclinic
P21/n
13.634(5)
20.831(7)
16.889(6)
90
110.676(5)
90
4488(3)
4
R/deg
â/deg
γ/deg
V/Å3
Z
reflns collected
independent reflns
28 914
5750
21 173
8926
23 466
7053
R1
wR2
0.1202
0.2976
0.0367
0.0887
0.0667
0.1510
(br m, 2H, m-py-H), 6.53 (s, 2H, p-Ar-H), 7.22 (dd, 2H, Ar-H),
7.29 (dd, 2H, Ar-H), 8.42 (br m, 2H, o-py-H), 8.46 (m, 4H, Ar-
H). 13C NMR (125.7 MHz) δ/ppm: 21.30 (C-(CH3)3), 31.84 (C-
CH3), 71.23 (C-(CH3)3), 114.61 (aryl-C), 120.44 (aryl-C), 121.68
(aryl-C), 123.59 (aryl-C), 124.43 (aryl-C), 126.16 (aryl-C), 126.29
(aryl-C), 130.04 (aryl-C), 132.44 (aryl-C), 138.87 (aryl-C), 151.33
(aryl-C).
General Details of X-ray Data Collection and Reduction.
X-ray diffraction data for 2‚C6H6 were collected on a Bruker CCD
platform diffractometer equipped with a CCD detector. Measure-
ments were carried out at 163 K using Mo KR (λ ) 0.71073 Å)
radiation, which was wavelength selected with a single-crystal
graphite monochromator. The SMART98 program package was used
to determine unit-cell parameters and for data collection. The raw
frame data were processed using SAINT99 and SADABS100 to yield
the reflection data files. Subsequent calculations were carried out
using the SHELXTL101 program suite. Analytical scattering factors
for neutral atoms were used throughout the analyses.102 Thermal
ellipsoid plots were generated using the XP program within the
SHELXTL suite. Diffraction data for 2‚C6H6 are shown in
Table 3.
X-ray diffraction data for 1and 6‚OEt2 were collected on a Bruker
D8 platform diffractometer equipped with an APEX CCD detector
at UC San Diego. Measurements were carried out at 100 K using
Mo KR (λ ) 0.71073 Å) radiation, which was wavelength selected
with a single-crystal graphite monochromator. The SMART98
program package was used to determine unit-cell parameters and
for data collection. The raw frame data were processed using
SAINT99 and SADABS100 to yield the reflection data files.
Subsequent calculations were carried out using the SHELXTL101
program suite. Analytical scattering factors for neutral atoms were
used throughout the analyses.102 Thermal ellipsoid plots were
generated using the XP program within the SHELXTL suite. In
the case of 1, poorly resolved solvent disorder was rendered using
SQUEEZE;103 all intensive properties contain the solvent contribu-
tions. Diffraction data for 1 and 6‚OEt2 are shown in Table 3.
Acknowledgment. The authors thank Antonio G. DiPasquale
(UCSD) for assisting in X-ray data collection of complexes 1
and 6, Jim Boncella for helpful suggestions, and the University
of California, Irvine, for financial support.
(98) SMART, Version 5.1; Bruker Analytical X-Ray Systems, Inc.:
Madison, WI, 1999.
(99) SAINT, Version 5.1; Bruker Analytical X-Ray Systems, Inc.:
Madison, WI, 1999.
(100) Sheldrick, G. M. SADABS, Version 2.05; Bruker Analytical X-Ray
Systems, Inc.: Madison, WI, 2001.
Supporting Information Available: Eyring analyses for 2 and
6, packing diagram for 2, and X-ray diffraction data for 1, 2, and
6 (as CIFs). This material is available free of charge via the Internet
at http://pubs.acs.org.
(101) Sheldrick, G. M. SHELXTL, Version 6.12; Bruker Analytical X-Ray
Systems, Inc.: Madison, WI, 2001.
OM0701219
(102) International Tables for X-Ray Crystallography; Kluwer Academic
Publishers: Dordrecht, 1992; Vol. C.
(103) Sluis, P. V. D.; Spek, A. L. Acta Crystallogr. 1990, A46, 194.