Chemistry of thiocarboxylates: Synthesis and structures of neutral copper(I) thiocarboxylates with triphenylphosphine

Article abstract of DOI:10.1021/ic9907314

The reactions of Na⁺ R{O}CS^- (R = Me, Ph) with mixtures of CuCl and PPh₃ in stoichiometric ratios yielded the compounds [Cu₄(SC{O}Me)₄(PPh₃)₄] (1), [Cu₄(SC{O}Ph)₄

Full text of DOI:10.1021/ic9907314

1028
Inorg. Chem. 2000, 39, 1028-1034
Chemistry of Thiocarboxylates: Synthesis and Structures of Neutral Copper(I)
Thiocarboxylates with Triphenylphosphine
Theivanayagam C. Deivaraj, Ghee Xiong Lai, and Jagadese J. Vittal*
Department of Chemistry, National University of Singapore, Lower Kent Ridge Road,
Singapore 119 260
ReceiVed June 22, 1999
The reactions of Na+ R{O}CS- (R ) Me, Ph) with mixtures of CuCl and PPh3 in stoichiometric ratios yielded
the compounds [Cu4(SC{O}Me)4(PPh3)4] (1), [Cu4(SC{O}Ph)4(PPh3)3] (2), [Cu2(SC{O}Me)2(PPh3)4] (3), [Cu-
(SC{O}Ph)(PPh3)2] (4), and [Cu2(SC{O}Ph)2(PPh3)3] (5) quantitatively. Compound 2 was also obtained from
mixtures of CuCl, PPh3, and NaSC{O}Ph in the ratio 1:1:1. The analogous thioacetate compound similar to 2
and the thiobenzoate analogue of 1 could not be obtained. Attempts to prepare the unsymmetrical dimer of a
thioacetate compound similar to 5 gave a mixture of 1 and 3. The structures of 1-4 have been determined by
single-crystal X-ray diffraction methods. Crystal data for 1: triclinic space group P1h, a ) 11.5844(3) Å, b )
13.2459(3) Å, c ) 14.3433(3) Å, R ) 64.019(1)°, â ) 79.297(1)°, γ ) 69.426(1)°, V ) 1850.98(7) Å3, Z ) 1,
Dcalcd ) 1.439 g‚cm-3. Crystal data for 2‚0.5CH2Cl2‚H2O: triclinic space group P1h, a ) 12.4413(1) Å, b )
15.5443(1) Å, c ) 20.4637(3) Å, R ) 94.974(1)°, â ) 95.976(1)°, γ ) 100.450(1)°, V ) 3848.09(7) Å3, Z ) 2,
Dcalcd ) 1.416 g‚cm-3. Single-crystal data for 3: monoclinic space group P21/n, a ) 15.2746(2) Å, b ) 23.2947(2)
Å, c ) 19.0518(3) Å, â ) 96.713(1)°, V ) 6732.5(2) Å3, Z ) 4, Dcalcd ) 1.309 g‚cm-3. Crystal data for 4:
triclinic space group P1h, a ) 10.2524(3) Å, b ) 12.9826(4) Å, c ) 14.5340(4) Å, R ) 87.723(1)°, â ) 75.322(1)°,
γ ) 75.978(1)°, V ) 1815.14(9) Å3, Z ) 2, Dcalcd ) 1.327 g‚cm-3. Compound 1, [(µ3-SC{O}Me-S)2(µ-SC{O}-
Me-S)2(CuPPh3)4], is a tetramer with a distorted stepladder structure in which two copper atoms are trigonally
coordinated and the other two are tetrahedrally coordinated. Two bonding modes, namely, µ3-S and µ2-S, were
observed for the Me{O}CS- anion. The structure of 2 may be described as a highly distorted cubanoid structure
and formulated as [(µ3-SC{O}Ph-S3)(µ3-SC{O}Ph-S2,O)3(Cu)(CuPPh3)3]. In 2, three copper atoms have tetrahedral
coordination geometry and one copper atom is trigonally coordinated. Unprecedented bonding modes, namely,
µ3-S, have been observed for the R{O}CS- anions, in 1 and 2 and µ3-S2,O in 2. Compound 3, [(µ-SC{O}Me-
S)(µ-SC{O}Me-S,O){Cu(PPh3)2}2] is a dimer with µ2-S and µ2-S,O bonding modes of Me{O}CS- ligands.
Monomeric structure was found in 4 in which the copper atom has trigonal planar geometry with a very weak
intramolecular interaction with O. Variable temperature 31P NMR studies in solution show the presence of various
species in equilibria.
Introduction
by Dance et al.9 There appears to be no extensive parallel
chemistry developed with other similar sulfur-containing ligands.
Monothiocarbamates and other structurally similar ligands
exhibit diversified bonding modes.10-12 An analogous thiocar-
boxylate ligand with a similar functionality is expected to exhibit
similar bonding modes. However, only a few have been
observed so far. For the past several years we have been
interested in the chemistry of the thiocarboxylates.13-20 For
Neutral monodentate tertiary phosphine and arsine complexes
of the copper(I) halides [(PR3)nCuX] (n ) 1-4) have been the
subject of extensive investigations. For the different values
1
of n, monomer, dimer, and tetramer compounds have been
2
isolated. Of these, [PR3CuX] display a wide diversity of
structural types involving varying degrees of association. For
example, [Cu4Cl4(PPh3)4] adopts a cubanoid structure, while
3
[Cu4Br4(PPh3)4] forms both cubanoid4 and stepladder structures,5
and [Cu4I4(PPh3)4] was found to have a step-like structure only.6
For this given composition, [Cy3PCuCl] exists as a dimer. 7 In
the corresponding thiolate chemistry a tetramer structure is
known for the monophosphine adducts of copper(I) thiolates.8
A trimer having a composition [(PPh3)4Cu3(SPh)3] was reported
(8) Dance, I. G.; Scudder, M. L.; Fitzpatrick, L. J. Inorg. Chem. 1985,
24, 2547.
(9) Dance, I. G.; Fitzpatrick, L.; Scudder, M. L. J. Chem. Soc., Chem.
Commun. 1983, 546.
(10) McCormick, B. J.; Bereman, R.; Baird, D. Coord. Chem. ReV. 1984,
54, 99.
(11) Casas, J. S.; Montera-Vazquez, P.; Sanchez, A.; Sordo, J.; Vazquez-
Lopez, E. M. Polyhedron 1998, 17, 2417.
(1) Hathaway, B. J. In ComprehensiVe Coordination Chemistry; Wilkin-
son, G., Gillard, R. D., McCleverty, J. A., Eds.; Pergamon: 1987,
Oxford, Vol. 5, p 533.
(2) Lippard, S. J.; Mayerle, J. J. Inorg. Chem. 1972, 11, 753.
(3) Churchill, M. R.; Kalra, K. L. Inorg. Chem. 1974, 13, 1065.
(4) Barron, P. F.; Dyason, J. C.; Engelhardt, L. M.; Healy, P. C.; White,
A. H. Inorg. Chem. 1984, 23, 3766.
(5) Churchill, M. R.; Kalra, K. L. Inorg. Chem. 1974, 13, 1427.
(6) Churchill, M. R.; DeBoer, B. G.; Donovan, D. J. Inorg. Chem. 1975,
14, 617.
(7) Pasquali, M.; Fiaschi, P.; Floriani, C.; Gaetani-Manfredoth, A. J. Chem.
Soc., Chem. Commun. 1983, 197.
(12) Chunggaze, M.; Malik, M. A.; O’Brien, P.; White, A. J. P.; Williams,
D. J. J. Chem. Soc., Dalton Trans. 1998, 3839.
(13) Vittal, J. J.; Dean, P. A. W. Inorg. Chem. 1993, 32, 791.
(14) Vittal, J. J.; Dean, P. A. W. Inorg. Chem. 1996, 35, 3089.
(15) Dean, P. A. W.; Vittal, J. J.; Craig, D. C.; Scudder, M. L. Inorg. Chem.
1998, 37, 1661.
(16) Vittal, J. J.; Dean, P. A. W. Polyhedron 1998, 17, 1937.
(17) Vittal, J. J.; Dean, P. A. W. Acta Crystallogr. 1997, C53, 409.
(18) Dean, P. A. W.; Vittal, J. J. Acta Crystallogr. 1998, C54, 319.
(19) Devy, R.; Dean, P. A. W.; Vittal, J. J. Inorg. Chem. 1998, 37, 6939.
(20) Sampanthar, J. T.; Deivaraj, T. C.; Vittal, J. J.; Dean, P. A. W. J.
Chem. Soc. Dalton Trans. 1999, 4419.
10.1021/ic9907314 CCC: $19.00 © 2000 American Chemical Society
Published on Web 02/18/2000

Neutral Copper(I) Thiocarboxylates with PPh3
Inorganic Chemistry, Vol. 39, No. 5, 2000 1029
3
1
PPh3: 128.3 (C3, J(P-C) ) 9.1 Hz), 130.9 (C4), 132.9 (C1, J(P-C)
) 30.3 Hz), 133.8 (C2, 2J(P-C) ) 14.7 Hz). 31P NMR: δ, ppm -1.66
(s). IR data (cm-1): 3052.9 (m), 2921.7 (w), 2852.2 (w), 1640.3 (m),
1582.4 (m), 1547.7 (s), 1532.2 (m), 1482.1 (m), 1435.7 (s), 1308.4
(w), 1200.3 (s), 1169.4 (s), 1096.1 (m), 999.6 (w), 922.4 (s), 867.7
(m), 775.8 (m), 744.9 (s), 690.9 (s), 648.4 (w), 521.0 (s).
group 12 metals, thiobenzoate ion acts like a hindered thiolate
ligand.14 The most common bonding mode is bidendate through
S and O.21 In other words, the S and O donor atoms of
R{O}CS- can be bidendate22,23 as well as a chelating19 ligand.
However, the µ2 bridging mode of the sulfur atom which is
ubiquitous in the thiolate chemistry24,25 has not been observed
in the thiocarboxylates except for the dimer [(PPh3)2Cu(µ-SC-
{O}Ph)2Cu(PPh3)].26
In this paper we present the synthesis and structural charac-
terization of several neutral triphenylphosphine copper thiocar-
boxylates exhibiting hitherto unknown bonding modes, namely,
µ3-S2,O and µ3-S in metal thiocarboxylate compounds. We have
also presented the variable temperature (VT) 31P NMR of these
compounds in solution.
The same compound was also obtained when the synthesis was
carried out using the starting materials according to the stoichiometric
ratio of the products. A similar synthetic attempt to prepare the
corresponding thioacetate analogue yielded 1.
[(µ-SC{O}Me-S)(µ-SC{O}Me-S,O){Cu(PPh3)2}2] (3). Compound
3 was obtained as yellow crystals, when the reaction was carried out
similarly to that described for 1 but the ratio of NaSC{O}Me, CuCl,
and PPh3 was 1:1:2. Yield: 84%. Anal. Calcd for C76H66Cu2O2P4S2
(mol wt 1326.37): C, 68.82; H, 5.02; P, 9.34; Cu, 9.58. Found: C,-
1
69.14; H, 4.73; P, 9.19; Cu, 9.37. H NMR (CDCl3): δ, ppm 2.03
(6H, CH3), 7.2-7.4 (60H, (C6H5)3P). 13C NMR: δ, ppm 36.1 (CH3-
Experimental Section
3
COS), 208.9 (CH3COS). For PPh3: 128.4 (C3, J(P-C) ) 8.8 Hz),
1
2
All materials were obtained commercially and used as received. The
solvents were dried by allowing them to stand over 3 Å molecular
sieves overnight. The preparations were carried out under a nitrogen
atmosphere. The yields are reported with respect to the metal salts.
The compounds are fairly stable; however, they were stored under
129.5 (C4), 133.2 (C1, J(P-C) ) 26.4 Hz), 133.7 (C2, J(P-C) )
15.1 Hz). 31P NMR: δ, ppm -2.025 (s). IR data (cm-1): 3050.2 (m),
2919 (m), 2851.5 (m), 1618.7 (s), 1541.5 (s), 1481.7 (m), 1434.6 (s),
1093.9 (s), 1026.4 (w), 951.1 (w), 743.2 (s), 694.9 (s), 515.1 (s).
[Cu(SC{O}Ph)(PPh3)2] (4). Greenish yellow crystals of 4 were
obtained when the synthesis was carried out similarly to that described
for 2 with the starting materials PPh3, CuCl, and NaSC{O}Ph in the
ratio 1:1:2. Yield: 73%. Anal. Calcd for C43H35P2CuSO (mol wt
725.25): C, 71.2; H, 4.86; S, 4.42; P, 8.54; Cu, 8.76. Found: C, 71.02;
H, 5.16; S, 4.43; P, 8.59; Cu, 8.61. 13C NMR data (CDCl3): δ, ppm.
For thiobenzoic acid ligand: 127.2 (C2/6 or C3/5), 128.2 (C2/6 or C3/5),
129.5 (C4), 142.5(C1), 205.3 (C6H5COS). For the PPh3: 128.4 (C3,
3J(P-C) ) 9.3 Hz), 130.4 (C4), 133.2 (C1, 1J(P-C) ) 27.1 Hz), 133.8
1
nitrogen at 5 °C to avoid any decomposition. The 13C{1H}, H, and
31P NMR spectra were recorded on a Bruker ACF300 FT- NMR
instrument using TMS as internal reference at 25 °C in CD2Cl2 or
CDCl3. The IR spectra (KBr pellet) were recorded using a Bio-Rad
FTIR spectrophotometer. The elemental analyses were performed in
the microanalytical lab in the Department of Chemistry, National
University of Singapore. The purity of the bulk of the materials was
checked by comparing the X-ray powder patterns obtained from a
D5005 Siemens X-ray diffractometer at 25 °C with those of the
simulated X-ray powder diagrams from the single-crystal studies.
[(µ3-SC{O}Me-S3)2(µ-SC{O}Me-S)2(CuPPh3)4] (1). To deproto-
nated thioacetic acid prepared in situ by reacting 0.5 mL of CH3{O}-
CSH (7.0 mmol) with 0.28 g of NaOH (7.0 mmol) in 10 mL of water
was added a suspension of CuCl (0.69 g, 7.0 mmol) in 20 mL of CH2-
Cl2 containing triphenylphosphine (1.84 g, 7.0 mmol). The reddish CH2-
Cl2 layer was separated and layered with Et2O. Orange color crystals
were filtered off, washed with Et2O, and dried under vacuum. Yield:
2.34 g (83.4%). Anal. Calcd for C80H72Cu4O4P4S4 (mol wt 1603.66):
C, 59.91; H, 4.53; S, 7.99; P, 7.73; Cu, 15.85. Found: C, 60.54; H,
4.25; S, 7.04; P, 7.62; Cu, 14.70. 1H NMR (CDCl3): δ, ppm 2.03 (12H,
CH3), 7.24-7.47 (60H, (C6H5)3P). 13C NMR(CDCl3): δ, ppm. For the
thioacetate ligand: 35.5 (CH3COS), 205.9 (CH3COS). For the PPh3:
128.4 (C3, 3J(P-C) ) 9.1 Hz), 129.6 (C4), 132.7 (C1, 1J(P-C) ) 31.6
Hz), 133.8 (C2, 2J(P-C) ) 14.8 Hz). 31P NMR: δ, ppm -2.10 (s). IR
data (cm-1): 3052.9 (w), 2921.7 (w), 2852.2 (w), 1648.0 (s), 1482.0
(m), 1435.7 (s), 1347.0 (w), 1119.3 (s), 1096.1 (s), 999.6 (w), 949.4
(m), 744.9 (s), 694.7 (s), 621.4 (m), 521.0 (s), 505.6 (s).
(C2, J(P-C) ) 15.1 Hz). 31P NMR: δ, ppm, -1.83. IR data (cm-1):
2
3052.1 (m), 2920.9 (w), 2851.5 (w), 1612.9 (w), 1585.9 (w), 1572.4
(w), 1518.3 (m), 1479.8 (s), 1433.5 (s), 1306.1 (w), 1207.7 (s), 1165.3
(m), 1092.0 (s), 1070.8 (w), 1026.4 (w), 997.4 (w), 947.3 (m), 912.6
(w), 773.6 (w), 744.7 (s), 692.6 (s), 648.2 (w), 519.0 (w), 501.6 (w).
[Cu2(µ-SC{O}Ph)2(PPh3)3] (5). When the ratio of starting materials
NaSC{O}Ph, CuCl, and PPh3 was 1:1:1.5, the preparation similar to
that described for 4 yielded 5 as red crystals. Yield: 73%. Anal. Calcd
for C68H55Cu2O2P3S2 (mol wt 1188.23): C, 68.73; H, 4.67; Cu, 10.69.
Found: C, 68.00; H, 4.20; Cu, 10.17. 13C NMR (CDCl3): δ, ppm. For
thiobenzoic acid ligand: 127.2 (C2/6 or C3/5), 128.4 (C2/6 or C3/5), 129.4
3
(C4), 141.1 (C1), 203(PhCOS). For the PPh3: 128.3 (C3, J(P-C) )
9.8 Hz), 130.7 (C4), 132.9 (C1, 1J(P-C) ) 29.4 Hz), 133.8 (C2, 2J(P-
C) ) 15.3 Hz). 31P NMR: δ, ppm -1.22 (s). IR data (cm-1): 3050.2
(w), 2921.7 (w), 2855.4 (w), 1609 (s), 1591.7 (s), 1568.5 (s), 1481.7
(s), 1434.3 (s), 1306.1 (m), 1210.2 (s), 1167.2 (s), 1095.8(s), 1090.6
(m), 1026.4 (s), 1000.3 (m), 940 (s), 914.5 (s), 849.5 (m), 779.7 (m),
748.4 (m), 690.2 (s), 520 (s), 506.3 (m).
Attempts to prepare the corresponding thioacetate analogue by a
similar synthetic route resulted in the formation of a mixture of reddish
block-like crystals of 1 and yellow platy crystals of 3.
A similar attempt to prepare the analogous thiobenzoate complex
gave 2 (see below).
[(µ3-SC{O}Ph-S3)(µ3-SC{O}Ph-S2,O)3(Cu)(CuPPh3)3] (2). This
compound was synthesized similarly to 1 except that NaSC{O}Ph was
used instead of NaSC{O}Me. The yield of reddish yellow crystals was
85%. Anal. Calcd for the desolvated 2, C82H65Cu4O4P3S4 (mol wt
1589.79): C, 61.95; H, 4.12. Found: C, 61.81; H, 4.40. 13C NMR
(CDCl3): δ, ppm. For thiobenzoic acid ligand: 127.2 (C2/6 or C3/5),
128.8 (C2/6 or C3/5), 129.4 (C4), 141.1(C1), 201.6(PhCOS). For the
X-ray Crystallography. The diffraction experiments were carried
out on a Bruker SMART CCD diffractometer with a Mo KR sealed
tube at 23 °C. The software SMART27 was used for collecting frames
of data, indexing reflection, and determination of lattice parameters,
SAINT27 for integration of the intensity of reflections and scaling,
SADABS28 for absorption correction, and SHELXTL29 for space group
and structure determination and least-squares refinements on F2. One
of the phenyl rings of the thiocarboxylate ligand (C31-C36), one
phenyl ring (C1I-C6I) attached to the P3 atom and the solvents were
found to be disordered in 2. Two orientations of the phenyl rings were
modeled for the thiocarboxylate ring and the PPh3 phenyl ring
(21) Livingstone, S. E. In ComprehensiVe Coordination Chemistry; Wilkin-
son, G., Gillard, R. D., McCleverty, J. A., Eds.; Pergamon: Oxford,
1987; Vol. 2, p 645.
(22) Mehmet, N.; Tocher, D. A. Inorg. Chim. Acta 1991, 188, 71.
(23) Cindric, M.; Vrdoljak, V.; Matkovic-Calogovic, D.; Kamenar, B. Acta
Crystallogr. 1996, C52, 3016.
(24) Dilworth, J. R.; Hu, J. In AdVances in Inorganic Chemistry; Sykes,
A. G., Ed.; Academic Press: San Diego, 1994; Vol. 40, p 411.
(25) Schro¨der, M. In Encyclopedia of Inorganic Chemistry; King, B. R.,
Ed.; John Wiley & Sons: New York, 1994; Vol. 7, pp 3577-3590.
(26) Speier, G.; Fulop, V.; Arguy, G. Transition Met. Chem. 1991, 16,
576.
(27) SMART & SAINT Software Reference manuals, Version 4.0; Siemens
Energy & Automation, Inc., Analytical Instrumentation: Madison, WI,
1996.
(28) Sheldrick, G. M. SADABS a software for empirical absorption
correction; University of Go¨ttingen: Go¨ttingen, Germany, 1996.
(29) SHELXTL Reference Manual, Version 5.03; Siemens Energy &
Automation, Inc., Analytical Instrumentation: Madison, WI, 1996.

1030 Inorganic Chemistry, Vol. 39, No. 5, 2000
Deivaraj et al.
Table 1. Crystallographic Data for Compounds [Cu4(SC{O}Me)4(PPh3)4] (1), [Cu4(SC{O}Ph)4(PPh3)3] (2), [Cu2(SC{O}Me)2(PPh3)4] (3), and
[Cu(SC{O}Ph)(PPh3)2] (4)
1
2
3
4
chem formula
fw
T, °C
C80H72Cu4O4P4S4
1603.66
23
C82.5H67ClCu4O5P3S4
1649.12
23
C76H66Cu2O2P4S2
1326.37
23
C43H35CuOP2S
725.25
23
λ, Å
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
0.71073
P1h
0.71073
P1h
0.71073
P2(1)/n
15.2746(2)
23.2987(2)
19.0518(3)
90
96.713(1)
90
6732.5(2)
4
0.71073
P1h
11.5844(3)
13.2459(3)
14.3433(3)
64.019(1)
79.297(1)
69.426(1)
1850.98(7)
1
12.4413(1)
15.5443(1)
20.4637(3)
94.974(1)
95.976(1)
100.450(1)
3848.09(7)
2
10.2524(3)
12.9826(4)
14.5340(4)
87.723(1)
75.322(1)
75.978(1)
1815.14(9)
2
F
calcd, g/cm3
1.439
1.382
0.0493
0.0982
1.416
1.346
0.0580
0.1163
1.309
0.834
0.0618
0.0996
1.327
0.780
0.0499
0.0958
abs coeff, mm-1
R1 (Fo g 4σ(Fo)a
wR2(Fo g 4σ(Fo)a
a R1 ) Σ(||Fï| - |Fc||)/|ΣFï|; wR2 ) [Σw(Fï - Fc2)2/ΣwFï ]1/2
.
2
4
(occupancies, 0.55/0.45; common isotropic thermal parameters for each
disordered ring). These disordered phenyl rings were treated as regular
hexagons. In the solvent region, one-half molecule of CH2Cl2 (common
isotropic thermal parameters for non-hydrogen atoms) and a H2O
(disordered over three sites with occupancies 0.5, 0.25, 0.25) were
found. In 3, a phenyl ring (C1D-C6D) attached to phosphorus atom
P2 was disordered. Two orientations were modeled with 0.5:0.5
occupancy. These two disordered rings were treated as regular hexagons,
and their common isotropic thermal parameters were refined for each
ring. The relevant crystallographic data and refinement details are shown
in Table 1.
Results and Discussion
Synthesis. The compounds 1-5 were prepared by the
addition of the corresponding thiocarboxylates to a CH2Cl2
solution containing PPh3 and a suspension of the CuCl. For a
1:1:1 stoichiometric ratio of CuCl:NaSC{O}R:PPh3, the thio-
acetate anion gave the tetramer 1, [(µ3-SC{O}Me-S)2(µ-SC-
{O}Me-S)2(CuPPh3)4], and the thiobenzoate ligand yielded the
product 2, [(µ3-SC{O}Ph-S3)(µ3-SC{O}Ph-S2,O)3(Cu)(CuPPh3)3],
with a different stoichiometric ratio. Compound 2 could also
be prepared by reacting CuCl, NaSC{O}Ph, and PPh3 in the
ratio 4:4:3. The corresponding reaction of NaSC{O}Me with
CuCl and PPh3 in the ratio 4:4:3 yielded 1 and not the thioacetate
analogue of 2. When the stoichiometric ratio CuCl:NaSC{O}R:
PPh3 is 1:1:2, the products obtained by thioacetate and thioben-
zoate ligands have the same ratio of the reactants, but different
molecular formula and structures. Thioacetate and thiobenzoate
ligands gave a dimer, 3, [(µ-SC{O}Me-S)(µ-SC{O}Me-S,O)-
{Cu(PPh3)2}2], and a monomer, [Cu(SC{O}Ph)(PPh3)2], 4,
respectively. The reactions are summarized in eqs 1-4.
Figure 1. Perspective view of 1 with 50% probability thermal
ellipsoids. The hydrogen atoms on the phenyl rings are omitted for
clarity.
which was obtained by a different route by Speier, Fulop, and
Arguy.26 It is interesting to note that, under the same experi-
mental conditions and reactant ratio, R ) Me gave a mixture
of 1 and 3.
2NaSC{O}Ph + 2CuCl + 3PPh3 f [Cu2(SC{O}Ph)2
(PPh3)3] (5)
Attempts to prepare the complex [Cu4(SC{O}Ph)4(PPh3)4] by
slow evaporation of the reaction mixture in toluene or benzene
as solvent yielded a mixture of 2 and the known unsymmetrical
dimer 5.
4NaSC{O}Me + 4CuCl + 4PPh3 f [Cu4(SC{O}Me)4
(PPh3)4] (1)
Structural Description
4NaSC{O}Ph + 4CuCl + 3PPh3 f [Cu4(SC{O}Ph)4
Structure of Compound 1. The results of X-ray diffraction
studies reveal that the unit cell contains one tetramer with a
crystallographic center of symmetry. A view of 1 is shown in
Figure 1, and selected bond distances and angles are given in
Table 2. In 1, the Cu and the S atoms are alternatively bonded
to form an eight-membered ring in which two sulfur atoms are
further bridging two copper atoms to form a highly distorted
stepladder arrangement or a highly distorted chair-like confor-
mation. The copper atoms are bonded to a phosphine ligand in
such a way that two Cu atoms have approximate CuPS2 trigonal
planar geometry and the other two have CuPS3 tetrahedral
(PPh3)3] (2)
2NaSC{O}Me + 2CuCl + 4PPh3 f [Cu2(SC{O}Me)2
(PPh3)4] (3)
NaSC{O}Ph + CuCl + 2PPh3 f [(Cu(SC{O}Ph)(PPh3)2]
(4)
When R ) Ph, the 1:1:1.5 ratio of the reactants gave the
expected unsymmetric dimer, [Cu2(µ-SC{O}Ph)2(PPh3)3] (5),

Neutral Copper(I) Thiocarboxylates with PPh3
Inorganic Chemistry, Vol. 39, No. 5, 2000 1031
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
Compound 1
Bond Lengths
Cu(1)-P(1)
Cu(1)-S(1)
Cu(1)-S(2)
Cu(2)-S(2)a
C(3)-S(2)
C(3)-O(2)
C(3)-C(4)
2.2372(9)
2.2792(9)
2.3123(9)
2.3790(9)
1.777(4)
1.205(4)
1.497(5)
Cu(2)-P(2)
Cu(2)-S(1)
Cu(2)-S(2)
C(1)-S(1)
C(1)-O(1)
C(1)-C(2)
Cu(1)-Cu(2)
2.2331(9)
2.3329(9)
2.5876(9)
1.786(4)
1.199(4)
1.503(5)
2.7477(6)
Bond Angles
P(1)-Cu(1)-S(1)
P(1)-Cu(1)-S(2)
P(2)Cu(2)-S(2)a
Cu(1)-S(2)-Cu(2)
Cu(2)-S(2)-Cu(2)a
S(1)-Cu(2)-S(2)
S(1)-Cu(2)-S(2)a
S(2)-Cu(2)-Cu(1)
S(2)-C(3)-C(4)
S(2)-C(3)-O(2)
O(2)-C(3)-C(4)
127.22(4) P(2)-Cu(2)-S(1)
122.05(3) P(2)-Cu(2)-S(2)
118.48(3) Cu(1)-S(1)-Cu(2)
125.05(3)
118.51(3)
73.12(3)
Figure 2. View of the compound 2. The atoms are drawn with 50%
probability thermal ellipsoids. The phenyl rings attached to the
phosphorus atoms and the hydrogen atoms are omitted for clarity.
67.95(2) Cu(1)-S(2)-Cu(2)a 126.87(4)
98.90(3) S(1)-Cu(1)-S(2)
99.36(3) S(2)-Cu(2)-S(2)a
104.72(3) S(2)a-Cu(2)-Cu(1)
51.26(2) S(1)-C(1)-C(2)
109.74(3)
81.10(3)
111.06(3)
119.5(3)
119.5(3)
121.0(4)
Table 3. Selected Bond Lengths (Å) and Angles (deg) for
Compound 2
116.5(3)
121.3(3)
122.2(3)
S(1)-C(1)-O(1)
O(1)-C(1)-C(2)
Bond Lengths
Cu(1)- P(1)
Cu(3)-P(3)
Cu(2)-S(2)
Cu(4)-S(1)
Cu(4)-S(3)
Cu(2)-S(4)
Cu(1)- O(3)
Cu(3)-O(2)
C(2)-S(2)
2.247(1)
2.231(2)
2.358(2)
2.247(2)
2.246(2)
2.344(2)
2.174(4)
2.179(4)
1.758(6)
1.813(6)
1.237(6)
1.202(7)
2.7526(9)
Cu(2)- P(2)
Cu(1)- S(1)
Cu(3)-S(3)
Cu(4)-S(2)
Cu(1)-S(4)
Cu(3)-S(4)
Cu(2)-O(1)
C(1)-S(1)
2.254(2)
2.511(2)
2.421(2)
2.304(2)
2.289(1)
2.307(2)
2.193(4)
1.763(6)
1.754(6)
1.238(6)
1.236(6)
2.8423(9)
2.966(1)
a Symmetry transformations used to generate equivalent atoms: 1
- x, 1 - y, 1 - z.
coordination geometry. There are two types of bridging sulfur
atoms present, namely, µ2- and µ3-S. The structure is similar to
the tetramer, [(µ3-SPh)2(µ-SPh)2 (CuPPh3)4]‚(2toluene) reported
by Dance, Scudder, and Fitzpatrick.8 The Cu-S distances at
the trigonal Cu center (2.2792(9) and 2.3123(9) Å) are shorter
than corresponding distances at the tetrahedral Cu center
(2.3329(9), 2.379(9), and 2.5876(9) Å). These Cu-S distances
are longer than the Cu-S distance, 2.151(3) Å, observed in the
[Cu(SC{O}Me)2]- anion30 with terminal thioacetate ligands. The
Cu(1)-S distances observed here are comparable to the corre-
sponding Cu-S distances observed in the copper thiolate
tetramer.8 However, the triply bridging sulfur atom S(2) in 1 is
not symmetrically bonded to the copper atoms in the central
plane. The lengthening of Cu(2)-S(2) bond may be attributed
to the steric crowd of the CH3 group along this bond. The central
Cu2S2 plane is reclined at an angle of 126.28(3)° with the Cu-
(1)Cu(2)S(2) plane. The Cu-P distances are normal and warrant
no further discussion. The atoms Cu(1), P(1), S(1), S(2) lie on
a plane (rms deviation, 0.056). The closest Cu‚‚‚O distance is
between Cu(1) and O(2), 3.238 Å, which rules out any
possibility of weak interaction between these two atoms.
Structure of Compound 2. A perspective view of 2 is shown
in Figure 2, and selected bond distances and angles are given
in Table 3. This neutral cluster consists of four Cu(I) atoms, of
which three form the triangular base of a tetrahedron. Each one
of these three copper atoms is bonded to a PPh3 ligand and
bridged by two Ph{O}CS- ions through S and O atoms in such
a way that all the sulfur atoms are above the Cu3 plane. These
sulfur atoms are further bonded to the fourth Cu atom at the
apex of Cu4 tetrahedron and provide a trigonal planar coordina-
tion geometry to Cu(4). The sulfur atom of the fourth thioben-
zoate ligand is bonded to Cu(1), Cu(2), and Cu(3) from the
bottom of the Cu4 tetrahedron, through a µ3 bridging. The copper
atoms Cu(1), Cu(2), and Cu(3), therefore, have a CuPOS2
skeleton and tetrahedral coordination geometry. Compound 2
may also be viewed as derived from a cubanoid structure. In a
cubane-like compound, [(Ph3PCu)4(µ3-Cl)4], all the chloride ions
are involved in µ3 bridging.3 On the other hand, each sulfur
atom of the three Ph{O}CS- anions is bonded to two Cu(I)
C(3)-S(3)
C(4)-S(4)
C(1)-O(1)
C(3)-O(3)
Cu(1)-Cu(4)
Cu(3)-Cu(4)
C(2)- O(2)
C(4)-O(4)
Cu(2)-Cu(4)
Bond Angles
P(1)-Cu(1)-S(1)
P(1)-Cu(1)-S(4)
P(2)-Cu(2)-S(2)
P(2)-Cu(2)-S(4)
P(3)-Cu(3)-S(3)
P(3)-Cu(3)-S(4)
Cu(1)-S(1)-Cu(4)
Cu(3)-S(3)-Cu(4)
Cu(2)-S(4)-Cu(3)
S(1)-Cu(4)-S(2)
S(1)-Cu(4)-S(3)
C(2)-S(2)-Cu(4)
C(1)-O(1)-Cu(2)
C(3)-O(3)-Cu(1)
S(2)-Cu(2)-S(4)
O(3)-Cu(1)-S(4)
O(2)-Cu(3)-S(4)
C(4)-S(4)-Cu(2)
S(1)-C(1)-O(1)
S(3)-C(3)-O(3)
102.02(6) P(1)-Cu(1)-O(3)
132.56(6) S(1)-Cu(1)-O(3)
114.34(6) P(2)- Cu(2)-O(1)
125.10(6) S(2)-Cu(2)-O(1)
112.83(6) P(3)-Cu(3)-(O2)
125.70(6) S(3)-Cu(3)-O(2)
73.13(5) Cu(2)-S(2)-Cu(4)
78.85(5) Cu(1)-S(4)-Cu(2) 105.95(6)
98.23(5) Cu(1)-S(4)-Cu(3) 101.19(6)
124.17(6) S(2)-Cu(4)-S(3)
123.99(6) C(1)-S(1)-Cu(4)
103.34(18) C(3)-S(3)-Cu(4)
102.5(1)
98.8(1)
94.1(1)
103.2(1)
104.1(1)
95.8(1)
72.36(4)
128.44(5)
73.13(5)
106.4(2)
126.4(3)
106.71(5)
107.21(5)
102.2(1)
113.9(2)
111.5(2)
123.3(4)
118.6(5)
132.6(4)
130.2(4)
112.24(5) S(3)-Cu(3)-S(4)
C(2)-O(2)-Cu(3)
S(1)-Cu(1)-S(4)
109.4(1)
106.8(1)
123.0(2)
122.9(4)
123.8(4)
O(1)-Cu(2)-S(4)
C(4)-S(4)-Cu(1)
C(4)-S(4)-Cu(3)
S(2)-C(2)-O(2)
S(4)-C(4)-O(4)
Cu(2)-Cu(4)-Cu(3) 75.77(3) Cu(1)-Cu(4)-Cu(3) 75.34(2)
Figure 3. Schematic representation of [(Ph3PCu)4(µ3-Cl)4] (left) and
2 (right) showing the relationship between these two structures.
atoms and the oxygen atom of the carbonyl group is bonded to
a third Cu(I) atom in 2 as in Figure 3. Only one thiobenzoate
anion is involved in the µ3-S bridging. The compound 2 is,
therefore, highly distorted from the cubanoid structure. The
(30) Sampanthar, J. T.; Vittal, J. J.; Dean, P. A. W. J. Chem. Soc., Dalton
Trans. 1999, 1993.

1032 Inorganic Chemistry, Vol. 39, No. 5, 2000
Deivaraj et al.
Table 4. Selected Bond Lengths (Å) and Angles (deg) for
Compound 3
Bond Lengths
2.3240(9)
Cu(1)-P(1)
Cu(2)-P(3)
Cu(1)-S(1)
Cu(2)-S(2)
C(3)-S(2)
C(1)-O(1)
C(1)-C(2)
Cu(1)-Cu(2)
Cu(1)-P(2)
Cu(2)-P(4)
Cu(1)-S(2)
Cu(2)-O(1)
C(1)-S(1)
C(3)-O(2)
C(3)-C(4)
2.3219(9)
2.2879(9)
2.3400(9)
2.173(2)
1.728(4)
1.213(4)
1.509(5)
2.2814(9)
2.365(1)
2.3128(9)
1.741(3)
1.221(4)
1.513(5)
4.074(1)
Figure 4. Structure of 3 showing 50% probability thermal ellipsoids.
Bond Angles
The phenyl rings attached to the phosphorus atoms have been omitted.
P(1)-Cu(1)-P(2) 109.41(3) P(3)-Cu(2)-P(4)
S(1)-Cu(1)-P(1) 100.17(3) S(2)-Cu(2)-P(3)
S(1)-Cu(1)-P(2) 115.59(4) S(2)-Cu(2)-P(4)
S(1)-Cu(1)-S(2) 104.73(3) O(1)-Cu(2)-S(2)
S(2)-Cu(1)-P(2) 107.87(3) O(1)-Cu(2)-P(3)
S(2)-Cu(1)-P(1) 119.22(3) O(1)-Cu(2)-P(4)
116.26(3)
120.72(3)
116.48(3)
88.61(7)
105.23(8)
101.78(7)
trigonal planar geometry causes Cu(4) to be closer to the Cu3
triangle. This resulted in shorter Cu‚‚‚Cu distances (2.753(1)-
2.966(1) Å) between Cu(4) and the rest of the copper atoms
and smaller Cu-S-Cu(4) angles (73.15(5)°, 72.36(4)°, and
78.85(5)°). Consequently, the distances between Cu(1), Cu(2),
and Cu(3) are longer (3.516(1)-3.700(1) Å) than Cu‚‚‚Cu(4)
distances. The S(4)-C(4) bond distance, 1.813(6) Å, of the µ3-S
bridged Ph{O}CS- ligand is longer than the other S-C
distances, 1.754(6)-1.763(6) Å. The oxygen atoms of the
thiobenzoate ligands are bonded to the tetrahedral Cu atoms;
as a result, the C(1)-O(1), C(2)-O(2), and C(3)-O(3) distances
(1.238(6), 1.237(6), and 1.236(7) Å, respectively) are longer
than the C(4)-O(4) distance, 1.202(7) Å. The Cu-S distances
around the trigonal planar copper(I) center, Cu(4) (2.246(2)-
2.304(2) Å), are shorter than the corresponding distances of the
tetrahedral copper(I) centers (2.289(1)-2.511(2) Å). A survey
of Cambridge Structure Database search31 shows that the Cu-S
distances in similar compounds containing bridging sulfur
ligands and trigonal CuS3 geometry are in the range 2.166-
2.371 Å. The nonbonded distance between Cu(4) and S(4) is
2.981(1) Å, which is less than the sum of the van der Waals
radii, 3.2 Å.32
S(1)-C(1)-O(1)
O(2)-C(3)-S(2)
S(2)-C(3)-C(4)
O(1)-C(1)-C(2)
127.2(3)
123.3(3)
116.6(3)
115.9(3)
Cu(1)-S(2)-Cu(2) 122.23(4)
O(2)-C(3)-C(4)
S(1)-C(1)-C(2)
C(1)-O(1)-Cu(2)
120.1(3)
116.9(3)
143.2(2)
are bonded to each copper atom to complete the tetrahedral
geometry with different coordination environments around two
copper atoms.
Selected bond distances and angles are displayed in Table 4.
The Cu-P distances around Cu(1) having a CuP2S2 skeleton
are slightly longer than the distances around Cu(2) with the
CuOP2S kernel. The bridging S(2) atom is unsymmetrically
bonded to the copper atoms. It is interesting to note that the
bridging Cu(1)-S(2) and Cu(2)-S(2) distances (2.340(1) and
2.313(1) Å respectively) are shorter than the Cu(1)-S(1)
distance, 2.365(1) Å, in which the sulfur atom is attached to a
Cu atom only. On the other hand, the S(2)-C(3) distance, 1.741-
(3) Å, is longer than the S(1)-C(1) distance, 1.728(4) Å. In
the bidentate CH3{O}CS- ligand, since both O(1) and S(1)
atoms are involved in bonding, one would expect that the
electrons are delocalized to give a partial double bond character
for S(1). It is, therefore, expected that S(1) would bind weakly
to Cu(1) as compared to S(2) and thus account for the observed
anomaly. The C-O distances also show the expected trend
(Table 4). The six-membered ring is highly distorted. The atoms
Cu(1), S(2), Cu(2), and S(1) are on one plane (rms deviation,
0.046 Å), and the S(1), C(1), and O(1) atoms are in another
plane (rms deviation, 0.002 Å). The dihedral angle between these
two planes is 18.5(1)°. The Cu(2)-O(1) distance, 2.173(2) Å,
is comparable to those observed in 2 (see Table 3).
From the thiobenzoate perspective, there are two types of
bonding modes present in 2. In one mode of bonding, the sulfur
atom is bridging two metal atoms while the oxygen atom is
bonded to the third. A different µ3-S2,O bonding mode was
observed in neutral metal-monothiocarbamate complexes of
the type [M(SC{O}NR2)]6 (M ) Cu and Ag)33,34 and [Ni(SC-
35
{O}NR2)2]6 in which S and O of the ligand are chelated to
the metal. In the second bonding mode, the thiobenzoate S atom
binds to three different metals. This µ3-S bridging is not known
either in monothioxanthates or in monothiocarbamates. How-
ever, such a bonding mode is quite common in metal thiolate
chemistry.8,24,25,36-38
Structure of Compound 4. The neutral (bisphosphine)
adduct of the copper thiobenzoate compound is a monomer in
the solid state as shown in Figure 5. Two PPh3 ligands and a
Ph{O}CS- anion are bonded to the copper atom. Table 5 shows
that the Cu-P distances are normal. The Cu(1), P(1), P(2), and
S(1) atoms are in a plane (rms deviation, 0.044 Å), and the
sum of the angles around Cu(1) is 359.4°. The thiobenzoate
ligand, therefore, is mainly bonded through the S atom to
provide a trigonal planar geometry for Cu(1) in 4. There is,
however, a weak interaction between Cu(1) and O(1) as shown
by the bond distance, 2.439(2) Å, which is less than the sum of
the van der Waals radii, 2.9 Å.32 The Cu-S distance, 2.3267(8)
Å, is slightly longer than those observed for the trigonal planar
copper in 2 (Table 3). The phenyl ring and the plane containing
the C(1), C(2), O(1), S(1), and Cu(1) atoms are twisted from
each other (dihedral angle, 5.4(2)°), which is quite normal in
the chemistry of metal thiobenzoates.14 The bond mode of sulfur
Structure of Compound 3. For the given stoichiometry, the
neutral bis(phosphine) adduct of the copper thioacetate com-
pound 3 exists as a dimer, [(µ-SC{O}Me-S)(µ-SC{O}Me-S,O)-
{Cu(PPh3)2}2], in the solid state as shown in Figure 4 In this
dimer two different bonding modes were observed for the
thioacetate ligands bridging the two copper atoms. One
Me{O}CS- is bridged through a S atom, and the other
thioacetate is bonded through S and O atoms. Two PPh3 ligands
(31) Allen, F. H.; Davies, J. E.; Galloy, J. J.; Johnson, O.; Kennard, O.;
Macreae, C. F.; Mitchell, E. M.; Mitchell, G. F.; Smith, J. M.; Watson,
D. G. J. Chem. Inf. Comput. Sci. 1991, 31, 187.
(32) Bondi, A. J. Phys. Chem. 1964, 68, 441.
(33) Hesse, R.; Aava, U. Acta Chem. Scand. 1970, 24, 1355.
(34) Jennische, P.; Hesse, R. Acta Chem. Scand. 1971, 25, 423.
(35) Hoskins, B. F.; Pannan, C. D. Inorg. Nucl. Chem. Lett. 1974, 10, 229.
(36) Dance, I. G. Polyhedron 1986, 5, 1037.
(37) Block, E.; Zubieta, J. In AdVances in sulfur chemistry; Block, E., Ed.;
Jai Press Inc.: Connecticut, 1994; Vol. 1, p 133.
(38) Blower, P. J.; Dilworth, J. R. Coord. Chem. ReV. 1987, 76, 121.

Neutral Copper(I) Thiocarboxylates with PPh3
Inorganic Chemistry, Vol. 39, No. 5, 2000 1033
Figure 5. Molecular structure of 4 showing 50% probability thermal
ellipsoids. The hydrogen atoms are not shown for clarity.
Table 5. Selected Bond Lengths (Å) and Bond Angles (deg) for the
Compound 4
Bond Lengths
Cu(1)-S(1)
Cu(1)-P(1)
C(1)-O(1)
2.3267(8)
2.2567(8)
1.242(3)
Cu(1)-O(1)
Cu(2)-P(2)
C(1)-S(1)
2.439(2)
2.2686(8)
1.708(3)
Bond Angles
P(1)-Cu(1)-P(2)
O(1)-Cu(1)-P(1)
S(1)-Cu(1)-P(1)
S(1)-C(1)-O(1)
S(1)-C(1)-C(2)
126.68(3)
113.02(7)
118.36(3)
120.3(2)
120.6(2)
O(1)-Cu(1)-S(1)
O(1)-Cu(1)-P(2)
S(1)-Cu(1)-P(2)
O(1)-C(1)-C(2)
65.19(6)
95.28(7)
114.36(3)
119.0(3)
in 4 is common and observed in many compounds of mono-
thioxanthates and monothiocarbamates.39,40
VT 31P NMR Studies. Phosphine adducts of neutral copper
halides and copper mono- and dithiocarbamate compounds are
known to associate and/or dissociate in solution.10,41,42 Tanaka
et al.43,44 have studied the nature of species formed by dissolving
the adducts of copper(I) monothiocarbamate with phosphine in
solution, using molecular weight determination, conductivity
measurements, and 1H NMR spectra and found that these
compounds undergo dissociation and/or association in solution
to give an equilibrium mixture of those with various copper
ligand ratios, depending on the composition of the adducts,
nature of the solvents, concentration, temperature, etc. The
solution structures of these compounds have not been probed
in detail by 31P NMR spectroscopy, probably due to fast
exchange between the phosphine and copper at all the temper-
atures.45
The general features observed in this study are summarized
as follows. (1) All the compounds gave broad singlets in 31P
spectra, as a result of rapid exchange of the PPh3 ligands at
room temperature in CDCl3 or CD2Cl2 solution. However, when
the solutions were cooled, more than one line was observed
(see Supporting Information). Figure 6 shows the low-temper-
ature spectra of compounds 1-5 and a 1:1 mixture of 2 and
PPh3. (2) A narrow range of chemical shifts were observed at
room temperature (-1.2 to -2.1 ppm) and at low temperatures
Figure 6. Low-temperature 31P NMR spectra for compounds 1-5 and
for a 2/PPh3 mixture.
(1.4 to -5.5 ppm). (3) The lines were broad and no couplings
were observed at any temperature. (4) Slow exchange limits
were not reached for any compound at any temperature studied.
The assignments of chemical shifts were only tentative and were
based on the assumption that the chemical shifts at low
temperatures vary according to the coordination geometry of
the copper atom to which the phosphorus atoms are attached,
in the following order: linear (δ g 1.5 ppm) > trigonal planar
(1.5 g δ g -1.0 ppm) > tetrahedral (-1.0 g δ g -4.0 ppm)
geometry.
(39) Pierpont, C. G.; Greene, D. L.; McCormick, B. J. J. Chem. Soc., Chem.
Commun. 1972, 960.
(40) Greene, D. L.; McCormick, B. J.; Pierpont, C. G. Inorg. Chem. 1973,
12, 2148.
(41) Muetterties, E. L.; Alegranti, C. W. J. Am. Chem. Soc. 1972, 94, 6386.
(42) Barron, P. F.; Dyason, J. C.; Healy, P. C.; Engelhardt, L. M.; Skelton,
B. W.; White, A. H. J. Chem. Soc., Dalton Trans. 1986, 1965.
(43) Nakajima, H.; Matsumoto, K.; Tanaka, K.; Tanaka, T. Inorg. Nucl.
Chem. 1975, 37, 2463.
(44) Nakajima, H.; Tanaka, T. Inorg. Nucl. Chem. 1977, 39, 991.
(45) Black, J. R.; Levason, W.; Spicer, M. D.; Webster, M. J. Chem. Soc.,
Dalton Trans. 1993, 3129.
The monomer 4 gave a broad single resonance at -1.90 ppm.
When the solution had been cooled, the line had broadened

1034 Inorganic Chemistry, Vol. 39, No. 5, 2000
Deivaraj et al.
(Supporting Information), and at 215 K, two signals were
observed at 0.25 (∆ν1/2 ≈ 73 Hz) and -2.26 ppm (∆ν1/2 ≈ 72
Hz). It is proposed that the parent monomer compound with
trigonal planar CuPS2 geometry (δ, 0.25 ppm) is in equilibrium
with the dimer, in which the Cu atoms have tetrahedral geometry
(δ, -2.26 ppm). The predominant species in solution is the
dimeric compound as seen by the intensity of the signal at -2.26
ppm (Figure 6a). Compound 5 with two different coordination
geometries gave similar chemical shifts at 218 K confirming
the assignments for 4. However, the resonance at -2.55 pm
(∆ν1/2 ≈ 22 Hz) in 5 has sharpened compared to that in 4. There
are some additional minor species present in the solution (as
indicated by asterisks in Figure 6b). The cubanoid compound
2 gives a broad singlet at room temperature at -1.48 ppm (∆ν1/2
≈ 63 Hz). The singlet is slightly shielded (δ, -2.71 ppm) and
sharpened at 220 K as shown in Figure 6c. It appears that the
cluster retains its core even in solution. Again the chemical shift
is assigned to the phosphorus in the tetrahedral CuPS3 core.
Compound 3 gave one broad singlet at room temperature at
-2.01 ppm (∆ν1/2 ≈ 85 Hz). On cooling of the solution at 203
K, the intensity of this singlet diminished and three additional
signals were observed at -2.67, -2.36, and +1.16 ppm (Figure
6d). On the basis of our assumption, the chemical shift at 1.15
ppm has been assigned to the phosphorus attached to the copper
with trigonal planar geometry, and the other two shifts have
been assigned to P atoms of the tetrahedral cores, CuPS3 and
CuP2OS. The LT 31P NMR spectrum for 3 appears to indicate
that the dimer is in equilibrium with monomer and the δ 1.16
ppm may be assigned to the CuP2S core.
the other for the tetrahedral CuPS3 core. The signal at -5.50
ppm is predominant and close to the chemical shift of the free
phosphine. If this is so, it may be assumed that the tetramer
loses PPh3 partially to give the cubanoid compound similar to
2. Additional resonance lines found in the region due to the
tetrahedral copper core appear to support this. In the absence
of slow exchange spectra, the chemical shift assignments are
only tentative; nevertheless, the 31P NMR studies indicate that
more than one species present is in equilibrium in solution.
To find out whether 2 forms a 1:1:1 compound analogous to
1, 31P NMR spectra were recorded at various temperatures for
the 2/PPh3 mixture (Supporting Information). While the room
temperature spectrum has a singlet at δ -1.15 ppm, the 31P
spectrum at 213 K shows several singlets spaced together in
two regions as given in Figure 6f. These two regions have been
assigned to trigonal and tetrahedral copper cores along with a
small amount of what appears to be free PPh3 as shown in Figure
6. Although the 31P NMR spectrum does not look quite similar
to Figure 6e, due to different substituents, chemical shifts were
observed as expected, in two regions, namely, trigonal and
tetrahedral copper centers. In other words, [(µ3-SC{O}Ph-S)2-
(µ-SC{O}Ph-S)2(CuPPh3)4] may be present in solution along
with 2.
Acknowledgment. This research work is supported by the
National University of Singapore through a research grant (Grant
RP970618) to J.J.V. G.X.L. from Raffles Junior College is under
Students Research Program.
Supporting Information Available: Complete variable temperature
31P NMR spectra for complexes 1-5. X-ray crystallographic files in
CIF format for the structure determinations of complexes 1-4. This
material is available free of charge via the Internet at http://pubs.acs.org.
Compound 1 gave a broad singlet at δ -2.11 ppm at ambient
temperatures. Upon lowering of the temperature to 223 K, five
signals appeared (0.93, -2.54, -2.68, -3.42, and -5.50 ppm,
Figure 6e). On the basis of the tetrameric structure of 1, only
two singlets are expected, one for the trigonal CuPS2 core and
IC9907314