Diphosphine mobility at a binuclear metal center: A concerted double trigonal-twist in bis(dithiolate) complexes [M2(CO) 4(μ-dppm){μ-S(CH2)nS}] (M = Fe, Ru; N = 2, 3)

Article abstract of DOI:10.1021/om100894w

Heating [M₂(CO)₆{μ-S(CH₂) _nS}] (M = Fe, Ru; n = 2 (edt), 3 (pdt)) with bis(diphenylphosphino) methane (dppm) in toluene affords the bridged-diphosphine complexes [M ₂(CO)₄(μ-dppm){μ-S(CH₂)_nS}]. At room temperature, all show two separate environments for the methylene protons of the diphosphine ligand, while at higher temperatures these coalesce to a single peak. This behavior, which interconverts the two sulfur atoms, is ascribed to a concerted double trigonal-twist of the M(CO)₂P moieties. No such fluxional behavior was observed for the nonlinked dithiolate complexes [Fe₂(CO)₄(μ-dppm)(μ-SR)₂] (R = Me, Ph, p-tolyl). The X-ray structures of [M₂(CO)₄(μ- dppm)(μ-edt)] (M = Fe, Ru) and [Fe₂(CO)₄(μ-dppm) (μ-SMe)₂] are presented in order to compare them to the previously reported [M₂(CO)₄(μ-dppm)(μ-pdt)].

Full text of DOI:10.1021/om100894w

Organometallics 2010, 29, 6559–6568 6559
DOI: 10.1021/om100894w
Diphosphine Mobility at a Binuclear Metal Center: A Concerted
Double Trigonal-Twist in Bis(dithiolate) Complexes
[M2(CO)4(μ-dppm){μ-S(CH2)nS}] (M = Fe, Ru; n = 2, 3)
Graeme Hogarth,*,† Shariff E. Kabir,‡ and Idris Richards†
†Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, U.K., and
‡Department of Chemistry, Jahangirnagar University, Savar, Dhaka-1342, Bangladesh
Received September 16, 2010
Heating [M2(CO)6{μ-S(CH2)nS}] (M=Fe, Ru; n=2 (edt), 3 (pdt)) with bis(diphenylphosphino)methane
(dppm) in toluene affords the bridged-diphosphine complexes [M2(CO)4( μ-dppm){μ-S(CH2)nS}]. Atroom
temperature, all show two separate environments for the methylene protons of the diphosphine ligand, while
at higher temperatures these coalesce to a single peak. This behavior, which interconverts the two sulfur
atoms, is ascribed to a concerted double trigonal-twist of the M(CO)2P moieties. No such fluxional behavior
was observed for the nonlinked dithiolate complexes [Fe2(CO)4(μ-dppm)(μ-SR)2] (R=Me, Ph,
p-tolyl). The X-ray structures of [M2(CO)4( μ-dppm)( μ-edt)] (M=Fe, Ru) and [Fe2(CO)4(μ-dppm)( μ-
SMe)2] are presented in order to compare them to the previously reported [M2(CO)4( μ-dppm)( μ-pdt)].
Introduction
this, a large number of phosphine-substituted derivatives of
these complexes have been reported.13-36
Dithiolate-bridged diiron complexes, [Fe2(CO)6( μ-dithio-
late)], have been known for 45 years1 but are currently the
focus of intense interest2-6 resulting from the realization that
they closely resemble the two-iron unit of the H-cluster active
site of iron-only hydrogenases.7-9 Consequently, the chemistry
of [Fe2(CO)6{ μ-S(CH2)nS}] (n = 2, 3; edt, pdt)10,11 and of [Fe2-
(CO)6{ μ-SCH2N(R)CH2S}]12 have been intensively studied. A
key step in the electrocatalytic conversion of protons to
hydrogen at the active center of iron-only hydrogenases is
believed to be the initial coordination of the proton(s). The
hexacarbonyls themselves are not basic enough to bind a
proton strongly, and the main approach adopted to cir-
cumvent this problem is to substitute one or more carbonyls
for more basic phosphine or cyanide ligands. As a result of
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*To whom correspondence should be addressed. E-mail: g.hogarth@
ucl.ac.uk.
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2010 American Chemical Society
Published on Web 11/16/2010
pubs.acs.org/Organometallics

6560 Organometallics, Vol. 29, No. 23, 2010
Hogarth et al.
Scheme 1
co-workers38 and [M2(CO)6( μ-edt)].11,39-45 As expected, each
complex is characterized by a singlet resonance in the 31P
NMR spectrum, showing the equivalent nature of the phos-
phorus atoms.
ii. Solid-State Structures. In previous work, single-crystal
X-ray structures of [Fe2(CO)4( μ-dppm)( μ-pdt)]13,14 and [Ru2-
(CO)4( μ-dppm)( μ-pdt)]37 were reported. In order to fully
characterize the full series, we have now carried out X-ray
analyses of [Fe2(CO)4( μ-dppm)( μ-edt)] and [Ru2(CO)4( μ-
dppm)( μ-edt)]. Large red truncated octahedral crystals of
[Fe2(CO)4( μ-dppm)( μ-edt)] were grown upon slow diffusion
of methanol into a saturated dichloromethane solution. The
molecule crystallizes in the tetragonal space group, P4(2)/
mbc, and the single molecule has a plane of symmetry that
contains the three methylene carbons and the two sulfur
atoms (Figure 1). The diruthenium complex [Ru2(CO)4( μ-
dppm)( μ-edt)] was also crystallized upon slow diffusion of
methanol into a saturated dichloromethane solution. Very
large yellow plates resulted, and one of these was cut to give a
large yellow block. The molecule crystallizes in the monoclinic
space group, Cc, with three independent molecules in the
asymmetric unit. This situation is somewhat akin to that found
for [Fe2(CO)4( μ-dppm)( μ-pdt)], which also has three indepen-
dent molecules in the asymmetric unit, but in this case there are
also solvent molecules.13 The three independent molecules of
[Ru2(CO)4( μ-dppm)( μ-edt)] do not differ significantly, and
thus only one is shown (Figure 2). Key structural parameters
for both [Fe2(CO)4( μ-dppm)( μ-edt)] and [Ru2(CO)4( μ-dppm)-
( μ-edt)] together with the corresponding pdt complexes13,14,37
and the parent edt complexes [Fe2(CO)6( μ-edt)]40-43 and
[Ru2(CO)6( μ-edt)]39 are given in Table 1.
Metric parameters for [Fe2(CO)4( μ-dppm)( μ-edt)] are
very similar to those found in the hexacarbonyl [Fe2(CO)6( μ-
edt)]. The iron-iron bond shortens slightly upon addition of
the diphosphine and is also somewhat shorter than those
found in the [Fe2(CO)4( μ-dppm)( μ-pdt)]. Iron-sulfur bonds
also vary only slightly upon diphosphine addition, that to the
sulfur trans to the diphosphine being very slightly shorter than
that to the cis thiolate sulfur, but these differences are only small
and lie within the range of iron-sulfur bonds in [Fe2(CO)6( μ-
edt)]. Hence, it can be seen that the diphosphine does not exert
any significant trans influence on the thiolate bridge. The
ruthenium-ruthenium bond length in [Ru2(CO)6( μ-edt)] lies
in between the range of those found in the three independent
molecules of [Ru2(CO)4( μ-dppm)( μ-edt)], and thus it can be
concluded that diphosphine addition has no significant effect
on this vector. All the ruthenium-sulfur distances in the latter
are slightly longer than those in the hexacarbonyl, with those cis
to the diphosphine being slightly longer than those trans to it.
This slight elongation of the cis thiolate group is reflected in the
In a recent contribution the dppm-bridged tetracarbonyl
complex [Fe2(CO)4( μ-dppm)( μ-pdt)] was prepared upon heat-
ing [Fe2(CO)6( μ-pdt)] and dppm in refluxing toluene.13,14 In
the solid state, the two sulfur atoms are inequivalent, one lying
trans to the diphosphine and the other cis. However, when a
d8-toluene solution of [Fe2(CO)4( μ-dppm)( μ-pdt)] was heated
1
while monitoring by H NMR spectroscopy the inequivalent
methylene protons broadened and collapsed. We attributed
these observations to a fluxional process that involved a con-
certed double trigonal-twist of the two Fe(CO)2P groups.13 In
order to fully investigate this process, we have now prepared
and examined by high-temperature 1H NMR spectroscopy the
series of dppm-bridged complexes [M2(CO)4( μ-dppm){ μ-S-
(CH2)nS}] (M=Fe, Ru; n=2, 3) with the anticipation that the
edt complexes (n=2) would offer extra insight since the methy-
lene protons of the dithiolate ligand would also act as a useful
probe, while analysis of related ruthenium complexes would
help to shed light on the proposed mechanistic details.
Results and Discussion
i. Synthesis and Characterization. Three of the dppm-
bridged complexes prepared for this study have previously been
reported. As detailed in the Introduction, [Fe2(CO)4( μ-dppm)-
(μ-pdt)] can prepared upon heating [Fe2(CO)6( μ-pdt)] with
dppm in toluene,13 a process that occurs via monodentate [Fe2-
(CO)5(κ1-dppm)( μ-pdt)].13,14 The two ruthenium complexes
[Ru2(CO)4( μ-dppm)( μ-pdt)] and [Ru2(CO)4(μ-dppm)( μ-edt)]
have previously been prepared in moderate yields upon heating
[Ru3(CO)10( μ-dppm)] with the appropriate dithiol.37 We have
now found that both ruthenium complexes can be prepared in
essentially quantitative yields upon refluxing the parent hexa-
carbonyls and dppm in toluene for 1-2 h (Scheme 1).
The diiron complex [Fe2(CO)4( μ-dppm)( μ-edt)] appears not
to have been previously reported. It is prepared in moderate
yield upon thermolysis of [Fe2(CO)6( μ-edt)] with dppm in
toluene for 12-14 h in the presence of Me3NO. Monitoring the
reaction of [Fe2(CO)6( μ-edt)] in the absence of Me3NO re-
vealed the formation of intermediates [Fe2(CO)5(κ1-dppm)( μ-
edt)] and [Fe2(CO)4(κ2-dppm)( μ-edt)] (see Experimental
Section), but these were not isolated in pure form. All com-
plexes are air stable in the solid state. The diiron complexes
decompose slowly in many organic solvents, but this is suffi-
ciently slow to allow crystallization in air. The diruthenium
complexes appear to be indefinitely stable in both the solid
state and solution. IR data are very characteristic for all four
complexes. For example, [Fe2(CO)4( μ-dppm)( μ-edt)] has car-
(38) Cabeza, J. A.; Martinez-Garcia, M. A.; Riera, V.; Ardura, D.;
Garcia-Grande, S. Organometallics 1998, 17, 1471.
(39) Hanif, K. M.; Kabir, S. E.; Mottalib, M. A.; Hursthouse, M. B.;
Malik, K. M. A.; Rosenberg, E. Polyhedron 2000, 19, 1073.
(40) Hasan, M. M.; Hursthouse, M. B.; Kabir, S. E.; Malik, K. M. A.
Polyhedron 2001, 20, 97.
(41) Hughes, D. L.; Leigh, G. J.; Paulson, D. R. Inorg. Chim. Acta
1986, 120, 191.
(42) Messelhaeuser, J.; Lorenz, I. P.; Haug, K.; Hiller, W. Z. Nat-
urforsch. Teil B 1985, 40, 1064.
(43) Kabir, S. E.; Rahman, A. F. M. M.; Parvin, J.; Malik, K. M. A.
bonyl absorptions at 1991m, 1958vs, 1924s, and 1905sh cm-1
,
while for the analogous diruthenium complexes they appear at
2004m, 1980vs, 1939s, and 1922sh cm-1. The higher frequencies
of the latter (average 17 cm-1) is typical and can be compared to
the homologous series of related 1,2-benzenedithiolate complexes
[M2(CO)6( μ-SC6H4S)] (M=Fe, Ru, Os) prepared by Riera and
Ind. J. Chem., Sect. A 2003, 42, 2518.
(44) Adams, R. D.; Yamamoto, J. H. Organometallics 1995, 14, 3704.
(45) Adams, R. D.; Chen, L.; Yamamoto, J. H. Inorg. Chim. Acta
1995, 229, 47.
(37) Hossain, G. M. G.; Hyder, Md. I.; Kabir, S. E.; Malik, K. M. A.;
Miah, Md. A.; Siddiquee, T. A. Polyhedron 2003, 22, 633.

Article
Organometallics, Vol. 29, No. 23, 2010 6561
Figure 1. Two views of the molecular structure of [Fe2(CO)4(μ-dppm)(μ-edt)].
Figure 2. Two views of the molecular structure of one molecule of [Ru2(CO)4(μ-dppm)(μ-edt)].
˚
decreasing angle it subtends with the two ruthenium centers.
A similar effect is seen in [Ru2(CO)4( μ-dppm)( μ-pdt)].
phorus atoms [P(1)] is displaced 0.307 A from the plane.
Thus, the M2P2C is less planar in the ruthenium versus the iron
complexes. This results from increases in the metal-metal and
metal-phosphorus bond lengths in the second-row complexes,
while the phosphorus-carbon bonds remain unchanged. The
distortion of the five-membered M2P2C ring is proposed to play
a key role in the fluxionality of these complexes (see below).
We also carried out the X-ray structure of [Fe2(CO)4( μ-
dppm)( μ-SMe)2] (Figure 3) in order to understand why the
diphosphine is not fluxional in this and other nonlinked
dithiolate complexes (see below). The main feature is the anti
arrangement (Scheme 2) of the two methyl groups, being
similar to that previously observed in [Fe2(CO)4( μ-dppm)-
( μ-SAr)2] (Ar=Ph, p-tol).46 This is presumably adopted in
order to minimize steric interactions between the two thiolate
substituents and also between them and the phenyl rings of
the diphosphine. All metric parameters are very similar to
those in [Fe2(CO)4( μ-dppm)( μ-edt)], the iron-iron bond
The iron-phosphorus bond lengths do not vary significantly
between [Fe2(CO)4( μ-dppm)( μ-edt)] and [Fe2(CO)4( μ-dppm)-
( μ-pdt)], and those in [Ru2(CO)4( μ-dppm)( μ-edt)] are only
slightly shorter than in [Ru2(CO)4( μ-dppm)( μ-pdt)]. As can
clearly be seen in Figures 1 and 2, diphosphine coordination
differentiates the two sulfur atoms: one lying trans and the
second cis. In the iron complexes, the P-M-Strans bond angles
are similar, varying only between 152.9° and 154.3°, but some
more notable differences are seen in the two ruthenium com-
plexes. Thus in [Ru2(CO)4( μ-dppm)( μ-edt)], the P-M-Strans
angles vary by nearly seven degrees (146.6-153.3°) in a single
independent molecule. The difference is less pronounced in
[Ru2(CO)4( μ-dppm)( μ-pdt)] (3.3°) but is also seen in the
P-M-Scis bond angles in both complexes. These differ-
ences between the iron and ruthenium complexes result from
the less planar nature of the M2P2 section of the M2P2C five-
membered ring in the second-row versus the first-row transition
metal complexes. Thus in [Fe2(CO)4( μ-dppm)( μ-edt)] all four
ꢀ
˚
ꢀ
˚
length of 2.5082(6) A being about 0.02 A longer.
˚
non-carbon atoms lie within 0.165 A of the plane, while in one
molecule of [Ru2(CO)4( μ-dppm)( μ-edt)], one of the phos-
(46) Hogarth, G.; O’Brien, M.; Tocher, D. A. J. Organomet. Chem.
2003, 672, 29.

6562 Organometallics, Vol. 29, No. 23, 2010
Hogarth et al.
ꢀ
˚
Table 1. Selected Bond Lengths (A) and Angles (deg) for [M2(CO)4(μ-dppm){μ-S(CH2)nS}] (M = Fe, Ru; n = 2, 3), [Fe2(CO)4(μ-
dppm)(μ-SMe)2], and [M2(CO)6(μ-edt)]
compound
M-M
M-Strans M-Scis
M-P
M-COap M-COba M-Strans-M M-Scis-M P-M-Strans P-M-Scis
[Fe2(CO)6(μ-edt)] 293 Ka,b
2.497(4)
2.502(1)
2.245(2)
2.239(1)
67.6(2)
67.92(3)
67.71(2)
193 Ka,c
d,e
2.5032(5) 2.2493(7) 2.2468(6)
2.2440(6) 2.2539(7)
2.4863(5) 2.2403(5) 2.2507(5) 2.2145(4) 1.778(2)
67.59(2)
[Fe2(CO)4(μ-dppm)(μ-edt)]
[Fe2(CO)4(μ-dppm)(μ-pdt)]f
1.767(2)
1.767(5)
1.769(5)
1.779(5)
1.771(5)
67.41(2)
67.41(4)
67.06(2)
67.70(4)
154.27(2)
152.90(5)
153.26(5)
152.18(5)
153.66(5)
86.13(2)
85.12(4)
85.56(5)
86.07(5)
83.72(5)
2.5076(9) 2.260(1)
2.259(1)
2.253(1)
2.249(1)
2.253(2)
2.213(1)
2.210(1)
2.217(1)
2.215(1)
1.782(5)
1.766(5)
1.774(6)
1.754(5)
2.510(1)
2.513(1)
2.244(1)
68.01(5)
67.97(5)
68.69(5)
67.69(6)
67.71(6)
68.84(4)
2.2480(6) 2.255(2)
[Ru2(CO)6(μ-edt)]g
2.6790(8) 2.375(2)
2.374(2)
2.370(2)
2.370(2)
2.382(1)
2.400(1)
2.394(1)
2.408(1)
2.394(1)
2.411(1)
2.407(1)
2.410(1)
[Ru2(CO)4(μ-dppm)(μ-edt)]
2.6830(7) 2.381(1)
2.380(1)
2.316(1)
2.321(1)
2.319(1)
2.319(1)
2.318(1)
2.319(1)
2.324(1)
2.343(1)
1.893(5)
1.904(5)
1.886(5)
1.911(6)
1.894(6)
1.904(6)
1.904(5)
1.889(5)
1.897(5)
1.876(5)
1.884(5)
1.874(5)
1.889(5)
1.874(5)
1.842(6)
1.870(5)
1.747(3)
1.747(3)
68.60(4)
68.38(4)
68.65(4)
67.96(3)
67.73(3)
68.25(4)
67.64(4)
67.86(4)
67.37(3)
67.07(3)
146.56(4)
153.28(4)
148.22(4)
152.46(4)
147.59(5)
152.56(5)
152.45(4)
149.12(4)
156.43(3)
147.69(3)
89.38(4)
86.23(4)
89.08(4)
85.88(4)
88.99(5)
86.25(4)
86.18(4)
84.62(4)
84.57(3)
89.19(3)
2.6730(7) 2.379(1)
2.378(1)
2.6823(8) 2.379(1)
2.378(1)
[Ru2(CO)4(μ-dppm)(μ-pdt)]h 2.6720(7) 2.392(1)
2.389(1)
[Fe2(CO)4(μ-dppm)(μ-SMe)2] 2.5082(6) 2.2472(9) 2.2616(9) 2.2131(9) 1.771(4)
2.2537(9) 2.2787(8) 2.2235(9) 1.772(3)
a Two molecules in the asymmetric unit; values given are averages. b D. L. Hughes, G. J. Leigh, and D. R. Paulson, Inorg. Chim. Acta 1986, 120, 191.
cJ. Messelhaeuser, I. P. Lorenz, K. Haug, and W. Hiller, Z. Naturforsch. Teil B 1985, 40, 1064. d Cocrystallizes with ferrocene. e S. E. Kabir, A. F. M. M.
Rahman, J. Parvin, and K. M. A. Malik, Ind. J. Chem., Sect. A 2003, 42, 2518. f F. A. Adam, G. Hogarth, and I. Richards, J. Organomet. Chem. 2007,
692, 3957. g K. M. Hanif, S. E. Kabir, M. A. Mottalib, M. B. Hursthouse, K. M. A. Malik, and E. Rosenberg, Polyhedron 2000, 19, 1073. h G. M. G.
Hossain, Md. I. Hyder, S. E. Kabir, K. M. A. Malik, Md. A. Miah, and T. A. Siddiquee, Polyhedron 2003, 22, 633.
Scheme 2
equal-intensity low-field aromatic resonances (multiplets at
δ 7.488 and 7.391 at 253 K and a sharp multiplet at δ 7.524 at
373 K). Using the modified Eyring equation47 free energies
of activation can be estimated from the methylene protons of
the diphosphine (Tc = 328 K, Δν 225 Hz; ΔG# 63.6 ( 0.5 kJ
mol-1), the methylene protons of the edt ligand (Tc = 303 K,
Δν 33 Hz; ΔG# 63.4 ( 0.5 kJ mol-1), and the low-field aromatic
resonances (Tc = 308 K, Δν 39 Hz; ΔG# 64.0 ( 0.5 kJ mol-1).
Thus, we conclude that the free energy of activation for [Fe2-
(CO)4( μ-dppm)( μ-edt)] is around 63.7 ( 1 kJ mol-1. Previous
analysis of VT NMR spectra of [Fe2(CO)4( μ-dppm)( μ-pdt)]13
led to the estimation of a free energy of activation of ca. 61.4 ( 1
kJ mol-1. This value was based solely on the coalescence of the
methylene protons of the diphosphine since the other regions
were less informative.
Figure 3. Molecular structure of [Fe2(CO)4(μ-SMe)2(μ-dppm)].
The ruthenium complexes behave analogously. For [Ru2-
(CO)4( μ-dppm)( μ-edt)] the methylene protons of the dipho-
sphine appear as two sharp and well-resolved doublets of
triplets at δ 3.536 and 3.299 at room temperature. The
methylene protons of the dithiolate bridge are also well-resolved
at this temperature, appearing as multiplets at δ2.153 and 2.035,
and the two low-field aromatic signals appear as multiplets cen-
tered at δ 7.495 and 7.252. Upon warming, all signals broaden
and coalesce. The presence of the residual toluene methyl reso-
nance makes estimation of the coalescence temperature of the
iii. Fluxionality. At low temperatures all four linked
dithiolate complexes show inequivalent methylene protons
of the diphosphine ligand, and upon warming, these broaden
and coalesce into a triplet, behavior illustrated (Figure 4)
for [Fe2(CO)4( μ-dppm)( μ-edt)] in d8-toluene. At 253 K the
methylene protons of the diphosphine appear as a pair of
doublets of triplets at δ 3.600 and 3.039, which upon warm-
ing collapse (ca. 328 K), reappearing as a triplet at δ 3.54 at
373 K. Concomitant changes are observed for the methylene
protons of the edt ligands (multiplets at δ 2.026 and 1.944 at
253 K and a sharp singlet at δ 2.104 at 373 K) and the two
€
(47) Gunther, H. NMR Spectroscopy; John Wiley: Chichester, U.K.,
1980; p 243.

Article
Organometallics, Vol. 29, No. 23, 2010 6563
Figure 4. Variable-temperature 1H NMR spectra of the diphosphine methylene region of [Fe2(CO)4(μ-dppm)(μ-edt)].
methylene groups of the dithiolate bridge difficult to estimate
accurately. Free energies of activation can be estimated from the
methylene protons of the diphosphine (Tc=368 K, Δν 95 Hz)
and the low-field aromatic resonances (Tc=368 K, Δν 97 Hz) as
74.4 (0.5 and 74.3 (0.5 kJ mol-1, respectively. Similar changes
are observed for [Ru2(CO)4( μ-dppm)( μ-pdt)]. The central
methylene group of the dithiolate ligand is partially obscured
by the solvent, but the methylene protons of the diphosphine
appear as two sharp doublets of triplets at δ 3.692 and 3.015,
which collapse upon heating, although even at 373 K they are
not fully coalesced. On estimating the coalescence temperature
at >378 K (Δν 271 Hz), a free energy of activation of g73.2 kJ
mol-1 can be estimated. Most informative are the low-field
aromatic resonances (Tc = 373 K, Δν 133 Hz), which give a free
energy of activation of 74.4 ( 0.5 kJ mol-1. All free energies of
activation are summarized in Table 2.
It is clear from these measurements that that the free
energy of activation for the fluxional process does not vary
significantly with the nature of the dithiolate ligand. This
suggests that this remains innocent throughout and does not
rearrange significantly during the process. There is, however,
a significant difference between the iron and ruthenium

6564 Organometallics, Vol. 29, No. 23, 2010
Hogarth et al.
Table 2. Free Energies of Activation for the Fluxional Process in
[M2(CO)4(μ-dppm){μ-S(CH2)nS}] (M = Fe, Ru; n = 2, 3)
Scheme 5
ΔG#
((1 kJ mol-1
)
[Fe2(CO)4(μ-dppm)(μ-edt)]
[Fe2(CO)4(μ-dppm)(μ-pdt)]
[Ru2(CO)4(μ-dppm)(μ-edt)]
[Ru2(CO)4(μ-dppm)(μ-pdt)]
63.7
61.4
74.3-74.4
74.4
The exchange of phosphine ligands between basal and apical
sites in mono- and disubstituted derivatives, [Fe2(CO)6-n
-
(PR3)n( μ-dithiolate)] (n=1, 2) has been studied to a far lesser
extent. Sun and co-workers have studied the unsymmetrically
substituted complex [Fe2(CO)4(PPh3)(PMe3)( μ-edt)].52 In the
solid state the bulky PPh3 ligand is coordinated in an apical site,
while the smaller PMe3 group occupies a basal site (Scheme 5).
Indeed, this trend;for the bulky phosphine to occupy an apical
site while smaller more basic phosphines occupy a basal site;
appears to be quite general in the solid state. At room tempera-
ture two singlets are observed in the 31P NMR spectrum, the
higher-field signal (attributed to the PMe3) being quite broad.
Upon cooling (213 K), this signal splits into two sharp signals
about 10.3 ppm apart (relative intensity ca. 10:1), while the high-
field resonance attributed to the PPh3 ligand splits into two
signals that are only 0.8 ppm apart. These observations have
been attributed to the slowing of the rotation of the Fe(CO)2-
(PMe3) moiety over this temperature range while the PPh3
ligand is static throughout. Unfortunately no coalescence data
are given, and hence a free energy of activation cannot be
estimated. Nevertheless, this shows that the phosphine can
undergo a trigonal-twist.
A number of possible mechanisms can be envisaged in
order to account for the observed fluxional behavior docu-
mented above. Four of the more probable are shown in
Figure 5. We cannot definitively rule out any of these possi-
ble pathways but prefer one whereby there is no metal-metal
bond scission. On this basis we rule out the pathways
shown that involve (i) metal-phosphorus bond cleavage
followed by a trigonal-twist and recoordination of the dipho-
sphine, (ii) a double metal-sulfur bond cleavage followed by
inversion at sulfur and recoordination of the bridging thio-
late ligand, and (iii) a double metal-sulfur bond cleavage
resulting in a planar intermediate. The main reasoning
behind this is that, as far as we are aware, there is no prece-
dent for the reversible scission-formation of metal-sulfur
or metal-phosphorus bonds in such systems, although there
is evidence of the former occurring upon reduction.53 We
also rule out a process (not shown) that would involve an
intermediate with two bridging carbonyl ligands. While such
mechanisms are common in binuclear organometallic chem-
istry, the formation of bridging carbonyls in diiron dithiolate
complexes is limited to one-electron oxidation products,54,55
and further there is no room for two bridging carbonyls in
the complexes under study here since they already have three
bridging groups.
Scheme 3
Scheme 4
complexes, with free energies of activation in the latter being
ca. 10 kJ mol-1 higher.
Interestingly, when the nonlinked dithiolate complexes [Fe2-
(CO)4( μ-dppm)( μ-SAr)2] (Ar = Ph, p-tolyl)46 were heated
to 100 °C in d8-toluene, no evidence for any fluxional process
was noted, two clearly defined and well-resolved methylene
signals being seen throughout. We initially considered that
this may be a consequence of the large aryl substituents;
however, similar behavior was also noted for [Fe2(CO)4( μ-
dppm)( μ-SMe)2].48 This also shows that the anti arrange-
ment of thiolate bridges is maintained even at higher tem-
peratures.
iv. Mechanistic Implications. The exchange of apical and
basal carbonyl groups in [Fe2(CO)6( μ-dithiolate)] is well docu-
mented,16,18,49-51 and since the metal coordination geometry is
best described as a square-based pyramid, this process has been
termed pyramidal rotation by Darensbourg.16 We prefer the
more widely used term trigonal rotation while accepting that
since the geometry is not octahedral this is not a true description
(Scheme 3). Activation barriers for this process are affected by
the nature of the dithiolate group, although in all cases they are
low. For example in [Fe2(CO)6( μ-pdt)] it is estimated at 36 kJ
mol
51 kJ mol-1 16
,
-1 51 while for [Fe2(CO)6( μ-edt)] it is considerably higher at
.
Likewise we use the term trigonal-twist (Scheme 4) in com-
plexes of this type to define a process whereby an Fe(CO)2P
subunit undergoes exchange of both phosphine and carbonyl
sites. The difference between this and the trigonal-twist
process is that the 120° rotation does not have to result in a
degenerate state; that is, the substituent can occupy either
apical or basal positions.
Consequently we prefer a process that we describe as a
concerted double trigonal-twist. Here, one of the Fe(CO)2P
subunits initially rotates, i.e., undergoes a trigonal-twist.
Since the second Fe(CO)2P group is unchanged, then this
results in a considerable strain being developed within the
(48) De Beer, J. A.; Haines, R. J.; Greatrex, R.; Greenwood, N. N.
J. Chem. Soc. A 1971, 3271.
(49) Singleton, M. L.; Jenkins, R. M.; Klemashevich, C. L.; Darensbourg,
(52) Li, P.; Wang, M.; He, C.; Liu, X.; Jin, K.; Sun, L. Eur. J. Inorg.
Chem. 2007, 3718 .
M. Y. C. R. Chim. 2008, 11, 861.
(53) Felton, G. A. N.; Petro, B. J.; Glass, R. S.; Lichtenberger, D. L.;
Evans, D. H. J. Am. Chem. Soc. 2009, 131, 11290.
(54) Liu, T.; Darensbourg, M. Y. J. Am. Chem. Soc. 2007, 129, 7008.
(55) Justice, A. K.; Rauchfuss, T. B.; Wilson, S. R. Angew. Chem., Int.
Ed. 2007, 46, 6152.
(50) Tye, J. W.; Darensbourg, M. Y.; Hall, M. B. Inorg. Chem. 2006,
45, 1552.
(51) Liu, T.; Li, B.; Singleton, M. L.; Hall, M. B.; Darensbourg, M. Y.
J. Am. Chem. Soc. 2009, 131, 8296.

Article
Organometallics, Vol. 29, No. 23, 2010 6565
Figure 5. Proposed fluxional process for the interconversion of dppm methylene protons in [M2(CO)4(μ-dppm){μ-S(CH2)nS}]
(shown for n = 2).
Fe2PCP ring. This can be relived upon reversing the original
twist or via a twisting at the second metal center in the same
direction. Hence we term this a concerted double trigonal-twist.
Such a process accounts for all of the experimental observations
as it interconverts (i) the methylene protons of the diphosphine
ligand, (ii) the sulfur-bound methylene protons of the dithiolate
bridge, and (iii) the phenyl groups on phosphorus. While the for-
mation of a strained twisted state may seen unusual, we note
that in the solid state the dppm ligand in [Fe3(CO)8( μ-CO)2( μ-
dppm)] binds in an axial site at one metal atom but an equatorial
site at the second.56 This introduces a significant degree of twist-
ing about the diiron vector such that the P-Fe-Fe-P torsion
angle is 30.0°. This compares with values of 0° in [Fe2(CO)4( μ-
dppm)( μ-edt)] and 7.2° (averaged over three independent mole-
cules) in [Ru2(CO)4( μ-dppm)( μ-edt)]. Hence, in some respects
the coordination of the diphosphine in [Fe3(CO)8( μ-CO)2( μ-
dppm)] can be viewed as being somewhat akin to that proposed
for the transition state of the concerted double trigonal-twist.
Further support for this process comes from a recent publica-
tion from Richmond and co-workers.57 As part of a study
concerning the ortho-metalation and ligand dynamics of
[Os3(CO)10( μ-dppm)], they calculated an energy barrier for
the twisting of the dppm ligand in [Os3(CO)9( μ-dppm)] (from
equatorial-equatorial to equatorial-axial) of 67.3 kJ mol-1
close to those measured in this study (Scheme 6).
,
Since the fluxional process does not directly involve any
changes to the bridging dithiolate ligand, then one might expect
free energies of activation to be insensitive to changes in this
group, which is precisely what is seen. The observed differences
between iron and ruthenium, the latter being ca. 10 kJ mol-1
higher, are more difficult to understand. Few data are available
for the barriers to trigonal rotation of analogous iron and
ruthenium complexes, but higher barriers are expected for the
heavier elements.
The free energies of activation for the concerted double
trigonal-twist noted here are significantly higher than those
previously reported for related trigonal-twist processes.58-62
For example in [Fe2(CO)5{P(OMe)3}( μ-PPh2)( μ-X)] (X =
carbene or acyl) (Scheme 7) the phosphite exchanges between
(58) Doherty, S.; Hogarth, G.; Elsegood, M. R. J.; Clegg, W.; Rees,
N. H.; Waugh, M. Organometallics 1998, 17, 3331.
(59) Cooke, J.; Takats, J. Organometallics 1995, 14, 698.
(60) Alex, R. F.; Pomeroy, R. K. Organometallics 1987, 6, 2437.
(61) Cooke, J.; McClung, R. E. D.; Takats, J.; Rogers, R. D. Orga-
nometallics 1996, 15, 4459.
(56) Adams, H.; Agustinho, S. C. M.; Chomka, K.; Mann, B. E.;
Smith, S.; Squires, C.; Spey, S. E. Can. J. Chem. 2001, 79, 760.
(57) Huang, S.-H.; Keith, J. M.; Hall, M. B.; Richmond, M. G.
Organometallics, DOI: 10.1021/om100475v.
(62) Hyes, S. J.; Gallop, M. A.; Johnson, B. F. G.; Lewis, J.; Dobson,
C. M. Inorg. Chem. 1991, 30, 3850.

6566 Organometallics, Vol. 29, No. 23, 2010
Hogarth et al.
Scheme 6
Scheme 9
Scheme 7
Scheme 8
Scheme 10
apical and basal sites with free energies of activation of be-
tween 39.7 and 43.5 kJ mol-1 58 while in [Os2Rh(CO)8(η5-
,
C5H5)(PMe3)] the free energy of activation for phosphine
exchange is 63.2 kJ mol
-1 59 This is to be expected due to the
.
requirement of a degree of ring strain being introduced during
the process. Unfortunately, as far as we are aware, despite the
widespread study of complexes of the type [Fe2(CO)6-n(PR3)n-
( μ-dithiolate)] (n=1, 2) as models for the active site of the iron-
only hydrogenase enzyme, free energies of activations for phos-
phine exchange have not been measured. From the data given in
ref 52 (Δν = 1667 Hz) and assuming a coalescence tempera-
ture of ca. 253 K, then a free energy of activation ca. 45 kJ mol-1
can be estimated, which is in line with related values for other
diiron complexes (see above).
A process that has been studied to a greater extent is the
interconversion of basal-basal and basal-apical isomers
of [Fe2(CO)4(κ2-diphosphine)( μ-dithiolate)].13,28,36 For ex-
ample, the free energy of activation for this process in
[Fe2(CO)4(κ2-Ph2PC6H4PPh2)( μ-pdt)] is estimated at 38 (
1 kJ mol-1 (Scheme 8).
v. Discussion and Conclusions. The realization that the
dppm ligand in these complexes was mobile led us to consider
whether this process could be more general. A vast number of
dimetal-bridged dppm complexes are in the literature,63-65 and
in many instances the 1H NMR data are poorly reported. In our
own work we have previously studied the bis(phosphido) com-
plexes [Fe2(CO)4( μ-PPh2)2( μ-dppm)] and [Fe2(CO)4( μ-PPh2)-
( μ-PCy2)( μ-dppm)] by VT 1H and 31P NMR spectroscopy.66
For [Fe2(CO)4( μ-PPh2)2( μ-dppm)] we found that the inequi-
valent methylene protons of the diphosphine exchanged at
higher temperatures, a free energy of activation of 60 ( 1 kJ
mol-1 being estimated. Concomitant with this was the collapse
of the inequivalent phosphido resonances in the 31P NMR
spectrum, a free energy of activation of 62 ( 1 kJ mol-1 being
estimated. Clearly these represent the same fluxional process,
and at the time we attributed this to the rocking of the phosphido
bridges, a process that was proposed to occur via a transition
state possessing a plane of symmetry (Scheme 9).
At the time we ruled out a mechanism that “involves move-
ment of the diphosphine moiety from one side of the molecule to
the other” on the grounds that such a process was unprece-
dented. However, we now feel that this is fully consistent with
the results presented for the linked dithiolate complexes. Inter-
estingly the mixed phosphido-bridge complex [Fe2(CO)4( μ-
PPh2)( μ-PCy2)( μ-dppm)] did not show this behavior. It would
interconvert isomers in which the diphosphine lies trans to the μ-
PCy2 and μ-PPh2 ligands. We attributed this to the differing
thermodynamic stabilities of these two isomers, presuming that
placing the dppm trans to the bulkier μ-PCy2 is thermodynami-
cally preferable.
We also note a recent publication that describes the synthesis
and spectroscopic properties of [Fe2(CO)4( μ-dppm){μ-SCH2N-
(Pr)CH2S}].14 Here the crystal structure shows (as expected)
that the diphosphine lies trans to one sulfur and cis to the second;
however, the methylene protons of the diphosphine are equiva-
lent at room temperature (described as a singlet and most
probably not exchanging fast enough at this temperature to
observe the coupling constant to phosphorus). Low-tempera-
ture data are not reported, so we cannot estimate the free energy
of activation, but it suggests that this process is common to
[Fe2(CO)4( μ-diphosphine)( μ-dithiolate)] complexes.
This then leads us to consider when such a process is not facile
in[Fe2(CO)4( μ-dppm)( μ-SAr)2] (Ar=Ph,p-tolyl) or [Fe2(CO)4-
( μ-dppm)( μ-SMe)2] (Scheme 10). The reason for this pro-
nounced difference between linked and nonlinked dithiolate-
bridged complexes probably results from the different
orientations of the substituents on sulfur, being syn for the linked
complexes but anti for the diphosphine-substituted nonlinked
(63) Puddpehatt, R. J. Chem. Soc. Rev. 1983, 99.
(64) Chaudret, B.; Delavaux, B.; Poilblanc, R. Coord. Chem. Rev.
1988, 86, 134.
(65) Anderson, G. K. Adv. Organomet. Chem. 1993, 35, 1.
(66) Hogarth, G.; Lavender, M. H. J. Chem. Soc., Dalton Trans.
1993, 143.

Article
Organometallics, Vol. 29, No. 23, 2010 6567
complexes.46 Hence in the nonlinked complexes, movement of
the diphosphine would need to be accompanied by inversion at
both sulfur atoms in order to alleviate adverse steric interactions
between the aryl groups on the diphosphine and thiolate ligands.
Thus, it may be that such an inversion is disfavored.
[Fe2(CO)4(κ2-dppm)( μ-edt)] a singlet was observed at 25.1 ppm.
When the reaction was carried out at room temperature in
acetonitrile with addition of two equivalents of Me3NO 2H2O,
3
immediate consumption of [Fe2(CO)6( μ-edt)] was noted and a
similar IR spectrum was seen. The 31P NMR spectrum was
similar but also included singlets at 35.4 and 19.8 ppm, which we
associate with [{Fe2(CO)5( μ-edt)}2( μ-dppm)] (two isomers). All
attempts to isolate these species pure proved unsuccessful.
Synthesis of [Ru2(CO)4( μ-dppm)( μ-edt)].37 A toluene solution
(80 cm3) of [Ru2(CO)6( μ-edt)] (0.10 g, 0.22 mmol) and dppm
(0.10 g, 0.26 mmol) was heated at reflux for 2 h, the pale yellow
solution darkening slightly over time. An IR spectrum revealed the
total consumption of starting materials and clean formation of
[Ru2(CO)4( μ-dppm)( μ-edt)]. After cooling, removal of volatiles
afforded a dry yellow solid, which was washed with 40:60 petrol
(3 Â 10 cm3) and dried (0.164 g, 94%). Slow diffusion of methanol
into a saturated dichloromethane solution afforded large yellow
We have also recently noted that a similar double trigonal-
twist process occurs in [Fe2(CO)4{μ-Ph2P(CH2)4PPh2}( μ-
pdt)], the free energy of activation being estimated at 67 (
1 kJ mol .
-1 36 The somewhat higher activation barrier versus
that seen in [Fe2(CO)4( μ-dppm)( μ-pdt)] seems at first sight
unusual, while such a process in [Fe2(CO)4( μ-dppm)( μ-pdt)]
must be concerted in nature since a transoid dibasal inter-
mediate is inaccessible due to steric strain. In [Fe2(CO)4{μ-
Ph2P(CH2)4PPh2}( μ-pdt)], as a result of the highly flexible
tetramethylene backbone, this need not be the case and may
account for the small, but significant, differences in the free
energies of activation.
In conclusion we have shown that the diphosphine in com-
plexes of the type [M2(CO)4( μ-dppm){μ-S(CH2)nS}] (M =
Fe, Ru) is fluxional and propose that this involves a concerted
double trigonal-twist, and it may be that such a process is more
common than previously thought for dppm and related dipho-
sphine complexes.
crystals. IR ν(CO) (CH2Cl2): 2004s, 1980vs, 1939s, 1922sh cm-1
.
1H NMR (CDCl3) 298 K: δ 7.73-6.96 (m, 20H, Ph), 3.66-3.46
(m, 2H, PCH2), 2.50 (m, 2H, SCH2), 2.39 (m, 2H, SCH2); (d8-
toluene) 298 K: δ7.50 (m, 4H, Ph), 7.25 (m, 4H, Ph), 7.01-6.77 (m,
12H, Ph), 3.536 (dt, 1H, J 14.2, 10.1, PCH2), 3.299 (dt, 1H, J 14.2,
10.8, PCH2), 2.15 (m, 2H, SCH2), 2.04 (m, 2H, SCH2). 31P{1H}
NMR (CDCl3) 298 K: δ 28.6 (s).
Synthesis of [Ru2(CO)4( μ-dppm)( μ-pdt)].37 This was carried
out as above and gave [Ru2(CO)4( μ-dppm)( μ-pdt)] cleanly in 92%
yield. IR ν(CO) (CH2Cl2): 2004s, 1980vs, 1939s, 1922sh cm-1. 1H
NMR (d8-toluene) 298 K: δ7.56 (q, 4H, J5.4, Ph), 7.21 (q, 4H, J5.4,
7.09-6.74 (m, 12H, Ph), 3.682 (dt, 1H, J 14.3, 10.3, PCH2), 3.015
(dt, 1H, J 14.3, 10.6, PCH2), ca. 2.09 (2H), 1.94 (m, 2H, SCH2), 1.75
(m, 2H, SCH2). 31P{1H} NMR (CDCl3) 298 K: δ 25.8 (s).
X-ray Data Collection and Solution. Single crystals were
mounted on glass fibers, and all geometric and intensity data were
taken from these samples using a Bruker SMART APEX CCD
diffractometer using graphite-monochromated Mo KR radiation
Experimental Section
All reactions were carried out under a nitrogen atmosphere in
dried degassed solvents, although reaction workup and product
crystallization were carried out in air. NMR spectra were run on
a Bruker AMX400 spectrometer and referenced internally to the
residual solvent peak (1H) or externally to P(OMe)3 (31P).
Infrared spectra were run on a Nicolet 205 FT-IR spectrometer
in a solution cell fitted with calcium fluoride plates, subtraction
of the solvent absorptions being achieved by computation.
Elemental analyses were performed in house.
˚
(λ = 0.71073 A) at 150 ( 2 K. Data reduction was carried out with
SAINT PLUS, and absorption correction applied using the pro-
gram SADABS. Structures were solved by direct methods and
developed using alternating cycles of least-squares refinement and
difference-Fourier synthesis. All non-hydrogen atoms were refined
anisotropically. For [Fe2(CO)4( μ-dppm)( μ-edt)], hydrogen atoms
were located from difference maps and refined isotropically, while
for [Ru2(CO)4( μ-dppm)( μ-edt)] they were placed in calculated
positions (riding model). Structure solution used the SHELXTL
PLUS V6.10 program package.
Synthesis of [Fe2(CO)4( μ-dppm)( μ-edt)]. A toluene solution
(80 cm3) of [Fe2(CO)6( μ-edt)] (0.10 g, 0.27 mmol), dppm (0.114 g,
0.30 mmol), and Me3NO 2H2O (0.066 g, 0.60 mmol) was heated at
3
reflux for 12 h. After cooling, removal of volatiles afforded an oily,
orange solid. This was washed with 40:60 petrol (3 Â 10 cm3) and
dried. The solid was dissolved in a minimum amount of dichloro-
methane (ca. 10 cm3), and an excess of hexane (ca. 100 cm3) was
then added. Removal of volatiles on a rotary evaporator gave a
slightly oily, orange solid, which was again washed with 40:60 petrol
(3 Â 10 cm3) and dried. This gave a dry orange solid. It was all
dissolved in a minimum amount of dichloromethane (ca. 2 cm3)
and layered with methanol (ca. 5 cm3). After slow mixing this
afforded large truncated octahedral red crystals of [Fe2(CO)4( μ-
dppm)( μ-edt)] as a dry orange solid (0.13 g, 34%). IR ν(CO) (CH2-
Cl2): 1992s, 1959vs, 1924s, 1905sh cm-1. 1HNMR(d8-toluene), 253
K: δ 7.49 (m, 4H, Ph), 7.39 (m, 4H, Ph), 6.95-6.88 (m, 12H, Ph),
3.60 (dt, 1H, J 14.0, 10.0, PCH2), 3.04 (dt, 1H, J 14.0, 10.8, PCH2),
2.03 (m, 2H, SCH2), 1.94 (m, 2H, SCH2); 373 K: δ 7.52 (s, 8H, Ph),
6.98 (s, 12H, Ph), 3.54 (t, J 10.0, 2H, PCH2), 2.10 (s, 4H, SCH2).
31P{1H} NMR (CDCl3) 298 K: δ 56.8 (s). Anal. Calcd for
Fe2P2S2O4C31H26: C, 53.14, H, 3.71. Found: C, 53.67, H, 3.84.
Crystallographic data for [Fe2(CO)4( μ-dppm)( μ-edt)]: red trun-
cated octahedron, dimensions 0.42 Â 0.42 Â 0.36 mm, tetragonal,
˚
˚
space group P4(2)/mbc, a = b = 17.2280(13) A, c = 20.132(3) A,
V = 5975.1(11) A , Z = 8, F(000) 2864, dcalc = 1.557 g cm-3, μ =
3
˚
1.254 mm-1; 48 601 reflections were collected, 3790 unique [R(int) =
0.0477], of which 3492 were observed [I > 2.0σ(I)]. At convergence,
R1 = 0.0272, wR2 = 0.0686 [I > 2.0σ(I)] and R1 = 0.0298, wR2 =
0.0699 (all data), for 247 parameters. Crystallographic data have
been deposited with the Cambridge Crystallographic Data Centre,
CCDC No. 751121.
Crystallographic data for [Ru2(CO)4( μ-dppm)( μ-edt)]: yellow
block, dimensions 0.45 Â 0.40 Â 0.36 mm, monoclinic, space group
˚
˚
˚
Cc, a = 19.998(4) A, b = 52.874(11) A, c = 8.7981(19) A, β =
96.520(3) , V=9243(3) A , Z=4, F(000) 4728, dcalc=1.705 g cm-3
,
o
3
˚
μ=1.255 mm-1; 40 263 reflections were collected, 20 988 unique
[R(int)=0.0421], of which 20 988 were observed [I>2.0σ(I)]. At
convergence, R1 = 0.0385, wR2 = 0.0871 [I > 2.0σ(I)] and R1 =
0.0414, wR2 = 0.0886 (all data), for 1103 parameters. Crystallo-
graphic data have been deposited with the Cambridge Crystallo-
graphic Data Centre, CCDC No. 751122.
When this reaction was carried out without added Me3NO
3
2H2O, a number of intermediates were clearly observed spec-
troscopically. Thus, after 30 min complete consumption of
[Fe2(CO)6( μ-edt)] was noted. At this stage the IR spectrum was
consistent with the formation of both [Fe2(CO)5(κ1-dppm)( μ-
edt)] (2047 cm-1) and [Fe2(CO)4(κ2-dppm)( μ-edt)] (2020 cm-1
)
in an approximate 6:1 ratio. Both 1H and 31P NMR spectra were
complex. It was clear from the latter that [Fe2(CO)5(κ1-dppm)-
( μ-edt)] was formed as a mixture of isomers (basal and apical) in
an approximate 2:1 ratio [major, 56.7 (d), -24.9 (d) ppm JPP
105.0 Hz; minor 53.0 (d), -24.5 (d) ppm, JPP 72.4 Hz]. For
Crystallographic data for [Fe2(CO)4( μ-dppm)( μ-SMe)2]: red
block, dimensions 0.26 Â 0.25 Â 0.25 mm, triclinic, space group,
˚
˚
˚
P1, a= 9.287(1) A, b= 10.919(1) A, c= 15.839(2) A, R =
o
3
˚
77.834(2)°, β=84.137(2)°, γ=73.505(2) , V=1504.0(3) A ,
Z=2, F(000) 720, dcalc = 1.551 g cm-3, μ= 1.246 mm-1; 7508

6568 Organometallics, Vol. 29, No. 23, 2010
Hogarth et al.
reflections were collected, 5879 unique [R(int)=0.0146], of
which 5259 were observed [I > 2.0σ(I)]. At convergence, R1=
0.0350, wR2 = 0.1000 [I > 2.0σ(I)] and R1 = 0.0414, wR2 =
0.1261 (all data), for 370 parameters. Crystallographic data
have been deposited with the Cambridge Crystallographic
Data Centre, CCDC No. 798796.
the preparation of [Fe2(CO)4( μ-dppm)( μ-SMe)2], and Prof.
Brian Mann for valuable discussions.
Supporting Information Available: This material is available
free of charge via the Internet at http://pubs.acs.org.
Acknowledgment. We thank The Royal Society (London)
for a short visit fellowship to S.E.K., Dr. Abil Aliev for NMR
support, Miss Faith Ridley for the preparation of [Fe2(CO)4-
( μ-dppm)( μ-SAr)2] (Ar = Ph, p-tolyl) and for carrying out
NMR experiments on these complexes, Mr. David Unwin for
Note Added after ASAP Publication. In the version of this
paper published on the web on November 16, 2010, the captions
within the graphic were incorrect, due to a production error. In
the version of the paper that appears as of December 6, 2010,
Figure 5 appears correctly.