Synthetic and structural studies of titanium aminotroponiminate complexes

Article abstract of DOI:10.1021/ic9909072

The synthesis and characterization of a series of Ti(III) and Ti(IV) aminotroponiminate complexes are described. Six-coordinate [TiMe₂(Me₂ATI)₂] and [TiPh₂(Me₂ATI)₂] were synthesized and st

Full text of DOI:10.1021/ic9909072

Inorg. Chem. 1999, 38, 6225-6233
6225
Synthetic and Structural Studies of Titanium Aminotroponiminate Complexes
Dietrich P. Steinhuebel and Stephen J. Lippard*
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
ReceiVed July 30, 1999
The synthesis and characterization of a series of Ti(III) and Ti(IV) aminotroponiminate complexes are described.
Six-coordinate [TiMe2(Me2ATI)2] and [TiPh2(Me2ATI)2] were synthesized and structurally characterized, where
Me2ATI is N,N′-dimethylaminotroponiminate. The mono-alkyl complexes [TiClR(Me2ATI)2], R ) Me, CH2-
SiMe3, were prepared, and treatment of the former, generated in situ, with PhMgCl yielded the alkyl-aryl complex
[TiMePh(Me2ATI)2]. The solid state structures of most of these complexes were determined and reveal slightly
distorted, trigonal-prismatic coordination geometries. Attempts to prepare alkyl complexes containing â-hydrogen
atoms resulted instead in the isolation of [Ti(Me2ATI)3] or [Ti2Cl2(Me2ATI)4], depending on the alkyl reagent
and stoichiometry. Because of the modest steric requirements of the {Ti(Me2ATI)2}2+ fragment, five-coordinate
Ti(IV) complexes were only generated with a bulky σ-2π donor ligand, [Ti(N-(2,6)-i-Pr2C6H3)(Me2ATI)2] being
a specific example. Attempts to prepare the isoelectronic oxo analogue afforded only dimeric [Ti2O2(Me2ATI)4].
Comparison of the metrical parameters for these complexes with those in the literature containing aryloxide and
benzamidinate ligands indicate that the {Ti(Me2ATI)2}2+ fragment is quite electron releasing.
Introduction
Inorganic chemistry continues to be enriched by the introduc-
tion of novel ligand systems. In addition to offering new
compositions, such ligands provide a means for controlling metal
center reactivity. In the case of early transition metals, noncy-
clopentadienyl compounds have been widely explored in an
attempt to improve upon existing metallocene-based olefin
polymerization catalysts. Various anionic nitrogen and oxygen
donor ligands of different denticity have been examined, with
most of the work having focused on Zr and Hf chemistry.1-4
There are only scattered reports of titanium compounds with
these types of ligands, most of which have attempted to stabilize
metal-ligand multiply bonded species or Ti(III) derivatives.5-10
Our laboratory has had a longstanding interest in the
tropocoronand ligand family H2TC-(n,m) as a means of control-
ling metal ion reactivity by varying the length of the linker
chains, n and m (Figure 1).11 Previously we reported the
chemistry of Zr and Hf tropocoronand complexes.12,13 More
Figure 1. Drawings of the H2TC-(n,m) and HR2ATI ligands.
recent efforts have focused on three-component carbonyl
coupling reactions, with the use of titanium aminotroponiminate
(ATI) compounds.14 The ATI ligand class was attractive since
its members are significantly easier to prepare than the tropo-
coronand macrocycles, and the steric properties of HR2ATI
(Figure 1) can be readily manipulated by varying the R groups.
Investigations of early transition metal chemistry with ami-
notroponiminate ligands are few, the only reports to our
knowledge involving [M(R2ATI)3] complexes, M ) V, Cr, and
(i-Pr)2ATI complexes with Zr, Hf, and related lanthanide
metals.15-19
The reaction chemistry of dialkyl titanium aminotroponimi-
nate complexes has benefitted from the steric and solubility
properties of the Me2ATI ligand. In this article, we describe
our investigations of the coordination chemistry of titanium
N,N′-dimethylaminotroponiminate complexes. The results con-
tribute significantly to the literature on complexes with ancillary
ligands other than cyclopentadienyl. From comparisons with
other work, we can gauge the donating capability and steric
(1) Hagadorn, J. R.; Arnold, J. J. Chem. Soc., Dalton Trans. 1997, 3087-
3096.
(2) Walther, D.; Fischer, R.; Go¨rls, H.; Koch, J.; Schweder, B. J.
Organomet. Chem. 1996, 508, 13-22.
(3) Black, D. G.; Swenson, D. C.; Jordan, R. F.; Rogers, R. D.
Organometallics 1995, 14, 3539-3550.
(4) Giannini, L.; Solari, E.; De Angelis, S.; Ward, T. R.; Floriani, C.;
Chiesi-Villa, A.; Rizzoli, C. J. Am. Chem. Soc. 1995, 117, 5801-
5811.
(5) Goedken, V. L.; Ladd, J. A. J. Chem. Soc., Chem. Commun. 1982,
142-144.
(6) Mountford, P. J. Chem. Soc., Chem. Commun. 1997, 2127-2134.
(7) Yang, C.-H.; Goedken, V. L. J. Chem. Soc., Chem. Commun. 1986,
1101-1102.
(13) Scott, M. J.; Lippard, S. J. J. Am. Chem. Soc. 1997, 119, 3411-3412.
(14) Steinhuebel, D. P.; Lippard, S. J. Organometallics 1999, 18, 109-
111.
(8) Budzelaar, P. H. M.; van Oort, A. B.; Orpen, A. G. Eur. J. Inorg.
Chem. 1998, 1485-1494.
(9) De Angelis, S.; Solari, E.; Gallo, E.; Floriani, C.; Chiesi-Villa, A.;
Rizzoli, C. Inorg. Chem. 1992, 31, 2520-2527.
(10) Kisko, J. L.; Hascall, T.; Parkin, G. J. Am. Chem. Soc. 1997, 119,
7609-7610.
(15) Roesky, P. W. Chem. Ber. 1997, 130, 859-862.
(16) Roesky, P. W. Eur. J. Inorg. Chem. 1998, 593-596.
(17) Roesky, P. W. Inorg. Chem. 1998, 37, 4507-4511.
(18) Eaton, D. R.; McClellan, W. R.; Weiher, J. F. Inorg. Chem. 1968, 7,
2040-2046.
(19) Dehnen, S.; Bu¨rgstein, M. R.; Roesky, P. W. J. Chem. Soc., Dalton
Trans. 1998, 2425-2429.
(11) Jaynes, B. S.; Ren, T.; Masschelein, A.; Lippard, S. J. J. Am. Chem.
Soc. 1993, 115, 5589-5599.
(12) Scott, M. J.; Lippard, S. J. Organometallics 1998, 17, 466-474.
10.1021/ic9909072 CCC: $18.00 © 1999 American Chemical Society
Published on Web 12/08/1999

6226 Inorganic Chemistry, Vol. 38, No. 26, 1999
Steinhuebel and Lippard
minimum amount of toluene, filtered, and carefully layered with
pentane. This solution was stored at -30 °C for 24 h during which
time more pentane was added. The deep red crystalline mass was
isolated on a frit, washed with cold pentane, and dried to yield
analytically pure product (471 mg, 61%). Crystals suitable for X-ray
crystallography were obtained in an analogous fashion. 1H NMR (C6D6,
250 MHz): δ 6.97 (4H, d, J ) 10.3 Hz), 6.52 (4H, d, J ) 11.2 Hz),
6.42 (2H, t, J ) 9.4 Hz), 3.09 (12H, s), 1.45 (6H, s). 13C{1H} (C6D6,
250 MHz): δ 164.6, 135.2, 120.7, 111.4, 64.8, 40.1. Anal. Calcd for
TiC20H28N4: C, 64.51; H, 7.58; N, 15.05. Found: C, 64.46; H, 7.58;
N, 14.89.
[TiPh2(Me2ATI)2] (4). A suspension of [TiCl2(Me2ATI)2] (204 mg,
0.494 mmol) in diethyl ether was cooled to -30 °C. To this suspension,
in dim room light, was added phenylmagnesium bromide (3 M in ether,
329 µL, 0.987 mmol), and the color of the resulting homogeneous
solution changed to deep red. After a few minutes, the product began
to precipitate and stirring was continued for 15 min. The red solid was
isolated on a frit, washed with pentane, and dried. This solid was then
dissolved in benzene and filtered, and the solvent was removed. The
residue was then collected with pentane, washed, and dried to yield
the product as a dull red powder (194 mg, 70%). Plates suitable for
X-ray crystallography were obtained by vapor diffusion of pentane into
a saturated dichloromethane solution at -30 °C. 1H NMR (C6D6, 250
MHz): δ 7.51 (4H, d, J ) 7.7 Hz), 7.07 (6H, m), 6.94 (4H, t, J ) 11.2
Hz), 6.51 (4H, d, J ) 11.2 Hz), 6.42 (2H, t, J ) 9.3 Hz) 2.88 (12H, s).
Anal. Calcd for TiC30H32N4: C, 72.57; H, 6.50; N, 11.28. Found: C,
72.59; H, 6.35; N, 10.42.
properties of aminotroponiminate titanium systems. The ultimate
goal is to use this knowledge in order to control the reactivity
of such complexes.
Experimental Section
Materials and Methods. Hexane and benzene were distilled from
sodium benzophenone ketyl under nitrogen. Toluene was distilled from
sodium and halogenated solvents were distilled from calcium hydride
under nitrogen. Diethyl ether was passed through a column of activated
alumina and pentane was passed through a column of Ridox catalyst
and alumina and then collected under vacuum. C6D6 and CD2Cl2 were
degassed three times and stored over molecular sieves. CDCl3 was
distilled from KHCO3, degassed three times, and stored over molecular
sieves. [TiCl2(NMe2)2]20 was prepared by slowly adding a toluene
solution of TiCl4 to Ti(NMe2)4 dissolved in toluene. After stirring for
3 h, the solution was evaporated and washed with cold toluene and
pentane to afford [TiCl2(NMe2)2] as a brown-red powder in 85% yield.
23
The reagents HMe2ATI,21 Li(NH-(2,6)-i-Pr2C6H3),22 and TiCl3(THF)3
were prepared as reported in the literature. All Grignard reagents,
n-BuLi, and trimethylsilyl triflate were purchased from Aldrich and
used as received. Experiments were either performed in a nitrogen-
filled glovebox or with conventional Schlenk line techniques under
argon. Evans method magnetic susceptibility measurements were made
as described in the literature.24 NMR spectra were recorded on a Bruker
AC 250, Varian Unity, or Mercury 300 spectrometer at ambient probe
1
temperature, 283 K, and referenced to the internal H and 13C solvent
peaks. Infrared spectra were recorded as pressed KBr disks with a
BioRad FTS-135 FTIR spectrometer. EPR spectra were recorded in
toluene solution on a Bruker model 300 ESP X-band spectrometer
operating at 9.47 GHz and running WinEPR software. Low temperatures
were maintained with a liquid He Oxford Instruments EPR 900 cryostat.
[TiCl2(Me2ATI)2] (1). To a rapidly stirred slurry of TiCl2(NMe2)2
(2.17 g, 10.49 mmol) in 150 mL of benzene/toluene (3:1) was added
a benzene solution of HMe2ATI (3.21 g, 21.7 mmol). The slurry
immediately turned purple and after 30 min it was almost black. The
thick suspension was vigorously stirred for an additional 4 h, and then
the fluffy purple product was collected on a frit. The solid was washed
with pentane until the washings were colorless and dried under vacuum
to yield the product (4.25 g, 95%). This material was used without
[TiCl(CH2SiMe3)(Me2ATI)2] (5). A suspension of [TiCl2(Me2ATI)2]
(292 mg, 0.707 mmol) in CH2Cl2 was treated with Me3SiCH2MgCl (1
M in Et2O, 707 µL, 0.707 mmol) at -30 °C. The red-purple solution
was stirred for 2 h, treated with dioxane (1-2 mL), and filtered. The
solvent was removed, and the red-brown solid was washed with pentane
and dried to yield 5 (280 mg, 85%). Vapor diffusion of pentane into a
saturated toluene solution at -30 °C yielded red blocks suitable for
1
X-ray work and elemental analysis. H NMR (C6D6, 250 MHz): δ
6.81 (4H, d, J ) 10.5 Hz), 6.27 (6H, m), 3.20 (12H, s), 2.33 (2H, s),
0.14 (9H, s). 13C{1H} (C6D6, 75.4 MHz): δ 164.4, 135.7, 122.4, 112.5,
92.4, 42.2, 3.5. Anal. Calcd for TiC22H33N4SiCl: C, 56.83; H, 7.15;
N, 12.05. Found: C, 56.23; H, 6.97; N, 11.54.
[TiMePh(Me2ATI)2] (6). A solution of [TiClMe(Me2ATI)2], 0.034
M in 15 mL of CH2Cl2, generated by treating 1 with MeMgCl (1 equiv)
in CH2Cl2, was allowed to react with PhMgBr (3 M in Et2O, 168 µL,
0.504 mmol) at -30 °C in dim room light. The red solution was stirred
for 30 min and then filtered to yield a red powder (120 mg, 55%) that
was dried. The solid was extracted with CH2Cl2, treated with dioxane
(1-2 mL), and filtered. The solvent was removed and the red residue
washed with pentane. Crystallization by vapor diffusion of pentane into
a toluene solution at -30 °C yielded red blocks suitable for X-ray work.
1H NMR (250 MHz, C6D6): δ 7.46 (2H, d, J ) 7.6 Hz), 7.14 (3H, m),
7.00 (4H, t, J ) 11.3 Hz), 6.59 (4H, d, J ) 11.2 Hz), 6.46 (2H, t, J )
9.3 Hz), 2.95 (12H, s), 1.49 (3H, s). Anal. Calcd for TiC25H30N4: C,
69.12; H, 6.96; N, 12.90. Found: C, 69.74; H, 7.07; N, 12.75.
[Ti(Me2ATI)3] (7). n-Butyllithium (1.6 M in hexanes, 987 µL, 1.58
mmol) was added to a stirred solution of HMe2ATI (234 mg, 1.58
mmol) in THF. After the orange-yellow solution was stirred for 30
min, it was added dropwise to a slurry of TiCl3(THF)3 (195 mg, 0.526
mmol) in THF. The dark brown solution was stirred overnight and
then filtered. The solvent was removed and the brown solid dissolved
in hot benzene (10-15 mL), filtered, and layered with pentane to yield
large, dark brown blocks (180 mg, 70%) suitable for X-ray crystal-
lography. UV-vis (THF) nm (M-1 cm-1): 822 (1399), 565 (1049),
480 (9860), 462 (10070), 432 (8180). EPR (toluene, 14.4 K): g )
1.95, 1.99. Anal. Calcd for TiC27H33N6: C, 66.25; H, 6.80; N, 17.17.
Found: C, 65.92; H, 6.12; N, 17.14.
1
further purification. H NMR (C6D6, 250 MHz): δ 6.62 (4H, t, J )
9.3 Hz), 6.13 (2H, t, J ) 9.4 Hz), 6.0 (4H, d, J ) 11.3 Hz), 3.38 (12H,
1
s). H NMR (CDCl3, 250 MHz): δ 7.17 (4H, t, J ) 10.1 Hz), 6.55
(6H, m), 3.48 (12H, s).
[Ti(OTf)2(Me2ATI)2] (2). To a rapidly stirred slurry of [TiCl2(Me2-
ATI)2] (173 mg, 0.419 mmol) in 25 mL of dichloromethane was added
neat trimethylsilyl triflate (176 µL, 0.838 mmol). The purple slurry
turned brilliant blue-purple and was stirred for 5 h. The solution was
filtered and the solvent removed. The purple residue was dissolved in
warm CH2Cl2 and filtered. After cooling, pentane was layered on the
filtrate. Storage at -30 °C yielded purple blocks (190 mg, 70%) suitable
for X-ray crystallography. 1H NMR (CD2Cl2, 300 MHz): δ 7.55 (4H,
q, J ) 10.8 Hz), 7.00 (2H, t, J ) 10.3 Hz), 6.87 (4H, d, J ) 11.2 Hz),
3.49 (12H, s). FTIR (KBr, cm-1) 3200, 3000, 2885, 1586, 1458, 1407,
1352, 1273, 1241, 1166, 1101, 1032, 916, 885, 843, 758, 744, 714,
692, 632, 592, 569, 520, 509, 482, 472. Anal. Calcd for
TiC20H22N4O6F6S2: C, 37.51; H, 3.46; N, 8.75. Found: C, 37.97; H,
3.38; N, 8.99.
[TiMe2(Me2ATI)2] (3). A suspension of [TiCl2(Me2ATI)2] (862 mg,
2.09 mmol) in 100 mL of diethyl ether was cooled to -30 °C.
Methylmagnesium chloride (3 M in THF, 1.46 mL, 4.38 mmol) was
added dropwise to the solution which immediately turned reddish
purple. After complete addition, the solution was a brilliant red color.
The slurry was stirred for 30 min and then filtered through Celite. The
solvent was evaporated to yield a red solid, which was dissolved in a
[Ti2Cl2(Me2ATI)4] (8). A suspension of [TiCl2(Me2ATI)2] (75 mg,
0.182 mmol) in diethyl ether was cooled to -30 °C. Isobutylmagnesium
chloride (2 M in diethyl ether, 91 µL, 0.182 mmol) was added, and
the red-brown solution was stirred for 5 min and then recooled to -30
°C for 15 min. The solution was quickly filtered and then stored at
-30 °C to yield brown blocks (25 mg, 36%) suitable for X-ray
crystallography. The sample for elemental analysis was crystallized by
(20) Benzing, E.; Kornicker, W. Chem. Ber. 1961, 94, 2263-2267.
(21) Dias, H. V. R.; Jin, W. Inorg. Chem. 1996, 35, 6546-6551.
(22) Berreau, L. M.; Young, V. G., Jr.; Woo, L. K. Inorg. Chem. 1995,
34, 527-529.
(23) Manzer, L. E. Inorg. Synth. 1982, 21, 135-140.
(24) Sur, S. K. J. Magn. Reson. 1989, 82, 169-173.

Titanium Aminotroponiminate Complexes
Inorganic Chemistry, Vol. 38, No. 26, 1999 6227
vapor diffusion of pentane into a toluene solution at -30 °C. UV-vis
(THF) nm (M-1 cm-1): 461 (10600), 432 (8385). Evans method:
(C6D6, 293 K) µeff ) 2.5 µB. EPR (toluene, rt): g ) 1.937. Anal. Calcd
for Ti2C36H44N8Cl2: C, 57.23; H, 5.87; N, 14.83. Found: C, 57.37; H,
5.80; N, 14.86.
[Ti(N-(2,6)-(i-Pr)2C6H3)(Me2ATI)2] (9). Solid Li(NH-(2,6)-
(i-Pr)2C6H3) (208 mg, 1.13 mmol) was added to a benzene suspension
of [TiCl2(Me2ATI)2] (234 mg, 0.57 mmol). The dark red solution was
stirred overnight and filtered, and then the solvent was removed. The
resulting solid was washed thoroughly with pentane and dried. The
residue was dissolved in hot toluene and, after cooling, the solution
was layered with pentane and stored at -30 °C to yield 200 mg (68%)
of dark red blocks after washing with cold pentane and drying. Crystals
suitable for X-ray crystallography were obtained in a similar manner.
1H NMR (C6D6, 250 MHz): δ 7.06 (2H, d, J ) 7.5 Hz), 6.88 (5H, m),
6.39 (4H, d, J ) 11.3 Hz), 6.29 (2H, t, J ) 9.2 Hz), 4.05 (2H, sept, J
) 6.9 Hz), 3.18 (12H, s), 1.30 (12H, d, J ) 6.9 Hz). 13C{1H} (C6D6,
75.4 MHz): δ 165.4, 158.5, 141.9, 135.5, 122.4, 121.2, 119.8, 113.1,
38.9, 29.4, 24.3. Anal. Calcd for TiC30H39N5: C, 69.62; H, 7.60; N,
13.53. Found: C, 69.67; H, 7.77; N, 13.68.
[Ti2O2(Me2ATI)4] (10). A benzene solution of [TiMe2(Me2ATI)2]
(86 mg, 0.231 mmol) was treated with degassed water (4 µL, 0.3 mmol).
The light red solution was stirred for 12 h during which time a dull
red powder precipitated from the solution. This material was collected,
washed with pentane, and dried (22 mg, 26%). Vapor diffusion of
pentane into a saturated benzene solution at room temperature yielded
1
long red-orange needles suitable for X-ray crystallography. H NMR
(CDCl3, 250 MHz): δ 6.94 (8H, m), 6.36 (8H, d, J ) 11.1 Hz), 6.27
(4H, t, J ) 9.3 Hz), 3.29 (12H, s), 2.88 (12H, s). 13C{1H} (CDCl3,
75.4 MHz): δ 165.4, 163.3, 135.2, 134.9, 118.7, 112.1, 109.9, 43.9,
38.6. FTIR (KBr, cm-1) 3200, 3000, 2868, 1592, 1517, 1451, 1432,
1339, 1384, 1346, 1268, 1228, 1146, 1100, 1042, 981, 888, 871, 823,
719, 638, 598, 500, 484. Anal. Calcd for Ti2C36H44N8O2: C, 60.34; H,
6.19; N, 15.64. Found: C, 60.68; H, 6.23; N, 15.49.
Collection and Reduction of X-ray Data. All crystals were covered
with Paratone-N (Exxon) and then removed from the drybox for
examination. Suitable single crystals were attached to the tips of quartz
fibers and transferred to a Bruker CCD X-ray diffraction system with
graphite-monochromatized Mo KR radiation (λ ) 0.71073 Å) controlled
by a pentium-based PC running the SMART software package. The
temperature of the crystal was maintained with a Bruker LT-2A nitrogen
cryostat. Procedures for data collection and reduction have been
previously reported.25 Space groups were determined by examining
systematic absences and confirmed by the successful solution and
refinement of the structures. The structures were solved by using either
the direct methods program SIR-92,26 XS or Patterson methods and
then refined by full matrix least squares and Fourier techniques with
SHELXTL-PLUS.27 In general all non-hydrogen atoms were refined
anisotropically; hydrogen atoms were either located from the difference
maps and refined isotropically or, for compound 8, assigned idealized
positions and given a thermal parameter 1.2 times the thermal parameter
of the carbon atom to which each was attached. Absorption corrections
were performed with the SADABS program.28 Compound 10 crystal-
lizes with two lattice benzene molecules, the carbon atoms of which
were refined anisotropically and hydrogen atoms were added. A
summary of X-ray crystallographic data for 2-10 is shown in Table
1. Labeled ORTEP plots of all structures representing 50% thermal
ellipsoids are shown in Figures 2 and 3. Full crystallographic informa-
tion and bond distances and angles can be found in Tables S1-S36.
(25) Feig, A. L.; Bautista, M. T.; Lippard, S. J. Inorg. Chem. 1996, 35,
6892-6898.
(26) Burla, M. C.; Camalli, M.; Cascarano, G.; Giacovazzo, C.; Polidori,
G.; Spagna, R.; Viterbo, D. J. Appl. Crystallogr. 1989, 22, 389-393.
(27) SHELXTL: Structure Analysis Program. 5.1; Bruker Analytical X-ray
Systems; Madison, WI, 1997.
(28) Program written by Professor George Sheldrick at University of
Go¨ttingen which corrects data collected on Bruker CCD and multiwire
detectors for absorption and decay.

6228 Inorganic Chemistry, Vol. 38, No. 26, 1999
Steinhuebel and Lippard
Figure 2. ORTEP diagrams of [Ti(OTf)2(Me2ATI)2] (2), [TiMe2(Me2ATI)2] (3), [TiPh2(Me2ATI)2] (4), [TiCl(CH2SiMe3)(Me2ATI)2] (5), [Ti(Me)-
(Ph)(Me2ATI)2] (6), and [Ti(Me2ATI)3] (7) showing 50% thermal ellipsoids and selected atom labels.
C6H6
Results and Discussion
TiCl (Me ATI)
(1)
2
TiCl2(NMe2)2 + 2 HMe2ATI
8
2
2
Preparation and Characterization of [TiCl2(Me2ATI)2]
and [Ti(OTf)2(Me2ATI)2]. A convenient entry into titanium
aminotroponiminate chemistry was obtained through the reaction
of HMe2ATI with TiCl2(NMe2)2 (eq 1). This chemistry afforded
[TiCl2(Me2ATI)2] (1) as a purple powder in nearly quantitative
yield on a 1-2 g scale. The 1H NMR spectrum of this complex
is consistent with C2 symmetry. The poor solubility of 1 has
1
prevented its full characterization. A more tractable derivative
was obtained by treatment of 1 with 2 equiv of Me3SiOTf in
CH2Cl2 to yield purple, crystalline [Ti(OTf)2(Me2ATI)2] (2) in
80% yield (Figure 4). Compound 2 is also C2-symmetric in
solution and contains strong bands in the infrared spectrum at

Titanium Aminotroponiminate Complexes
Inorganic Chemistry, Vol. 38, No. 26, 1999 6229
Figure 3. ORTEP diagrams of [Ti2Cl2(Me2ATI)4] (8), [Ti(N-(2,6)-i-Pr2C6H3)(Me2ATI)2] (9), and [Ti2O2(Me2ATI)4] (10) showing 50% thermal
ellipsoids and selected atom labels.
1352, 1032, and 632 cm-1, consistent with the presence of a
triflate group. The structure of 2 determined by X-ray crystal-
lography reveals nearly octahedral coordination geometry with
two monodentate triflate ligands (Figure 2). The three trans-
angles, N(1a)-Ti-O(1a), N(2)-Ti-N(2a), and N(1)-Ti-O(1)
are 163.9(1)°, 176.7(2)°, and 163.9(1)°, respectively. The Ti-O
bond distance of 2.046(2) Å is in the range of other structurally
characterized titanium triflate complexes.29
Preparation and Characterization of [TiMe2(Me2ATI)2]
and [TiPh2(Me2ATI)2]. The chloride ligands of 1 can be
substituted by either methyl or phenyl groups. Reaction with
the appropriate Grignard reagent gave dark red, crystalline
[TiMe2(Me2ATI)2] (3) or [TiPh2(Me2ATI)2] (4) after workup
(Figure 4). Compound 3 is best isolated after filtration of the
ether solution, evaporation, and crystallization from toluene.
Compound 4 can be obtained as a crude, thermally sensitive
powder in reasonable yield. Recrystallization of 4 is challenging
due to its moderate solubility and instability in solution. These
factors account for the modest isolated yield of 30-40%. Both
3 and 4 display NMR spectra consistent with C2-symmetric
molecules. The structure of 3 has been determined by X-ray
crystallography and displays cis stereochemistry. The complex
can be described as distorted trigonal prismatic (Figure 2).30
Complex 3 contains Ti-C bond distances of 2.145(2) and 2.166-
(2) Å, and the C-Ti-C angle is 86.29(7)°. The solid-state
structure of 4 is very similar to that of 3 and the Ti-C bond
distances of 2.170(3) and 2.185(3) Å are longer than those
observed in 3 (Figure 2). The sterically more demanding phenyl
group has also increased the C-Ti-C angle to 96.7(1)°. The
(29) Donkervoort, J. G.; Jastrzebski, J. T. B. H.; Deelman, B.-J.; Kooijman,
H.; Veldman, N.; Spek, A. L.; van Koten, G. Organometallics 1997,
16, 4174-4184.
(30) Kepert, D. L. Progress in Inorganic Chemistry; Lippard, S. J., Eds.;
John Wiley & Sons: New York, 1975; Vol. 23, pp 1-65.

6230 Inorganic Chemistry, Vol. 38, No. 26, 1999
Steinhuebel and Lippard
Figure 4. Summary of the reaction chemistry of [TiCl2(Me2ATI)2].
Ti-C bond distance is 2.122(2) Å for the titanium trimethylsilyl
substituted benzamidinate complex [TiMe2{PhC(NSiMe3)2}2],31
and the average Ti-C bond lengths of the aryloxide titanium
phenyl complex [TiPh2(OAr)2] is 2.088 Å,32 both shorter than
the Ti-C bond lengths in 3 and 4. The Ti-C bond length of
2.15(1) Å for the salen complex [TiMe2(salen)] is very close to
the average Ti-C bond distance of 2.155 Å for 3.33 These data
suggest that the {Ti(Me2ATI)2}2+ fragment is more electron rich
than the corresponding aryloxide and benzamidinate fragments
and comparable to the salen complex. The {Cp2Ti}2+ fragment
is even more electron releasing, consistent with its formally
higher electron count.34,35
tadienyl diphenyl complexes has been reported previously,
although this reaction typically proceeds under photochemical
conditions.36,37 In contrast to the solution chemistry of [TiMe2-
(salen)], 3 and 4 display no propensity for the methyl group to
migrate to the imine carbon atom.33
Preparation and Characterization of [TiCl(CH2SiMe3)-
(Me2ATI)2] and [TiMePh(Me2ATI)2]. A titanium alkyl-
chloride complex would be a versatile starting material for the
synthesis of mixed alkyl complexes. The reaction of [TiCl2(Me2-
ATI)2] with 1 equiv of Me3SiCH2MgCl allows isolation of
[TiCl(CH2SiMe3)(Me2ATI)2] (5), which has been fully charac-
terized, including an X-ray structural determination (Figure 2).
The important features in the 1H NMR spectrum of 5 are a 2H
singlet at 2.33 ppm, a 9H singlet at 0.14 ppm, and a 12H singlet
at 3.2 ppm corresponding to the two signals for the trimethylsilyl
methyl and aliphatic signals of the Me2ATI ligand, respectively.
Compound 5 is probably fluxional in solution at room temper-
ature since it displays C2-symmetric 1H and 13C NMR spectra.
The X-ray structure of 5 has been determined and confirms
nearly octahedral coordination geometry characterized by the
three trans angles N(3)-Ti-C(19), N(1)-Ti-N(4), and N(2)-
Ti-Cl of 160.57(9)°, 160.49(8)°, and 165.67(6)° (Figure 2,
Table 2). The Ti-C bond length is 2.154(3) Å, whereas the
Ti-Cl distance is 2.3287(7) Å. Apparently, one trimethylsilyl
methyl group is the steric maximum for the {Ti(Me2ATI)2}2+
fragment, since the reaction of 2 equiv of Me3SiCH2MgCl with
Compound 3 is thermally robust in the solid state but less so
in solution; it is best stored as a solid at -30 °C. Compound 4,
however, is significantly less thermally stable than 3, especially
in solution. Storage of C6D6 solutions of 4 for greater than 45
min at room temperature, even in the dark, results in decom-
position. This decomposition is characterized by a decrease in
1
intensity of all the resonances in the H NMR spectrum of 4
and the appearance of peaks most likely corresponding to
biphenyl. Production of biphenyl from early metal cyclopen-
(31) Thiele, K.-H.; Windisch, H.; Windisch, H.; Edelmann, F. T.; Kilimann,
U.; Noltemeyer, M. Z. Anorg. Allg. Chem. 1996, 622, 713-716.
(32) Chesnut, R. W.; Durfee, L. D.; Fanwick, P. E.; Rothwell, I. P.; Folting,
K.; Huffman, J. C. Polyhedron 1987, 6, 2019-2026.
(33) Floriani, C.; Solari, E.; Corazza, F.; Chiesi-Villa, A.; Guastini, C.
Angew. Chem., Int. Ed. Engl. 1989, 28, 64-66.
(34) Thewalt, U.; Wo¨hrle, T. J. Organomet. Chem. 1994, 464, C17-C19.
(35) Kocman, V.; Rucklidge, J. C.; O’Brien, R. J.; Santo, W. J. Chem.
Soc., Chem. Commun. 1971, 1340.
(36) Erker, G. J. Organomet. Chem. 1977, 134, 189-202.
(37) Rausch, M. D.; Boon, W. H.; Mintz, E. A. J. Organomet. Chem. 1978,
160, 81-92.

Titanium Aminotroponiminate Complexes
Inorganic Chemistry, Vol. 38, No. 26, 1999 6231
Table 2. Selected Bond Distances and Anglesa
spectra to that of 5, with 3H singlets at 1.59 or 1.55 ppm,
complex
distances (Å)
angles (deg)
C6D6
TiX2(Me2ATI)2
X ) Cl, OTf
+ TiMe2(Me2ATI)2
8
2
Ti-N(1)
2.006(3) N(1a)-Ti-O(1a)
163.9(1)
176.7(2)
163.9(1)
83.7(2)
72.36(4)
83.12(6)
79.68(6)
86.29(7)
147.84(6)
123.25(5)
72.77(10)
80.86(11)
78.39(11)
96.7(1)
151.52(10)
119.82(11)
160.57(9)
160.49(8)
165.67(6)
92.04(8)
Ti-N(2)
Ti-O(1)
2.045(3) N(2)-Ti-N(2a)
2.046(2) N(1)-Ti-O(1)
O(1)-Ti-O(1a)
2TiXMe(Me2ATI)2
(2)
X ) Cl, OTf
3
4
5
6
Ti-N(1)
Ti-N(2)
Ti-N(3)
Ti-N(4)
Ti-C(20)
Ti-C(19)
Ti-N(1)
Ti-N(2)
Ti-N(3)
Ti-N(4)
Ti-C(19)
Ti-C(25)
Ti-N(1)
Ti-N(2)
Ti-N(3)
Ti-N(4)
Ti-Cl(1)
Ti-C(19)
Ti-N(1)
Ti-N(2)
Ti-N(3)
Ti-N(4)
Ti-C(19)
Ti-C(25)
Ti-N(1)
Ti-N(2)
Ti-N(3)
2.125(1) N(4)-Ti-N(3)
2.095(1) C(19)-Ti-N(1)
2.120(1) C(20)-Ti-N(2)
2.114(1) C(19)-Ti-C(20)
2.166(2) N(3)-Ti-C(20)
2.145(2) N(2)-Ti-N(4)
2.104(3) N(4)-Ti-N(3)
2.082(3) N(1)-Ti-C(19)
2.116(3) N(2)-Ti-C(25)
2.062(2) C(19)-Ti-C(25)
2.185(3) N(1)-Ti-N(3)
2.170(3) C(19)-Ti-N(4)
2.087(2) N(3)-Ti-C(19)
2.091(2) N(1)-Ti-N(4)
2.117(2) N(2)-Ti-Cl(1)
2.098(2) Cl(1)-Ti-C(19)
2.3287(7)
respectively, for the methyl groups. Generation of [TiMeCl-
(Me2ATI)2] in CH2Cl2 provides a convenient starting material
for the preparation of [TiMeR′(Me2ATI)2] complexes. Treatment
of [TiMeCl(Me2ATI)2], formed in situ, with PhMgCl in diethyl
ether provides [TiMePh(Me2ATI)2] (6) after crystallization.
Although the yield of crude 6 is good (65%), recrystallization
1
is difficult and the isolated yield is therefore modest. The H
NMR spectrum of 6 is consistent with a C2-symmetric molecule
and comprises a singlet at 1.49 ppm for the methyl group in
addition to aromatic resonances. The X-ray crystal structure of
6 has been determined and is very similar to the solid-state
structures of 3 and 4 (Figure 2, Table 2). The Ti-C(methyl)
and Ti-C(phenyl) bond distances are 2.148(3) and 2.171(2) Å,
whereas the C-Ti-C angle is 93.3(1)°, comparable to the
values of 86.29(7)° in 3 and 96.7(1)° in 4. Compound 6 displays
thermal stability between that of 3 and 4; it is best stored at
-35 °C as a solid. Interestingly, 6 cannot be prepared by mixing
2.154(3)
2.079(2) N(1)-Ti-N(2)
2.122(2) N(4)-Ti-C(25)
2.116(2) N(3)-Ti-C(19)
2.102(2) C(19)-Ti-C(25)
2.171(2) N(3)-Ti-N(2)
2.148(3) C(19)-Ti-N(1)
2.121(1) N(3)-Ti-N(1a)
2.099(2) N(2)-Ti-N(2a)
2.110(1) N(1)-Ti-N(3a)
72.96(7)
79.32(11)
81.45(8)
93.30(12)
154.32(7)
119.66(9)
167.26(6)
163.87(8)
167.26(6)
1
3 and 4 in C6D6, as revealed by H NMR spectroscopy.
Preparation and Characterization of [Ti(Me2ATI)3] and
[Ti2Cl2(Me2ATI)4]. Certain aminotroponiminate ligands afford
Ti(IV) dialkyl complexes that contain â-hydrogen atoms.38 For
this reason, reaction of 1 with other Grignard and lithium
reagents was investigated. Treatment of 1 with 2 equiv of n-BuLi
in ether resulted in an immediate color change to brown-black,
7
8
Ti(1)-N(5) 2.092(3) N(8)-Ti(1)-N(5) 165.4(1)
Ti(1)-N(6) 2.088(3) Cl(2)-Ti(1)-N(7) 161.26(9)
Ti(1)-N(7) 2.081(3) Cl(1)-Ti(1)-N(6) 164.75(9)
Ti(1)-N(8) 2.112(3) N(3)-Ti(2)-Cl(2) 165.16(8)
Ti(1)-Cl(1) 2.550(2) N(1)-Ti(2)-Cl(1) 163.52(9)
Ti(1)-Cl(2) 2.526(1) N(4)-Ti(2)-N(2) 161.51(11)
Ti(2)-N(1) 2.086(3) Ti(2)-Cl(2)-Ti(1) 98.29(5)
Ti(2)-N(2) 2.116(3) Cl(2)-Ti(2)-Cl(1) 82.12(5)
Ti(2)-N(3) 2.094(3) Cl(2)-Ti(1)-Cl(1) 80.70(5)
Ti(2)-N(4) 2.107(3) Ti(2)-Cl(1)-Ti(1) 97.97(5)
Ti(2)-Cl(1) 2.496(1) Ti(2)-Cl(2)-Ti(1) 98.29(5)
Ti(2)-Cl(2) 2.508(1)
1
and no resonances were observed in the H NMR spectrum of
the reaction mixture. A few brown-black crystals of [Ti(Me2-
ATI)3] (7) could be isolated, and the X-ray structure revealed
nearly octahedral coordination geometry with three trans
N-Ti-N angles (N(2a)-Ti-N(2), N(3a)-Ti-N(1), and N(3)-
Ti-N(1a)) of 163.87(8)°, 167.26(6)°, 167.26(6)° and Ti-N
bond distances of 2.099(2), 2.110(1), and 2.121(1) Å (Figure
2, Table 2). The overall structure is similar to that of other TiL3
(L ) bidentate ligand) complexes,39,40 but it differs slightly from
the solid-state structure of [Sc(trop)3], which has a coordination
geometry between octahedral and trigonal prismatic.41 Toluene
solutions of 7 at room temperature display an isotropic EPR
signal at g ) 1.96, which resolves into an axial spectrum with
g| ) 1.99 and g ) 1.95 at 14.4 K. These spectra are consistent
with the presence of a symmetric, mononuclear Ti(III) complex
and are very similar to those reported in the literature for TiL3
complexes, where L is either a monodentate or bidentate
monoanionic ligand.39,40,42-45 A more efficient, higher yielding
route to 7 is the reaction of [TiCl3(THF)3] with 3 equiv of LiMe2-
ATI in THF (eq 3). The preparation of [Ti(Me2ATI)3] completes
the series of Me2ATI tris-chelate complexes from titanium
through cobalt.18
Ti(1)-Ti(2) 3.808(2)
9
Ti-N(1)
Ti-N(2)
Ti-N(3)
Ti-N(4)
Ti-N(5)
2.089(1) N(4)-Ti-N(1)
2.098(1) N(2)-Ti-N(3)
2.105(1) N(3)-Ti-N(5)
2.099(1) N(5)-Ti-N(2)
1.734(1) Ti-N(5)-C(19)
162.10(5)
121.93(5)
118.37(6)
119.51(6)
167.1(1)
10
Ti(1)-N(5) 2.113(3) N(7)-Ti(1)-N(5) 156.7(1)
Ti(1)-N(6) 2.129(2) O(2)-Ti(1)-N(6) 158.8(1)
Ti(1)-N(7) 2.098(3) O(1)-Ti(1)-N(8) 163.0(1)
Ti(1)-N(8) 2.154(3) N(3)-Ti(2)-O(2) 163.2(1)
Ti(1)-O(1) 1.876(2) N(2)-Ti(2)-O(1) 159.4(1)
Ti(1)-O(2) 1.835(2) N(4)-Ti(2)-N(1) 157.8(1)
Ti(2)-N(1) 2.118(3) O(1)-Ti(2)-O(2)
Ti(2)-N(2) 2.138(3) O(1)-Ti(1)-O(2)
Ti(2)-N(3) 2.143(2) Ti(1)-O(1)-Ti(2)
Ti(2)-N(4) 2.091(3) Ti(1)-O(2)-Ti(2)
Ti(2)-O(1) 1.841(2)
Ti(2)-O(2) 1.878(2)
Ti(1)-Ti(2) 2.775(1)
83.18(9)
83.41(9)
96.56(9)
96.71(9)
(38) Steinhuebel, D. P.; Lippard, S. J. Organometallics 1999, 18, 3959-
3961.
(39) Cotton, F. A.; Wojtczak, W. A. Polyhedron 1994, 13, 1337-1341.
(40) Spannenberg, A.; Tillack, A.; Arndt, P.; Kirmse, R.; Kempe, R.
Polyhedron 1998, 17, 845-850.
(41) Anderson, T. J.; Neuman, M. A.; Melson, G. A. Inorg. Chem. 1974,
13, 158-163.
a Numbers in parentheses are estimated standard deviations of the
last significant figure. Atoms are labeled as indicated in Figures 2 and
3.
(42) Latesky, S. L.; Keddington, J.; McMullen, A. K.; Rothwell, I. P.;
Huffman, J. C. Inorg. Chem. 1985, 24, 995-1001.
(43) Bradley, D. C.; Copperthwaite, R. G.; Cotton, S. A.; Sales, K. D.;
Gibson, J. F. J. Chem. Soc., Dalton Trans. 1973, 191-194.
(44) Covert, K. J.; Wolczanski, P. T.; Hill, S. A.; Krusic, P. J. Inorg. Chem.
1992, 31, 66-78.
1 yields mostly 5 whereas reaction of lithium reagents or excess
Me3SiCH2MgCl with 1 affords Ti(III) complexes.
Mixing either 1 or 2 with equimolar amounts of 3 produces
solutions of either [TiMeCl(Me2ATI)2] or [TiMe(OTf)(Me2-
1
ATI)2], judging by H NMR spectroscopy (eq 2). These two
(45) Lukens, W. W., Jr.; Smith, M. R., III.; Andersen, R. A. J. Am. Chem.
Soc. 1996, 118, 1719-1728.
complexes are C2-symmetric in solution and display similar

6232 Inorganic Chemistry, Vol. 38, No. 26, 1999
Steinhuebel and Lippard
THF
1.734(1) Å; the Ti-N-C angle is 167.1(1) (Figure 3). The
remaining Ti-N bond distances are in the usual range. Titanium
aryl imido complexes are common in complexes having multiple
nitrogen ligands and many five-coordinate titanium aryl imido
analogues have been structurally characterized.6,22,54-56 Of this
group, [Ti(NPh)Cl2(tmeda)] has the shortest Ti-N bond length,
1.702(6) Å, whereas the salen complex [TiNAr(salen)] has the
longest one, 1.725(2) Å.57,58 Compound 9 is distinguished in
this class by having one of the longer Ti-N bond distances
and the smallest Ti-N-C angle. These data reflect the electron-
releasing character of the {Ti(Me2ATI)2}2+ fragment.
Preparation and Characterization of [Ti2O2(Me2ATI)4].
The steric influence of the isopropyl groups in the imido ligand
just discussed is further manifest by attempts to prepare the
isoelectronic oxo analogue, TiO(Me2ATI)2, which instead
resulted in isolation of dimeric [Ti2O2(Me2ATI)4] (10). Com-
pound 10 is best prepared by treating 3 with 1 equiv of water
in benzene solution (eq 4), although it can also be obtained in
Ti(Me ATI)
TiCl3(THF)3 + 3 LiMe2ATI
8
(3)
2
3
7
A different Grignard reagent, i-BuMgCl gives another
paramagnetic product in low yield. This material was identified
by X-ray crystallography as [Ti2Cl2(Me2ATI)4] (8) (Figure 3).
The X-ray structure of 8 reveals two nearly octahedral Ti(III)
centers with long Ti-Cl distances of 2.496(1), 2.508(1), 2.526-
(1), and 2.550(2) Å and a Ti‚‚‚Ti separation of 3.808(2) Å (Table
2). The i-BuMgCl reagent acts as a single electron reductant in
this reaction, and the resulting {TiCl(Me2ATI)2} complex
dimerizes. The {Ti2Cl2}4+ motif is common in titanium
chemistry and has been supported by several different classes
of ligands.46-50 The Ti‚‚‚Ti distance can vary in these complexes
from almost 4 Å in [Ti2Cl2Cp4] to 2.9 Å in either [Ti2Cl2(OAr)4]
or a dinuclear cyclohexyl substituted formamidinate complex
[Ti2Cl2{HC(NCy)2}4].46,47,50 Formation of [Ti2Cl2(Me2ATI)4]
fulfills the coordinative unsaturation of the {TiCl(Me2ATI)2}
fragment. The unsaturated character must not be of great
consequence since, by increasing the size of the R substituent
from Me to i-Pr, we were able to isolate monomeric [TiCl((i-
Pr)2ATI)2].51 Similar results, especially with amidinate and
cyclopentadienyl ligands, have been reported in the literature.52,53
(4)
Reaction of [TiCl2(Me2ATI)2] with allyl, vinyl, neopentyl
Grignard, or lithium phenyl acetylide under a variety of
conditions resulted in paramagnetic reaction mixtures. In some
cases, 6 or 7 could be isolated depending on the number of
equivalents of Grignard reagent that were used. Reaction of 1
with 2 equiv of neopentyl Grignard in the presence of excess
PMe3 also gave a paramagnetic reaction mixture. These synthetic
studies show that 1 is especially susceptible to reduction by
alkylating reagents and that the steric constraints of the {Ti-
(Me2ATI)2}2+ fragment only allow formation of monoalkyl
complexes, such as [TiCl(CH2SiMe3)(Me2ATI)2], having a bulky
group.
lower yield by the air oxidation of 7 in toluene solution. The
1H NMR spectrum of 7 in CDCl3 comprises two equal intensity
singlets for the methyl groups of Me2ATI, consistent with two
distinct methyl environments for the ATI ligand. The X-ray
crystal structure of 10 was determined and revealed both
titanium centers to have nearly octahedral coordination geometry
(Figure 3, Table 2). The Ti-O distances are short, 1.835(2),
1.876(2), 1.841(2), 1.878(2) Å, whereas the Ti-N distances are
in their normal range (2.1 Å). The {Ti2O2}4+ core has also been
previously described, and several examples have been structur-
ally characterized.59-62 The direct comparison of the results to
those for 10 is not straightforward because of differences in
coordination number and charge. The Ti-O bond distances in
10, at least when compared to those of [Ti2O2(acac)4], 1.831-
(3) Å, 1.824(4) Å, support the idea that the Me2ATI ligand is
a strong donator of electron density.61,62
Preparation and Characterization of [Ti(N-(2,6)-i-Pr2C6H3)-
(Me2ATI)2]. Since the putative five-coordinate {TiCl(Me2-
ATI)2} species readily dimerizes, we were interested to test
whether a five-coordinate Ti(IV) complex might be prepared
by using a bulky σ-2π ligand such as a 2,6-i-Pr-substituted
imide. Reaction of 2 equiv of Li(NH(2,6)-i-Pr2C6H3) with 1
afforded a new titanium complex and 1 equiv of arylamine
(Figure 4). The 1H NMR spectrum of the new complex displayed
a 12H doublet at 1.30 ppm and a 2H septet at 4.05 ppm,
1
consistent with a single i-Pr group environment. The H and
13C signals corresponding to Me2ATI were also consistent with
C2-symmetry. The structure of 9 was determined by X-ray
crystallography, revealing that the bulky aryl-imido ligand had
indeed stabilized a five-coordinate complex. The imido ligand
occupies the equatorial position of a trigonal bipyramidal
coordination polyhedron and the Ti-N bond distance is short,
Summary and Conclusions
The use of N,N′-dimethyl-substituted aminotroponiminates
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Titanium Aminotroponiminate Complexes
Inorganic Chemistry, Vol. 38, No. 26, 1999 6233
as ancillary ligands for the preparation of titanium complexes
has been demonstrated. A series of dialkyl derivatives and an
alkyl-aryl analogue have been prepared and structurally
characterized. Trivalent complexes were obtained by using an
appropriate â-hydrogen-containing Grignard or alkyllithium
reagent. The steric properies of the {Ti(Me2ATI)}2+ fragment
are not demanding, so that five-coordinate titanium(IV) com-
plexes were obtained only when a bulky σ-2π ligand was
employed. Otherwise, dinuclear complexes formed. Compari-
sons of structural data for this family of complexes to those in
the literature suggest that dialkyl-substituted aminotroponiminate
ligands are good donors of electron density; the {Ti(Me2ATI)}2+
fragment is electron rich.
Acknowledgment. This work was supported by a grant from
the National Science Foundation. We thank Dongwhan Lee and
Dr. Roman Davydov for assistance with EPR spectroscopy and
Dan Mindiola for assistance with Evans Method.
Supporting Information Available: Tables and figures reporting
bond distances, angles, and positional and thermal parameters for all
structurally characterized compounds including CIF files. This material
is available free of charge via the Internet at http://pubs.acs.org.
IC9909072