Synthesis and reactivity of titanium(IV)-salen complexes containing oxygen and chloride ligands

Article abstract of DOI:10.1021/om980414p

The reaction of in situ-generated Ti(OⁱPr)₂(X)₂ (X = OAr, OTf) with H₂salen or H²salen* yields the stable, well-characterized Ti(salen)X₂ series of complexes. Ti(salen*)(OTf)₂ could also be synthesized by reacting the previously unknown Ti(salen*)Cl₂ with TMSOTf or AgOTf. The ditriflates could be converted back to the aryloxides upon reaction with 2 equiv of NaOAr. Ti(salen)(4-tert-butyphenoxy)₂ was characterized by X-ray crystallography and found to contain a pseudoplanar salen ligand with two axially coordinated aryloxide ligands. H₂salen and H₂salen* were also found to cleanly react with in situ-generated Ti(OⁱPr)₃(X) (X = OC(O)R, OTf) to yield the unsymmetrically substituted Ti(salen)(OⁱPr)(X) and Ti(salen*)(OⁱPr)(X) complexes, respectively. In the case of X = OTf, the isopropoxide ligand could be cleanly protonated with 4-fert-butylphenol to yield Ti(salen)(OAr)(OTf) in high yield. This complex could also be accessed by the comproportionation reaction of Ti(salen)(OAr)₂ and Ti(salen)(OTf)₂.

Full text of DOI:10.1021/om980414p

5358
Organometallics 1998, 17, 5358-5366
Syn th esis a n d Rea ctivity of Tita n iu m (IV)-Sa len
Com p lexes Con ta in in g Oxygen a n d Ch lor id e Liga n d s
Huiyuan Chen, Peter S. White, and Michel R. Gagne´*
Department of Chemistry CB#3290, The University of North Carolina,
Chapel Hill, North Carolina 27599-3290
Received May 22, 1998
The reaction of in situ-generated Ti(OiPr)2(X)2 (X ) OAr, OTf) with H2salen or H2salen*
yields the stable, well-characterized Ti(salen)X2 series of complexes. Ti(salen*)(OTf)2 could
also be synthesized by reacting the previously unknown Ti(salen*)Cl2 with TMSOTf or AgOTf.
The ditriflates could be converted back to the aryloxides upon reaction with 2 equiv of
NaOAr. Ti(salen)(4-tert-butyphenoxy)2 was characterized by X-ray crystallography and found
to contain a pseudoplanar salen ligand with two axially coordinated aryloxide ligands.
H2salen and H2salen* were also found to cleanly react with in situ-generated Ti(OiPr)3(X)
(X ) OC(O)R, OTf) to yield the unsymmetrically substituted Ti(salen)(OiPr)(X) and Ti(salen*)-
(OiPr)(X) complexes, respectively. In the case of X ) OTf, the isopropoxide ligand could be
cleanly protonated with 4-tert-butylphenol to yield Ti(salen)(OAr)(OTf) in high yield. This
complex could also be accessed by the comproportionation reaction of Ti(salen)(OAr)2 and
Ti(salen)(OTf)2.
In tr od u ction
(salen)TiCl2 complexes with achiral or chiral salen deriv-
atives.10 The chemical reactivity of these complexes has
been limited to alkylations or arylations of the apical
chloride ligands and reduction (Ti(IV) to Ti(III)).11 Re-
cently, a structurally characterized chiral titanium salen
complex containing two axial chloride ligands was
shown to be an active catalyst for the asymmetric addi-
tion of TMSCN to benzaldehyde.12 This study was an
extension of earlier studies wherein two groups indepen-
dently reported the use of in situ-generated chiral
“(salen)Ti(OiPr)2” complexes (from Ti(OiPr)4) as catalysts
for this reaction, each group proposing that the reaction
proceeds by a different mechanism.13,14 Contributing
to the uncertainty in this mechanistic debate is the
lack of structural models for reasonable catalyst inter-
mediates.
N,N′-Ethylenebis(salicylideneiminate) dianion (salen)
is a well-known tetradentate Schiff base ligand which
normally provides a rigid, planar coordination environ-
ment for a metal.1 The synthesis and reactivity of nu-
merous metal complexes containing various salen de-
rivatives have been extensively studied. Most studies
to date have focused on salen complexes of the middle
and late d-block metals due to their use as asymmetric
catalysts for olefin epoxidation,2 cyclopropanation,3 and
aziridination,4 sulfide5 oxidation, the Diels-Alder reac-
tion,6 C-H activation,7 and the asymmetric ring-open-
ing of epoxides.8
Literature references on metal-salen complexes of
the group 4 elements are, unexpectedly, rather sparse.9
The best known group 4 metal-salen complexes are
(7) (a) Kaufman, M. D.; Greico, P. A.; Bougie, D. W. J . Am. Chem.
Soc. 1993, 115, 11648-11649. (b) Larrow, J . F.; J acobsen, E. N. J . Am.
Chem. Soc. 1994, 116, 12129-12130. (c) Hamachi, K.; Irie, R.; Katsuki,
L. Tetrahedron Lett. 1996, 37, 4979-4982.
(8) (a) J acobsen, E. N.; Kakiuchi, F.; Konsler, R. G.; Larrow, J . F.;
Tokunaga, M. Tetrahedron Lett. 1997, 38, 773-776. (b) Tokunaga, M.;
Larrow, J . F.; Kakiuchi, F.; J acobsen, E. N. Science 1997, 277, 936-
938. (c) Leighton, J . L.; J acobsen, E. N. J . Org. Chem. 1996, 61, 389-
390. (d) Mart´ınez, L. E.; Leighton, J . L.; Carsten, D. H.; J acobsen, E.
N. J . Am. Chem. Soc. 1995, 117, 5897-5898.
(9) McAuliffe, C. A.; Barratt, D. S. In Comprehensive Coordination
Chemistry; Wilkinson, G., Gillard, R. D., McCleverty J . A., Eds.;
Pergamon Press: Oxford, 1987; Vol. 3, Chapter 31.
(10) (a) Gilli, G.; Cruickshank, D. W. J .; Beddoes, R. L.; Mills, O. S.
Acta Crystallogr. 1972, B28, 1889-1893. (b) Gurian, P. L.; Cheatham,
L. K.; Ziller, J . W.; Barron, A. J . Chem. Soc., Dalton Trans. 1991,
1449-1456. (c) Solari, E.; Corazza, F.; Floriani, C.; Chiesi-Villa, A.;
Gusati, C. J . Chem. Soc., Dalton Trans. 1990, 1345-1355. (d) Repo,
T.; Klinga, M.; Leskela¨, M.; Pietika¨inen, P.; Brunow, G. Acta Crystal-
logr. 1996, C52, 2742-2745.
(11) (a) Dell’Amico, G.; Marchetti, F.; Floriani, C. J . Chem. Soc.,
Dalton Trans. 1982, 2197-2202. (b) Solari, E.; Floriani, C.; Chiesi-
Villa, A.; Rizzoli, C. J . Chem. Soc., Dalton Trans. 1992, 367-373. (c)
Carroll, K. M.; Schwartz, J .; Ho, D. M. Inorg. Chem. 1994, 33, 2707-
2708. (d) Kelly, D. G.; Toner, A. J .; Walker, N. M.; Coles, S. J .;
Hursthouse, M. B. Polyhedron 1996, 15, 4307-4310.
(12) Tararov, V. I.; Hibbs, D. E.; Hursthouse, M. B.; Ikonnikov, N.
S.; Abdul Malik, K. M.; North, M.; Orizu, C.; Belokon, Y. N. Chem.
Commun. 1998, 387-388.
(1) Calligaris, M.; Randaccio, L. In Comprehensive Coordination
Chemistry; Wilkinson, G., Gillard, R. D., McCleverty J . A., Eds.;
Pergamon Press: Oxford, 1987; Vol. 2, Chapter 20.
(2) (a) J acobsen, E. N. Asymmetric Catalytic Epoxidation of Un-
functionalized Olefins. In Catalytic Asymmetric Synthesis; Ojima, I.,
Ed.; VCH Publishers: New York, 1993; pp 159-202. (b) Katsuki, T.
Coord. Chem. Rev. 1995, 140, 189-214. (c) J ogensen, A. K. Chem. Rev.
1989, 89, 431-458. (d) Pospisil, P. J .; Carsten, D. H.; J acobsen, E. N.
Chem. Eur. J . 1996, 2, 974-980, and references therein. (e) Vander
Velde, S. L.; J acobsen, E. N. J . Org. Chem. 1995, 60, 5380-5381. (f)
Srinivasan, K.; Perrier, S.; Kochi, J . K. J . Am. Chem. Soc. 1986, 108,
2309-2320.
(3) Fukuda, T.; Katsuki, L. Tetrahedron 1997, 53, 7201-7208.
(4) (a) Du Bois, J .; Tomooka, C. S.; Hong, J .; Carreira, E. M. Acc.
Chem. Res. 1997, 30, 364-372. (b) Noshikori, H.; Katsuki, T. Tetra-
hedron Lett. 1996, 37, 9245-9248.
(5) (a) Kagan, H. B. Asymmetric Oxidation of Sulfides. In Catalytic
Asymmetric Synthesis; Ojima, I., Ed.; VCH Publishers: New York,
1993; pp 203-226. (b) Sasaki, C.; Nakajima, K.; Kojima, M.; Fujita, J .
Bull. Chem. Soc. J pn. 1991, 64, 1318-1324. (c) Bolm, C.; Bienewald,
F. Angew. Chem., Int. Ed. Engl. 1995, 34, 2640-2642. (d) Palucki, M.;
Hanson, P.; J acobsen, E. N. Tetrahedron Lett. 1992, 33, 7111-7114.
(e) Fukuda, T.; Katsuki, T. Tetrahedron Lett. 1997 38, 3435-3438.
(6) (a) Schaus, S. E.; Brånalt, J .; J acobsen, E. N. J . Org. Chem. 1998,
63, 403-405. (b) Yamashita, Y.; Katsuki, T. Synlett 1995, 829-830.
(c) Hollis, T. K.; Oldenkirk, W.; Robinson, N. P.; Whelan, J .; Bosnich,
B. Tetrahedron 1993, 49, 5415-5430.
10.1021/om980414p CCC: $15.00 © 1998 American Chemical Society
Publication on Web 10/30/1998

Ti(IV)-Salen Complexes
Organometallics, Vol. 17, No. 24, 1998 5359
Our interest in titanium salen complexes stems from
the rapid development of titanium reagents or catalysts
in asymmetric synthesis15 and the power of chiral salen
derivatives in asymmetric catalysis. The expansion of
Ti-salen-based catalytic methods, however, is hindered
by the lack of synthetic routes to well-characterized
complexes. To begin filling this void, we present herein
our efforts to discover new syntheses of symmetric and
asymmetrically disubstituted titanium(IV)-salen com-
plexes possessing oxygen-donor ligands. We have ex-
amined methods for their synthesis, explored their
substitution reactivity, and characterized a homobisad-
duct by X-ray crystallography.
cesses under catalytic conditions, further clouding the
mechanistic issues in the Belekon/J iang debate.13,14
In contrast to the reaction of H2salen* with Ti(OiPr)4,
the reaction of in situ-generated Ti(OiPr)2(OAr)2 with
either H2salen or H2salen* produces a single titanium
complex. Thus, a CH2Cl2 solution of Ti(OiPr)4, when
sequentially treated with phenol (2 equiv) and H2salen
(1 equiv), selectively eliminates 2-propanol to yield Ti-
(salen)(OPh)2 (2), (eq 2). Using this method, Ti(salen)-
(4-tert-butylphenolate)2 (3) and Ti(salen*)(4-tert-bu-
tylphenolate)2 (4) were similarly prepared from the
reactions of Ti(OiPr)4, 4-tert-butylphenol (2 equiv), and
the corresponding salen ligands. The bulky tert-butyl
groups in 3 and 4 make them significantly more soluble
than 2 in CH2Cl2 and CH3CN.
Resu lts
Syn th esis of Sym m etr ica lly Disu bstitu ted Tita -
n iu m (IV) Sa len Com p lexes. Symmetrically disub-
stituted six-coordinate titanium(IV) salen complexes can
be synthesized through two independent routes: direct
addition of H2salen to a suitable Ti-precursor or ligand
substitution at a Ti-salen complex. Analogous to the
method reported for the synthesis of Ti(salen)Cl2,8a,b
direct reaction of H2salen* (N,N′-ethylenebis(5-tert-
butylsalicylideneimine)) with TiCl4 or TiCl4‚2THF in
methylene chloride or THF solvent cleanly produces Ti-
(salen*)Cl2 (1) (eq 1). Unlike Ti(salen)Cl2, however, 1
has good solubility in organic solvents (e.g., CH2Cl2,
CH3CN, and THF), allowing for full characterization by
1H and 13C NMR spectroscopy.
An alternative method for preparing symmetrically
disubstituted titanium salen complexes is through
ligand substitution. For example, when 3 was treated
with TMSOTf (2 equiv), the two aryloxide ligands were
each silylated and replaced by OTf (eq 3).17 The 1H
NMR spectrum of the product Ti(salen)(OTf)2 (5) in CD3-
CN indicates a single set of salen resonances shifted
downfield from H2salen, 2 and 3. The singlet at -77.3
ppm in the 19F NMR is assigned to a coordinated OTf
ligand (vide infra), shifted slightly downfield of
TMSOTf (-78.2 ppm). In addition to silyl ether elimi-
nation, TMS-Cl elimination was also found to be facile,
as the dichloride 1 could be cleanly converted to 6 upon
treatment with TMSOTf (eq 4). Although slightly less
convenient, the elimination of AgCl from the reaction
of 1 with AgOTf (2 equiv) also gives 6.
When Ti(OiPr)4 in CH2Cl2 or CH3CN is similarly
treated with H2salen* (1 equiv) at ambient temperature,
an uncharacterizable yellow insoluble solid precipitates
from even dilute solutions. In situ monitoring of this
reaction by 1H NMR (CD2Cl2) indicates that the starting
materials are initially converted into a pair of titanium
salen products in a 2:1 ratio. The spectrum of the major
product is consistent with the expected Ti(salen*)-
(OiPr)2 product,16 but over the course of several minutes,
this mixture leads to the insoluble yellow material
described above. The instability of the expected product
at least suggests that chiral versions of the diisopro-
poxide may also be prone to ligand distribution pro-
(13) Belokon, Y. N.; Ikonnikov, N.; Moscalenko, M.; North, M.;
Orlova, S.; Vitali, T.; Yashkina, L. Tetrahedron Asymm. 1996, 7, 851-
855.
(14) J iang, Y.; Gong, L.; Feng, X.; Hu, W.; Pan, W.; Li, Z.; Mi, A.
Tetrahedron 1997, 53, 14327-14338.
In comparison to the known (salen)TiCl2 derivatives,
the spectral properties of 1-6 are also consistent with
six-coordinate monomeric structures containing a pseu-
doplanar salen and apical aryloxide, chloro, or OTf
ligands.8 The X-ray crystallographic analysis of 3 (vide
infra) also confirms this structural assignment. In the
1H NMR spectra of these homobisadducts the imine and
aryl proton resonances are shifted downfield by 0.1-
0.5 ppm compared to those of H2salen or H2salen*.
(15) For a series of reviews highlighting the utility of titanium
reagents or catalysts in synthesis, see: (a) Nelson S. G. Tetrahedron
Asymm. 1998, 9, 357-389. (b) Maruoka, K.; Yamamoto, H. Asymmetric
Reactions with Chiral Lewis Acid Catalysts. In Catalytic Asymmetric
Synthesis; Ojima, I., Ed.; VCH Publishers: New York, 1993; pp 413-
440. (c) Duthaler, R. O.; Hafner, A. Chem. Rev. 1992, 92, 807-832. (d)
Kagan, H. B.; Riant, O. Chem. Rev. 1992, 92, 1007-1020. (e) Mikami,
K.; Shimizu, M. Chem. Rev. 1992, 92, 1021-1050. (f) J ohnson, R. A.;
Sharpless, K. B. Catalytic Asymmetric Epoxidation of Allylic Alcohols.
In Catalytic Asymmetric Synthesis; Ojima, I., Ed.: VCH Publishers:
New York, 1993; pp 103-158. (g) Knochel, P.; Singer, R. D. Chem.
Rev. 1993, 93, 2117-2188.
(17) For several examples of Ti-OTf complexes (coordinated and
uncoordinated), see: (a) Donkervoort, J . G.; J astrzebski, J . T. B. H.;
Deelman, B.-J .; Kooijman, H.; Veldman, N.; Spek, A. L.; van Koten,
G. Organometallics 1997, 16, 4174-4184. (b) J aquith, J . B.; Levy, C.
J .; Bondar, G. V.; Wang, S.; Collins, S. Organometallics 1998, 17, 914-
925. (c) Winter, C. H.; Zhou, X.-X.; Heeg, M. J . Organometallics 1991,
10, 3799-3801.
(16) 1H NMR of Ti(salen*)(OiPr)2 (CD2Cl2): δ 8.32 (s, 2H, H-Cd
N), 7.45 (dd, J ) 8.8, 2.5 Hz, 2H, Ar), 7.30 (d, J ) 2.5 Hz, 2H, Ar), 6.67
(d, J ) 8.8 Hz, 2H, Ar), 3.99 (septet, J ) 6.3 Hz, 2H, CH), 3.96 (s, 4H,
CH2), 1.30 (s, 18H, CH3), 0.69 (d, J ) 6.3 Hz, 12H, CH3).

5360 Organometallics, Vol. 17, No. 24, 1998
Chen et al.
Ta ble 1. Selected NMR Da ta for Tita n iu m Sa len
Com p lexesa
Sch em e 1
δ p p m (1H)
δ p p m (13C)
δ p p m (19F)
compound NdC-H CH2-CH2 NdC CH2-CH2 (CF3SO3)-
H2salen
H2salen*
1
2
8.26 s 3.80 s
8.38 s 3.93 s
8.41 s 4.21 s
8.29 s 3.69 s
8.32 s 3.71 s
8.36 s 3.74 s
8.75 s 4.20 s
8.68 s 4.20 s
8.67 s 4.05 m
8.50 s 4.20/3.92 m 165.8
8.36 s 4.20/3.85 m 164.1
8.47 s 4.15 m
8.39 s 4.33/4.00 m 163.7
8.41 s 4.36/4.04 m 164.4
8.39 s 4.30/3.82 m 163.7
8.39 s 4.31/3.83 m 163.8
166.8
164.1
164.1
163.3
163.3
163.6
167.8
166.8
167.1
60.0
59.2
59.2
58.8
58.9
58.9
60.0
59.3
59.7
59.2
59.0
59.2
59.2
59.2
59.0
59.2
59.2
3
4
5b
6b
7b
8
-77.3
-80.0
-78.0
-76.0
9
10
11
12
13
14
15
165.7
-78.1b
(Scheme 1). The product 7 was isolated by solvent
removal in vacuo followed by washing with a hexane
solution containing Ti(OiPr)4. The presence of Ti(OiPr)4
effectively removed traces of water and allowed for the
isolation of product free of the µ-oxo dimer hydrolysis
product. The 1H NMR spectra of hetero bis-substituted
compounds such as 7 are diagnostic in that the bridging
methylene resonances are transformed from the singlet
observed in the symmetric complexes to a set of AA′BB′
multiplets. Consistent with a stepwise conversion of 3/4
to 5/6, the addition of a second equivalent of TMSOTf
to 7 cleanly produces 5. The ditriflate complex 5 also
proved to be synthetically useful, as reaction with 1 or
2 equiv of potassium 4-tert-butylphenolate gives 7 and
3, respectively. The ability to interconvert between 3,
5, and 7 is highlighted in Scheme 1. The complex 4
undergoes similar reactions with 1 and 2 equiv of
TMSOTf to produce Ti(salen*)(4-tert-butylphenolate)-
(OTf) (8) and 6, respectively.
The comproportionation reaction of symmetrically
disubstituted titanium(IV) salen complexes was also
found to be useful for the synthesis of heterosubstituted
complexes, as complete conversion to clean products was
generally obtained. For example, a combination of 1
and 4 in acetonitrile at room temperature produces Ti-
(salen*)(4-tert-butylphenolate)Cl (9) exclusively over the
course of 16 h (eq 5). The reactions between diarylox-
ides and ditriflates at room temperature (3 and 5 (eq 6)
or 4 and 6 (eq 7)) also result in complete conversion to
the expected comproportionation products, Ti(salen)(4-
tert-butylphenolate)(OTf) (7) and Ti(salen*)(4-tert-bu-
tylphenolate)(OTf) (8), although much quicker (min). To
the extent that 1H NMR is sensitive to exchange, a
mixture of 2 and 4 (1:1, CD2Cl2), on the other hand, did
not react over the course of 2 days. It appears that
maximization of electronic asymmetry (i.e., basicity) in
the axial ligands is the driving force for these reactions.
These observations are consistent with previous octa-
hedral Ti(IV) porphyrin comproportionation studies20
and a series of mononuclear octahedral Ti(IV) com-
plexes,21 where the weakest ligands are found to always
coordinate trans to the strongest.
8.35 s 3.68 t
164.4
a
b
Obtained in CD2Cl2 unless otherwise noted. acetonitrile-d3.
Especially diagnostic of the symmetric structure is a
methylene singlet in the 3.6-4.2 ppm region, assigned
to the four equivalent bridging methylene protons (Table
1). Although the point group symmetry of these struc-
tures requires unique pseudoaxial and -equatorial posi-
tions in the ethylene bridge, a net C2v symmetry is
observed due to a rapid interconversion of the accessible
conformers.
Complexes 1 and 2 are relatively resistant to air
hydrolysis in the solid state, but are water sensitive in
solution and form µ-oxo-bridged dinuclear complexes
that usually precipitate.18 The ditriflates (5 and 6) are
highly sensitive to moisture both in solution and in
the solid state, yielding a relatively insoluble material
which is consistent with the µ-oxo-dimeric structure [Ti-
(salen)(OTf)]2(µ2-O).19 Fortunately, treatment of the
crude mixture containing [Ti(salen)(OTf)]2(µ2-O) with
Ti(OiPr)4 breaks up the oxo-bridge and regenerates 5
as the sole Ti-salen product. In suitable cases, a small
amount of Ti(OiPr)4 in the solvents used for the pre-
cipitation and washing process helps to reduce µ-oxo
dimer formation (see Experimental Section).
Syn th esis of Un sym m etr ica lly Disu bstitu ted Ti-
ta n iu m (IV) Sa len Com p lexes. The above symmetri-
cally disubstituted titanium(IV) salen complexes are
useful precursors for the synthesis of new heterosub-
stituted products through ligand substitution and com-
proportionation. They may also be prepared by direct
reaction of H2salen with appropriate XTi(OiPr)3 precur-
sors.
The diaryloxides 3 and 4 readily react with 1 equiv
of TMSOTf to selectively produce monosubstitution
products. For example, when 3 was treated with 1 equiv
of TMSOTf in CH2Cl2, the monotriflate 7 was obtained
(18) The synthesis and characterization of oxo-bridged titanium
salen complexes have been reported: (a) Franceschi, F.; Gallo, E.;
Solari, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C.; Re, N.; Sgamellotti,
A. Chem. Eur. J . 1996, 2, 1466-1476. (b) Sasaki, C.; Nakajima, K.;
Kojima, M.; Fujita, J . Bull. Chem. Soc. J pn. 1991, 64, 1318-1324. 1H
NMR of [Ti(salen*)Cl]2(µ2-O), (CD2Cl2): δ 7.87 (s, 4H, H-CdN), 7.36
(dd, J ) 8.3, 2.0 Hz, 4H, Ar), 7.27 (d, J ) 2.0 Hz, 4H, Ar), 7.02 (d, J )
8.3 Hz, 4H, Ar), 3.88 (m, 8H, CH2), 1.37 (s, 36H, CH3).
In addition to ligand substitution reactions on pre-
formed Ti(IV)-salen precursors, a variety of hetero-
bisadducts could be synthesized from the reaction of in
situ-derived XTi(OiPr)3 precursors with H2salen and
H2salen*. For example, when Ti(OiPr)4 was pretreated
with 1 equiv of TMSOTf in CH2Cl2 followed by H2salen
(1 equiv, eq 8), a clear yellow solution was obtained.
Solvent removal in vacuo cleanly yielded complex 10,
(19) 1H NMR of [Ti(salen)(OTf)]2(µ2-O), (CD3CN/CD2Cl2 (1:1)):
δ
8.18 (s, 4H, H-CdN), 7.46 (ddd, J ) 11.2, 9.2, 2.0 Hz, 4H, Ar), 7.22
(dd, J ) 9.5, 2.0 Hz, 4H, Ar), 6.91 (dd, J ) 9.2, 1.5 Hz, 4H, Ar), 6.79
(dd, J ) 10.5, 1.5 Hz, 4H, Ar), 4.00 (brs, 8H, CH2).
1
the H NMR of which features two bridging methylene

Ti(IV)-Salen Complexes
Organometallics, Vol. 17, No. 24, 1998 5361
suggests that the initially formed Ti(salen)(OiPr)(4-tert-
butylphenolate) disproportionates to 4 and unstable Ti-
(salen)(OiPr)2 (vide supra).
The coordination geometry of titanium in these het-
erobisadducts (7-12) is undoubtedly similar to the
homobisadducts. 1H NMR spectra of those complexes
that have Cs symmetry feature two multiplets for the
two sets of chemically inequivalent bridging methylene
protons, diagnostic signatures for asymmetric apical
1
ligation. The H NMR spectra of the Ti(salen)(OiPr)X
(X ) OTf, carboxylate, and aryloxide) series of complexes
show that electron-deficient trans ligands shift the salen
and isopropoxide resonances downfield, indicating that
there is electronic communication between the ligands
on the metal (e.g., compare 1, 2, 5, 7, and 11; Table 1).
Su bstitu tion Rea ctivity of Tita n iu m (IV) Sa len
Com p lexes. When the titanium diaryloxide complex
3 is treated with acetic acid, a rapid equilibrium is
established with a new titanium complex 13 and 4-tert-
butylphenol. The 1H NMR spectrum of the reaction
mixture clearly shows the free 4-tert-butylphenol and
new methyl/tert-butyl resonances at 1.53 and 1.17 ppm,
respectively, with a carbonyl resonance at 175.8 ppm
in the 13C NMR. The combined spectroscopic analysis
suggests that 13 is the monosubstitution product Ti-
(salen)(4-tert-butylphenolate)(OC(O)CH3). More than 4
equiv of acetic acid is required for a >90% conversion
of 3 to 13. In situ monitoring of the reaction between 3
and methoxyacetic acid (1.1 equiv) in CD2Cl2 shows that
an equilibrium between the expected product Ti(salen)-
(4-tert-butylphenolate)(OC(O)CH2OCH3) (14), 3, and a
third titanium complex (presumably the disubstitution
product) is quickly established (10:1:1 respectively). The
more extensive conversion for the latter acid likely
reflects its enhanced pKa relative to acetic acid.23
Attempts to isolate 13 by the above synthetic method
were unsuccessful, as solvent removal under vacuum
selectively removed acetic acid from the system and
regenerated 3. Attempts to isolate an analytically pure
sample of 14 were frustrated by the formation of µ-oxo
dimeric complexes during workup. Unfortunately, Ti-
(OiPr)4 was found to react with 14 in a complicated
fashion.
multiplets at 4.27 and 4.02 ppm, characteristic of an
unsymmetrical axial substitution pattern. In an op-
erationally similar synthetic method, Ti(salen)(OiPr)-
(OC(O)CH3) (11) and Ti(salen)(OiPr)(OC(O)CH2OCH3)
(12) were prepared in analytically pure form by treating
Ti(OiPr)4 with the corresponding carboxylic acid, fol-
lowed by H2salen (eq 9). These heterobisadducts are
extremely moisture sensitive, and so dilute Ti(OiPr)4
solutions were used to inhibit product hydrolysis (7, 10-
12) in the workup. In addition to sequestering H2O,
Ti(OiPr)4 was also found to selectively convert any
bridging oxo-dimers present back to the mixed carboxy-
late/isopropoxide bisadducts.
The limitation of this experimental protocol was
revealed by the reaction of H2salen with in situ-derived
Ti(OiPr)3(OPhtBu). In a variety of solvents and tem-
peratures, the reaction leads to a complex mixture
containing the putative Ti(salen)(OiPr)(4-tert-butylphe-
nolate)22 and 4 as the major products. Optimized
conditions for the synthesis of the mixed isopropoxide/
phenoxide require a mixture of Ti(OiPr)4 and 4-tert-
butylphenol (0.25 equiv) in diethyl ether to be treated
with H2salen. From the resulting clear orange solution,
The titanium salen complexes 10-12 were used to
react with 1 equiv of 4-tert-butylphenol. While 10 reacts
with 4-tert-butylphenol to exclusively produce 7, the
reactions of 11 and 12 with 4-tert-butylphenol proceed
with poor chemoselectivity to ultimately yield a mixture
of the starting material, 3, and the corresponding
heterobisadducts 13 and 14. The product ratios from
these reactions are summarized in eq 10.
1
yellow crystals gradually precipitate. The H NMR of
these isolated yellow crystals (CD2Cl2) show that they
are primarily a mixture of Ti(salen)(OiPr)(4-tert-bu-
tylphenolate) and 4 (combined yield is > 90%). How-
ever, continued monitoring of this sample indicates that
the mixture is unstable since after 8 h the initial
product:4 ratio (7:1) decreases to 2.5:1. This observation
(20) Gray, S. D.; Thorman, J . L.; Berreau, L. M.; Woo, L. K. Inorg.
Chem. 1997, 36, 278-283.
(21) Gau, H., M.; Lee, C. S.; Lin, C. C.; J iang, M. K.; Ho, Y. C.; Kuo,
C. N. J . Am. Chem. Soc. 1996, 118, 2936-2941.
(22) 1H NMR of Ti(salen)(OiPr)(4-tert-butylphenolate) (CD2Cl2): δ
8.33 (s, 2H, H-CdN), 7.46 (m, 4H, Ar), 6.91 (m, 4H, Ar), 6.86 (d, J )
8.8 Hz, 2H, Ar), 5.99 (d, J ) 8.8 Hz, 2H, Ar), 4.23 (septet, J ) 6.3 Hz,
1H, CH), 3.90 (m, 2H, CH2), 3.77 (m, 2H, CH2), 1.14 (s, 9H, CH3), 0.81
(d, J ) 6.3 Hz, 6H, CH3).
Ti(salen)(4-tert-butylphenolate)(OTf) (7) reacts with
sodium acetate to produce 13 as the major species and
(23) Bordwell F. G. Acc. Chem. Res. 1988, 21, 456-463.

5362 Organometallics, Vol. 17, No. 24, 1998
Chen et al.
Ta ble 2. Cr ysta llogr a p h ic Da ta a n d Collection
P a r a m eter s for 3
compound
Ti(salen)(4-tert-butylphenolate)2
formula
molecular weight, g/mmol
C36H40N2O4Ti
612.62
color, habit
cryst size, mm
cryst system
space group
a, Å
orange red, crystal
0.40 × 0.30 × 0.20
orthorhombic
Fd2d
15.5667(7)
17.8314(8)
69.531(3)
19300.1(15)
24
b, Å
c, Å
V, Å3
Z
3
Dc, g/cm
1.265
diffractometer
F(000)
radiation
µ, mm-1
T, °C
scan mode
data collected
2θmax, deg
total no. of rflns
no. of unique reflns
no. of rflns with I > 3.0σ(I)
Rmerge
Siemens SMART
7786.93
MoKR (0.710 73)
0.31
-100
Ω
(h, (k, (l
50.0
39 580
8537
F igu r e 1. ORTEP drawings and atom-numbering scheme
for 3.
several unidentified byproducts. In contrast, reactions
with sodium or potassium aryloxide salts cleanly pro-
duce the monosubstitution products by elimination of
NaOTf or KOTf (Scheme 1). For example, 7 reacts with
sodium 3,5-dimethylphenoxide to give a new titanium
complex Ti(salen)(4-tert-butylphenolate)(3,5-dimeth-
7852
0.034
no. of variables
582
0.045
0.049
2.75
0.001
-0.340, 0.510
a
Rf
b
Rw
GoFc
1
ylphenolate) (15). The H NMR of this complex (CD2-
max ∆/σ
residual density, e/Å3
Cl2) surprisingly shows a singlet (albeit broadened) for
the methylene bridge, indicating that although hetero-
disubstituted, the two faces are chemically similar.
When the neutral nucleophiles pyridine and SMe2
were combined with 7, no triflate displacement reactions
a
b
2 1/2
c GoF
] . )
Rf ) ∑(Fo-Fc)/∑Fo. Rf ) [∑w(Fo-Fc)2/∑wFo
[∑w(Fo-Fc)2/(n-p)]1/2, where n ) number of reflections and p )
number of parameters.
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 3a
1
were observed. The H NMR spectrum of a mixture of
7 and PPh3 does show broadened phenyl and bridging
methylene resonances; however, starting material is
recovered upon precipitation with hexanes. A compari-
son of the 19F NMR spectra of 7 in the presence and
absence of PPh3 shows no observable shift in the fluorine
resonance, suggesting weak binding at best.
Molecule 1b
1.899(2) O(1)-Ti(1)-O′(21)
2.159(2) N(3)-Ti(1)-N′(3)
1.862(2) N(3)-Ti(1)-O(21)
Ti(1)-O(1)
Ti(1)-N(3)
Ti(1)-O(21)
94.07(9)
75.30(11)
87.30(9)
88.54(9)
88.54(9)
O(1)-Ti(1)-O′(1) 114.94(9)
N(3)-Ti(1)-O′(21)
O(1)-Ti(1)-N(3) 84.90(10) N(3)′-Ti(1)-O(21)
O(1)-Ti(1)-N′(3) 160.12(10) O(21)-Ti(1)-O′(21) 174.74(8)
Cr ysta l a n d Molecu la r Str u ctu r e of Ti(sa len )(4-
ter t-bu tylp h en ola te)2 (3). Orange-red crystals of 3
suitable for X-ray diffraction studies were grown at room
temperature under N2 from a saturated solution of CH2-
Cl2/Et2O (1:1) with slow diffusion of hexanes. Two
independent molecules of 3 were found in the ortho-
rhombic unit cell. ORTEP drawings and the numbering
schemes for the two molecules are shown in Figure 1.
Structure acquisition data and selected bond distances
and angles are listed in Tables 2 and 3, respectively.
The two structures are rather similar, with the main
distinction being that molecule 1 has crystallographic
O(1)-Ti(1)-O(21)
88.76(8)
Ti(1)-O(21)-C(21) 156.8(2)
Molecule 2
Ti(2)-O(31)
Ti(2)-N(33)
Ti(2)-N(36)
Ti(2)-O(38)
Ti(2)-O(61)
Ti(2)-O(71)
O(31)-Ti(2)-N(33)
1.889(2) O(31)-Ti(2)-O(71)
2.147(2) N(33)-Ti(2)-N(36)
2.168(2) N(33)-Ti(2)-O(38) 161.14(8)
1.884(2) N(33)-Ti(2)-O(61)
1.867(2) N(33)-Ti(2)-O(71)
1.870(2) O(38)-Ti(2)-O(71)
87.26(8)
75.27(8)
87.24(8)
86.59(8)
93.29(9)
84.71(8)
O(61)-Ti(2)-O(71) 172.44(9)
Ti(2)-O(61)-C(61) 159.6(2)
Ti(2)-O(71)-C(71) 153.9(2)
O(31)-Ti(2)-N(36) 159.12(8)
O(31)-Ti(2)-O(38) 114.13(8)
O(31)-Ti(2)-O(61)
96.51(8)
a
The number in parentheses is the standard deviation and
b
1
C2 symmetry24 while molecule 2 is asymmetric. A H
refers to the last significant digit. The ′ symbol refers to the
symmetry equivalent atom related by a crystallographic 2-fold.
NMR spectrum of the orange-red crystals indicates a
single species with C2v symmetry, suggesting that
molecules 1 and 2 simply represent accessible, dynamic
conformers of 3.
In both molecules, the coordination around titanium
is best described as a distorted octahedron with the
titanium atom lying in the plane of the N2O2 core with
short Ti-O bond lengths (∼1.89 Å) and longer Ti-N
bonds (∼2.16 Å), Table 3. The two aryloxide ligands
are bound to the Ti(salen) moiety in a trans arrange-
ment (O(21)-Ti(1)-O′(21) ) 174.74(8)°), with the two
axial Ti-O bonds not quite orthogonal to the N2O2
plane and slightly bent toward the imine nitrogens. A
comparison of the metrical parameters for the two
molecules indicates that aside from conformation, mol-
ecules 1 and 2 have similar bond lengths. In both
molecules the aromatic portion of the salen ligand is
canted above and below the TiO2N2 square plane,
symmetrically (necessarily) for molecule 1 and asym-
metrically for molecule 2.
(24) As indicated by several large thermal parameters in the tert-
butyl groups of this molecule, disorder was observed in these positions.
Attempts to resolve the disorder using isotropic partially occupied
carbon atoms did not give rise to fits that were chemically any more
reasonable than the anisotropic model.

Ti(IV)-Salen Complexes
Discu ssion
Organometallics, Vol. 17, No. 24, 1998 5363
is restricted to systems that can readily associate to
facilitate ligand exchange (e.g., four-coordinate) or that
can dissociate a ligand to open up a coordination site
on the metal for facilitating the transfer. The rapidity
with which complexes 5 and 6 comproportionate sug-
gests that dissociation of the OTf ligand is possible,29
as the formation of bridged intermediates is not likely
given the steric saturation of each Ti center. An
example of a Ti-OTf complex that does not dissociate
OTf was found to also not participate in comproportion-
ation reactions.17a The inability of neutral ligands such
as phosphines and pyridines to coordinate to 5 and 6
suggests that if the triflate does dissociate, the ion pair
is not especially stable. Since comproportionation activ-
ity was also found to occur with dichlorides and di-
aryloxides, but not with two sets of diaryloxides, sug-
gests that chloride ligands may also access ion-paired
intermediates (albeit slowly), but that aryloxide ligands
cannot.
The facility of axial ligand substitution in the de-
scribed Ti-salen complexes is primarily dictated by the
acidity of the incoming ligand relative to the outgoing
ligand, with isopropoxide being the easiest to remove
and triflate being the easiest to add (OiPr < OAr < OC-
(O)R < OTf). For nonoxygenated ligands the substitu-
tion potential is more complex since, for example, 3 does
not react with N-benzyltriflamide (PhCH2NH-SO2CF3)
even though the sulfonamide is more acidic than phenol
by 7 orders of magnitude (pKa ) ∼11 and pKa ) 18.4 in
DMSO, respectively).23 The attenuated π-basicity of
this nitrogen ligand almost certainly contributes to its
low stability.
Salen ligands have been a source of interest for
inorganic and organic chemists due to their ability to
support catalytically active metal complexes while
providing electronically and sterically tunable structural
features.1-8,25 Despite the potential utility of these
ligands for modifying the reactivity and selectivity of
titanium Lewis acid catalysts, little work has appeared
regarding the synthesis and structure of Ti-salen
coordination complexes. In the present study, Ti(OiPr)4
and several mixed titanium isopropoxides have been
used as precursors for the synthesis of a family of new
six-coordinate Ti(IV)(salen) complexes.
The in situ generation of functional equivalents of Ti-
(OiPr)2(OAr)2 and Ti(OiPr)2(OTf)2 from Ti(OiPr)4 plus
HOAr and TMSOTf, respectively, followed by reaction
with H2salen(*), offers a convenient and high yielding
route to symmetrically disubstituted Ti(IV)salen com-
plexes (2-6). It is known that the reaction of phenols
with Ti(OiPr)4 requires azeotropic removal of 2-propanol
for the synthesis of (ArO)2Ti(OiPr)2-type complexes.26
This suggests that Ti(OiPr)4 reacts first with H2salen-
(*) to access (salen)Ti(OiPr)2 and that this intermediate
gets trapped with ArOH. For the synthesis of mixed
acetoxy/isopropoxy complexes (11, 12) from in situ-
generated Ti(OiPr)3OC(O)R, a similar mechanistic pic-
ture unfolds, as the reported syntheses of the titanium
carboxylates (e.g., Ti(OiPr)3(OAc)),27 require reflux con-
ditions for the azeotropic removal of 2-propanol.
The stepwise addition of TMSOTf and H2salen(*), on
the other hand, is on slightly better mechanistic footing,
as in situ monitoring of the addition of 1 equiv of
TMSOTf to Ti(OiPr)4 (CD3CN) quickly generates 1 equiv
of TMSOiPr and a new Ti-isopropoxide whose methine
resonance shifts downfield by 0.55 ppm relative to Ti-
(OiPr)4. This observation suggests that the TMSOTf
initially reacts with the starting material to form a
species with the composition Ti(OiPr)3OTf, and it is this
species that reacts with H2salen(*) to yield 10. Simi-
larly, the reaction of Ti(OiPr)4 and 2 equiv of TMSOTf
results in the rapid formation of 2 equiv of TMSOiPr
and a new Ti-isopropoxide. The methine resonance of
this new species shifts 0.65 ppm downfield of Ti(OiPr)4,
consistent with a substantial net reduction in electron
density at the Ti center. The direct reaction of this
ditriflate complex with H2salen(*) is the most likely
pathway to compounds 5 and 6. The driving force for
formation of a Ti-OTf bond is noteworthy in these
complexes, as the ditriflates are also accessible from the
reaction of the diaryloxides with TMSOTf, or dichlorides
with TMSOTf or AgOTf.
To our knowledge, 3 represents the first structurally
characterized transition metal salen complex containing
two trans aryloxide ligands. Five-coordinate monoary-
loxide metal salen complexes are known for Al(III) and
Fe(III), with these complexes adopting a square-
pyramidal geometry with the metal residing above the
N2O2 plane and with an axial aryloxide.30 Titanium-
(IV) complexes prefer to adopt the more rigid octahedral
geometry, and thus the bond angles around titanium
and the four coordinating atoms in the salen ligand are
10a
in good agreement with Ti(salen)Cl2
and Ti(salen)-
Me2.11b A comparison of the Ti-O and Ti-N bond
lengths in the salen ligands of the three compounds
highlighted in Table 4 clearly shows that the axial
ligands have a significant effect on the Ti-O bond
lengths and a moderate effect on the Ti-N bond lengths.
The enhanced σ- and π-donating ability of the aryloxy
ligands in 3, and to a lesser extent the chloride ligands
in Ti(salen)Cl2, accounts for the lengthened Ti-O and
Ti-N bonds.31,32 In addition to trends in the bond
The comproportionation reactivity noted herein (eqs
5-7) has also been observed in several TiX4 (X ) OAr,
OiPr, NR2, and Cl)28 and six-coordinate titanium por-
phyrin complexes ((tetraphenylporphyrin)TiX2; X ) Cl,
NPh2, OPh, OMe, OtBu).20 In general, this reactivity
(28) (a) Encyclopedia of Organic Reagents; Paquette, L. A., Ed.; J ohn
Wiley and Sons: Chichester, 1995; Vol. 3, pp 1732-1733. (b) Renziger,
E.; Kornicker, W. Chem. Ber. 1961, 94, 3-2267. (c) Armistead, L. T.;
White, P. W.; Gagne´, M. R. Organometallics 1998, 17, 216-220.
(29) The availability of a coordinatively unsaturated cationic Ti
center suggests that these complexes might act as efficient Lewis acid
catalysts in organic synthesis. Experiments to address this issue are
currently under way.
(30) (a) Gurian, P. L.; Cheatham, L. K.; Ziller, J . W.; Barron, A. R.
J . Chem. Soc., Dalton Trans. 1991, 1449-1456. (b) Heistand, R. H.;
Roe, A. L.; Que, L., J r. Inorg. Chem. 1982, 21, 676-681.
(31) For the effect of dπ-pπ bonding in Ti-aryloxide complexes,
see: (a) Latesky, S. L.; Keddington, J .; McMullen, A. K.; Rothwell, I.
P. Inorg. Chem. 1985, 24, 995-1001. (b) Durfee, L. D.; Latesky, S. L.;
Rothwell, I. P.; Huffman, J . C.; Folting, K. Inorg. Chem. 1985, 24,
45669-4573.
(25) Palucki, M.; Finney, N. S.; Pospisil, P. J .; Gu¨ler, M. L.; Ishida,
T.; J acobsen, E. N. J . Am. Chem. Soc. 1998, 120, 948-954.
(26) (a) Shah, A.; Singh, A.; Mehrotra, R. C. Ind. J . Chem. 1993,
32A, 632-635. (b) Malhotra, K. C.; Martin, R. L. J . Organomet. Chem.
1982, 239, 159-187.
(27) (a) Riman, R. E.; Landham, R. R.; Bowen, H. K. J . Am. Ceram.
Soc. 1989, 821-826. (b) Saxena, A. K.; Rai. A. K. Synth. React. Inorg.
Mater.-Org. Chem. 1990, 21-37. (c) Alcock, N. W.; Brown, D. A.; Illson,
T. F.; Roe, S. M.; Wallbridge, M. G. H. J . Chem. Soc., Dalton Trans.
1991, 873-881.

5364 Organometallics, Vol. 17, No. 24, 1998
Chen et al.
Ta ble 4. Metr ica l P a r a m eter s for th e Th r ee
Kn ow n Ti(sa len ) Sym m etr ica lly Disu bstitu ted
Com p lexes
Deuterated solvents (CD2Cl2 and CD3CN) were vacuum trans-
ferred from CaH2 and degassed via several freeze-pump-
thaw cycles prior to use. Air and moisture sensitive reagents
were handled using standard syringe techniques or in the
glovebox. N,N′-Ethylenebis(5-tert-butylsalicylideneimine) was
prepared according to a literature procedure.34 Triethylamine
was distilled from CaH2, while all the other reagents were used
as received except that they were deoxygenated prior to use.
Sodium acetate was dried under high vacuum at 100 °C for
10 h prior to use.
3,
3,
a
b
Ti(salen)Me2 Ti(salen)Cl2 molecule 1 molecule 2
Distances (Å)
Ti-O
Ti-O′
Ti-N
Ti-N′
1.829(11)
1.864(10)
2.142(14)
2.153(15)
1.835(5)
1.835(5)
2.141(5)
2.141(5)
1.899(2)
1.899(2)
2.159(2)
2.159(2)
1.889(2)
1.884(2)
2.147(2)
2.168(2)
Routine 1H NMR spectra were recorded at ambient tem-
perature on a Brucker AC200 spectrometer (200 MHz, 1H
NMR) or a Brucker MW250 spectrometer (250 MHz, 1H NMR)
unless otherwise noted. Routine 13C NMR spectra were
recorded at ambient temperature on a Brucker AC200 spec-
trometer (50 MHz, 13C NMR) or a Varian Gemini 2000
spectrometer (75 MHz, 13C NMR) unless otherwise noted.
Chemical shifts are recorded in ppm and are referenced to
residual solvent peaks. All 19F NMR spectra were recorded
on a Varian Gemini 2000 spectrometer (288 MHz, 19F NMR)
with either C6F6 as external reference in CD2Cl2 or CFCl3 as
external reference in CD3CN. E+R Microanalytical Labora-
tory Inc., Corona, New York, performed elemental analyses.
For completeness, the 1H NMR data for Ti(salen)Cl2 are
presented here.10a,b 1H NMR (CD2Cl2): δ 8.42 (s, 2H, H-Cd
N), 7.63 (m, 2H, Ar), 7.60 (m, 2H, Ar), 7.14 (dd, 2H, Ar), 6.84
(dd, 2H, Ar), 4.22 (s, 4H, CH2).
Angles (deg)
113.2(2)
85.4(2)
O-Ti-O′
O-Ti-N
N-Ti-N′
O′-Ti-N′
110.9(4)
86.5(5)
76.5(6)
86.1(5)
114.94(9) 114.13(8)
84.9(1)
75.3(1)
84.9(1)
84.7(2)
75.27(8)
85.9(2)
76.1(2)
85.4(2)
a
b
Reference 10b. Reference 9a.
lengths, the axial ligands in each of the compounds are
distorted toward the nitrogen ligands with the C-Ti-C
(154.9°), Cl-Ti-Cl (168.7°), and O-Ti-O angles (174.7°
and 172.4°) tracking with both π-basicity and size of the
axial ligands. Although the in-plane Ti-N bond lengths
are substantially longer than the Ti-O bond lengths of
the salen, the cause of the axial distortion is not
completely obvious.
Ti(sa len *)Cl2 (1). A solution of TiCl4‚2THF (605 mg, 1.81
mmol) in THF (8 mL) was added slowly to a solution of H2-
salen* (695 mg, 1.83 mmol) in THF (7 mL), resulting in a red
solution. The reaction mixture was stirred and refluxed at
70 °C for 1 h, then cooled to ambient temperature, and
concentrated in vacuo to dryness. The orange-brown solid was
slurried with Et2O (20 mL), filtered through a fine-fritted
funnel, washed with additional Et2O, and dried under high
vacuum at 80 °C for 2 h. Yield of orange-brown solid: 897
mg (1.80 mmol, 99%). 1H NMR (CD2Cl2): δ 8.41 (s, 2H, H-Cd
N), 7.64 (dd, J ) 9.0, 2.5 Hz, 2H, Ar), 7.54 (d, J ) 2.5 Hz, 2H,
Ar), 6.76 (d, J ) 9.0 Hz, 2H, Ar), 4.21 (s, 4H, CH2), 1.35 (s,
18H, CH3). 13C NMR (CD2Cl2): δ 164.1 (CdN), 160.8, 146.4,
134.4, 131.8, 125.0, 115.9, 59.2 (CH2), 34.7 (C(CH3)3), 31.4
(CH3). Anal. Calcd for C24H30Cl2N2O2Ti: C, 57.96; H, 6.08;
N, 5.63. Found: C, 57.74; H, 6.30; N, 5.44.
Ti(sa len )(OP h )2 (2). A CH2Cl2 solution (1 mL) of Ti(Oi-
Pr)4 (60.7 mg, 0.203 mmol) was combined with a CH2Cl2
solution (1 mL) of PhOH (38.0 mg, 0.404 mmol), resulting in
a yellow solution. To this reaction mixture was added H2salen
(54.8 mg, 0.204 mmol) in CH2Cl2 (1.5 mL), producing an
orange-yellow solution. After 5 min, the reaction mixture was
concentrated in vacuo to dryness. The solid was slurried with
hexanes (10 mL), filtered through a fine-fritted funnel, washed
with additional hexanes, and dried under high vacuum at 80
°C for 1 h. Yield of orange-yellow solid: 90.2 mg (0.180 mmol,
89%). 1H NMR (CD2Cl2): δ 8.29 (s, 2H, H-CdN), 7.52 (m,
4H, Ar), 6.92 (m, 8H, Ar), 6.59 (t, J ) 7.0 Hz, 2H, Ar), 6.23 (d,
J ) 7.5 Hz, 4H, Ar), 3.69 (s, 4H, CH2). 13C NMR (CD2Cl2): δ
165.9, 164.6, 163.3 (CdN), 136.4, 134.5, 129.1, 123.7, 119.6,
119.5, 118.6, 118.0, 58.8 (CH2). Anal. Calcd for C28H24N2O4-
Ti: C, 67.21; H, 4.83; N, 5.60. Found: C, 67.41; H, 4.86; N,
5.59.
Su m m a r y
In this study we have demonstrated that a variety of
six-coordinate Ti-salen complexes can be synthesized
by (1) direct reaction of H2salen with several Ti(OiPr)2X2
and Ti(OiPr)3X functional equivalents, (2) ligand sub-
stitution on preformed Ti(salen)X2 complexes, and (3)
comproportionation reaction of two homobis-substituted
Ti(salen)X2 complexes. These products were fully char-
acterized by H and 13C NMR spectroscopy, and each
1
was consistent with an octahedral titanium center
containing a pseudoplanar four-coordinate salen ligand
and two axially coordinated ligands. The X-ray struc-
ture of 3 confirmed this assignment. The reactivity of
several symmetrically and unsymmetrically disubsti-
tuted complexes toward axial substitution was found to
be primarily dominated by the acidity of the involved
oxygen ligands, but that non-oxygen ligands did not
necessarily follow this trend. These results underpin
future studies utilizing chiral Ti(IV)-salen complexes
as chiral Lewis acid catalysts for a variety of organic
transformations.
Exp er im en ta l Section
Abbr evia tion s. Salen ) N,N′-ethylenebis(salicylideneimi-
nate); salen* ) N,N′-ethylenebis(5-tert-butylsalicylideneimi-
-
nate); OTf ) CF3SO3
.
Gen er a l P r oced u r es. All reactions were conducted under
an atmosphere of dry, oxygen-free nitrogen or argon using
standard Schlenk techniques or in a Vacuum Atmospheres Co.
glovebox. All solvents except THF (CH2Cl2, hexanes, diethyl
ether, and pentane) were dried by running through a column
of activated alumina.33 THF was refluxed for at least 8 h over
sodium/benzophenone and freshly distilled. The dry solvents
were freeze-pump-thaw degassed and stored in the glovebox.
Ti(sa len )(4-ter t-bu tylp h en ola te)2 (3). A CH2Cl2 solution
(1 mL) of Ti(OiPr)4 (563 mg, 1.98 mmol) was combined with a
CH2Cl2 solution (3 mL) of 4-tert-butyl-PhOH (636 mg, 4.23
mmol), resulting in a yellow solution. To this reaction mixture
was added H2salen (509 mg, 1.90 mmol) in CH2Cl2 (3.5 mL),
producing an orange solution. After 10 min, the contents were
concentrated in vacuo to dryness. The solid was slurried with
hexanes (10 mL), filtered through a medium-fritted funnel,
(32) For a discussion of the problems associated with utilizing the
C-O-Ti bond angle in early transition metal aryloxide complexes as
a probe for the magnitude of dπ-pπ bonding, see: Steffey, B. D.;
Fanwick, P. E.; Rothwell, I. P. Polyhedron 1990, 9, 963-968.
(33) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, K. R.;
Timmers, F. Organometallics 1996, 15, 1518-1520.
(34) Kerr, J . M.; Sucking, C. J .; Bamfield, P. J . Chem. Soc., Perkin
Trans. 1 1990, 887.

Ti(IV)-Salen Complexes
Organometallics, Vol. 17, No. 24, 1998 5365
washed with additional hexanes (3 × 5 mL), and dried under
high vacuum at 100 °C for 3 h. Yield of orange solid: 1.113 g
(1.82 mmol, 92%). 1H NMR (CD2Cl2): δ 8.32 (s, 2H, H-Cd
N), 7.53 (m, 4H, Ar), 6.98 (m, 4H, Ar), 6.94 (m, 4H, Ar), 6.15
(m, 4H, Ar), 3.71 (s, 4H, CH2), 1.16 (s, 18H, CH3). 13C NMR
(CD2Cl2): δ 165.0, 164.0, 163.3 (CdN), 142.2, 136.3, 134.5,
125.9, 123.8, 119.4, 118.2, 118.0, 58.9 (CH2), 34.3 (C(CH3)3),
31.8 (CH3). Anal. Calcd for C36H40N2O4Ti: C, 70.58; H, 6.58;
N, 4.57. Found: C, 70.60; H, 6.57; N, 4.61.
Ti(sa len *)(4-ter t-bu tylp h en ola te)2 (4). A CH2Cl2 solution
(2.5 mL) of Ti(OiPr)4 (204 mg, 0.682 mmol) was combined with
a CH2Cl2 solution (3 mL) of 4-tert-butyl-PhOH (206 mg, 1.372
mmol) to yield a clear yellow solution. To this was added
H2salen* (259 mg, 0.681 mmol) in CH2Cl2 (4.5 mL), producing
an orange-red solution, which after 10 min was concentrated
in vacuo to dryness. The solids were slurried with hexanes
(10 mL), filtered through a fine-fritted funnel, washed with
additional hexanes (3 × 5 mL), and dried under high vacuum
at 100 °C for 3 h. Yield of orange solid: 439 mg (0.605 mmol,
89%). 1H NMR (CD2Cl2): δ 8.36 (s, 2H, H-CdN), 7.63 (dd, J
) 8.8, 2.4 Hz, 2H, Ar), 7.50 (d, J ) 2.4 Hz, 2H, Ar), 6.98
(dd, J ) 6.8, 2.0 Hz, 4H, Ar), 6.87 (d, J ) 8.8 Hz, 2H, Ar), 6.20
(dd, J ) 6.8, 2.0 Hz, 4H, Ar), 3.74 (s, 4H, CH2), 1.41 (s, 18H,
CH3), 1.22 (s, 18H, CH3). 13C NMR (CD2Cl2): δ 164.0, 163.6
(CdN), 162.9, 142.2, 141.9, 133.9, 130.7, 125.7, 123.1, 117.9,
117.5, 58.9 (CH2), 34.4 (C(CH3)3), 34.2 (C(CH3)3), 31.8 (CH3),
31.6 (CH3). Anal. Calcd for C44H56N2O4Ti: C, 72.91; H, 7.79;
N, 3.86. Found: C, 72.65; H, 7.93; N, 4.01.
Ti(sa len )(OTf)2 (5). Upon the addition of TMSOTf (125.3
mg, 0.564 mmol) to a concentrated solution of 3 (164.0 mg,
0.268 mmol) in CH2Cl2 (3 mL) a black-brown solid precipitated
from the solution. The resulting slurry was filtered through
a fine-fritted funnel, washed with CH2Cl2, and dried in vacuo.
Yield of black-brown solid: 149.0 mg (0.243 mmol, 91%). 1H
NMR (CD3CN): δ 8.75 (s, 2H, H-CdN), 7.71 (m, 4H, Ar), 7.25
(t, J ) 7.5 Hz, 2H, Ar), 6.80 (d, J ) 8.0 Hz, 2H, Ar), 4.20 (s,
4H, CH2). 13C NMR (CD3CN): δ 167.8 (CdN), 162.5, 138.6,
136.7, 125.8, ∼118 (aryl carbon resonance overlap with the
solvent peak), 60.0 (CH2), the CF3 quartet was not observed
due to the product’s low solubility in CD3CN. 19F NMR (282.88
MHz, CD3CN): δ -77.3 (s). Anal. Calcd for C18H14F6N2O8S2-
Ti: C, 35.31; H, 2.30; N, 4.57. Found: C, 35.42; H, 2.27; N,
4.43.
NMR (CD3CN, 100 MHz): δ 167.1 (2CdN), 166.0, 163.5, 147.2,
137.8, 136.0, 126.9, 124.4, 122.5, 117.5, 117.1, 59.7 (CH2), 34.9
(C(CH3)3), 31.6 (CH3), the CF3 quartet was not observed due
to the product’s low solubility in CD3CN. 19F NMR (282.88
MHz, CD3CN): δ -78.0 (s). Anal. Calcd for C27H27F3N2O6-
STi: C, 52.95; H, 4.44; N, 4.57. Found: C, 52.96; H, 4.58; N,
4.44.
Ti(sa len *)(4-ter t-bu tylp h en ola te)(OTf) (8). The tita-
nium complex 9 (122 mg, 0.199 mmol) was dissolved in CH2-
Cl2 (2 mL), and to it was added an acetonitrile (1.5 mL)
solution of AgOTf (52.2 mg, 0.203 mmol), causing a pale white
solid to precipitate. The resulting slurry was filtered through
a fine-fritted funnel, and the orange-red filtrate concentrated
in vacuo to dryness. Yield of red-brown solid: 95.3 mg (0.132
mmol, 66%). 1H NMR (CD2Cl2): δ 8.50 (s, 2H, H-CdN), 7.66
(dd, J ) 8.6, 2.4 Hz, 2H, Ar), 7.54 (d, J ) 2.4 Hz, 2H, Ar), 7.07
(d, J ) 8.6 Hz, 2H, Ar), 6.84 (d, J ) 8.6 Hz, 2H, Ar), 6.43 (d,
J ) 8.6 Hz, 2H, Ar), 4.20 (m, 2H, CH2), 3.92 (m, 2H, CH2),
1.37 (s, 18H, CH3), 1.20 (s, 9H, CH3). 13C NMR (CD2Cl2): δ
165.8 (2CdN), 165.0, 161.7, 146.2, 144.5, 134.8, 131.2, 126.1,
123.1, 117.0, 116.4, 59.2 (CH2), 34.5 (C(CH3)3), 31.5 (CH3), 31.4
(CH3), the CF3 quartet was not observed due to the product’s
low solubility in CD2Cl2. 19F NMR (282.88 MHz, CD2Cl2): δ
-76.0 (s). Anal. Calcd for C35H43F3N2O6STi: C, 58.01; H, 5.98;
N, 3.87. Found: C, 57.81; H, 5.85; N, 3.88. 8 can also be
prepared cleanly by the comproportionation of 4 and 6.
Ti(sa len *)(4-ter t-bu tylp h en ola te)Cl (9). A Schlenk flask
was charged with 1 (166 mg, 0.333 mol) and 4 (241 mg, 0.332
mmol). Dichloromethane (4 mL) was added, producing an
intense orange-red solution that was stirred for 16 h at
ambient temperature and then concentrated in vacuo to
dryness. The solid was slurried with hexanes (2 mL × 5),
filtered through a fine-fritted funnel, washed, and dried in
vacuo. Yield of dark tan solid: 358 mg (0.587 mmol, 88%).
1H NMR (CD2Cl2): δ 8.36 (s, 2H, H-CdN), 7.63 (dd, J ) 8.7,
2.6 Hz, 2H, Ar), 7.49 (d, J ) 2.6 Hz, 2H, Ar), 7.02 (d, J ) 8.7
Hz, 2H, Ar), 6.81 (d, J ) 8.7 Hz, 2H, Ar), 6.32 (d, J ) 8.7 Hz,
2H, Ar), 4.20 (m, 2H, CH2), 3.85 (m, 2H, CH2), 1.36 (s, 18H,
CH3), 1.18 (s, 9H, CH3). 13C NMR (CD2Cl2): δ 164.8, 164.1
(2CdN), 161.9, 144.6, 143.9, 134.2, 131.1, 126.0, 123.6 117.5,
116.7, 59.0 (CH2), 34.5 (C(CH3)3), 34.4 (C(CH3)3), 31.6 (CH3),
31.5 (CH3). Anal. Calcd for C34H43ClN2O3Ti: C, 66.83; H, 7.09;
N, 4.58. Found: C, 66.77; H, 7.08; N, 4.38.
Ti(sa len *)(OTf)2 (6). To a solution of 1 (83.4 mg, 0.168
mmol) in CH2Cl2 (1.5 mL) was added an acetonitrile solution
(7 mL) of AgOTf (89.4 mg, 0.0506 mL), producing a pale white
precipitate. The dark red slurry was filtered through a fine
fritted funnel, and the filtrate was concentrated to dryness.
The solid was triturated with CH2Cl2 to remove acetonitrile,
and the resulting solid isolated. Yield of black-brown solid:
82.5 mg (0.114 mmol, 68%). 1H NMR (CD3CN): δ 8.68 (s, 2H,
H-CdN), 7.74 (dd, J ) 9.0, 2.4 Hz, 2H, Ar), 7.69 (d, J ) 2.4
Hz, 2H, Ar), 6.70 (d, J ) 9.0 Hz, 2H, Ar), 4.20 (s, 4H, CH2),
1.33 (s, 18H, CH3). 13C NMR (75 MHz, CD3CN): δ 166.8 (2Cd
N), 160.6, 148.3, 135.6, 132.3, 124.6, 115.2, 59.3 (CH2), 34.8
(C(CH3)3), 31.2 (CH3), the CF3 quartet was not observed due
to the product’s low solubility in CD3CN. 19F NMR (282.88
MHz, CD3CN): δ -80.0 (s). Anal. Calcd for C26H30F6N2O8S2-
Ti: C, 43.10; H, 4.17; N, 3.87. Found: C 42.99; H, 4.17; N,
3.93.
Ti(sa len )(4-ter t-bu tylp h en ola te)(OTf) (7). The titanium
complex 3 (57.6 mg, 0.0940 mol) was dissolved in CH2Cl2 (1.1
mL), and to it was added a solution of 5 (57.9 mg, 0.0945 mmol)
in acetonitrile (0.8 mL). After stirring for 5 min, the solution
was concentrated in vacuo to dryness. The resulting red oil
was triturated with CH2Cl2, to yield 76.6 mg (0.125 mmol, 66%)
of a crystalline golden solid. 1H NMR (CD3CN, 400 MHz): δ
8.67 (s, 2H, H-CdN), 7.66 (dd, J ) 7.6, 1.6 Hz, 2H, Ar), 7.62
(td, J ) 7.6, 1.6 Hz, 2H, Ar), 7.11 (d, J ) 6.8 Hz, 2H, Ar), 7.09
(d, J ) 8.8 Hz, 2H, Ar), 6.84 (d, J ) 6.8 Hz, 2H, Ar), 6.44 (d,
J ) 8.8 Hz, 2H, Ar), 4.05 (m, 4H, CH2), 1.16 (s, 9H, CH3). 13C
Ti(sa len )(OiP r )(OTf) (10). A solution of Ti(OiPr)4 (239.7
mg, 0.818 mmol) in CH2Cl2 (0.9 mL) was combined with a
solution of TMSOTf (176.4 mg, 0.794 mmol) in CH2Cl2 (0.9
mL). To this mixture was added H2salen (218 mg, 0.813 mmol)
in CH2Cl2 (0.6 mL), producing a clear yellow solution which
after 2 min, was concentrated in vacuo to dryness. The
resulting solid was slurried with a solution of Ti(OiPr)4 (209
mg) in hexanes (6 mL), filtered through a fine-fritted funnel,
washed with a diethyl ether solution of Ti(OiPr)4, and dried
under high vacuum at 80 °C for 10 h. Yield of yellow solid:
372.4 mg (0.674 mmol, 85%). 1H NMR (CD2Cl2): δ 8.47 (s,
2H, H-CdN), 7.56 (m, 4H, Ar), 7.01 (td, J ) 7.0, 1.2 Hz, 2H,
Ar), 6.86 (dd, J ) 8.2, 1.2 Hz, 2H, Ar), 4.66 (septet, J ) 6.4
Hz, 1H, CH), 4.15 (m, 4H, CH2), 1.01 (d, J ) 6.4 Hz, 6H, CH3).
13C NMR (CD2Cl2): δ 165.7 (CdN), 163.8, 137.0, 134.8, 123.1,
120.6, 119.8 (q, J CF ) 319 Hz), 117.2, 85.5 (CH), 59.2 (CH2),
24.8 (CH3). 19F NMR (282.88 MHz, CD3CN): δ -78.1 (s).
Anal. Calcd for C22H21F3N2O6STi: C, 45.99; H, 4.05; N, 5.36.
Found: C, 46.08; H, 4.04; N, 5.47.
Ti(sa len )(OiP r )(OC(O)CH3) (11). A solution of Ti(OiPr)4
(117 mg, 0.385 mmol) in CH2Cl2 (0.5 mL) was combined with
a solution of acetic acid (35.7 mg, 0.595 mmol) in CH2Cl2 (0.6
mL). To this mixture was added H2salen (82.4 mg, 0.307
mmol) in CH2Cl2 (0.4 mL) and after 2 min was concentrated
in vacuo to dryness. The solid was slurried first by a solution
of Ti(OiPr)4 (280 mg) in Et2O (3 mL) and then by a hexanes
solution (5 mL) of Ti(OiPr)4, filtered through a fine-fritted

5366 Organometallics, Vol. 17, No. 24, 1998
Chen et al.
funnel, washed with a hexanes solution of Ti(OiPr)4, and dried
in vacuo for 2 h. Yield of yellow solid: 116 mg (0.268 mmol,
87%). 1H NMR (CD2Cl2): δ 8.39 (s, 2H, H-CdN), 7.50 (m,
4H, Ar), 6.91 (td, J ) 7.4, 1.0 Hz, 2H, Ar), 6.83 (d, J ) 8.2 Hz,
2H, Ar), 4.36 (septet, J ) 6.4 Hz, 1H, CH), 4.33 (m, 2H, CH2),
4.00 (m, 2H, CH2), 1.41 (s, 3H, CH3), 0.87 (d, J ) 6.4 Hz, 6H,
CH3). 13C NMR (CD2Cl2): δ 174.6 (CdO), 164.6, 163.7 (2Cd
N), 136.1, 134.4, 123.1, 119.3, 117.7, 80.2 (CH), 59.2 (CH2),
25.1 (CH3), 24.4 (CH3). Anal. Calcd for C21H24N2O5Ti: C,
58.34; H, 5.60; N, 6.48. Found: C, 58.33; H, 5.60; N, 6.37.
Ti(sa len )(OiP r )(OC(O)CH 2OCH 3) (12). A solution of
Ti(OiPr)4 (332 mg, 1.102 mmol) in CH2Cl2 (0.9 mL) was
combined with a solution of methoxyacetic acid (115.8 mg,
1.260 mmol) in CH2Cl2 (1.0 mL). To this mixture was added
H2salen (267 mg, 0.993 mmol) in CH2Cl2 (0.7 mL), which after
2 min was concentrated in vacuo to dryness. The resulting
solid was slurried with a solution of Ti(OiPr)4 (300 mg) in Et2O
(4 mL), followed by the addition of Ti(OiPr)4 (256 mg) in
hexanes (4 mL). The final slurry was filtered through a fine-
fritted funnel, washed with a Ti(OiPr)4 solution in hexanes,
and dried in vacuo for 2 h. Yield of yellow solid: 415 mg (0.898
mmol, 90%). 1H NMR (CD2Cl2): δ 8.41 (s, 2H, H-CdN), 7.50
(m, 4H, Ar), 6.91 (td, J ) 7.6, 1.0 Hz, 2H, Ar), 6.83 (d, J ) 8.4
Hz, 2H, Ar), 4.39 (septet, J ) 6.4 Hz, 1H, CH), 4.36 (m, 2H,
CH2), 4.04 (m, 2H, CH2), 3.30 (s, 2H, CH2), 2.95 (s, 3H, OCH3),
0.89 (d, J ) 6.4 Hz, 6H, CH3). 13C NMR (CH2Cl2): δ 173.2
(CdO), 164.4, 163.9 (CdN), 136.1, 134.4, 123.1, 119.4, 117.6,
80.6 (CH), 71.5 (OCH2), 59.2 (CH2), 58.3 (OCH3), 25.0 (CH3).
Anal. Calcd for C22H26N2O6Ti: C, 57.15; H, 5.67; N, 6.06.
Found: C, 57.22; H, 5.80; N, 6.05.
Ti(sa len )(4-ter t-bu tylp h en ola te)(OC(O)CH3) (13). A so-
lution of the titanium complex 7 (0.180 mmol) was prepared
by the combination of a CH2Cl2 solution (1.0 mL) of 3 (55.2
mg, 0.090 mmol) and an acetonitrile solution (1.0 mL) of 5 (55.3
mg, 0.090 mmol). To the orange-red solution was added an
acetonitrile solution of dry sodium acetate (15.7 mg, 0.191
mmol). The slurry was stirred at ambient temperature for 6
h and then concentrated in vacuo to dryness. The solid was
dissolved with CH2Cl2 (3 mL) and filtered through a fine-fritted
funnel, and the solvent was removed in vacuo to yield 69.8
mg of orange-red solid. 1H NMR of the solid indicates a
mixture of 13 (∼80%), starting material, and oxo-bridged
dimer. 1H NMR (CD2Cl2): δ 8.38 (s, 2H, H-CdN), 7.53 (m,
4H, Ar), 6.99 (m, 4H, Ar), 6.88 (d, J ) 8.6 Hz, 2H, Ar), 6.23 (d,
J ) 8.6 Hz, 2H, Ar), 4.30 (m, 2H, CH2), 3.82 (m, 2H, CH2),
1.53 (s, 3H, CH3), 1.17 (s, 9H, CH3). 13C NMR (CD2Cl2): δ
173.2 (CdO), 164.7, 164.3, 163.7 (CdN), 144.4, 136.3, 134.7,
126.0, 123.6, 120.4, 117.5, 117.2, 59.0 (CH2), 34.4, 31.5 (CH3),
23.7 (CH3).
Ti(sa len )(4-ter t-bu tylp h en ola te)(OC(O)CH2OCH3) (14).
A red solution of 3 (110 mg, 0.179 mmol) in CH2Cl2 (0.6 mL)
was combined with a solution of methoxyacetic acid (17.6 mg,
0.195 mmol) in CH2Cl2 (0.3 mL) to give a cherry red solution.
After 5 min, the solution was diluted with dry tert-butyl methyl
ether (22 mL), and with stirring, hexanes (50 mL) was slowly
added to precipitate out an orange solid. The slurry was
filtered through 15/M fritted funnel, washed with hexanes, and
1
dried in vacuo. Yield of orange solid: 58.9 mg. By H NMR,
the product was a mixture of 14 (∼80%), starting material,
and oxo-bridged dimeric complexes. 1H NMR (CD2Cl2): δ 8.39
(s, 2H, H-CdN), 7.53 (m, 4H, Ar), 6.99 (m, 6H, Ar), 6.26 (d, J
) 8.6 Hz, 2H, Ar), 4.31 (m, 2H, CH2), 3.83 (m, 2H, CH2), 3.43
(s, 2H, OCH2), 3.01 (s, 3H, OCH3), 1.19 (s, 9H, CH3). 13C NMR
(CD2Cl2): δ 173.2 (CdO), 164.3, 162.9 (3q), 163.8 (CdN), 144.4,
136.5, 134.7, 126.1, 123.8, 120.5, 117.7, 117.4, 71.4 (OCH2),
59.2, 58.6, 34.5 (C(CH3)3), 31.7 (CH3).
Ti(sa len )(4-ter t-b u t ylp h en ola t e)(3,5-d im et h ylp h en o-
la te) (15). The titanium complex 7 (95.5 mg, 0.156 mmol) was
dissolved in acetonitrile (1.5 mL), and the mixture was added
to a suspension of sodium 3,5-dimethylphenoxide (22.2 mg,
0.154 mmol) in acetonitrile (1.5 mL). After stirring for 20 min,
the red slurry cleared to a homogeneous orange solution and
was concentrated in vacuo to dryness. The oily solid was
triturated with a 1:1 mixture of CH2Cl2 and hexanes. The
resulting orange solid was redissolved in CH2Cl2, filtered
through a fine fritted funnel, and dried in vacuo. Yield of
orange solid: 81.3 mg (0.139 mmol, 90%). 1H NMR (CD3CN):
δ 8.35 (s, 2H, CdN), 7.49 (m, 4H, Ar), 6.93 (m, 4H, Ar), 6.83
(m, 2H, Ar), 6.23 (s, 1H, Ar), 6.11 (m, 2H, Ar), 5.84 (s, 2H,
Ar), 3.68 (br t, J ) 4.0 Hz, 4H, CH2), 1.94 (s, 6H, CH3), 1.12
(s, 9H, CH3). 13C NMR (CD3CN): δ 166.6, 164.9, 164.5, 164.4
(CdN), 142.5, 139.0, 136.6, 135.5, 126.4, 124.6, 121.8, 120.1,
118.4, 118.0, 116.9, 59.2 (CH2), 34.5 (C(CH3)3), 31.8 (CH3), 21.3
(CH3). Anal. Calcd for C34H36N2O4Ti: C, 69.86; H, 6.21; N,
4.79. Found: C, 69.85; H, 6.27; N, 4.95.
Ack n ow led gm en t. We wish to thank the Hoechst
Celanese Company for financial support of this research
under the auspices of a Discovery Award, and Mr. Brian
Santora for performing several critical experiments.
M.R.G. is a NSF CAREER Award recipient.
OM980414P