X-Ray and NMR study of the structural features of SCS-pincer metal complexes of the group 10 triad

Article abstract of DOI:10.1021/om800324w

SCS-pincer metal complexes [MX(SCS)] (SCS = [2,6-(RSCH₂) ₂C₆H₃]^-; R = Ph: ^phSCS; R = Me: ^MeSCS; M = Pd, Pt, Ni) have been synthesized via mild and tolerant oxidative addition procedures. The complexes have been characterized by ¹H and ¹³C NMR spectroscopy and X-ray crystal structure determination. Interestingly, the crystal structures of [NiBr(^MeSCS)] 4, [PdBr(^MeSCS)] 5, [PtBr(^MeSCS)] 6, and [PtBr( ^phSCS)J 8 each have a unit cell with a unique set of independent [MBr(^RSCS)] molecules; each of these structures has a different conformation of the five-membered ortho-chelate ring (including the configuration of the coordinated S-center) in the solid state. The temperature-dependent ¹H NMR resonance patterns of these complexes in solution were related to structural features encountered in the solid state and allowed us to assign all dynamic processes (rac/meso isomerizations) that occurred in solution.

Full text of DOI:10.1021/om800324w

4928
Organometallics 2008, 27, 4928–4937
X-Ray and NMR Study of the Structural Features of SCS-Pincer
Metal Complexes of the Group 10 Triad
Cornelis A. Kruithof,† Harmen P. Dijkstra,† Martin Lutz,‡ Anthony L. Spek,‡
Robertus J. M. Klein Gebbink,*,† and Gerard van Koten*,†
Chemical Biology and Organic Chemistry, Debye Institute for NanoMaterials Science, Faculty of Science,
Utrecht UniVersity, Padualaan 8, 3584 CH, Utrecht, The Netherlands, and Crystal and Structural
Chemistry, BijVoet Center for Biomolecular Research, Faculty of Science, Utrecht UniVersity,
Padualaan 8, 3584 CH Utrecht, The Netherlands
ReceiVed April 10, 2008
SCS-pincer metal complexes [MX(SCS)] (SCS ) [2,6-(RSCH2)2C6H3]-; R ) Ph: PhSCS; R ) Me:
MeSCS; M ) Pd, Pt, Ni) have been synthesized via mild and tolerant oxidative addition procedures. The
1
complexes have been characterized by H and 13C NMR spectroscopy and X-ray crystal structure
determination. Interestingly, the crystal structures of [NiBr(MeSCS)] 4, [PdBr(MeSCS)] 5, [PtBr(MeSCS)]
6, and [PtBr(PhSCS)] 8 each have a unit cell with a unique set of independent [MBr(RSCS)] molecules;
each of these structures has a different conformation of the five-membered ortho-chelate ring (including
1
the configuration of the coordinated S-center) in the solid state. The temperature-dependent H NMR
resonance patterns of these complexes in solution were related to structural features encountered in the
solid state and allowed us to assign all dynamic processes (rac/meso isomerizations) that occurred in
solution.
catalyst immobilization and recycling set-ups,4 materials science
Introduction
such as gas or metal sensor materials, 2b,5 the synthesis of ECE-
pincer metal complexes (Li, Au, Pt, Ru complexes),5-7 and the
field of supramolecular chemistry.8 An important reason for
the broad applicability of the ECE-pincer ligand system is the
possibility to introduce a wide variety of transition metals. By
virtue of the high chemical stability, alterations of the electronic
environment of the metal can easily be accomplished by
changing the nature of both the donor atoms (E) and its
substituents (R). In addition, ancillary groups (Z)9 have been
introduced into the ligand system using straightforward synthetic
methods, which also have significantly contributed to the wide
Since the first reports on organometallic complexes bearing
the potentially terdentate, monoanionic ECE-pincer ligand ([2,6-
(ECH2)2C6H3]-, E ) SR, NR2, PR2, Figure 1) in the 1970s,1 a
large number of reports have appeared describing its intriguing
properties.2 One of the main features of ECE-pincer metal
complexes is the chemical stability of the metal-to-carbon
σ-bond, a characteristic feature that has prompted many studies
with pincer complexes in a variety of areas. Examples include
their use in mechanistic studies involving elementary steps in
metal catalyzed reactions,2 synthetic catalytic applications,3
* To whom correspondence should be addressed. E-mail:
r.j.m.kleingebbink@uu.nl; g.vankoten@uu.nl
(4) (a) Dijkstra, H. P.; Kruithof, C. A.; Ronde, N.; van de Coevering,
R.; Ramon, D. J.; Vogt, D.; van Klink, G. P. M.; van Koten, G. J. Org.
Chem. 2003, 68, 675. (b) Dijkstra, H. P.; Ronde, N.; Vogt, D.; van Klink,
G. P. M.; van Koten, G. AdV. Synth. Catal. 2003, 345, 364. (c) Kleij, A. W.;
Gossage, R. A.; Jastrzebski, J. T. B. H.; Boersma, J.; van Koten, G. Angew.
Chem., Int. Ed. 2000, 39, 176.
† Chemical Biology and Organic Chemistry.
‡ Crystal and Structural Chemistry, Bijvoet Center for Biomolecular
Research.
(1) (a) Moulton, C. J.; Shaw, B. L. J. Chem. Soc., Dalton Trans. 1976,
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Soc., Chem. Commun. 1978, 250, 252. (c) van Koten, G.; Jastrzebski,
J. T. B. H.; Noltes, J. G.; Spek, A. L.; Schoone, J. C. J. Organomet. Chem.
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A. L. J. Am. Chem. Soc. 1982, 104, 4285–4286. (g) Grove, D. M.; van
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10.1021/om800324w CCC: $40.75
2008 American Chemical Society
Publication on Web 09/04/2008

SCS-Pincer Metal Complexes of the Group 10 Triad
Organometallics, Vol. 27, No. 19, 2008 4929
metalation procedures are desirable. Accordingly, here we report
milder metalation of SCS-pincer ligands via oxidative addition
procedures, which resulted in the synthesis of a small series of
SCS-pincer Pt- and Pd-complexes and also in the first example
of a square planar SCS-pincer Ni-complex [NiBr(MeSCS)].
Metalated SCS-pincer complexes are versatile materials and
are often used as homogeneous (pre)catalysts15 or as building
blocks in organometallic materials.14,16 For such applications,
it is important to know and to understand the fluxional processes
occurring around the metal center, as they will (partly) determine
the outcome of the reactions. A preliminary study by Pfeffer
and co-workers revealed that MeSCS-pincer palladium com-
plexes possess fluxional behavior in solution in which the
stereochemistry on the chiral sulfur atoms can interconvert and
that concurrent ring puckering inversion of the two metallacycles
can occur.13b Such studies have not been performed with SCS-
platinum and -nickel complexes. Consequently, we decided to
study the fluxional behavior and stereochemical effects of the
prepared SCS-pincer nickel(II), palladium(II), and platinum(II)
complexes in greater detail both in solution (NMR spectroscopy)
and in the solid state (X-ray diffraction). This allowed us to
determine the influence of the metal center on these fluxional
processes.
Figure 1. Potentially six electron-donating (three electron pairs)
monoanionic ECE-pincer system. E ) for example, PR2 (PCP),
SR (SCS), NR2 (NCN); Z ) ancillary group.
applicability of pincer metal complexes. For example, Z was
used to fine-tune the electronic configuration of the pincer metal
center10 or to anchor pincer catalysts to supports for catalyst
recycling purposes.4
Recent research efforts in our group involve the covalent
attachment of SCS-pincer metal-d8 complexes to the active site
of a lipase using an active site-directed anchoring protocol.11
This was achieved by functionalization of the complexes with
an inhibitory active phosphonate probe via a robust 1,3-
propanediyl tether (Scheme 1). Pincer metal-d8 complexes were
chosen because they are stable and relatively small and should
therefore be accommodated suitably by the active site of
enzymes. Moreover, they are multifunctional and have, for
example, proven to be good catalysts using solely a basic
aqueous solution as solvent.12 In the course of our studies, we
realized that common SCS-pincer metalation procedures, for
example, by CH activation methods of the corresponding
SCS(H) arene ligand,13 were incompatible with the phosphonate
functionality attached to the SCS-pincer arene ligands. In
addition, also for the incorporation of SCS-metal complexes in
multimetallic materials, for example, metallodendrimers or
pincer functionalized porphyrins,14 milder and high yielding
Results and Discussion
Syntheses of Ligands and Complexes. The reported meta-
lation procedures for SCS-pincer arene ligands mainly rely on
C-H activation reactions of the arene ligand with cationic metal
complexes. For the synthesis of SCS-pincer palladium com-
plexes, mainly [PdCl2(RCN)2] or [Pd(RCN)4](BF4)2 (R ) Me,
Ph) as palladium source have been used.13 Whereas the
syntheses of two platinum complexes (prepared by CH activa-
tion using PtCl2(COD))17 and of various SCS-pincer palladium
complexes have been described, the synthesis of the corre-
sponding nickel complexes has to the best of our knowledge
not been reported.
In general, oxidative addition reactions of suitable metal
precursors to the Cipso-halide bond of pincer ligands take place
under very mild reaction conditions and are therefore desirable
metalation routes when multiple or sensitive functionalities are
present. This procedure is well documented for NCN-type
ligands;2 however, it has never been applied to SCS-pincer
bromide ligands.18-20 The required ligand syntheses are outlined
in Scheme 2. The aryl halide substrates for this approach were
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4930 Organometallics, Vol. 27, No. 19, 2008
Kruithof et al.
Scheme 1. ECE-Pincer Metal Complex Functionalized Phosphonates Inhibiting the Active Site of a Lipase11
Scheme 2. Synthetic Procedure Applied for the Synthesis of
RSCS-Pincer Metal Complexesa
Oxidative addition of 2 and 3 to [Pd2dba3] · CHCl3 in benzene
at room temperature afforded the corresponding SCS-pincer
palladium complexes 5 and 7 as yellow solids in 71 and 69%
yield, respectively. In the 1H NMR spectrum of 7, the chemical
shift of the CH2 resonance appeared as a sharp singlet at 3.76
ppm, confirming the coordination of both S-donor atoms to the
palladium center (∆δ ) -0.28 ppm as compared to the chemical
shift of these resonances in 3). The corresponding MeSCS-pincer
palladium complex 5 showed two broad overlapping signals at
3.48 and 3.27 ppm for the benzylic protons (cf. the singlet at
3.60 ppm in 2). These spectral features have also been observed
for the benzylic protons in the 1H NMR spectrum of the
corresponding chloride complex [PdCl(MeSCS)] (9) reported by
Pfeffer et al. (Vide infra).13b
a
Reaction conditions: (i) NaSMe, RT, 16 h, THF; (ii) Thiophenol,
K2CO3, 18-crown-6, RT, 16 h, Et2O; (iii) [Ni(COD)2], -80 °C f RT,
16 h, THF or [Pd2dba3] · CHCl3, RT, 16 h, C6H6 or [{Pt(p-tol)2(µ-
SEt2)}2], reflux, 1 h, C6H6.
The SCS-pincer Pt complexes 6 and 8 were prepared by
reacting either 2 or 3 in benzene with the platination agent [Pt-
(p-tol)2(µ-SEt2)].20 The products were obtained as crystalline,
prepared by reacting bis(benzylic bromide) 121 with NaSMe (for
2) or with thiophenol in the presence of K2CO3 and 18-crown-6
(for 3, Scheme 2). Both reactions were performed at room
temperature, yielding 222 (95%) and 323 (97%) as pale yellow
oils.
1
light-yellow solids in 76% yield. In the H NMR spectrum of
8 in CDCl3, the benzylic protons appeared as a broad doublet
with the shape of an unresolved AB pattern (δ 4.89 and 4.47
ppm). The platinum satellites, also unresolved, appeared as small
shoulders on each doublet. The 1H NMR spectrum of 6 (C6D6),
however, showed two distinct patterns for the CH2 and CH3
resonances (Figure 2). The signals for the benzylic protons in
SCS-pincer Ni complex 4 was prepared by oxidative addition
of ligand 2 to [Ni(COD)2] at -80 °C. The product is obtained
as a diamagnetic yellow, air-stable solid in 72% yield. Addition
of an excess of CCl4 to the complex (in C6D6) did not show
any evidence of the formation of a nickel-d7 complex. This is
in striking contrast to the high reactivity of [NiCl(NCN)]
complexes, which oxidize readily with CCl4 to air- and water-
stable nickel-d7 complexes [NiCl2(NCN)]. CV analysis of 4
showed an irreversible oxidation curve starting at 300 mV (200
mV/s, MeCN, 8 mM). Presumably, an irreversible reaction
occurs in which a Ni-d7 complex is formed, which subsequently
initiates a sulfur oxidation reaction or a reaction involving the
aromatic backbone. Comparison of the 1H NMR chemical shifts
of 4 with those of the starting material 2 in C6D6 revealed a
shift to lower frequency of the signal for the methylene groups
of 4 (∆δ ) -0.34 ppm), which appeared at 3.26 ppm as a
slightly broadened singlet. The methyl protons of 4 appear as a
sharp peak at higher frequency as compared to 2 (2.14 ppm,
∆δ ) 0.45 ppm).
2
this case appear as an AX (3.73, 3.15 ppm, JAX ) 15.7 Hz)
and an AB pattern (3.69, 3.27 ppm, 2JAB ) 15.7 Hz), both with
platinum satellites. The presence of the two patterns is due to
the stereogenity of each of the coordinated sulfur centers and,
therefore, the complex exists in solution as two diastereoisomers,
that is, rac (as RR and SS enantiomers) and meso (as RS and
SR enantiomers) respectively, which are in slow exchange (Vide
infra).24 For 6 and 8, this is also reflected by the observation of
two resonances in the 195Pt NMR. For 6 singlets are found at
-3967 and -3980 ppm and for 8 at -3967 and -4001 ppm.25
1
Noteworthy are the different H-195Pt coupling constants for
each of the diastereotopic benzylic protons of 6 (Vide infra).
Furthermore, two singlets at 2.25 and 2.18 ppm were observed
for the S-methyl protons, accompanied by platinum satellites
3
with a JPtH coupling of 52.8 and 53.4 Hz, respectively.
Structures of 4-6, 8, and 9 in the Solid State. The
structures of complexes 4, 5, 6, 8, and 9 in the solid state were
studied by X-ray crystal structure determination. Single crystals
of the complexes were obtained by slow evaporation of a
concentrated solution in CH2Cl2. A selection of the crystal-
(21) (a) Amijs, C. H. M.; van Klink, G. P. M.; van Koten, G. Green
Chem. 2003, 5, 470–474. (b) Terheijden, J.; van Koten, G.; van Beek,
J. A. M.; Vriesema, B. K.; Kellogg, R. M.; Zoutberg, M. C.; Stam, C. H.
Organometallics 1987, 6, 89–93. (c) Vo¨gtle, F. Chem. Ber. 1969, 102, 1784–
1788.
(22) The compound was prepared using a modified synthetic procedure
as reported by: (a) Evans, D. R.; Huang, M.; Seganish, W. M.; Chege,
E. W.; Lam, Y.-F.; Fettinger, J. C.; Williams, T. L Inorg. Chem. 2002, 41,
2633–2641. (b) Bergholdt, A. B.; Kobayashi, K.; Horn, E.; Takahashi, O.;
Sato, S.; Furukawa, N.; Yokoyama, M.; Yamagushi, K J. Am. Chem. Soc.
1998, 120, 1230–1236. Spectral data are in accordance with the published
results.
(23) The compound is prepared using a modified procedure as reported
by: Akiba, K.-Y.; Moriyama, Y.; Mizozoe, M.; Inohara, H.; Nishii, T.;
Yamamoto, Y.; Minoura, M.; Hashizume, D.; Iwasaki, F.; Takagi, Y.;
Ishimura, K.; Nagase, S. J. Am. Chem. Soc. 2005, 127, 5893–5901. Spectral
data are in accordance with the published results.
(24) (a) Evans, D. R.; Huang, M.; Seganish, M. W.; Fettinger, J. C.;
Williams, T. L. Organometallics 2002, 21, 893–900. (b) Amijs, C. H. M.;
van Klink, G. P. M.; Lutz, M.; Spek, A. L.; van Koten, G. Organometallics
2005, 24, 2944–2958.
(25) It must be noted that in 195Pt NMR (64.4 MHz) one can still observe
processes that are roughly a factor 100 faster than exchange processes
observed in the 1H NMR (300 MHz) spectrum. The meso related conformers
exist as the pairs asymm Rax,Seq-Seq,Rax and Req,Sax-Sax,Req and as (true-)
meso R,S-S,R (see also later explanations in main text). These three pairs
are likely responsible for the broadened signal at lower field in the 195Pt
NMR giving rise to the two observed shoulders.

SCS-Pincer Metal Complexes of the Group 10 Triad
Organometallics, Vol. 27, No. 19, 2008 4931
1
Figure 2. H NMR spectrum of the aliphatic part of [PtBr(MeSCS)] 6 in C6D6 at room temperature of the diastereoisomers rac-6 and
meso-6. Inset: 195Pt NMR spectrum of 6.
Table 1. Selected Bond Distances and Angles and Torsion Angles of Structures 4-6, 8, and 9
4 NiBr(MeSCS)]
5a[PdBr(MeSCS)]
9a[PdCl(MeSCS)]
6 [PtBr(MeSCS)]
8 [PtBr(PhSCS)]
Interatomic distances (Å)
1.982(4) rac
M–C1
M–S1
M–S2
M–X
1.9001(16)
1.984(2) meso
1.986(2) rac
1.987(2) asymm
2.2832(6) meso
2.2847(6) rac
2.3012(6) asymm
2.2843(6) meso
2.2894(6) rac
2.2899(6) asymm
2.5244(3) rac
1.973(4)
1.979(3)
1.988(4) meso
1.992(4) asymm
2.2831(11) rac
2.2838(11) meso
2.3011(10) asymm
2.2834(11) meso
2.2882(10) asymm
2.2911(11) rac
2.1601(5)
2.1606(5)
2.3587(3)
2.2570(9)
2.2750(9)
2.5116(4)
2.2674(7)
2.2746(7)
2.5213(4)
2.4406(10) rac
2.5149(3) asymm
2.5361(3) meso
2.4229((10) asymm
2.4412(9) meso
Bond angles (deg)
83.93(12) rac
85.01(11) asymm
85.42(12) meso
84.57(12) rac
83.65(11) asymm
85.66(12) meso
173.99(11) asymm
177.41(11) rac
177.41(11) meso
165.22(4) meso
167.18(4) asymm
168.38(4) rac
C1–M–S1
C1–M–S2
C1–M–X
S1–M–S2
84.41(6)
84.95(6)
83.92(7) rac
83.93(11)
85.70(11)
175.80(10)
167.78(3)
86.15(9)
86.45(9)
85.29(6) asymm
85.34(6) meso
83.74(6) asymm
84.55(7) rac
85.57(6) meso
177.68(6) rac
173.35(6) asymm
177.53(6) meso
164.28(2) meso
167.42(2) asymm
168.39(2) rac
176.65(5)
169.270(19)
178.96(9)
171.95(3)
Torsion angles and interplanar angles (deg)
C1-C6-C8–S2
C1-C2-C7–S1
Interplanar angle Ωb
22.3(2)
23.9(3)
19.18(8)
-11.5(3) meso
-11.6(5) meso
-17.5(6)
-5.8(4)
-13.7(3)
5.14(11)
23.1(3) rac
24.9(4) rac
24.7(3) asymm
17.6(3) rac
25.3(5) asymm
17.6(5) rac
-24.3(5)
20.0(3) asymm
20.3(3) meso
3.11(8) meso
13.73(8) rac
14.05(8) asymm
19.8(5) meso
20.6(5) asymm
3.03(15) meso
13.91(14) rac
14.07(15) asymm
11.40(19)
a Bond lengths are organized in ascending order. b Interplanar angle (Ω) is defined as the angle between the least-squares plane of the anionic aryl
ligand and the coordination plane.
lographic data obtained is listed in Table 1. Nickel complex 4
only exists in the rac-conformation and has approximate,
noncrystallographic C2 symmetry with the C2-axis collinear to
the Br-Ni1-C1 bond (Figure 3). The methyl groups occupy
equatorial positions and are orientated in opposite direction with
respect to the square planar coordination plane (rac conforma-
tion). As the crystal structure is centrosymmetric, the unit cell
contains both enantiomers (Req,Req and Seq,Seq) of the rac-
isomer, which form pairs in parallel alignment with opposite
Cipso-Ni-Br directions.26 A search in the Cambridge Crystal-
lographic Database on organometallic nickel complexes bearing
two trans-positioned thioether ligands revealed only a small
number of structures. This was rather surprising given the fact
that nickel sulfur complexes have received considerable attention
in biomimetic studies related to their reactivity and role in
biocatalytic pathways.27 The few reported organometallic Ni(II)
thioether complexes comprised only tetrahedral structures.27a
It is obvious that this geometry is less likely in rac-4 type

4932 Organometallics, Vol. 27, No. 19, 2008
Kruithof et al.
Figure 3. ORTEP representation of the molecular structure of one
of the two enantiomers (Req,Req, Seq,Seq not shown) of rac-4.
Displacement ellipsoids are drawn at the 50% probability level.
(Inset) View along the axis through Br-Ni-C1-C4.
complexes as the pincer ligand with trans sulfur donor atoms
imposes a square planar geometry around the metal-d8 nickel
center, illustrating the special coordination mode of ECE-pincer
ligands in organometallic chemistry. Similar NCN- and PCP-
pincer Ni(II) complexes have been prepared, and their crystal
structures have been reported. The Ni-C1 bond in the NCN
complex [NiBr(EtNCN)]28 is slightly shorter (1.825 Å) compared
to rac-4 (1.9001(16) Å), whereas the same bond in the PCP
complex [NiBr(CyPCP)]29 has nearly the same length (1.908 Å).
Also the C1-Ni-E (E ) donor atom) angles of rac-4 (84.41(6)
and 84.95(6)°) are similar to those of the PCP complex (86.29
and 84.70°) and the NCN complex (84.14 and 84.45°). Further
evidence for deviation from an ideal square planar geometry is
indicated by significant puckering of the two five membered
metallacycles and the torsion angles C1-C6-C8-S2 (22.3(2)°)
and C1-C2-C7-S1 (23.9(2)°). Consequently, a relatively large
interplanar angle (Ω, 19.18(8)°), defined as the angle between
the calculated least-squares plane of the arene and the coordina-
tion plane, is found in rac-4.
Figure 4. View of the molecular structure of rac-5. Displacement
ellipsoids are drawn at the 50% probability level. Inset: View along
the axis through Br-Pd-C1-C4 of the various isomers found in
the crystal lattice.
The crystal structure of [PdBr(MeSCS)] 5 contains three
independent molecules in the asymmetric unit, which represent
three different isomers of the complex (Figure 4). The first
molecule, rac-5, has approximate C2-symmetry similar to rac-
4. The second has one methyl group in axial and the other in
equatorial position. Due to the presence of ring puckering in
the two metallacycles, the molecule lacks any symmetry element
and is therefore labeled as asymm-5. The third molecule is
disordered. The major disorder component (95%) has an
approximate mirror plane though the Br-Pd-C bond and is
the meso isomer, labeled meso-5 (Cs symmetry). The minor
component is a distorted rac-5 structure (5%).
During our first attempts to obtain suitable crystals for X-ray
structure determination of 5 using chloroform as solvent, we
found that the bromide atom was replaced by a chloride, giving
chloride complex 9 [PdCl(MeSCS)] instead. Traces of HCl in
the solvent are most likely the cause of this halide exchange
reaction during the recrystallization process. A similar observa-
tion has been made earlier by Bergbreiter et al.30 The crystals
of 5 and 9 are nearly isomorphic, with the only difference that
the 5% disorder observed for 5 is absent in the unit cell of 9.
Hence, in the case of 9 the unit cell contains the rac-9, asymm-
Figure 5. ORTEP representation of the molecular structure of
asymm-6. Displacement ellipsoids are drawn at the 50% probability
level. (Inset) View along the axis through Br-Pt-C1-C4.
9, and meso-9 isomers. Bond lengths and angles differ only
marginally in the corresponding isomers of 5 and 9, indicating
that the halide ligand has only a small effect on their structural
features (Table 1). The Pd-C bond lengths for the different
conformations of 5 are between 1.984(2) and 1.987(2) Å and
between 1.982(4) and 1.992(4) Å for 9, which is within the
range of reported SCS-pincer palladium complexes (1.964-1.994
Å).13 Also the distortions from an ideal square planar geometry,
dictated by the S1-Pd-S2 bond angles (164.28(2)-168.39(2)°,
in 5) and the C1-Pd-S angles (83.65-85.57°, in 5) do not
deviate from reported [Pd(halide)(SCS)] structures.
The SCS-pincer Pt complex 6 [PtBr(MeSCS)] crystallized in
a single conformational structure with one axial and one
equatorial orientated S-methyl group (asymm-6, Figure 5). The
molecule has a similar structure as the corresponding Pd-
complex asymm-5. Bond lengths involving the platinum atom
are shorter compared to asymm-5, which is due to the smaller
ionic radius of Pt(II) and a stronger binding of the donor atoms
to the metal center.31 The Cipso-Pt bond in asymm-6 has a length
of 1.973(4) Å, which is shorter than those found in the two
reported SCS-pincer Pt complexes (1.982 and 2.040 Å).17 The
C-Pt-S angles are 83.93(11) and 85.70(11)° and the interplanar
angle Ω is 11.40(19)°, being slightly smaller as compared to
asymm-5.
(26) The abbreviations eq or ax indicate the orientation of the methyl
group, equatorial or axial, respectively.
(27) (a) Schebler, P. J; Mandimutsira, B. S.; Riordan, C. G.; Liable-
Sands, L. M.; Incarvito, C. D; Rheingold, A. L. J. Am. Chem. Soc. 2001,
123, 331–332. (b) Stavropoulos, P.; Muetterties, M. C.; Carrie, M.; Holm,
R. H. J. Am. Chem. Soc. 1991, 113, 8485–8492.
(28) Schimmelpfennig, U.; Zimmering, R.; Schleinitz, K. D.; Stosser,
R.; Wenschuh, E.; Baumeister, U.; Hartung, H. Z. Anorg. Allg. Chem. 1993,
619, 1931–1938.
The platinum complex [PtBr(PhSCS)] rac-8 has both thiophe-
nyl substituents in axial position with respect to the coordination
(29) Kennedy, A. R.; Cross, R. J.; Muir, K. W. Inorg. Chim. Acta 1995,
231, 195–200.
(30) Bergbreiter, D. E.; Frels, J. D.; Rawson, J.; Li, J.; Reibenspies,
J. H. Inorg. Chim. Acta 2006, 359, 1912–1922.
(31) Ionic radii of Ni(II), Pd(II), and Pt(II) atoms in a square planar
geometry are 0.49, 0.64, and 0.60 Å respectively. Handbook of Chemistry
and Physics, 85th ed.; 2004, 12-14.

SCS-Pincer Metal Complexes of the Group 10 Triad
Organometallics, Vol. 27, No. 19, 2008 4933
Scheme 3. Dynamic Processes between rac and meso
Isomers of the MX-SCS Complexesa
Figure 6. ORTEP representation of the molecular structure of rac-
8. Displacement ellipsoids are drawn at the 50% probability level.
Left: View along the axis through Br-Pt-C1-C4.
plane (Figure 6). Both the Pt-C (1.979(3) Å) and the Pt-S1
(2.2674(7) Å) bond lengths are slightly longer compared to those
in asymm-6 (Table 1). The C-Pt-S angles (86.16(9) and
86.44(9)°) are larger as those in asymm-6, whereas the
C1-C6-C8-S2 and C1-C2-C7-S1 torsion angles (5.8(4)
and 13.7(3)°, respectively) are smaller as in asymm-6, suggesting
that a lower ring strain is present in the metallacycles of rac-8
compared to asymm-6.
The observed rac isomers with methyl groups in equatorial
positions for 4-6 and 9 are most probably a result of the small
size of the methyl substituent. Larger substituents are likely
directed into the axial position (see 8, Figure 6) to obtain an
optimal spatial arrangement and morphology during crystal-
lization. Apparently, MeSCS-pincer complexes show different
structural behavior because the thiomethyl substituents require
less space and therefore can adopt various orientations in the
solid-state, as found in the crystal structures of complexes 4-6
and 9.
Structures in Solution. The fluxional behavior of SCS-metal
complexes in solution, as studied by NMR spectroscopy, is
rather complicated.13b However, with the structural data of
complexes 4-6 and 8 found in the solid-state now in hand, we
can try to visualize possible exchange processes for these
complexes in solution (Scheme 3). Two concurrent processes
can be envisaged: (1) inversion of the sulfur configuration (s.i.)
and (2) concomitant ring puckering inversion (r.i.) of the two
metallacycles, which have been suggested by Pfeffer et al. in
their preliminary study of the exchange behavior of complex 9
in solution.13b As illustrated in Scheme 3, different isomers,
which can exist in a number of conformations, are considered
to be involved in this mechanism. Scheme 3 considers two rac
isomers: a raceq complex with equatorial methyl groups and a
racax complex with the methyl in axial position. These two rac
conformations are interconvertable by ring puckering inversion.
The three other structures presented in Scheme 3 are one meso
and two asymm isomers, of which the latter two are enantiomers.
The meso structure can be regarded as the time-average
conformer of both asymm conformations of which the latter have
substantially more ring puckering. In the 1H NMR spectrum of
MeSCSPtBr 6, two molecules are observed (Figure 2), which
means that one of the above-mentioned processes is in the slow
exchange limit range at room temperature (Vide supra). For the
actual exchange process in solution, four possibilities can now
be envisaged: (1) both processes (r.i. and s.i.) are fast, (2) both
processes are slow, (3) only sulfur inversion is fast, or (4) only
ring inversion is fast on the NMR time scale. In the fast
exchange limit, both processes occur fast on the NMR time
a
The dynamic processes in solution involving a single-site sulphur
inversion (s.i.) and ring puckering inversion (r.i.). Some of the structures
found in the unit cell of the crystal structure of 9 are used for this
picture (i.e. meso-9, raceq-9, asymm-9; structure racax-9 is not present
in the crystal structure of 9 therefore a molecular model (SPARTAN
Software package) of this conformer was used to illustrate the possible
structures).
scale: that is, one benzylic resonance should be observed for
all the complexes. This is not the case. If the ring puckering
and sulfur inversion would both be in the slow exchange limit,
one would expect to see more than two AB patterns (or AB
and AX), at least one for each unique conformation. In that
case, conformer raceq, racax, and meso will all give one AB or
AX pattern and asymm an AB and AX pattern, since it lacks
any symmetry. In total, at least 5 pairs of doublets for the
benzylic protons would be expected in the 1H NMR spectrum,
which is clearly not the case. If only ring puckering is in the
slow exchange limit and sulfur inversion would be fast, no meso
or rac conformer would be observed in solution due to the fast
exchange of the methyl groups in the structures. The time
average structure would only have two different conformers
having opposite ring puckering orientations. These structures
are enantiomers and would thus result in only one AB pattern
in the slow exchange limit in the 1H NMR spectrum. Therefore,
the only option left is that sulfur inversion is in the slow
exchange limit and ring puckering is fast on NMR time scale.
Since ring puckering (r.i.) is fast in this case, the puckering
time-average isomers have a structure related to the meso (since
the asymm-conformers are in fast exchange) and rac (raceq and
racax, Scheme 3) conformers and will together give two AB
(or AB and AX) patterns in the 1H NMR spectrum, as observed
for 6. We have to note here that the assumption was made that
sulfur inversion occurs without decoordination of the sulfur
atom, which is the generally accepted mechanism for thioether
platinum complexes.32 In addition, no evidence was found for
uncoordinated sulfur atoms in the 1H NMR spectra at low
temperature (Vide infra).
The H NMR spectra of 4 ([NiBr(MeSCS)]) and 5 ([PdBr-
1
(
MeSCS)]) at low temperatures (<240 K, toluene-d8) showed
(32) Oki, M. Pure Appl. Chem. 1989, 61, 699–708.

4934 Organometallics, Vol. 27, No. 19, 2008
Kruithof et al.
Figure 8. Part of the 1H NMR spectra showing the two patterns of
CH2 resonances of complexes 4-8 at room temperature (C6D6).
Table 2. Coalescence Temperature of the Benzylic Protons
(Toluene-d8)
complex
Tc (K)
4
5
6
7
8
274
305
370
<223
308
Figure 7. 1H NMR (toluene-d8) of the benzylic protons of
[NiBr(MeSCS)] 4 at various temperatures showing the coalescence
of the AB and AX patterns of RR/SS (rac-4) and SS/SR (meso-4).
of exchanging resonances in platinum and palladium complexes
bearing chelating thioether ligands has been reported before for
other complexes. The relative exchange rate is believed to
depend on the metal mass and size and reflects the relative
strength of the M-S bond, which is the strongest for the
platinum complexes.33 Thus, even though M-S bond breaking
does not occur during these exchange processes (Vide supra),
the strength of the M-S bond definitely plays an important role
in the fluxional behavior occurring at the metal center. Whereas
SCS-pincer palladium complexes bearing phenyl,13c t-butyl,13a
i-propyl,13n or ethyl13c groups on the sulfur donor atoms show
in the 1H NMR spectrum (CDCl3) a (in some cases broadened)
singlet for the benzylic protons, the spectrum of 5 showed two
broad, overlapping signals (3.6-3.0 ppm) at 3.48 and 3.27 ppm
in the same solvent.13b In general, compounds with larger
substituents on the sulfur donor atoms give lower coalescence
temperatures of the benzylic-CH2 resonances (also compare 5
and 7).33
features that are consistent with the presence of two complexes
in solution, similar to 6 at room temperature. Clearly, separated
AB and AX patterns were observed for the diastereotopic
benzylic protons of both 4 and 5 (Figure 7 shows typical
example for 4). The same phenomenon has also been observed
in the spectrum of 9 at 233 K.13b It appears that at the slow
exchange limit one of the isomers or conformers is preferred.
For both 4 and 5, the two isomers are observed in a 6:4 molar
ratio with the isomer giving rise to the AB pattern being the
more abundant.
At 223 K the benzylic resonances showed a broad singlet
for Pd-complex 7 ([PdBr(PhSCS)]), indicating similar behavior
as observed for 4-6. Unfortunately, the coalescence temperature
for the CH2 resonances could not be observed for 7 due to
insolubility of the complex in toluene-d8 below 223 K. The
spectrum of Pt-complex 8 displayed an unresolved AB pattern
at 273 K, this in contrast to the Pt-complex 6, which showed
two distinct patterns at room temperature. In this case. the slow
exchange limit could be observed since the complex was still
slightly soluble at 248 K. Full separation of the AB and AX
signals was observed, although the platinum satellites were not
Assignment of the AB and AX Patterns. On the basis of
the given structural data in solution and in the solid-state, an
accurate estimate can now be made to assign the AX or AB
1
patterns in the H NMR of 6 to a rac or meso structure. Since
we have obtained the rac and meso isomers of complex 9 only
in the solid state, we can compare the dihedral angles (Pd-S-C7/
8-HA/B) of rac-9 and meso-9 and translate this data to the
platinum analogue 6. Hereby, we assume that the metal center
has little influence on the observed dihedral angles, which is
confirmed upon comparison of the various dihedral angles of
the X-ray structures of MeSCSPtBr asymm-6 (only crystallized
conformation of 6) and MeSCSPdCl asymm-9; only minor
differences were observed and they show the same absolute
trend. We observed that the difference between the appropriate
dihedral angles of the geminal protons HA and HB of 9 is smaller
for the meso isomer than for the rac isomer (∆ ) 41 (meso) vs
49 (rac) for H7 and ∆ ) 21 (meso) vs 57 (rac) for H8, Table
3). The 1H NMR spectrum of the SCS-pincer platinum complex
1
visible in the H NMR spectrum.
1
At room temperature, the H NMR spectra of 4, 5, and 6
bearing the MeSCS ligand displayed three different exchange
stages (Figure 8). The CH2 resonances for the Ni-complex 4
are in the fast exchange limit (singlet), the same resonances for
the Pd complex 5 are in the intermediate exchange (broad
doublet) and the corresponding resonances for the Pt complex
6 are in the slow exchange limit (AB and AX patterns). The
same trend is also observed for the thiophenyl complexes 7 and
8. This trend was also reflected in the coalescence temperatures
of the benzylic proton signals, which are listed in Table 2
(toluene-d8). Comparing the Tc values for 4, 5, and 6, an increase
in coalescence temperature for the benzylic protons in the series
was observed. This dependence of the coalescence temperature
(33) Orrel, K. G.; Sik, V.; Brubaker, C. H.; McCulloch, B. J. Organomet.
Chem. 1984, 267, 267.

SCS-Pincer Metal Complexes of the Group 10 Triad
Organometallics, Vol. 27, No. 19, 2008 4935
Table 3. Absolute Dihedral Angles of Two Isomers of 9
important since it will influence the outcome of e.g. a catalytic
reaction. For the SCS-pincer Pt complexes, 195Pt NMR of SCS-
pincer Pt complexes can show directly the relative abundance
of conformational structures in solution, that is, rac versus meso.
It is very interesting to investigate whether it is possible to
influence the rac:meso ratio with an external stimulus since this
might create chiral pockets (S-atoms are chiral) around the metal
center and is thus a way to influence (selective) processes
occurring at the metal center. We are currently studying this in
conjunction with the application of SCS-pincer Pd-complexes
as catalysts embedded in a lipase as it is known that the protein
modification process (see Scheme 1) is sensitive toward small
changes in the pincer ligand moiety.11
dihedral angles
meso-9
∆
rac-9
∆
C9-S1-C7-H7a
C9-S1-C7-H7b
C10-S2-C8-H8a
C10-S2-C8-H8b
Pd-S1-C7-H7a
Pd-S1-C7-H7b
Pd-S2-C8-H8a
Pd-S2-C8-H8b
11
108
116
3
100
141
110
131
97
16
103
19
100
96
145
92
149
19
113
41
81
49
57
21
Experimental Section
General. All reactions were performed under a dry nitrogen
atmosphere by standard Schlenk techniques. Solvents were carefully
dried and distilled from sodium benzophenone (pentane, hexane,
toluene, C6H6, THF, Et2O) or CaH (CH2Cl2) prior to use. The
6 has different accompanying platinum satellite coupling
constants (JHPt) for the observed four doublets of the benzylic
resonances as well as for both methyl signals in the slow
exchange limit (room temperature). Similar to the Karplus
relation for JHH coupling constants of vicinal protons, a relation
between dihedral angles and JHPt coupling constants is known.34
It was reported that the JHPt increases with increasing dihedral
angle, with a maximum at an angle of 180° and a minimum at
0°. From this theory, it follows that the structure with the largest
difference in dihedral angles, that is, between Pd-S-C7-H7a
and Pd-S-C7-H7b and between Pd-S-C8-H8a and
Pd-S-C8-H8b, will also exhibit the largest difference in JHPt
coupling constants for 6, that is, between JHPt(HA) and JHPt(HB)
in both isomers (meso and rac). When we measured the JHPt
coupling constants (room temperature, slow exchange limit) of
the platinum complex 6, we observed that for the AX pattern
the difference between JHPt(HA) and JHPt(HB) of the correspond-
ing doublets is smaller than that of the AB pattern (∆8.9 vs
∆12.0 Hz). This would mean that the AX pattern corresponds
to the isomer with the smallest dihedral angle difference. Hence,
from this analysis, it was concluded that the meso configuration
gives rise to the AX pattern in the NMR spectrum and the rac
configuration to the AB pattern.
36
compounds 1,21a [{Pt(p-tol)2(µ-SEt2)}2]35 and [Pd2dba3] · CHCl3
were synthesized according to literature procedures. All other
chemicals were obtained commercially and were used without
further purification. NMR spectra were recorded at 298 K on a
Varian Inova 300 spectrometer and the chemical shifts were
referenced to residual solvent resonances (ppm). 195Pt {1H} NMR
(64.4 MHz) spectra referenced using an external reference (1 M
K2PtCl6 in D2O, δ ) 0 ppm). Elemental analyses were performed
by Dornis and Kolbe, Mikroanalytisches Laboratorium (Mu¨llheim
a/d Ruhr, Germany).
[C6H2(CH2SMe)2-2,6-Br-1] (2). Solid 1 (1.0 g, 2.92 mmol) was
dissolved in THF (100 mL) and NaSMe (0.97 g, 13.8 mmol) was
added in one portion. The reaction mixture was stirred for 16 h at
room temperature. Diethyl ether (100 mL) and an aqueous solution
of NaOH (1 M, 100 mL) were added and the mixture stirred for
30 min. The organic phase was separated and the aqueous phase
extracted with diethyl ether (2 × 150 mL). The organic fractions
were combined, dried on MgSO4, and concentrated to colorless oil,
which solidified upon standing to a white solid. Yield 0.78 g (97%).
1H NMR (200 MHz, CDCl3): δ 7.23 (bs, ArH, 3H), 3.85 (s, CH2S,
4H), 2.06 (s, SMe, 6H). 13C NMR (CDCl3): δ 138.86, 129.62,
127.62, 127.00 (s, ArC), 39.62 (s, CH2), 15.58 (s, SMe). Anal. Calcd
for C10H13BrS2: C, 43.32; H, 4.73; S, 23.13. Found: C, 43.28; H,
4.76; S, 23.05.
[C6H2(CH2SPh)2-2,6-Br-1] (3). Thiophenol (3.02 g, 2.82 mL,
27.4 mmol), K2CO3 (5.68 g, 41.1 mmol), 1 (2.35 g, 6.85 mmol)
and 18-crown-6 (5 mg, 15.3 mmol) were dissolved in diethyl ether
(100 mL) and stirred for 16 h at room temperature. A solution of
NaOH (4 M, 100 mL) was added and the mixture stirred for 30
min. The organic phase was separated and the aqueous phase
extracted with diethyl ether (2 × 100 mL). The organic fractions
were combined, dried on MgSO4 and concentrated to a yellowish
oil. Yield 2.61 g (95%). 1H NMR (300 MHz, CDCl3): δ 7.36-7.04
(bm, ArH, 13H), 4.29 (s, CH2). 13C NMR (75 MHz, CDCl3): δ
138.05, 136.00, 131.01, 129.88, 129.16, 127.15, 127.03, 126.96 (s,
ArC), 40.84 (s, CH2S). Anal. Calcd for C20H17BrS2: C, 59.85; H,
4.27; S, 15.98. Found: C, 60.08; H, 4.36; S, 15.86.
[NiBr(C6H2(CH2SMe)2-2,6)] (4). The complex was prepared
according a modified literature procedure.18 A yellow solution of
[Ni(COD)2] (0.34 g, 1.23 mmol) in THF (150 mL) was cooled to
-78 °C and a solution of 2 (0.34 g, 1.23 mmol) in THF (50 mL)
was added dropwise. The reaction mixture was stirred for 30 min
at -80 °C and subsequently allowed to warm to room temperature
Conclusion
The present study shows that oxidative addition metalation
procedures provide facile access to SCS-pincer metal complexes
(M ) Ni, Pd, Pt). Various crystal structures of SCS complexes
containing Ni, Pd, and Pt are described and each of these
structures shows a unit cell with a unique set of independent
[MBr(RSCS)] molecules. Crystal structures of the Pd complexes
5 and 9 even showed the presence of three independent
molecules in a single unit cell with rac, meso, and asymmetric
conformations. NMR studies revealed that in solution pyramidal
sulfur inversion is a much slower process than the ring puckering
inversion for these types of complexes. By relating the solid
state structures of [PdCl(MeSCS)] 9 to the fluxional behavior
of [PtBr(MeSCS)] 6 in solution, assignment of the meso- and
rac-isomers in solution was possible.
Understanding the dynamic processes that take place at the
metal site of these SCS pincer metal complexes in solution is
(34) Similar to the Karplus relationship for JH,H coupling constants of
vicinal protons, a Karplus-like relationship between dihedral angles and
JH,Pt has been reported. However, whereas the traditional Karplus relation-
ship has a minimum JH,H at an angle of 90°, the JPt,H has a minimum at an
angle of 0°. See also: (a) Erickson, L. E.; McDonald, J. W.; Howie, J K.;
Clow, R. P. J. Am. Chem. Soc. 1968, 90, 6371–6382. (b) Sarneski, J. E.;
Erickson, L. E.; Reilley, C. N. Inorg. Chem. 1981, 20, 2137–2146.
(35) Steele, B. R.; Vrieze, K. Transition Met. Chem. 1977, 2, 140–144.
(36) Komiya, S. Synthesis of Organometallic Compounds; Wiley:
Chichester, U.K., 1997.

4936 Organometallics, Vol. 27, No. 19, 2008
Kruithof et al.
Table 4. Experimental Details for the X-Ray Crystal Structure Determinations
4
5
6
8
9
formula
fw
C10H13BrNiS2
335.94
C10H13BrPdS2
383.63
C10H13BrPtS2
472.32
C20H17BrPtS2
596.46
C10H13ClPdS2
339.17
crystal color
crystal size [mm3]
crystal system
space group
a [Å]
red
yellow
yellow
yellow
yellow
0.36 × 0.24 × 0.06
monoclinic
P21/c (no. 14)
13.9357(2)
5.4349(1)
19.5421(2)
126.9595(5)
1182.69(3)
4
0.27 × 0.15 × 0.12
monoclinic
P21/c (no. 14)
8.9406(1)
33.1246(2)
13.0758(1)
110.1258(2)
3635.99(5)
12
0.42 × 0.24 × 0.24
monoclinic
P21/c (no. 14)
8.8451(7)
15.6207(9)
11.1398(6)
128.208(6)
1209.42(17)
4
0.45 × 0.30 × 0.30
monoclinic
C2/c (no. 15)
15.2670(6)
11.6724(6)
20.2824(13)
94.243(6)
3604.5(3)
8
0.24 × 0.18 × 0.09
monoclinic
P21/c (no. 14)
8.8210(1)
33.1239(2)
12.9573(1)
109.5799(3)
3567.02(5)
12
b [Å]
c [Å]
ꢀ [°]
V [Å3]
Z
Dx [g/cm3]
1.887
5.329
2.102
5.131
2.594
15.210
2.198
10.233
1.895
2.094
µ [mm-1
]
abs. corr. method
abs. corr. range
refl. (meas./unique)
param./restraints
R1/wR2 [I > 2σ(I)]
R1/wR2 [all refl.]
S
analytical
0.42-0.80
21903/2687
129/0
0.0204/0.0503
0.0243/0.0523
1.037
multiscan
0.41-0.54
58090/8315
395/3
0.0198/0.0437
0.0256/0.0458
1.041
analytical
0.02-0.20
25739/2781
129/0
0.0193/0.0499
0.0217/0.0512
1.168
multiscan
0.57-1.00
27679/4146
217/0
0.0194/0.0441
0.0276/0.0468
1.096
multiscan
0.68-0.83
64109/8109
385/0
0.0358/0.0945
0.0441/0.0990
1.059
Fmin/max [e/Å3]
-0.57/0.35
-0.64/0.42
-1.74/0.82
-1.45/0.68
-1.85/2.18
while stirring was continued for 2 h. During the reaction, the initially
light yellow colored solution became more intensely yellow colored
when warmed to room temperature. The solvent was removed in
Vacuo and the product dissolved in benzene (40 mL) and filtrated
through a short pad of Celite. The filtrated was concentrated to 5
mL and the product precipitated by adding hexanes as nonsolvent.
The product was obtained as a yellow solid after removal of all
volatiles in Vacuo. Yield: 0.30 g (72%). Yellow crystals suitable
for X-ray diffraction were obtained by slow evaporation of a
solution of the product in CH2Cl2.1H NMR (300 MHz, C6D6): δ
of a CH2Cl2 solution. 1H NMR (300 MHz, C6D6): δ 6.89, 6.88 (t,
ArH, 3JHH ) 7.6 Hz, 1H), 6.63 (d, ArH, 3JHH ) 7.6 Hz, 2H), 3.73
(d, CH2, 2JHH ) 15.7 Hz, 3JHPt ) 42.4 Hz, 2H), 3.69 (d, CH2, 2JHH
) 15.2 Hz, 3JHPt ) 31.38 Hz, 2H), 3.27 (d, CH2, 2JHH ) 15.2 Hz,
3JHPt ) 19.4 Hz, 2H), 3.15 (d, CH2, 2JHH ) 15.7 Hz, 3JHPt ) 33.47
Hz, 2H), 2.25 (t, SMe, 3JHPt ) 52.8 Hz, 6H), 2.18 (t, SMe, 3JHPt
)
53.4 Hz, 6H). 13C NMR (CDCl3): δ 152.41, 152.17 (s, ArCipso),
146.15 (t, ArCortho, 2JCPt ) 109.86 Hz), 124.53 (s, ArCpara), 121.90,
3
2
121.81 (t, ArCmeta, JCPt ) 39.1 Hz), 52.24 (t, CH2, JCPt ) 34.2
2
2
Hz), 52.08 (t, CH2, JCPt ) 33.0 Hz), 24.96 (t, SMe, JCPt ) 20.7
6.86 (t, ArH, 1H,3JHH ) 7.5 Hz), 6.50 (d, ArH, 2H, JHH ) 7.2
Hz), 24.45 (t, SMe, JCPt ) 21.0 Hz). 195Pt NMR (toluene-d8): δ
3
2
Hz), 3.26 (bs, CH2SMe, 4H), 2.14 (s, SMe, 6H). 13C NMR (75
MHz, C6D6): δ 155.59 (s, ArCPd), 150.16, 124.98, 121.42 (s, ArC),
74.14 (s, CH2), 51.64 (s, SMe). Anal. Calcd for C10H13BrNiS2: C,
35.75; H, 3.90; S, 19.09. Found: C, 35.71; H, 4.08; S, 19.07.
[PdBr(C6H2(CH2SMe)2-2,6)] (5). The palladium source [Pd2-
dba3] · CHCl3 (0.39 g, 0.38 mmol) and 2 (0.21 g, 0.76 mmol) were
dissolved in benzene (30 mL) and the resulting dark-purple solution
was stirred at room temperature for 16 h. The solvent was removed
in Vacuo and the residue dissolved in CH2Cl2 (20 mL) and
subsequently filtrated through a short path of Celite. The yellow
residue was concentrated to 3-5 mL and Et2O was added to
precipitate the product. After a second precipitation from CH2Cl2
and drying in vacuo the product was obtained as a yellow solid.
Yield: 0.20 g (69%). Yellow needle-shaped crystals suitable for
X-ray diffraction were obtained by slow diffusion of Et2O into a
solution of 20 mg of the product in 20 mL CH2Cl2.1H NMR (300
MHz, CDCl3): δ 6.81 (t, ArH, 1H,3JHH ) 7.6 Hz), 6.56 (d, ArH,
-3967.36, -3980.18. Anal. Calcd for C10H13BrPtS2: C, 25.43; H,
2.77; S, 13.58. Found: C, 25.54; H, 2.67; S, 13.67.
[PdBr(C6H2(CH2SPh)2-2,6)] (7). Solid [Pd2dba3] · CHCl3 (0.29
g, 0.28 mmol) was added to a solution of 3 (0.23 g, 0.57 mmol) in
benzene (20 mL) and the resulting dark-purple solution was stirred
for 16 h at room temperature. The solvent was removed under
reduced pressure. The residue was dissolved in CH2Cl2 (20 mL)
and filtrated through a short pad of Celite. The yellow filtrate was
concentrated to 2-3 mL and diethyl ether was slowly added to
precipitate the product. The solid was collected, dissolved in CH2Cl2
(2 mL), and precipitated again until the mother liquor was nearly
colorless. The product was dried in Vacuo and obtained as a yellow
1
solid. Yield: 0.21 g (71%). H NMR (300 MHz, CDCl3): δ 7.86
(m, ArH, 4H), 7.38 (m, ArH, 6H), 6.96 (m, ArH, 3H), 4.63 (s,
CH2S, 4H). 13C NMR (CDCl3): δ 164.50 (s, ArCPd), 149.64 (s,
ArCCH2), 132.63 (s, ArS), 131.77, 130.05, 129.82, 125.22, 122.29
(s, ArC), 52.83 (s, CH2). Anal. Calcd for C20H17BrPdS2: C, 47.30;
H, 3.37; S, 12.63. Found: C, 47.30; H, 3.37; S, 12.72.
3
2H, JHH ) 7.7 Hz), 3.47 (bs, CH2S, 2H), 3.24 (bs, CH2S, 2H),
2.24 (s, SMe, 6H). 13C NMR (CDCl3): δ 162.76 (bs, ArCPd),
148.74 (s, ArCCH2), 125.24, 122.64 (s, ArC), 49.89 (s, CH2), 23.67
(s, SMe). Anal. Calcd for C10H13BrPdS2: C, 31.31; H, 3.42; S, 16.72.
Found: C, 31.20; H, 3.50; S, 16.61.
[PtBr(C6H2(CH2SPh)2-2,6)] (8). The pincer aryl halogen starting
material 2 (0.14 g, 0.36 mmol) and [{Pt(p-tol)2(µ-SEt2)}2] (0.17 g,
0.18 mmol) were added to benzene (30 mL), and the resulting white
suspension was heated to reflux for 1 h. The yellowish clear solution
was allowed to cool to room temperature and the volatiles removed
under reduced pressure. The residue was dissolved in CH2Cl2 (15
mL) and filtrated through a short pad of Celite. The filtrate was
concentrated to 2-3 mL and Et2O was added slowly to precipitate
the product. The solid was collected and the precipitation repeated
once. The product was dried in Vacuo and obtained as a yellowish
solid. Yield: 0.16 g (76%). Yellow needle-shaped crystals suitable
for X-ray diffraction were obtained by slow evaporation of the
solvent CH2Cl2. 1H NMR (300 MHz, CDCl3): δ 7.81 (m, ArH,
4H), 7.37 (m, ArH, 6H), 7.08 (m, ArH, 3H), 4.91 (bd, CH2S, 3JHH
[PtBr(C6H2(CH2SMe)2-2,6)] (6). To benzene (30 mL) was added
the aryl bromide 2 (0.21 g, 0.76 mmol) and [{Pt(p-tol)2(µ-SEt2)}2]
(0.36 g, 0.38 mmol). The white suspension was heated to reflux
for 1 h. The resulting yellowish clear solution was allowed to cool
to room temperature and the volatiles were removed in vacuo. The
residue was dissolved in CH2Cl2 (15 mL) and filtrated through a
short path of Celite. The filtrate was concentrated to 2-3 mL and
Et2O (∼20 mL) was slowly added to precipitate the product. The
solid was collected and the precipitation repeated once more. The
product was dried under reduced pressure and obtained as a
yellowish solid. Yield: 0.16 g (76%). If necessary the product can
be recrystallized from hot toluene. Yellow needle-shaped crystals
suitable for X-ray diffraction were obtained by slow evaporation
3
) 29.8 Hz, 2H), 4.45 (bd, CH2, JHH ) 27.6 Hz, 2H). 13C NMR
(CDCl3): 146.92, 132.67, (bs, ArC), 132.67, 130.57, 129.72, 124.54
(s, ArC), 121.37 (s, 2JCPt ) 36.62 Hz), 56.05 (bs, CH2). 195Pt NMR

SCS-Pincer Metal Complexes of the Group 10 Triad
Organometallics, Vol. 27, No. 19, 2008 4937
(toluene-d8): δ -3967.36, -4000.50. Anal. Calcd for C20H17BrPtS2:
C, 40.21; H, 3.04; S, 10.73. Found: C, 40.08; H, 2.89; S, 10.79.
VT NMR Experiments. Saturated solutions of the various
complexes (4 - 8) were prepared in 0.5 mL toluene-d8. An additional
0.1 mL toluene-d8 was added to prevent precipitation at low
temperatures. First, NMR spectra were recorded at 298 K on a
Varian Inova 300 spectrometer. Next, VT NMR experiments were
(program DIRDIF,37 compounds 4 and 5) or Direct Methods
(program SHELXS-97,38 compounds 6 and 8). The initial coordi-
nates for 9 were taken from the isostructural compound 5.
Refinement was performed with SHELXL-9738 on F2 of all
reflections. Non-hydrogen atoms were refined freely with aniso-
tropic displacement parameters. In 4, all hydrogen atoms were
located in the difference Fourier map; in all other structures
hydrogen atoms were introduced in calculated positions. In all
structures hydrogen atoms were refined as rigid groups. Geometry
calculations, drawings and checks for higher symmetry were
performed with the PLATON software package.39 Further crystal-
lographic details are given in Table 4.
1
conducted: for each solution, H NMR spectra were recorded at
various temperatures, starting at the lowest temperature, and after
each measurement the solution was slowly warmed up in steps of
10-20 K. Prior to each measurement, the sample was allowed to
equilibrate for 15 min at that specific temperature. The temperature
ranges used for each complex are as follows: 4 [NiBr(MeSCS)]:
193-303 K, 5 [PdBr(MeSCS)]: 203-373 K, 6 [PtBr(MeSCS)]:
203-380 K, 7 [PdBr(PhSCS)]: 223-373 K. Please note that below
230 K complex 7 started to precipitate, which gave poor NMR
spectra. [PtBr(PhSCS)] 8 (246-353 K) already showed clear
platinum satellites at the benzylic-CH2 signal (showing a sharp
singlet) at 353 K (1H NMR (300 MHz, toluene-d8): δ 4.00 ppm (s,
Acknowledgment. We kindly acknowledge NRSC-
Catalysis (HPD) and the Council for Chemical Sciences of
The Netherlands Organisation for Scientific Research (CW-
NWO) (M.L., A.L.S.) for financial support.
OM800324W
(37) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;
Garcia-Granda, S.; Gould, R. O.; Smits, J. M. M.; Smykalla C. The
DIRDIF99 program system; Technical Report of the Crystallography
Laboratory at University of Nijmegen; University of Nijmegen: Nijmegen,
The Netherlands, 1999.
(38) SHELXS-97: Program for crystal structure solution; Universita¨t
Go¨ttingen: Go¨ttingen, Germany, 1997.
3
CH2, JHPt ) 36.4 Hz, 4H)).
Crystal Structure Determinations. X-ray intensities were
measured on a Nonius KappaCCD diffractometer with rotating
anode and graphite monochromator (λ ) 0.71073 Å) at a temper-
ature of 150(2) K up to a resolution of (sin θ/λ)max ) 0.65 Å-1
.
The structures were solved with automated Patterson methods
(39) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7–13.