Unexpected binuclear bis(phenolato) titanium (IV) {[(L)Ti(Ph)] 2(μ-OEt)2} assisted by carbon-oxygen bond cleavage and alkali-metal-containing titanium(III) complexes [Ti(L)2· M(solv)2] (M = Li, Na, K; solv = THF, DME)

Article abstract of DOI:10.1021/om700298f

Titanium complex [(L)Ti(CH₂Ph)₂] (2) was prepared by reaction of [(L)TiCl₂] (L = 2,2′-methylenebis(6-tert-butyl-4- methylphenolato)) (1) with PhCH₂MgCl in a 1:2 ratio in Et ₂O in 69% yield, while the reaction of 1 with PhLi under the same conditions yields [(L)Ti(Ph)₂] (3) in less than 40% yield and an unexpected rare phenyl alkoxide-bridged compound {[(L)-Ti(Ph)] ₂(μ-OEt)₂}(4) in ca. 9% yield. According to the crystal structure, 2 and 3 are monomeric and tetrahedral, with boat-conformation ligands. The X-ray structure of 4 showed the complex to be dimeric, with titanium in a distorted pyramidal coordination geometry. The reduction of 1 with 1.0 equiv of LiBEt₃H, excess Na/Hg, or 1.0 equiv of KC₈ gave the titanium-(III) salts [Ti(L)₂·M(THF)₂] (M = Li, 5; M = Na, 6) and [Ti-(L)₂·K(DME)₂] (7), respectively. The molecular structures of 5 and 7 were confirmed by single-crystal X-ray analysis. The titanium atom in complexes 5 and 7 is four-coordinate, with a distorted tetrahedral arrangement and the same ligand orientations as in 2-4. The lithium atom in 5 is four-coordinate with two coordinated THF molecules, while the big potassium ion in 7 is six-coordinate with two chelated DME molecules added to the two bridging oxygen atoms of the bis(phenolato) ligands.

Full text of DOI:10.1021/om700298f

4072
Organometallics 2007, 26, 4072-4075
Notes
Unexpected Binuclear Bis(phenolato) Titanium (IV)
{[(L)Ti(Ph)]2(µ-OEt)2} Assisted by Carbon-Oxygen Bond Cleavage
and Alkali-Metal-Containing Titanium(III) Complexes
[Ti(L)2‚M(solv)2] (M ) Li, Na, K; solv ) THF, DME)
Dao Zhang*
Department of Chemistry, Fudan UniVersity, Shanghai 200433, People’s Republic of China
ReceiVed March 28, 2007
Summary: Titanium complex [(L)Ti(CH2Ph)2] (2) was prepared
by reaction of [(L)TiCl2] (L ) 2,2′-methylenebis(6-tert-butyl-
4-methylphenolato)) (1) with PhCH2MgCl in a 1:2 ratio in Et2O
in 69% yield, while the reaction of 1 with PhLi under the same
conditions yields [(L)Ti(Ph)2] (3) in less than 40% yield and
an unexpected rare phenyl alkoxide-bridged compound {[(L)-
Ti(Ph)]2(µ-OEt)2}(4) in ca. 9% yield. According to the crystal
structure, 2 and 3 are monomeric and tetrahedral, with boat-
conformation ligands. The X-ray structure of 4 showed the
complex to be dimeric, with titanium in a distorted pyramidal
coordination geometry. The reduction of 1 with 1.0 equiV of
LiBEt3H, excess Na/Hg, or 1.0 equiV of KC8 gaVe the titanium-
(III) salts [Ti(L)2‚M(THF)2] (M ) Li, 5; M ) Na, 6) and [Ti-
(L)2‚K(DME)2] (7), respectiVely. The molecular structures of 5
and 7 were confirmed by single-crystal X-ray analysis. The
titanium atom in complexes 5 and 7 is four-coordinate, with a
distorted tetrahedral arrangement and the same ligand orienta-
tions as in 2-4. The lithium atom in 5 is four-coordinate with
two coordinated THF molecules, while the big potassium ion
in 7 is six-coordinate with two chelated DME molecules added
to the two bridging oxygen atoms of the bis(phenolato) ligands.
The aryloxide-based multidentate ligands continue to attract
considerable attention for their use in stabilizing reactive metal
centers for a number of unusual reactions.4 So we chose to
explore the chemistry of transition metal complexes with such
ligands. Over the last several years, we have been investigating
the use of multidentate aryloxides ligands to generate S-block
and group 4 metal species and nickel complexes.5 Aiming to
explore more unusual aryloxide-containing compounds such as
low-valent metal derivatives, we have now turned to the study
of the reactivity of these mononuclear Ti-aryloxide complexes.
Recently, we reported the facile formation of six-membered ring
[Al3O2Cl] aluminum and alkoxide-bridged titanium complexes
by the reactions of AlMe3 with [(L)TiCl2] (L ) 2,2′-methyl-
enebis(6-tert-butyl-4-methylphenolato)) (1).5a The present work
describes the synthesis and characterization of the unexpected
alkoxide-bridged titanium product generated from C-O bond
rupture of diethyl ether as well as the reduction of dichloride
titanium(IV) compound 1 by different reducing agents to
generate some alkali-metal-containing low-valent titanium spe-
cies (Scheme 1).
Introduction
(3) For recent examples of carbon-oxygen bond cleavage using group
4 transition metal complexes, see: (a) Bradley, C. A.; Veiros, L. F.; Pun,
D.; Lobkovsky, E.; Keresztes, I.; Chirik, P. J. J. Am. Chem. Soc. 2006,
128, 16600-16612. (b) Burlakov, V. V.; Arndt, P.; Baumann, W.;
Spannenberg, A.; Rosenthal, U. Organometallics 2006, 25, 1317-1320.
(c) Hsu, S.-H.; Chang, J.-C.; Lai, C.-L.; Hu, C.-H.; Lee, H. M.; Lee, G.-
H.; Peng, S.-M.; Huang, J.-H. Inorg. Chem. 2004, 43, 6786-6792. (d)
Basuli, F.; Tomaszewski, J.; Huffman, J. C.; Mindiola, D. J. Organometallics
2003, 22, 4705-4714. (e) Fandos, R.; Hernandez, C.; Otero, A.; Rodriguez,
A.; Ruiz, M. J.; Terreros, P. J. Chem. Soc., Dalton Trans. 2002, 11-13. (f)
Covert, K. J.; Mayol, A.-R.; Wolczanski, P. T. Inorg. Chim. Acta 1997,
263, 263-278.
(4) For recent reviews, see: (a) Britovsek, G. J. P.; Gibson, V. C.; Wass,
D. F. Angew. Chem., Int. Ed. 1999, 38, 428-447. (b) Bradley, D. C.;
Mehrotra, R. C.; Rothwell, I. P.; Singh, A Alkoxo and Aryloxo DeriVatiVes
of Metals; Academic Press: London, 2001. (c) Mikami, K.; Terada, M.;
Matsuzawa, H. Angew. Chem., Int. Ed. 2002, 41, 3554-3572. (d) Knight,
P. D.; Scott, P. Coord. Chem. ReV. 2003, 242, 125-143. (e) Kawaguchi,
H.; Matsuo, T. J. Organomet. Chem. 2004, 689, 4228-4243.
Group 4 transition metal complexes have been the most
extensively studied for their promotion of numerous organic
transformations, in part due to their steric and electronic
modularity and convenient synthetic access to low-valent
derivatives by treatment with alkyl lithium reagents or alkali
metal reductants.1 However, a better understanding of the
synthesis, structure, and reactivity of reduced titanium com-
plexes is needed in order to achieve a greater mechanistic
understanding and better control over selectivity of the reactions.
Hence, increased effort has been focused on developing the
synthesis and reactivity of well-characterized low-valent group
4 metal complexes. For example, some titanium complexes have
been investigated for their promotion of small molecule activa-
tion processes and carbon-oxygen bond cleavage.2,3
(5) (a) Zhang, D. Eur. J. Inorg. Chem. 2007, in press. (b) Zhang, D.;
Aihara, H.; Watanabe, T.; Matsuo, T.; Kawaguchi, H. J. Organomet. Chem.
2007, 692, 234-242. (c) Zhang, D.; Kawaguchi, H. Organometallics 2006,
25, 5506-5509. (d) Zhang, D.; Jin. G. Inorg. Chem. Commun. 2006, 9,
1322-1325. (e) Zhang, D.; Jin, G.; Weng, L.; Wang, F. S. Organometallics
2004, 23, 3270-3275. (f) Zhang, D.; Jin, G. Organometallics 2003, 22,
2851-2854. (g) Zhang, D.; Jin, G.; Hu, N. Chem. Commun. 2002, 574-
575.
* Corresponding author. Fax: +86 21 65641740. E-mail: daozhang@
fudan.edu.cn.
(1) For a recent review, see: Marek, I. Titanium and Zirconium in
Organic Synthesis; Wiley-VCH: Weinheim, 2002.
(2) (a) Pool, J. A.; Chirik, P. J. Can. J. Chem. 2005, 83, 286-295. (b)
Fryzuk, M. D.; Johnson, S. A. Coord. Chem. ReV. 2000, 200-202, 379-
409.
10.1021/om700298f CCC: $37.00 © 2007 American Chemical Society
Publication on Web 06/26/2007

Notes
Scheme 1. Synthesis of Titanium Complexes 2-7a
Organometallics, Vol. 26, No. 16, 2007 4073
Chart 1
to afford a red crystalline compound, {[(L)TiPh]2(µ-OEt)2}(4)
(Scheme 1). Complex 4 is stable in the solid state but slowly
decomposed to unidentified compounds in C6D6 at room
temperature. Single-crystal X-ray analysis confirms that com-
pound 4 is a dimer, with two ethoxo-oxygens bridging the two
titanium atoms (see the Supporting Information).
The unexpected formation of 4 clearly indicates the alkyl-
oxygen bond cleavage of diethyl ether. It has been observed
that some Sc, Ti, and Zr complexes could promote C-O bond
cleavage of Et2O and THF.3e,g The force of this process is
ascribed to the low oxidation states of the transition metal. For
example, the η9,η5-bis(indenyl)zirconium sandwich complex was
just reported to promote the C-O bond cleavage of dialkyl
ethers such as diethyl ether, CH3OR (R ) Et, nBu, tBu), nBu2O,
or iPr2O by Chirik et al.3a The η2-benzyne titanium intermediate
complex could be generated from the thermolysis of diphe-
nylzirconocene, and the nascent benzyne complex can be used
as a means for carbon-carbon bond formation in organic
synthesis.7 Herein we suppose that the titanium(II) complexes,
e.g., the η2-benzyne titanium complex (Chart 1), are possible
intermediates in the formation of 4. Although trace ethylbenzene
was detected in reaction mixture by GC-MS, unfortunately until
now it is not clear which phenyl carbon the ethyl migrates to
because there are five H atoms on the phenyl ring and a hydride
shift is required.
a Reagents and conditions: (i) 2 PhCH2MgCl/Et2O, -78 °C to rt,
overnight; (ii) 2 PhLi/Et2O, -78 °C to rt, 3 days; (iii) for 5: LiBEt3H/
THF, -78 °C to rt, overnight; for 6: excess Na/Hg/THF, rt, 2 days;
(iv) KC8/DME/toluene, -29 °C to rt, overnight.
Given that only few low-valent species of phenolato titanium
complexes have been reported,8 several kinds of reducing agents
including Mg powder, Na/Hg, LiBEt3H, and KC8 were used to
reduce dichloride titanium complex 1. The experimental results
showed that Mg powder almost has no reducing ability and
compound 1 could be retrieved from the reaction mixture in
87% yield. Treatment of 1 with LiBEt3H in THF at -78 °C led
to a color change from yellow to pale green, which changed to
yellow-green on warming to room temperature. The Ti(III)
reduction product, [Ti(L)2‚Li(THF)2] (5), was isolated as yellow-
green plate crystals. Titanium complexes [Ti(L)2‚Na(THF)2] (6)
and [Ti(L)2‚K(DME)2] (7) were similarly prepared from the
reaction of 1 with excess sodium amalgam in THF and 1.0 equiv
of KC8 in toluene/DME, respectively (Scheme 1). The composi-
tions of 5, 6, and 7 were confirmed by elemental analysis, and
the X-ray structures of complexes 5 and 7 were determined (see
the Supporting Information).
The titanium atom in complex 5 is four-coordinate, with a
distorted tetrahedral arrangement and the same ligand orienta-
tions as in 2-4. Two oxygen atoms from the aryloxide ligands
are also involved in oxygen bridges between the lithium and
titanium atoms. The lithium atom is four-coordinate, with two
coordinated THF molecules added to the bridging oxygen atoms.
The titanium(III) coordination geometry in 7 (a distorted
Results and Discussion
Complex [(L)TiCl2] (1) could readily be converted to the bis-
(alkyl) or bis(aryl) compounds [(L)TiR2] by salt metathesis using
Grignard or organolithium reagents.6 In this way complex [(L)-
Ti(CH2Ph)2] (3) was made by addition of PhCH2MgCl reagent
to a cooled (-78 °C) suspension of dichloride complex in ether
and subsequent workup from pentane in 69% yield. Moreover,
protonolysis of the readily available precursor Ti(CH2Ph)4 with
chelating bisphenol at 20 °C could yield 3 with concomitant
liberation of toluene, but the product includes a small amount
of impurities. In a similar way, complex 1 reacts with 2.0 equiv
of PhLi in diethyl ether to give the corresponding diphenyl
complex [(L)TiPh2] (2) in less than 40% yield. The syntheses
of 2 and 3 have been described elsewhere,6a,c but no detailed
NMR spectra and X-ray single-crystal analyses have been given
due to their thermal- and light-instability. In this paper
complexes 2 and 3 were fully characterized by 1H and 13C{1H}
NMR spectroscopy and X-ray single-crystal determination (see
Experimental Section and the Supporting Information).
The yield of diphenyl titanium complex 3 is very low, less
than 40%, which made us wonder what the other products are.
After complex 3 was completely extracted with pentane, the
resultant crude was washed with hexane and treated with toluene
(7) Buchwald, S. L.; Watson, B. T. J. Am. Chem. Soc. 1986, 108, 7411-
7413.
(8) (a) Durfee, L. D.; Latesky, S. L.; Rothwell, I. P.; Huffman, J. C.;
Folting, K. Inorg. Chem. 1985, 24, 4569-4573. (b) Sarazin, Y.; Howard,
R. H.; Hughes, D. L.; Humphrey, S. M.; Bochmann, M. Dalton Trans. 2006,
340-350.
(6) (a) Floriani, C.; Corazza, F.; Lesueur, W.; Chiesi-Villa, A.; Guastini,
C. Angew. Chem., Int. Ed. Engl. 1989, 28, 66-67. (b) Corazza, F.; Floriani,
C.; Chiesi-Villa, A.; Guastini, C. Inorg. Chem. 1991, 30, 145-148. (c)
Okuda, J.; Fokken, S.; Kang, H.-C.; Massa, W. Chem. Ber. 1995, 128, 221-
229.

4074 Organometallics, Vol. 26, No. 16, 2007
Notes
Scheme 2. Synthesis of Complex 8
over a potassium mirror and vacuum transferred prior to use. H2-
(L) (L ) 2,2′-methylenebis(6-tert-butyl-4-methylphenolato)) and
[(L)TiCl2] (1) were prepared by a literature procedure.6 NMR
spectra were recorded on a Bruker AVANCE-DMX 500 spectrom-
Figure 1. Molecular structure of 7. All hydrogen atoms are omitted
for clarity.
1
eter. H and 13C{1H} NMR are reported with reference to solvent
tetrahedral arrangement) is very similar to that in complex 5.
The big potassium ion is six-coordinate, with two chelated DME
molecules added to the two bridging oxygen atoms of the bis-
(phenolato) ligands (Figure 1).
resonances (residual C6D5H in C6D6, δ 7.15 and 128.0 ppm).
Elemental analysis was performed on an Elementar Vario EL III
analyzer.
Synthesis of [(L)Ti(CH2Ph)2] (2). Path A.6c C6H5CH2MgCl
(1.6 mL, 1.0 M solution in diethyl ether, 1.6 mmol) was added
dropwise to a precooled suspension of 1 (0.373 g, 0.816 mmol) in
Et2O (30 mL) at -78 °C. The mixture was slowly warmed to room
temperature and stirred overnight. The solvent was removed under
vacuum, and CH2Cl2 (20 mL) was added to the solid residue. The
suspension was centrifuged to remove formed salt, and the upper
clear solution was evacuated to dryness. The orange-red crude was
purified by recrystallization from hexane/Et2O to afford 0.32 g of
orange, block-like crystals in 69% yield.
Although we did not isolate the titanium(II) compounds using
the above-mentioned reducing agents, treatment of 1 with 2
equiv of nBuLi in THF for 3 days at room temperature afforded
a dark blue mixture that continuously reacted with 1.0 equiv of
tBu-N3 to afford the yellow-orange titanium(IV) complex [Ti2-
1
(µ-NBut)2(L)2] (8) (Scheme 2). The H NMR spectrum of 8
exhibits a singlet for the tert-butyl imido group at δ 0.98 ppm
and two doublets for bridged methylene at δ 4.41 and 3.53 ppm
with the coupling constant JH-H ) 14.2 Hz. Orange crystals of
complex 8 suitable for X-ray analysis could be obtained although
their quality was not ideal because they are very thin platelets.
The outline of the solid-state structure of 8 clearly indicates its
dimeric structure with two bridged imido (µ-NtBu) moieties.9
Clearly the process includes a dark blue titanium(II) intermediate
compound.
In summary, we have demonstrated the formation of an
unexpected alkoxide-bridged diphenyl titanium(IV) bis(pheno-
late) complex by carbon-oxygen bond cleavage. Upon reduc-
tion, some alkali-metal-containing low-valent titanium species
can be achieved. Further experiments are now in progress.
Path B. A sample of Ti(CH2Ph)4 (0.405 g, 1.0 mmol) in 20 mL
of hexane, precooled to -40 °C, was added dropwise to a
suspension of H2L (0.340 g, 1.0 mmol) in 20 mL of hexane, also
cooled to -40 °C. After addition, the reaction mixture was allowed
to warm slowly to room temperature and stirred overnight. The
resulting red-colored solution was stripped under vacuum to give
a red foam. Crystallization of a concentrated hexane solution at
1
-30 °C gave 0.31 g of a microcrystalline solid in 55% yield. H
NMR (C6D6, 500 MHz): δ 7.37 (d, 2H, JH-H ) 7.08), 7.23 (m,
2H, H-Ar), 7.06-6.88 (m, 10H, H-Ar), 6.75 (m, 1H, H-Ar), 3.25,
3.22 (d, 1H, JH-H ) 14.4, 1H, CH2), 3.16, 3.13 (d, 1H, JH-H
)
14.4, CH2), 3.14 (s, 1H, Ti-CH2Ph), 2.77 (s, 1H, Ti-CH2Ph), 2.08
(s, 6H, p-CH3), 1.54 (s, 18H, o-C(CH3)3). 13C{1H} NMR (C6D6,
127 MHz): δ 160.95 (O-CAr), 146.48, 141.24, 135.92, 135.37,
131.73, 130.02, 129.56, 129.23, 128.81, 128.30, 127.37, 125.83,
125.43, 123.33 (CHAr), 83.39 (d, J ) 69.5 Hz, Ti-CH2Ph), 35.24
(Ar-CH2-Ar), 34.15, (o-C(CH3)3), 30.41 (o-C(CH3)3), 21.03 (p-CH3).
Anal. Calcd for C37H44O2Ti: C, 78.15; H, 7.80. Found: C, 77.94;
H, 7.82.
Experimental Section
General Procedures. Unless otherwise noted, all operations were
performed either under an inert atmosphere of argon using standard
Schlenk techniques or under nitrogen in an MBraun glovebox. All
dried solvents and chemicals commercially available were used as
received without further purification. C6D6 was dried and degassed
Synthesis of [(L)TiPh2] (3) and {[(L)Ti(Ph)]2(µ-OEt)2} (4).
LiPh (1.2 M, 1.65 mL, 1.98 mmol) was added to a diethyl ether
solution (20 mL) of 1 (0.432 g, 0.94 mmol) at room temperature.
The resulting solution was allowed to stand for 3 days, then
evaporated to dryness. The resulting solid was extracted with
pentane (20 mL), and LiCl was removed by centrifugation. The
pentane solution, upon cooling to -30 °C, gave green needles of
(9) For titanium imido complexes, see: (a) Owen, C. T.; Bolton, P. D.;
Cowley, A. R.; Mountford, P. Organometallics 2007, 26, 83-92. (b) Bolton,
P. D.; Adams, N.; Clot, E.; Cowley, A. R.; Wilson, P. J.; Schro¨der, M.;
Mountford, P. Organometallics 2006, 25, 5549-5565. (c) Dunn, S. C.;
Hazari, N.; Jones, N. M.; Moody, A. G.; Blake, A. J.; Cowley, A. R.; Green,
J. C.; Mountford, P. Chem.-Eur. J. 2005, 11, 2111-2124. (d) Said, M.;
Hughes, D. L.; Bochmann, M. Dalton Trans. 2004, 359-360. (e) Abarca,
A.; Go´mez-Sal, P.; Mart´ın, A.; Mena, M. J.; Poblet, M.; Ye´lamos, C. Inorg.
Chem. 2000, 39, 642-651. (f) Benito, J. M.; Are´valo, S.; de Jesu´s, E.; de
la Mata, F. J.; Flores, J. C.; Go´mez, R. J. Organomet. Chem. 2000, 610,
42-48. (g) Li, Z.; Huang, J.; Yao, T.; Qian, Y.; Leng, M. J. Organomet.
Chem. 2000, 598, 339-347. (h) Collier, P. E.; Blake, A. J.; Mountford, P.
J. Chem. Soc., Dalton Trans. 1997, 2911-2919.
1
3 in 40% yield (0.20 g). H NMR (C6D6, 500 MHz): δ 8.23 (d,
1H, JH-H ) 1.95, H-Ar), 8.22 (m, 1H, H-Ar), 8.13 (m, 1H, H-Ar),
8.12 (d, 1H, JH-H ) 1.95, H-Ar), 7.11 (d, 1H, JH-H ) 1.95, H-Ar),
7.09 (d, 1H, JH-H ) 1.95, H-Ar), 7.07 (d, 1H, JH-H ) 2.2, H-Ar),
7.06 (d, 1H, JH-H ) 1.2, H-Ar), 7.02 (q, 2H, JH-H ) 1.95, H-Ar),

Notes
Organometallics, Vol. 26, No. 16, 2007 4075
3.97 (d, JH-H ) 14.65 Hz, 1H, CH2), 3.40 (d, JH-H )14.65 Hz,
1H, CH2), 2.08 (s, 6H, p-CH3), 1.59 (s, 18H, o-C(CH3)3). 13C{1H}
NMR (C6D6, 127 MHz): δ 196.63, 196.35, 196.05, 161.09 (O-
CAr), 150.04, 136.33, 135.90, 132.21, 131.90, 131.63, 131.22,
131.17, 129.55, 128.49, 127.92, 126.23 (CH), 36.02 (C(CH3)3),
35.54 (Ar-CH2-Ar), 30.59 (C(CH3)3), 21.23 (Ar-CH3). Anal. Calcd
for C35H40O2Ti: C, 77.77; H, 7.46. Found: C, 77.64; H, 7.52. The
above residual crude solid was washed with hexane (5 mL) and
then extracted with toluene (10 mL). The resulting red solution
was concentrated to ca. 2 mL and cooled at -19 °C for several
days to give 45 mg of 4 as orange-red crystals in ca. 9% yield. 1H
NMR (C6D6, 500 MHz): δ 8.24 (d, 2H, JH-H ) 6.4, H-Ar), 7.23
(m, 3H, H-Ar), 6.97 (s, 2H, H-Ar), 6.83 (s, 2H, H-Ar), 5.31 (br,
2H, CH2), 3.26 (br, 2H, µ-OCH2CH3), 2.06 (s, 6H, p-CH3), 1.47
(s, 18H, o-C(CH3)3), 1.24 (br, 2H, µ-OCH2CH3). Anal. Calcd for
C62H80O6Ti2: C, 73.22; H, 7.94. Found: C, 73.14; H, 8.01.
Synthesis of [Ti(L)2‚Li(THF)2] (5). A solution of 1 (0.229 g,
0.5 mmol) in toluene (10 mL) was cooled to -78 °C in a methanol/
N2(liquid) bath, and 1.0 equiv of LiBEt3H (0.5 mL, 1.0 M solution
in THF, 0.5 mmol) was added slowly via a syringe. The color
changed rapidly from red to yellow. The mixture was allowed to
warm to room temperature and was stirred another 4 h, when the
color gradually turned very dark green. The solution was filtered,
and the solvent was concentrated to ca. 2 mL under vacuum, layered
with 1 mL of hexane, and cooled at -29 °C for a week to afford
0.21 g of 5‚(C6H14) as yellow-green plate crystals in 43% yield.
Anal. Calcd for C60H90LiO6Ti: C, 74.90; H, 9.43. Found: C, 74.86;
H, 9.42. The paramagnetic nature of 5 precluded the acquisition of
suitable NMR data.
Synthesis of [Ti(L)2‚Na(THF)2] (6). THF (15 mL) was added
at -78 °C to a freshly prepared sodium amalgam (mercury: 2.0 g,
10.1 mmol; sodium: 0.02 g, 0.85 mmol). A solution of 1 (0.229 g,
0.5 mmol) in THF (20 mL) was cooled to -78 °C and added slowly
to the Hg/Na amalgam. The mixture was allowed to warm to room
temperature and was stirred 2 days, when the color gradually turned
very dark green. The solution was filtered to remove the excess of
Hg/Na, and the solvent was removed under vacuum to yield 6 as
a green crystalline compound. Yield: 0.19 g (42%). We tried but
failed to obtain X-ray quality crystals. Anal. Calcd for C54H76NaO6-
Ti: C, 72.71; H, 8.59. Found: C, 72.36; H, 8.32. The paramagnetic
nature of 6 precluded the acquisition of suitable NMR data.
Synthesis of [Ti(L)2‚K(DME)2] (7). A solution of 1 (0.229 g,
0.5 mmol) in toluene/DME (20/10 mL) was cooled to -29 °C,
and 1.0 equiv of KC8 (0.068 g, 0.5 mmol) was added slowly in a
glovebox. The color changed rapidly from red to yellow-green. The
mixture was allowed to warm to room temperature and was stirred
overnight, when the color gradually turned very dark green. The
solution was filtered to remove the carbon, and the solvent was
removed to give a blue-green powder in 38% yield. Blue-green,
needle-like, X-ray quality crystals were obtained by storing its
saturated solution of hexane/toluene/DME (0.5/0.5/0.5) at 4 °C for
2 weeks. Anal. Calcd for C54H80KO8Ti: C, 68.69; H, 8.54. Found:
C, 68.46; H, 8.43. The paramagnetic nature of 7 precluded the
acquisition of suitable NMR data.
Synthesis of [Ti2(µ-NtBu)2(L)2] (8). To a solution of 1
(0.229 g, 0.5 mmol) in THF (20 mL) was slowly added the hexane
solution of nBuLi (0.6 mL, 1.6 M, 1.0 mmol) at -78 °C. The
mixture was slowly warmed to room temperature and continuously
stirred for 72 h to give a dark blue solution. Then tBu-N3 (0.050 g,
0.5 mmol) was added at -40 °C. The reaction mixture was slowly
warmed to room temperature and stirred for another 8 h. The solvent
was evaporated to dryness. Extraction of the residue with THF/
1
hexane gave an orange solid (0.133 g) in 58% yield. H NMR
(C6D6, 500 MHz): δ 7.01 (s, 2 H, H-Ar) 6.93(s, 2 H, H-Ar), 4.41
(d, 1H, JH-H ) 14.2, 1H, CH2), 3.57 (br, 2H, THF), 3.53 (d, 1H,
JH-H ) 14.2, 1H, CH2), 2.06 (s, 6H, p-Me), 1.58 (s, 18H,
o-C(CH3)3), 1.41 (br, 2H, THF), 0.98 (s, dNC(CH3)3). Anal. Calcd
for C54H78N2O4Ti2: C, 70.89; H, 8.59; N, 3.06. Found: C, 70.46;
H, 8.63; N, 3.12.
Crystallographic Data. A suitable crystal was immersed in
mineral oil and mounted on a nylon loop in a random orientation
under a cold stream of dry nitrogen. Diffraction experiments were
performed with Mo KR radiation (λ ) 0.710 70 Å) on a Rigaku
CCD diffractometer. The data were collected in a hemisphere of
data in 720 frames with 20-40 s exposure times. The data sets
were collected (4.0° < 2θ < 45-55°). The data were processed
using Crystal Clear Processing packages.10 The structures were
determined by routine heavy-atom and Fourier methods by using
SHELXS 9711 and refined by full-matrix least-squares with the non-
hydrogen atoms anisotropic and hydrogen with fixed isotropic
thermal parameters of 0.07 Å by means of the SHELXL 97
program.12 The hydrogens were partially located from difference
electron-density maps, and the rest were fixed at predetermined
positions. Scattering factors were from common sources.13 Some
details of data collection and refinement are given in the Supporting
Information.
Acknowledgment. Financial support from the National
Science Foundation of China (Grant No. 20671021) is gratefully
acknowledged. The author also thanks Prof. Dr. H. Kawaguchi
for his help.
Supporting Information Available: For compounds 2-5 and
7, crystallographic data in CIF format, figures of the molecular
structure, tables of selected bond lengths and angles, and a
discussion of the X-ray data of these compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM700298F
(10) (a) CrystalClear Software Package; Rigaku and Molecular Structure
Corp., 1999. (b) Pflugrath, J. W. Acta Crystallogr. 1999, D55, 1718-1725.
(11) Sheldrick, G. M. SHELXS 97, Program for the Solution of Crystal
Structures; University of Go¨ttingen: Germany, 1990.
(12) Sheldrick, G. M. SHELXL 97, Program for Refining Crystal
Structures; University of Go¨ttingen: Germany, 1997.
(13) Cromer, D. T.; Waber, J. T. International Tables for X-ray
Crystallography; Kynoch Press: Birmingham, 1974; Vol. IV, pp 99 and
149.