Reactivity of the bridged-sulfide complex Pd2Cl 2(μ-S)(μ-dmpm)2 toward electrophiles

Article abstract of DOI:10.1039/c1dt11961c

The dipalladium(i) complex Pd₂Cl₂(dmpm)₂ (1a) [dmpm = bis(dimethylphosphino)methane] is known to react with elemental sulfur (S₈) to give the bridged-sulfide complex Pd₂Cl ₂(μ-S)(dmpm)₂ (2a) but, in the presence of excess S₈, PdCl₂[P,S-dmpm(S)] (4a) and dmpm(S)₂ are generated. Treatment of 1a with elemental selenium (Se₈), however, gives only Pd₂Cl₂(μ-Se)(dmpm)₂ (3a). Complex 4a is best made by reaction of trans-PdCl₂(PhCN)₂ with dmpm(S). Complex 2a reacts with MeI to yield initially Pd₂I ₂(μ-S)(dmpm)₂ and MeCl, and then Pd₂I ₂(μ-I)₂(dmpm)₂ and Me₂S, whereas alkylation of 2a with MeOTf generates the cationic, bridged-methanethiolato complex [Pd₂Cl₂(μ-SMe)(dmpm)₂]OTf (5). Oxidation of 2a with m-CPBA forms a mixture of Pd₂Cl ₂(μ-SO)(dmpm)₂ and Pd₂Cl₂(μ- SO₂)(dmpm)₂, whereas Pd₂Br₂(μ-S) (dmpm)₂ reacts selectively to give Pd₂Br ₂(μ-SO)(dmpm)₂ (6b). Treatment of the Pd ₂X₂(μ-S)(dmpm)₂ complexes with X₂ (X = halogen) removes the bridged-sulfide as S₈, with co-production of Pd^II(dmpm)-halide species. X-ray structures of 3a, 5 and 6b are presented. Reactions of dmpm with S₈ and Se₈ are clarified. Differences in the chemistry of the dmpm systems with that of the corresponding dppm systems [dppm = bis(diphenylphosphino)methane] are discussed.

Full text of DOI:10.1039/c1dt11961c

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PAPER
Reactivity of the bridged-sulfide complex Pd2Cl2(l-S)(l-dmpm)2 toward
electrophiles†
Craig B. Pamplin, Steven J. Rettig,§ Brian O. Patrick and Brian R. James*
Received 17th October 2011, Accepted 1st November 2011
DOI: 10.1039/c1dt11961c
The dipalladium(I) complex Pd2Cl2(dmpm)2 (1a) [dmpm = bis(dimethylphosphino)methane‡] is known
to react with elemental sulfur (S8) to give the bridged-sulfide complex Pd2Cl2(m-S)(dmpm)2 (2a) but, in
the presence of excess S8, PdCl2[P,S-dmpm(S)] (4a) and dmpm(S)2 are generated. Treatment of 1a with
elemental selenium (Se8), however, gives only Pd2Cl2(m-Se)(dmpm)2 (3a). Complex 4a is best made by
reaction of trans-PdCl2(PhCN)2 with dmpm(S). Complex 2a reacts with MeI to yield initially
Pd2I2(m-S)(dmpm)2 and MeCl, and then Pd2I2(m-I)2(dmpm)2 and Me2S, whereas alkylation of 2a with
MeOTf generates the cationic, bridged-methanethiolato complex [Pd2Cl2(m-SMe)(dmpm)2]OTf (5).
Oxidation of 2a with m-CPBA forms a mixture of Pd2Cl2(m-SO)(dmpm)2 and Pd2Cl2(m-SO2)(dmpm)2,
whereas Pd2Br2(m-S)(dmpm)2 reacts selectively to give Pd2Br2(m-SO)(dmpm)2 (6b). Treatment of the
Pd2X2(m-S)(dmpm)2 complexes with X2 (X = halogen) removes the bridged-sulfide as S8, with
co-production of PdII(dmpm)-halide species. X-ray structures of 3a, 5 and 6b are presented. Reactions
of dmpm with S8 and Se8 are clarified. Differences in the chemistry of the dmpm systems with that of
the corresponding dppm systems [dppm = bis(diphenylphosphino)methane‡] are discussed.
Introduction
We published recently
the bis(dimethylphosphino)methane
Pd2X2(dmpm)2 (X halogen) with H2S, S8, COS, and
a
paper describing reactions of
(dmpm) complexes
=
CS2.1 The studies evolved from earlier findings from our
laboratory on the stoichiometric reaction of the corresponding
bis(diphenylphosphino)methane (dppm) species, Pd2X2(dppm)2,
with H2S to generate Pd2X2(m-S)(dppm)2 and H2, as well as an
associated catalytic conversion of H2S and dppm to H2 and
the monosulfide dppm(S), see Scheme 1.2 Related to this is
a more recent report noting that PMe3-stabilized Mo-sulfide
species correspondingly catalyse conversion of H2S to H2 and
SPMe3.3 Within Scheme 1, any reagent that can remove the
bridging sulfur to regenerate the reactive Pd–Pd bond will clearly
lead to a catalytic process utilising H2S. Other strategies have
involved, for example, oxidation of the bridged-sulfide with H2O2
or m-chloroperbenzoic acid (m-CPBA), which results in the
formation of a bridged-sulfur dioxide complex that subsequently
Scheme 1 Pd-catalysed reaction between H2S and dppm to form H2 and
dppm(S).
eliminates SO2 and regenerates the reactive Pd(I) species;4 thus a
two-stage process effecting catalysis of the reaction shown in eqn
(1) could certainly be realised.
(1)
H2S + 2 “O” → H2 + SO2
The findings of the enhanced reactivity of Pd2Cl2(dmpm)2 (1a),
compared to that of Pd2Cl2(dppm)2, toward H2S,1 and SO2,5
and discovery of reactions of 1a with COS and CS2 while the
dppm analogue is unreactive,1 prompted us to investigate the
reactivity of the bridged-sulfide derivative Pd2Cl2(m-S)(dmpm)2
(2a). The solubility of Pd-dmpm species in water, in contrast
to the non-solubility of the dppm analogues,5 was also a key
factor in motivating our studies. This paper mainly describes
reactivity of 2a toward some electrophilic reagents, where again
some unusual behaviour (not seen in the dppm analogue) is
observed. For example, reaction with elemental sulfur (S8) leads
Department of Chemistry, University of British Columbia, Vancouver, British
Columbia, Canada, V6T 1Z. E-mail: brj@chem.ubc.ca
† Electronic supplementary information (ESI) available: ORTEP of
1
dmpm(S)2, 31P{ H}-NMR spectra of dmpm(Se)2, dmpm(S)(Se) and
complex 5. CCDC reference numbers 849399–849401. For ESI and
crystallographic data in CIF or other electronic format see DOI:
10.1039/c1dt11961c
‡ In all the dipalladium complexes mentioned in this paper, the dmpm and
dppm ligands (unless stated otherwise) are bridging, but for convenience
the m-symbol is omitted.
§ Deceased October 27, 1998.
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Table 1 Selected NMR data for the dmpm derivatives, and some new Pd-complexesa
1
Compound
dH (PCH2P protons)
dP (31P{ H})b
dmpm
dmpm(S)
dmpm(S)2
dmpm(S)(Se)
1.33
-54.5c
2.01 (13.5)c
-48.1, 40.7 (53.4)d
32.5
2.67 (13.4)e
2.84 (13.3)f
12.6, 33.9 (16.4)d,g
12.9 (17.0)h
-13.6
dmpm(Se)2
3.01 (13.4)e
Pd2Cl2(m-Se)(dmpm)2 (3a)
PdCl2[P,S-dmpm(S)] (4a)j
PdI2[P,S-dmpm(S)] (4c)j
PdCl2[P,Se-dmpm(Se)]
[Pd2Cl2(m-SMe)(dmpm)2]OTf (5)l
Pd2Cl2(m-SO)(dmpm)2 (6a)o
Pd2Br2(m-SO)(dmpm)2 (6b)
2.15 (3.3, 13.4)i; 3.41 (5.7, 13.4)i
3.49 (12.3)f
33.6, 63.8 (22.5)d
35.5, 69.6 (32.4)d
32.6, 36.1 (29.0)d
-8.3, 0.2n
3.37k
Unidentified
2.02 (14.7)m; 2.47 (15.4)m; 2.73 (15.4)m; 3.11 (14.7)m
2.54 (10.0, 14.4)p; 3.13 (12.5, 12.7)p
-12.9, 4.8n
1.07 (7.3, 12.1, 14.3)q; 1.36 (6.6, 11.6, 13.2)q; 2.60 (10.1, 14.3)p; 3.18 (12.8, 13.3)p
-13.5, 4.5n
a
1
1
dH = H shift for PCH2P protons; dP
=
31P{ H} shift; JPH and JHH values in Hz given in parentheses. b Singlets in CDCl3 at 20 ◦C, unless indicated
otherwise. c Pseudodoublet (2JPH). d AB pattern (2JPP). e Triplet (2JPH). f Pseudotriplet (2JPH). g JPSe = -705 Hz. h 2JPP value determined from 77Se satellites;
1
1JPSe = -707 Hz. i Doublet of quintets (2JPH
,
2JHH). j In DMSO-d6. k Multiplet, overlap with H2O signal (dH 3.32). -60 ◦C in CD2Cl2. m Doublet of
l
multiplets (2JPH unresolved, 2JHH shown). n AA¢BB¢ pattern. o Two sets of CH2 signals hidden in the CH3-region. p Doublet of triplets for one CH2-proton
(2JPH, 2JHH). q Doublet of triplets of triplets for one CH2 proton (4JPH, 2JPH, 2JHH).
to decomposition of the Pd(II)-dmpm framework with oxidation
of dmpm to the phosphine sulfides. Related studies with elemental
selenium (Se8) are described, as well as reactions with m-CPBA
and halogens, and methylation reactions with MeOTf and MeI.
were characterised by melting point, elemental analysis, and NMR
spectroscopy.
The 2JPP value for dmpm(S) is in the 50–85 Hz range reported
for several unsymmetrical bis(diphenylphosphino)methane com-
pounds, including dppm(S) (2JPP = 76 Hz).9 The CH2 protons of
dmpm(S) appear as a pseudodoublet (dH 2.01, 2JPH = 13.5 Hz), the
2JPH coupling to one of the P-atoms not being resolved. A doublet
Results and discussion
signal has similarly been reported for Ph2PCH2P(S)Me2 (2JPH
=
Sulfur and selenium derivatives of dmpm
14.0 Hz).6
Slow evaporation of a solution of analytically pure dmpm(S)
in EtOH, PrOH, or H2O surprisingly yielded colourless crystals
of dmpm(S)2 and, as a result, the molecular structure of this
compound was accidentally redetermined. The ORTEP diagram
and selected geometric parameters are shown in Figure S1†, and
the data are essentially identical to those previously reported.7
The reactions to be described reveal formation of sulfur and
selenium derivatives of dmpm as co-products, and thus the
characterisation of these compounds was investigated. The mono-
and di-sulfides, dmpm(S) and dmpm(S)2, were obtained pure from
reaction of dmpm with elemental sulfur. The NMR data are given
in Table 1 with those of some new Pd complexes discussed in this
paper.
i
Both P-atoms are in distorted tetrahedral environments, and the
10
˚
P–S distances of 1.950 and 1.952 A are in the standard range.
The P–C–P angle (118.75◦) is larger than that of 114(3)◦ observed
for gas-phase dmpm.11 In contrast to behaviour in the polar protic
solvents, a CDCl3 solution of dmpm(S) was stable, even in air,
for days. The disproportionation reaction, readily detected by
the distinctive smell of dmpm and the associated dP -54.5 singlet
(Table 1), was not light-induced.
Reaction of dmpm with elemental sulfur
The in situ reaction of dmpm with elemental S8 (2.2 mole equiv.)
in CDCl3 at room temperature (r.t., ~295 K) generates dmpm(S)2
in quantitative yield as indicated by a single resonance at dP
1
32.5 in the 31P{ H} NMR spectrum, but a 1 : 1 reaction gave a
The facile dispropoprtionation of dmpm(S) contrasts with
the stability of dppm(S) under similar conditions,2b and in-
deed dppm(S) has been made by direct reaction of dppm and
dppm(S)2.12 Whether the difference in reactivity between dmpm(S)
and dppm(S) arises from steric or electronic effects is unclear.
Enthalpy values show that protonation is much more favourable
for the dmpm system,13 but such protonated species were not
observed in this work. Lack of steric protection in dmpm(S)
might allow closer contact between the P-lone pair and the S-
atom of an adjacent molecule, and facilitate S-atom transfer; in
any case, the volatility and air-sensitivity of the dmpm will likely
force the disproportionation to completion, especially when the
reaction is carried out in air. Of note, a mixture of the dmpm
sulfides has been used to promote the Rh-catalysed acetic acid
synthesis from CO and MeOH, and dmpm(S) was patented for
use as a co-catalyst, although its role was not identified.8 The
colourless mixture of dmpm (dP -54.5), dmpm(S) (dP = -48.1,
dPS = 40.7, 2JPP = 53.4 Hz) and dmpm(S)2. The well-characterised
disulfide has been isolated previously from a similar phosphine/S8
method,6 as well as a by-product from the reaction of S8 with
Ge[(Me2P)2CH(SiMe3)]2.7 A 1 : 1 preparative scale reaction in
benzene, after removal of the volatile components in vacuo, gave
a solid mixture of dmpm(S) and dmpm(S)2 that was isolated
as described previously in a BP patent.8 Attempts to separate
the components by column chromatography were unsuccessful,
but pure dmpm(S) was isolated from the mixture by vacuum
sublimation as an air-stable, white solid in 46% yield. The air-
stability contrasts with the pyrophoric nature of dmpm, the
reactivity of the P(III) atom presumably being attenuated by the
P(V) site. Dissolution of the non-volatile, white residue in CH2Cl2,
followed by filtration, evaporation, and recrystallisation allowed
for isolation of pure dmpm(S)2 (in 18% yield). The dmpm sulfides
1992 | Dalton Trans., 2012, 41, 1991–2002
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˚
Table 2 Selected bond lengths (A) of Pd2Cl2(m-Se)(dmpm)2 (3a),
[Pd2Cl2(m-SMe)(dmpm)2]OTf (5), and Pd2Br2(m-SO)(dmpm)2 (6b), with
estimated standard deviations in parentheses
carbonylation process takes place in neat MeOH under conditions
where disproportionation would likely take place. Our finding that
dmpm(S) readily decomposes to the volatile and pyrophoric dmpm
makes dmpm(S) an unlikely candidate for large-scale catalytic
processes.
3a
Pd(1) ◊ ◊ ◊ Pd(2)
Pd(1)–Cl(1)
Pd(2)–Cl(2)
5
Pd(1) ◊ ◊ ◊ Pd(2)
Pd(1)–Cl(1)
Pd(2)–Cl(2)
S(1)–C(11)
6b
Pd(1) ◊ ◊ ◊ Pd(2)
Pd(1)–Br(1)
Pd(2)–Br(2)
S(1)–O(1)
3.0961(3)
2.3730(9)
2.3831(10)
Pd(1)–P(1)
Pd(1)–Se(1)
Pd(2)–Se(1)
2.2944(9)
2.4142(4)
2.4182(5)
Reaction of dmpm with elemental selenium
3.1933(3)
2.3430(7)
2.3412(7)
1.809(3)
Pd(1)–P(1)
Pd(1)–S(1)
Pd(2)–S(1)
2.3410(7)
2.2929(6)
2.2879(6)
The addition of a CDCl3 suspension of amorphous, red Se8 to a
CDCl3 solution of dmpm (Se: dmpm = 2) generated quantitatively
in situ a single product showing a 31P{ H} singlet resonance
1
1
2
at dP 12.9 and characteristic, satellites doublets of 77Se (I =
,
3.2007(4)
2.5202(5)
2.5195(5)
1.502(3)
Pd(1)–P(1)
Pd(1)–S(1)
Pd(2)–S(1)
2.3137(11)
2.2729(10)
2.2706(10)
7.6% abundant), data that are consistent with the presence of
dmpm(Se)2 (Fig. S2-a†). This known compound, identified in situ
as a by-product in the reaction of Ge[(Me2P)2CH(SiMe3)]2 with
Se, has a dP value of 10.4 in C6D6, but the 1JPSe coupling was not
2
given.7 In addition, the JPP coupling constant (17.0 Hz) could
˚
Table 3 Selected bond angles (A) of Pd2Cl2(m-Se)(dmpm)2 (3a),
[Pd2Cl2(m-SMe)(dmpm)2]OTf (5), and Pd2Br2(m-SO)(dmpm)2 (6b), with
estimated standard deviations in parentheses
also be determined from the 77Se satellites in CDCl3 even though
the P-atoms are chemically equivalent.9,14 The value is consistent
with the dmpm(E)2 formulation (E = O, S, Se), as monosubstituted
3a
2
diphosphines typically have larger JPP values, for example, 76.0
Hz for dppm(S)8 and 53.4 Hz for dmpm(S) (see above). For
Pd(1)–Se(1)–Pd(2)
Cl(1)–Pd(1)–Se(1)
Cl(1)–Pd(1)–P(1)
Cl(1)–Pd(1)–P(3)
Se(1)–Pd(1)–P(1)
5
79.687(14)
176.89(3)
96.20(3)
88.63(3)
82.58(3)
P(1)–Pd(1)–P(3)
Pd(1)–P(1)–C(1)
Pd(1)–P(1)–C(3)
P(1)–C(1)–P(2)
Se(1)–Pd(1)–P(3)
173.35(3)
110.67(13)
115.25(14)
113.53(19)
92.36(2)
1
dmpm(Se)2, JPSe = -707 Hz, comparable to values of -684 and
-752 Hz, respectively, for SePMe315 and dppm(Se)2;9 such coupling
constants are negative, as determined by a triple resonance NMR
technique.15,16
Pd(1)–S(1)–Pd(2)
Cl(1)–Pd(1)–S(1)
Cl(1)–Pd(1)–P(1)
Cl(1)–Pd(1)–P(3)
S(1)–Pd(1)–P(1)
Pd(1)–S(1)–C(11)
6b
Pd(1)–S(1)–Pd(2)
Br(1)–Pd(1)–S(1)
Br(1)–Pd(1)–P(1)
Br(1)–Pd(1)–P(3)
S(1)–Pd(1)–P(1)
S(1)–Pd(1)–P(3)
Pd(1)–S(1)–O(1)
88.39(2)
175.81(2)
86.93(2)
92.67(2)
97.00(2)
111.91(10)
P(1)–Pd(1)–P(3)
Pd(1)–P(1)–C(1)
Pd(1)–P(1)–C(2)
P(1)–C(1)–P(2)
S(1)–Pd(1)–P(3)
Pd(2)–S(1)–C(11)
173.38(2)
122.00(8)
108.32(11)
114.59(13)
83.26(2)
An attempted, preparative scale synthesis from a 1 : 1 Se/dmpm
reaction in C6H6 yielded a pink solid, which on vacuum sublima-
tion gave a white solid, whose C/H analysis was between those
calculated for dmpm(Se) and dmpm(Se)2 but closer to that of the
1
monoselenide. The 1H and 31P{ H} NMR spectra (CDCl3) of the
117.26(10)
sublimed material imply rapid disproportionation to dmpm(Se)2
and dmpm, with no signals for dmpm(Se) being seen. Attempts
to isolate dmpm(Se)2 from a 2 : 1 Se/dmpm reaction in CH2Cl2
yielded initially a colourless material, but this rapidly turned pink
at r.t., presumably due to elimination of elemental Se. The findings
suggest that dmpm(Se) readily disproportionates in the solid state
and in solution, and that dmpm(Se)2 readily eliminates Se under
ambient conditions. The dmpm(Se) and dmpm(Se)2 compounds
(like the corresponding sulfides) are less stable than the easily
characterised dppm analogues;9 like the S-analogues, dppm(Se)2
and dppm readily react in EtOH to give quantitatively isolable
dppm(Se).17
89.57(3)
169.24(3)
91.48 (3)
88.04(3)
92.87(5)
90.26(4)
115.32(15)
P(1)–Pd(1)–P(3)
Pd(1)–P(1)–C(1)
Pd(1)–P(1)–C(2)
P(1)–C(1)–P(2)
P(3)–C(6)–P(4)
Pd(2)–S(1)–O(1)
165.08(4)
114.94(15)
111.71(18)
116.0(2)
113.1(2)
113.82(15)
Reactions of Pd2Cl2(l-S)(dmpm)2 (2a) and the selenide analogue
(3a) with sulfur
When the bridged-sulfide complex 2a was synthesised by reaction
of Pd2Cl2(dmpm)2 (1a) with sulfur,1 an observation that use of
excess S8 initiated formation of an insoluble, reddish precipitate
prompted an investigation of the reactivity of 2a with S8. The find-
ings were unexpected since other Pd2Cl2(m-S)(P–P)2 complexes,
where P–P = bis(diethylphosphino)methane (depm)1 or dppm,4b
were stable toward S8. The enhanced reactivity led to studies on
reactions of 2a with other reagents, and a study of the reaction of
the selenide analogue with S8.
Reaction of dmpm(S) with elemental selenium
In order to characterise the mixed chalcogenide derivative, a
CDCl3 suspension of Se8 was added to a CDCl3 solution of
1
dmpm(S) at r.t. [Se:dmpm(S) = 1]. The in situ 31P{ H} NMR
data (Table 1) are consistent with formation of dmpm(S)(Se)
(Fig. S2-b†), dPSe being at a higher field than dPS (cf. d 12.9
The brown Pd2Cl2(m-Se)(dmpm)2 complex (3a) was best made
from the reaction of Pd2Cl2(dmpm)2 with excess Se8 (which does
not react with 3a) in CH2Cl2. Crystals were grown by diffusion
of Et2O into a CH2Cl2 solution of the complex, and the structure
determined by X-ray analysis (Fig. 1, Tables 2–4). The structure
resembles closely that of 2a.1 The Pd-atoms are in approximately
square planar environments, but the two P–Pd–P axes are twisted
so that the Pd2P4C2 ring is distorted into an extended boat
conformation; such distortions, which are not apparent in the
1
2
for dmpm(Se)2 and d 32.5 for dmpm(S)2); the JPSe and JPP
values resemble those reported previously for dppm(S)(Se).9,17
The dppm(S)(Se) compound has been similarly isolated from a
Se/dppm(S) reaction,9 or as a 1 : 1 mixture with dppm(Se) from
the reaction of dppm(Se)2 and dppm(S).17 In contrast to the
quantitative reactions of dmpm(S) or dppm(S) with selenium, the
1 : 1 reaction of dppm(Se) with elemental sulfur gives a mixture of
dppm(Se)2, dppm(S)(Se) and dppm(S)2.17
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Table 4 Crystallographic dataa for Pd2Cl2(m-Se)(dmpm)2 (3a), [Pd2Cl2(m-SMe)(dmpm)2]OTf (5), and Pd2Br2(m-SO)(dmpm)2 (6b)
3a
5
6b
Empirical formula
fw
C10H28Cl2P4Pd2Se
634.86
C12H31Cl2F3O3P4Pd2S2
752.07
C10H28Br2OP4Pd2S
692.88
Colour, habit
Cryst. size/mm
Cryst. system
Space group
Brown, prism
0.20 ¥ 0.35 ¥ 0.40
Monoclinic
P21 (#4)
8.1062(1)
8.5205(3)
15.3582(4)
93.511(1)
1058.8(2)
2
1.991
39.59
4623
0.021
4366
180
0.021
0.053
1.05
-1.36
Yellow, prism
0.30 ¥ 0.35 ¥ 0.40
Orthorhombic
Pbca (#61)
12.2968(2)
15.1722(1)
27.7363(3)
90
5174.8(1)
8
1.931
20.39
7341
0.030
6229
262
0.034
0.089
1.16
-1.27
Red, irregular
0.35 ¥ 0.40 ¥ 0.45
Orthorhombic
P212121 (#19)
10.794(1)
13.7756(3)
14.8223(4)
90
2204.0(2)
4
2.088
56.5
5409
0.027
5121
190
0.026
0.066
1.03
-0.84
˚
a/A
˚
b/A
˚
c/A
b (◦)
3
˚
V/A
Z
Dc/g cm-3
m/cm-1
Unique reflns
Rint
No. with I ≥ 2s(I)
No. of variables
R(F) (I ≥ 2s(I))
Rw(F2) (all data)
GOF
3
˚
residual density, e/A
2
2
2
4 1/2
a Function minimised Rw(Fo - Fc2)2, where w = 1/s (Fo2); R = RꢀFo2| - |Fc ꢀ/R|Fo2|, Rw = [Rw(|Fo2| - |Fc2|)2/RwFo
] .
An NMR-scale, r.t. reaction of 2a with S8 (~8 mole equiv. S)
in CDCl3 gave a dark red precipitate and a colourless solution
containing dmpm(S)2 as the only 31P-containing co-product. After
collection of the solid, washing with hexanes and redissolving
1
in DMSO-d6, a new AB pattern was noted in the 31P{ H}
2
spectrum (dP 33.6, dPS 63.8; JPP = 22.5 Hz), with an associated
1H pseudotriplet signal for the CH2 protons at dH 3.49 (2JPH = 12.3
1
31
Hz) (Fig. 2); these data (aided by the H{ P} spectrum) are due
to the P,S-chelate complex PdCl2[dmpm(S)] (4a) (Scheme 2). An
in situ 2a/S8 reaction in DMSO-d6 at 50 ◦C showed after 10 min
formation of 4a, dmpm(S)2, and ~15% of an unidentified species
1
characterised by a 31P{ H} AB pattern (dP 34.3, 38.5; 2JPP = 14.1).
Analytically pure 4a was obtained in 89% yield as a yellow solid by
a 1 : 1 reaction of dmpm(S) with trans-PdCl2(PhCN)2 in CH2Cl2
in which 4a is insoluble. The iodo analogue PdI2[dppm(S)] (4c)
was similarly made from the nitrile precursor, but using added
NaI for the halide exchange, and was characterised by NMR data,
which were similar to those of 4a. The analogous PdX2[dppm(S)]
complexes (X = halogen) have also been made from this nitrile
precursor.19
Fig. 1 ORTEP diagram of Pd2Cl2(m-Se)(dmpm)2 (3a) with 50% proba-
bility thermal ellipsoids.
Scheme 2 Reaction of 2a with S8.
structure of 2a, relieve the Pd2P4C2 ring strain, and allow for closer
˚
contact between the Pd-atoms (3.096 vs. 3.342 A in 2a). The Pd(1)–
In an attempt to determine more precisely the fate of the
bridged-chalcogenide ligand in the Scheme 2 reaction, an in situ
reaction of Pd2Cl2(m-Se)(dmpm)2 (3a) with S8 (7.7 mole equiv. S)
was monitored in DMSO-d6. The initial red-brown suspension
was heated at 50 ◦C for 10 min, when NMR analysis showed
the presence of a mixture of 4a, dmpm(S)2, and a species almost
certainly PdCl2[dmpm(Se)], formed via net insertion of the m-Se
˚
Cl(1) and Pd(2)–Cl(2) bond lengths of 2.373 and 2.383 A suggest
that the m-Se ligand may have a somewhat stronger trans influence
than the m-S ligand in 2a, where the corresponding distances are
˚
2.365 and 2.361 A. The NMR data for 3a (Table 1) are very similar
to those described for 2a.1 The Pd2Cl2(m-Se)(depm)2 complex has
also been made.18
1994 | Dalton Trans., 2012, 41, 1991–2002
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because of the poor signal-to-noise ratio of the spectrum. Of note,
dmpm(S)(Se), dmpm(Se), and dmpm(Se)2, were not detected.
The reaction shown in Scheme 2 and the corresponding
3a/S8 reaction likely involves initial attack of the S8 ring by
the bridged-chalcogenide ligand, just as elemental sulfur reacts
with nucleophilic phosphines.20 Direct insertions of elemental
sulfur into metal-carbon and -hydride bonds,21–23 and insertion
of a S-atom into a Ge–P bond,7 have been reported, but the
distribution of products obtained in the 3a/S8 reaction suggests
1
possible reactivity via an undetected PdII(h -dmpm) species,
with the “dangling” P-atom being oxidised by S8. It is known
also that S8 can act as a multidentate ligand, for example, in
structurally characterised polymeric Rh complexes containing
1,3- and 1,3,6-coordinated S8 ligands.24 A speculative mechanism
for the reaction of S8 with 2a and 3a is shown in Scheme 3.
The reddish precipitates seen during the reactions are likely the
eliminated PdS species of which many phases, typically red-
brown, are known,25 but this material was characterised only by
a broad absorption band at ~360 nm in a UV-vis spectrum in
DMSO.
Reactions of 2a–c with methyl iodide and methyl triflate
Tests for S-abstraction from the m-S complexes were made using
alkyl halides: MeI showed reactivity, while EtI was completely
unreactive. The r.t. reaction of 2a with MeI (10.0 equiv.) in
CDCl3, monitored by NMR spectroscopy, rapidly gave a mixture
of Pd2Cl(I)(m-S)(dmpm)2 (2a¢) and Pd2I2(m-S)(dmpm)2 (2c) [1] via
halide metathesis, concomitant with increasing amounts of the
MeCl (dH 3.00); 2a¢ (also formed exclusively in a 1 : 1 2a/NaI
31
1
Fig.
2
1H, 1H{ P} (300.1 MHz,
a
and b) and 31P{ H} (121.5
MHz, c) NMR spectra (DMSO-d6) of the products formed when
Pd2Cl2(m-S)(dmpm)2 (2a) is treated with excess S8. The peaks labeled with
an asterisk indicate a minor, unidentified species.
1
reaction) shows an expected 31P{ H} AA¢BB¢ pattern. Addition of
further MeI (~135 equiv.) then converted both 2a¢ and 2c quantita-
tively to the known, purple species Pd2I2(m-I)2(dmpm)2,26 with co-
production of Me2S. The reactions are outlined in Scheme 4. The
Pd2Br2(m-S)(dmpm)2 (2b)1 reacts similarly, with corresponding
generation of MeBr (dH 2.67). With Pd2I2(m-S)(dmpm)2 (2c) as
reactant, no mixed halide species can be seen, of course, and just
Me2S is formed along with the (m-I)2 complex, which has been
structurally characterised previously, following its synthesis via
I2-oxidation of Pd2I2(dmpm)2.26 The complexes Pd2Cl2(dmpm)2
(1a) and Pd2I2(dmpm)2 (1c) were unreactive toward Me2S at r.t.
in CDCl3. Solutions of Pd2Cl2(m-S)(dppm)2 react similarly with
into a Pd–P bond. Unfortunately, its independent synthesis was
not possible because of the instability of dmpm(Se) (see above).
The in situ 31P{ H} spectrum shows an AB pattern (dP 32.6, dPSe
1
36.1; JPP = 29.0), with the higher field resonance close to that
seen in 4a; the dPSe value (vs. dPS = 63.8 for 4a) also follows the
established trend (dPO < dPSe < dPS).9 The 77Se satellites expected
in the 31P{ H} spectrum of PdCl2[dmpm(Se)] were not resolved
1
Scheme 3 Speculative mechanism for the reaction of Pd2Cl2(m-E)(dmpm)2 with S8; E = S (2a), Se (3a).
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Fig. 3 ORTEP diagram of [Pd2Cl2(m-SMe)(dmpm)2]OTf (5) with 50% probability thermal ellipsoids.
found in the neutral complex cis-Pd2Cl2(m-Cl)(m-SMe)(PMe3)2,
formed via reaction of [PdCl(PMe3)]2(m-Cl)2 with MeSH,28 and in
the cationic cluster complex [Pd4(m-Cl)2(m-SMe)4(dmpm)2][BF4]2,
made by protonation of [PdCl]2(m-MeSC CSMe)(dmpm)2 with
HBF4.29 The C, H, and S elemental analyses for 5, together with the
solution NMR data (see below) and the conductivity in acetone,30
are consistent with the solid state structure.
The r.t. NMR spectra of 5 show broad resonances due to flux-
ional behaviour, but at -60 ◦C the dynamic process is ‘frozen out’,
1
and a 31P{ H}-AA¢BB¢ pattern is resolved and readily simulated
(Fig. 4); coalescence to a single broad resonance occurs at ~60 ◦C
in CD3NO2 (Fig. S3†). The AA¢BB¢ spectrum and JPP values
are similar to those seen in r.t. spectra ◦of other unsymmetrical
1
Pd2 A-frame complexes.4a,31,32 The -60 C, H NMR spectrum
reveals broad multiplets that appear to be comprised of two
doublets of triplets and two doublets of triplets of triplets for the
four diastereotopic dmpm-CH2 protons; these signals are better
Scheme 4 Stepwise reaction of Pd2Cl2(m-S)(dmpm)2 (2a) with MeI.
1
31
resolved as doublets in the H{ P} spectrum. The SMe protons
excess MeI to yield MeCl and Me2S, with the iodo product being
PdI2(dppm).27
appear as a broad singlet at dH 2.28.
The fluxionality most likely occurs via intramolecular inversion
of the pyramidal S-atom via a planar, trigonal transition state,
as suggested for [RhMn(CO)4(m-SMe)(dppm)2]OTf, where the
The r.t. reaction of 2a with MeOTf in CH2Cl2 generates
quantitatively [Pd2Cl2(m-SMe)(dmpm)2]OTf (5) that was isolated
as a yellow solid in 70% yield; crystals were obtained from a
concentrated CDCl3 solution of the complex. The structure of the
cation (Fig. 3, Tables 2–4) confirms methylation of the bridged-
◦
coalescence temperature in the 31P{ H} spectra was about -30 C;
this complex was also made by methylation of the m-S species with
MeOTf.33 The complex [Pt2(H)2(m-SMe)(dppm)2]PF6, prepared
from the corresponding m-H precursor by reaction with MeSH
with elimination of H2, also shows similar dynamic behaviour.34
It is interesting that, although MeOTf is a mild and effective
halide abstracting agent,35 the terminal chlorides of Pd2Cl2(m-
S)(dmpm)2 and [Pd2Cl2(m-SMe)(dmpm)2]+ remain unaffected in
the presence of excess MeOTf. In contrast, when Pd2Cl2(m-
S)(dppm)2 or Pd2Cl2(m-S)(depm)2 are treated with MeOTf (1–15
equiv.) in CH2Cl2, the solutions rapidly become dark red and
1
˚
˚
sulfide. The Pd ◊ ◊ ◊ Pd distance of 3.193 A is ~0.15 A shorter than
that in 2a1 due to increased twisting about the Pd ◊ ◊ ◊ Pd axis
within a Pd2P4C2 boat conformation. The average Pd–Cl distance
˚
˚
(2.342 A) is also marginally shorter than in 2a (2.362 A), but
a comparison of the relative trans influence of the sulfide and
thiolato ligands is likely tenuous when comparing neutral and
cationic species. The S-atom is approximately pyramidal, and there
are no significant interactions between the methyl C-atom and
the O-atoms of the triflate counterion. The Pd ◊ ◊ ◊ Pd and other
bond lengths, and the Pd–S–Pd angle in 5, are similar to those
1
MeCl is evolved; several new 31P{ H} NMR singlet resonances
1996 | Dalton Trans., 2012, 41, 1991–2002
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conversion to a mixture that included Pd2Cl2(m-SO)(dmpm)2 (6a)
and the known Pd2Cl2(m-SO2)(dmpm)2 complex,5 along with
unidentified products (dP singlets at -20.4, -7.2 and 44.8). The
m-SO species was indentified by comparison with NMR data for
isolated Pd2Br2(m-SO)(dmpm)2 (6b), which was formed exclusively
in the corresponding reaction of Pd2Br2(m-S)(dmpm)2 with m-
1
CPBA. The r.t. 31P{ H} and 1H NMR spectra of 6b, which
was characterised crystallographically using red crystals grown
from a CH2Cl2/Et2O solution (Fig. 5, Tables 2–4), are consistent
with reduced symmetry introduced by a pyramidal S-atom. The
1
31P{ H} spectrum is an AA¢BB¢ pattern centered at dP -13.5 and
4.5, similar to that observed for the m-SMe complex (5) at low
temperature. For 6a, the AA¢BB¢ pattern is centered at dP -12.9
1
and 4.8. The H NMR spectrum of 6b like that for 5 reveals
four inequivalent dmpm-CH2 protons, two appearing as doublets
of triplets, and two consisting of doublets of triplets of triplets;
with 6a, two of the CH2 proton signals are obscured within the
complicated methyl region (see Table 1).
1
Fig. 4 Simulated and (b) actual 31P{ H} NMR spectra (121.5 MHz,
CD2Cl2, -60 ◦C) of [Pd2Cl2(m-SMe)(dmpm)2]OTf (5). Coupling constants
were determined from the simulated spectrum: JAA¢ = 45.4, JAB = JA¢B¢
522.8, JBB¢ = 13.2, JAB¢ = JA¢B = -0.4 Hz.
=
at dP -41.0, -38.1 and 15.5, and multiplets in the dP 48.4–57.7 and
66.6–86.5 regions, are seen, but work-up methods provided only
intractable dark red or black oils.
The Pd2Cl2(dmpm)2 complex is also completely unreactive to-
ward MeOTf, whereas Pd2Cl2(dppm)2 reacts instantaneously with
2.0 equiv. of MeOTf to yield MeCl and [Pd4(m-Cl)2(dppm)4][OTf]2
(Scheme 5), that was isolated as CH2Cl2 solvated crystals. Since the
-
-
-
corresponding PF6 , ClO4 and BF4 salts of this cationic cluster
were characterised previously, the first two by X-ray analysis,36
no such analysis was carried out on the new triflate salt, which
1
was characterised by 31P{ H} NMR spectroscopy and elemental
analysis. The formation of MeCl was also seen in the reaction of
Pd2Cl2(depm)2 with MeOTf, but the NMR spectra were poorly
resolved and no product isolation methods were attempted.
Fig. 5 ORTEP diagram of Pd2Br2(m-SO)(dmpm)2 (6b) with thermal
ellipsoids shown at the 50% probability level.
Reactions of 2a–c with m-chloroperbenzoic acid (m-CPBA)
Compared to structural data for Pd2Br2(m-S)(dmpm)2 (2b),1 the
˚
˚
From solutions of 2a in CD2Cl2 or CDCl3 treated with 1 equiv.
Pd ◊ ◊ ◊ Pd distance of 3.201 A in 6b is 0.13 A longer, the Pd–S bond
◦
˚
˚
m-CPBA at r.t. or at -30 C, an isolated residue showed partial
lengths of 2.271 and 2.273 A are ~0.03 A shorter, and the Pd–S–Pd
Scheme 5 Reaction of Pd2Cl2(dppm)2 with MeOTf.
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angle of 89.57◦ is 6◦ is more obtuse, showing that the S-atom of
the distinctive fragmentation pattern of the S8, presumably formed
the m-SO ligand is closer to the center of the Pd ◊ ◊ ◊ Pd vector. The
Pd–Br distances are of ~0.03 A longer than those in 2b, implying
via catenation of the liberated sulfur.
˚
a slightly stronger trans influence for m-SO vs. m-S; data for the
corresponding dppm analogues4a lead to the same conclusion.
The structure of 6b in general closely resembles that of the dppm
analogue, Pd2Cl2(m-SO)(dppm)2,4a although in the dppm structure
the O-atoms were disordered over two sites, with S–O bond lengths
Conclusions
The studies clarify syntheses, characterisation, and properties
of dmpm(E), dmpm(E)2 (E = S, Se), and dmpm(S)(Se), the
findings being complicated by facile disproportionation of the
dmpm(E) compounds; such behaviour contrasts with that of the
corresponding stable dppm compounds.
Further examples of the different reactivity of Pd-dmpm species
compared to that of the dppm analogues are presented (these are
in addition to those we reported recently on reactivity toward
CS2 and COS).1 They include: (i) breakdown of the Pd2Cl2(m-
E)(dmpm)2 framework by reaction with elemental sulfur to give
PdCl2[P,S-dmpm(E)], whereas the dppm analogue is unreac-
tive, (ii) the conversion of Pd2Cl2(m-S)(dmpm)2 to [Pd2Cl2(m-
SMe)(dmpm)2]OTf by reaction with MeOTf, whereas the dppm
analogue does not undergo methylation, and (iii) Pd2Cl2(dmpm)2
does not react with MeOTf, while the dppm analogue gives a
Pd4-cluster product.
Similarities between the dmpm and dppm systems are also
presented: (i) Pd2Cl2(m-S)(dmpm)2 with MeI initially results in
halide metathesis to give iodo-species with subsequent removal of
the m-S as Me2S and generation of Pd2I2(m-I)2(dmpm)2; the dppm
species reacts similarly but the final Pd-product is PdI2(dppm),
(ii) the Pd2X2(m-S)(dmpm)2 complexes (X = halogen) react with
m-CPBA to give m-SO and m-SO2 derivatives, analogous to the
dppm species, (iii) the Pd2X2(m-S)(dmpm)2 complexes react with
X2, similarly to the dppm analogues, with oxidation of the m-S to
elemental sulfur and co-production of Pd-halide-dmpm species.
˚
of 1.34(4) and 1.45(3) A that are significantly shorter than the 1.502
˚
˚
A length in 6b. Remarkably, the ‘same’ value (1.504 A) is reported
for [CpMn(CO)2]2(m-SO), in which the S-atom has trigonal planar,
sp2-hybridized geometry and the m-SO ligand acts as a 4-electron
donor.37 The pyramidal geometry in 6b implies a 3 center, 2-
electron donor, and the single IR band at 932 cm-1 supports this.19
To the best of our knowledge, 6b is only the fifth dimetallic m-SO
complex to be characterised crystallographically.4a,38
A brown solid, isolated from the reaction of Pd2I2(m-S)(dmpm)2
(2c) with m-CPBA, contained ~95% of an unidentified species
(Z) that was associated with a singlet in CD2Cl2 at dP -18.1,
a CH2 quintet at dH 3.57 (JPH = 4.3 Hz), and a CH3 singlet
resonance at dH 2.11, implying a symmetric species that is not
Pd2I2(m-I)2(dmpm)2.26 This (m-I)2 complex is often formed as an
impurity during reactions involving Pd2I2(dmpm)2 (1c) or 2c (e.g.
in reactions with MeI, and with I2 -see below). The brown solid
contains small amounts of Pd2I2(dmpm)2 (dP -38.4; dH 2.82 qn,
JPH = 3.6 Hz),26 and a further unidentified species (dP -20.5; dH
1.75–1.89 m).
Reaction of 2a–c with halogens
Previous studies from this group19 have demonstrated the chem-
istry of eqn (2) for the dppm systems, where the m-S is oxidised to
elemental sulfur (X = halogen). The “face-to-face” intermediates,
trans-[PdX2(dppm)]2, were also detected in the reaction between
Pd2X2(dppm)2 and X2;39 in the corresponding dmpm systems, the
analogous X = Cl and Br, yellow complexes were isolated, and
the X = I species was isolated as the purple-coloured Pd2I2(m-
I)2(dmpm)2.26
Experimental section
General
Unless otherwise noted, all synthetic procedures were carried
out using standard Schlenk techniques under dry N2. Reagent
grade solvents were distilled under N2 from the appropriate
standard drying agent. Deuterated solvents were obtained from
Cambridge Isotope Laboratories and were used as received. Gas-
tight Sample-LokTM syringes (Dynatech) were used for handling
gaseous reagents.
The dmpm (Strem), S8 (Fisher Scientific), Cl2 (UHP), Br2
(Acros), and I2 (AnalaR) were used as received, as were the Aldrich
products: dppm, MeI, MeOTf, and m-CPBA (available as 57–
86%, impurities being m-chlorobenzoic acid and H2O). Amor-
phous red Se (Se8) was available in this laboratory, having been
prepared by reaction of SeO2 (Alfa) with aq. N2H4 (Alfa).40 The
complexes trans-PdCl2(PhCN)2,41 Pd2X2(dmpm)2 (X = halogen),26
Pd2Cl2(depm)2,26 Pd2X2(m-S)(dmpm)2 and Pd2Cl2(m-S)(depm)2,1
were prepared as reported in the given references.
1
−
S
8
8
Pd2X2(m-S)(dppm)2 + X2 ⎯⎯⎯→
trans-[PdX2(dppm)]2 → 2 PdX2(dppm)
(2)
The sulfide oxidation process was studied in this present work
using the Pd2X2(m-S)(dmpm)2 complexes as reactants, and the
findings establish the chemistry of eqn (2) for the dmpm analogues.
The chloro and bromo species at r.t. in CHCl3/CDCl3 gave
the trans-[PdX2(dppm)]2 products, and the iodo species formed
Pd2I2(m-I)2(dmpm)2 (Scheme 6). In the iodo system, the S8 co-
product was isolated as a residue from the filtrate following
extraction of the (m-I)2 complex with CS2 and passage through a
short column of neutral alumina; EI mass spectral analysis showed
NMR spectra were recorded on a Bruker AV300 spectrometer
1
(300.13 MHz for H, 121.49 MHz for 31P). Residual deuterated
solvent proton (relative to external SiMe4) or external P(OMe)3
(31P, dP 141.0 relative to 85% H3PO4) were used as references
(s = singlet, d = doublet, t = triplet, qn = quintet, m = multiplet,
br = broad, ps = pseudo). J values are reported in Hz. UV-vis
absorption spectra were recorded on a Hewlett Packard 8452A
Scheme 6 Reaction of Pd2I2(m-S)(dmpm)2 (2c) with I2.
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diode-array spectrometer, data being presented as lmax (nm) (emax
¥
for C5H14P2Se: C, 27.92; H, 6.56. Calcd for C5H14P2Se2: C, 20.42;
H, 4.80. Found: C, 26.75; H, 6.54. The remaining off-white residue
was dissolved in CH2Cl2 (10 mL) and the solution eluted through
a short column of neutral alumina; evaporation of the eluent gave
a white solid, whose NMR data again corresponded to those of
dmpm(Se)2.
10-3, M-1 cm-1). Conductivity measurements were made at 298 K
using a model RCM151B Serfass conductance bridge (A. H.
Thomas Co. Ltd.) connected to a 3403 cell from the Yellow Springs
Instrument Co. The cell was calibrated using a standard 0.01000
M aq. KCl solution (KM = 141.3 X-1 cm2 mol-1 at 298 K), the
cell constant being 1.016 cm-1. Low resolution electron impact
mass spectra (EIMS) were obtained on a Kratos MS-50 double-
focusing spectrometer. Elemental analyses were performed by Mr.
P. Border of the UBC Microanalytical Service.
Reaction of dmpm(S) with elemental Se
A solution of dmpm(S) (11 mg, 0.065 mmol) in C6H6 (2 mL)
was treated with Se8 (5.2 mg, 0.066 mmol Se). The mixture was
stirred for 30 min and then filtered through Al2O3; evaporation of
the eluent provided a pale pink residue still containing dmpm(S).
However, a corresponding in situ reaction in CDCl3 (~1 mL)
Preparation of dmpm(S) and dmpm(S)2
A suspension of S8 (139 mg, 4.33 mmol S) in C6H6 (10 mL) was
added dropwise to a solution of dmpm (0.688 mL, 590 mg, 4.33
mmol) in C6H6 (20 mL), and the resulting colourless solution was
stirred for 1 h. Evaporation of the solvent provided a white solid
that was dried in vacuo at r.t. for 16 h in order to remove unreacted
1
showed quantitative formation of dmpm(S)(Se) after 5 min. H
2
3
NMR (CDCl3): d 1.98 (d, 6H, CH3, JPH = 13.1, JSeH = 12.7),
2.19 (d, 6H, CH3, 2JPH = 13.3), 2.84 (ps t, 2H, CH2, 2JPH = 13.3).
1
31P{ H} NMR (CDCl3): dPSe 12.6, dPS 33.9 (AB, 2JPP = 16.4, 1JPSe
1
dmpm; 31P{ H} data for a CDCl3 solution of the solid showed
= 705).
a composition of dmpm(S) (70%) and dmpm(S)2 (30%). Vacuum
◦
sublimation at 50 C at ~0.1 torr provided pure dmpm(S) as an
Preparation of PdX2[dmpm(S)], X = (4a) and I (4c)
air-stable, white solid. Yield: 336 mg (46% based on dmpm). Mp
◦
1
58–60 C. H NMR (CDCl3): d 1.20 (m, 6H, PCH3), 1.78 (m,
To a solution of dmpm(S) (62 mg, 0.369 mmol) in CH2Cl2 (10 mL)
was added a solution of trans-PdCl2(PhCN)2 (141 mg, 0.368 mmol)
in CH2Cl2 (10 mL). The yellow precipitate of 4a was filtered off,
washed with CH2Cl2 (2 ¥ 5 mL) and hexanes (2 ¥ 5 mL), and dried
2
1
6H, P(S)CH3), 2.01 (ps d, 2H, CH2, JPH = 13.5). 31P{ H} NMR
2
(CDCl3): dP -48.1, dPS 40.7 (AB, JPP = 53.4). Anal. Calcd for
C5H14P2S: C, 35.71; H, 8.39; S, 19.06. Found: C, 35.83; H, 8.28; S,
19.11.
1
in vacuo. Yield: 113 mg (89%). H NMR (DMSO-d6): d 1.80 (d,
2
2
The white residue remaining after the sublimation was dissolved
in CH2Cl2 (20 mL) and the solution eluted through a column of
neutral Al2O3. The filtrate was evaporated and the resulting white
solid was recrystallised from hot EtOH to yield colourless crystals
of dmpm(S)2. Yield: 158 mg (18% based on dmpm). Mp 163–165
◦C. 1H NMR (CDCl3): d 1.99 (d, 12H, CH3, 2JPH = 12.3), 2.67 (t,
6H, CH3, JPH = 13.2), 2.09 (d, 6H, CH3, JPH = 14.1), 3.49 (ps
2 1 31
t, 2H, CH2, JPH = 12.3). H{ P} NMR (DMSO-d6): d 1.80 (s,
6H, CH3), 2.09 (s, 6H, CH3), 3.49 (s, 2H, CH2). 31P{ H} NMR
1
2
(DMSO-d6): dP 33.6, dPS 63.8 (dd, JPP = 22.5). Anal. Calcd for
C5H14Cl2P2PdS: C, 17.38; H, 4.08. Found: C, 17.61; H, 4.10.
To a solution of PdCl2(PhCN)2 (30 mg, 0.079 mmol) and NaI
(197 mg, 1.31 mmol) in MeOH (5 mL) was added a solution of
dmpm(S) (16 mg, 0.094 mmol) in CH2Cl2 (5 mL). The brown
1
2H, CH2, 2JPH = 13.4). 31P{ H} NMR (CDCl3): d 32.5 (s); d 31.1
in C6D6.9 1H NMR (DMSO-d6): d 1.87 (d, 12H, CH3, 2JPH = 12.6),
◦
31
3.01 (t, 2H, CH2, 2JPH = 13.7). 1H{ P} NMR (DMSO-d6): d 1.87
suspension was refluxed at 50 C for 2 h and then evaporated to
1
(s, 12H, CH3), 3.01 (s, 2H, CH2). 31P{ H} NMR (DMSO-d6): d
dryness. The orange residue was washed with H2O (5 ¥ 5 mL),
38.2 (s). Anal. Calcd for C5H14P2S2: C, 29.99; H, 7.05; S, 32.02.
Found: C, 30.24; H, 6.91; S, 31.81.
dried in vacuo overnight and extracted with DMSO-d6. 1H NMR
2
(DMSO-d6): d 2.04 (d, 6H, CH3, JPH = 12.3), 2.07 (d, 6H, CH3,
Recrystallisation of dmpm(S) from H2O or alcohols in air
resulted in X-ray diffraction quality crystals of dmpm(S)2.
2JPH = 14.1), 3.37 (m, 2H, partially obscured by an intense signal
1
due to H2O at d 3.32). 31P{ H} NMR (DMSO-d6): dP 35.5, dPS 69.6
(dd, 2JPP = 32.4). Successful elemental analysis of 4c was thwarted
by the presence of water.
Reaction of dmpm with elemental Se
An NMR scale, in situ reaction in CDCl3 between dmpm and a
suspension of Se8 (Se:P = 2) generated dmpm(Se)2 quantitatively.
1H NMR (CDCl3): d 2.20 (d, 12H, CH3, 2JPH + 4JPH = 12.4), 3.01
In situ reaction of Pd2Cl2(l-S)(dmpm)2 (2a) with S8
To a red solution of 2a (8 mg, 0.014 mmol) in DMSO-d6 (0.6 mL)
was added S8 (3.5 mg, 0.109 mmol S). The suspension was heated
to ~50 ◦C for 10 min, and the NMR-tube was then shaken for
31
(t, 2H, CH2, 2JPH = 13.4). 1H{ P} NMR (CDCl3): d 2.20 (s, 12H,
1
CH3), 3.01 (s, 2H, CH2). 31P{ H} NMR (CDCl3): d 12.9 (s, 1JPSe
=
-707, 2JPP = 17.0). Evaporation initially yielded a white solid, but
this rapidly turned pink, presumably due to elimination of Se8.
A suspension of Se8 (75 mg, 0.95 mmol Se) in C6H6 (5 mL)
was added dropwise to a solution of dmpm (0.150 mL, 129 mg,
0.95 mmol) in C6H6 (5 mL). The red solution became colourless
on being stirred for 1 h. Evaporation provided 180 mg of a pink
mixture (likely dmpm, dmpm(Se) and dmpm(Se)2) that was dried
in vacuo for 1 h at r.t. to remove the dmpm. Vacuum sublimation
of the residue provided 21 mg of a waxy, white solid. The NMR
data (CDCl3) corresponded to those of dmpm(Se)2. Anal. Calcd
1 min prior to analysis. H NMR (DMSO-d6): d 1.57 (d, CH3,
1
2
JPH = 13.3, unidentified), 1.80 (d, CH3, JPH = 13.2, 4a), 1.87 (d,
CH3, 2JPH = 12.6, dmpm(S)2), 2.09 (d, CH3, 2JPH = 14.1, 4a), 2.72
(t, CH2, 14.0, unidentified), 3.01 (t, CH2, 2JPH = 13.7, dmpm(S)2),
31
3.49 (pseudotriplet, CH2, 2JPH = 12.3, 4a). 1H{ P} NMR (DMSO-
d6): d 1.57 (s, CH3, unidentified), 1.80 (s, CH3, 4a), 1.87 (s, CH3,
dmpm(S)2), 2.09 (s, CH3, 4a), 2.72 (s, CH2, unidentified), 3.01 (s,
1
CH2, dmpm(S)2), 3.49 (s, CH2, 4a). 31P{ H} NMR (DMSO-d6):
dP 33.6, dPS 63.8 (dd, 2JPP = 22.5, 4a), 34.3, 38.5 (dd, 2JPP = 14.1,
unidentified), 35.4 (s, dmpm(S)2).
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Preparation of Pd2Cl2(l-Se)(dmpm)2 (3a)
Preparation of [Pd4(l-Cl)2(dppm)4][OTf]2 ·2 CH2Cl2
To a solution of 1a (247 mg, 0.445 mmol) in CH2Cl2 (20 mL) was
added Se8 (105 mg, 1.33 mmol Se). The resulting brown suspension
was stirred for 2 h, and then filtered through Celite to remove excess
Se8. The filtrate was concentrated to ~5 mL and Et2O (5 mL) was
added to precipitate a brown solid that was collected, washed with
Et2O (2 ¥ 5 mL) and dried in vacuo at 78 ◦C. Yield: 237 mg (84%).
1H NMR (CD2Cl2): d 1.65 (br s, 12H, CH3), 1.69 (br s, 12H, CH3),
2.15 (dqn, 2H, CH2, 2JPH = 3.3, 2JHH = 13.4), 3.41 (dqn, 2H, CH2,
To a solution of Pd2Cl2(dppm)2 (73 mg, 0.069 mmol) in acetone
(10 mL) was added MeOTf (0.039 mL, 57 mg, 0.346 mmol). The
resulting orange solution darkened slightly, and was stirred at r.t.
for 16 h, filtered through Celite and evaporated to ~5 mL, when
1
31P{ H} data in CDCl3 revealed quantitative formation of the title
complex (AA¢BB¢ pattern centred at d -6.9, -15.5). Addition of
hexanes (10 mL) generated a red oil from which 5.2 mg (~3% yield)
of solid was obtained by dissolving the oil in CH2Cl2/Et2O and
leaving it to stand ~24 h. Red crystals, grown from concentrated
CH2Cl2 solutions of the oil and dried at 78 ◦C in vacuo, gave good
31
2JPH = 5.7, 2JHH = 13.4). 1H{ P} NMR (CD2Cl2): d 1.65 (s, 12H,
2
CH3), 1.69 (s, 12H, CH3), 2.15 (d, 2H, CH2, JHH = 13.4), 3.41
2
1
1
(d, 2H, CH2, JHH = 13.4). 31P{ H} NMR (CD2Cl2): d -13.6 (s).
UV-vis (CH2Cl2): 482 (0.70). Anal. Calcd for C10H28Cl2P4Pd2Se:
C, 18.92; H, 4.45. Found: C, 19.23; H, 4.45.
C/H analyses, and 31P{ H} data consistent with those reported
for the PF6 , BF4 and ClO4 salts.36 UV-vis (relative intensities,
CH2Cl2): 264 (1.0); 346 (0.34); 430 (0.40); 510 (0.33). Anal. Calcd
for C104H92Cl6F6O6P8Pd4S2: C, 49.92; H, 3.71. Found: C, 49.84; H,
3.63.
-
-
-
In situ reaction of Pd2Cl2(l-Se)(dmpm)2 (3a) with S8
To a brown solution of 3a (12 mg, 0.019 mmol) in DMSO-d6
(0.6 mL) was added S8 (4.7 mg, 0.147 mmol S). The resulting
suspension was heated to ~50 ◦C for 10 min, and the NMR-
Reaction of Pd2Cl2(l-S)(dmpm)2 (2a) with m-CPBA
The purity of m-CPBA was assumed to be 57% to ensure the
presence of at least 1.0 oxidising equiv.
1
tube was then shaken for 1 min. The 31P{ H} NMR spectra were
of poor quality compared to those noted for the reaction of 2a
To an orange solution of 2a (76 mg, 0.11 mmol) in CH2Cl2
(10 mL) at -30 ◦C was slowly added a cold solution of m-CPBA
(33 mg, ~1 equiv.) in CH2Cl2 (2 mL), when the solution darkened
from yellow-orange to red. After 5 min, the addition of hexanes
(10 mL) generated a red oil. The reaction vessel was pumped on
1
with S8 (see above). 31P{ H} NMR: d -3.0 to 18.7 (overlapping
2
multiplets, unidentified), dP 32.6 and dPSe 36.1 (dd, JPP = 29.0,
PdCl2[dmpm(Se)]), dP 33.6 and dPS 63.8 (dd, 2JPP = 22.5, 4a), 38.2
(s, dmpm(S)2).
1
overnight, and the residue analysed. 31P{ H} (CDCl3): d -20.4
In situ reaction of Pd2Cl2(l-S)(dmpm)2 (2a) with MeI
(s, unidentified), -12.9, 4.8 (AA¢BB¢, Pd2Cl2(m-SO)(dmpm)2 (6a)),
-11.6 (s, 2a), -7.2 (s, unidentified), 8.8 (s, Pd2Cl2(m-SO2)(dmpm)2),
44.8 (br s, unidentified). 1H NMR (CDCl3): d 1.55–2.25 (overlap-
ping multiplets, CH3), 2.54 (dt, 1H, CH2, 2JPH = 10.0, 2JHH = 14.4),
3.13 (dt, 1H, CH2, 2JPH = 12.5, 2JHH = 12.7), 7.40 to 7.80 (m, Ph,
traces of m-CPBA or 3-chlorobenzoic acid), 9.44 (br s, OH, traces
of m-CPBA or m-chlorobenzoic acid).
A solution of 2a (7 mg, 0.012 mmol) in CDCl3 was treated with
MeI (0.007 mL, 0.12 mmol), and the NMR spectra were recorded
periodically. After ~15 min, the solution contained 2a, Pd2Cl(I)(m-
S)(dmpm)2 (2a¢), Pd2I2(m-S)(dmpm)2 (2c) and MeCl (dH 3.00).
Addition of further MeI (0.100 mL, 1.61 mmol) led to complete
conversion over 24 h of 2a, 2a¢, and 2c to Pd2I2(m-I)2(dmpm)2
1
and generation of Me2S (dH 2.05). 31P{ H} NMR of 2a¢ (CDCl3):
d -16.6, -12.2 (AA¢BB¢). NMR data for 2a, 2c and the (m-I)2
Preparation of Pd2Br2(l-SO)(dmpm)2 (6b)
complex are given in our earlier publications.1,26
To a red solution of 2b (63 mg, 0.093 mmol) in CH2Cl2 (10 mL) at
-30 ◦C was added a cold solution of m-CPBA (28 mg, ~1 equiv.)
in CH2Cl2 (3 mL). The solution was stirred for 5 min, warmed
slowly to r.t., stirred for 1 h, and then concentrated to ~5 mL.
Slow addition of Et2O (15 mL) yielded a reddish precipitate that
was collected, washed with Et2O (3 ¥ 5 mL) and dried in vacuo at
78 ◦C. Yield: 32 mg (49%). The pale red filtrate was stored in the
freezer when after 24 h more red crystals (25 mg) were isolated.
Preparation of [Pd2Cl2(l-SMe)(dmpm)2]OTf (5)
To a solution of 2a (41 mg, 0.069 mmol) in CH2Cl2 (5 mL)
was added MeOTf (0.078 mL, 0.689 mmol). The resulting yellow
solution was stirred for 1 h, filtered through Celite and evaporated
to ~2 mL. Slow addition of cold hexanes (10 mL) at 0 ◦C
precipitated a yellow solid that was collected, washed with hexanes
1
1
(3 ¥ 10 mL) and dried in vacuo. Yield: 36 mg (70%). H NMR
Combined yield: 88%. H NMR (CDCl3): d 1.07 (dtt, 1H, CH2,
(CD2Cl2, -60 ◦C): d 1.60 to 1.74 (m, 24H, CH3), 2.02 (br m,
4JPH = 7.3, 2JPH = 12.1, 2JHH = 14.3), 1.36 (dtt, 1H, CH2, 4JPH = 6.6,
2JPH = 11.6, 2JHH = 13.2), 1.53 (m, 6H, CH3), 1.67 (m, 6H, CH3),
1H, CH2), 2.28 (br s, 3H, SCH3), 2.47 (br m, 1H, CH2), 2.73
(br m, 1H, CH2), 3.11 (br m, 1H, CH2). 1H{ P} NMR (CD2Cl2,
1.71 (m, 6H, CH3), 1.85 (m, 6H, CH3), 2.60 (dt, 1H, CH2, 2JPH
=
31
-60 ◦C): d 1.63 (s, 6H, CH3), 1.64 (s, 6H, CH3), 1.69 (s, 6H, CH3),
10.1, JHH = 14.3), 3.18 (dt, 1H, CH2, JPH = 12.8, JHH = 13.3).
2
2
2
2
31
1.74 (s, 6H, CH3), 2.02 (d, 1H, CH2, JHH = 14.7), 2.28 (s, 3H,
1H{ P} NMR (CDCl3): d 1.06 (d, 1H, CH2, 2JHH = 14.3), 1.34 (d,
2
2
SCH3), 2.47 (d, 1H, CH2, JHH = 15.4), 2.73 (d, 1H, CH2, JHH
=
1H, CH2, 2JHH = 13.2), 1.53 (s, 6H, CH3), 1.67 (s, 6H, CH3), 1.71
2
1
2
15.4), 3.11 (d, 1H, CH2, JHH = 14.7). 31P{ H} NMR (CD2Cl2,
-60 ◦C): d -0.2, -8.3 (AA¢BB¢, JAA¢ = 45.4, JAB = JA¢B¢ = 522.8,
JBB¢ = 13.2. JAB¢ = JA¢B = -0.4). UV-vis (CH2Cl2): 236 (17.8); 264
(18.5); 312 (9.40). KM (acetone): 98 X-1 mol-1 cm2. Anal. Calcd
for C12H31Cl2F3O3P4Pd2S2: C, 19.16; H, 4.15; S, 8.53. Found: C,
19.28; H, 4.16; S, 8.68.
(s, 6H, CH3), 1.85 (s, 6H, CH3), 2.59 (d, 1H, CH2, JHH = 14.3),
3.19 (d, 1H, CH2, 2JHH = 13.3). 31P{ H} NMR (CDCl3): d -13.5,
1
4.5 (AA¢BB¢, JAA¢ = 100, JAB = JA¢B¢ = 395, JBB¢ = 58.5, JAB¢ = JA¢B
=
-3.2). UV-vis (CH2Cl2) = 300 (18.5), 380 (8.2), 424 (12.6). IR (KBr
pellet): n(SO) = 932 cm-1. Anal. Calcd for C10H28Br2OP4Pd2S: C,
17.33; H, 4.07; S, 4.63. Found: C, 17.57; H, 4.09; S, 4.88.
2000 | Dalton Trans., 2012, 41, 1991–2002
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Reaction of Pd2I2(l-S)(dmpm)2 (2c) with m-CPBA
Notes and references
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Can. J. Chem., 1989, 67, 2009.
To a brown solution of 2c (58 mg, 0.075 mmol) in CH2Cl2
(10 mL) at -30 ◦C was added a cold solution of m-CPBA
(23 mg, ~1.0 equiv.) in CH2Cl2 (1 mL). The solution became dark
brown and was stirred for 30 min at r.t. In situ NMR analysis
revealed small amounts of 2c and Pd2I2(dmpm)2 (1c), and a new,
unidentified species (Z) as the major product. Addition of Et2O
(10 mL) and hexanes (10 mL) precipitated the Pd-containing
species as a brown solid mixture that contained Z in ~95% purity
(1H NMR). The solid was collected, washed with hexanes (2 ¥
10 mL) and dried at 78 ◦C in vacuo for 24 h. 1H NMR (CDCl3): d
1.75–1.89 (m, unidentified), 1.81 (s, CH3, 1c), 2.11 (s, 12H, CH3,
Z), 2.82 (qn, 4H, CH2, JPH = 3.6, 1c), 3.57 (qn, 2H, CH2, JPH
= 4.3, Z), 7.38, 7.41, 7.92 and 7.77 (m, traces of m-CPBA or
m-chlorobenzoic acid), 9.44 (br s, OH, traces of m-CPBA or m-
3 D. E. Schwarz, T. B. Rauchfuss and S. R. Wilson, Inorg. Chem., 2003,
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1
chlorobenzoic acid). 31P{ H} NMR (CDCl3): d -38.4 (s, 1c), -20.5
(s, unidentified), -18.1 (s, Z). Anal. Found: C, 20.44; H, 3.52. Anal.
Calcd for Pd2I2(m-SO)(dmpm)2 (6c), C10H28I2OP4Pd2S: C, 15.26;
H, 3.59. Anal. Calcd for Pd2I2(m-SO2)(dmpm)2 C10H28I2O2P4Pd2S:
C, 14.96; H, 3.51.
13 J. R. Sowa and R. J. Angelici, Inorg. Chem., 1991, 30, 3534.
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Reaction of Pd2I2(l-S)(dmpm)2 (2c) with I2
15 W. McFarlane and D. S. Rycroft, J. Chem. Soc., Dalton Trans., 1973,
Addition of I2 (1 equiv.) to a solution of 2c in CDCl3 results in
the instantaneous formation of Pd2I2(m-I)2(dmpm)2 and elemental
sulfur. The purple solution was evaporated and the residue was
extracted with CS2, and this suspension was filtered through a
short column of alumina to remove traces of the insoluble Pd
complex. The filtrate was evaporated to provide a pale yellow
residue, and the low-resolution EI mass spectrum of this material
exhibited the characteristic fragmentation pattern of S8.42
2162.
16 H. Duddeck, Prog. Nucl. Magn. Reson. Spectrosc., 1995, 27, 1.
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1999, 38, 2143.
20 For example: (a) N. K. Gusarova, S. I. Verkhoturova, T. I. Kazantseva,
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X-ray crystallographic analyses
Crystalline samples of 3a, 5 and 6b were prepared as described in
the Results and discussion sections. X-ray analyses were carried
out at 180 K on a Rigaku/ADSC CCD area detector with graphite
˚
monochromated Mo-Ka radiation (0.71069 A). The structures are
shown in Fig. 1, 3 and 5. Selected bond lengths and angles are
given in Tables 2 and 3, and some associated crystallographic
data are given in Table 4, with more details being provided
in the Supporting Information.† The final unit-cell parameters
were based on 9184 reflections with 2qmax = 60.1◦ for 3a, 44930
reflections with 2qmax = 61.0◦ for 5, and 16508 reflections with
2qmax = 60.1◦ for 6, in a series of f and w scans in oscillations of
0.50◦ (for 3a and 6b) and 0.30◦ (for 5), with respective exposures
of 15, 5 and 30.0 s; the crystal-to-detector distance was ~39 mm.
Data were processed using the d*TREK area detector program,43
and the structures were solved by direct methods.44 All refinements
were performed using the SHELXL-97 program45 via the WinGX
interface.46 All non-H-atoms in the three structures were refined
anisotropically. All the H-atoms were fixed in idealised, calculated
positions.
25 (a) Dictionary of Inorganic Compounds, 1st ed. Chapman and Hall, New
York, 1992, vol. 3, IC-021792; (b) N. E. Brese, P. J. Squattrito and J. A.
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26 C. B. Pamplin, S. J. Rettig, B. O. Patrick and B. R. James, Inorg. Chem.,
2003, 42, 4117.
27 T. Y. H. Wong, Ph.D. Thesis, The University of British Columbia,
Vancouver, British Columbia, Canada, 1996.
28 E. M. Padilla, J. A. Golen, P. N. Richmann and C. M. Jensen,
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29 C. Kluwe and J. A. Davies, Organometallics, 1995, 14, 4257.
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Lilga, Organometallics, 1986, 5, 2220.
32 A. L. Balch, C. T. Hunt, C. L. Lee, M. M. Olmstead and J. P. Farr, J.
Am. Chem. Soc., 1981, 103, 3764.
Acknowledgements
33 L.-S. Wang, R. McDonald and M. Cowie, Inorg. Chem., 1994, 33, 3735.
34 M. P. Brown, J. R. Fisher, R. J. Puddephatt and K. R. Seddon, Inorg.
Chem., 1979, 18, 2808.
We thank the Natural Sciences and Engineering Council of
Canada for funding and Dr Terrance Y. H. Wong for some initial
investigations in this area.
35 D. L. Oliver and G. K. Anderson, Polyhedron, 1992, 11, 2415.
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©

View Article Online
36 (a) P. Braunstein, M. A. Luke, A. Tiripicchio and M. Tiripicchio-
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37 I.-P. Lorenz, J. Messelha¨user, W. Hiller and K. Huag, Angew. Chem.,
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38 R. Wang, M. S. Mashuta, J. F. Richardson and M. E. Noble, Inorg.
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39 C. T. Hunt and A. L. Balch, Inorg. Chem., 1981, 20, 2267.
40 H. Richter, W. Hulcke and H. Specht, Z. Naturforsch, 1952, 7A, 511.
41 G. K. Anderson and M. Lin, Inorg. Synth., 1990, 28, 61.
42 G. Dudek and E. P. Dudek, J. Chem. Educ., 1989, 66, 304.
43 d*TREK. Area Detector Software, version 4.13. Molecular Structure
Corp: The Woodlands, TX, 1996–1998.
44 A. Altomare, M. C. Burla, M. Camalli, G. L. Cascarano, C. Giacov-
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Appl. Crystallogr., 1999, 32, 115.
45 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr., 2008,
A64, 112.
46 WinGX-V1.80.05; L. J. Farrugia, J. Appl. Crystallogr., 1999, 32, 837.
2002 | Dalton Trans., 2012, 41, 1991–2002
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The Royal Society of Chemistry 2012
©