Reactions of a diruthenium complex with sulfur, selenium and sulfur dioxide

Article abstract of DOI:10.1039/a706728c

Reaction of the complex [Ru₂(CO)₄(μ-CO)(μ-dppm)₂] 1 (dppm = Ph₂PCH₂PPh₂) with sulfur or selenium gave the corresponding [Ru₂(CO)₄(μ-E)(μ-dppm)₂] (E = 2 or 3) in high yield. Both 2 and 3 reacted with an excess of sulfur to give the disulfido, μ-sulfido complex [Ru₂(CO)₂(μ-CO)(μ-S)(S₂)(μ-dppm) ₂] 4. Complex 1 reacted readily with SO₂ to give [Ru₂(CO)₄(μ-SO₂)(μ-dppm)2] 5, containing a bridging S-bonded SO₂ ligand. The complexes 1, 4 and 5 have been characterized by crystal structure determinations and are shown to contain Ru-Ru single bonds.

Full text of DOI:10.1039/a706728c

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Reactions of a diruthenium complex with sulfur, selenium and sulfur
dioxide
Joshi Kuncheria, Hameed A. Mirza, Hilary A. Jenkins, Jagadese J. Vittal and
Richard J. Puddephatt*
Department of Chemistry, University of Western Ontario, London, N6A 5B7, Canada
Reaction of the complex [Ru2(CO)4(µ-CO)(µ-dppm)2] 1 (dppm = Ph2PCH2PPh2) with sulfur or selenium gave the
corresponding [Ru2(CO)4(µ-E)(µ-dppm)2] (E = 2 or 3) in high yield. Both 2 and 3 reacted with an excess of sulfur
to give the disulfido, µ-sulfido complex [Ru2(CO)2(µ-CO)(µ-S)(S2)(µ-dppm)2] 4. Complex 1 reacted readily with SO2
to give [Ru2(CO)4(µ-SO2)(µ-dppm)2] 5, containing a bridging S-bonded SO2 ligand. The complexes 1, 4 and 5 have
been characterized by crystal structure determinations and are shown to contain Ru᎐Ru single bonds.
The complex [Ru2(CO)4(µ-CO)(µ-dppm)2]
1 (dppm = Ph2-
PCH2PPh2),1–3 like related diphosphine derivatives of the
unstable [Ru2(CO)9],4 displays high reactivity towards both
electrophilic and nucleophilic reagents and so is an interesting
reagent for study of co-ordination chemistry at a diruthenium
centre.1–4 Although this topic is of current interest and though
there are many examples of ruthenium complexes with bridging
sulfur- or selenium-donor ligands,5–10 there appear to be no
reports on complexes derived from 1 with sulfur or selenium
reagents.4 Since it seemed probable that interesting chemistry
relevant to the role of RuS2 in catalytic hydrodesulfurization5
would result, such a study was initiated and this article reports
the reactions of 1 with the reagents sulfur (and some other
potential sulfur atom donors), selenium, and sulfur dioxide.
Results and Discussion
The chemistry below leads to a series of complexes [Ru2(CO)4-
(µ-E)(µ-dppm)2] (E = S, Se or SO2) by displacement in complex 1
with E = CO. It was of interest to compare the properties of
these complexes. The structure of 1 as a solvate with 1,2-
C2H4Cl2 has been determined but the data were of poor quality,2
so we have therefore redetermined it, this time as the acetone
solvate. Whilst this work was in progress the structure of 1 as
the acetonitrile solvate was reported.1 The new structure is
shown in Fig. 1 and selected distances and angles are given in
Table 1.
The structure contains a trans,trans-Ru2(µ-dppm)2 unit in the
extended boat conformation with the methylene flaps directed
away from the bridging carbonyl ligand. Hence, the axial phenyl
groups are all directed towards the bridging carbonyl, which is
small enough to fit between them (Fig. 1). The bond distances
and angles are similar to those found in the other solvates.1,2
Thus, the Ru᎐Ru distance is 2.903(2), 2.903(2) and 2.907(9) Å
in the acetone, 1,2-dichloroethane2 and acetonitrile1 solvates
respectively.
Fig. 1 View of the structure of [Ru2(CO)4(µ-CO)(µ-dppm)2] 1
1
tored by H and 31P NMR spectroscopy, though, at least with
H2S as reagent, they must be formed transiently. Complex 2 did
not react further with either H2S or with propylene sulfide, but
did react with an excess of sulfur as described later.
Complex 2 was readily characterized by analytical and spec-
troscopic methods. The significant feature which differentiated
the IR spectrum from that of its precursor was the four ter-
minal carbonyl stretching bands but no bridging carbonyl band
1
(observed at 1701 cmϪ1 for 1).2 The H NMR spectrum was
typical of an ‘A-frame’ complex, containing two multiplets due
to the CHaHb protons of the dppm ligands at δ 5.1 and 3.1. The
31P NMR spectrum showed a singlet at δ 27.5 as expected for a
symmetrical compound.
Reactions with sulfur and selenium
The reaction of complex 1 with grey selenium proceeded in an
analogous way to give the bridging selenido complex 3 (Scheme
1), which was isolated as a stable, dark brown solid. Its spectro-
scopic properties were very similar to those of 2. In addition, it
gave a parent ion in the FAB mass spectrum, as well as peaks due
to fragments from sequential loss of the four carbonyl ligands.
The reaction of complex 1 or 2 with an excess of sulfur gave a
new complex characterized as [Ru2(CO)2(µ-CO)(µ-S)(S2)-
(µ-dppm)2] 4 (Scheme 1), and this could be isolated as air-stable
red crystals. The reaction with 1 proceeded sequentially to give
When [Ru2(CO)4(µ-CO)(µ-dppm)2] 1 was treated with elem-
ental sulfur in a ratio Ru2 :S = 1:1 the bridging sulfido complex
[Ru2(CO)4(µ-S)(µ-dppm)2] 2 was obtained by displacement of
the bridging carbonyl by the sulfide ligand. The reaction was
complete in 10 min at room temperature and the product was
obtained as an air-stable, orange-brown solid in high yield. The
same product 2 was obtained by reaction of 1 with either of the
sulfur atom donors H2S or propylene sulfide, with evolution of
hydrogen or propene respectively as well as CO (Scheme 1). No
intermediates were observed when the reactions were moni-
1
2 and then 4, as monitored by H and 31P NMR spectroscopy.
J. Chem. Soc., Dalton Trans., 1998, Pages 285–290
285

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Table 1 Selected bond lengths (Å) and angles (Њ) for complex
1ؒ0.5Me2CO
Table
2
Selected bond distances (Å) and bond angles (Њ) in
[Ru2(CO)2(µ-CO)(µ-S)(S2)(µ-dppm)2]ؒMe2CO
Ru(1)᎐C(1)
Ru(1)᎐C(5)
Ru(1)᎐P(2)
Ru(2)᎐C(3)
Ru(2)᎐C(5)
Ru(2)᎐P(4)
O(2)᎐C(2)
O(4)᎐C(4)
1.98(2)
2.13(2)
2.352(4)
1.96(2)
2.13(2)
2.327(4)
1.13(2)
1.13(2)
Ru(1)᎐C(2)
Ru(1)᎐P(1)
Ru(1)᎐Ru(2)
Ru(2)᎐C(4)
Ru(2)᎐P(3)
O(1)᎐C(1)
O(3)᎐C(3)
O(5)᎐C(5)
1.90(2)
2.346(4)
2.903(2)
1.87(2)
2.347(4)
1.11(2)
1.14(2)
1.18(2)
Ru(1)᎐C(1)
Ru(1)᎐P(2)
Ru(1)᎐S(2)
Ru(1)᎐Ru(2)
Ru(2)᎐C(2)
Ru(2)᎐P(3)
Ru(2)᎐S(1)
C(2)᎐O(2)
2.18(3)
Ru(1)᎐P(1)
Ru(1)᎐S(1)
Ru(1)᎐S(3)
Ru(2)᎐C(3)
Ru(2)᎐C(1)
Ru(2)᎐P(4)
S(2)᎐S(3)
2.395(6)
2.404(9)
2.434(7)
1.80(2)
2.25(3)
2.415(6)
2.13(1)
1.22(2)
2.403(6)
2.430(7)
2.935(3)
1.86(3)
2.415(6)
2.535(9)
1.15(3)
C(3)᎐O(3)
C(2)᎐Ru(1)᎐C(1)
C(1)᎐Ru(1)᎐C(5)
C(1)᎐Ru(1)᎐P(1)
C(2)᎐Ru(1)᎐P(2)
C(5)᎐Ru(1)᎐P(2)
C(2)᎐Ru(1)᎐Ru(2)
C(5)᎐Ru(1)᎐Ru(2)
P(2)᎐Ru(1)᎐Ru(2)
C(4)᎐Ru(2)᎐C(5)
C(4)᎐Ru(2)᎐P(4)
C(5)᎐Ru(2)᎐P(4)
C(3)᎐Ru(2)᎐P(3)
P(4)᎐Ru(2)᎐P(3)
C(3)᎐Ru(2)᎐Ru(1)
P(4)᎐Ru(2)᎐Ru(1)
O(1)᎐C(1)᎐Ru(1)
O(3)᎐C(3)᎐Ru(2)
O(5)᎐C(5)᎐Ru(1)
Ru(1)᎐C(5)᎐Ru(2)
115.8(7)
145.3(7)
85.1(5)
89.5(5)
93.8(4)
145.8(5)
47.0(4)
91.2(1)
107.9(7)
87.1(5)
89.7(4)
90.3(5)
117.2(2)
86.9(5)
91.1(1)
178(2)
C(2)᎐Ru(1)᎐C(5)
C(2)᎐Ru(1)᎐P(1)
C(5)᎐Ru(1)᎐P(1)
C(1)᎐Ru(1)᎐P(2)
P(1)᎐Ru(1)᎐P(2)
C(1)᎐Ru(1)᎐Ru(2)
P(1)᎐Ru(1)᎐Ru(2)
C(4)᎐Ru(2)᎐C(3)
C(3)᎐Ru(2)᎐C(5)
C(3)᎐Ru(2)᎐P(4)
C(4)᎐Ru(2)᎐P(3)
C(5)᎐Ru(2)᎐P(3)
C(4)᎐Ru(2)᎐Ru(1)
C(5)᎐Ru(2)᎐Ru(1)
P(3)᎐Ru(2)᎐Ru(1)
O(2)᎐C(2)᎐Ru(1)
O(4)᎐C(4)᎐Ru(2)
O(5)᎐C(5)᎐Ru(2)
98.9(6)
91.3(5)
92.8(4)
88.4(5)
173.1(2)
98.4(5)
91.9(1)
118.1(7)
133.9(7)
90.3(5)
90.2(5)
91.8(4)
154.9(6)
47.0(4)
91.7(1)
177(2)
C(1)᎐Ru(1)᎐P(1)
P(1)᎐Ru(1)᎐P(2)
P(1)᎐Ru(1)᎐S(1)
C(1)᎐Ru(1)᎐S(2)
P(2)᎐Ru(1)᎐S(2)
C(1)᎐Ru(1)᎐S(3)
P(2)᎐Ru(1)᎐S(3)
S(2)᎐Ru(1)᎐S(3)
P(1)᎐Ru(1)᎐Ru(2)
S(2)᎐Ru(1)᎐Ru(2)
C(3)᎐Ru(2)᎐C(2)
C(2)᎐Ru(2)᎐C(1)
C(2)᎐Ru(2)᎐P(3)
C(3)᎐Ru(2)᎐P(4)
C(1)᎐Ru(2)᎐P(4)
C(3)᎐Ru(2)᎐S(1)
C(1)᎐Ru(2)᎐S(1)
P(4)᎐Ru(2)᎐S(1)
C(2)᎐Ru(2)᎐Ru(1)
O(1)᎐C(1)᎐Ru(1)
Ru(1)᎐C(1)᎐Ru(2)
S(2)᎐S(3)᎐Ru(1)
O(3)᎐C(3)᎐Ru(2)
95(2)
174.0(2)
90.9(3)
107.1(7)
92.8(2)
156.6(8)
82.1(2)
51.8(3)
93.3(1)
156.0(2)
92(1)
171(2)
87.4(8)
89.3(8)
96(2)
174.6(8)
98.8(7)
85.5(3)
137.9(9)
134(2)
83(1)
C(1)᎐Ru(1)᎐P(2)
C(1)᎐Ru(1)᎐S(1)
P(2)᎐Ru(1)᎐S(1)
P(1)᎐Ru(1)᎐S(2)
S(1)᎐Ru(1)᎐S(2)
P(1)᎐Ru(1)᎐S(3)
S(1)᎐Ru(1)᎐S(3)
C(1)᎐Ru(1)᎐Ru(2)
P(2)᎐Ru(1)᎐Ru(2)
S(3)᎐Ru(1)᎐Ru(2)
C(3)᎐Ru(2)᎐C(1)
C(3)᎐Ru(2)᎐P(3)
C(1)᎐Ru(2)᎐P(3)
C(2)᎐Ru(2)᎐P(4)
P(3)᎐Ru(2)᎐P(4)
C(2)᎐Ru(2)᎐S(1)
P(3)᎐Ru(2)᎐S(1)
C(3)᎐Ru(2)᎐Ru(1)
Ru(1)᎐S(1)᎐Ru(2)
O(1)᎐C(1)᎐Ru(2)
S(3)᎐S(2)᎐Ru(1)
O(2)᎐C(2)᎐Ru(2)
90(2)
105.1(7)
91.5(3)
82.3(2)
147.5(3)
92.1(2)
97.1(3)
49.5(7)
92.6(2)
152.2(2)
83(1)
91.3(8)
85(2)
91.8(8)
179.0(2)
86.7(9)
93.8(3)
130.1(9)
72.9(2)
143(2)
64.2(3)
177(3)
178(2)
138(1)
86.0(6)
177(2)
136(1)
64.0(3)
177(2)
P
Ru
P
P
Ru
P
P
OC
P
OC
OC
CO
CO
CO
CO
Ru
Ru
S
OC
S
O
O
P
P
(i)
(v)
2
5
P
P
Ru
P
OC
OC
CO
CO
(iii)
Ru
P
C
O
1
(ii)
O
P
Ru
P
P
Ru
P
P
Ru
P
P
Ru
P
S
S
CO
CO
OC
OC
CO
CO
C
S
(iv)
Se
3
4
Scheme 1 Reagents: (i) S8, ϪCO; (ii) Se, ϪCO; (iii) S8, ϪCO; (iv) S8,
ϪCO, ϪSe; (v) SO2, ϪCO
The IR spectrum of 4 contained three carbonyl bands at 2020,
1960, and 1836 cmϪ1, consistent with the presence of two ter-
minal carbonyls and one bridging carbonyl group. The 1H
NMR spectrum contained two broad multiplets at δ 2.8 and 4.5
due to the CHaHb protons of the dppm ligands, while the 31P
NMR spectrum contained two multiplets of equal intensity
at δ 10.5 and 18.0, indicating the inequivalence of the two
ruthenium centres. The FAB mass spectrum showed the parent
peak for [Ru2(CO)2(µ-CO)(µ-S)(S2)(µ-dppm)2]ϩ at m/z = 1151
and fragmentation peaks at m/z = 1087, 1059, 1031 and 1003,
attributed to ions formed by sequential loss of S2, followed by
one, two, and three CO groups respectively.
The spectroscopic data did not define the nature of the
sulfur-donor ligands in complex 4 so it was also characterized
by a crystal structure determination. A view of the structure is
given in Fig. 2 and selected bond distances and angles are in
Table 2. There was disorder between the µ-S and µ-CO ligands
of 4, but this was successfully resolved; Fig. 2 shows only one of
the two arrangements.
Fig. 2 View of the structure of [Ru2(CO)2(µ-CO)(µ-S)(S2)(µ-dppm)2] 4.
Only one of the arrangements of the disordered µ-S and µ-CO groups is
shown
The structure contains the expected trans,trans-Ru2(µ-dppm)2
unit in an extended chair conformation. This conformation
results in the presence of two axial phenyl groups on each side
of the molecule, and so to two similarly sized cavities for the µ-S
and µ-CO ligands to fit into. Atom Ru(1) is bonded to a ter-
minal η2-disulfide ligand while Ru(2) is bonded to two terminal
carbonyls. There is a bridging sulfide ligand and a bridging car-
bonyl. The Ru᎐Ru distance of 2.935(3) Å indicates the presence
of a metal–metal bond; although the distance is at the long end
286
J. Chem. Soc., Dalton Trans., 1998, Pages 285–290

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of the Ru᎐Ru single bond range [2.707(6)–3.02(1)],1–4 there are
precedents for the elongation of metal–metal bonds when they
are bridged by sulfur.11 Hence each ruthenium atom can be con-
sidered to be seven-co-ordinate with highly distorted pen-
tagonal bipyramidal stereochemistry. Since Ru(1) is bound to
three sulfur atoms and Ru(2) is bound to only one, the simplest
way of dealing with the electron configuration is to consider
that Ru(1) and Ru(2) carry a negative and a positive charge
respectively; each ruthenium is then co-ordinatively saturated
and has a formal oxidation state of . If the ruthenium
atoms are initially considered to be neutral, the formal oxidation
states are RuIII(1) and RuI(2) and then a donor–acceptor
bond(2)→Ru(1) must be invoked in order for each ruthenium
to attain the 18-electron configuration, leading to effectively
the same electron configuration as in the situation above.
The bridging sulfide ligand is bound asymmetrically, as indi-
cated by the distances Ru(1)᎐S(1) and Ru(2)᎐S(1) of 2.404(9)
and 2.535(9) Å respectively. The disulfide ligand is bound in a
symmetrical η2-chelate mode with Ru(1)᎐S(2) and Ru(1)᎐S(3)
distances of 2.430(7) and 2.434(7) Å respectively. The S᎐S dis-
tance S(2)᎐S(3) 2.13(1) Å is at the long end of the range found
in other disulfido complexes for which the S᎐S distances range
between the S᎐S double bond (1.88 Å) and S᎐S single bond
᎐
Fig. 3 View of the structure of [Ru2(CO)4(µ-SO2)(µ-dppm)2] 5
(2.09 Å) distances.5–7,12 Although η2 chelation by disulfide lig-
ands is common for many transition metals,5 complex 4 appears
to be the first example for a diruthenium complex.4–7 In the
known disulfido complexes of ruthenium, the disulfido group
bridges in the bridging η2-|| bonding mode and there is evidence
for partial SS and RuS double bonding. For example, the com-
plex [Ru2(µ-S2)(µ-SPri)2(η-C5Me5)2] has Ru᎐S 2.215(4) and
2.209(5) and S᎐S 2.008(6) Å, all significantly shorter than the
corresponding distances in 4.6
Table 3 Selected bond distances (Å) and angles (Њ) in [Ru2(CO)4-
(µ-SO2)(µ-dppm)2]ؒEtOHؒH2O
Ru(1)᎐C(1)
Ru(1)᎐S
Ru(1)᎐P(1)
Ru(2)᎐C(3)
Ru(2)᎐S
Ru(2)᎐P(4)
S᎐O(2)
C(2)᎐O(4)
C(4)᎐O(6)
1.90(2)
2.386(4)
2.393(4)
1.91(2)
2.354(4)
2.402(4)
1.53(1)
1.16(2)
1.21(2)
Ru(1)᎐C(2)
Ru(1)᎐P(2)
Ru(1)᎐Ru(2)
Ru(2)᎐C(4)
Ru(2)᎐P(3)
S᎐O(1)
1.90(2)
2.391(4)
2.925(2)
1.95(2)
2.386(4)
1.48(1)
1.16(2)
1.13(2)
Attempts were made to prepare mixed chalcogenide com-
plexes but without success. Thus complex 2 failed to react with
an excess of selenium. Complex 3 did react with an excess of
sulfur but the only product formed in detectable quantity was 4;
hence this reaction leads to displacement of the bridging selen-
ide ligand in 3 by sulfide.
C(1)᎐O(3)
C(3)᎐O(5)
C(1)᎐Ru(1)᎐C(2)
C(2)᎐Ru(1)᎐S
C(2)᎐Ru(1)᎐P(2)
C(1)᎐Ru(1)᎐P(1)
S᎐Ru(1)᎐P(1)
C(1)᎐Ru(1)᎐Ru(2)
S᎐Ru(1)᎐Ru(2)
P(1)᎐Ru(1)᎐Ru(2)
C(3)᎐Ru(2)᎐S
C(3)᎐Ru(2)᎐P(3)
S᎐Ru(2)᎐P(3)
C(4)᎐Ru(2)᎐P(4)
P(3)᎐Ru(2)᎐P(4)
C(4)᎐Ru(2)᎐Ru(1)
P(4)᎐Ru(2)᎐Ru(1)
O(1)᎐S᎐Ru(2)
110.6(7)
134.2(5)
91.3(4)
85.8(5)
91.0(1)
166.6(6)
51.4(1)
93.5(1)
90.0(6)
92.4(5)
91.6(2)
89.8(4)
175.1(1)
120.7(5)
89.1(1)
114.7(6)
120.3(5)
76.2(1)
176(1)
C(1)᎐Ru(1)᎐S
C(1)᎐Ru(1)᎐P(2)
S᎐Ru(1)᎐P(2)
115.2(6)
86.4(5)
91.1(1)
92.7(4)
172.1(2)
82.8(5)
93.8(1)
96.9(8)
173.0(5)
87.1(4)
91.8(5)
91.0(1)
142.4(6)
89.2(1)
108.5(7)
114.8(5)
119.2(5)
174(2)
C(2)᎐Ru(1)᎐P(1)
P(2)᎐Ru(1)᎐P(1)
C(2)᎐Ru(1)᎐Ru(2)
P(2)᎐Ru(1)᎐Ru(2)
C(3)᎐Ru(2)᎐C(4)
C(4)᎐Ru(2)᎐S
C(4)᎐Ru(2)᎐P(3)
C(3)᎐Ru(2)᎐P(4)
S᎐Ru(2)᎐P(4)
C(3)᎐Ru(2)᎐Ru(1)
P(3)᎐Ru(2)᎐Ru(1)
O(1)᎐S᎐O(2)
O(2)᎐S᎐Ru(2)
O(2)᎐S᎐Ru(1)
Reaction of complex 1 with sulfur dioxide
Complex 1 reacts readily with sulfur dioxide to give [Ru2(CO)4-
(µ-SO2)(µ-dppm)2] 5, which was isolated as air-stable yellow
crystals (Scheme 1). The reaction involves the displacement of
the bridging carbonyl of 1 by a bridging S᎐bonded SO2 ligand.
Complexes 5 and 2 are closely related, but efforts to prepare 5
by oxidation of the sulfide ligand in 2 using hydrogen peroxide
or trimethylamine N-oxide were unsuccessful. The symmetrical
nature of complex 5 is shown by the 31P NMR spectrum, which
contains a sharp singlet at δ 34.7 due to the equivalent phos-
1
phorus atoms of the dppm ligands. The H NMR spectrum
O(1)᎐S᎐Ru(1)
exhibited two resonances at δ 2.7 and 4.6 due to the CHaHb
protons of the dppm ligands, as expected for an A-frame
structure. The IR spectrum contained only terminal carbonyl
stretching bands at 2070, 2007, 1972 and 1943 cmϪ1. The ν(SO)
bands were observed at 1210 (sym. stretch) and 1050 cmϪ1
(asym. stretch), and their separation of 160 cmϪ1 indicates a
symmetrical S-bonded co-ordination of the SO2 ligand.13
Ru(2)᎐S᎐Ru(1)
O(4)᎐C(2)᎐Ru(1)
O(6)᎐C(4)᎐Ru(2)
O(3)᎐C(1)᎐Ru(1)
O(5)᎐C(3)᎐Ru(2)
176(2)
169(2)
ligand adopts the symmetrical bridging mode, as predicted
from the spectroscopic data. Nevertheless the arrangement of
the carbonyl ligands is much less symmetrical and this appears
to be due to steric effects with the axial phenyl substituents of
the dppm ligands. Note for example the large differences in
bond angles C(2)᎐Ru(1)᎐Ru(2) 82.8(5) and C(4)᎐Ru(2)᎐Ru(1)
120.7(5), and C(1)᎐Ru(1)᎐Ru(2) 166.6(6) and C(3)᎐Ru(2)᎐
Ru(1) 142.4(6)Њ. In order to avoid the axial phenyl groups
C(2)O(4) moves from its natural position towards Ru(2) while
C(4)O(6) moves away from Ru(1). The Ru᎐Ru separation of
2.925(2) Å indicates the presence of a metal–metal single
bond.1–4 The acute Ru᎐S᎐Ru angle of 76.2(1)Њ also indicates
compression along the Ru᎐Ru axis and is comparable to other
such values where SO2 bridges a metal–metal bond [69.6(1)–
79.8(1)Њ];14 the M᎐S᎐M angle is significantly larger [91.2(1)–
Complex 5 was further characterized by a crystal structure
determination of a solvate 5ؒEtOHؒH2O. A view of the struc-
ture is given in Fig. 3 and selected bond distances and angles are
in Table 3. The structure contains the trans,trans-Ru2(µ-dppm)2
unit in the extended boat conformation. This conformation
with the methylene flaps towards the µ-SO2 ligand creates a
larger cavity on this side of the molecule, since the phenyl sub-
stituents are all equatorial, as needed to accommodate the SO2
ligand. Note that in 1, with the smaller µ-CO ligand, the
extended boat conformation is also observed but with the
methylene flaps away from the bridging ligand (Fig. 1). In 5
each ruthenium has two terminal carbonyl ligands and the SO2
J. Chem. Soc., Dalton Trans., 1998, Pages 285–290
287

View Article Online
118.0(2)Њ] when SO2 bridges two non-bonded metal atoms.13,14
Thus, each ruthenium atom is considered to have distorted
octahedral stereochemistry. The symmetrical bridging of the
SO2 is illustrated by the similarity of the Ru᎐S distances
Ru(1)᎐S and Ru(2)᎐S of 2.386(4) and 2.354(4) Å respectively,
fit. In complex 4 the µ-S and µ-CO groups have about equal size
(thus allowing them to be disordered on either side) and there is
also one S and one CO on either side. Hence, the elongated
chair conformation is adopted, leading to equal sized cavities
on each side of the Ru2(µ-dppm)2 plane. In complexes 1 and 5
there is a µ-CO and µ-SO2 group respectively on one side of the
molecule and two terminal axial carbonyls on the other. Both
adopt the extended boat conformation, but in 1 the methylene
flaps are away from the µ-CO ligand whereas in 5 they are
towards the µ-SO2 ligand. We suggest that this occurs because
the steric effects follow the series µ-SO2 > 2 × terminal CO > µ-
CO. In 5 it seems that steric effects with the axial phenyl groups
cause a major distortion of the angles involving the terminal
carbonyl ligands.
In terms of reactivity complex 1 is electron-rich and is air-
sensitive. All the complexes 2–5 are air-stable and presumably
all have lower electron density at ruthenium. This can be attrib-
uted to formal oxidation in the case of 2, 3 and, especially,
4, but to the better electron-withdrawing ability of µ-SO2
compared to µ-CO in 5.
while the S᎐O distances S᎐O(1) 1.48(1) and S᎐O(2) 1.53(1) Å are
᎐
significantly different although within the range for other µ-SO2
complexes.13,14 The elongation of the S᎐O bonds compared to
᎐
those in free SO2 [1.432(3) Å] is expected since the orbital used
for M᎐SO2 back bonding is S᎐O antibonding in nature.7,13–15
These are few other binuclear SO2 complexes of ruthen-
ium.7,10,13–15 The complex [Ru2(µ-SO4)2(SO2)2(PPh3)4] contains
a sulfur dioxide molecule co-ordinated to each ruthenium
as a terminal S᎐bonded ligand.10 The closest analogy to 5
appears to be [Ru2(CO)2(η-C5Me5)2(µ-SO2)], which is charac-
terized as having a bridging SO2 group from its spectroscopic
properties.10 Complex 5 is thus the first Ru2(µ-SO2) complex to
be characterized crystallographically.
Conclusion
The reactions described between complex 1 and sulfur or selen-
ium lead to formal oxidation of the complexes from the initial
Ru0Ru0 state. Thus, 2 and 3 are considered as RuIRuI com-
plexes, while 4 can be considered either as RuIIRuII or RuIRuIII.
The SO2 complex 5 would normally be considered as Ru0Ru0,
with its formation involving a simple ligand displacement.
However, all the complexes contain a metal–metal single bond
whose distance appears to depend primarily on the nature of
the bridging group(s). Thus, 1, which has a bridging carbonyl
only, has the shortest Ru᎐Ru distance of 2.903(2) Å, while 4
and 5, which each have a sulfur donor bridge, have approxi-
mately equal but longer Ru᎐Ru distances of 2.935(3) and
2.925(2) Å respectively.
Experimental
Complex 1 was synthesized as reported elsewhere,2 and all
experiments were carried out using Schlenk techniques with an
atmosphere of nitrogen. The NMR spectra were recorded by
usingaVarianGemini300MHzspectrometerandchemicalshifts
are given with respect to SiMe4 (1H) or phosphoric acid (31P).
Preparations
[Ru2(CO)4(ì-S)(ì-dppm)2] 2. The complex [Ru2(CO)4(µ-CO)-
(µ-dppm)2] (0.11 g) was mixed with elemental sulfur
(0.0032 g) and CH2Cl2 (15 cm3) added. The reaction mixture
was stirred under nitrogen for 0.5 h. Solvent was then removed
under reduced pressure. The orange-brown compound thus
obtained was washed with pentane (5 cm3) and dried under
vacuum. Yield = 96%. It was recrystallized from CH2Cl2–
pentane (Found: C, 57.5; H, 4.0. Calc. for C54H44O4P4Ru2S: C,
58.2; H, 3.9%). IR (Nujol): ν (CO) 2035, 1980, 1943 and 1916
The bonding in complex 4 is of interest since the metal atoms
have high co-ordination numbers for a M2(dppm)2 complex. If
the axes are defined as in 4A, the ruthenium atoms use the
2
2
2
orbitals 4dyz, 4dx Ϫy , 4dz , 5s, 5px, 5py, 5pz primarily for σ bond-
ing, while 4dxy and 4dyz are used in π bonding. Strong inter-
actions are expected between the π orbitals of the sulfide ligand
and the filled π* orbitals of the disulfide ligand with the metal
orbitals of π symmetry.5–7 Extended Hückel molecular orbital
calculations indicate that the HOMO (highest occupied
molecular orbital) is an antibonding combination of such filled
orbitals as shown in 4B, while the LUMO (lowest unoccupied
molecular orbital) is a combination of the metal–metal σ*
cmϪ1. NMR (acetone): δ(1H) 3.1 (m, 2 H, JHH = 13, JPH = 4,
2
CHaHb), 5.1 (m, 2 H, JHH = 13, JPH = 5 Hz, CHaHb) and 7.0–
2
8.0 (m, 40 H, C6H5); δ(31P) 27.3 (s, dppm).
To a stirring solution of [Ru2(CO)4(µ-CO)(µ-dppm)2] (0.15 g)
in tetrahydrofuran (thf) (20 cm3) was injected H2S (10 cm3). The
reaction mixture was then stirred for 3 h after which the solvent
was removed under vacuum. The brown solid thus obtained
1
2
2
orbital (mostly dz –dz ) and π* orbitals of the carbonyl ligands
shown as 4C.
was characterized as [Ru2(CO)4(µ-S)(µ-dppm)2] by IR, H and
31P NMR spectroscopy. Yield = 94%.
Propylene sulfide (10 µl) was added to a solution of [Ru2-
(CO)4(µ-CO)(µ-dppm)2] in thf (20 cm3) After stirring the reac-
tion mixture for 3 h it was evaporated to dryness. The resulting
orange-brown solid was then washed with hexane (10 cm3) and
dried in vacuo. The product was identified as [Ru2(CO)4(µ-S)-
(µ-dppm)2] by its IR, 1H and 31P NMR spectra. Yield = 96%.
y
P
P
O
O
S
S
S
+
C
C
–
x
Ru2
P
Ru1
P
z
C
O
4A
[Ru2(CO)4(ì-Se)(ì-dppm)2] 3. To a mixture of [Ru2(CO)4-
(µ-CO)(µ-dppm)2] (0.15 g) and elemental grey selenium (0.035
g) was added thf (25 cm3). The reaction mixture was then
stirred for 5 h. The unchanged selenium (excess) was filtered
off. Removal of solvent yielded the product as a dark brown
solid. Yield = 97%. It was recrystallized from CH2Cl2–pentane
(Found: C, 56.2; H, 3.9. Calc. for C54H44O4P4Ru2Se: C, 55.8;
O
O
P
P
P
P
P
P
P
O
O
S
S
S
S
S
S
C
C
C
C
C
C
P
O
O
4B
4C
H, 3.8%). IR (Nujol): ν (CO) 2036, 1981, 1944 and 1921 cmϪ1
.
Another interesting feature of the structures is that the dppm
ligands adopt different conformations in the complexes 1, 4 and
5. Complexes with the trans,trans-M2(µ-dppm)2 group usually
adopt an envelope conformation of each M2(µ-dppm) group
with the CH2 flap directed towards the side of the molecule
where the bulkier ligands are located. This naturally leads to the
phenyl groups on this side of the molecule being equatorial and
there is a larger natural cavity in which the other ligands must
NMR (acetone): δ(1H) 3.5 (m, 2 H, 2JHH = 13, JPH = 4, CHaHb),
5.5 (m, 2 H, 2JHH = 13, JPH = 6 Hz, CHaHb) and 7.0–7.8 (m, 40
H, C6H5); δ(31P) 27.8 (s, dppm). FAB mass spectrum:
m/z = 1161 (Mϩ), 1133, 1105 and 1049.
[Ru2(CO)2(ì-CO)(ì-S)(S2)(ì-dppm)2] 4. The complex
[Ru2(CO)4(µ-CO)(µ-dppm)2] (0.11 g) was mixed with an excess
288
J. Chem. Soc., Dalton Trans., 1998, Pages 285–290

View Article Online
Table 4 Crystal data and structure refinements* for complexes 1, 4 and 5
1ؒ0.5(CH3)2CO
4ؒ(CH3)2CO
5ؒC2H5OHؒH2O
Formula
M
T/K
C56.5H47O5.5P4Ru2
1139.96
295
C56H50O4P4Ru2S3
1209.16
298
C56H52O8P4Ru2
1211.06
298
Space group
a/Å
b/Å
c/Å
P21/c
P21/n
P21/n
11.989(2)
22.496(3)
22.188(5)
104.94(3)
5782(2)
1.310
12.877(5)
37.69(1)
13.303(5)
117.46(1)
5729(4)
1.402
20.700(3)
12.944(2)
22.913(4)
91.08(1)
6138(2)
1.284
β/Њ
U/Å3
Dc/Mg mϪ3
µ/mmϪ1
0.676
0.790
0.695
Tmin, Tmax
F(000)
0.312, 0.339
2312
0.844, 0.896
2456
0.723, 0.827
2416
No. observations [I > 2σ(I)]
No parameters
R1, wR2
6620
632
0.0834, 0.1931
3515
348
0.1146, 0.2334
4864
402
0.0963, 0.2715
* In each case the wavelength of X-rays was 0.710 73 Å, monoclinic, Z = 4.
of elemental sulfur (0.026 g) and thf (20 cm3) added. The reac-
tion mixture was stirred overnight upon which a yellow-brown
precipitate was formed. This was filtered off, washed with pen-
tane (2 × 5 cm3) and dried under vacuum. Recrystallization
from CH2Cl2 gave red crystals. Yield = 55% (Found: C, 55.0; H,
4.0. Calc. for C53H44O3P4Ru2S3: C, 55.2; H, 3.8%). IR (Nujol):
ν (CO) 2020, 1960 and 1836 cmϪ1. NMR (CD2Cl2): δ(1H) 2.82
(m, 2 H, CHaHb), 4.5 (m, 2 H, CHaHb) and 6.9–8.0 (m, 40 H,
C6H5); δ(31P) 10.5 and 18.0 (m, dppm). FAB mass spectrum:
m/z = 1151, 1087, 1059, 1031 and 1003.
Alternatively, [Ru2(CO)4(µ-Se)(µ-dppm)2] (0.10 g) was mixed
with elemental sulfur (0.025 g) to which thf (15 cm3) was
added. The reaction mixture was stirred under nitrogen over-
night. Solvent was than removed under reduced pressure. The
brown solid product thus obtained was crystallized from
CH2Cl2, and identified by its IR and 1H and 31P NMR spectra.
Yield = 32%.
refining site occupancy factors to each bridging unit 0.6:0.4.
The sulfur atom S(1) having occupancy of 0.6 was refined aniso-
tropically whereas only isotropic refinement was possible for
S(1a), C(1), O(1), C(1a) and O(1a). The C᎐O distances
C(1)᎐O(1) and C(1a)᎐O(1a) were fixed at 1.20 Å. Isotropic
thermal parameters were refined for all the phenyl carbon atoms
and a C2 symmetry restraint was imposed on all the phenyl
rings. All hydrogen atoms were placed in the calculated posi-
tions for the purpose of structure-factor calculations only. The
Fourier-difference map revealed two regions of disordered acet-
one. In one region the disordered methyl carbons were related
by rotation along the C᎐C bond and in the other region the
᎐
carbonyl carbon atom was found at the origin (crystallographic
disorder). The site occupancies of these disorder models are
arbitrary and were not refined in the least-squares cycles. Ideal
constraints were imposed on the geometry (C᎐C 1.54 and C᎐O
᎐
1.20 Å). Common isotropic thermal parameters were refined for
each set of disordered solvent molecules and no hydrogen atoms
were included for the solvent molecules.
[Ru2(CO)4(ì-SO2)(ì-dppm)2] 5. Sulfur dioxide was bubbled
into a greenish yellow solution of [Ru2(CO)4(µ-CO)(µ-dppm)2]
(0.15 g) in CH2Cl2 (15 cm3) for 5 min. Ethanol (40 cm3) was
added to the resulting wine-red solution and the mixture was set
aside. The product, which slowly deposited as yellow needles,
was filtered off, washed with ethanol and vacuum dried.
Yield = 61% (Found: C, 55.2; H, 4.4. Calc. for C54H44O6P4-
SRu2ؒC2H5OHؒH2O: C, 55.5; H, 4.3%). IR (Nujol):
ν (CO) 2070, 2007, 1972 and 1943 cmϪ1. NMR (CDCl3): δ(1H)
2.68 (m, 2 H, 2JHH = 12, JPH = 4, CHaHb), 4.6 (m, 2 H, 2JHH = 12,
JPH = 6 Hz, CHaHb) and 6.6–7.6 (m, 40 H, C6H5); δ(31P) 34.7
(s, dppm).
The crystals of complex 5 diffracted weakly. In the neutral
molecule all the non-hydrogen atoms except the phenyl carbons
were assigned anisotropic thermal parameters and refined. Iso-
tropic thermal parameters were refined for all the phenyl car-
bon atoms. A C2 symmetry restraint was imposed on all these
phenyl rings. All hydrogen atoms were placed in the calculated
positions for the purpose of structure-factor calculations only.
The Fourier-difference map revealed the regions of highly dis-
ordered solvent molecule and they were assigned to be one
ethanol (in three regions with occupancies of 0.5, 0.25 and 0.25)
and one water molecule (in four positions in the crystal lattice
with occupancy of 0.25 each). Ideal constraints were imposed
on the geometry of ethanol molecules (C᎐C 1.54, C᎐O 1.40 Å).
Common isotropic thermal parameters were refined for each set
of disordered solvent molecules and no hydrogen atoms were
included for them.
X-Ray crystallography
The structure determinations were carried out using a Siemens
P4 diffractometer, with XSCANS software and the crystals
were sealed in glass capillary tubes. The data processing, solu-
tion by direct methods and refinements were carried out using
SHELXTL programs.16 For complexes 1 and 5 an empirical
absorption correction was made using ψ scans, while for 4 a
Gaussian absorption correction was applied to the data. Full
details are given in Table 4.
CCDC reference number 186/783.
See http://www.rsc.org/suppdata/dt/1998/285/ for crystallo-
graphic files in .cif format.
Acknowledgements
In refinement of the structure of complex 1 an acetone mol-
ecule with occupancy of 0.5 was located and refined, but a
second area of residual electron density (1.44 e ÅϪ3) could not
be modelled; it may due to partial occupation by a disordered
water molecule.
During the least-squares cycles refinement for complex 4 the
positions of the bridging groups S(1) and C(1)᎐O(1) were found
to be disordered. This disorder was successfully resolved by
We thank the Natural Sciences and Engineering Research
Council of Canada for financial support.
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Received 16th September 1997; Paper 7/06728C
290
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