Early transition metal complexes bearing a C-capped tris(phenolate) ligand incorporating a pendant imine arm: Synthesis, structure, and ethylene polymerization behavior

Article abstract of DOI:10.1021/ic702506w

The ligand 3-[2,2′-methylenebis(4,6-di-tert-butylphenol)-5-tert- butylsalicylidene-(2,6-diisopropyl)phenylimine] (L¹H₃) was reacted with MCl₄ (M = Ti, Zr) or MCl₅ (M = Nb, Ta) to give complexes of the type [MCl₂(L¹H₂) ₂] (M = Ti (1); Zr (2)), [NbCl₃(L¹H)] (3), or [TaCl₄(L¹H₂)] (4), respectively. Single crystal X-ray diffraction of 1-4 revealed common iminium species resulting in zwitterionic complexes. Reaction of [V(Np-tol)(On-Pr)₃] with L¹H₃ afforded [{(VNp-tol)(L¹H)} ₂(μ-On-Pr)₂] (5), and a second complex [(VO) ₂(μ-O)(L³H)₂] (6) (L³H being derived from 3-[2,2′-methylenebis(4,6-di-tert-butylphenol)-5-tert- butylsalicylidene-p-tolylimine]). The condensation reaction between 3-[2,2′-methylenebis(4,6-di-tert-butylphenol)-5-tert-butyl-2- hydroxybenzaldehyde] (L⁰H₃) and o-phenylenediamine (1, 2-diaminobenzene) afforded two products: a pseudo-16-membered hydrogen bonded macrocyclic structure {1,2-bis-3-[2,2′-methylenebis(4,6-di-tert- butylphenol)-5-tert-butylsalicylidene-benzyldiimine]} (L⁵H ₆), or the benzimidazolyl bearing ligand (L⁶H ₃). The reaction of L⁵H₆ or L⁶H ₃ with [VO(On-Pr)₃] under varying conditions produced the complexes [(VO)(L⁵H₄)] (7), [(VO)₂(L ⁵H)] (8), or [VO(L⁶H₂)₂] (9). L ⁰H₃ was reacted with a number of anilines to give the proligands {3-[2,2′-methylenebis(4,6-di-tert-butylphenol)-5-tert- butylsalicylidene-R-imine]}, where R = NC₆H₅ (L ²H₃), NC₆H₄-Me (L³H ₃), and NC₆H₂-Me₃ (L ⁴H₃). Reactions of these ligands with [VO(On-Pr) ₃] formed bischelating complexes of the form [(VO)(L ^2-4H₂)₂] (10, 11, and 12, respectively). The reaction of L¹H₃ with trimethylaluminum led to a bis-aluminum complex {(AlMe₂)[AlMe(NCMe)]L¹} (13). The ability of complexes 1-12 to polymerize ethylene in the presence of an organoaluminum cocatalyst was investigated. Procatalysts 1 and 2 were found to produce negligible activities in the presence of dimethylaluminum chloride (DMAC) and the reactivator ethyltrichloroacetate (ETA), whereas 3 and 4 were found to be completely inactive for polymerization using a variety of different organoaluminum cocatalysts. Using the combination of DMAC and ETA, complexes 5-12 were found to be highly active catalysts; in all cases, the polymer formed was of high molecular weight linear polyethylene.

Full text of DOI:10.1021/ic702506w

Inorg. Chem. 2008, 47, 5799-5814
Early Transition Metal Complexes Bearing a C-Capped Tris(phenolate)
Ligand Incorporating a Pendant Imine Arm: Synthesis, Structure, and
Ethylene Polymerization Behavior
Damien Homden,† Carl Redshaw,*,† Joseph A. Wright,† David L. Hughes,† and Mark R. J. Elsegood‡
School of Chemical Sciences and Pharmacy, UniVersity of East Anglia, Norwich, NR4 7TJ, U.K.,
and Chemistry Department, Loughborough UniVersity, Loughborough,
Leicestershire, LE11 3TU, U.K.
Received December 28, 2007
The ligand 3-[2,2′-methylenebis(4,6-di-tert-butylphenol)-5-tert-butylsalicylidene-(2,6-diisopropyl)phenylimine] (L1H3)
was reacted with MCl4 (M ) Ti, Zr) or MCl5 (M ) Nb, Ta) to give complexes of the type [MCl2(L1H2)2] (M ) Ti
(1); Zr (2)), [NbCl3(L1H)] (3), or [TaCl4(L1H2)] (4), respectively. Single crystal X-ray diffraction of 1-4 revealed
common “iminium” species resulting in zwitterionic complexes. Reaction of [V(Np-tol)(On-Pr)3] with L1H3 afforded
[{(VNp-tol)(L1H)}2(µ-On-Pr)2] (5), and a second complex [(VO)2(µ-O)(L3H)2] (6) (L3H being derived from 3-[2,2′-
methylenebis(4,6-di-tert-butylphenol)-5-tert-butylsalicylidene-p-tolylimine]). The condensation reaction between 3-[2,2′-
methylenebis(4,6-di-tert-butylphenol)-5-tert-butyl-2-hydroxybenzaldehyde] (L0H3) and o-phenylenediamine (1,
2-diaminobenzene) afforded two products: a pseudo-16-membered hydrogen bonded macrocyclic structure {1,2-
bis-3-[2,2′-methylenebis(4,6-di-tert-butylphenol)-5-tert-butylsalicylidene-benzyldiimine]} (L5H6), or the benzimidazolyl
bearing ligand (L6H3). The reaction of L5H6 or L6H3 with [VO(On-Pr)3] under varying conditions produced the complexes
[(VO)(L5H4)] (7), [(VO)2(L5H)] (8), or [VO(L6H2)2] (9). L0H3 was reacted with a number of anilines to give the proligands
{3-[2,2′-methylenebis(4,6-di-tert-butylphenol)-5-tert-butylsalicylidene-R-imine]}, where R ) NC6H5 (L2H3), NC6H4-
Me (L3H3), and NC6H2-Me3 (L4H3). Reactions of these ligands with [VO(On-Pr)3] formed bischelating complexes of
the form [(VO)(L2-4H2)2] (10, 11, and 12, respectively). The reaction of L1H3 with trimethylaluminum led to a bis-
aluminum complex {(AlMe2)[AlMe(NCMe)]L1} (13). The ability of complexes 1-12 to polymerize ethylene in the
presence of an organoaluminum cocatalyst was investigated. Procatalysts 1 and 2 were found to produce negligible
activities in the presence of dimethylaluminum chloride (DMAC) and the reactivator ethyltrichloroacetate (ETA),
whereas 3 and 4 were found to be completely inactive for polymerization using a variety of different organoaluminum
cocatalysts. Using the combination of DMAC and ETA, complexes 5-12 were found to be highly active catalysts;
in all cases, the polymer formed was of high molecular weight linear polyethylene.
Introduction
Kakugo,2 who reported good activities for ethylene polym-
erization when using X2Tidiphenolate/MAO (X ) Cl, i-Pr)
systems. Extensive alkylation studies followed by Schaverien
et al.,3 using Cl2Mdiphenolate (or binaptholate) type com-
plexes (M ) Ti, Zr) with lithium alkyls or via reaction of
the tetrabenzyls M(CH2Ph)4 with the appropriate biphenol
or binapthol. Cationic complexes were available on treatment
of the dialkyls with the likes of B(C6F5)3. Such species
proved useful procatalysts for the cyclotrimerization of
Chelating aryloxides represent a useful class of ancillary
ligand in postmetallocene R-olefin polymerization catalysis.1
Early breakthroughs included work by Miyatake and
* To whom correspondence should be addressed. E-mail: carl.redshaw@
uea.ac.uk.
†
University of East Anglia.
Loughborough University.
‡
(1) (a) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew Chem. 1999,
111, 448; Angew Chem. Int. Ed. Engl. 1999, 38, 428. (b) Gibson, V. C.;
Spitzmesser, S. K. Chem. ReV. 2003, 103, 283. (c) Gibson, V. C.;
Marshall, E.L. ComprehensiVe Coordination Chemistry II; McCleverty,
J. A., Meyer, T. J., Ward, M. D., Eds; Elsevier: Amsterdam, 2004; p
9.
(2) Miyatake, T.; Mizunuma, K.; Seki, Y.; Kakugo, M. Makromol. Chem.
Rapid Commun. 1989, 10, 349.
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Orpen, A. G. J. Am. Chem. Soc. 1995, 117, 3008.
10.1021/ic702506w CCC: $40.75  2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 13, 2008 5799
Published on Web 06/05/2008

Homden et al.
Figure 1. Examples of previously reported capped-metal catalysts.
terminal alkynes, as well as in ethylene and butadiene
polymerization. Subsequent work by Okuda et al.,4 revealed
how the nature of the bridging group (-CH2-, -CH2CH2-,
-S-, -SO-) in diphenolate ancillary ligands could impact
upon the resulting catalytic activity in the copolymerization
of styrene with ethylene. Other bridging groups, including
-Te- and -SO2-, have also been successfully used in
ethylene polymerization.5,6 Such studies no doubt led to the
development and use of more functionalized bridges in
bis(phenolate)-type ligands, typified by amine bis(phenolate)
ligands with a -CH2N(R)CH2- bridge (R ) CH2CH2CH3,
CH2CH2NMe2) developed by Kol et al. primarily for 1-hex-
ene polymerization.7 Similar ligands were used more recently
by Lorber et al. in ethylene polymerization,8 as were the
phosphorus-bridged ligands -P(R)- (R ) Ph, t-Bu, C6H4-
2-CH2NMe2, C6F5, C6H4-2-OMe) developed in the labora-
tories of the Sumitomo Chemical Co.9 The coordination
chemistry associated with linear triphenols is an emerging
area,10 but their use in catalysis is somewhat limited.11
Macrocyclic aryloxides, namely, calixarenes, have shown
catalytic potential in this area, particularly when they possess
dimethylene oxa bridges (-CH2-O-CH2-).12 Tripodal
ligands, such as tris(3,5-di-tert-butyl-2-hydroxyphenyl/ben-
zyl)methane, tris(2-hydroxyphenyl)amine, and 2,2′,2′′-ni-
trilotris(methylene)tris(4,6-dialkylphenol), are useful as tri-
anionic supports for transition metals13,14 (Figure 1), and
work by Nomura et al. (triaryloxoamine), Sundararajan et
al. (trialkoxyamine) and by Subhakar (trialkoxyamine) using
group IV metals (Ti, Zr) has shown such systems to be useful
for the polymerization of 1-alkenes.15 Bruno, Verkade,
Davidson, and Scott have employed such complexes for a
variety of other polymerization processes,16–20 including
styrene polymerization, lactide polymerization and the co-
polymerization of carbon dioxide with epoxides. Half-
sandwich titanium complexes incorporating ligands derived
from trialkanolamine have been used in the syndiospecific
polymerization of styrene.21
(4) Sernetz, F. G.; Mülhaupt, R.; Fokken, S.; Okuda, J. Macromolecules
1997, 30, 1562.
(11) Redshaw, C.; Homden, D. M.; Rowan, M. A.; Elsegood, M. R. J.
Inorg. Chim. Acta 2005, 358, 4067.
(5) Nakayama, Y.; Watanabe, K.; Ueyama, N.; Nakamura, A.; Harada,
A.; Okuda, J. Organometallics 2000, 19, 2498.
(12) Redshaw, C.; Rowan, M. A.; Warford, L.; Homden, D. M.; Arbaoui,
A.; Elsegood, M. R. J.; Dale, S. H.; Yamato, T.; Casas, C. P.; Matsui,
S.; Matsuura, S. Chem. Eur. J. 2007, 13, 1090.
(6) Takaoki, K.; Miyatake, T. Macromol. Symp. 2000, 157, 251.
(7) (a) Tshuva, E. Y.; Versano, M.; Goldberg, I.; Kol, M.; Weitman, H.;
Goldschmidt, Z. Inorg. Chem. Commun. 1999, 2, 371. (b) Tshuva,
E. Y.; Goldberg, I.; Kol, M. J. Am. Chem. Soc. 2000, 122, 10706. (c)
Tshuva, E. Y.; Goldberg, I.; Kol, M.; Weitman, H.; Goldschmidt, Z.
Chem. Commun. 2000, 379. (d) Tshuva, E. Y.; Goldberg, I.; Kol, M.;
Goldschmidt, Z. Inorg. Chem. Commun. 2000, 3, 611. (e) Tshuva,
E. Y.; Goldberg, I.; Kol, M.; Weitman, H.; Goldschmidt, Z. Orga-
nometallics 2001, 20, 3017. (f) Tshuva, E. Y.; Goldberg, I.; Kol, M.;
Weitman, H.; Goldschmidt, Inorg. Chem. 2001, 40, 4263. (g) Tshuva,
E. Y.; Goldberg, I.; Kol, M.; Weitman, H.; Goldschmidt, Z. Chem.
Commun. 2001, 2120. (h) Tshuva, E. Y.; Groysman, S.; Goldberg, I.;
Kol, M.; Goldschmidt, Z. Organometallics 2002, 21, 662. (i) Segal,
S.; Goldberg, I.; Kol, M. Organometallics 2005, 24, 200. (j) Gendler,
S.; Segal, S.; Goldberg, I.; Goldschmidt, Z.; Kol, M. Inorg. Chem.
2006, 45, 4783.
(13) Kol, M.; Shamis, M.; Goldberg, I.; Goldschmidt, Z.; Alfi, S.; Hayut-
Salant, E. Inorg. Chem. Commun. 2001, 4, 177.
(14) Akagi, F.; Matsuo, T.; Kawaguchi, H. J. Am. Chem. Soc. 2005, 127,
11936.
(15) (a) Wang, W.; Fujiki, M.; Nomura, K. Macromol. Rapid Commun.
2004, 25, 504. (b) Sudhakar, P.; Amburose, C. V.; Sundararajan, G.;
Nethaji, M. Organometallics 2004, 23, 4462. (c) Sudhakar, P.;
Sundararajan, G. Macromol. Rapid Commun. 2005, 26, 1854. (d)
Sudhakar, P. J. Polym. Sci. A., Polym. Chem. 2007, 45, 5470.
(16) Bruno, J. W.; Michalczyk, L.; de Gala, S. Organometallics 2001, 20,
5547.
(17) Kim, Y.; Jnaneshwara, G. K.; Verkade, J. G. Inorg. Chem. 2003, 42,
1437.
(18) Dinger, M. B.; Scott, M. J. Inorg. Chem. 2001, 40, 1029.
(19) Chmura, A. J.; Chuck, C. J.; Davidson, M. G.; Jones, M. D.; Lunn,
M. D.; Bull, S. D.; Mahon, M. F. Angew. Chem. Int. Ed. 2007, 46,
2280.
(8) Lorber, C.; Wolff, F.; Choukroun, R.; Vendier, L. Eur. J. Inorg. Chem.
2005, 2850.
(9) Hanaoka, H.; Imamoto, Y.; Hino, T.; Kohno, T.; Yanagi, K.; Oda, Y.
J. Polym. Sci., A, Polym. Chem. 2007, 45, 3668.
(20) Kim, Y. J.; Kapoor, P. N.; Verkade, J. G. Inorg. Chem. 2002, 41,
4834.
(10) Kawaguchi, H.; Matsuo, T. J. Organomet. Chem. 2004, 689, 4228.
(21) Kim, Y.; Do, Y. J. Organomet. Chem. 2002, 655, 186.
5800 Inorganic Chemistry, Vol. 47, No. 13, 2008

Early Transition Metal Complexes
Scheme 1. Representation of Zwitterionic Complexes 1-4
As an extension to the “tripod” family, Scott et al. reported
a method whereby an aldehyde group was readily appended
ortho to one of the phenolic groups. Subsequent condensation
chemistry proved facile, and new NO3-type “imine-tripod”
ligands bearing an imine arm were readily available; the
ligand 3-[2,2′-methylenebis(4,6-di-tert-butylphenol)-5-tert-
butylsalicylidene-benzylimine] (see Scheme 3 in ref 22) has
been reported and structurally characterized by Scott et al.22
Such imine-tripods can be viewed and, indeed, act as a
new class of phenoxyimine ligand. Phenoxyimine ligands
have been extensively studied, primarily by Fujita et al. at
Mitsui Chemicals,23,24 and found to be versatile ligands for
the production of highly active R-olefin polymerization
catalysts based on group IV and V metals. Titanium-based
systems, so-called Ti-FI catalysts, bearing two fluorinated
phenoxy rings have proved particularly successful in the
development of thermally robust, living ethylene and pro-
pylene (syndiotactic) polymerization systems. The activity
of such species can be controlled by varying the nature of
the substituents on the imine nitrogen or indeed on the
phenoxy ring. For example, the steric bulk associated with
the substituent ortho to the phenoxy-oxygen plays a pivotal
role in dictating catalytic activity and polymer molecular
weight. Activation of bis[N-(3-tert-butylsalicylidene)-anili-
nato]zirconium dichloride using i-Bu3Al (30 equiv), followed
by subsequent hydrolysis, led to the isolation of phenoxy-
amine ligands, leading Fujita et al. to suggest that the active
species formed when using i-Bu3Al /[CPh3][B(C6F5)4] may
well contain the reduced form of the ligand, that is, a
phenoxy-amine. Interestingly however, NMR/EPR spectros-
copy for the pentafluoroaniline/3-tert-butylsalicylaldehyde
derived Cl2TiFI system indicated that, in the absence of
monomer, reaction with either MAO or Me3Al/[CPh3]-
[B(C6F5)4], deactivation occurred via transfer of the phenoxy-
imine ligand to aluminum.25
To date, much of the coordination chemistry of this imine
tripod ligand family is restricted to complexes of aluminum
and of nickel,22,26 while in a preliminary communication,
we have reported the complex [VO(L1H2)2] (L1H2 is the
monodeprotonated form of 3-[2,2′-methylenebis(4,6-di-tert-
butylphenol)-5-tert-butylsalicylidene-(2,6-diisopropyl)phe-
nylimine]), (Scheme 1) which upon activation with dime-
thylaluminum chloride (DMAC) was found to be active for
ethylene homopolymerization.27 We have now embarked
upon a synthetic program to study the coordinating charac-
teristics of this relatively new class of phenoxyimine ligand
family. Here, we present our results using the early transition
metals, specifically of groups IV and V, and report results
of their polymerization behavior toward ethylene in the
presence of a variety of organoaluminum cocatalysts.
(22) Scott, M. J.; Cottone, A.; Morales, D.; Lecuivre, J. L. Organometallics
2002, 21, 418.
(23) (a) Matsui, S.; Tohi, Y.; Mitani, M.; Saito, J.; Makio, H.; Tanaka, H.;
Matsukawa, N.; Nitabaru, M.; Nakano, T.; Kashiwa, N.; Fujita, T.
Chem. Lett. 1999, 1065. (b) Fujita, T.; Saito, J.; Mitani, M.; Mohri,
J.; Yoshida, Y.; Matsui, S.; Ishii, S.; Kojoh, S.; Kashiwa, N. Angew.
Chem. Int. Ed. 2001, 40, 2918. (c) Matsui, S.; Mitani, M.; Saito, J.;
Tohi, Y.; Makio, H.; Matsukawa, N.; Takagi, Y.; Tsuru, K.; Nitabaru,
M.; Nakano, T.; Tanaka, H.; Kashiwa, N.; Fujita, T. J. Am. Chem.
Soc. 2001, 123, 6847. (d) Matsui, S.; Fujita, T. Catal. Today 2001,
66, 63. (e) Mitani, M.; Mohri, J.; Yoshida, Y.; Saito, J.; Ishii, S.; Tsuru,
K.; Matsui, S.; Furuyama, R.; Nakano, T.; Tanaka, H.; Kojoh, S.;
Matsugi, T.; Kashiwa, N.; Fujita, T. J. Am. Chem. Soc. 2002, 124,
3327. (f) Mitani, M.; Furuyama, R.; Mohri, J.; Saito, J.; Ishii, S.; Terao,
H.; Kashiwa, N.; Fujita, T. J. Am. Chem. Soc. 2002, 124, 7888. (g)
Makio, H.; Kashiwa, N.; Fujita, T. AdV. Synth. Catal. 2002, 344, 477.
(h) Furuyama, R.; Saito, J.; Ishii, S.; Mitani, M.; Matsui, S.; Tohi, Y.;
Makio, H.; Matsukawa, N.; Tanaka, H.; Fujita, T. J. Mol. Catal. 2003,
200, 31. (i) Nakayama, Y.; Bando, H.; Sonobe, Y.; Suzuki, Y.; Fujita,
T. Chem. Lett. 2003, 32, 766. (j) Nakayama, Y.; Bando, H.; Sonobe,
Y.; Fujita, T. Bull. Chem. Soc. Jpn. 2004, 77, 617. (k) Nakayama, Y.;
Bando, H.; Sonobe, Y.; Fujita, T. J. Mol. Catal. 2004, 213, 141. (l)
Makio, H.; Fujita, T. Bull. Chem. Soc. Jpn. 2005, 78, 52. (m) Fujita,
T.; Furuyama, R.; Saito, J.; Ishii, S.; Makio, H.; Mitani, M.; Tanaka,
H. J. Organomet. Chem. 2005, 690, 4398.
Results and Discussion
The condensation reaction to form the pendant imine arm
28
of L1H3 was carried out in refluxing ethanol for 1 h with
a catalytic amount of formic acid. Upon cooling of the
reaction mixture, removal of solvent in vacuo yielded L1H3
as a crude yellow solid. Extraction into hot acetonitrile,
followed by slow evaporation, produced yellow/green prisms
suitable for single crystal X-ray analysis (Figure 2).
(26) Libra, E. R.; Scott, M. J. Chem. Commun. 2006, 1485.
(24) Fujita, T.; Tohi, Y. (Mitsui. Chemicals. Inc.) Eur. Patent 874,005,A1,
1998.
(27) Redshaw, C.; Rowan, M. A.; Homden, D. M.; Dale, S. H.; Elsegood,
M. R. J.; Matsui, S.; Matsuura, S. Chem. Commun. 2006, 3329.
(28) Synthesis of the previously reported proligand L1H3 (see Figure 2 and
Scheme 1) was carried out following the method of Scott et al. with
benzylamine replaced by 2,6-diisopropylaniline (see ref 22).
(25) Bryliakov, K. P.; Kravtsov, E. A.; Pennington, D. A.; Lancaster, S. J.;
Bochmann, M.; Brintzinger, H. H.; Talsi, E. P. Organometallics 2005,
24, 5660.
Inorganic Chemistry, Vol. 47, No. 13, 2008 5801

Homden et al.
Figure 2. ORTEP representation of the structure of L1H3. Hydrogen atoms
(except H1 and H3a) have been omitted for clarity; thermal ellipsoids are
drawn at the 50% probability level.
Both intramolecular and intermolecular hydrogen bonding
is observed in L1H3. The intramolecular interaction involves
the nitrogen atom of the imine arm and the closest phenolic
group: O(1)-H(1) · · · N(1) [O · · · N ) 2.604(4) Å]. The
intermolecular hydrogen bonds O(3)–H(3A) · · ·O(1′) [O· · ·O
) 2.971(6) Å] are formed by the same oxygen atom, acting
as an acceptor, and a free phenolic unit from a second ligand
molecule. The two molecules form a pseudo-16-membered
ring system about a center of inversion.
Figure 3. ORTEP representation of the structure of 1. Alkyl groups, solvent
molecules of acetonitrile, and hydrogen atoms (except H5 and H5′) have
been omitted for clarity; thermal ellipsoids are drawn at the 50% probability
level.
Table 1. Selected Bond Lengths (Å) and Angles (deg) with Estimated
Standard Deviations of 1 and 2
(a)
(b)
Titanium and Zirconium. The reaction between
[TiCl4(THF)2] or [ZrCl4] and L1H3 at a 1:1 ratio in refluxing
toluene, followed by removal of solvents in vacuo and
extraction into warm acetonitrile, afforded the complexes 1
and 2 as deep red diamonds and yellow blocks (yields of
83% and 81%), respectively.
Single crystal X-ray analysis of both species show similar
complexes of the form [MCl2(L1H2)2] (M ) Ti (1); Zr (2)),
both exhibiting a metal oxidation state of +4. In 1, there is
a crystallographic 2-fold symmetry axis through the titanium
atom; in 2 the two metal-bound ligands are only pseudo-
symmetrical (there are also two independent molecules in
the asymmetric unit). Both 1 and 2 show iminium species
by X-ray analysis (three crystals of each were selected at
random), with CdN bond lengths of 1.290(3) Å for 1 and
in the range of 1.286(4)-1.299(3) Å for 2. In each instance,
the hydrogen atom attached to the nitrogen was located in
the Fourier difference map.
Complexes 1 and 2 are both bis-chelating, with each metal
center displaying a pseudo-octahedral environment with four
oxygens (from two ligands) and two cis-chlorine atoms
bound to the metal center completing the coordination sphere;
angles around the metal centers range from 82° to 100°.
With titanium (Figure 3, Table 1a), the Ti-O bond lengths
are within the normal range for these types of bonds.23c,29,30
As expected, Ti-O(1) is elongated [1.9744(14) Å compared
to Ti-O(2), 1.8509(13) Å] because of a reduction in
π-donation ability caused by additional hydrogen bonding
to the iminium hydrogen: N(5)-H(5) · · · O(1) [N · · · O )
2.714(2) Å]. There is also additional hydrogen bonding
between an unbound phenolic unit of one chelating ligand
and its symmetry related equivalent in the second chelated
Ti-O(1)
Ti-O(2)
Ti-Cl(1)
1.9744(14) Zr(1)-O(11)
1.8509(13) Zr(1)-O(71)
2.1078(18)
1.9804(18)
2.5529(7)
2.4789(6)
Zr(1)-Cl(11)
O(1)-Ti-O(1′) 164.17(8)
O(11)-Zr(1)-O(61) 167.57(7)
O(1)-Ti-O(2)
O(1)-Ti-O(2′)
O(1)-Ti-Cl(1)
O(1)-Ti-Cl(1′)
95.33(6)
94.92(6)
85.39(4)
82.79(4)
O(11)-Zr(1)-O(21)
O(11)-Zr(1)-O(71)
O(11)-Zr(1)-Cl(11)
O(11)-Zr(1)-Cl(12)
93.70(7)
94.35(7)
85.94(5)
84.25(5)
O(2)-Ti-Cl(1′) 171.98(5)
O(21)-Zr(1)-Cl(12) 172.11(6)
ligand: O(36)-H(36) · · · O(36′) [O· · · O ) 2.876(2) Å]. The
Ti-Cl bond length [2.4789(6) Å] is longer than that observed
in similar phenoxyimine systems [2.261(2)-2.305(2) Å],23b,m
again the likely cause being the additional hydrogen bonds
to the iminium proton: N(5)-H(5) · · · Cl(1′) [N· · ·Cl )
3.301(3) Å].
In the case of the zirconium compound 2 (Table 1b), a
similar pattern is observed. The Zr-Ophenolate bond lengths
[av 1.977 Å] are within previously reported ranges,23c,29,30
with longer Zr-Oimine bonds [2.0886(19)-2.1078(18) Å]
because of hydrogen bonding: N-H · · · O [N · · ·O(av) )
2.709 Å]. The Zr-Cl bonds [2.5351(8)-2.5529(7) Å] are
also longer than previously reported values for N-H · · ·Cl
hydrogen bonding29,30 [N · · · Cl(av) ) 3.3505 Å].
Niobium. The reaction between L1H3 and [NbCl5] at a
1:1 ratio in refluxing toluene produced, after extraction into
acetonitrile and prolonged standing at -25 °C, X-ray quality
orange/red crystals of [NbCl3(L1H)] (3) (Scheme 1) in good
yield (51%). The solid state structure of 3 (Figure 4) revealed
a mononuclear zwitterionic structure, with two independent
molecules, whose bond lengths and angles are essentially
identical, in the asymmetric unit. The environment around
the niobium(V) center is pseudo-octahedral formed by the
three oxygens of the ligand molecule and three chlorine
atoms arranged in a fac-manner. The presence of an iminium
species was confirmed by the C-N bond lengths of 1.279(7)
and 1.295(7) Å in the two molecules, with the hydrogen
(29) Bott, R. K. J.; Hughes, D. L.; Schormann, M.; Bochmann, M.;
Lancaster, S. J. J. Organomet. Chem. 2003, 665, 135.
(30) Zhang, D.; Jin, G. X. Appl. Catal. A 2004, 262, 85.
5802 Inorganic Chemistry, Vol. 47, No. 13, 2008

Early Transition Metal Complexes
Figure 4. ORTEP representation of the structure of one of the independent
molecules of 3. Alkyl groups, three molecules of acetonitrile and hydrogen
atoms (except H4) have been omitted for clarity; thermal ellipsoids are drawn
at the 50% probability level.
Figure 5. ORTEP representation of the structure of 4. Alkyl groups and
hydrogen atoms (except H5) have been omitted for clarity; thermal ellipsoids
are drawn at the 50% probability level.
atoms attached to the nitrogen atoms being located in a
Fourier difference map. Once again hydrogen bonding to the
protonated phenol is observed, with an N · · · O average
distance of 2.671 Å. 1H NMR spectroscopy indicates
retention of the solid state structure in solution, displaying a
doublet for the NdCH proton at 7.92 ppm because of
coupling to the iminium hydrogen. The coupling constant
(3J ) 15.9 Hz) is close to that reported by Scott et al. (3J )
14.4 Hz), for the related complex [(L2)+AlMe-].22
The Nb · · · Ophenolate distances [av 1.872 Å] lie within the
range previously observed for niobium aryloxide bonds
[1.730(5)-1.985(4) Å].11 The niobium-oxygen bond formed
by the phenolate group located next to the iminium species
(Nb-Oimine), displays a significantly longer bond length [av
2.003 Å], a possible explanation being the reduction in
π-donation from the oxygen atom because of its involvement
in hydrogen bonding (vide supra). Two Nb-Cl bonds [av
2.387 Å] lie within previously reported Nb-Cl values
[2.250(6)-2.4339(10) Å];11 the third Nb-Climine bond is
longer [av 2.456 Å], possibly because of the additional
hydrogen bond to the iminium species: N · · · Cl(av) )
3.43 Å.
Tantalum. Analogous reaction conditions using a 1:1 ratio
of [TaCl5] and L1H3 led to the isolation of bright yellow
crystals in high yield (62%) (Scheme 1). An X-ray diffraction
study revealed a monomeric complex of the form
[TaCl4(L1H2)] (4), whose structure is shown in Figure 5 with
bond lengths and angles given in Table 2.
The structure of 4 is similar to that of the niobium
analogue; here, however, four chlorines are bound to the
metal center, the extra chlorine taking preference over the
binding of a second phenolate group. The geometry around
the metal center is again octahedral, with two cis-oxygen
atoms and four chlorine atoms completing the coordination
sphere.
Table 2. Selected Bond Lengths (Å) and Angles (deg) with Estimated
Standard Deviations of 4
Ta-O(1)
1.965(4)
1.845(4)
Ta-O(2)
Ta-Cl(3)
2.3771(18)
2.3329(18)
2.4078(15)
2.3639(16)
93.85(15)
92.93(11)
169.09(12)
81.38(11)
86.79(11)
177.38(6)
173.99(13)
Ta-Cl(4)
Ta-Cl(5)
Ta-Cl(6)
O(1)-Ta-O(2)
O(1)-Ta-Cl(3)
O(1)-Ta-Cl(4)
O(1)-Ta-Cl(5)
O(1)-Ta-Cl(6)
Cl(3)-Ta-Cl(6)
O(2)-Ta-Cl(5)
reported bond lengths [1.8375(18)-2.025(7) Å]31 but differ
considerably in length from one another. Similar reasoning
to that of the niobium analogue can be applied here: the
oxygen atom of the longer Ta-O(1) bond is also involved
in hydrogen bonding to the iminium group, N(5) · · ·O(1) )
2.791 Å, leading to a reduction in π-donation to the metal
center, evident also by the reduction in carbon-oxygen-metal
bond angle [C(11)-O(1)-Ta ) 134.9(3)° compared with
C(21)-O(2)-Ta ) 163.7(4)°]. The Ta-Cl bonds are all very
similar and lie within previously reported values [1.913(2)-
2.500(1) Å];31 the longest bond length is Ta-Cl(5), in which
the chlorine atom is also involved in hydrogen bonding:
N(5)-H(5) · · · Cl(5) [N· · · Cl ) 3.334 Å].
Vanadium-imido Chemistry. In the following section,
we have chosen to use alkoxide starting materials rather than
vanadium oxytrichloride for two reasons: namely, we have
found that liberated HCl can be problematic, particularly
when using imido compounds, and second, our previous
experience using the oxytrisalkoxides, [VO(OR)3], has
revealed a pronounced tendency for forming highly crystal-
line materials. The reaction between L1H3 (3-[2,2′-methyl-
enebis(4,6-di-tert-butylphenol)-5-tert-butylsalicylidene-(2,6-
diisopropyl)phenylimine]) and [V(Np-tol)(On-Pr)3] produced
the acetonitrile-insoluble complex [{V(N-p-tol)(L1H1)}2(µ-
The presence of an iminium species was confirmed by a
C(121)-N(5) bond length of 1.280(6) Å with the hydrogen
atom attached to N(5) located in a Fourier difference map.
The two Ta-O bonds lie within the range for previously
(31) (a) Mulford, D. R.; Clark, J. R.; Schweiger, S. W.; Fanwick, P. E.;
Rothwell, I. P. Organometallics 1999, 18, 4448. (b) Thorn, M. G.;
Parker, J. R.; Fanwick, P. E.; Rothwell, I. P. Organometallics 2003,
22, 4658.
Inorganic Chemistry, Vol. 47, No. 13, 2008 5803

Homden et al.
Figure 7. ORTEP representation of one of the two independent molecules
of 6. Alkyl groups (except C7 and C54), solvent molecules of acetonitrile,
and hydrogen atoms have been omitted for clarity; thermal ellipsoids are
drawn at the 30% probability level.
[C(51)-N(5)-V ) 174.4(2)°] and a datively bound alkoxide
occupy the axial positions. Unlike that previously found in
the vanadyl case,27 here the phenoxy-imine group does not
interact with the metal center, rather it is involved in
Figure 6. ORTEP representation of the structure of 5. Alkyl groups (except
C541 and C541′) and hydrogen atoms (except H3 and H3′) have been
omitted for clarity; thermal ellipsoids are drawn at the 50% probability level.
intramolecular
hydrogen
bonding:
O(3)-
Table 3. Selected Bond Lengths (Å) and Angles (deg) with Estimated
Standard Deviations of 5
H(3) · · · N(4) [O · · · N ) 2.633(4) Å]. The V-O phenoxide
bonds [1.826(2) and 1.824(2) Å] and VdN imido bond
[1.664(3) Å] are normal with respect to previously reported
structures of V(V) aryloxide complexes [V-O in the range
of 1.754(5)-1.8632(13) Å; VdN in the range of 1.652(2)–
1.669(3) Å].12,32
V-O(1)
1.826(2)
1.824(2)
1.664(3)
1.866(2)
2.178(2)
V-O(2)
V-N(5)
V-O(6)
V-O(6′)
O(2)-V-O(1)
N(5)-V-O(1)
O(1)-V-O(6)
O(1)-V-O(6′)
N(5)-V-O(2)
O(2)-V-O(6)
O(2)-V-O(6′)
N(5)-V-O(6)
N(5)-V-O(6′)
O(6)-V-O(6′)
109.47(10)
98.90(12)
118.07(10)
86.31(9)
97.88(12)
124.55(10)
84.78(9)
101.19(12)
172.91(12)
72.01(10)
A second complex, [(VO)2(µ-O)(L3H)2] (6) (L3H ) doubly
deprotonated (3-[2,2′-methylenebis(4,6-di-tert-butylphenol)-
5-tert-butylsalicylidene-p-tolylimine]) was isolated from the
acetonitrile fraction of the filtration as brown needles in low
yield (25%). Structural analysis using synchrotron radiation,33
revealed a bimetallic system (Figure 7) with a bridging oxo
group and the chelation of two ligand molecules also bridging
the metal centers each through two of the three phenolic
oxygens. Two independent molecules are found in the
asymmetric unit and possess similar geometrical parameters.
There is no retention of the imido group from the metal
precursor, the loss presumably caused by hydrolysis ac-
counting for the two vanadyl functionalities observed.
Surprisingly, an imido exchange has occurred between the
initial vanadium-bound imido group and the pendant imine
arm such that the 2,6-diisopropylphenyl groups have been
replaced by the p-tolyl groups. In the solid-state structure,
V(2) is found to be tetrahedral in geometry, the other V(1)
On-Pr)2] (5) (L1H1 ) doubly deprotonated L1H3) in good
yield (70%). Crystals suitable for X-ray diffraction were
grown from a saturated solution of dichloromethane on
prolonged standing (2-3 days) at ambient temperature.
Structural analysis revealed a dimeric arrangement, formed
though two asymmetrically bridged n-propoxide groups
(Figure 6, Table 3); the asymmetric nature is apparent in
the differing bond lengths, V-O(6) 1.866(2) Å, being within
the range for a formal bonding interaction, compared to the
longer V-O(6′) 2.178(2) Å, which is indicative of a dative
interaction. A center of symmetry is located between the
bridging alkoxide groups.
The environment around the vanadium center is best
described as pseudo trigonal bipyramidal with one metal
center bonding to two phenolate oxygens and an alkoxide
oxygen in the equatorial sites; an almost linear imido group
(32) Redshaw, C.; Gibson, V. C.; Elsegood, M. R. J. J. Chem. Soc., Dalton
Trans. 2001, 767.
(33) (a) Clegg, W.; Elsegood, M. R. J.; Teat, S. J.; Redshaw, C.; Gibson,
V. C. J. Chem. Soc., Dalton Trans. 1998, 767. (b) Clegg, W. J. Chem.
Soc., Dalton Trans. 2000, 3223.
5804 Inorganic Chemistry, Vol. 47, No. 13, 2008

Early Transition Metal Complexes
approximately square pyramidal with the vanadyl group in
the apical position and the vanadium atom positioned 0.52
Å out of the square-based plane; the increased coordination
of V(2) is caused by the binding of one of the pendant imine
arms. Both vanadyl bond lengths are typical; however the
V-Ophenoxide bond lengths about Vsp in comparison to Vtet
vary dramatically. In the case of Vtet, the increase in Lewis
acidity of the metal center (caused by the lower coordination
number) shortens the V-O bond lengths [1.696(7)-1.808(6)
Å].Ontheotherhand,Vsp displayslongerbonds[1.880(8)-1.972(8)
Å] more akin to those seen in I and 7, where the additional
donation by the imine nitrogen leads to a decrease in the
Lewis acidity of the metal center. Because of this difference
in the Lewis acidity of the two vanadium centers, the bridging
oxygen is asymmetric [av Vsp-O 1.9675 ) Å; Vtet-O )
1.709 Å] and acts as O2- giving each metal center a +5
oxidation state.
In solution, complex 6 adopts a different geometry. The
1H NMR spectrum shows only one set of sharp peaks for
the hydrogen atoms, implying that in solution the complex
1
Figure 8. ORTEP representation of the structure of L5H6. Alkyl groups,
solvent molecules of acetonitrile, and hydrogen atoms (except H21, H31,
H51, and H71) have been omitted for clarity; thermal ellipsoids are drawn
at the 50% probability level.
is C2-symmetric. The H NMR spectrum also displays a
single sharp resonance at ∼4.20 ppm that integrates to 2
hydrogens; although the phenolic hydrogens could not be
located in the difference map, the NMR data implies that
these hydrogens, with such a downfield shift, are involved
in a dramatic level of hydrogen bonding within the complex.
Both metal centers are V(V) and give two distinct peaks in
the 51V NMR at δ ) -510.4 and -567.2 ppm. The mass
spectrum shows a single peak at 1525.9, showing clearly
the molecular ion peak and also the relative stability of the
complex.
Bis-Capped System. Given the bidentate chelating nature
of the ligands observed in complexes 1-5, we targeted a
ligand system with sufficient binding sites to satisfy the
coordination needs of a vanadium center. To this end, the
precursor 3-[2,2′-methylenebis(4,6-di-tert-butylphenol)-5-
tert-butyl-2-hydroxybenzaldehyde (L0H3) was reacted with
o-phenylenediamine (1,2-diaminobenzene) in a 2:1 molar
ratio. Reaction in refluxing ethanol with a catalytic amount
of formic acid for 1 h, removal of solvent, and recrystalli-
zation from hot acetonitrile gave L5H6 in moderate yield
(50%). Structural analysis (Figure 8) shows a pseudo 16-
membered macrocyclic structure because of a series of
intramolecular hydrogen bonds (Table 4) involving both
phenolic and imine groups (cf., L1H3).
Table 4. Hydrogen Bond Parameters for L5H6
D-H
(Å)
D-H· · ·A
(deg)
D· · ·A
(Å)
H· · ·A
(Å)
O(21)-H(21)· · ·O(31)
N(38)-H(31)· · ·O(31)
O(51)-H(51)· · ·O(21)
O(71)-H(71)· · ·N(47)
0.98(4)
1.26(5)
1.06(5)
0.91(3)
167(3)
143(3)
164(4)
151(3)
2.713(3)
2.560(3)
2.708(3)
2.604(3)
1.75(4)
1.44(5)
1.68(5)
1.77(3)
produced a bright orange compound L6H3 in low yield
(18%). Crystals of L6H3 were grown from a saturated ethanol
solution, and X-ray diffraction revealed the formation of a
benzimidazolyl moiety rather than the phenoxy-imine moi-
eties previously seen (Figure 9).
Proligand L6H3 exhibits two intramolecular hydrogen
bonds in the solid state: O(1)-H(1)· · ·N(1) [donor-acceptor
) 2.563(3) Å] and O(3)-H(3) · · · O(1) [donor-acceptor )
2.832(3) Å] (Figure 9). As a result, the mean planes of the
imidazole ring [N(1)-C(9)] and the benzene ring bearing
O(1) [C(2)-C(7)] have almost parallel normal vectors: the
angle between these is 6.75°. The benzimidazole groups in
Both H(31) and H(71) were located on the Fourier
difference map, indicating the presence of both an imine and
iminium species within the ligand backbone. As in 1, 2, and
4, the 1H NMR spectrum of L5H6 shows that in solution the
imine species predominates, exhibiting singlets at δ 8.65 and
8.19 ppm (each 1H) for each of the imine groups; the
presence of two peaks resulting from the differing nature of
hydrogen bonding related with each imine moiety. A single
peak in the mass spectrum at m/z 1273 represents the
moleular ion, while bands in the IR spectrum at 1622 and
1576 cm-1 are assignable to the two CdN stretches.
A change in the molar ratio of L0H3 to o-phenylenediamine
from 2:1 to 1:1 and an extended reaction time of 12 h
Figure 9. ORTEP representation of the structure of L6H3. Alkyl groups,
one molecule of ethanol, and hydrogen atoms (except H1, H2a, and H3)
have been omitted for clarity; thermal ellipsoids are drawn at the 50%
probability level.
Inorganic Chemistry, Vol. 47, No. 13, 2008 5805

Homden et al.
Figure 10. View of L6H3 illustrating intramolecular hydrogen bonding and π-stacking of benzimidazoze group.
for minor component, 0.103(3) site occupancy]; however,
only the principal component is shown. Occupying the
cavities opposite the vanadyl centers are disordered molecules
of acetonitrile. In each case, the vanadium center is five
coordinate and can be best described as having a square
pyramidal geometry. The binding of the metal center is
through both phenoxy-imine groups of the ligand in an
analogous manner to the previously reported nickel and
palladium structures by Scott et al.,26 such that the remaining
four phenols remain unaffected.
The result of using o-phenylenediamine to form a bridged
bis-imine ligand is that binding of the metal center to the
phenoxy-imine moieties can only proceed in a cis manner
compared to that of I, wherein the two free phenoxy-imine
arms bind trans with respect to each other. Although the
difference between the cis and trans binding motifs does not
appear to affect bond lengths dramatically, the rigidity of
the central phenyl ring in the o-phenylenediimine group
produces a more symmetrical binding of the metal center
with trans angles in the N2O2 plane in 7 deviating by less
than 1°. In the case of I, the lack of conformational rigidity
is evident by trans angles in the N2O2 plane deviating by
over 23°. Of the remaining unbound phenolic groups in 7,
twoformhydrogenbondswithintheligand:O(3)-H(3) · · ·O(1)
[donor-acceptor ) 2.784(5) Å] and O(6)-H(6) · · ·O(3)
[donor-acceptor ) 2.852(6) Å]; the latter bonds intramo-
lecularly to an opposite arm of the ligand forming a pseudo-
macrocycle similar to that seen with the parent pro-ligand
(Figure 8). The remaining two phenolic hydrogens have no
close neighbors.
The use of L5H6 in a 2:1 molar ratio with [VO(On-Pr)3],
under analogous conditions to those used for 7, produced
small dark brown needles of [(VO)2(L5H)] (8) in moderate
yield (33%). Structural characterization by single-crystal
X-ray crystallography (Figure 12, Table 6) revealed the
binding of two vanadium centers; the binding of the vanadyl
groups proceeds in an identical manner to that of 7 with the
V(IV) center, V(1), adopting a square-based pyramidal
geometry, with the vanadium located 0.628 Å out of the
mean plane of the basal atoms [O(1), O(4), N(18), and
N(48)]. A second vanadyl group, V(2)-O(8), is bound
through three of the remaining phenolic units in a tetrahedral
arrangement.
Figure 11. ORTEP representation of the structure of 7. Minor component
V2-O(7A), alkyl groups, solvent molecules of acetonitrile and hydrogen
atoms (except H3 and H6) have been omitted for clarity; thermal ellipsoids
are drawn at the 50% probability level.
Table 5. Selected Bond Lengths (Å) and Angles (deg) with Estimated
Standard Deviations of 7
V-O(7)
1.599(4)
1.950(3)
2.055(4)
2.043(4)
1.937(3)
V2-O(7A)
V2-O(1)
V2-N(18)
V2-N(48)
V2-O(4)
1.604(17)
1.956(10)
2.117(10)
2.155(10)
2.014(10)
V-O(1)
V-N(18)
V-N(48)
V-O(4)
V· · ·V(2)
1.374(9)
O(7)-V-O(1)
O(7)-V-O(4)
O(7)-V-N(18)
O(7)-V-N(48)
N(18)-V-O(4)
N(48)-V-O(1)
110.62(17)
110.58(16)
103.47(16)
104.11(18)
145.28(15)
144.71(16)
O(7A)-V2-O(1)
O(7A)-V2-O(4)
O(7A)-V2-N(18)
O(7A)-V2-N(48)
N(18)-V2-O(4)
N(48)-V2-O(1)
110.0(7)
115.4(6)
109.6(7)
114.0(7)
134.5(5)
135.6(5)
L6H3 are arranged in antiparallel π-stacks (Figure 10). The
planes defined by the 5-membered imidazole rings are 3.422
Å apart, with a centroid-centroid distance of 3.485 Å.
The reaction of L5H6 with [VO(O-n-Pr)3] in refluxing
toluene afforded, after workup into acetonitrile, black prisms
of the complex [(VO)(L5H4)] (7) in moderate yield (33%).
During the reaction the metal center is reduced from V(V)
to V(IV).
Structural analysis (Figure 11, Table 5) indicates the
presence of two forms of the complex with the vanadyl group
pointing above or below the N2O2 plane [deviation of 0.594
Å for major component, 0.897(3) site occupancy; 0.778 Å
The bond lengths about V(1) are similar to those found in
7; however the binding of a second vanadium atom drasti-
5806 Inorganic Chemistry, Vol. 47, No. 13, 2008

Early Transition Metal Complexes
croanalysis; Evans’ method NMR experiment, together with
EPR measurements, verified the presence of a V(IV) species.
Changing Aniline. Proligands 3-[2,2′-methylenebis(4,6-
di-tert-butylphenol)-5-tert-butylsalicylidene-R-imine, where
R ) NC6H5 (L2H3), NC6H4Me (L3H3) and NC6H2Me3 (L4H3)
were synthesized using a 1:1 ratio of the appropriate aniline
to L0H3 in refluxing ethanol with a catalytic amount of formic
1
acid. Upon removal of solvents in vacuo, H NMR spec-
troscopy indicated that the crude products were pure and
needed no further recrystallization. Following the method
previously published by our group,27 the vanadyl bearing
complexes [VO(L2-4H2)2] (10-12) were synthesized in low
yields (20-26%) of high purity as indicated by elemental
analysis. In all cases, a reduction occurred at the metal center
from V(V) to V(IV), as confirmed by magnetic moment
measurements by Evans’ method34 and EPR.
Oxidation States of Vanadium Complexes. During the
extensive reactions involving different vanadium alkoxide
starting materials both V(V) and V(IV) species have been
isolated and characterized in the final complexes. The V(V)
Figure 12. ORTEP representation of the structure of 8. Alkyl groups,
hydrogen atoms (except H2), and solvent molecules of acetonitrile have
been omitted for clarity; thermal ellipsoids are drawn at the 50% probability
level.
1
species were characterized by H and 51V NMR, shifts for
which are given in Table 7.12 For V(IV) systems, the
magnetic moment and EPR isotropic and anisotropic values
are given in Table 8.
Table 6. Selected Bond Lengths (Å) and Angles (deg) with Estimated
Standard Deviations of 8
V(1)-N(18)
2.056(6)
2.059(6)
1.914(5)
1.926(5)
1.594(5)
1.784(5)
1.764(5)
1.777(5)
1.589(6)
86.39(19)
86.4(2)
137.3(2)
113.0(2)
148.1(2)
113.1(2)
110.1(2)
112.6(3)
105.3(3)
109.3(2)
106.2(3)
The 51V NMR shifts for 5 and 6 follow trends that have
previously been noted. The shift for 5 is typical of the range
previously observed for the O4N donor set, while for 6 the
peaks at δ -510.43 and -567.23 are consistent with VO3N
and VO4 environments, respectively.35 In particular it has
been found that imido-bearing vanadium centers display
peaks shifted to more positive values compared to those
arising from vanadyl groups. The corresponding line widths
for imido groups are also broader than those of oxo groups.
A plot of the inverse line-width against chemical shift for 5
and 6 revealed two distinct environments for the vanadium
atoms.36 Results suggest that in solution complex 5 exhibits
a 4-coordinate vanadium center arising, most probably, from
cleavage of both dative alkoxide bonds leading to a mono-
meric complex. In solution, complex 6 displays two 5-co-
ordinate vanadium centers, which can be achieved by
interactions of the two metal centers with the two imine
nitrogen atoms.
V(1)-N(48)
V(1)-O(1)
V(1)-O(4)
V(1)-O(7)
V(2)-O(3)
V(2)-O(5)
V(2)-O(6)
V(2)-O(8)
O(1)-V(1)-O(4)
O(1)-V(1)-N(18)
O(1)-V(1)-N(48)
O(1)-V(1)-O(7)
O(4)-V(1)-N(18)
O(3)-V(2)-O(5)
O(3)-V(2)-O(6)
O(3)-V(2)-O(8)
O(5)-V(2)-O(8)
O(5)-V(2)-O(6)
O(6)-V(2)-O(8)
cally alters the angles around V(1). Comparisons show that
for 8 the angles around V(1) are closer to those of the trans-
bound complex I with trans angles varying by 11°. Because
of the flexibility and rotational freedom of the phenolic
groups, the angles around V(2) are close to ideal for
tetrahedral geometry, deviating by a maximum of 4°. The
V-O and VdO bond lengths around V(2) are all within
previously stated ranges (vide supra). The one remaining free
hydroxyl group hydrogen bonds intramolecularly to O(1):
O(2)-H(2) · · ·O(1) [donor-acceptor ) 2.780(6) Å]. The 1H
NMR spectrum of 8 shows broad, featureless lines because
of the paramagnetic V(IV) center within the complex, while
a peak at m/z 1402 in the mass spectrum shows the [M -
O]+ peak; the composition has also been confirmed by CHN
analysis.
All V(IV) species were characterized by room-temperature
and low-temperature (40 K) X-band EPR measurements. As
expected, a characteristic 8-line spectrum (d1) was obtained
in all cases at room temperature (I ) 7/2). Anisotropic
parameters were collected from frozen toluene solutions,
analysis of which (as well as room temperature results) were
carried out by simulation using SIMFONIA.37 Values for
g⊥ and g| (Table 8) compare well with those reported
previously for oxovanadium(IV) systems,38a,b and in-
(34) Evans, D. F. J. Chem. Soc. 1959, 2003.
(35) (a) Santoni, G.; Licini, G.; Rehder, D. Chem. Eur. J. 2003, 9, 4700.
(b) Rehder, D.; Weidemann, C.; Duch, A.; Priebsch, W. Inorg. Chem.
1988, 27, 584. (c) Priebsch, W.; Rehder, D. Inorg. Chem. 1985, 24,
3058.
Ligand L6H3 (Figures 9 and 10) was reacted with [V(O)(On-
Pr)3] at a 2:1 ratio affording, following workup, the analogous
(to that of I) bis-chelating structure [VO(L6H2)2] 9 in 61%
yield. The purity of the complex was confirmed by mi-
(36) Crans, D. C.; Shin, P. K. J. Am. Chem. Soc. 1994, 116, 1305.
(37) Simfonia, Bruker Analytische Messentechnik, GmbH, version 1.25,
Shareware version, 1996.
Inorganic Chemistry, Vol. 47, No. 13, 2008 5807

Homden et al.
Table 7. 51V NMR Data for V(V) Complexes
complex
∆ (ppm)
ω1/2 (Hz)
ref
5
6
-480.84
-510.43
-567.23
-321.3
-216.2
-586.6
-545.6
-592.9
-352.8
-354.6
-332.6
-371.5
320
60
80
this work
this work
this work
6
[V(O)-tert-butylhexahomooxacalix[3]arene]
[V(N-p-tol)-tert-butylhexahomooxacalix[3]arene]
[{VO(O-t-Bu)}2(µ-O)Cax(OMe)2(O)2]·2MeCN
[{VO(O-n-Pr)}2(µ-O)Cax(OMe)2(O)2]·2MeCN
[VO(O-t-Bu)]2(µ-O)Li4O2Cax(OMe)2(O)2]·8MeCN
[V(N-p-tolyl)(O-t-Bu)2Cax(OMe)2(O)(OH)]·5MeCN
[VOCax(O)3(OMe)(NCMe)]
143
1998
134
144
865
353
907
925
2170
12
12
12
12
12
12
12
12
12
[V(N-p-tolyl)Cax(O)3(OMe)(NCMe)]
[{VOCax(O)4}2(µ-2,6-(CH2)2C5H5N)]
Table 8. Magnetic Moments, Isotropic, and Anisotropic Values for V(IV) Complexes
complex
µeff
giso
Aiso
g⊥
A⊥
g|
A|
[VO(L1H2)2] (I)26
[VO(L2H2)2] (10)
[VO(L3H2)2] (11)
[VO(L4H2)2] (12)
[VO(L5H4)] (7)
1.76
1.33
1.33
1.39
1.15
1.83
1.86
1.99
2.01
1.98
2.01
1.99
1.99
2.00
94
96
96
95.5
95
1.98
1.99
1.99
1.99
1.99
1.99
1.99
67
64
65
64.5
65
1.95
1.95
1.95
1.96
1.96
1.96
1.96
185
185
185
180
183
181
186
[(VO)2(L5H)] (8)
[VO(L6H2)2] (9)
100
95
64
63
particular with those reported for the VO[N2O2] coordination
set, though the A| values are a little on the high side (usual
range 160-170 × 10-4 cm-1).38c Both isotropic and aniso-
tropic parameters were found to be comparable in all cases
implying similar metal environments for all complexes.
Magnetic moments expected for oxovanadium(IV) com-
plexes, when the orbital contribution is quenched, are 1.73
µB; experimentally observed values for complexes 7 and
10-12 were notably lower.
Insight into the Imine Functionality. The imine group
in these complexes appears to be relatively inert. Attempts
to reduce the CdN linkage using standard reducing agents
such as LiAlH4 and NaBH4 were unsuccessful. Even 10-
fold loadings of reducing agent led to the recovery of
unreacted imine ligand. Furthermore, imines are known to
react with trialkylaluminum reagents, with transfer of an alkyl
group to the imine backbone often observed.39 Here,
however, treatment of L1H3 with trimethylaluminum (3.3
equivalents) afforded the complex {(AlMe2)[AlMe-
(NCMe)]L1} (13) in moderate yield (38%). Single crystal
X-ray analysis (Figure 13) shows 13 to be comparable to
that previously reported by Scott et al.,22 whose structure
included a molecule of DMSO in place of the molecule of
MeCN found in 13. The complex displays two different
Al(III) centers, one bound through the phenoxy-imine moiety
with two methyl groups still intact, the second being bound
to two phenolate oxygens with one methyl group on the
aluminum center; the coordination sphere is completed by a
molecule of solvent. Bond lengths and angles are given in
Table 9 and compared to those of the structure previously
reported by Scott.
All bond lengths and angles for 13 are comparable to those
of the DMSO analogue (see Table 9) with both aluminum
centers adopting pseudo tetrahedral geometry. It was found
that upon increasing the molar ratio of proligand to aluminum
to as high as 1:6, there was no evidence of methyl transfer
to the imine backbone.
Ethylene Polymerization. Initial screening of complexes
1-4 (Scheme 1), employing a variety of organoaluminum
cocatalysts [dimethylaluminum chloride (DMAC), methy-
laluminoxane (MAO), and trimethylaluminum (TMA)] at
ambient temperature over prolonged time periods yielded
negligible or no polymeric material, and further screening
involving these complexes was not carried out.
Vanadium-based systems are emerging as a promising
class of R-olefin polymerization catalyst.12,23i,27,40 It was
therefore not unexpected that procatalysts 5-12 and the
previously reported procatalyst I, when screened in the
presence of DMAC and the reactivating substance ethyl-
(38) (a) Selbin, J. Chem. ReV. 1965, 65, 153. (b) Costa Pessoa, J.; Calhorda,
M. J.; Cavaco, I.; Correia, I.; Duarte, M. T.; Felix, V. J. Chem. Soc.,
Dalton Trans. 2002, 4407. (c) Yue, H.; Zhang, D.; Shi, Z.; Feng, S.
Solid State Sci. 2006, 8, 1368.
(39) (a) Gibson, V. C.; Redshaw, C.; White, A. J. P.; Williams, D. J. J.
Organomet. Chem. 1998, 550, 453. (b) Bruce, M.; Gibson, V. C.;
Redshaw, C.; Solan, G. A.; White, A. J. P.; Williams, D. J. Chem.
Commun. 1998, 2523. (c) Milione, S.; Cavallo, C.; Tedesco, C.; Grassi,
A. J. Chem. Soc., Dalton Trans. 2002, 8, 1839. (d) Knijnenburg, Q.;
Smits, J. M. M.; Budzelaar, P. H. M. Organometallics 2006, 25, 1036.
Figure 13. ORTEP representation of the structure of 13. Alkyl groups,
hydrogen atoms, and solvent molecules of acetonitrile have been omitted
for clarity; thermal ellipsoids are drawn at the 50% probability level.
5808 Inorganic Chemistry, Vol. 47, No. 13, 2008

Early Transition Metal Complexes
Table 9. Selected Bond Lengths (Å) and Angles (deg) with Estimated Standard Deviations of 13
13
Scott complex22
Al(1)-O(1)
1.7664(19)
1.979(2)
1.946(3)
1.946(3)
1.731(2)
1.7018(19)
1.947(3)
1.984(3)
Al(2)-O(3)
Al(2)-N(1)
Al(2)-C(40)
Al(2)-C(41)
Al(1)-O(1)
Al(1)-O(2)
Al(1)-C(39)
Al(1)-O(4) (DMSO)
O(3)-Al(2)-N(1)
O(3)-Al(2)-C(40)
O(3)-Al(2)-C(41)
O(1)-Al(1)-O(2)
O(1)-Al(1)-C(39)
O(1)-Al(1)-O(4)
1.7726(15)
1.980(2)
1.943(3)
Al(1)-N(1)
Al(1)-C(53)
Al(1)-C(54)
1.961(3)
Al(2)-O(2)
1.7169(16)
1.7553(15)
1.949(2)
1.8238(16)
93.66(8)
110.39(10)
110.37(10)
115.11(7)
111.10(10)
107.31(7)
Al(2)-O(3)
Al(2)-C(55)
Al(2)-N(2) (MeCN)
O(1)-Al(1)-N(1)
O(1)-Al(1)-C(53)
O(1)-Al(1)-C(54)
O(2)-Al(2)-O(3)
O(2)-Al(2)-C(55)
O(2)-Al(2)-N(2)
94.06(9)
111.82(13)
112.16(13)
113.99(9)
117.22(12)
97.49(10)
Table 10. Polymerization Runs for 5-12 and I in the Presence of
DMACa
trichloroacetate (ETA), produced highly active polymeriza-
tion systems (1000-7000 g/mmol h bar) as defined by the
Gibson criteria.1a
activity (g[PE]/
mmol[V] h bar)
Mw
Mn
run
procatalyst
(g mol-1
)
(g mol-1
)
PDI
1b
2c
3c
4
5
6
7
8
6798
5204
2452
4224
3032
1062
1668
1948
4192
236 000
262 000
245 000
293 000
230 000
226 000
338 000
137 000
110 000
98 200
107 000
102 000
136 000
101 000
81 100
145 000
46 300
37 900
2.4
2.5
2.4
2.2
2.3
2.8
2.7
2.8
2.9
The use of ETA as a reactivator in vanadium systems is
now well established.41 Extended reaction time profiles for
the vanadium-based procatalysts displayed general trends
previously observed for vanadium-based ethylene polymer-
ization: an initial higher level of activity over the initial 5-10
min of the polymerization reaction, after which a decrease
in activity (often as much as 50% of the initial value) leads
to a lower but sustained level of polymerization.12,27,40
Procatalyst 5 produced the highest activity (∼6800 g/mmol
h bar), higher than the isoelectronic vanadyl analogues; this
again is a trend that has been previously observed.12
Procatalysts 6 and 8 are the most active of the vanadyl-
bearing complexes (activities of ∼5200 and 4200 g/mmol h
bar, respectively), possibly because of a cooperative effect
brought about by the close proximity of the two metal
centers. Interestingly, for 7 (run 3) containing only one
vanadyl center (cf., 8), the activity is ∼2450 g/mmol h bar.
The previously reported procatalyst I exhibited a high level
of initial activity (∼8500 g/mmol h bar) after 5 min; this
system however is deactivated rapidly, producing a final
sustained activity of 4200 g/mmol h bar. Similar activities
(∼5900 g/mmol h bar) for I were observed previously under
increasing diluted conditions; the slight increase in activity
is caused by the reduction of mass transport issues.27 The
effect of substitution upon the pendent imine (Table 10, runs
6-9) produced activities in the range of ∼1000-4000
g/mmol h bar, with the trend, whereby the increased sterics
of the aniline led to increased activity. The exact nature of
the active species in these systems still remains unknown,
although in the context of propylene polymerization Zambelli
and Allegra have suggested that a 5-coordinate V(III) center
is required to carry out the polymerization reaction,42 with
5c
6
9
10
11
12
I
7
8
9c
a Conditions: 0.5 µmol of [V] per run, 50 mL of toluene, 45 °C, 5000
equiv DMAC, 0.1 mL of ETA, 60 min (unless otherwise indicated). GPC
analysis was conducted in 1,2,4-trichlorobenzene against a polystyrene
calibrant. b 20 min. c 30 min.
chlorines bridging the aluminum and vanadium centers, while
Gambarotta et al. have postulated a vanadium-aluminum-
phenoxide cluster that also contains chloro groups bridging
the vanadium and aluminum centers.40b As mentioned earlier,
for group IV phenoxyimine systems using i-Bu3Al /[CPh3]-
[B(C6F5)4] as cocatalyst, phenoxyamine ligands have been
isolated via hydrolysis of the catalyst solution.23c,l Such
behavior, the result of the susceptibility of the imine group
to attack by electrophiles, is not observed when using MAO
as cocatalyst23c but cannot be overlooked in the present
systems using DMAC.
In this work (Table 10), all polymers obtained were of
high molecular weight (monomodal), with narrow polydis-
persity indices (PDI), indicative of single-site catalysis. The
melting points of the polymers fall within approximately a
2 °C range (133.9-136.1 °C) and are typical of linear
polyethylene.
Full catalytic screening was carried out with the diiso-
propyl derivative I. The combination of the organoaluminum
cocatalysts MAO/TMA, with and without the reactivator
ETA, produced negligible or no polymer, whereas the use
of DMAC without reactivator (Table 11, run 20) produced
an active system, albeit with a level of activity an order of
magnitude less than the corresponding run with reactivator
present. Over the temperature range of 0-80 °C (Table 11,
runs 10-14), the catalyst performed well, showing a good
level of thermal stability with activities increasing with
increasing temperature. However, for lifetime studies, a
reaction temperature of 45 °C was chosen to prevent any
mass transport issues often encountered at higher tempera-
(40) (a) Milione, S.; Cavallo, G.; Tedesco, C.; Grassi, A. J. Chem. Soc.,
Dalton Trans. 2002, 1839. (b) Gambarotta, S. Coord. Chem. ReV. 2003,
237, 229. (c) Redshaw, C.; Warford, L.; Elsegood, M. R. J.; Dale,
S. H. Chem. Commun. 2004, 1954. (d) Tomov, A. K.; Gibson, V. C.;
Zaher, D.; Elsegood, M. R. J.; Dale, S. H. Chem. Commun. 2004,
1956. (e) Wang, W.; Nomura, K. Macromolecules 2005, 38, 5905.
(41) For early examples, see: (a) Gumboldt, A.; Helberg, J.; Schleitzer, G.
Makromol. Chem. 1967, 101, 229. (b) Christman, D. L. J. Polym. Sci.,
Part A 1972, 10, 471. (c) Addison, E.; Deffieux, A.; Fontanille, M.;
Bujadoux, K. J. Polym. Sci., Part A: Polym. Chem. 1994, 32, 1033.
(42) Zambelli, A.; Allegra, G. Macromolecules 1980, 13, 42.
Inorganic Chemistry, Vol. 47, No. 13, 2008 5809

Homden et al.
Table 11. Variation of Temperature and DMAC Concentration during Ethylene Polymerization Using Ia
run
temp (°C)
[Al]/[V]
activity (g[PE]/mmol h bar)
Mw (g mol-1
)
Mn (g mol-1
)
PDI
10
11
12
13
14
15
16
17
18
19
20b
0
25
45
60
80
25
25
25
25
25
45
8000
8000
8000
8000
8000
2000
4000
8000
2051
4708
7385
17 324
24 900
0
2077
3728
4327
7096
536
524 000
514 000
335 000
200 000
59 400
177 000
106 000
98 500
53 100
26 900
3.0
4.8
3.4
3.8
2.2
586 000
572 000
621 000
516 000
200 000
242 000
246 000
159 000
51 800
2.4
2.3
3.9
10.0
2.9
12 000
16 000
5000
69 000
a Conditions: 0.5 mmol of [V] per run, 50 mL of toluene, 0.1 mL of ETA, 30 min. b Without ETA.
tures. As expected, increasing polymerization temperature
led to a fall in molecular weight of the resulting polymer
because of an increase in frequency of termination reactions
compared to propagation reactions. The PDI of the polymers
was found to increase slightly but was still suggestive of
single site catalysis. With only 2000 equiv of DMAC (Table
11, run 15), no polymerization took place, presumably
because of the need for a minimum quantity of cocatalyst to
act as a scavenger. At 16 000 equiv of DMAC (Table 11,
run 19), although the catalytic activity is increasing, the PDI
of the resulting polymer was also found to have increased
from a PDI of ∼4 for 12 000 equiv of DMAC to a value of
10, suggesting that at such high [Al]/[V] ratios as 16 000:1,
other reactions are occurring with multiple bond breakage
leading to loss of single-site catalysis.
of ∼1000 g/mmol h bar. All catalysts producing high
molecular weight polymer with a narrow PDI for [Al]/[V]
ratios of e12 000. Further screening of I gave evidence of
a high degree of thermal stability (up to 80 °C) of these types
of catalysts, although an increase in temperature led to a
reduction in the molecular weight of the polymer (524 000
g mol-1 at 0 °C compared to 60 000 g mol-1 at 80 °C).
Experimental Section
General experimental and ethylene polymerization procedures
were performed as described elsewhere.12 The precursors 3-[2,2′-
methylenebis(4,6-di-tert-butylphenol)-5-methyl-2-hydroxybenzal-
dehyde] L0H3,22 [TiCl4(THF)2],43 and procatalyst I27 were prepared
as previously described. All other chemicals were obtained com-
mercially and used as received unless otherwise stated.
Preparation of Ligands. Preparation of L2H3. Aniline (0.17
mL, 1.83 mmol) and L0H3 (1.00 g, 1.66 mmol) in ethanol (25 mL)
were brought to reflux. A drop of formic acid was added to catalyze
the reaction, and a Dean-Stark condenser was attached. The
solution was refluxed for 1 h and then allowed to cool. The solvents
were removed in vacuo affording L2H3 as a yellow/orange powder.
Yield: 660 mg, 59%. mp: 180 °C. C46H61NO3 Calcd (found): C,
81.8 (81.7); H, 9.1 (9.1); N, 2.1 (2.1). 1H NMR (CDCl3, 400 MHz):
δ 8.65 (1H, s, CHdN), 7.6-6.6 (11H, m, Ar-H), 6.10 (1H, s,
Ar3CH), 1.37 (18H, s, t-Bu), 1.17 (9H, s, t-Bu), 1.16 (18H, s, t-Bu).
MS m/z (EI): 676 (M)+. IR (Nujol mull, cm-1): 3499m, 3452m,
3184w, 1619m, 1580m, 1293w, 1246w, 1188m, 1145w, 1118w,
1071w, 1021w, 974w, 943w, 924w, 877m, 819w, 753m, 718m,
664m.
Preparation of L3H3. Preparation was done as for L2H3 but using
L0H3 (1.00 g, 1.66 mmol) and p-toluidene (0.20 g, 1.83 mmol),
affording L3H3 as a yellow powder. Yield: 1.10 g, 96%. mp: 182
°C. C47H63NO3 Calcd (found): C, 79.95 (79.95); H, 9.45 (9.50); N,
1.90 (1.81). 1H NMR (CDCl3, 400 MHz): δ 8.32 (1H, s, CHdN),
7.4-6.8 (10H, m, Ar-H), 6.08 (1H, s, Ar3CH), 5.51 (2H, s, OH),
2.28 (3H, s, tolyl-CH3), 1.37 (18H, s, C(CH3)3), 1.20 (9H, s,
C(CH3)3), 1.18 (18H, s, C(CH3)3). MS m/z (EI): 690 (M)+. IR (Nujol
mull, cm-1): 3188m, 2725m, 2656w, 1363m, 1287w, 1259m,
1187m, 1169w, 1151w, 1093m, 1014m, 982w, 874w, 860w, 838w,
802m, 716m.
Conclusion
We have prepared and structurally characterized a number
of group IV and V complexes containing imine-tripodal
ligands. In the case of group IV metals (Ti and Zr),
bischelating zwitterionic structures were observed and found
to be inactive toward ethylene polymerization using a wide
range of organoaluminum cocatalysts. Although in both cases
cis-chlorines were present, it is thought that the steric bulk
of the C-capped triphenol moiety shielded the metal center
such that no polymer chain growth could occur. In the case
of niobium and tantalum, monochelating zwitterionic struc-
tures were observed, which upon activation with common
organoaluminum cocatalysts gave negligible activities.
The previously reported complex I was found to be highly
active for the polymerization of ethylene using DMAC as
cocatalyst in the presence of the reactivating agent ETA.
Encouraged by these results, a family of vanadium-based
imine-tripodal complexes were synthesized and screened as
potential procatalysts. Complex 5/DMAC/ETA, the van-
adium-imido-bearing procatalyst, displayed the highest
activities (∼6800 g/mmol h bar), while for the vanadyl
complexes, systems employing 6 and 8, both of which
contain two vanadyl groups, gave the highest activities
∼5200 and 4200 g/mmol h bar, respectively. Where the
pendent imine arm was formed from a substituted aniline, it
was found that reduction in steric bulk of the substituted
groups led to a reduction in activity, such that the diisopropyl
derivative yielded the highest activities, while the unsubsti-
tuted aniline derivative 10 gave the lowest overall activity
Preparation of L4H3. Preparation was done as for L2H3 but using
L0H3 (1.00 g, 1.66 mmol) and 2,4,6-trimethylaniline (0.26 mL, 1.83
mmol) affording L4H3as a bright yellow powder. Yield: 1.08 g, 82%.
mp: 186 °C. C49H67NO3 Calcd (found): C, 82.0 (81.9); H, 9.4 (9.5);
1
N, 2.0 (2.1). H NMR (CDCl3, 400 MHz): δ 8.66 (1H, s, CHdN),
7.4-6.8 (10H, m, Ar-H), 6.10 (1H, s, Ar3CH), 5.40 (2H, s, OH),
(43) Manzer, L. E. Inorg. Synth. 1982, 21, 84.
5810 Inorganic Chemistry, Vol. 47, No. 13, 2008

Early Transition Metal Complexes
Inorganic Chemistry, Vol. 47, No. 13, 2008 5811

Homden et al.
2.38 (3H, s, tolyl-p-CH3), 2.16 (6H, s, tolyl-o-CH3), 1.37 (18H, s, t-Bu),
1.20 (9H, s, t-Bu), 1.17 (18H, s, t-Bu). MS m/z (EI): 718 (M)+. IR
(Nujol mull, cm-1): 3506m, 3487m, 3417bm, 3172bm, 1623m, 1592m,
1359m, 1285w, 1246w, 1192w, 1153w, 1118w, 1009w, 978w, 928w,
877w, 811w, 765w, 714w, 660m.
Preparation of L5H6. L0H3 (1.00 g, 4.27 mmol) and o-
phenylenediamine (0.23 g, 2.14 mmol) were brought to reflux in
ethanol (25 mL). A catalytic amount of formic acid was added and
the reflux maintained for 1 h. The solvent was removed under
reduced pressure, and the solid was recrystallized from hot
acetonitrile (30 mL) to give L5H6 as orange prisms. Yield: 1.35 g,
50%. mp: 149-154 °C. C86H116N2O6 Calcd (found): C, 81.09
(81.19); H, 9.18 (9.26); N, 2.20 (2.19). 1H NMR (CDCl3, 400 MHz):
δ 8.63 (2H, s, CHdN), 7.31-6.79 (16H, overlapping signals,
Ar-H), 6.77 (4H, s, OH), 6.18 (2H, s, Ar3CH), 1.26 (27H, s, t-Bu),
1.17 (27H, s, t-Bu), 1.14 (36H, s, t-Bu). MS m/z (MALDI): 1273
(M)+. IR (Nujol mull, cm-1): 3508bm (N-H stretch), 3339bm,
3176bm, 2364w, 1782w, 1709w, 1686w, 1622m (CdN stretch),
1576m, 1528w, 1417m, 1363m, 1295m, 1261m, 1244m, 1213m,
1190s, 1151m, 1121m, 1026m, 971w, 931w, 882m, 817m, 802m,
769m, 745m, 722m, 668m, 647m.
Preparation of L6H3. L0H3 (1.00 g, 4.27 mmol) and o-
phenylenediamine (0.46 g, 4.27 mmol) were brought to reflux in
ethanol (100 mL). A catalytic amount of formic acid was added,
and the reflux was maintained for 12 h. The solution was cooled
and filtered to give L6H3 as an orange powder. Yield: 525 mg,
18%. mp: 264 °C. C46H62N2O3 Calcd (found): C, 80.20 (79.97);
1
H, 9.07 (9.13); N, 4.07 (4.12). H NMR (CDCl3, 400 MHz): δ
8.67 (1H, s, OH), 7.36-7.19 (6H, overlaying signals, Ar-H), 7.16
(2H, s, Ar-H), 6.81 (2H, s, Ar-H), 6.19 (1H, s, Ar3CH), 5.71
(2H, bs, OH), 1.26 (18H, s, t-Bu), 1.18 (9H, s, t-Bu), 1.15 (18H, s,
t-Bu). MS m/z (MALDI): 690 (M + H)+. IR (Nujol mull, cm-1):
3293bs, 2726m, 2267m, 2248m, 1588m, 1460s, 1417m, 1378s,
1359s, 1300m, 1258m, 1211m, 1161m, 1118m, 1091m, 1060m,
1033m, 994m, 873m, 838m, 803m, 784m, 765w, 733w, 726w,
667w.
Preparation of Complexes. Preparation of [TiCl2(L1H2)2]
(1). [TiCl4(THF)2] (0.27 g, 0.81 mmol) and L1H3 (0.60 g, 0.79
mmol) were combined in a Schlenk flask in a glovebox. Toluene
(40 mL) was added, and the solution was refluxed for 12 h. Upon
cooling, the solvents were removed in vacuo, and the residue
was extracted into warm acetonitrile (30 mL) affording 1 as deep
red prisms upon standing at ambient temperature (1-2 days).
Yield: 0.56 g, 83%. mp: 237 °C (dec). C104H144N2O6Cl2Ti Calcd
1
(found): C, 76.59 (76.30); H, 8.63 (8.87); N, 1.70 (1.71). H
NMR (CDCl3, 400 MHz) δ: 7.67 (2H, s, CdNH), 7.59 (2H, d,
3J 15.9 Hz, CHdN), 7.49-6.00 (18H, overlapping signals,
Ar-H), 4.95 (2H, s, Ar3CH), 3.63 (2H, bm, i-Pr), 3.11 (2H,
bm, i-Pr), 1.20-0.98 (114H, overlapping signals, t-Bu and i-Pr).
MS m/z (FAB): 1563 (M - 2Cl)+, 759 (ligand)+. IR (Nujol mull,
cm-1): 3478m (N-H stretch), 2959s, 2897m, 2866m, 2359m,
2330w, 1634s (CdN stretch), 1544m, 1463s, 1390w, 1362m,
1332w, 1265m, 1230s, 1168m, 1122m, 1024w, 904w, 881w,
858m, 797m, 761m, 737m, 666w.
Preparation of [ZrCl2(L1H2)2] (2). Preparation was done as for
1 but using [ZrCl4] (0.14 g, 0.60 mmol) and L1H3 (0.40 g, 0.53
mmol) affording 2 as yellow prisms upon standing at ambient
temperature (1-2 days). Yield: 0.40 g, 81%. mp: >250 °C.
C
104H144N2O6Cl2Zr Calcd (found): C, 74.57 (74.34); H, 8.69
(8.64); N, 1.74 (1.67). 1H NMR (CDCl3, 400 MHz): δ 7.98 (2H,
3
s, CdNH), 7.89 (2H, d, J 19.9 Hz, CHdN), 7.49-6.75 (18H,
overlapping signals, Ar-H), 5.12 (2H, s, Ar3CH), 3.68 (2H, bm,
i-Pr), 3.28 (2H, bm, i-Pr), 1.39-1.22 (114H, overlapping signals,
5812 Inorganic Chemistry, Vol. 47, No. 13, 2008

Early Transition Metal Complexes
3
t-Bu and i-Pr). MS m/z (FAB): 1679 (M - H)+, 1642 (M - Cl
- 2H)+, 759 (ligand)+. IR (Nujol mull, cm-1): 3458m (N-H
stretch), 1635m (CdN stretch), 1557w, 1544w, 1303m, 1280m,
1261m, 1230m, 1211m, 1168m, 1120w, 1022m, 972m, 853m,
816m, 766m, 736m.
Preparation of [NbCl3(L1H)] (3). Preparation was done as for
1 but using [NbCl5] (0.39 g, 1.45 mmol) and L1H3 (1.00 g, 1.32
mmol). Prolonged standing (4-5 days) at -25 °C afforded orange/
red plates of 3. Yield: 0.31 g, 24%. Further crops of 3 can be
obtained from the mother liquor upon concentration and consequent
isolation. Total yield: 0.65 g, 51%. mp: 217 °C (dec).
C52H71NO3Cl3Nb Calcd (found): C, 65.24 (65.43); H, 7.47 (7.47);
3J ) 8 Hz, N-p-tol), 6.71 (2H, s, Ar-H), 6.57 (4H, d, J ) 8 Hz,
N-p-tol), 6.22 (2H, Ar3CH), 4.19 (2H, s, OH), 1.97 (6H, s, N-p-
tol), 1.75 (18H, s, t-Bu), 1.39 (18H, s, t-Bu), 1.35 (18H, s, t-Bu),
1.25 (18H, s, t-Bu), 1.21 (18H, s, t-Bu). 51V (C6D6, 105.1 MHz):
δ -510.43 (ω1/2 ) 60), -567.23 (ω1/2 ) 80). MS m/z (MALDI):
1526 (M)+. IR (Nujol mull, cm-1): 3495m, 1611m, 1603m, 1553w,
1502,m 1308m, 1269m, 1242m, 1184m, 1153m, 1122m, 1075m,
1040m, 1017m, 982s, 924m, 869m, 827m, 811m, 765w, 722m,
664m.
Preparation of [VO(L5H4)] (7). To a solution of L5H6 (1.00 g,
0.79 mmol) in toluene (30 mL) was added [VO(O-n-Pr)3] (0.18
mL, 0.79 mmol). The solution was refluxed overnight before being
cooled, and the solvent was removed in vacuo. The crude material
was extracted into acetonitrile (40 mL) and filtered giving 7 as
purple brown plates. Yield: 350 mg, 33%. mp: >250 °C.
C86H114O7N2V Calcd (found): C, 76.91 (77.15); H, 8.61 (8.58); N,
2.17 (2.09). MS m/z (Maldi): 1337.6 (M + H)+. IR (Nujol mull,
cm-1): 3379m, 2725w, 2364w, 1607w, 1591m, 1546m, 1413w,
1364m, 1330m, 1311m, 1261s, 1197m, 1161m, 1099bs, 1018bs,
976m, 926m, 882m, 847m, 802s, 741m, 673m, 661m. Magnetic
1
3
N, 1.46 (1.50). H NMR (CDCl3, 400 MHz): δ 7.92 (1H, d, J )
15.9 Hz, CHdN), 7.60 (1H, s, CdNH), 7.37-7.06 (9H, overlapping
3
signals, Ar-H), 5.17 (1H, s, Ar3CH), 3.16 (2H, septet J ) 7.0
Hz, i-Pr), 1.43 (18H, s, t-Bu), 1.29 (27H, s, t-Bu), 1.18 (12H, s,
i-Pr). MS m/z (FAB): 921 (M - Cl)+, 886 (M - 2Cl)+, 851 (M -
3Cl)+, 759 (ligand)+. IR (Nujol mull, cm-1): 3584m (N-H stretch),
1631m (CdN stretch), 1593m, 1590m, 1407w, 1377s, 1365s,
1325w, 1261m, 1222m, 1202m, 1156m, 1135m, 1097m, 1059w.
1027m, 921m, 909w, 899m, 859s, 800s, 762m, 738w, 726w, 676w,
665m, 625m.
Preparation of [TaCl4(L1H2)] (4). Preparation was done as for
1 but using [TaCl5] (0.52 g, 1.45 mmol) and L1H3 (1.00 g, 1.32
mmol), affording 4 as pale yellow plates upon standing at ambient
temperature (5-6 days). Yield: 0.89 g, 62% . mp: 219 °C (dec).
C52H72NO3Cl4Ta Calcd (found): C, 57.73 (57.87); H, 6.71 (6.70);
N, 1.29 (1.50). 1H NMR (CDCl3, 400 MHz): δ 7.96 (1H, s, CHdN),
7.46-6.92 (9H, overlapping signals, Ar-H), 4.96 (1H, s, Ar3CH),
3.35 (1H, bm, i-Pr), 3.13 (1H, bm, i-Pr), 1.56 (9H, s, t-Bu), 1.35
(9H, s, t-Bu), 1.33 (12H, s, i-Pr), 1.31 (9H, s, t-Bu), 1.26 (9H, s,
t-Bu), 1.18 (9H, s, t-Bu). MS m/z (FAB): 1081 (M)+, 1046 (M -
Cl)+, 1011 (M - 2Cl)+, 975 (M - 3Cl)+, 759 (ligand)+. IR (Nujol
mull, cm-1): 3540bm, 2363w, 1638m (CdN stretch), 1597w,
1561w, 1459m, 1377m, 1366m, 1260m, 1217m, 1092s, 1019s,
863w, 799s, 666m.
moment: µ ) 1.15 µB. EPR (toluene, 298 K): giso ) 1.99, Aiso
95 G; (toluene, 10 K) g⊥ ) 1.99, A⊥ ) 65 G, g| ) 1.96, A| ) 183
G.
)
Preparation of [(VO)2(L5H)] (8). To a solution of L5H6 (1.00
g, 0.79 mmol) in toluene (30 mL) was added [VO(O-n-Pr)3] (0.10
mL, 0.40 mmol). The solution was refluxed overnight before being
cooled, and the solvent was removed in vacuo. The crude material
was extracted into acetonitrile (40 mL) and filtered, giving 8 as a
yellow/brown solid. Yield: 680 mg, 62%. mp: >350 °C.
C86H111O8N2V2 Calcd (found): C, 73.6 (73.6); H, 8.0 (8.0); N, 2.0
(2.1). MS m/z (MALDI): 1401 (M - O)+. IR (Nujol mull, cm-1):
3499m, 3335m, 1604m, 1580m, 1539m, 1460m, 1440m, 1376m,
1362m, 1330w, 1291w, 1215w, 1194m, 1154m, 1115m, 1099m,
1020m, 996m, 924w, 908w, 874m, 844m, 803m, 768m, 753m,
722w. Magnetic moment: µ ) 1.83 µB. EPR (toluene, 298 K): giso
) 1.99, Aiso ) 100 G; (toluene, 10 K) g⊥ ) 1.99, A⊥ ) 64 G, g| )
1.96, A| ) 181 G.
Preparation of [(VN-p-tol(L1H))2(µ-O-n-Pr)2] (5) and
[(VO)2(µ-O)(L3H)2] (6). [VN-p-tol(O-n-Pr)3] (0.44 g, 1.32 mmol)
and L1H3 (1.00 g, 1.32 mmol) were combined in a dry box. Toluene
(30 mL) was added, and the solution refluxed for 12 h. Upon
cooling, the solvents were removed in vacuo, and the residue was
extracted into warm acetonitrile (30 mL).
Preparation of [VO(L6H2)2] (9). To a solution of L6H3 (1.00
g, 1.45 mmol) in toluene (30 mL) was added [VO(O-n-Pr)3] (0.17
mL, 0.73 mmol). The solution was stirred at room temperature for
4 h after which the solvents were removed in vacuo. The crude
material was extracted into cold acetonitrile (40 mL) and filtered
giving 9 as brown blocks. Yield: 647 mg, 61%. C92H118O7N4V
Calcd (found): C, 76.58 (76.46); H, 8.24 (8.35); N, 3.88 (3.82). IR
(Nujol mull, cm-1): 3479m, 3335m, 3161m, 2723m, 2671m, 1673m,
1612m, 1592m, 1577m, 1455m, 1376m, 1293m, 1260m, 1191m,
1165m, 1161m, 1094bm, 1018bm, 979m, 884m, 862w, 846w,
801m, 753m, 665m. Magnetic moment: µ ) 1.86 µB. EPR (toluene,
298 K): giso ) 2.00, Aiso ) 95 G; (toluene, 10 K) g⊥ ) 1.99, A⊥ )
63 G, g| ) 1.96, A| ) 186 G.
Compound 5was isolated as an orange/red solid upon filtration.
Yield: 900 mg, 70%. mp: 157 °C (dec). C124H170N4O8V2 Calcd
1
(found): C, 76.52 (76.59); H, 8.80 (8.76); N, 2.88 (2.79). H
NMR (C6D6, 400 MHz): δ 8.22 (2H, s, CHdN), 7.95 (2H, s,
Ar-H), 7.88 (4H, s, Ar-H), 7.70 (2H, bs, OH), 7.26 (4H, s,
Ar-H), 7.26-6.97 (8H, overlapping signals, Ar-H), 7.10 (2H,
3
3
s, Ar3CH), 6.40 (4H, d, J 8 Hz, N-p-tol), 6.10 (4H, d, J 8 Hz,
3
N-p-tol), 5.95 (4H, bm, O-n-Pr), 2.94 (4H, sept, J ) 6.8 Hz,
i-Pr), 2.77 (4H, bm, O-n-Pr), 1.80 (6H, s, N-p-tol), 1.73 (24H,
s, i-Pr), 1.37 (36H, s, t-Bu), 1.24 (18H, s, t-Bu), 1.05 (18H, s,
Preparation of [VO(L2H2)2] (10). [V(O)(O-n-Pr)3] (0.17 mL,
0.74 mmol) and L2H3 (1.00 g, 1.48 mmol) were refluxed in toluene
(40 mL) for 12 h. Upon cooling, the solvents were removed in
vacuo, and the brown residue was extracted into dichloromethane
(30 mL). Standing at ambient temperature for 24 h afforded 10 as
a yellow/brown solid. Yield: 550 mg, 26%. mp: 275 °C (dec).
C92H122N2O7V·CH2Cl2 Calcd (found): C, 74.38 (74.58); H, 8.19
(8.29); N, 1.87 (1.75). MS m/z (EI): 1416 (M+). IR (Nujol mull,
cm-1): 3507(m), 3174(m) 1614(m), 1584(m), 1410(m), 1360(m),
1314(w), 1291(w), 1254(m), 1185(m), 1152(m), 1119(m), 1093(m),
1020(m), 977(m), 921(w), 878(w), 799(w), 763(w), 717(w).
3
t-Bu), 1.03 (18H, s, t-Bu), 0.94 (6H, t, J ) 7.2 Hz, O-n-Pr).
51V (C6D6, 105.1 MHz): δ -480.84 (ω1/2 ) 320). MS m/z
(Maldi): 760 (ligand)+. IR (Nujol mull, cm-1): 3464m, 3165m,
2718m, 2656m, 1619m (CdN stretch),1584m, 1541m, 1258m,
1211w, 1207w, 1168w, 1100m, 1017w, 974w, 881m, 842m,
800m, 757m, 726m.
Compound 6 was isolated as dark brown crystals from the filtrate.
Yield: 248 mg, 25%. mp: 85 °C (dec). C94H122N2O9V2 Calcd
(found): C, 74.0 (73.9); H, 8.1 (8.0); N, 1.8 (1.9). 1H NMR (C6D6,
400 MHz): δ 7.55 (2H, s, CHdN), 7.48-7.39 (10H, overlapping
signal, Ar-H), 7.15 (6H, overlapping signal, Ar-H) 6.83 (4H, d,
Inorganic Chemistry, Vol. 47, No. 13, 2008 5813

Homden et al.
Magnetic moment: µ ) 1.31 µB. EPR (toluene, 298 K): giso ) 2.01,
Aiso ) 96 G; (toluene, 10 K) g⊥ ) 1.99, A⊥ ) 64 G, g| ) 1.95, A|
) 185 G.
radiation (λ ) 0.71073 λ) and graphite monochromator, except for
compound 6 which was measured at a synchrotron source. In all
cases intensity data were measured by thin-slice ω- and -scans.
Data were processed using the CrysAlis-RED,44 DENZO/
SCALEPACK45 or SAINT46 programs. The structures were
determined by the direct methods routines in the SHELXS47 or
SIR-9248 programs and refined by full-matrix least-squares methods,
on F2, in SHELXL.47 The non-hydrogen atoms were refined with
anisotropic thermal parameters, except in some disordered groups
and solvent molecules where the partial atoms were refined
isotropically. In several compounds, the phenolic hydrogen atoms
were located in difference maps and were refined freely; all other
hydrogen atoms in all samples were included in idealized positions
and their Uiso values were set to ride on the Ueq values of the parent
carbon or nitrogen atoms. Scattering factors for neutral atoms were
taken from reference.49 Crystal data and refinement results are
collated in Table 12.
Preparation of [VO(L3H2)2] (11). Preparation was done as for
10 but using L3H3 (1.00 g, 1.45 mmol) and [V(O)(O-n-Pr)3] (0.16
mL, 0.73 mmol), affording 11 as a yellow/green solid. Yield: 430
mg, 20%. mp: 260 °C (dec). C94H126N2O7V Calcd (found): C, 78.14
(77.79); H, 8.65 (8.59); N, 1.94 (1.52).MS m/z (EI): 1444 (M+).
IR (Nujol mull, cm-1): 3530(bm), 3188(bm), 1620(m), 1585(m),
1363(m), 1287(m), 1259(m), 1187(m), 1169(w), 1151(w), 1187(m),
1093(m), 982(w), 874(w), 860(w), 838(w), 802(s), 716(m). Mag-
netic moment: µ ) 1.33 µB. EPR (toluene, 298 K): giso ) 1.98,
Aiso ) 96 G; (toluene, 10 K) g⊥ ) 1.99, A⊥ ) 65 G, g| ) 1.95, A|
) 185 G.
Preparation of [VO(L4H2)2] (12). Preparation was done as for
10, but using L4H3(1.00 g, 1.39 mmol) and [V(O)(O-n-Pr)3] (0.16
mL, 0.70 mmol) affording 12 as a yellow/brown solid. Yield:
478 mg, 23%. mp: 255 °C (dec). C98H134N2O7V · CH2Cl2 Calcd
(found): C, 74.97 (74.64); H, 8.52 (8.74); N, 1.77 (1.54). MS
m/z (EI): 1500 (M+ - H). IR (Nujol mull, cm-1): 3425(bm),
3192(bm), 1611(m), 1586(m), 1255(s), 1187(m), 1151(w),
1118(m), 1090(m), 1011(m), 878(m), 845(m), 795(s), 763(m),
719(m), 662(m). Magnetic moment: µ ) 1.39 µB. EPR (toluene,
298 K): giso ) 2.01, Aiso ) 96 G; (toluene, 10 K) g⊥ ) 1.99, A⊥
) 65G, g| ) 1.96, A| ) 180 G.
Acknowledgment. The University of East Anglia and the
EPSRC are thanked for financial support. We thank the
EPSRC Mass Spectrometry Service Centre (Swansea, U.K.).
The EPSRC X-ray Crystallography Service, Southampton,
U.K., is thanked for data collection of 13, and the EPSRC
is also thanked for the award of beamtime at Daresbury
Laboratory (Station 9.8 SMX) and Drs. John Warren and
Tim Prior for scientific support. We would also like to thank
Rapra Scientific Ltd. for GPC measurements and Dr Myles
Cheesman (UEA) for help with recording EPR spectra.
Preparation of {(AlMe2)[AlMe(NCMe)]L1} (13). To a solution
of L1H3 (1.00 g, 1.32 mmol) in toluene (30 mL) was added 3.1
equiv of trimethylaluminum (2.0 M solution, 2.04 mL, 4.08
mmol). The solution was refluxed overnight, and the solvent was
removed in vacuo. Extraction into warm acetonitrile (25 mL)
and cooling to ambient temperature gave yellow prisms of 13
(400 mg, 34%). mp: >350 °C. C57H82N2O3Al2 Calcd (found):
IC702506W
1
(44) CrysAlis-CCD and -RED; Oxford Diffraction Ltd.: Abingdon, U.K.,
2005.
C, 76.3 (76.0); H, 9.2 (9.5); N, 3.1 (2.9). H NMR (CDCl3, 400
MHz): δ 8.23 (1H, s, CHdN), 7.55-6.98 (9H, m, Ar-H), 5.29
(1H, s, Ar3CH), 3.00 (2H, m, i-Pr), 1.95 (12H, s, i-Pr), 1.48-1.22
(45H, overlaying signals, t-Bu), 0.07 (3H, s, MeCN), -0.51 (3H,
s, Al-CH3), -0.81 (3H, s, Al-CH3), -1.61 (3H, s, Al-CH3).
MS m/z (MALDI): 799 (M - AlMe2 - MeCN). IR (Nujol mull,
cm-1): 3131(bm), 1611(s), 1398(m), 1260(m), 1093(m), 1019(m),
858(s), 800(m), 600(s).
Crystallographic Analyses. For each sample, a crystal was
mounted in oil on a glass fiber and fixed in the cold nitrogen stream
on an automated CCD diffractometer equipped with Mo KR
(45) Otwinowski, Z.; Minor, W. Processing of X-ray diffraction data
collected in the oscillation mode. Macromolecular Crystallography,
Part A; Methods in Enzymology 276; Carter, C. W., Jr., Sweet, R. M.,
Eds.; Academic Press: San Diego, CA. , 1997; pp 307-326.
(46) SAINT software for CCD diffractometers, Bruker AXS, Inc., Madison,
WI, 2001.
(47) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112–122.
(48) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliadi, A. J. Appl.
Crystallogr. 1993, 26, 343.
(49) International Tables for X-ray Crystallography; Kluwer Academic
Publishers: Dordrecht, The Netherlands, 1992; Vol C, pp. 500, 219,
193.
5814 Inorganic Chemistry, Vol. 47, No. 13, 2008