Palladium(II) phosphine thiocarboxylates. Structures of cis-Pd(κS-SOCMe)2(dppf) [dppf=1,1′-bis(diphenylphosphino)ferrocene] and trans-Pd(κS-SOCMe)2(PPh3)2

Article abstract of DOI:10.1016/S0022-328X(01)00916-0

Although palladium phosphine acetates are generally unstable and served as catalytic precursors, their monothioacetate analogues can be isolated and structurally characterized. Spectroscopic and X-ray single-crystal crystallographic analyses suggested that Pd(κS-S{O}CMe)₂(P₂) [P₂=dppf, I; P=PPh₃, II] are mononuclear with thioacetate coordinates in a unidentate manner through sulfur. Dppf imposes a cis configuration on I whereas PPh₃ promotes a trans-structure for II. The compounds are obtained in isomerically pure form - there is no evidence for chelating or bridging thioacetate or bridging diphosphine. The Me group of thioacetate is significantly more shielded in II than I by the Ph rings of the neighboring phosphine.

Full text of DOI:10.1016/S0022-328X(01)00916-0

Journal of Organometallic Chemistry 637–639 (2001) 757–761
www.elsevier.com/locate/jorganchem
Note
Palladium(II) phosphine thiocarboxylates. Structures of
cis-Pd(kS-SOCMe)2(dppf)
[dppf=1,1%-bis(diphenylphosphino)ferrocene] and
trans-Pd(kS-SOCMe)2(PPh3)2
Yew Chin Neo, Jagadese J. Vittal, T.S. Andy Hor *
Department of Chemistry, National Uni6ersity of Singapore, 3 Science Dri6e 3, Singapore 117543, Singapore
Received 2 February 2001; received in revised form 28 March 2001; accepted 28 March 2001
Abstract
Although palladium phosphine acetates are generally unstable and served as catalytic precursors, their monothioacetate
analogues can be isolated and structurally characterized. Spectroscopic and X-ray single-crystal crystallographic analyses
suggested that Pd(kS-S{O}CMe)2(P2) [P2=dppf, I; P=PPh3, II] are mononuclear with thioacetate coordinates in a unidentate
manner through sulfur. Dppf imposes a cis configuration on I whereas PPh3 promotes a trans-structure for II. The compounds
are obtained in isomerically pure form—there is no evidence for chelating or bridging thioacetate or bridging diphosphine. The
Me group of thioacetate is significantly more shielded in II than I by the Ph rings of the neighboring phosphine. © 2001 Elsevier
Science B.V. All rights reserved.
Keywords: Palladium; Ferrocenylene phosphine; Thioacetate; Diphosphine
1. Introduction
tion. Their coordination commonly takes the following
forms shown in Scheme 1.
Monothiocarboxylate, RC{O}S−, is a interesting
class of ligands. With both soft (S) and hard (O)
binding sites, it shows diverse bonding modes [1,2] and
the ability to stabilize a range of homonuclear [3,4] and
heterometallic [5] systems of both early and late metals.
Among the monothiocarboxylates, thioacetate [1,4,6–8]
and thiobenzoate [1–5,8–10] have received most atten-
It is therefore surprising that metal thiocarboxylates
have been relatively unexplored compared to that of
their thiolate, thiocarbamate and dithiocarboxylates
counterparts [1]. Palladium phosphine carboxylates are
active catalyst precursors especially in Heck-type reac-
tions [11]. Their ready decomposition to Pd(0) species
and its relationship to the electronic and molecular
structure of the complex as well as the catalytic mecha-
nism is a subject of contemporary interest [12]. In this
paper, we examine two thiocarboxylate analogues of
this system in an attempt to understand its structural
behavior. The choice of monothiocarboxylate as a
model is logical due to its resemblence to carboxylates
and the higher stability it brings to the Pd(II) system.
Two representative phosphines are chosen—PPh3,
which is commonly use as a stabilizer in the catalytic
system, and Fe(h5-C5H4PPh2)2 [dppf], whose catalytic
function is a subject of our recent review [13].
Scheme 1.
* Corresponding author. Tel.: +65-77-22-917; fax: +65-77-89-
437.
E-mail address: andyhor@nus.edu.sg (T.S.A. Hor).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)00916-0

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Y.C. Neo et al. / Journal of Organometallic Chemistry 637–639 (2001) 757–761
Table 1
IR and NMR spectroscopic data of Pd(kS-S{O}CMe)2(dppf) (I) and trans-Pd(S{O}CMe)2(PPh3)2 (II)
Complex
w(CꢀO) cm−1 w(C–S) cm−1
lH (ppm)
lP (ppm)
I
1614 vs
947 s
1.87 (s, Me, 6H); 4.29 (dd, Cp–Ha, 4H); 3JHH=1.60 Hz; 3JHP=1.60 Hz; 4.31 (d, 25.75 (s)
Cp–Hb, 4H); 3JHH=1.60 Hz; 7.34–7.40 (m, Ph, 8H); 7.41–7.48 (m, Ph, 4H);
7.80–7.88 (m, Ph, 8H)
II
1620 vs
948 s
1.33 (s, Me, 6H); 7.32–7.43 (m, Ph, 18H); 7.71–7.79 (m, Ph, 12H)
28.79 (s)
IR spectra were recorded in KBr and NMR in CDCl3.
(Tables 2 and 3; Figs. 2 and 3) and found to be
consistent with the solution structures. Both are
mononuclear with thioacetate opts for an S-coordina-
tion with a pendant O site. The two pendant oxygen
atoms in both cases adopts the sterically more favor-
able anti conformation. The chelating dppf imposes a
cis configuration on I whereas the trans configuration in
II is promoted by the sterically demanding PPh3 in II.
The preference for thioacetate to use the S site for
donation is not surprising considering that trans-
Ni(kS-S{O}CMe)2(PPh3)2 [7] and [Pd(kS-S{O}CPh)2-
(L2)] (L=PPh3, PMePh2, PMe2Ph, AsPh3, SbPh3, py;
L2=bipy, PPh2CH2PPh2, PPh2(CH2)2PPh2) [10] have
been reported to behave similarly. Although there are
reports suggesting that some Pd(II) monothiobenzoate
could show dimeric or monothiocarboxylates bridging
structures with both Pd–O and Pd–S functionalities
[10], this is not observed in our system. The reluctance
for the thioacetate to use the O site despite some
favourable steric factors also points to a softer charac-
ter for Pd(II). The isolation of these complexes suggests
that the geometric isomeric preference of Pd(II) can be
dictated by the phosphine. The Pd–X (X=P, S)
2. Results and discussion
Although metathesis reaction of PdX2(dppf) with
alkali salts of carboxylate were unsuccessful with the
starting materials largely recover unreacted [14], similar
reactions of PdBr2(P2) [P2=dppf; P=PPh3] with excess
potassium thioacetate gave Pd(S{O}CMe)2(P2) in mod-
erate yields. The spectroscopic data of Pd(kS-
S{O}CMe)2(dppf) (I), and trans-Pd(kS-S{O}CMe)2-
(PPh3)2 (II) are given in Table 1. The presence of the
thioacetate ligands is inferred by the strong IR absorp-
tion bands in the 1500–1650 cm−1 (C–O) and 900–950
cm−1 (C–S) regions [2,10,15]. Both complexes display
IR bands in ꢀ1600 and 940 cm−1 that characterize
strong Pd–S and weak Pd–O interactions [10]. This is
the first indication for a unidentate coordination of
thioacetates via the S atom, thus ruling out an O-dona-
tion or bridging formation. The 1H- and 31P-NMR data
are consistent with that expected from the complex
Pd(kS-S{O}CMe)2(P2) [P2=dppf, I; P=PPh3, II]. An
unexpected feature is the higher shielding effect of the
Me group of thioacetate in II (lH 1.33 ppm). This has
also been observed in similar acetate complexes, viz.
Pt(O2CMe)2(P2) [P=PPh3 1.35 ppm; P2=dppm 1.96
ppm, dppf 1.93 ppm] [16]. This could be explained by
the proximity effect of the neigboring Ph rings due to
steric congestion. Examination of the methyl shift trend
in Pd(O2CMe)2(PPh3)2 (0.85 ppm [10]), Pd(O2CMe)2-
(PMePh2)2 (1.64 ppm) [10] and Pd(O2CMe)2(PMe2Ph)2
(2.00 ppm) [10] tends to support this postulate. The
ROSEY spectrum of II (Fig. 1) gives the clearest in-
dication that spatial interaction between the Me and
Ph protons is active. Shielding of the Me group origi-
nates from the delocalised electrons of the Ph rings of
PPh3.
The solid-state structures of both complexes have
been examined by X-ray single-crystal crystallography
Fig. 1. ROSEY spectra of trans-Pd(kS-S{O}CMe)2(PPh3)2 (II). NOE
contacts are mark by the * signs.

Y.C. Neo et al. / Journal of Organometallic Chemistry 637–639 (2001) 757–761
759
Table 2
a monothiocarboxylate entity, thereby offering a natu-
ral protection to a catalytically active functionality is
intriguing. We are currently investigating this system in
this direction in together with their chemical and ther-
mal stabilities.
Crystallographic data and refinement details for Pd(kS–S{O}CMe)2-
(dppf) (I) and trans-Pd(kS-S{O}CMe)2(PPh3)2 (II)
I
II
Empirical
formula
Mr
Temperature (K) 223(2)
Diffractometer Bruker AXS
C
38H34FeO2P2PdS2
C40H36O2P2PdS2
781.15
810.96
3. Experimental
Bruker AXS
0.71073
Triclinic
3.1. General procedures
,
Wavelength (A)
0.71073
Monoclinic
P21/n
Crystal system
Space group
Unit cell
(
P1
All reactions were performed under pure dry argon
using standard Schlenk techniques. The products are
stable and hence recrystallizations were done in air. All
solvents and reagents were of reagent grade obtained
from commercial sources and used without further
purification.
dimensions
,
a (A)
10.458(1)
18.326(1)
17.834(1)
90
90.661(2)
90
3417.7(4)
4
1.200
8.071(1)
10.796(2)
11.116(2)
114.500(2)
95.761(3)
95.806(3)
865.9(2)
1
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
PdBr2(dppf) and PdBr2(PPh3)2 were prepared using
literature method [18].
3
,
V (A )
Z
All 1H- and 31P-NMR spectra except ROSEY spec-
trum were recorded at ca. 300 K at operating frequency
v (mm−1
)
0.784
0.20×0.20×0.14
Crystal size
0.24×0.20×0.16
(mm3)
q range (°)
h, k, l
2.22 to 30.01
−14 to 14,−14 to
25,−23 to 25
28126
2.04 to 30.02
−11 to 11,−15 to 13,
0 to 15
Table 3
,
Selected bond lengths (A) and bond angles (°)
Reflections
collected
Independent
reflections
Completeness to 99.3
q (%)
Absorption
correction
Max./min.
transmission
Refinement
method
Data/restraints/
parameters
Goodness-of-fit
on F2
Final R indices
[I\2|(I)] a
R indices (all
data)
4997
Pd(kS-S{O}CMe)2(dppf) (I)
9907 [Rint=0.0441]
10327 [Rint=0.0515]
Bond lengths
98.6
Pd(1)–P(1)
Pd(1)–S(1)
S(1)–C(11)
O(1)–C(11)
C(11)–C(12)
2.2996(6)
2.3231(7)
1.727(3)
1.209(3)
1.490(4)
Pd(1)–P(2)
Pd(1)–S(2)
S(2)–C(13)
O(2)–C(13)
C(13)–C(14)
2.3168(6)
2.3542(6)
1.746(3)
1.214(3)
1.511(4)
SADABS (Sheldrick,
1996)
0.8522, 0.6359
SADABS (Sheldrick,
1996)
0.8981, 0.8589
Full-matrix
Full-matrix
Bond angles
least-squares on F2
9907/0/417
least-squares on F2
4997/0/227
P(1)–Pd(1)–P(2)
P(2)–Pd(1)–S(1)
P(2)–Pd(1)–S(2)
C(1)–P(1)–Pd(1)
C(11)–S(1)–Pd(1)
O(1)–C(11)–C(12)
C(12)–C(11)–S(1)
O(2)–C(13)–S(2)
P(1)···xA···B···P(2) a
99.55(2)
169.97(2)
83.56(2)
113.63(8)
102.71(9)
121.1(3)
113.6(2)
124.4(2)
37.2
P(1)–Pd(1)–S(1)
P(1)–Pd(1)–S(2)
S(1)–Pd(1)–S(2)
C(6)–P(2)–Pd(1)
C(13)–S(2)–Pd(1)
O(1)–C(11)–S(1)
O(2)–C(13)–C(14)
C(14)–C(13)–S(2)
xA···Fe···xA
89.88(2)
173.77(2)
87.37(2)
123.04(7)
100.22(9)
125.3(2)
122.3(2)
113.3(2)
177.04
1.061
1.016
R1=0.0356,
wR2=0.0858
R1=0.0481,
wR2=0.0921
R1=0.0435,
wR2=0.0962
R1=0.0510,
wR2=0.1009
1.224,−1.384
(Dz)max, (Dz)min 0.732,−0.578
Trans-Pd(kS-S{O}CMe)2(PPh3)2 (II)
−3
,
(e A
)
Bond lengths
Pd–S(1–1A)
S(1)–C(1)
C(1)–C(2)
P(1)–C(1B)
a R1=ꢀꢁꢁFoꢁ−ꢁFcꢁꢁ/ꢀꢁFoꢁ. wR2={ꢀwꢁ[(Fo2−Fc2)2]/ꢀ wFo4}1/2
.
2.3264(7)
1.748(3)
1.508(4)
1.815(3)
Pd–P(1–1A)
O(1)–C(1)
P(1)–C(1A)
P(1)–C(1C)
2.3343(7)
1.219(3)
1.826(3)
1.822(3)
lengths are within expectations [17]. The influence of
the Ph ring on the methyl protons in II is exemplified in
,
the close contact of the Me and Ph groups (3.172 A for
nearest HMe···CPh).
Bond angles
S(1)–Pd(1)–S(1A)
S(1)–Pd(1)–P(1)
S(1)–Pd(1)–P(1A)
C(1)–S(1)–Pd(1)
O(1)–C(1)–S(1)
180.00(3)
87.49(3)
92.51(3)
104.01(10) O(1)–C(1)–C(2)
125.1(2) C(2)–C(1)–S(1)
S(1A)–Pd(1)–P(1)
S(1A)–Pd(1)–P(1A)
P(1)–Pd(1)–P(1A)
92.51(3)
87.49(3)
180.0
120.6(3)
114.3(2)
The Pd(II) phosphine carboxylates are valuable pre-
catalysts but they are usually too unstable to be isolated
or stored. The higher stability of the thiocarboxylate
analogues could provide some solutions although their
catalytic activities, which are largely unknown, may be
sacrificed. The potential for an in situ S–O switching in
a xA and xB is the centroid of C(1)–C(5) and C(6)–C(10), respec-
tively.

760
Y.C. Neo et al. / Journal of Organometallic Chemistry 637–639 (2001) 757–761
Anal Calc.: C, 56.28; H, 4.23. Found: C, 55.35; H,
4.18%.
3.3. Pd(sS-S{O}CMe)2(PPh3)2 (II)
cis-PdBr2(PPh3)2 (0.200 g, 0.253 mmol) and
KSC{O}CH3 (0.064 g, 0.560 mmol) in CH2Cl2 (50 cm3)
were stirred at r.t. for ca. 20 h. The resulting lime-yel-
low suspension was filtered, and hexane added to crys-
tallize the compound, Pd(kS-S{O}CMe)2(dppf). Yield,
0.192 g (97%). Anal Calc.: C, 61.50; H, 4.64. Found: C,
61.01; H, 4.58%.
4. Supplementary material
Fig. 2. ORTEP drawing of the molecular structure of Pd(kS-
S{O}CMe)2(dppf) (I).
Crystallographic data (CIF files) for the structural
analysis have been deposited with the Cambridge Crys-
tallographic Data Centre, CCDC no. 155772 for I and
CCDC no. 155773 for II. Copies of this information
may be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
(Fax: +44-1223-336033; e-mail: deposit@ccdc.cam.
ac.uk or http://www.ccdc.cam.ac.uk).
Acknowledgements
We acknowledge the National University of Singa-
pore (NUS) for financial support (RP 960664/A) and
technical assistance from our Department. We thank
G.K. Tan for assistance in X-ray analysis. Y.C. Neo is
grateful to NUS for a research scholarship.
Fig. 3. ORTEP drawing of the molecular structure of trans-Pd(kS-
S{O}CMe)2(PPh3)2 (II).
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