Solution 31P and 113Cd NMR studies of phosphine adducts of monomeric cadmium (bisphenoxide) complexes and the solid-state structures of (2,6-di-tert-butylphenoxide)2Cd(PCy3) and (2,6-di-tert-butylphenoxide)2Cd(PMe3)2

Article abstract of DOI:10.1021/ic991008g

Monomeric phosphine derivatives of cadmium phenoxides, (phenoxide)₂CdL(n), where the phenoxide ligands contain sterically demanding substituents in the 2,6-positions (2,6-di-tert-butylphenoxide and 2,6-diphenylphenoxide) are described. These derivatives were synthesized from the reaction of Cd[N(SiMe₃)₂]₂ and the corresponding phenol followed by the addition of the phosphine. For the large PCy₃ ligand (Tolman's cone angle (θ) = 170°) n = 1, whereas for the smaller Me₃P (θ = 118°) and n-Bu₃P (θ = 132°) ligands both mono- and bis(phosphine) derivatives (n = 1 and 2) were prepared. The (2,6-di-tert-butylphenoxide)₂Cd(PCy₃) and (2,6-di-tert-butylphenoxide)₂Cd-(PMe₃)₂ were characterized in the solid-state by X-ray crystallography. The structure of the monophosphine adduct of PCy₃ consists of a near trigonal planar geometry about the cadmium center, where the average P-Cd-O angle of 131.4°is larger than the O-Cd-O angle of 96.72°with a Cd-P bond length of 2.5247(12) A. On the other hand, the bis(phosphine) adduct, Cd(O-2,6-(t)Bu₂C₆H₃)₂(PMe₃)₂ is a distorted tetrahedral structure with O-Cd-O and P-Cd-P bond angles of 116.7(6)°and 104.3(2)°, respectively. The average Cd-P bond length in this derivative was determined to be 2.737[5] A. The monotricyclohexylphosphine derivatives of these cadmium bisphenoxides were shown by ³¹P NMR spectroscopy not to be undergoing facile exchange with free phosphine in solution at ambient temperature. On the contrary, the corresponding Me₃P and n-Bu₃P analogues readily undergo self-exchange with free phosphine in solution via a rapid equilibrium between monophosphine adduct plus free phosphine and the bis(phosphine) adduct. The ¹¹³Cd chemical shifts in the CdO₂P moieties shift downfield and the ¹¹³Cd-³¹P coupling constants decrease by about 900 Hz upon binding an additional phosphine ligand.

Full text of DOI:10.1021/ic991008g

Inorg. Chem. 2000, 39, 473-479
473
31
Solution P and 113Cd NMR Studies of Phosphine Adducts of Monomeric Cadmium
(Bisphenoxide) Complexes and the Solid-State Structures of
(2,6-Di-tert-butylphenoxide)2Cd(PCy3) and (2,6-Di-tert-butylphenoxide)2Cd(PMe3)2
†
Donald J. Darensbourg,* Patrick Rainey, David L. Larkins, and Joseph H. Reibenspies
Department of Chemistry, Texas A&M University, P.O. 30012, College Station, Texas 77842-3012
ReceiVed August 20, 1999
Monomeric phosphine derivatives of cadmium phenoxides, (phenoxide)2CdLn, where the phenoxide ligands contain
sterically demanding substituents in the 2,6-positions (2,6-di-tert-butylphenoxide and 2,6-diphenylphenoxide) are
described. These derivatives were synthesized from the reaction of Cd[N(SiMe3)2]2 and the corresponding phenol
followed by the addition of the phosphine. For the large PCy3 ligand (Tolman’s cone angle (θ) ) 170°) n ) 1,
whereas for the smaller Me3P (θ ) 118°) and n-Bu3P (θ ) 132°) ligands both mono- and bis(phosphine) derivatives
(n ) 1 and 2) were prepared. The (2,6-di-tert-butylphenoxide)2Cd(PCy3) and (2,6-di-tert-butylphenoxide)2Cd-
(PMe3)2 were characterized in the solid-state by X-ray crystallography. The structure of the monophosphine adduct
of PCy3 consists of a near trigonal planar geometry about the cadmium center, where the average P-Cd-O
angle of 131.4° is larger than the O-Cd-O angle of 96.72° with a Cd-P bond length of 2.5247(12) Å. On the
other hand, the bis(phosphine) adduct, Cd(O-2,6-tBu2C6H3)2(PMe3)2 is a distorted tetrahedral structure with
O-Cd-O and P-Cd-P bond angles of 116.7(6)° and 104.3(2)°, respectively. The average Cd-P bond length
in this derivative was determined to be 2.737[5] Å. The monotricyclohexylphosphine derivatives of these cadmium
bisphenoxides were shown by 31P NMR spectroscopy not to be undergoing facile exchange with free phosphine
in solution at ambient temperature. On the contrary, the corresponding Me3P and n-Bu3P analogues readily undergo
self-exchange with free phosphine in solution via a rapid equilibrium between monophosphine adduct plus free
phosphine and the bis(phosphine) adduct. The 113Cd chemical shifts in the CdO2P moieties shift downfield and
the 113Cd-31P coupling constants decrease by about 900 Hz upon binding an additional phosphine ligand.
Introduction
the conditions of catalysis. The sparsity of coordination
chemistry of zinc with phosphine ligands has led us to focus
Our keen interest in monomeric zinc bis(phenoxide) com-
plexes is based on the observations that these derivatives are
effective catalysts for the homopolymerization of epoxides to
polyethers or copolymerization of CO2 and epoxides to poly-
carbonates.1,2 These zinc complexes, typified by (2,6-diphen-
ylphenoxide)2Zn(THF)2 (where THF is tetrahydrofuran), are
rendered monomeric by virtue of the steric requirements of the
bulky phenoxide ligands employed in these studies.3 Relevant
to the copolymerization of CO2 and epoxides catalyzed by zinc
bis(phenoxide) derivatives is the simultaneous production of
polyether linkages, a process which is diminished in importance
in the presence of added tricyclohexylphosphine.4 This phe-
nomenon appears to be the consequence of PCy3 occupying one
of the coordination sites of zinc. Indeed, the trigonal planar
adduct, (2,6-di-tert-butylphenoxide)2Zn‚PCy3, has been isolated
and characterized crystallographically.5 Furthermore, PCy3 has
been shown by 31P NMR to be bound to the zinc center under
some of our attention on this subject. Herein, we wish to extend
these investigations to include the coordination chemistry of
the cadmium analogues, for these not only can exhibit more
diverse structural features, but can be probed by both 31P and
113Cd NMR spectroscopies.6 113Cd and 111Cd are nuclei with
relatively high sensitivity for use as NMR probes, spanning a
chemical shift range of more than 1000 ppm. Indeed, because
of this feature 113Cd NMR probes have been extensively
employed in the study of cadmium-substituted zinc enzymes
and/or proteins.7-12
Pertinent to these studies cadmium(II) phosphine complexes
were first synthesized nearly 60 years ago.13 Since that time,
many investigations have been undertaken utilizing 31P and
113Cd solution and solid-state NMR and X-ray crystallog-
(6) Darensbourg, D. J.; Niezgoda, S. A.; Draper, J. D.; Reibenspies, J. H.
Inorg. Chem. 1997, 36, 5686.
* To whom correspondence should be addressed.
† Dedicated to Professor Dirk Walthers on the occasion of his 60th
birthday.
(1) Darensbourg, D. J.; Holtcamp, M. W. Macromolecules 1995, 28, 7577.
(2) Darensbourg, D. J.; Holtcamp, M. W.; Struck, G. E.; Zimmer, M. S.;
Niezgoda, S. A.; Rainey, P.; Robertson, J. B.; Draper, J. D.;
Reibenspies, J. H. J. Am. Chem. Soc. 1999, 121, 107.
(3) Geerts, R. L.; Huffman, J. C.; Caulton, K. G. Inorg. Chem. 1986, 25,
1803.
(7) Jonsson, N. B. H.; Tibell, L. A. E.; Evelhoch, J. L.; Bell S. J.;
Sudmeier, J. L. Proc. Natl. Acad. Sci. U.S.A. 1980, 7, 3269.
(8) Armitage, I. H.; Pajer, R. T.; Schoot Uiterkamp, A. J. M.; Chlebowski,
J. F.; Coleman, J. E. J. Am. Chem. Soc. 1976, 98, 5710.
(9) Armitage, I. H.; Schoot Uiterkamp, A. J. M.; Chlebowski, J. F.;
Coleman, J. E. J. Magn. Reson. 1977, 29, 375.
(10) Sudmeier, J. L.; Bell S. J. J. Am. Chem. Soc. 1977, 99, 4499.
(11) Evelhoch, J. L.; Bocian, D. F.; Sudmeier, J. L. Biochemistry 1981,
20, 4950.
(4) Darensbourg, D. J.; Zimmer, M. S.; Rainey, P.; Larkins, D. L. Inorg.
Chem., in press.
(5) Darensbourg, D. J.; Zimmer, M. S.; Rainey, P.; Larkins, D. L. Inorg.
Chem. 1998, 37, 2852.
(12) Bertini, I.; Gray, H. B.; Lippard, S. J.; Valentine, J. S. In Bioinorganic
Chemistry; University Science Books: Mill Valley, CA, 1994.
(13) Evans, R. C.; Mann, F. G.; Peiser, H. S.; Purdie, D. J. Chem. Soc.
1940, 1209.
10.1021/ic991008g CCC: $19.00 © 2000 American Chemical Society
Published on Web 01/13/2000

474 Inorganic Chemistry, Vol. 39, No. 3, 2000
Darensbourg et al.
Synthesis of Cd(O-2,6-di-tBuC6H3)2(PCy3) (1). Cd-bishexamethyl-
disilylamide (0.20 g, 0.46 mmol) was dissolved in 5 mL of toluene,
and 2,6-di-tBuphenol (0.19 g, 0.92 mmol) dissolved in 5 mL of toluene
was cannulated onto the Cd-bishexamethyl-disilylamide solution result-
ing in some solid formation. Addition of tricyclohexylphosphine (PCy3)
(0.13 g, 0.46 mmol) to the solution obtained above provided initially
a clear yellow solution, which within a few minutes formed a precipitate.
Evacuation of the solvent produced a pale yellow powder in 91% yield.
Anal. Calcd for CdC46H75O2P: C, 68.76; H, 9.41. Found: C, 65.67;
H, 9.30. 1H NMR (298 K C6D6 solvent) δ 7.38 (d, 2H, m-aryl), δ 6.79
(t, 1H, p-aryl), δ 0.9-1.9 (m, 33H, P(C6H11)3), δ 1.77 (s, 9H, C(CH3)3).
13C NMR (298 K C6D6 solvent) δ 31.6, 30.4, 28.0, 26.9 (P(C6H11)3), δ
167.8, 139.6, 125.3, 115.2, 35.9, 31.2 (2,6-O[(CH3)C]2C6H3). 31P NMR
raphy.14-23 Most of these studies involved cadmium(II) phos-
phine complexes with various anions including halides, nitrate,
carboxylates, thiocyanates, and perchlorate. Dakternieks ob-
served that in these systems, phosphine exchange and anion
exchange occurred in solution and that several different mo-
lecular species ranging from monomeric to symmetrical and
unsymmetrical dimeric complexes could exist depending upon
the number of equivalents of trialkyl phosphine (one or two)
used.24 It was also determined by Dakternieks and co-workers
that in systems where the ligands are labile, lattice and solvation
effects are the predominant factors in determining which
complex crystallized from solution.25 Therefore, what is ob-
served in solution is not necessarily the same as that observed
in the solid state. Similar phosphine and anionic ligand lability
has been reported by many different research groups.26-28 By
way of contrast the phenoxide ligands in the complexes reported
upon within were not observed to be labile in solution in the
absence of protic reagents.
1
(298 K C6D6 solvent) δ 31.3 J113Cd-31P ) 2274 Hz. 113Cd NMR (298
K C6D6 solvent) δ 240 (d) 1J113Cd-31P ) 2279 Hz. There was no change
in 31P NMR spectrum signal for complex 1 upon the addition of a
second equivalent of PCy3.
Synthesis of Cd(O-2,6-Diphenyl C6H3)2(PCy3) (2). An analogous
procedure for the synthesis of complex 2 as employed in the preparation
of complex 1 was followed, except that 2,6-diphenylphenol (0.23 g,
0.92 mmol) was used in place of 2,6-di-tBuphenol and benzene was
used as solvent. Complex 2 remained in solution and upon evacuation
of the solvent a yellow oil was obtained. Three washings with 5 mL of
hexanes produced a white powder in 78% yield. 1H NMR (298 K C6D6
solvent) δ 7.80 (br), 7.38 (br), 7.19 (t), 7.09 (d), 6.80 (br) (13H, 2,6-O
(C6H5)2C6H3), δ 0.8-1.9 (m, 33H, P(C6H11)3). 13C NMR (298 K C6D6
solvent) δ 31.5, 29.9, 27.3, 25.7 (P(C6H11)3), δ 162.4, 143.6, 131.1,
130.3, 129.6, 129.1, 126.2, 115.2 (2,6-O[C6H5]2C6H3). 31P NMR (298
K C6D6 solvent) δ29.8 1J113Cd-31P ) 2156 Hz. 113Cd δ 288 (d) 1J113Cd-31P
) 2163 Hz. There was no change in the 31P NMR signal for complex
2 upon the addition of a second equivalent of PCy3.
Synthesis of Cd(O-2,6-Di-tBuC6H3)2(PnBu3)1,2 (3),(4). The prepara-
tion of the bis(phenoxide) cadmium derivative was identical to that
described in the synthesis of complex 1. Addition of tri-n-butylphos-
phine (P(nBu)3) (115 mL, 0.46 mmol) resulted in a bright yellow, clear
solution. Evacuation of toluene solvent produced a yellow powder in
63% yield. For 4, an extra equivalent of P(nBu)3 was added directly to
the NMR tube prior to 31P and 113Cd NMR spectral analysis. 1H NMR
complex 3 (298 K C6D6 solvent) δ 7.38 (d, 2H, m-aryl), δ 6.79 (t, 1H,
p-aryl), δ 1.73 (s, 9H, C(CH3)3), δ 1.18 (m), 1.11 (m), 0.88 (m), 0.73
(t) (27H, P(C4H9)3). 13C NMR complex 3 (298 K C6D6 solvent) δ 25.9
(s), 24.2 (d), 21.8 (d), 13.8 (s), (P(C4H9)3), δ 168.1, 138.3, 125.2, 114.7,
35.9, 31.9 (2,6-O[(CH3)3C)]2C6H3). 31P and 113Cd NMR data are listed
in Table 3.
Experimental Section
Methods and Materials. All syntheses and manipulations were
carried out on a double-manifold Schlenk line or in a glovebox under
argon. Glassware was flamed out thoroughly before use. Toluene,
hexane, and benzene were freshly distilled from sodium benzophenone
and dichloromethane was distilled from P2O5 prior to their use.
Trimethylphosphine was purchased from Strem and stored in a Schlenk
tube under an atmosphere of argon. Tricyclohexylphosphine was
purchased from Aldrich and was stored in a glovebox. Tri-n-butylphos-
phine (>90% purity) was purchased from Aldrich packaged as a sure-
seal container and was stored under an argon atmosphere. All phos-
phines were used without further purification. The phenols, 2,6-di-tert-
butylphenol and 2,6-diphenylphenol, were purchased from Aldrich. Cd-
[N(SiMe3)2]2 was synthesized and distilled according to the literature
procedure.29 This material is extremely moisture sensitive and, as such,
was stored in a glovebox and used immediately after removal from
the box. 31P NMR data were acquired on Varian XL200 and Unity+
300 MHz superconducting NMR spectrometers operating at 81 and
121 MHz, respectively. Both instruments are equipped with variable-
temperature control modules. All 31P NMR data are referenced to H3-
PO4 (85% in D2O). 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. 1H and 13
C
Synthesis of Cd(O-2,6-Diphenyl C6H3)2(PnBu3)1,2 (5),(6). The
preparation of the bis(phenoxide) cadmium derivative was identical to
that described in the synthesis of complex 1. One equiv of tri-n-
butylphosphine (115 mL, 0.46 mmol) was added via syringe to the
above solution. Evacuation of the benzene solvent produced a waxy,
yellow solid. The same procedure was followed with 2 equiv of P(nBu)3
resulting in another waxy, yellow solid of complex 6. 1H NMR complex
5 (298 K C6D6 solvent) δ 1.21 (m), 1.13 (m), 0.88 (m), 0.73 (t) (27H,
P(C4H9)3), δ 7.80 (br), 7.38 (br), 7.19 (br), 7.09 (br), 6.80 (br) (13H,
2,6-O (C6H5)2C6H3). 13C NMR complex 5 (298 K C6D6 solvent) δ 25.9
(s), 24.4 (d), 21.7 (d), 13.8 (s), (P(C4H9)3), δ 161.9, 144.3, 131.2, 130.3,
129.9, 129.1, 126.2, 114.2 (2,6-O[C6H5]2C6H3). 31P and 113Cd NMR
data are listed in Table 3.
Synthesis of Cd(O-2,6-Di-tBuC6H3)2(PMe3)1,2 (7),(8). The prepara-
tion of the bis(phenoxide) cadmium derivative was identical to that
described in the synthesis of complex 1. Addition of trimethylphosphine
(PMe3) (42.9 mL, 0.46 mmol) and subsequent evacuation of solvent
resulted in a yellow powder in 90% yield. An extra equivalent of PMe3
was added directly to the NMR tube containing 7 prior to 31P and 113Cd
NMR spectral analysis to provide spectra of complex 8. 1H NMR
complex 7 (298 K C6D6 solvent) δ 0.63 (s, 9H, P(CH3)3), δ 1.71 (s,
9H, C(CH3)3), δ 7.38 (d, 2H, m-aryl), δ 6.78 (t, 1H, p-aryl). 13C NMR
complex 7 (298 K C6D6 solvent) δ 13.6 (d, P(CH3)3) δ 168.1, 138.3,
125.2, 114.7, 35.9, 31.9 (2,6-O[(CH3)3C)]2C6H3). 31P and 113Cd NMR
data are listed in Table 3.
NMR spectra were acquired on Varian XL200E, Unity+ 300 MHz,
and VXR 300 MHz superconducting NMR spectrometers. The operating
frequencies for 13C experiments were 50.29 and 75.41 MHz for the
200 and 300 MHz instruments, respectively. Infrared spectra were
recorded on a Mattson 6021 FT-IR spectrometer with DTGS and
mercury cadmium telluride (MCT) detectors.
(14) Coates, G. E.; Ridley, D. J. Chem. Soc. 1964, 166.
(15) Mann, B. E. Inorg. Nucl. Chem. Lett. 1971, 7, 595.
(16) Cameron, A. F.; Forrest, K. P.; Ferguson, G. J. Chem. Soc. A 1971,
1286.
(17) Goel, R. G.; Ogini, W. O. Inorg. Chem. 1977, 16, 1968.
(18) Colton, R.; Dakternieks, D. Aust. J. Chem. 1980, 33, 955.
(19) Bell, N. A.; Dee, T. D.; Goldstein, M.; Nowell, I. W. Inorg. Chim.
Acta 1980, 38, 191.
(20) Goel, R. G.; Henry, W. P.; Olivier, M. J.; Beauchamp, A. L. Inorg.
Chem. 1981, 20, 3924.
(21) Goel, R. G.; Henry, W. P.; Srivastava, R. C. Inorg. Chem. 1981, 20,
1727.
(22) Goel, R. G.; Henry, W. P.; Jha, N. K. Inorg. Chem. 1982, 21, 2551.
(23) Kessler, J. M.; Reeder, J. H.; Vac, R.; Yeung, C.; Nelson, J. H.; Frye,
J. S.; Alcock, N. W. Magn. Reson. Chem. 1991, 29, 594.
(24) Dakternieks, D. Aust. J. Chem. 1982, 35, 469.
(25) Colton, R.; Dakternieks, D. Aust. J. Chem. 1980, 33, 1677.
(26) Dakternieks, D.; Rolls, C. L. Inorg. Chim. Acta 1985, 105, 213.
(27) Dakternieks. D.; Rolls, C. L. Inorg. Chim. Acta 1984, 87, 5.
(28) Bond, A. M.; Colton, R.; Ebner, J.; Ellis, S. R. Inorg. Chem. 1989,
28, 4509.
Synthesis of Cd(O-2,6-Diphenyl C6H3)2(PMe3)1,2 (9),(10). The
preparation of the bis(phenoxide) cadmium derivative was identical to
(29) Bu¨rger H.; Sawodny, W.; Wannagat, V. J. Organomet. Chem. 1965,
3, 113.

Phosphine Adducts of Monomeric Cadmium
Inorganic Chemistry, Vol. 39, No. 3, 2000 475
Table 1. Crystallographic Data and Data Collection Parameters for
Complexes 1 and 8
Scheme 1
1
8
formula
fw
cryst syst
space group
a, Å
C46H75CdO2P‚C7H8 C34H60CdO2P2‚C7H8
895.56
767.29
orthorhombic
C2221
11.002(2)
22.452(5)
17.572(4)
4340.4(15)
4
orthorhombic
P212121
10.8553(9)
18.832(2)
23.952(2)
4896.4(7)
4
b, Å
c, Å
V, Å3
Z
d (calcd), g/cm3
abs coeff, mm-1
1.215
0.516
1.174
4.939
goodness of fit on F 2 0.989
1.061
λ, Å
0.710 73
193(2)
5.54
1.541 78
173(2)
5.67
indicated acceptable crystal quality. Data were collected for 8.0° )
2θ ) 120°. Three control reflections collected for every 97 reflections
showed no significant trends. Lorentz and polarization corrections were
applied as was a semiempirical absorption correction to each. Structures
were solved by direct methods [SHELXS, SHELXTL-Plus program
package]. Full-matrix least-squares anisotropic refinement for all non-
hydrogen atoms yielded R, Rw(F2), and S values at convergence.
Hydrogen atoms were placed at idealized positions with isotropic
thermal parameters fixed at 0.08. Neutral-atom scattering factors and
anomalous scattering correction terms were taken from the International
Tables for X-ray Crystallography.
T, K
R,a %
Rw,b %
12.21
13.55
a R ) ∑||Fo| - |Fc||/∑Fo. b Rw ) {[∑w(Fo2 - Fc2)2}/(∑w(Fo )2]}1/2
.
2
that described in the synthesis of complex 1. Addition of 1 equiv of
PMe3 (42.9 mL, 0.46 mmol) to the above solution and subsequent
evacuation of benzene solvent resulted in a yellow waxy solid. The
same procedure using 2 equiv of PMe3 also produced a yellow waxy
solid, complex 10. 1H NMR complex 9 (298 K CD2Cl2 solvent) δ 0.58
(s, 9H, P(CH3)3), δ 6.78 (t, 1H, p-aryl), δ 7.13 (d, 2H, m-aryl), δ 7.21
(m, 6H, m/p-aryl), δ 7.98 (d, 4H, o-aryl). 13C NMR complex 9 (298 K
CD2Cl2 solvent) δ 13.2 (d, P(CH3)3), δ 115.1 (s), δ 125.8 (s), δ 128.6
(s), δ 129.9 (s), δ 130.2 (s), δ 131.3 (s), δ 142.2 (s), δ 165.1 (s) (2,6-
O-[C6H5]2C6H3). 31P and 113Cd NMR data are listed in Table 3.
X-ray Crystallography. Single crystals of complex 1 were obtained
from a concentrated solution of 1 in toluene at -20 °C. The X-ray
data collection covered more than a hemisphere of reciprocal space by
a combination of three sets of exposures; each exposure set had a
different æ angle for the crystal orientation and each exposure covered
0.3° in ω. The crystal-to-detector distance was 4.9 cm. Crystal decay
was monitored by repeating the data collection for 50 initial frames at
the end of the data set and analyzing the duplicate reflections; crystal
decay was negligible. The space group was determined based on
systematic absences and intensity statistics.30 The structure was solved
by direct methods and refined by full-matrix least-squares techniques.
All non-H atoms were refined with anisotropic displacement parameters.
The H-atoms attached to the N and O atoms were located from a
difference map, and were refined using a riding model. All H atoms
attached to C atoms were placed in ideal positions and refined using a
riding model with aromatic C-H ) 0.96 Å, methyl C-H ) 0.98 Å,
and with fixed isotropic displacement parameters equal to 1.2 (1.5 for
methyl H atoms) times the equivalent isotropic displacement parameter
of the atom to which they were attached. The methyl groups were
allowed to rotate about their local 3-fold axis during refinement.
For complex 1, data collection: SMART;31 cell refinement: SAINT
(Siemens32); data reduction: SAINT (Siemens31); program(s) used to
solve structures: SHELXTL-Plus (Sheldrick30); program(s) used to
refine structures: SHELXTL-Plus (Sheldrick, 1996); molecular graph-
ics: SHELXTL-Plus (Sheldrick30); software to prepare material for
publication: SHELXTL-Plus (Sheldrick30).
Results and Discussion
Preparations. The synthesis of monomeric mono- or bis-
(phosphine) derivatives of cadmium phenoxides, where the
phenoxides contain sterically demanding substituents in the 2,6-
positions, is relatively straightforward. Typically, 2 equiv of
the phenol dissolved in toluene or benzene is cannulated onto
a solution of Cd[N(SiMe3)2]2 in the respective hydrocarbon, and
the solution is stirred for 1 h at ambient temperature. To the
resultant bright yellow, clear solution is added 1 or 2 equiv of
the desired phosphine by microliter syringe, or as a hydrocarbon
solution in the case of solid phosphines. The solution was stirred
for an additional 30 min at ambient temperature, and the solvent
was removed under vacuum to provide a solid product. Scheme
1 summarizes the synthetic methodology along with the specific
derivatives reported upon herein.
Molecular Structures. X-ray quality crystals of complexes
1 and 8, Cd(O-2,6-tBu2C6H3)2(PCy3) and Cd(O-2,6-tBu2C6H3)2-
(PMe3)2, respectively, were obtained from toluene at -20 °C,
and their solid-state structures were determined by X-ray
crystallographic analysis. Figure 1 contains a thermal ellipsoid
drawing of complex 1, along with a partial atomic numbering
scheme. A molecule of toluene was found in the crystal lattice.
The structure of complex 1, like its zinc analogue, consists of
a nearly planar arrangement of cadmium along with the three
ligands’ binding atoms (two oxygens and phosphorus). This is
apparent from the sum of the angles O(2)-Cd(1)-O(1), O(1)-
Cd(1)-P(1), and O(2)-Cd(1)-P(1) which is 359.52°. Selected
bond lengths and bond angles are provided in Table 2. The
average Cd-O bond length of 2.089[3] Å is 0.22 Å longer than
that found in the zinc analogue which is consistent with the
difference in the radii of cadmium and zinc.5,33 On the other
hand, the Cd-P distance of 2.5247(12) Å is shorter than
expected on the basis of the corresponding Zn-P bond length
of 2.433(2) Å.5
Crystal data and details of the data collections are provided in Table
1. A colorless block crystal of 8 was mounted on a glass fiber with
epoxy cement at room temperature and cooled to 163 K in a N2 stream.
Preliminary examination and data collection were performed on a
Rigaku AFC5 X-ray diffractometer (Cu KRλ ) 1.54178 Å radiation).
Cell parameters were calculated from the least-squares fitting of the
setting angles for 25 reflections. ω scans for several intense reflections
Like complex 1, complex 8 crystallized with a toluene
molecule in its crystal lattice. A thermal ellipsoid drawing of 8
is depicted in Figure 2, along with a partial atomic numbering
(30) Sheldrick, G. M. SHELXTL-Plus Reference Manual, Version 5.1;
Bruker Analytical X-ray Systems Inc.: Madison, WI, 1996.
(31) SMART Software Reference Manual, Version 4.043; Siemens Analyti-
cal X-ray Systems Inc.: Madison, WI, 1996.
(32) SMART Software Reference Manual, Version 4.050; Siemens Analyti-
cal X-ray Systems Inc.: Madison, WI, 1996.
(33) Cotton, F. A.; Wilkinson, G. AdVanced Inorganic Chemistry, 5th ed.;
John Wiley & Sons: New York, 1988; p 1387.

476 Inorganic Chemistry, Vol. 39, No. 3, 2000
Darensbourg et al.
Figure 2. Thermal ellipsoid representation of Cd(O-2,6-tBu2C6H3)2‚
2PMe3, complex 8.
Figure 1. Thermal ellipsoid representation of Cd(O-2,6-tBu2C6H3)2‚
PCy3, complex 1.
Table 2. Selected Bond Distances (Å) and Bond Angles (deg) for
Complexes 1 and 8a,b
Complex 1: Cd(O-2,6-tBu2C6H3)2(PCy3)
Cd(1)-O(1)
2.092(3)
2.5274(12) O(1)-C(1)
1.332(5)
Cd(1)-O(2)
2.086(3)
1.340(5)
Cd(1)-P(1)
O(2)-C(15)
O(2)-Cd(1)-O(1)
96.72(11)
O(1)-Cd(1)-P(1) 137.18(8)
O(2)-Cd(1)-P(1) 125.62(9)
C(1)-O(1)-Cd(1) 128.7(3)
C(15)-O(2)-Cd(1) 135.9(3)
Complex 8: Cd(O-2,6-tBu2C6H3)2(PMe3)2
c
Cd(1)-O(1)
O(1)-C(1)
2.043[10] Cd(1)-P(1)
2.737[5]
Figure 3. 31P NMR spectra of complex 1. (A) in C6D6. (B) In C6D6
with 1 equiv of added PCy3.
1.353[18]
O(1)-Cd(1)-O(1A) 116.7(6)
P(1)-Cd(1)-P(1A) 104.3(2)
O(1′)-Cd(1)-P(1′) 97.2(5)
C(1′)-O(1′)-Cd(1) 135.3(14)
O(1)-Cd(1)-P(1)
C(1)-O(1)-Cd(1)
123.9(4)
128.3(13)
are illustrated in Figure 3. There is a large downfield shift in
the 31P resonance of the bound vs free PCy3 ligand, from 10.6
ppm for free to 31.3 ppm for bound. The 113Cd-31P coupling
constant is also quite large at 2274 Hz. In contrast, in the zinc
analogue the chemical shift for the bound PCy3 ligand exhibits
a much smaller upfield shift from that of free PCy3 at 7.74
ppm.4,5 Note that as was noted for the zinc derivative, the 31P
resonance in complex 1 does not shift upon addition of a second
equivalent of PCy3. Concomitantly, there is no change in the
113Cd-31P coupling constant. As depicted in Figure 3, upon
addition of the second equivalent of PCy3 an equally intense
resonance is seen at 10.6 ppm which corresponds to that of free
PCy3. Similar observations were noted for analogous experi-
ments carried out with the Cd(O-2,6-Ph2C6H3)2 complex (2),
where the bound PCy3 signal appeared at 29.8 ppm with a
slightly smaller J113Cd-31P value of 2156 Hz. Attendantly, the
113Cd NMR spectra of complexes 1 and 2 at 298 K in the
presence of 1 equiv of PCy3 both show well-defined doublets
centered at 240 and 288 ppm, respectively, with coupling
constants of the same magnitude as observed in the 31P NMR
spectra. As expected, there was no change in the 113Cd NMR
spectra upon addition of a second equivalent of PCy3. On the
other hand, the addition of 2 equiv of a small phosphine ligand
(e.g., PMe3) to Cd(O-2,6-tBu2C6H3)2 or Cd(O-2,6-Ph2C6H3)2
results in a triplet in the 113Cd NMR spectra (vide infra).
a Estimated standard deviations given in parentheses. b Symmetry-
generated atoms designated by (XA). c Atoms labeled with primes are
the other interpenetrating set of tetrahedrally arranged ligands about
the cadmium center.
scheme. The solid-state structure of 8 consisted of two
interpenetrating [CdO2P2] distorted tetrahedra 50% disordered
about a common cadmium center. The structural parameters
were quite similar and selected values are contained in Table
2. The average Cd-O bond length was found to be 2.043[10]
Å and the average Cd-P bond length observed was 2.737[5]
Å, with the latter being considerably longer than that determined
for complex 1. The O-Cd-O bond angle of 116.7(6) is less
obtuse than that found in other tetrahedral cadmium phenoxide.
As in the zinc analogue the O-Cd-P bond angles varied widely
from 97.2(5)° to 123.9(4)°. Note that the structure of 8 greatly
contrasts that of its THF adduct counterpart, Cd(O-2,6-tBu2C6-
H3)2(THF)2, which is square planar.6,34 This observation is
supportive of the assertion that the latter structure is the result
of a linear cadmium bis(phenoxide) species with weak THF
interactions.34 PMe3 is expected to be a much stronger base than
THF, leading to a tetrahedral structure. In the two cadmium
structures the toluene solvate is almost perpendicular to the
phenyl ring of the aryloxide, i.e., there is no π-stacking between
the two aromatic systems.
Hence, these NMR data indicate that the cadmium centers
of these bulky phenoxide derivatives are incapable of binding
two large phosphine ligands. Indeed, the X-ray structures of
both M(O-2,6-tBu2C6H3)2(PCy3) (M ) Zn or Cd) derivatives
indicate that the metal center is congested and can only
accommodate the addition of a small fourth ligand (see Figure
4 for a space-filling model). Furthermore, the cadmium-
NMR Spectroscopy. The 31P NMR spectra of Cd(O-2,6-
tBu2C6H3)2 in C6D6 in the presence of 1 and 2 equiv of the
sterically demanding phosphine, PCy3 (cone angle (θ) ) 170°),35
(34) Goel, S. C.; Chiang, M. Y.; Buhro, W. E. J. Am. Chem. Soc. 1990,
112, 6724.
(35) Colton, R.; Dakternieks, D. Aust. J. Chem. 1980, 33, 955.

Phosphine Adducts of Monomeric Cadmium
Inorganic Chemistry, Vol. 39, No. 3, 2000 477
Figure 5. Temperature-dependent 31P NMR spectra of Cd(O-2,6-
Ph2C6H3)2‚PnBu3 in the present of a slight amount of excess PnBu3. (a)
31P resonance for mono-n-Bu3P adduct. (b) 31P resonance for bis-n-
Bu3P adduct. Overlay represents a 31P NMR spectra of Cd(O-2,6-
Ph2C6H3)2 in the presence of <1 equiv of n-Bu3P at ambient
temperature.
Figure 4. Space-filling model of complex 1.
phosphine interaction is quite strong such as to make phosphine
exchange via the required dissociative mechanism in this
instance highly unfavorable. On the contrary, the zinc derivative
was shown to undergo a facile exchange process with PMe3,
presumably by an associative mechanism.
Proceeding to the less sterically hindered phosphines, PMe3
(θ ) 118°) and PnBu3 (θ ) 132°), the possibility exists for
binding two phosphines at the cadmium center. In these
instances a route exists for facile ligand exchange between the
monophosphine derivative and free phosphine in solution via
an associative process (eq 1). That is, rapid phosphine exchange
can occur by way of a bis(phosphine) species which itself
undergoes rapid phosphine dissociation. This is indeed what is
noted when slightly more than 1 equiv of n-Bu3P is added to a
methylene chloride solution of Cd(O-2,6-Ph2C6H3)2.
PR3
Cd(phenoxide)2(PR3) y z Cd(phenoxide)2(PR3)2 (1)
Figure 6. Temperature-dependent 113Cd NMR spectra of Cd(O-2,6-
Ph2C6H3)2‚PnBu3.
Figure 5 displays the 31P NMR spectra of complex 5 in the
presence of 1.05 equiv of n-Bu3P as a function of temperature.
Notably, there is a significant downfield shift of ∼27 ppm of
the 31P chemical shift upon n-Bu3P binding to cadmium in
complex 5. Furthermore, the 31P resonance is broad with poorly
resolved 113Cd-P and 111Cd-P coupling at ambient temperature.
Upon lowering the temperature the phosphorus signal shifts
further downfield and sharpens with the simultaneous appear-
ance of a weak sharp signal due to the bis(phosphine) derivative
(6) at ∼ -15 ppm (vide infra). On the other hand, as indicated
in the spectral overlay in Figure 5, Cd(O-2,6-Ph2C6H3)2 in the
presence of a deficiency of n-Bu3P exhibits a sharp 31P
resonance at -1.80 ppm at ambient temperature with 113Cd-
31P and 111Cd-31P coupling constants of 2325 and 2222 Hz,
respectively. There was only a small, upfield 31P chemical shift
upon lowering the temperature to -80 °C. Similar observations
were noted for the bis-tBu2phenoxide cadmium mono-nBu3P
analogue, where the 31P resonance occurred at -3.20 ppm at
-80 °C with a 113Cd-31P coupling constant of 2434 Hz (see
Table 3). The 113Cd NMR spectrum of complex 5 (Figure 6)
consists of a doublet centered at 325 ppm at -80 °C with a
J113Cd-31P value of 2490 Hz, whereas the corresponding
parameters in the 2,6-tBu2phenoxide analog (complex 3) are 276
ppm and J113Cd-31P ) 2434 Hz.
downfield from that of free PMe3 (-61.9 ppm in CH2Cl2) at
-35.9 ppm. The 31P signal remains sharp and undergoes only
a small downfield chemical shift as the temperature is incre-
mently lowered to -80 °C, where the value is -34.3 ppm (Table
3). The 113Cd-31P coupling constant increases slightly over this
temperature range from 2325 to 2533 Hz. As expected, the 113Cd
NMR spectrum consists of a doublet at ambient temperature
with a δ value of 247 ppm, which shifts downfield to 267 ppm
upon lowering the temperature to -80 °C.
Unlike what was observed for the voluminous PCy3 ligand,
notable changes in both the 31P and 113Cd NMR spectra from
the corresponding spectra of the monophosphine derivatives
occurred upon the addition of 2 equiv of the sterically less-
encumbered phosphines, PMe3 and PnBu3, to the cadmium bis-
(phenoxide) derivatives. Figures 7 and 8 illustrate representative
31P and 113Cd NMR spectra of these bis(phosphine) species,
namely those of complex 6, Cd(O-2,6-Ph2C6H3)2(PnBu3)2 (see
Table 4). As is readily apparent in Figure 7, at 0 °C the 31P
resonance of complex 6 is broad, with unresolved 113Cd-31P
1
coupling. The J(Cd-P) is not completely resolved until the
temperature is lowered to -40 °C, at which time the 31P
resonance sharpens. Only a small upfield shift (∼1 ppm) in the
31P chemical shift is noted upon further lowering of the
temperature to -80 °C. The 31P resonance appeared at -14.7
ppm with a J113Cd-31P value of 1582 Hz. The 113Cd NMR
spectrum of complex 6 as depicted in Figure 8 consists of a
1:2:1 triplet centered at 392 ppm at -20 °C. This triplet became
The 31P and 113Cd NMR spectra of the monotrimethylphos-
phine derivative of Cd(O-2,6-tBu2C6H3)2, complex 7, are closely
akin to those observed for its n-Bu3P analogue. That is, the 31
P
spectrum exhibits a single 31P resonance significantly shifted

478 Inorganic Chemistry, Vol. 39, No. 3, 2000
Darensbourg et al.
Table 3. 31P and 113Cd NMR Data for Cd(2,6-di-tBuphenoxide)2Ln Complexes in CD2Cl2 Solutiona
31P NMRd
113Cd NMR
L
n
T (°C)
31P (ppm)
113Cd (ppm)
1J(113Cd-31P)b
1J(113Cd-31P)b
P(nBu)3 complex 3
1
20
0
-20
-40
-60
-80
20
-4.6 (br)
-4.2 (br)
-4.4 (br)
-3.5 (br)
-3.3 (br)
-3.2 (br)
-10.3 (s)
-10.3 (s)
-10.3 (s)
-10.3 (s)
-10.3 (s)
-10.3 (s)
-35.9 (s)
-35.7 (s)
-35.4 (s)
-34.9 (s)
-34.6 (s)
-34.3 (s)
-40.6 (br)
-40.2 (br)
-39.8 (s)
-39.4 (s)
-39.1 (s)
-38.8 (s)
c
c
c
c
c
c
c
c
c
262 (d)
267 (d)
273 (d)
276 (d)
c
c
c
277 (br)
284 (t)
290 (t)
247 (d)
253 (d)
258 (d)
262 (d)
263 (d)
267 (d)
c
2372
2464
2437
2434
c
2417
c
P(nBu)3 complex 4
P(Me)3 complex 7
P(Me)3 complex 8
2
1
2
0
c
c
c
c
-20
-40
-60
-80
20
1628
1638
1648
1658
2325
2356
2390
2452
2499
2533
c
1598
1604
2337
2479
2459
2512
2542
2575
c
0
-20
-40
-60
-80
20
0
c
c
c
c
c
c
c
c
-20
-40
-60
-80
1561
1573
1583
352 (t)
356 (t)
1602
1631
a 121.43 MHz 31P{1H} NMR data with chemical shifts (in ppm) relative to external 85% H3PO4 reference. 88.71 MHz 113Cd{1H} NMR data with
chemical shifts (in ppm) relative to external 0.1 M Cd(ClO4)2 reference, (br), broad; (s), singlet; (d), doublet; (t), triplet. b Coupling constants are
in Hz. c The spectrum is too noisy to determine chemical shifts or coupling constants. d In all 31P NMR spectra, 113Cd-31P and 111Cd-31P coupling
1
35
113
31
were seen. The larger J value was assigned to J
.
P
Cd-
Figure 7. Temperature-dependent 31P NMR spectra of Cd(O-2,6-
Ph2C6H3)2‚2PnBu3.
Figure 8. Temperature-dependent 113Cd NMR spectra of Cd(O-2,6-
Ph2C6H3)2‚2PnBu3.
more resolved and shifted downfield to 409 ppm as the
temperature was lowered to -80 °C.
triplet as the temperature is lowered with little shifting of the
113Cd resonance.
A comparison of the data in Tables 3 and 4 for the mono-
and bis(phosphine) derivatives of Cd(O-2,6-Ph2C6H3)2 reveals
that the 31P resonance shifts upfield (toward that for free PnBu3)
proceeding from the mono- to bis(phosphine) adducts (i.e., from
1.0 ppm to -14.0 ppm at -80 °C) with a corresponding
decrease in the 1J(Cd-P) values by about 900 Hz. This upfield
shift and decreased coupling constant upon binding a second
phosphine ligand is expected as the coordination number of the
cadmium center is increased from three to four. The broadness
of the signals and the unresolved coupling in both the 31P and
113Cd NMR spectra at higher temperatures (between -20 and
20 °C) is indicative of rapid phosphine exchange via eq 1 (vide
supra). However, in the presence of 2 equiv of phosphine the
equilibrium, as defined in eq 1, lies far to the right (in favor of
the bis(phosphine) derivative) because the 31P NMR chemical
shift is not significantly changed as the temperature is lowered.
Concomitantly, the 113Cd NMR spectra exhibit a well-defined
The 31P NMR chemical shifts and J(Cd-P) parameters listed
in Table 3 for complex 4, Cd(O-2,6-tBu2C6H3)2(PnBu3)2, suggest
that the PnBu3 ligands bind more strongly to the cadmium center
in this instance than in complex 6, Cd(O-2,6-Ph2C6H3)2(PnBu3)2.
That is, the 31P signal is shifted less upfield at -10.3 ppm at
ambient temperature and does not change position as the
temperature is lowered. This appears to be contradictory to the
assumption that the more electron withdrawing phenyl substit-
uents in complex 6 should result in the cadmium binding the
phosphine ligands more strongly. Hence, this phenomenon is
again ascribed to steric effects being less significant in the case
of the symmetrical tert-butyl substituents. On the other hand,
this steric argument should be of less importance for the more
compact PMe3 ligand. Indeed, from the data in Tables 3 and 4
only modest differences in chemical shifts and 1J(Cd-P) values
were observed in the corresponding complexes 8 and 10.

Phosphine Adducts of Monomeric Cadmium
Inorganic Chemistry, Vol. 39, No. 3, 2000 479
Table 4. 31P and 113Cd NMR Data for Cd(2,6-di-phenylphenoxide)2Ln Complexes in CD2Cl2 Solutiona
31P NMRd
113Cd NMR
L
n
T (°C)
31P (ppm)
113Cd (ppm)
1J(113Cd-31P)b
1J(113Cd-31P)b
P(nBu)3 complex 5
1
20
0
-20
-40
-60
-80
20
-2.1 (s)
-1.4 (s)
-0.7 (s)
-0.0 (s)
0.5 (s)
1.0 (s)
c
c
c
c
c
c
c
c
317 (d)
319 (d)
322 (d)
325 (d)
c
2396
2448
2468
2491
c
2430
2457
2476
c
P(nBu)3 complex 6
2
0
-13.9 (br)
-14.3 (s)
-14.4 (s)
-14.6 (s)
-14.7 (s)
-
-39.6 (br)
-38.9 (br)
-38.7 (br)
-38.5 (s)
-37.9 (s)
-37.4 (s)
384 (br)
392 (t)
397 (t)
403 (t)
409 (t)
-
c
c
-20
-40
-60
-80
-
20
0
-20
-40
-60
-80
1572
1579
1581
1582
-
1584
1585
1586
1594
-
P(Me)3e complex 9
P(Me)3 complex 10
1
2
c
c
c
c
c
c
c
c
c
c
c
c
393 (t)
394 (t)
1552
1560
1568
1584
a 121.43 MHz 31P{1H} NMR data with chemical shifts (in ppm) relative to external 85% H3PO4 reference. 88.71 MHz 113Cd{1H} NMR data with
chemical shifts (in ppm) relative to external 0.1 M Cd(ClO4)2 reference, (br), broad; (s), singlet; (d), doublet; (t), triplet. b Coupling constants are
in Hz. c The spectrum is too noisy to determine peaks or coupling constants. d In all 31P NMR spectra, 113Cd-31P and 111Cd-31P coupling were
1
35
e The 31P and 113Cd NMR data for this compound are discussed within the text due to their
113
31
seen. The larger J value was assigned to J
complexity.
.
P
Cd-
Conclusions
derivatives, there is no tendency for the Cd(O-2,6-tBu2C6H3)2-
(PCy3) to undergo a facile exchange process with free PCy3
We described the synthesis of monomeric phosphine deriva-
tives of cadmium bis(phenoxides), along with their solution and
solid-state structures. In general these cadmium derivatives
mimic their zinc analogues, where the large basic phosphine
Cy3P forms a mono-adduct and the sterically less-demanding
basic phosphines, Me3P and n-Bu3P, form both mono- and bis-
(phosphine) derivatives. Interestingly, upon replacing the weakly
coordinating bases (THF, tetrahydrothiophene, and propylene
carbonate) in the (2,6-di-tert-butylphenoxide)2Cd(base)2 deriva-
tives (which have been structurally characterized to be square-
planar6,34) with PMe3 results in the formation of a distorted
tetrahedral structure. As might be anticipated, the Cd-P bond
in Cd(O-2,6-tBu2C6H3)2(PCy3) was found to be stronger than
the corresponding Zn-P bond in Zn(O-2,6-tBu2C6H3)2(PCy3)
as indicated by a Cd-P bond distance of 2.5247(12) Å which
is only 0.09 Å longer than the Zn-P bond length. This is
consistent with our previous findings of a thermodynamic
preference of 2.5 times for PCy3 binding to cadmium vs zinc
in competition studies.4
via a four-coordinate intermediate. On the other hand, the
smaller phosphine ligands, PMe3 and n-Bu3P in Cd bis-
(phenoxide)L derivatives (L ) PMe3 and n-Bu3P) readily
undergo rapid self-exchange in solution by way of a Cd-
(bisphenoxide)L2 species. That is, phosphine exchange on Cd-
(OAr)2L via an associative mechanism is fast, whereas exchange
via a dissociative process is quite slow on the NMR time scale
investigated.
Acknowledgment. The financial support of this research by
the National Science Foundation (Grants CHE96-15866 and
CHE98-07975 for the purchase of X-ray equipment) and the
Robert A. Welch Foundation is greatly appreciated.
Supporting Information Available: X-ray crystallographic files
in CIF format for complexes 1 and 8. This material is available free of
charge via the Internet at http://pubs.acs.org.
Although the ionic radius of cadmium(II) in four-coordinate
derivatives is 0.18 Å longer than the similar value in zinc(II)
IC991008G