Copolymerization by Zinc Phenoxide Catalysts
J. Am. Chem. Soc., Vol. 120, No. 19, 1998 4691
for NMR experiments were purchased from Cambridge Isotope
Laboratories. Benzene-d6 was distilled over calcium hydride and stored
in the glovebox over molecular sieves. 1H NMR and 13C NMR spectra
were recorded on a Varian XL-200E superconducting high-resolution
spectrometer. 113Cd NMR spectra were recorded on a Varian XL-400E
superconducting high-resolution spectrometer operating at 88 MHz
using an external 0.1 M Cd(ClO4)2/D2O reference. Elemental analysis
were carried out by Canadian Microanalytical Services, Ltd.
Scheme 1
Synthesis of Cd(O-2,6-tBu2C6H3)2(THF)2 (1). Synthesis was
carried out in a manner similiar to the published procedure.6 Cd-
[N(SiMe3)2]2 (0.48 g, 1.11 mmol) in 2 mL of THF was stirred with a
solution of 2,6-di-tert-butylphenol (0.458 g, 2.22 mmol) in 2 mL of
THF. After the yellow solution was stirred for 2 h, the flask was placed
at -20 °C. Colorless crystals formed overnight. The supernate was
cannulated to a clean flask, and a second crop of crystals were isolated.
With both yields, after removal of the supernate, the crystals were
washed quickly with very cold THF and dried briefly under vacuum.
The combined yields totaled 0.327 g (44%) of pale yellow crystalline
solid. Anal. Calcd for C36H58O4Cd: C, 64.8; H, 8.76. Found: C,
63.19; H, 8.51. 1H NMR (C6D6): δ 1.25 [m, 4H, {THF}], 1.60 [s,
18H, {-CMe3}], 3.48 [m, 4H, {THF}], 6.78 [t, 1H, {4-H}], 7.28 [d,
2H, {3,5-H}].
Synthesis of Cd(O-2,6-tBu2C6H3)2(THT)2 (2). Cd[N(SiMe3)2]2
(0.20 g, 0.46 mmol) in 1 mL of THT was stirred while 2,6-di-tert-
butylphenol (0.19 g, 0.92 mmol) in 1 mL of THT was added. The
resulting yellow solution was stirred for 2 h, then placed at -20 °C
for 2 days while crystals of the product formed. The supernate was
removed from the crystals by cannula, and the crystals were dried in
vacuo to give 0.246 g (76%) of a yellow crystalline solid. Anal. Calcd
for C36H58O4Cd: C, 61.83; H, 8.36. Found: C, 60.47; H, 8.24. 1H
NMR (C6D6): δ 1.38 [4H, m, {THT}], 1.66 [18H, s, -tBu2}], 2.47
[4H, m, {THT}], 6.8 [1H, t, {4-C6H3}], 7.3 [2H, d, {3,5-C6H3}].
Synthesis of Cd(O-2,6-tBu2C6H3)2(pyridine)3 (3). A 2-mL pyridine
solution of 2,6-di-tert-butylphenol (0.19 g, 0.92 mmol) was added to a
solution of Cd[N(SiMe3)2]2 (0.20 g, 0.46 mmol) in 2 mL of pyridine.
After stirring for 1 h, the yellow solution was placed at -20 °C for 2
days. Pale yellow crystals formed and were isolated by removing the
supernate, washing quickly with cold fresh pyridine and drying under
vacuum to give 0.250 g (71%) of a yellow crystalline solid. Crystals
suitable for X-ray diffraction were grown by dissolving the yellow
crystals in toluene after removing the supernate and storing at -20 °C
for 2 days. Anal. Calcd for C43H57O2N3Cd: C, 67.0; H, 7.69; N, 5.53.
Found: C, 66.41; H, 7.48; N, 5.76. 1H NMR (C6D6): δ 1.66 [18H, s,
{-C-tBu}], 6.58 [3H, t, {C5H5N}], 6.88 [2H, t, {p-C6H3}], 6.9 [6H, t,
{C5H5N}], 7.42 [4H, d, {m-C6H3}], 8.53 [6H, d, {C5H5N}]. 13C{H}
NMR (C6D6): δ 31.7 {-CMe3}, 35.9 {-CMe3}, 114.5 {4-C6H3}, 124.3
{C5H5N}, 125.3 {3,5-C6H3}, 134.0 {C5H5N}, 139.0 {2,6-C6H3}, 150.4
{C5H5N}, 168.5 {ipso-C6H3}.
Herein, we have synthesized a family of Cd(II) bis(phenox-
ides) analogous to our zinc catalysts. The solid-state structures
of these complexes of the general formula Cd(O-2,6-R2C6H3)2-
(solvent)2-3 adopt a variety of solid-state conformations,
depending on the identity of the phenoxy substituents and the
coordinating base. One derivative, Cd(O-2,6-tBu2C6H3)2(THF)2
(1), previously reported by Buhro,7 had an unexpected square-
planar ligand arrangement which is considerably different from
its tetrahedral zinc analogue. Recently, we have reported the
structures of three more complexes of this family which each
took on a different solid-state geometry: Cd(O-2,6-tBu2C6H3)2-
(THT)2 (2) is another square-planar complex, Cd(O-2,6-t-
Bu2C6H3)2(py)3 (3) is trigonal bypyramidal, and Cd(O-2,6-
Ph2C6H3)2(THF)2 (4) has distorted tetrahedral geometry.8 The
syntheses and X-ray crystal structures of these and three more
derivatives are reported here, including the results of structural
redetermination of Buhro’s complex carried out at low temper-
ature. Nevertheless, it is important to note that all structural
parameters in complex 1 determined at 193 K are quite similar
to those previously reported at ambient temperature. Addition-
ally, the results of solution 1H, 13C, and 113Cd NMR experiments
to determine the identity of these species in solution and to study
the catalytic activity of these Cd(II) complexes are provided.
In particular, reactions with the small molecules CO2, COS, and
CS2 were carried out and a novel xanthate product formed from
CS2 insertion has been isolated and characterized.
Synthesis of Cd(O-2,6-Ph2C6H3)2(THF)2 (4). 2,6-Diphenylphenol
(0.455 g, 1.86 mmol) was dissolved in 4 mL of THF and added to a
solution of Cd[N(SiMe3)2]2 (0.40 g, 0.92 mmol) in 2 mL of THF. The
pale yellow solution stirred for 3 h at room temperature, then was
concentrated to less than 1 mL and placed at -20 °C. After 2-3 days,
colorless crystals formed. They were isolated by removing the
supernate and drying briefly under vacuum to give a yield of 0.360 g
(52%) of pale yellow powder. The crystals may be washed with very
cold THF to remove reaction byproducts, although the yield is variably
reduced due to the high solubility of 2 in THF. Anal. Calcd for
C44H42O4: C, 70.73; H, 5.67. Found: C, 68.79; H, 5.50. 1H NMR
(C6D6): δ 6.8-7.3 (br, 13H, 2,6-Ph2C6H3-), 3.59 (m, 4H, THF), 1.43
(m, 4H, THF). 13C{H} NMR (C6D6): δ 168.1 {ipso-C6O}, 125-132
{2,6-Ph2C6}, 67.9 {THF}, 25.9 {THF}.
Experimental Section
Methods and Materials. All complexes are extremely air- and
moisture-sensitive and were handled using Schlenk and glovebox
techniques under an argon atmosphere. Solvents were freshly distilled
before use except for tetrahydrothiophene (THT) and pyridine, which
were distilled over calcium hydride and stored over molecular sieves.
Phenols and propylene carbonate were purchased from Aldrich and
used as received. Cd[N(SiMe3)2]2 was synthesized and distilled
according to the literature procedure.9 All isotopically labeled chemicals
(6) (a) Darensbourg, D. J.; Niezgoda, S. A.; Holtcamp, M. W.; Draper,
J. D.; Reibenspies, J. H. Inorg. Chem. 1997, 36, 2424. (b) Darensbourg, D.
J.; Holtcamp, M. W.; Khandelwal, B.; Klausmeyer, K. K.; Reibenspies, J.
H. J. Am. Chem. Soc. 1995, 117, 538.
(7) Goel, S. C.; Chiang, M. Y.; Buhro, W. E. J. Am. Chem. Soc. 1990,
112, 6724.
(8) Darensbourg, D. J.; Niezgoda, S. A.; Reibenspies, J. H.; Draper, J.
D. Inorg. Chem. 1997, 36, 5686.
(9) Bu¨rger, H.; Sawodny, W.; Wannagat, U. J. Organomet. Chem. 1965,
3, 113.
Synthesis of Cd(O-2,6-Ph2C6H3)2(THT)2 (5). A 3-mL THT
solution of 2,6-diphenylphenol (0.228 g, 0.93 mmol) was added to a
neat sample of Cd[N(SiMe3)2]2 (0.20 g, 0.46 mmol), and the resulting
pale yellow solution was stirred for 1 h at room temperature. The
solution was concentrated to approximately half-volume and placed at
-20 °C for 2 days. Opaque crystals formed and were isolated by
removing the supernatant solution and drying under vacuum for 20