A series of mononuclear quasi-two-coordinate copper(l) complexes employing a sterically demanding thiolate ligand

Article abstract of DOI:10.1021/ic801836k

A series of two-coordinate thiolate complexes [Cu(SAr*)L] was synthesized as possible reactants in forming analogues of the active site of Mo/Cu-containing carbon monoxide dehydrogenase. Complexes with L = PPh ₃ (1), 2,6-lutidine (2), and the W

Full text of DOI:10.1021/ic801836k

Inorg. Chem. 2009, 48, 621-627
A Series of Mononuclear Quasi-Two-Coordinate Copper(I) Complexes
Employing a Sterically Demanding Thiolate Ligand
Stanislav Groysman and R. H. Holm*
Department of Chemistry and Chemical Biology, HarVard UniVersity,
Cambridge, Massachusetts 02138
Received September 25, 2008
A series of two-coordinate thiolate complexes [Cu(SAr*)L] was synthesized as possible reactants in forming analogues
of the active site of Mo/Cu-containing carbon monoxide dehydrogenase. Complexes with L ) PPh3 (1), 2,6-lutidine
(2), and the N-heterocyclic carbene Pri2NHCMe2 (3) have been prepared by the reaction of [CuCl(PPh3)3] (1) or
[CuBr(SMe2)] (2, 3) with ligand L and the exceptionally sterically encumbered ligand Ar*S ) 2,6-bis(2,4,6-
triisopropylphenyl)benzenethiolate(1-). The reaction of [CuBr(SMe2)] with the thiolate in the absence of added L
afforded trinuclear [Cu3(SAr*)2Br] (7). The carbene complex (3) undergoes Cu-C bond insertion with sulfur to form
the thiourea complex [Cu(SAr*)(Pri2Me2ImS)] (4). The complexes [Cu(Ar*)L] with L ) tetrahydrothiophene (5) and
2,6-lutidine (6) were obtained by reaction of Ar*Li(OEt2) with CuBr/L. These species did not undergo clean Cu-C
bond insertion with sulfur transfer agents; the disulfide Ar*SSCH2Ph (9) was isolated from the reaction of 6 with
(PhCH2S)2S. The structures of all complexes and 9 were determined. Whereas 5 and 6 are strictly two-coordinate
with linear C-Cu-L angles, 1-4 are quasi-two-coordinate because of weak 3d-C(pπ) interactions with a phenyl
group, leading to nonlinear structures (S-Cu-L ) 135-164 °).
Introduction
We have recently synthesized structural analogues of
catalytic sites in the xanthine oxidoreductase family of
enzymes.1,2 These molecules are exemplified by square-
pyramidal [WVIO2S(bdt)]2- in which benzene-1,2-dithiolate
occupies basal sites and simulates the stereochemical and
electronic features of the native pyranopterindithiolate co-
factor ligand.3,4 A key feature of this molecule is the presence
of one terminal sulfido ligand in a basal position; the two
oxo ligands are apical and basal. As such, the molecule
resembles the catalytic center of not only enzymes such as
xanthine and aldehyde oxidoreductases but also molybdenum-
containing carbon monoxide dehydrogenase, which catalyzes
the interconversion of carbon monoxide and carbon dioxide.
Figure 1. Depictions indicating the structural relationship between
[WO2S(bdt)]2- and the oxidized active site of a bacterial carbon monoxide
dehydrogenase.
The structural relationship between [WO2S(bdt)]2- and the
oxidized site of CODH5 from an aerobic bacterium6,7 is
evident from Figure 1. Inasmuch as isoligated MoVI and WVI
molecules are always isostructural, the tungsten complex is
stereochemically acceptable as a precursor to a structural
analogue of the CODH site. The analogous molybdenum
* Author to whom correspondence should be addressed. E-mail:
holm@chemistry.harvard.edu.
(1) Hille, R. Chem. ReV. 1996, 96, 2757–2816.
(2) Hille, R. Eur. J. Inorg. Chem. 2006, 1913–1926.
(3) Wang, J.-J.; Groysman, S.; Lee, S. C.; Holm, R. H. J. Am. Chem.
Soc. 2007, 7512–7513.
(4) Groysman, S.; Wang, J.-J.; Tagore, R.; Lee, S. C.; Holm, R. H. J. Am.
Chem. Soc. 2008, 130, 12794–12807.
(5) Abbreviations are given in Chart 1.
(6) Dobbek, H.; Gremer, L.; Kiefersauer, R.; Huber, R.; Meyer, O. Proc.
Natl. Acad. Sci. U.S.A. 2002, 99, 15971–15976.
(7) Gnida, M.; Ferner, R.; Gremer, L.; Meyer, O.; Meyer-Klaucke, W.
Biochemistry 2003, 42, 222–230.
10.1021/ic801836k CCC: $40.75  2009 American Chemical Society
Inorganic Chemistry, Vol. 48, No. 2, 2009 621
Published on Web 01/12/2009

Groysman and Holm
Chart 1. Designation of Compounds and Abbreviationsa
complex is unstable to autoreduction and has not been
isolated.
Realization of the desired structure requires binding of a
suitable CuI thiolate complex as a two-coordinate entity at
the sulfido site. Copper(I) thiolates tend to be polymeric or,
if molecular, polynuclear. Sterically bulky thiolates can form
two-coordinate complexes of the type [Cu(SR)2]1
,
8-10 but
-
these species do not contain a good leaving group. Potentially
more effective as a reactant would be [Cu(SR)L], where L
is labile neutral ligand and substituent R provides sufficient
steric encumbrance to stabilize two-coordinate CuI. Several
such species are known. These include [Cu(SSiPh3)(PBut3)]11
with, however, the likelihood of oxo silylation, a known
reaction type with WVIO groups.4,12 The complexes [Cu(S-
R)(carbene)] have been prepared, but with relatively small
R groups and a hindered, N,N′-disubstituted heterocyclic
carbene.13 The lability of carbenes in such complexes has
not been established. In this work, we have undertaken an
investigation of the synthesis and structures of mononuclear
complexes of the type [CuI(SR)L] with a sterically demand-
ing R group and variant ligands L. Among the potential
applications of these compounds is their use in the synthesis
of analogues of the CODH catalytic site by a building-block
approach.
a Ad ) adamantyl, Ar* ) 2,6-bis(2,4,6-triisopropyl)phenyl)phenyl, Ar*S
) 2,6-bis(2,4,6-triisopropylphenyl)benzenethiolate(1-), CODH ) carbon
monoxide dehydrogenase, lut ) lutidine, mes ) mesityl, Pri2NHCMe2 )
1,3-diisopropyl-4,5-dimethylimidazol-2-xylidene, Pri2Me2ImS ) 1,3-diiso-
propyl-4,5-dimethyl-2(3H)-thione, tht ) tetrahydrothiophene, tu ) thiourea
(generalized).
δ 7.33 (m, 6), 7.30 (s, 4), 6.73 (m, 12), 3.26 (sept, 4), 2.52 (sept,
2), 1.58 (d, 12), 1.25 (d, 12), 1.06 (d, 12). 13C{1H} NMR (100.59
MHz): δ 153.1 (C), 146.9 (C), 145.8 (C), 141.2 (C), 138.9 (C),
2
134.2 (CH, JCP ) 17.5 Hz, o-P-Ph), 129.3 (br s, CH, p-P-Ph),
128.7 (CH, 3JCP ) 7.6 Hz, m-P-Ph), 123.0 (CH), 120.6 (CH), 34.2
(ArCH(CH3)2), 31.4 (ArCH(CH3)2), 25.0 (ArCH(CH3)2), 24.9
(ArCH(CH3)2), 23.9 (ArCH(CH3)2). One CH resonance of the Ar*S
ligand was not observed, being possibly obscured by the doublet
at 128.7 ppm. The [CP] resonance of PPh3 was not observed. 31P
{1H} NMR (C6D6): δ -15.8. Anal. Calcd for C54H64CuPS: C, 77.24;
H, 7.68; S, 3.82. Found: C, 77.81; H, 7.43; S, 3.26.
Experimental Section
Preparation of Compounds. All operations were carried out
under a pure dinitrogen atmosphere using standard Schlenk
techniques or an inert atmosphere box. Solvents were passed
through an MBraun or Innovative Technology solvent purification
system prior to use. All volume reduction steps were performed in
[Cu(SAr*)(2,6-lut)] (2). A solution of 37 mg (0.35 mmol) of
2,6-lutidine in 2 mL of THF was added to a stirred suspension of
18 mg (0.087 mmol) of [CuBr(SMe2)]16 in 2 mL of THF, resulting
in a nearly clear solution. A solution of 46 mg (0.087 mmol) of
NaSAr* in 1 mL of THF was added dropwise, producing a fine
precipitate. The reaction mixture was stirred for 30 min and filtered,
and the filtrate taken to dryness. The off-white oily residue was
extracted with 4 mL of hexane, and solvent was removed from the
extract. The residue was recrystallized from hexane at -30 °C.
The crystalline solid was washed quickly with cold hexane and
dried, giving the product as 20 mg (33%) of colorless crystals. 1H
NMR (C6D6): δ 7.23 (s, 4), 7.18 (d, 2), 7.04 (m, 1), 6.58 (br s, 1),
6.10 (br s, 2), 3.34 (sept, 4), 2.75 (sept, 2), 2.10 (s, 6), 1.64 (d, 12),
1.22 (d, 12), 1.14 (d, 12). 13C{1H} NMR (C6D6, 100.59 MHz): δ
158.3 (C), 146.9 (C), 146.8 (C), 142.3 (C), 141.4 (C), 129.1 (CH),
123.1 (CH), 121.3 (CH), 120.6 (CH), 34.5 (ArCH(CH3)2), 31.3
(ArCH(CH3)2), 25.0 (ArCH(CH3)2), 24.6 (ArCH(CH3)2), 24.5 (lut-
CH3), 24.2 (ArCH(CH3)2).
1
vacuo. Routine characterization of metal complexes included H
and 13C (13C{1H} and DEPT-135) NMR experiments, performed
in benzene and referenced to the solvent peaks at 7.15 ppm (1H)
and 128.0 ppm (13C). Compounds were identified by a combination
of elemental analyses (representative compounds; H. Kolbe, Mul-
heim, Germany) and X-ray structure determinations. The compound
2,6-bis(2,4,6-triisopropylphenyl)benzenethiol was prepared by a
reported procedure.14 Its sodium salt was obtained from the thiol
and NaOMe in THF. Compounds are designated according to
Chart 1.
[Cu(SAr*)(PPh3)] (1). A mixture of 5.0 mg (0.090 mmol) of
NaOMe and 29 mg (0.055 mmol) of Ar*SH was stirred for 1 h,
filtered, and added to 50 mg (0.056 mmol) of [CuCl(PPh3)3]15 in 2
mL of THF. The reaction mixture was stirred for 2 h and filtered,
and the filtrate was taken to dryness. The solid residue was extracted
with 2 mL of hexane. The extract was filtered, and the filtrate was
maintained at -30 °C overnight. The solid that separated was
washed with a miminal amount of cold hexane and dried to afford
the product as 30 mg (63%) of colorless crystals. 1H NMR (C6D6):
[Cu(SAr*)(Pri2NHCMe2)] (3). A mixture of 4.0 mg (0.070
mmol) of NaOMe in 2 mL of THF and 29 mg (0.055 mmol) of
Ar*SH was stirred for 2 h and filtered. The filtrate was added
dropwise to a stirred mixture of 12 mg (0.057 mmol) of [Cu-
Br(SMe2)] and 10 mg of Pri2NHCMe2 in 2 mL of THF. The nearly
clear solution was stirred for 90 min and filtered, and the filtrate
was reduced to dryness. The oily solid residue was extracted with
2 mL of hexanes, and the solvent was removed, giving the product
(8) Koch, S. A.; Fikar, R.; Millar, M.; O’Sullivan, T. Inorg. Chem. 1984,
23, 122–124.
(9) Fujisawa, K.; Imai, S.; Kitajima, N.; Moro-oka, Y. Inorg. Chem. 1998,
37, 168–169.
(10) Zeevi, S.; Tshuva, E. Y. Eur. J. Inorg. Chem. 2007, 5369–5376.
(11) Medina, I.; Jacobsen, H.; Mague, J. T.; Fink, M. J. Inorg. Chem. 2006,
45, 8844–8846.
(12) Wang, J.-J.; Holm, R. H. Inorg. Chem. 2007, 46, 11156–11164.
(13) Delp, S. A.; Munro-Leighton, C.; Goj, L. A.; Ramirez, M. A.; Gunnoe,
T. B.; Petersen, J. L.; Boyle, P. D. Inorg. Chem. 2007, 46, 2365–
2367.
1
as 28 mg (66%) of white solid. H NMR (C6D6): δ 7.26 (s, 4),
7.20 (d, 2), 7.06 (t, 1), 4.54 (br s, 2), 3.66 (sept, 4), 2.81 (sept, 2),
1.67 (d, 12), 1.40 (s, 6), 1.34 (d, 12), 1.15 (d, 12), 1.07 (d, 12).
(14) Niemeyer, M.; Power, P. P. Inorg. Chem. 1996, 35, 7264–7272.
(15) Reichle, W. Inorg. Chim. Acta 1971, 5, 325–332.
622 Inorganic Chemistry, Vol. 48, No. 2, 2009

Mononuclear Quasi-Two-Coordinate Cu(I) Complexes
Table 1. Crystallographic Dataa for CuI Complexes with Sterically Hindering Ligands
1
2
3
4
5
6
7
8
9d
formula
fw
cryst syst
space group
Z
C54H64CuPS C43H58CuNS C47H69CuN2S C47H69CuN2S2 C40H57CuS
C43H57CuN C72H98BrCu3 C41H52Cu2PS2 C43H56S2
839.62
monoclinic monoclinic
P21/n
684.50
756.64
monoclinic
P21/n
789.70
monoclinic
P21/c
633.46
orthorhombic triclinic
Pbca
651.44
1298.15
monoclinic
P21/c
767.00
monoclinic
P21/c
637.00
monoclinic
P21/n
j
P1
C2/c
4
8
4
4
8
2
4
4
8
a, Å
b, Å
c, Å
R, deg
ꢀ, deg
γ, deg
V, A3
17.615(1)
14.463(1)
19.931(2)
90.00
108.956(1)
90.00
4802.4(6)
1.161
0.565
32.258(2)
18.700(1)
16.959(1)
90.00
107.120(1)
90.00
9776.8(9)
0.930
0.512
13.179(1)
24.460(2)
14.141(1)
90.00
100.244(4)
90.00
4485.8(5)
1.122
0.565
13.676(3)
19.847(4)
17.741(3)
90.00
104.665(4)
90.00
4659 (2)
1.126
0.590
18.793(1)
16.612 (1)
24.220 (1)
90.00
90.00
90.00
7561.4(6)
1.113
0.657
12.249(5)
12.703(5)
13.849(5)
112.348(5) 90.00
102.337(5) 94.754(1)
90.850(5)
1936(1)
1.118
0.592
50.00
13.549(1)
17.287(1)
28.753(2)
11.389(1)
17.975(1)
18.152(1)
90.00
94.287(1)
90.00
3705.5(4)
1.375
1.332
20.260(1)
16.548 (1)
25.200(1)
90.00
113.215(1)
90.00
7764.6(7)
1.090
0.164
90.00
6711.2(7)
1.285
1.639
55.80
0.0406
0.0998
1.017
dcalcd, g/cm3
µ, mm-1
2θ, deg
50.00
0.0569
50.00
50.00
50.00
50.00
55.78
50.00
b
R1 [I > 2σ(I)]
0.0491
0.1284
0.913
0.0732
0.1713
1.012
0.0504
0.1150
1.019
0.0525
0.1476
1.033
0.0473
0.1333
1.069
0.0475
0.1011
1.019
0.0808
0.2255
1.039
c
wR2 [I > 2σ(I)] 0.1231
GOF (F2)
1.021
a Mo KR radiation (λ ) 0.71073 Å), 193(2) K. b R1 ) ∑|Fo| - |Fc|/∑|Fo|. wR2 ) {∑ [w(Fo - Fc2)2/(Fo )2]}1/2
.
d Organic disulfide.
c
2
2
Table 2. Selected Bond Distances (Å) and Angles (deg) in Mononuclear [CuI(SAr*)L] and [CuI (Ar*)L] Complexes
L ) PPh3
2,6-luta
Pri2NHCMe2
Pri2Me2ImS
tht
2,6-lutb
Cu-S(Ar*)
Cu-C(Ar*)
Cu-L
2.194(1)
2.122(1)
2.122(2)
2.157(1)
1.915(3)
2.181(1)
1.913(2)
1.946(2)
2.210(1)
134.84(4)
1.929(2)
157.31(6)
1.902(6)
164.0(2)
2.196(1)
152.98(4)
(Ar*)S-Cu-L
(Ar*)C-Cu-L
174.0(1)
178.5(1)
C6H2Pr3 · · ·Cu
2.31
2.90
3.40
2.47
3.12, 3.21d
3.18, 3.20d
c
i
a Complex 2. b Complex 6. c Perpendicular distance of Cu atom to the nearest phenyl ring. d Cu· · ·Cipso distances; atom not positioned over phenyl rings.
13C{1H} NMR (C6D6, 100.59 MHz): δ 176.9 (NCN), 150.1 (C),
146.63 (C), 146.59 (C), 142.4 (C), 141.5 (C), 128.8 (CH), 123.8
(NC), 121.3 (CH), 120.3 (CH), 53.1 (NCH(CH3)2), 34.9
(ArCH(CH3)2), 31.3 (ArCH(CH3)2), 25.2 (ArCH(CH3)2), 24.6
(ArCH(CH3)2), 24.3 (ArCH(CH3)2), 22.5 (NC(CH3)), 9.5
(NCH(CH3)2). Anal. Calcd for C47H69CuN2S: C, 74.50; H, 9.18;
N, 3.70. Found: C, 74.30, H, 9.20; N, 3.69.
with ether (4 mL), and the ether solution was concentrated to ca.
2 mL and was stored at -30 °C. The product was obtained as three
1
successive crops of colorless crystals totaling 282 mg (61%). H
NMR (C6D6): δ 7.20-7.30 (m, 3), 7.13 (s, 4), 3.40 (sept, 4), 2.80
(sept, 2), 2.19 (br s, 4), 1.37 (d, 12), 1.25 (d, 12), 1.20 (d, 12), 1.16
(m, 4). 13C{1H} NMR (C6D6, 100.59 MHz): δ 168.2 (CuC), 149.6
(C), 146.9 (C), 146.5 (C), 145.9 (C), 124.9 (CH), 124.8 (CH), 120.4
(CH), 34.8 (ArCH(CH3)2), 34.3 (S-CH2), 30.56 (S-CH2CH2), 30.53
(ArCH(CH3)2), 25.0 (ArCH(CH3)2), 24.59 (ArCH(CH3)2), 24.53
(ArCH(CH3)2). The product analyzed satisfactorily as a monoet-
herate solvate. Anal. Calcd for C40H57CuS ·C4H10O: C, 74.68; H,
9.54; S, 4.53. Found: C, 74.58; H, 9.12; S, 4.92.
[Cu(Ar*)(2,6-lut)] (6). A solution of 54 mg (0.096 mmol) of
[Ar*Li(OEt2)] in 2 mL of ether was added to a suspension of CuBr
(14 mg, 0.097 mmol) in 2 mL of ether at -30 °C in the dark. The
mixture was stirred for 30 min, and a solution of 32 mg (0.29 mmol)
of 2,6-lutidine in 1 mL of ether was added. The mixture was stirred
for 30 min, and volatiles were removed. The white residue was
extracted with hexanes (4 mL), and the solvent was removed to
give the product as 52 mg (83%) of a white solid. 1H NMR (C6D6):
δ 7.29 (m, 3), 7.15 (s, 4), 6.47 (t, 1), 6.05 (d, 2), 3.51 (sept, 4),
2.88 (sept, 2), 1.69 (s, 6), 1.35 (d, 12), 1.31 (d, 12), 1.28 (d, 12).
13C{1H} NMR (C6D6, 100.59 MHz): δ 167.0 (CuC), 159.4 (C),
150.2 (C), 147.2 (C), 146.49 (C), 146.46 (C), 137.8 (CH), 125.1
(CH), 124.3 (CH), 121.5 (CH), 120.4 (CH), 34.9 (ArCH(CH3)2),
30.5 (ArCH(CH3)2), 24.74 (ArCH(CH3)2), 24.71 (ArCH(CH3)2),
24.6 (ArCH(CH3)2), 23.7 (lut-CH3).
[Cu(SAr*)(Pri2Me2ImS)] (4). A solution containing 35 mg
(0.046 mmol) of [Cu(SAr*)(Pri2NHCMe2)] in 2 mL of THF at -30
°C was treated with a solution of 1.6 mg (0.05 mmol) of sulfur in
0.2 mL of THF. The reaction mixture was allowed to warm to room
temperature and stirred for 20 min, resulting in a color change to
bright orange. The solvent was removed. The yellow residue was
extracted with 3 mL of hexane, and the extract was filtered. The
filtrate was taken to dryness, and the solid residue was recrystallized
from hexanes at -30 °C to yield the product as 23 mg (63%) of
colorless crystals. 1H NMR (C6D6): δ 7.36 (s, 4), 7.10 (d, 2), 6.98
(t, 1), 5.47 (br s, 2), 3.28 (sept, 4), 2.92 (sept, 2), 1.72 (d, 12), 1.33
and 1.32 (d, d, 24), 1.20 (br s, 6), 0.97 (br s, 12). 13C{1H} NMR
(C6D6, 100.59 MHz): δ 153.0 (C), 147.4 (C), 146.4 (C), 141.4 (C),
139.6 (C), 128.7 (CH), 123.1 (NC(CH3)), 122.1 (CH), 120.3 (CH),
50.4 (NCH(CH3)2), 34.8 (ArCH(CH3)2), 31.3 (ArCH(CH3)2), 25.1
(ArCH(CH3)2), 24.9 (ArCH(CH3)2), 24.6 (ArCH(CH3)2), 20.4
(NCH(CH3)2), 9.5 (NC(CH3)). The signal of the thione carbon atom
was not observed. Anal. Calcd for C47H69CuN2S2: C, 71.48; H, 8.81;
S, 8.12. Found: C, 71.55; H, 9.05; S, 7.89.
[Cu(Ar*)(tht)] (5). A solution of 411 mg (0.730 mmol) of
[Ar*Li(OEt2)]17 in 3 mL of ether was added to a suspension of
CuBr (103 mg, 0.730 mmol) in 2 mL of ether at -30 °C in the
dark. The mixture was stirred for 20 min, and 1.5 mL (17 mmol)
of tetrahydrothiophene was added. The mixture was stirred for 30
min, and volatiles were removed. The solid residue was extracted
[Cu3(SAr*)2Br] (7). A mixture of 4.0 mg (0.070 mmol) of
NaOMe and 29 mg (0.055 mmol) of Ar*SH in 7 mL of THF was
stirred for 4 h. The solution was filtered and added dropwise to a
stirred suspension of 11 mg (0.053 mmol) of [CuBr(SMe2)] in 2
mL of THF. The nearly clear reaction mixture was stirred overnight
and filtered. The solvent was removed from the filtrate, and the
oily solid residue was extracted with 2 mL of hexane. The solvent
(16) House, H. O.; Chu, C.-Y.; Wilkins, J. M.; Umen, M. J. J. Org. Chem.
1975, 40, 1460–1469.
Inorganic Chemistry, Vol. 48, No. 2, 2009 623

Groysman and Holm
Figure 2. Synthesis of two-coordinate CuI complexes 1-6 and trinuclear 7 derived from Ar*S, complex 8 from S-1-Ad, and disulfide 9.
was removed from the extract, and the residue was recrystallized
from hexane to afford the product as 20 mg (85% based on Cu) of
colorless crystals. 1H NMR (C6D6): δ 7.26 (s, 8), 6.82 (m, 6), 2.96
(sept, 4), 2.75 (sept, 8), 1.38 (d, 48), 1.07 (br d, 24). 13C{1H} NMR
(C6D6, 100.59 MHz): δ 149.4 (C), 145.5 (br s, C), 143.2 (C), 139.7
(C), 136.3 (C), 130.3 (CH), 124.7 (CH), 123.0 (CH), 34.8
(ArCH(CH3)2), 31.5 (ArCH(CH3)2), 24.9 (ArCH(CH3)2), 24.6
(ArCH(CH3)2), 24.5 (ArCH(CH3)2).
[Cu4(S-1-Ad)4(PPh3)2] (8). To a stirred solution of 44 mg
(0.028 mmol) of [Cu4Br4(PPh3)4] in 4 mL of toluene was added
a suspension of NaS-1-Ad (21 mg, 0.11 mmol) in 1 mL of
toluene. The reaction mixture became yellow following the
addition and was filtered. The filtrate was reduced to ca. 2 mL
and was layered with 10 mL of hexanes. The mixture was
maintained at -30 °C overnight, during which time the product
separated as 29 mg (71%) of very pale yellow crystals. 1H NMR
(C6D6): δ 7.57 (t, 12), 7.06 (m, 18), 2.40 (s, 24), 1.92 (s, 12),
1.59 (d, 12), 1.50 (d, 12). 31P NMR (C6D6): δ 3.72. The
compound analyzed satisfactorily as a hexane monosolvate. Anal.
Calcd for C76H90Cu4P2S4 · C6H14: C, 64.20; H, 6.83. Found: C,
63.89; H, 6.31.
Ar*SSCH2Ph (9). A solution of [Cu(Ar*)(2,6,-lut)] (28 mg,
0.043 mmol) in 0.5 mL of C6D6 was treated with 16 mg (0.057
mmol) of dibenzyltrisulfide in 0.5 mL of C6D6. As the solution
1
was stirred, the reaction was monitored by H NMR. After 2
days, no starting material was observed, and a brown precipitate
was removed by filtration. Solvent was removed, and the residue
was extracted with hexanes. The filtrate was concentrated to a
colorless oily residue, which was heated at 90 °C/0.005 mm Hg
for 2 h, resulting in the formation of 10 mg (37%) of colorless
1
crystals. H NMR (C6D6): δ 7.23 (s, 4), 7.13 (m, 2), 7.02 (m, 1),
6.86-6.95 (m, 5) 2.87 (sept, 4), 2.81 (sept, 2), 2.72 (s, 2), 1.38 (d,
12), 1.20 (d, 12), 1.12 (d, 12).). 13C{1H} NMR (C6D6, 100.59 MHz):
δ 148.9 (C), 146.7 (C), 145.7 (C), 138.3 (C), 137.9 (C), 136.9 (C),
131.0 (CH), 129.5 (CH), 128.3 (CH), 128.0 (CH), 127.2 (CH), 121.3
(CH), 44.0 (CH2), 34.8 (ArCH(CH3)2), 31.4 (ArCH(CH3)2), 25.6
(ArCH(CH3)2), 24.4 (ArCH(CH3)2), 23.4 (ArCH(CH3)2).
X-Ray Structure Determinations. Structures of the nine
compounds in Table 1 were determined. Diffraction-quality
crystals were obtained as follows: recrystallization from con-
centrated hexane solutions at -30 °C (1-4, 7, 9), hexane
diffusion into a concentrated toluene solution at -30 °C (8),
624 Inorganic Chemistry, Vol. 48, No. 2, 2009

Mononuclear Quasi-Two-Coordinate Cu(I) Complexes
affecting to some extent the quality of the structures. Two-site
disorder modeling did not significantly improve resolution of the
large thermal motion. Crystallographic data and final agreement
factors are given in Table 1.19
Results and Discussion
The reactions leading to compounds 1-9 reported here
are summarized in Figure 2. Selected structures of reaction
products are provided in Figures 3-5, and selected metric
features of Ar*S and Ar* complexes are summarized in
Table 2.
Preparation of Two-Coordinate CuI Complexes. In
view of the synthesis of linear [Cu(S-1-Ad)2]1-,9 attempts
to prepare mononuclear two-coordinate complexes of the
type [CuI(SR)L] first involved adamantane-1-thiolate.
Reaction of [CuCl(PPh3)3]14 with NaS-1-Ad did not yield
a
characterizable product. However, reaction with
[Cu4Br4(PPh3)4],20 utilized because of a lesser Cu/PPh3
ratio, afforded the tetranuclear complex 8. The molecule
is built of a Cu4(µ2-S)4 ring in which there are two
trigonal-planar CuI sites with bound phosphine and two
two-coordinate sites whose bond angles deviate 14° from
linearity (Figure 3). The structure is similar to that of
[Cu4(SBut)4(PPh3)2].21 Because of this result and a previ-
ous finding that adamantane-1-thiolate can form at least
one polynuclear complex9 in addition to mononuclear
[Cu(S-1-Ad)2]1-, we directed our attention to a more
hindered ligand system.
2,6-Bis(2,4,6-triisopropylphenyl)benzenethiolate(1-)(Ar*S)
was introduced by Niemeyer and Power14,22 as an
especially capacious ligand, a property demonstrated by
its ability to form homoleptic two-coordinate complexes
with MgII, divalent ions of the first transition series,23 and
EuII and YbII.24 Thiolate complexes were prepared by
reactions 1 and 2. Complexes 1 (63%), 2 (33%), and 3
(66%) were obtained in the indicated yields by reaction
1. The only previously reported two-coordinate CuI
phosphinethiolate species similar to 1 is nearly linear
[Cu(SSiPh3)(PBut3)].11 No aminethiolate complexes related
to 2 have been described; several complexes analogous
to 3 have been prepared by thiolate ligand displacement
of preisolated carbene complexes.13 The reaction of
[CuBr(SMe2)] with equimolar thiolate did not lead to
Figure 3. Structures of polynuclear CuI complexes showing 50% probability
ellipsoids, partial atom numbering schemes, and selected bond distances
(Å) and angles (deg). [Cu3(Ar*S)2Br] (upper): Cu1-S1 2.174(1), Cu1-S2
2.173(1), Cu2-S1 2.186(1), Cu3-S2 2.198(1), Cu2-Br 2.301(1), Cu3-Br
2.317(1), S1-Cu1-S2 161.27(3), Cu1-S1-Cu2 77.59(2), Cu1-S2-Cu3
73.36(2), S1-Cu2-Br 149.43(2), S2-Cu3-Br 148.24(2), Cu2-Br-Cu3
74.40(1). [Cu4(S-1-Ad)4(PPh3)2] (lower, crystallographyically imposed
centrosymmetry): Cu1-P1 2.252(1), Cu1-S1 2.286(1), Cu1-S2 2.227(1),
Cu2-S2 2.173(1), Cu2-S1 2.157(1), P1-Cu1-S1 105.75(3), P1-Cu1-S2
139.47(3), S1-Cu1-S2 113.34(3), S2-Cu2-S1′ 165.71(3).
and concentration of ether (5) and hexane (6) solutions. Crystal
mounting and data collections were performed as described18
on a Siemens (Bruker) SMART CCD instrument using Mo KR
radiation. Data out to a 2θ of 50° were used for 1-6 and 9
because of the somewhat lower quality of the high-angle data;
for 7 and 8, higher-angle data were employed.
Data reductions were performed with SAINT, which corrects
for Lorentz polarization and decay. Space groups were assigned
by analysis of symmetry and systematic absences determined by
XPREP. Structures were solved by direct methods and SHELXL-
97 and refined against all data in the 2θ ranges by full-matrix least-
squares on F2. All non-hydrogen atoms were refined anisotropically.
Hydrogen atoms at idealized positions were included in final
refinements. Compound 8 occupies a special position; therefore,
only half a molecule constitutes an asymmetric unit. It contains
one hexane solvate molecule per cluster. Compound 2 contained
traces of unidentified solvate (one peak of ca. 2e-, another of ca.
1.5e-) which could not be modeled satisfactorily and was therefore
removed using the SQUEEZE program of the PLATON package.
In the structure of 5, the disorder of the tht ligand was modeled by
two conformations. In some of the structures (especially those of
3 and 9), peripheral isopropyl groups display a wagging motion,
(19) See the Supporting Information.
(20) Costa, G.; Reisenhofer, E.; Stefani, L. J. Inorg. Nucl. Chem. 1965,
27, 2581–2584.
(21) Dance, I. G.; Fitzpatrick, L. J.; Craig, D. C.; Scudder, M. L. Inorg.
Chem. 1989, 28, 1853–1861.
(22) Niemeyer, M.; Power, P. P. Inorg. Chim. Acta 1997, 263, 201–207.
(23) Nguyen, T.; Panda, A.; Olmstead, M. M.; Richards, A. F.; Stender,
M.; Brynda, M.; Power, P. P. J. Am. Chem. Soc. 2005, 127, 8545–
8552.
(24) Niemeyer, M. Eur. J. Inorg. Chem. 2001, 1969–1981.
(25) Ferrari, M. B.; Fava, G. G.; Pelizzi, G.; Tarasconi, P. Inorg. Chim.
Acta 1985, 97, 99–109.
(26) Skoulika, S.; Aubry, A.; Karagianidis, P.; Aslandis, P.; Papastefanou,
S. Inorg. Chim. Acta 1991, 183, 207–211.
(27) Singh, R.; Dikshit, S. K. Polyhedron 1995, 14, 1799–1807.
(28) Aslandis, P.; Cox, P. J.; Karagianidis, P.; Hadjikakou, S. K.;
Antoniadis, C. D. Eur. J. Inorg. Chem. 2002, 2216–2222.
(29) Kaltzoglou, A.; Cox, P. J.; Aslandis, P. Inorg. Chim. Acta 2005, 358,
3048–3056.
(17) Schiemenz, B.; Power, P. P. Organometallics 1996, 15, 958–964.
(18) Groysman, S.; Holm, R. H. Inorg. Chem. 2007, 46, 4090–4102.
(30) Niemeyer, M. Organometallics 1998, 17, 4649–4656.
Inorganic Chemistry, Vol. 48, No. 2, 2009 625

Groysman and Holm
Figure 4. Structures of quasi-two-coordinate CuI complexes [Cu(SAr*)L]: L ) PPh3 and 2,6-lut (upper) and Pri2NHCMe2 and Pri2Me2ImS (lower), showing
50% probability ellipsoids. Metric data are summarized in Table 2.
anticipated [Cu(SAr*)(Me2S)] but instead to trinuclear 7
(85%, see below). Reaction 2 is exemplified by sulfur
insertion into the Cu-C bond of 3 to afford complex 4
(63%). Three- and four-coordinate CuI-thiourea com-
plexes with two, three, and four thiourea ligands are
numerous. Those with one such ligand are nearly exclu-
sively the tetrahedral species [Cu(PR3)2X(tu)].25-29 Com-
plex 4 is the first example of a [Cu(SR)(tu)] complex.
(ArS * )Na + [CuXLn] f [Cu(SAr*)L] + NaX + (n - 1)L
(1)
[Cu(Ar * S)L] + S f [Cu(SAr*)(SL)]
(2)
Because direct synthesis of the complex with L ) Me2S by
reaction 1 was unsuccessful, its formation by sulfur insertion
into a CuI-C bond was investigated. The two-coordinate
complexes [Cu(Ar*)L] with L ) tht (5, 61%) and 2,6-lut (6,
83%) were obtained by the reaction of [(Ar*)Li(OEt2)] with
CuBr and L in a manner similar to the preparation of
[Cu(Ar*)(SMe2)].17 The reaction of 5 with the sulfur transfer
reagents Ph3SbS, (PhCH2S)2S, and elemental sulfur failed to
give a well-defined product. Similarly, the reaction of 6 with
Ph3SbS and sulfur was unsuccessful. Treatment of 6 with
(PhCH2S)2S led unexpectedly to the mixed disulfide 9 (37%)
together with an insoluble brown precipitate (presumably Cu2S).
The previously unknown disulfide was identified by an X-ray
structure determination.19
Figure 5. Structures of two-coordinate CuI complexes [Cu(Ar*)L]: L )
tht and 2,6-lut, showing 50% probability ellipsoids. Metric data are
summarized in Table 2.
from S-Cu-L linearity in structures described as quasi-
two-coordinate, owing to interactions of CuI with a phenyl
ring in the 2,6-position in each molecule (Table 2). Intramo-
lecular CuI-olefin and -arene interactions are frequently
encountered, including several recent instances.30-32 Com-
Structures of Ar*S and Ar* Complexes. The structures
of Ar*S complexes 1-4 (Figure 4) reveal varying departures
626 Inorganic Chemistry, Vol. 48, No. 2, 2009

Mononuclear Quasi-Two-Coordinate Cu(I) Complexes
putational results for CuI-arene interactions indicate that
these are likely of 3d-C(pπ*) origin.32 In the set 1-4, these
interactions are described by the perpendicular distance
between the metal and the interacting phenyl ring. This
distance maximizes in the nonlinear phosphine complex 1
(2.31 Å) where the metal has pseudotrigonal coordination
and the smallest CuI bond angle (135°). The weakest or nil
interaction occurs in carbene complex 3 (3.40 Å), which
displays the largest bond angle (164°). Complexes 4 (2.47
Å, 153°) and 2 (2.90 Å, 157°) are intermediate cases.
The structure of trinuclear 7 (Figure 3) is based on a
Cu3S2Br ring, which is unique to this structure but reminis-
cent of the cyclic nonplanar Cu3(SR)3 motif relatively
abundant in CuI-thiolates.33-36 The ring contains two-
coordinate Cu1 and quasi-two-coordinate Cu2 and Cu3,
which show weak secondary interactions with nearly phenyl
rings (2.44, 2.48 Å), similar to 1, 2, and 4. It might be noted
that these interactions in two-coordinate complexes were first
observed in sterically crowded [Fe(SC6H3-2,6-mes2)2] and
[Fe(SC6H3-2,6-mes2)(N(SiMe3)2)] with Fe · · · C separations
of ca. 2.5 Å.37 In the molecules, the interactions likely
involve C(pπ) electron donation to incompletely filled 3d
iron orbitals as a means of redressing electron deficiency at
the metal sites. In the present group of CuI thiolates, electron
donation in the opposite sense is probable.
negligible secondary interactions with phenyl rings and thus
are strictly two-coordinate with nearly linear structures (Table
2). In 6, the central phenyl and pyridyl rings are nearly
coplanar, with a C-Cu-N bond angle of 178.5°, and a
dihedral angle of 9°, and the rings in the 2,6- positions are
nearly perpendicular to the central ring with dihedral angles
of 81° and 87°. This stereochemistry sets a distance of ca.
3.4 Å between the 2,6-methyl groups of lutidine and the rings
and leads to intramolecular CH(σ*)/π interactions of a type
previously catalogued38 and treated theoretically.39 An
apparent effect of this situation is enhanced shielding of the
methyl protons in 6 (1.69 ppm) compared to 2 (2.10 ppm),
which lacks the same ring orientation, and free 2,6-lutidine
(2.38 ppm) in C6D6.
Summary
This work describes the synthesis of a set of complexes
[CuI(SAr*)L] whose actual or quasi-dicoordinate formulation
arises from the uncommon steric shielding of the metal center
by the thiolate ligand Ar*S introduced by Niemeyer and
Power.14,22 Also demonstrated is the formation of a trinuclear
structure from the reaction of [CuBr(SMe2)] and thiolate in
the absence of ligand L, the conversion of a carbene complex
to a thiourea complex by sulfur insertion into a Cu-C bond,
and the occurrence of weak secondary bonding interactions
between the metal and phenyl groups that contribute to
nonlinear structures and quasi-two-coordination. Current
research is concerned with the role of these complexes in
constructing analogues of the CODH site.
Structures of the two Ar* complexes 5 and 6 were also
determined (Figure 5, Table 2); the structure of 5 resembles
[Cu(Ar*)(SMe2)].17 These complexes manifest essentially
(31) Sundararaman, A.; Lalancette, R. A.; Zakharov, L. N.; Rheingold,
A. L.; Ja¨kle, F. Organometallics 2003, 22, 3526–3532.
(32) Osako, T.; Tachi, Y.; Doe, M.; Shiro, M.; Ohkubo, K.; Fukuzumi, S.;
Itoh, S. Chem.sEur. J. 2004, 10, 237–246.
(33) Dance,I.G.;Fitzpatrick,L.J.;Scudder,M.L.J.Chem.Soc.,Chem.Commun.
1983, 546–548.
Acknowledgment. This research was supported by NSF
Grant CHE 00547734. We thank Dr. L. Deng for a sample
of carbene.
(34) Pulla Rao, C.; Dorfman, J. R.; Holm, R. H. Inorg. Chem. 1986, 25,
428–439.
(35) Knotter, D. M.; van Maanen, H. L.; Grove, D. M.; Spek, A. L.; Van
Koten, G. Inorg. Chem. 1991, 30, 3309–3317.
(36) Togni, A.; Rihs, G.; Blumer, R. E. Organometallics 1992, 11, 613–
621.
Supporting Information Available: X-ray crystallographic files
in CIF format for the nine compounds in Table 1 and a structural
depiction of compound 9. This material is available free of charge
via the Internet at http://pubs.acs.org.
(37) Ellison, J. J.; Ruhlandt-Senge, K.; Power, P. P. Angew. Chem., Int.
Ed. Engl. 1994, 33, 1178–1180.
(38) Umezawa, Y.; Tsuboyama, S.; Takahashi, H.; Uzawa, J.; Nishio, M.
Tetrahedron 1999, 55, 10047–10056.
IC801836K
(39) Tsuzuki, S.; Honda, K.; Uchimaru, T.; Mikami, M.; Tanabe, K. J. Am.
Chem. Soc. 2000, 122, 3746–3753.
Inorganic Chemistry, Vol. 48, No. 2, 2009 627