Reactions of [Mo2(u-RC2R)(CO)4Cp2] (R = CO2Me, Cp = η-C5H5) with P2Ph4, PPh2H and R1SH (R1 = Et, Pr', C6H4Me-/; or Bul): Stabilisation of u-vinyl complexes by chelating substituents

Article abstract of DOI:10.1039/b004210m

The dimolybdenum alkyne complex [Mo₂(u-C₂R₂)(CO)₄Cp₂] 1 (R = CO₂Me; Cp = n-C₅H₅) reacts with P₂Ph₄ to afford three major products, which have been identified as the phosphido-bridged vinyl complexes cis- and tram[Mo₂(u-CR=CHR)(u-PPh₂)(CO)₂Cp₂] (two separable isomers, 2 and 3 respectively) and [Mo₂(u-CR=CRCHO)(u-PPh₂)(CO)₂Cp₂] 4. The crystal structure of 3 has been determined and shows that the CO₂Me group attached to the β-carbon of the vinyl ligand is co-ordinated to one metal atom through the carbonyl group, thus forming a five-membered chelate ring. The reaction of 1 with PPh2H in refluxing toluene gave the same three complexes, whereas treatment of 1 with PPh₂H at room temperature in the presence of trimethylamine W-oxide afforded the monosubstituted complex [Mo₂(u-C₂R₂)(CO)₃(PPh ₂H)Cp₂] 6 together with a small amount of 4; thermolysis of 6 also yields 2, 3 and 4. Treatment of 1 with thiols R'SH (R1 = Et, Pr1 or C6H4Me-/>) afforded the complexes [Mo₂(u-CR=CHR)(n-SR')(CO)₂Cp2] 7a-7c which are analogous to 3; the structure of the complex with R¹ = Pr¹ has been determined. In contrast, treatment of 1 with Bu'SH affords the unusual complex [Mo₂(u-S)₂(u-RCH=CHR)Cp₂] 8 in which the alkyne ligand has been hydrogenated to an alkene which is bonded in an r|2 manner to one metal atom and through both CO₂Me groups to the other. The complexes [Mo₂(u-CH=CHR)(u-SR')(CO)₂Cp₂] 10, derived from the methyl propiolate complex [Mo₂(u-HC₂R)(CO)₄Cp₂], are also described. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b004210m

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Reactions of [Mo2(ꢀ-RC2R)(CO)4Cp2] (R ؍ CO2Me, Cp ؍
ꢁ-C5H5) with P2Ph4, PPh2H and R1SH (R1 ؍ Et, Pri, C6H4Me-p
or But): stabilisation of ꢀ-vinyl complexes by chelating substituents
Harry Adams,a Andreas Biebricher,a Sally R. Gay,a Trevor Hamilton,a Paul E. McHugh,a
Michael J. Morris*a and Martin J. Mays*b
a Department of Chemistry, University of Sheffield, Sheffield, UK S3 7HF
b University Chemical Laboratory, Cambridge, UK CB2 1EW
Received 26th May 2000, Accepted 19th July 2000
Published on the Web 4th August 2000
The dimolybdenum alkyne complex [Mo2(µ-C2R2)(CO)4Cp2] 1 (R = CO2Me; Cp = η-C5H5) reacts with P2Ph4 to
afford three major products, which have been identified as the phosphido-bridged vinyl complexes cis- and trans-
[Mo (µ-CR᎐CHR)(µ-PPh )(CO) Cp ] (two separable isomers, 2 and 3 respectively) and [Mo (µ-CR᎐CRCHO)-
᎐
᎐
2
2
2
2
2
(µ-PPh2)(CO)2Cp2] 4. The crystal structure of 3 has been determined and shows that the CO2Me group attached
to the β-carbon of the vinyl ligand is co-ordinated to one metal atom through the carbonyl group, thus forming
a five-membered chelate ring. The reaction of 1 with PPh2H in refluxing toluene gave the same three complexes,
whereas treatment of 1 with PPh2H at room temperature in the presence of trimethylamine N-oxide afforded the
monosubstituted complex [Mo2(µ-C2R2)(CO)3(PPh2H)Cp2] 6 together with a small amount of 4; thermolysis of 6
also yields 2, 3 and 4. Treatment of 1 with thiols R1SH (R1 = Et, Pri or C6H4Me-p) afforded the complexes
[Mo (µ-CR᎐CHR)(µ-SR1)(CO) Cp ] 7a–7c which are analogous to 3; the structure of the complex with R1 = Pri has
᎐
2
2
2
been determined. In contrast, treatment of 1 with ButSH affords the unusual complex [Mo (µ-S) (µ-RCH᎐CHR)Cp ]
᎐
2
2
2
8 in which the alkyne ligand has been hydrogenated to an alkene which is bonded in an η2 manner to one metal atom
and through both CO Me groups to the other. The complexes [Mo (µ-CH᎐CHR)(µ-SR1)(CO) Cp ] 10, derived from
᎐
2
2
2
2
the methyl propiolate complex [Mo2(µ-HC2R)(CO)4Cp2], are also described.
which were separated by a combination of careful column
chromatography and preparative TLC techniques. In order of
elution from a column, the three major products are brown 2,
red 3, and orange-red 4 (Scheme 1).
Introduction
Dinuclear complexes containing bridging phosphido (µ-PR2) or
thiolato (µ-SR) ligands are of continuing interest because the
presence of these ligands has been shown to help maintain the
structural integrity of the dinuclear unit during further reac-
tions.1 We have explored in detail the influence of such ligands
on the organometallic chemistry of a variety of homo- and
hetero-bimetallic centres, with a particular interest in alkyne-
bridged systems. Some time ago, we reported that the reaction
of [Mo2(CO)6Cp2] with tetraphenyldiphosphane led to the bis-
phosphido bridged complex [Mo2(µ-PPh2)2(CO)2Cp2],2 and
subsequently showed that a similar reaction with the but-2-yne
The red product (the highest-yielding of the three) was char-
acterised as [Mo (µ-CR᎐CHR)(µ-PPh )(CO) Cp ] 3 on the
᎐
2
2
2
2
basis of its spectroscopic data and also by crystal structure
determination (see below). Its IR spectrum in KBr shows two
terminal CO peaks (1900 and 1865 cmϪ1), an ester carbonyl
stretch (1659 cmϪ1) and a peak at 1553 cmϪ1 corresponding to
an ester group which is co-ordinated to molybdenum. The mass
spectrum showed a molecular ion envelope at m/z 706, corre-
sponding to the addition of PPh2H and the loss of two carbonyl
ligands. The downfield shift observed in the 31P NMR spectrum
(δ 145.5) is indicative of the presence of a bridging phosphido
group. The organic ligand has been converted from an alkyne
complex [Mo2(µ-C2Me2)(CO)4Cp2] also produced
a bis-
phosphido complex, [Mo2(µ-PPh2)2(CO)(η-C2Me2)Cp2], in
which the alkyne was retained as a terminal ligand.3 In this
paper we describe the reaction of P2Ph4 with the related alkyne
complex [Mo2(µ-C2R2)(CO)4Cp2] 1 (R = CO2Me) which in con-
trast leads to a variety of products, all of which contain only
one phosphido ligand and a bridging vinyl group derived from
the alkyne. In keeping with their structures, these complexes are
also accessible from the reaction of the alkyne complex with
diphenylphosphine. We also provide full details of the structur-
ally analogous thiolate-bridged products which are formed by
the reaction of 1 with thiols, as mentioned in a preliminary
account.4
into a µ-vinyl (CR᎐CHR), as shown by the presence of a signal
᎐
1
at δ 3.37 due to a single proton in the H NMR spectrum.
In addition the 13C NMR shifts for the α-carbon (δ 138.5) and
β-carbon (δ 36.3) are typical for such σ, π-bound vinyls, which
are well known in dinuclear species.
A crystal of complex 3 suitable for X-ray diffraction was
grown by diffusion of hexane into a dichloromethane solution;
the molecular structure is shown in Fig. 1, with selected bond
lengths and angles collected in Table 1. The molecule consists
of a dimolybdenum centre [Mo(1)–Mo(2) 2.9261(5) Å] with
each metal atom bearing a Cp ligand and a carbonyl group;
these are arranged in a trans configuration. The phosphido
bridge is bonded virtually symmetrically, with the Mo(1)–P(1)–
Mo(2) angle of 73.83(3)Њ typical for such an arrangement. The
remaining ligand is the µ-vinyl group, σ-bound to Mo(1) and
π-bound to Mo(2). The carbonyl oxygen of the β-CO2Me sub-
stituent is also joined to Mo(1) [O(3)–Mo(1) 2.215(2) Å], thus
Results and discussion
Reactions with phosphines
The reaction of [Mo2(µ-C2R2)(CO)4Cp2] 1 (R = CO2Me) with
an equimolar amount of tetraphenyldiphosphane in toluene at
reflux produced three major products and several minor ones,
DOI: 10.1039/b004210m
J. Chem. Soc., Dalton Trans., 2000, 2983–2989
This journal is © The Royal Society of Chemistry 2000
2983

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Scheme 1 Reaction of complex 1 with phosphines. Reagents and conditions: (i) P2Ph4 (1 equivalent), toluene, reflux, 43 h; or PPh2H (1 equivalent),
toluene, reflux, 18 h; (ii) Me3NO (3 equivalent), MeCN, r.t., PPh2H (1 equivalent); (iii) toluene, reflux, 2.5 h.
in equilibrium: over a period of 2–3 days, solutions of the pure
isomers re-establish an equilibrium mixture containing a ratio
of approximately 8:1 in favour of 3 by NMR integration. The
same conversion of 2 into 3 occurs more slowly in the solid
state. The nature of the isomerism is uncertain, but the dis-
position of the Cp ligands is a strong possibility, an idea sup-
ported by the fact that whereas the Cp ligands of 3 (and 4)
1
appear as doublets in the H NMR spectra due to small phos-
phorus couplings, those of 2 both appear as singlets. The 13C
NMR spectrum of 2 is very similar to that of 3, the major
difference being that the CO ligands are somewhat shifted to
higher field. Only two CO peaks are observed, thus ruling out
the possibility that 2 contains an additional carbonyl ligand
and converts into 3 by decarbonylation and co-ordination of
the β-CO2Me of the vinyl group. Both isomers are also formed
6
᎐
in the reaction of [Mo (µ-H)(µ-PPh )(CO) Cp ] with RC᎐CR.
᎐
2
2
4
2
The orange-red product 4 was characterised as [Mo2-
(µ-CR᎐CRCHO)(µ-PPh )(CO) Cp ]. Its spectroscopic data are
᎐
2
2
2
also very similar to those of 2 and 3, indicating a related phos-
phido- and vinyl-bridged structure, but with two additional
features: first in the 1H NMR spectrum, the presence of a low-
Fig. 1 Molecular structure of complex 3 in the crystal, showing the
numbering scheme.
field singlet at δ 9.54, and secondly a peak at δ 211.5 in the 13
C
Table 1 Selected bond lengths [Å] and angles [Њ] for complex 3
NMR spectrum. These are due to the aldehyde functionality
which is a β-substituent on the µ-vinyl group and is also co-
ordinated to the metal, forming a five-membered chelate ring.
Of the minor products, two are worthy of mention. The first
of these is a purple complex which we identify as [Mo2O-
Mo(1)–C(24)
Mo(1)–O(3)
Mo(1)–Mo(2)
Mo(2)–C(28)
Mo(2)–P(1)
O(2)–C(24)
O(6)–C(29)
C(27)–C(28)
1.977(4)
2.215(2)
2.9261(5)
2.158(4)
2.4416(10)
1.156(4)
1.220(4)
1.450(5)
Mo(1)–C(28)
Mo(1)–P(1)
Mo(2)–C(23)
Mo(2)–C(27)
O(1)–C(23)
O(3)–C(26)
C(26)–C(27)
C(28)–C(29)
2.170(4)
2.4301(10)
1.949(4)
2.252(4)
1.158(5)
1.247(4)
1.423(5)
1.472(5)
(µ-CH᎐CHR)(µ-PPh )(CO)Cp ] 5 by comparison with several
᎐
2
2
similar complexes prepared both by us and also initially by
Ziegler and co-workers,7 which differ only in the substituents
present on the vinyl ligand. The loss of a CO2Me group during
the reaction is unusual but not unprecedented; the constitution
of the vinyl ligand is unambiguous from the 1H NMR spectrum
which displays two doublets of doublets for the vinylic protons.
The stereochemistry around the vinyl ligand is difficult to assign
with certainty, but probably has the two hydrogens in cis posi-
C(28)–Mo(1)–O(3)
C(24)–Mo(1)–O(3)
C(28)–Mo(1)–Mo(2) 47.28(10)
P(1)–Mo(1)–Mo(2)
C(23)–Mo(2)–P(1)
C(27)–Mo(2)–P(1)
76.20(12)
80.76(12)
C(24)–Mo(1)–P(1)
C(28)–Mo(1)–P(1)
C(24)–Mo(1)–Mo(2) 81.60(11)
C(28)–Mo(2)–C(27)
C(28)–Mo(2)–P(1)
C(23)–Mo(2)–Mo(1) 121.55(11)
P(1)–Mo(2)–Mo(1)
C(26)–O(3)–Mo(1)
O(2)–C(24)–Mo(1)
C(26)–C(27)–C(28) 114.1(3)
C(27)–C(28)–Mo(1) 109.9(2)
83.99(11)
78.09(10)
53.27(2)
94.66(11)
114.56(10)
38.32(13)
78.05(10)
C(28)–Mo(2)–Mo(1) 47.62(9)
52.90(2)
112.3(2)
172.9(3)
tions. The related complex with a µ-CH᎐CHEt ligand displayed
᎐
almost identical shifts and couplings.3 Complex 5 is presumably
formed by the oxidation of the corresponding carbonyl com-
plex by adventitious air; indeed a weak orange band which
Mo(1)–P(1)–Mo(2)
O(1)–C(23)–Mo(2)
O(3)–C(26)–C(27)
73.83(3)
174.5(3)
122.6(3)
Mo(2)–C(28)–Mo(1) 85.10(12)
forming a five-membered chelate ring. These parameters are
very similar to those observed for the related complex [Mo2-
(µ-CH᎐CHCOPh)(µ-PPh )(CO) Cp ] by Knox and co-workers,
᎐
2
2
2
and for the analogous thiolate-bridged complex described
below.5
The brown complex 2 is an isomer of complex 3. Although
the two are easily separated by chromatography, they are in fact
2984
J. Chem. Soc., Dalton Trans., 2000, 2983–2989

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Table 2 Selected bond lengths [Å] and angles [Њ] for complex 7b
gradually converts into purple 5 during elution was observed on
the chromatography column, and we suspect this may be the
precursor complex. The final band eluted from the column can
tentatively be identified as the related oxo complex [Mo2O-
Mo(1)–C(1)
Mo(1)–C(14)
Mo(1)–Mo(2)
Mo(2)–C(13)
Mo(2)–S(1)
O(1)–C(1)
1.952(4)
2.226(4)
2.8621(5)
2.157(4)
2.4661(10)
1.150(6)
1.251(5)
1.460(5)
Mo(1)–C(13)
Mo(1)–S(1)
Mo(2)–C(2)
Mo(2)–O(3)
S(1)–C(19)
O(2)–C(2)
2.151(4)
2.4331(10)
1.979(4)
2.208(3)
1.839(4)
1.146(6)
1.214(5)
1.437(5)
(µ-CR᎐CHR)(µ-PPh )(CO)Cp ] on the basis of the similarity
᎐
2
2
of its 1H spectroscopic data to those of 2 and 3, and the similar-
ity of its 31P shift to that of 5. However the small amount
prepared did not allow 13C NMR or analytical data to be
acquired.
O(3)–C(15)
C(13)–C(14)
O(6)–C(17)
C(14)–C(15)
Since the formation of compounds 2–4 involves the effective
addition of PPh2 and H to the starting material, it was decided
to investigate the reaction of 1 with PPh2H itself. As expected,
this produced the same products, though the yield distribution
of the reaction is noticeably different; from P2Ph4 the major
product is 3, whereas from PPh2H the yields of 3 and 4 are
virtually identical.
C(13)–Mo(1)–C(14)
C(13)–Mo(1)–S(1)
C(1)–Mo(1)–Mo(2) 118.68(13)
S(1)–Mo(1)–Mo(2)
C(13)–Mo(2)–O(3)
C(13)–Mo(2)–S(1)
C(13)–Mo(2)–Mo(1) 48.27(11)
Mo(1)–S(1)–Mo(2)
O(1)–C(1)–Mo(1)
C(14)–C(13)–Mo(2) 109.6(2)
C(15)–C(14)–C(13) 112.6(3)
38.91(13)
82.39(10)
C(1)–Mo(1)–S(1)
C(14)–Mo(1)–S(1)
C(13)–Mo(1)–Mo(2) 48.46(10)
C(2)–Mo(2)–O(3)
C(2)–Mo(2)–S(1)
C(2)–Mo(2)–Mo(1)
S(1)–Mo(2)–Mo(1)
C(15)–O(3)–Mo(2)
O(2)–C(2)–Mo(2)
94.17(13)
119.19(10)
54.79(3)
75.99(12)
81.48(11)
85.02(14)
77.37(12)
79.17(12)
53.72(2)
112.5(2)
172.5(4)
71.49(3)
177.7(4)
Monosubstituted phosphine complexes have been prepared
from alkyne complexes of type 1 by UV irradiation. Recent
work by one of us, however, has shown that a carbonyl ligand
can be removed from 1 by treatment with Me3NO in
acetonitrile; if carried out in the presence of additional ligands
such as P(OMe)3 or ButNC, good yields of the appropriate
monosubstituted complex can be isolated.8 This methodology
was also successful with diphenylphosphine: stirring 1 at room
temperature with an excess of Me3NO in the presence of PPh2H
afforded a 65% yield of [Mo2(µ-C2R2)(CO)3(PPh2H)Cp2] 6,
together with a small amount of 4. The complex showed similar
spectroscopic properties to those previously prepared; two
diagnostic features are the 31P chemical shift (δ 38.4), indicative
of a terminal phosphine ligand rather than a phosphido bridge,
Mo(1)–C(13)–Mo(2) 83.27(14)
O(3)–C(15)–C(14) 122.0(3)
1
and the presence of a doublet at δ 6.50 in the H NMR spec-
trum with a characteristically large coupling of 369 Hz due to
the P–H group. Thermolysis of 6 in refluxing toluene gave 2, 3
and 4, the last of these being the major product, in 2.5 h.
Thermolysis in THF produced a similar yield of 4, accom-
panied by much smaller amounts of 2 and 3, over a period of
4 d.
Reactions with thiols
Treatment of complex 1 with an excess of the thiols R1SH
Fig. 2 Molecular structure of complex 7b in the crystal, showing the
numbering scheme.
(R1 = Et, Pri or p-C6H4Me) afforded the new vinyl complexes
[Mo (µ-CR᎐CHR)(µ-SR1)(CO) Cp ] 7a–7c in good yields
᎐
2
2
2
(Scheme 2). Of these, 7a and 7b exist as two isomers which
isomer and a cis arrangement for the minor; however the dis-
position of the R1 substituent of the thiolate bridge is also a
possibility, and is perhaps more likely in view of the very close
similarity of the spectroscopic data for the two isomers. The
isomer ratios for 7a and 7b are approximately 3:1 and 1.5:1
which may reflect the changing steric bulk of R1, in accord with
the fact that 7c exists as a single isomer.
Crystals of complex 7b suitable for X-ray diffraction were
grown by diffusion of light petroleum into a THF solution. The
molecular structure is shown in Fig. 2, with selected bond
lengths and angles collected in Table 2. The crystal selected
contains only one isomer. The Mo–Mo bond, 2.8621(5) Å, is
shorter than that in 3, and the Mo(1)–S(1)–Mo(2) angle of
71.49(3)Њ in the almost symmetrically bound thiolato bridge is
slightly smaller than in the phosphido group of 3. The geom-
etry within the chelating µ-vinyl ligand is almost identical to
that in 3. As expected, the Cp ligands (and consequently the
carbonyls) occupy a trans arrangement.
In contrast to the reactions of complex 1 with other thiols,
that with ButSH occurred much more rapidly to give the
Scheme 2 Reactions of complex 1 with thiols. Reagents and condi-
tion: (i) R1SH (5 equivalents), toluene, reflux, 21–24 h; (ii) ButSH
(5 equivalents), toluene, reflux, 6 h.
unusual complex [Mo (µ-S) (µ-RCH᎐CHR)Cp ] 8 in 83% yield
᎐
2
2
2
(Scheme 2). Its IR spectrum contained no carbonyl peaks, and
its 1H and 13C NMR spectra were extremely simple, indicating a
highly symmetrical structure, and contained no signals for But
groups. The crystal structure of 8 was reported in our prelimin-
ary communication and confirmed that two bridging sulfido
groups had been formed by incorporation and dealkylation of
could not be separated by column chromatography. The nature
of the isomerism is again uncertain, though by analogy with the
phosphido-bridged species 2 and 3 above it is tempting to
ascribe a trans arrangement of the Cp ligands for the major
J. Chem. Soc., Dalton Trans., 2000, 2983–2989
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two molecules of thiol, and that the alkyne had become hydro-
ing in toluene, this compound underwent P–C bond cleavage,
followed by migration of the phenyl group to a carbonyl ligand
and then migration of the resulting benzoyl group to the alkyne
genated to the cis-alkene dimethyl maleate.4 This ligand is co-
ordinated to one metal through the C᎐C bond, and to the other
᎐
through the carbonyl groups of both CO2Me substituents, thus
ligand to give [Mo {µ-CH᎐CHC(Ph)O}(µ-PPh )(CO) Cp ]. A
᎐
2 2 2 2
acting as a six electron donor overall.
range of phosphines was explored and it was found that, if
PPh2H was used, P–H cleavage took precedence over P–C
cleavage to give a compound analogous to 4. In the reaction of
1 with P2Ph4, we propose that the CO ligand is replaced by a
PPh2 radical formed by thermal dissociation of the diphos-
phine. Abstraction of a hydrogen, presumably from the solvent,
would afford the same products.
᎐
The reactions of the related alkyne complex [Mo (µ-HC᎐
᎐
2
CR)(CO)4Cp2] 9, derived from methyl propiolate, with R1SH
(R1 = Et, Pri or But) were also investigated, and gave rise to
good or moderate yields of the vinyl complexes [Mo(µ-CH᎐
᎐
CHR)(µ-SR1)(CO)2Cp2] 10a–10c with structures analogous to
that of 7 (Scheme 3). Only complex 10b exists as a mixture of
It is noticeable that no products are formed in which the
phosphido group is coupled to the alkyne, despite the fact that
attack of a nucleophilic PPh2 on the electrophilic dimethyl
acetylenedicarboxylate (dmad) is known to be possible. For
example, we have previously shown that thermal reaction of 1
with PPh Cl leads exclusively to [Mo (µ-Cl)(µ-PPh CR᎐CR)-
᎐
2
2
2
(CO)2Cp2] in which P–C bond formation has occurred.11 We
attributed this to the relative tendency of the PPh2 and Cl to
bridge the two metals in the intermediate formed by oxidative
addition of the P–Cl bond. Clearly in the current reaction the
phosphido group can assume the bridging role in preference to
the hydride or formyl ligands, which in turn migrate to the
alkyne.
In the reactions with thiols a similar mechanism is assumed
for the formation of complexes 7 and 10 to that proposed for 2
and 3. It is interesting however that no complexes analogous to
4 were formed in the reactions of 1 with thiols; migration of the
hydride to a CO is evidently disfavoured in this case. The lesser
degree of steric crowding in the thiolate intermediate, due to the
presence of only one substituent R1 as opposed to two phenyl
rings, might account for this.
Perhaps a further indication of a less sterically crowded
environment is the observation that the reactions with thiols
can proceed further. In the case of R1 = But, a complex is
formed which clearly involves addition of two thiols, and in all
of these reactions the compounds [Mo2(µ-S)2(µ-SR1)2Cp2] are
formed in small amounts; amounts which are, however, larger
for the methyl propiolate complexes compared to the more
strongly bound dmad. We have previously shown that the reac-
tion of [Mo2(µ-C2Me2)(CO)4Cp2], in which the alkyne is weakly
bound, with thiols leads exclusively to [Mo2(µ-S)2(µ-SR1)2Cp2],
and indeed this forms a useful route to these compounds.3 The
results here indicate that the pathway for their formation prob-
ably proceeds by way of the sequential oxidative addition of
two thiol molecules, with the transfer of their hydrogen atoms
onto the alkyne ligand to create first a µ-vinyl and than an
alkene. In cases such as R = Me this is then lost, and the reac-
tion can proceed to give [Mo2(µ-S)2(µ-SR1)2Cp2] by addition of
two more thiols. By incorporation of the CO2Me substituents
on the alkyne, the intermediate stages in this process can be
stabilised and isolated, with compounds such as 7 and 10 repre-
senting the addition of one thiol, and complex 8 the addition of
two.
Scheme 3 Reactions of complex 9 with thiols. Reagents and condi-
tions: (i) R1SH (5 equivalents), toluene, reflux, 15–17 h.
isomers, in a ratio of 3:1. The nature of the vinyl ligand is
shown clearly by the presence of two doublets (one at low field,
typical of µ-CH) in the 1H NMR spectrum of each compound;
thus, the hydrogen atom migrates regiospecifically onto the
more substituted end of the alkyne, which in turn relieves steric
crowding at the bridging position in the resulting vinyl ligand. It
is noticeable that as the steric bulk of R1 increases the yield of
10 diminishes and the amount of the by-product [Mo2(µ-S)2-
(µ-SR1)2Cp2] increases. No complex analogous to 8 was
observed.
Possible mechanism of the reactions
In previous papers we have noted that µ-vinyl complexes of
the type [Mo (µ-CR1᎐CHR2)(µ-PPh )(CO) Cp ] (R1, R2 = H,
᎐
2
2
3
2
alkyl, aryl, etc.) cannot be isolated by insertion of alkynes
into [Mo2(µ-H)(µ-PPh2)(CO)4Cp2], unlike the corresponding
µ-PMe2 species.3 The main products of their decomposition are
oxo-complexes such as 5; it appears that the µ-vinyl complexes
are particularly susceptible to oxidation, possibly for steric
reasons. A similar pattern is evident in the thiolate-bridged
series. Thus, Pétillon and co-workers have described how the
complexes [Mo (µ-CMe᎐CHMe)(µ-SR1)(CO) Cp ] (R1 = Me
᎐
2
3
2
or Ph) can be isolated from the reactions of [Mo2(µ-H)(µ-SR1)-
(CO)4Cp2] with but-2-yne, but are readily oxidised to the
corresponding [Mo O(µ-CMe᎐CHMe)(µ-SR1)(CO)Cp ]. Other
᎐
2
2
alkynes led to intractable products.9 The exception for both
classes of bridging ligand appears to be as described here, i.e.
cases where the substituents on the vinyl ligand can co-ordinate
to the metal, thus stabilising the vinyl unit by chelation. The
resulting ligand is a relatively common motif in dinuclear com-
plexes, and examples have been characterised on a wide range
of metal centres.10
Experimental
General experimental techniques were as described in recent
papers from these laboratories.12,13 Infrared spectra were
recorded in CH2Cl2 solution on a Perkin-Elmer 1600 FT-IR
machine, 1H, 13C and 31P NMR spectra in CDCl3 solution on a
Bruker AC250 machine with automated sample-changer or an
AMX400 spectrometer. The 13C-{1H} NMR spectra were rou-
tinely recorded using an attached proton test technique (JMOD
pulse sequence). Chemical shifts are given on the δ scale relative
to SiMe4 (0.0 ppm) for 1H and 13C; the 31P-{1H} NMR spectra
were referenced to 85% H3PO4 (0.0 ppm) with downfield shifts
reported as positive. Mass spectra were recorded on a Fisons/
BG Prospec 3000 instrument operating in fast atom bombard-
ment mode with m-nitrobenzyl alcohol as matrix. Elemental
In terms of the mechanism of the thermal reaction of com-
plex 1 with PPh2H, we propose that the initial step is CO loss
and co-ordination of PPh2H to give 6. Oxidative addition of the
P–H bond could then be followed by the diphenylphosphido
group adopting a bridging position and migration of the
hydride to the alkyne to give a vinyl group, resulting ultimately
in 2 and 3 after co-ordination of the carbonyl of the CO2Me
group. Migration of the hydride to the CO ligand followed by
attack of the resulting formyl on the alkyne would give 4. Com-
plexes related to 4 were first observed by Knox and co-workers,5
who prepared the mono-substituted alkyne complex [Mo2-
(µ-C2H2)(CO)3(PPh3)Cp2] and studied its thermolysis. On heat-
2986
J. Chem. Soc., Dalton Trans., 2000, 2983–2989

View Article Online
analyses were carried out by the Microanalytical Services of
the Department of Chemistry and the University Chemical
Laboratory.
Trimethylamine N-oxide was dehydrated by azeotropic distil-
lation in toluene. The alkyne complexes 1 and 9 were prepared
by the literature procedure.14 Light petroleum refers to the
fraction boiling in the range 60–80 ЊC.
µ-C), 145.3 (d, J = 35, Cipso), 144.6 (d, J = 28 Hz, Cipso), 133.6–
127.3 (m, Ph), 93.9, 92.2 (both s, Cp), 61.1 (s, CCO2Me), 50.9,
50.2 (both s, Me); 31P NMR δ 138.9 (Found: C, 50.60; H, 3.66;
P, 4.09. Calc. for C31H27Mo2O7P: C, 50.68; H, 3.68; P, 4.22%).
MS m/z 706 (M Ϫ COϩ) and 650.
(vii) A small amount of a further red complex was eluted
with methanol and tentatively identified as [Mo O(µ-CR᎐
᎐
2
CHR)(µ-PPh2)(CO)Cp2]. IR (CH2Cl2): 1917s, 1722m and
1676m cmϪ1. H NMR δ 7.92–6.78 (m, 10 H, Ph), 5.76 (d,
J = 0.5, 5 H, Cp), 5.04 (d, J = 1.1, 5 H, Cp), 4.65 (d, J = 2.4 Hz,
1 H), 3.71, 3.47 (both s, 3 H, Me). 31P NMR δ 190.1; MS: m/z
694 and 668.
1
Thermal reaction of [Mo2(ꢀ-C2R2)(CO)4Cp2] 1 with P2Ph4
A solution of PPh2H (0.60 cm3, 3.52 mmol) and PPh2Cl (0.62
cm3, 3.45 mmol) in heptane (150 cm3) was heated to reflux for 3
h. After cooling, the solvent was removed in vacuo to leave
P2Ph4 as a snow-white powder,15 to which was added complex 1
(2.0 g, 3.47 mmol) and toluene (175 cm3). The resulting solution
was heated to reflux for 43 h. After addition of a small amount
of silica, the solvent was removed under vacuum and the resi-
due chromatographed. The following bands were collected. (i)
Green, eluted with light petroleum–dichloromethane (1:1) and
consisting of [Mo2(µ-PPh2)2(CO)2Cp2] (6.7 mg, 0.25%) identi-
fied by comparison with previous data. (ii) Orange, eluted with
same solvent mixture, identity unknown (13.5 mg); readily con-
verts into 5 and is followed by a faint purple zone presumably
consisting of 5. (iii) A large dark brown zone, eluted in CH2Cl2.
This was subjected to further separation by preparative TLC in
CH2Cl2, yielding 239.6 mg (9.8%) of brown solid identified as
Thermal reaction of complex 1 with PPh2H
A solution of complex 1 (1.0 g, 1.74 mmol) in toluene (175 cm3)
was treated with diphenylphosphine (0.3 cm3, 1.73 mmol) and
heated to reflux for 18 h. The solvent was removed and the
residue subjected to column chromatography as above. The
major products were: brown 2 (152.4 mg, 12.4%), eluted in
CH2Cl2; red 3 (393.5 mg, 32.1%), eluted in CH2Cl2; an
unidentified green band (41.2 mg) eluted in CH2Cl2–acetone
(24:1); an unidentified purple zone (75.9 mg), eluted in CH2Cl2–
acetone (9:1); and orange-red 4 (410.0 mg, 32.2%), eluted in a
4:1 mixture of the same solvents.
Synthesis of [Mo2(ꢀ-C2R2)(CO)3(PPh2H)Cp2] 6
cis-[Mo (µ-CR᎐CHR)(µ-PPh )(CO) Cp ] 2.
᎐
2
2
2
2
Data for 2: IR (CH2Cl2) 1929m, 1893s, 1726m and 1656m
Complex 1 (412.9 mg, 0.72 mmol) was dissolved in dry
acetonitrile (40 cm3) and treated with solid anhydrous Me3NO
(178.2 mg, 2.38 mmol) followed by PPh2H (0.25 cm3, 1.47
mmol). The solution was stirred at room temperature for 18 h,
at which point spot TLC monitoring showed the presence of a
single red zone. After addition of silica (5 g) the solvent was
removed in vacuo at room temperature and the residue loaded
onto a chromatography column. Removal of several minor
bands was achieved by gradually changing the eluting solvent
from light petroleum to dichloromethane. Elution with
dichloromethane–acetone (19:1) produced a red band of com-
plex 6 (339.0 mg, 64.4%). Continued elution with a 17:3 mix-
ture of the same solvents gave an orange band of complex 4
(46.5 mg, 8.8%).
1
cmϪ1; H NMR δ 7.85–7.01 (m, 10 H, Ph), 5.46 (s, 5 H, Cp),
4.97 (s, 5 H, Cp), 4.22 (s, 1 H, CH), 3.76, 3.16 (both s, 3 H, Me);
13C NMR δ 236.5 (d, J = 20, CO), 233.9 (d, J = 15, CO), 187.0,
181.3 (both s, CO2Me), 146.1 (d, J = 36, Cipso), 144.4 (d, J = 29
Hz, Cipso), 135.9 (s, µ-C), 134.6–126.9 (m, Ph), 93.1, 91.2 (both s,
Cp), 52.7. 51.4 (both s, Me) and 41.6 (CHCO2Me); 31P NMR
δ 155.2; MS m/z 706 and 678. It was not possible to obtain a
pure sample for elemental analysis as 2 converts into its isomer
3 both in solution and in the solid state.
(iv) Purple, eluted in dichloromethane–acetone (9:1) as a
mixture with the following band which was then separated
by preparative TLC in CH2Cl2. This band is identified as
[Mo O(µ-CH᎐CHCO Me)(µ-PPh )(CO)Cp ] 5 (25.6 mg, 1.2%)
᎐
2
2
2
2
by its spectroscopic properties [IR (CH2Cl2): 1877, 1711 cmϪ1
;
Data for 6: IR (CH2Cl2) 1931s, 1814m and 1682m cmϪ1; H
1
1H NMR δ 9.31 (dd, JHH = 9.0, JPH = 1.0, 1 H, µ-CH), 7.96–
7.03 (m, 10 H, Ph), 5.46 (d, J = 0.7, 5 H, Cp), 4.97 (d,
JHH = 9.0, 1 H, CH), 4.59 (d, J = 1.2 Hz, 5 H, Cp) and 3.64
(s, 3 H, Me); 31P NMR δ 184.5; MS m/z 636 (Mϩ) and 608
(M Ϫ COϩ)].
NMR δ 7.73–7.30 (m, 10 H, Ph), 6.50 (d, J = 369 Hz, 1 H, PH),
5.05 (s, 5 H, Cp), 4.93 (s, 5 H, Cp), 3.64 (s, 3 H, Me) and 3.56 (s,
3 H, Me); 13C NMR δ 238.2 (s, CO), 235.6 (d, J = 13, CO), 230.5
(s, CO), 178.2, 175.8 (both s, CO2Me), 134.3 (d, J = 39, Cipso),
134.0 (d, J = 34 Hz, Cipso), 132.5–127.7 (m, Ph), 92.8, 91.7 (both
s, Cp), 52.2, 51.7 (both s, Me); 31P NMR δ 38.4 (Found: C,
50.38; H, 3.52. Calc. for C31H27Mo2O7P: C, 50.68; H, 3.68%);
MS m/z 735 (M ϩ Hϩ), 703, 679, 651 and 623.
(v) Red, identified as trans-[Mo (µ-CR᎐CHR)(µ-PPh )-
᎐
2
2
(CO)2Cp2] 3. After TLC separation from the previous band, the
yield was 697.5 mg (28.5%). Mp 262 ЊC. IR: (CH2Cl2): 1878s
1
and 1655m; (KBr) 1900, 1865, 1659 and 1553 cmϪ1; H NMR
δ 7.48–7.05 (m, 10 H, Ph), 5.31 (d, J = 1.5, 5 H, Cp), 4.73 (d,
J = 1.1 Hz, 5 H, Cp), 3.46 (s, 3 H, Me), 3.37 (s, 1 H, CH) and 3.05
(s, 3 H, Me); 13C NMR δ 257.8 (d, J = 12, CO), 245.0 (d, J = 9,
CO), 194.4, 180.9 (both s, CO2Me), 145.5 (d, J = 33, Cipso), 145.2
(d, J = 25, Cipso), 138.5 (d, J = 26 Hz, µ-C), 133.6–127.2 (m, Ph),
92.9, 91.6 (both s, Cp), 53.2, 50.4 (both s, Me), 36.3 (s,
CHCO2Me); 31P NMR δ 145.5 (Found: C, 50.96; H, 4.06;
P, 4.19. Calc. for C30H27Mo2O6P: C, 50.99; H, 3.82; P, 4.39%).
MS m/z 706 (Mϩ) and 678 (M Ϫ COϩ).
Thermolysis of complex 6
A solution of complex 6 (162.8 mg, 0.22 mmol) in toluene (30
cm3) was heated to reflux for 2.5 h. Column chromatography
gave 2 and 3 (combined yield 39.9 mg, 25.5%) followed by 4
(56.0 mg, 34.4%). A similar reaction in refluxing THF for 4 d
gave the same products in yields of 4 and 36% respectively.
Reactions of complex 1 with thiols R1SH (R1 ؍ Et, Pri or
C6H4Me-p)
(vi) Red, eluted in dichloromethane–acetone (4:1) and
further purified by preparative TLC in a 9:1 mixture of the
same solvents to remove a small amount of a brown impurity.
This yielded an orange powder of complex [Mo (µ-CR᎐CR-
(a) R1 ؍ Et. A solution of complex 1 (1.00 g, 1.74 mmol) in
toluene (125 cm3) was treated with five equivalents of EtSH
(0.65 cm3, 8.7 mmol) and heated to reflux for 21 h, the progress
of the reaction being monitored by spot TLC. The solvent was
removed, the residue absorbed onto a small amount of silica,
and then loaded onto a chromatography column. Elution with
light petroleum–CH2Cl2 (1:1) afforded a purple band and a
pink band due to small amounts of the two isomers of [Mo2-
(µ-S)2(µ-SEt)2Cp2] (combined yield 140 mg, 16%). Further
᎐
2
CHO)(µ-PPh2)(CO)2Cp2] 4 (207.5 mg, 8.1%). Mp 149–150 ЊC.
1
IR (CH2Cl2): 1928m, 1896s and 1677m cmϪ1; H NMR δ 9.54
(s, 1 H, CH), 7.59–7.04 (m, 10 H, Ph), 5.34 (d, J = 1.6, 5 H, Cp),
4.87 (d, J = 1.1 Hz, 5 H, Cp), 3.62 (s, 3 H, Me) and 3.07 (s, 3 H,
Me); 13C NMR δ 257.2 (d, J = 12, CO), 238.5 (d, J = 9, CO),
211.5 (s, CHO), 179.2, 170.8 (both s, CO2Me), 151.3 (d, J = 27,
J. Chem. Soc., Dalton Trans., 2000, 2983–2989
2987

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elution with CH2Cl2 and acetone (19:1) produced a red band
Reactions of [Mo2(ꢀ-HC2R)(CO)4Cp2] 9 with thiols R1SH
of [Mo (µ-CR᎐CHR)(µ-SEt)(CO) Cp ] 7a (750 mg, 74%). Mp
(R1 ؍ Et, Pri or But)
᎐
2
2
2
1
227–229 ЊC. IR (CH2Cl2): 1905 (sh), 1877 and 1667 cmϪ1. H
NMR (values for minor isomer given in square brackets where
visible): δ 5.28 [5.24], 5.04 [5.02] (both s, 5 H, Cp), 3.39 [3.38] (s,
1 H, CH), 3.36 [3.35], 3.16 [3.14] (both s, 3 H, CO2Me), 2.68
(dq, 1 H of CH2), 2.20 (dq, 1 H of CH2) and 1.04 [0.94] (t, 3 H,
Me); 13C NMR δ 262.2 [264.0], 242.9 [242.8] (both s, CO),
193.3 [192.8], 182.2 [181.5] (both s, CO2Me), 145.3 [145.3]
(s, µ-C), 94.0 [93.3], 92.5 [91.8] (both s, Cp), 53.5 [53.3], 51.0
[51.0] (both s, CO2Me), 39.1 [35.8] (s, CHR), 33.0 [29.7] (s, CH2)
and 17.7 [17.8] (s, Me) (Found: C, 41.37; H, 3.72; S, 5.81. Calc.
for C20H22Mo2O6S: C, 41.25; H, 3.81; S, 5.51%). MS m/z 583
(Mϩ).
(a) R1 ؍ Et. A solution of complex 9 (0.70 g, 1.21 mmol) in
toluene (125 cm3) was treated with EtSH (0.5 cm3, 6.05 mmol)
and heated to reflux for 15 h. The solvent was removed and the
residue absorbed on a small amount of silica. Column chrom-
atography, eluting with light petroleum–CH2Cl2 (7:3) afforded
an orange band from which [Mo (µ-CH᎐CHR)(µ-SEt)(CO) -
᎐
2
2
Cp2] 10a (400 mg, 63%) was obtained. Further elution with a
1:1 mixture of the same solvents gave two weak purple bands
which were identified as the two isomers of [Mo2(µ-S)2(µ-SEt)2-
Cp2] (combined yield 110 mg, 18%). Data for 10a: mp 221–
1
224 ЊC; IR(CH2Cl2) 1867 (sh) and 1859 cmϪ1; H NMR δ 7.51
(d, J = 4 Hz, 1 H, µ-CH), 5.28, 5.09 (both s, 5 H, Cp), 3.42 (s,
3 H, CO2Me), 3.19 (d, J = 4, 1 H, CH), 2.26 (dq, J = 13 and 6.5,
1 H of CH2), 2.01 (dq, J = 13 and 6.5, 1 H of CH2) and 1.17
(t, J = 6.5 Hz, Me); 13C NMR δ 263.2, 248.3 (both s, CO), 192.4
(s, CO2Me), 146.0 (s, µ-C), 92.4, 92.3 (both s, Cp), 53.1 (s,
CO2Me), 35.4 (s, CHR), 35.2 (s, CH2) and 17.5 (s, Me) (Found:
C, 41.16; H, 3.68; S, 6.30. Calc. for C18H19Mo2O4S: C, 41.24; H,
3.85; S, 6.12%); MS m/z 525 (Mϩ).
(b) R1 ؍ Pri. In a similar manner, reaction of complex 1 (1.0
g, 1.74 mmol) with PriSH (5 equivalents, 0.80 cm3, 8.7 mmol)
for 24 h afforded a small amount of [Mo2(µ-S)2(µ-SPri)2Cp2] (60
mg, 6%) and a small red band of unidentified material, followed
by red [Mo (µ-CR᎐CHR)(µ-SPri)(CO) Cp ] 7b (690 mg, 67%),
᎐
2
2
2
which was eluted from the chromatography column with
CH2Cl2. Mp 206–208 ЊC. IR (CH2Cl2): 1910 (sh), 1884 and 1668
cmϪ1. 1H NMR (values for minor isomer given in square brack-
ets where visible): δ 5.45 [5.29], 5.10 [5.06] (both s, 5 H, Cp),
3.75 [3.71] (s, 3 H, CO2Me), 3.54 [3.88] (s, 1 H, CHR), 3.42
[3.43] (s, 3 H, CO2Me), 3.18 [2.59] (m, 1 H, CHMe2), 1.20 [1.02]
and 0.85 [0.94] (both d, J = 7 Hz, 3 H, Me); 13C NMR δ 262.1
[263.9], 244.1 [243.1] (both s, CO), 193.2 [192.7], 182.0 [180.3]
(both s, CO2Me), 145.7 [140.2] (s, µ-C), 94.1 [93.3], 92.7
[91.7] (both s, Cp), 53.5 [53.3], 51.0 [51.0] (both s, CO2Me), 40.5
[44.5] (s, CHR), 38.1 [36.4] (s, CH), 27.6 [27.1] and 25.4 [25.4]
(both s, Me) (Found: C, 39.13; H, 3.83; S, 4.76. Calc. for
C21H24Mo2O6SؒCH2Cl2: C, 38.76; H, 3.82; S, 4.70%). MS: m/z
598 (M ϩ Hϩ).
(b) R ؍ Pri. In a similar manner, complex 9 (0.70 g, 1.21
mmol) reacted with PriSH (0.6 cm3, 6.0 mmol) in refluxing tolu-
ene over 16 h to give 240 mg (37%) of orange-red [Mo2(µ-
CH᎐CHR)(µ-SPri)(CO) Cp ] 10b, and 190 mg (29%) of the
᎐
2
2
combined isomers of purple [Mo2(µ-S)2(µ-SPri)2Cp2], separated
as above. Data for 10b: mp 170–172 ЊC; IR(CH2Cl2) 1890 (sh)
and 1859 cmϪ1 1H NMR (values for minor isomer given
;
in square brackets where visible) δ 7.61 [6.99] (d, J = 4, 1 H,
µ-CH), 5.37 [5.27], 5.09 [5.07] (both s, 5 H, Cp), 3.40 [3.41] (s, 3
H, CO2Me), 3.19 [3.30] (d, J = 4 Hz, CHR), 2.37 (m, CHMe2),
0.99 [0.94], 0.94 [0.86] (both d, J = 7 Hz, Me); 13C NMR δ 263.4,
249.5 (both s, CO), 192.5 (CO2Me), 146.6 [141.4] (µ-C), 92.8
[92.4], 92.7 [91.8] (both s, Cp), 53.2 [53.1] (s, CO2Me), 42.3
[43.8] (s, CH), 27.7 [27.0], 25.4 [25.6] (both s, Me) (Found: C,
42.34; H, 4.17; S, 5.81. Calc. for C19H21Mo2O4S: C, 42.39; H,
4.12; S, 4.96%); MS m/z 538 (Mϩ).
(c) R1 ؍ C6H4Me-p. In an analogous manner, complex 1
(1.16 g, 2.01 mmol) reacted with toluene-p-thiol (1.25 g, 10
mmol) in refluxing toluene over 24 h to give, on column chro-
matography, several minor bands, followed by the dark red
2
6
4
2
2
(c) R ؍ But. In a similar manner, complex 9 (0.5866 g, 1.13
mmol) reacted with ButSH (0.65 cm3, 5.6 mmol) in refluxing
toluene over 17 h to give 211.4 mg (34%) of orange-red [Mo2-
major product, [Mo (µ-CR᎐CHR)(µ-SC H Me-p)(CO) Cp ]
᎐
7c (640 mg, 50%), which was eluted with CH2Cl2. Mp 209–
211 ЊC. IR (CH2Cl2): 1910 (sh), 1884 and 1734 cmϪ1; 1H NMR
δ 6.82 (s, 4 H, C6H4), 5.38, 4.65 (both s, 5 H, Cp), 3.70 (s, 3 H,
CO2Me), 3.53 (s, 1 H, CH), 3.34 (s, 3 H, CO2Me) and 2.18 (s, 3
H, Me); 13C NMR δ 261.7, 244.1 (both s, CO), 193.0, 180.8
(both s, CO2Me), 141.1 (s, µ-C), 139.4–128.3 (m, C6H4), 94.0,
93.5 (both s, Cp), 53.4, 51.2 (both s, CO2Me), 36.3 (s, CHR) and
20.8 (s, Me) (Found: C, 46.43; H, 3.60; S, 4.98. Calc. for
C25H24Mo2O6S: C, 46.58; H, 3.75; S, 4.97%). MS: m/z 647
(M ϩ Hϩ).
(µ-CH᎐CHR)(µ-SBut)(CO) Cp ] 10c, followed by the two iso-
᎐
2
2
mers of purple [Mo2(µ-S)2(µ-SBut)2Cp2] (117.9 mg, 18.5%),
eluted with CH2Cl2–light petroleum (1:1) and CH2Cl2 respec-
tively. Data for 10c: mp 173–176 ЊC; IR(CH2Cl2) 1885 (sh) and
1
1858 cmϪ1; H NMR δ 7.83 (d, J = 4, 1 H, µ-CH), 5.42, 5.09
(both s, 5 H, Cp), 3.40 (s, 3 H, CO2Me), 3.09 (d, J = 4 Hz, 1 H,
CH) and 1.13 (s, 9 H, Me); 13C NMR δ 263.3, 250.8 (both s,
CO), 192.5 (s, CO2Me), 147.4 (s, µ-C), 93.0, 92.4 (s, Cp), 53.2
(s, CO2Me), 48.0 (CMe3) and 32.2 (s, CMe3) (Found: C, 43.86;
H, 4.46; S, 6.00. Calc. for C20H23Mo2O4S: C, 43.49; H, 4.38;
S, 5.80%). MS: m/z 552 (Mϩ).
Reaction of complex 1 with ButSH
A solution of complex 1 (1.0 g, 1.74 mmol) in toluene (125 cm3)
was treated with ButSH (1.0 cm3, 8.8 mmol) and heated to
reflux. After 2 h the solution had turned brown and spot TLC
showed almost complete reaction; reflux was continued for 4 h.
The solvent was removed and the residue chromatographed. A
weak pink-purple band due to one isomer of [Mo2(µ-S)2(µ-
SBut)2Cp2] was obtained by elution with light petroleum and
CH2Cl2 (1:1). Careful elution with CH2Cl2 separated the sec-
ond isomer of this compound as a small red-purple band, fol-
Crystal structure determinations of complexes 3 and 7b
Crystal data for the two complexes are in Table 3. Data col-
lected were measured on a Bruker Smart CCD area detector
with an Oxford Cryosystems low temperature system. Cell
parameters were refined from the setting angles of 160 (θ range
2.29–28.29Њ) for 3 or 969 reflections (θ 1.96 to 28.32Њ) for 7b.
Reflections were measured from a hemisphere of data collected
of frames each covering 0.3Њ in ω. Of the reflections measured,
all of which were corrected for Lorentz and polarisation effects
and for absorption by semiempirical methods based on
symmetry-equivalent and repeated reflections, those independ-
ent reflections which exceeded the significance level |F|/
σ(|F|) > 4.0 were used in refinement. The structures were solved
by direct methods and refined by full matrix least squares
methods on F2. Hydrogen atoms were placed geometrically
lowed closely by a large brown band of [Mo (µ-S) (µ-RCH᎐
᎐
2
2
CHR)Cp2] 8 (770 mg, 83%) which was then eluted with CH2Cl2
and acetone (19:1). Mp 197–199 ЊC. IR(CH2Cl2): 1552 cmϪ1. 1H
NMR: δ 6.04, 6.00 (both s, 5 H, Cp), 3.44 (s, 6 H, Me) and 3.29
(s, 2 H, CH); 13C NMR δ 174.7 (s, CO2Me), 99.3, 97.2 (both s,
Cp), 52.1 (s, CO2Me) and 38.2 (CH) (Found: C, 37.08; H, 3.79;
S, 11.39. Calc. for C8H9MoO2S: C, 36.24; H, 3.42; S, 12.09%).
MS: m/z 530 (Mϩ).
2988
J. Chem. Soc., Dalton Trans., 2000, 2983–2989

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Table 3 Summary of crystallographic data for complexes 3 and 7b
for M. J. Morris at Cambridge (1986–1987), during which time
this work was commenced, and for a studentship (S. R. G.).
A. B. is an Erasmus student from the University of Heidelberg
(1999–2000).
3
7b
Empirical formula
Formula weight
C30H27Mo2O6P
706.37
C21H24Mo2O6S
596.34
T/K
Crystal system
Space group
150(2)
Monoclinic
P21/n
150(2)
Monoclinic
P21/n
References
1 F. Y. Pétillon, P. Schollhammer, J. Talarmin and K. W. Muir, Coord.
Chem. Rev., 1998, 178–180, 203.
2 T. Adatia, M. J. Mays, M. McPartlin, M. J. Morris and P. R.
Raithby, J. Chem. Soc., Dalton Trans., 1989, 1555.
3 G. Conole, M. McPartlin, M. J. Mays and M. J. Morris, J. Chem.
Soc., Dalton Trans., 1990, 2359.
4 H. Adams, N. A. Bailey, S. R. Gay, T. Hamilton and M. J. Morris,
J. Organomet. Chem., 1995, 493, C25.
5 G. R. Doel, N. D. Feasey, S. A. R. Knox, A. G. Orpen and
J. Webster, J. Chem. Soc., Chem. Commun., 1986, 542; N. D. Feasey,
Ph.D. Thesis, University of Bristol, 1984.
6 M. J. Mays and M. J. Morris, unpublished work.
7 K. Endrich, R. Korswagen, T. Zahn and M. L. Ziegler, Angew.
Chem., Int. Ed. Engl., 1982, 21, 919; Angew. Chem. Suppl., 1982,
1906.
8 J. C. Stichbury, M. J. Mays, J. E. Davies, P. R. Raithby and G. P.
Shields, J. Chem. Soc., Dalton Trans., 1997, 2309.
9 P. Schollhammer, F. Y. Pétillon, S. Poder-Guillou, J. Talarmin,
K. W. Muir and D. S. Yufit, J. Organomet. Chem., 1996, 513, 181.
10 J. D. King, M. J. Mays, G. E. Pateman, P. R. Raithby, M. A. Rennie,
G. A. Solan, N. Choi, G. Conole and M. McPartlin, J. Chem. Soc.,
Dalton Trans., 1999, 4447 and references therein.
a/Å
b/Å
c/Å
9.3859(7)
17.7550(14)
16.2444(13)
93.291(2)
2702.6(4)
4
1.031
17492
6317
9.9710(6)
15.3616(9)
14.0659(9)
92.4760(10)
2152.5(2)
4
1.298
13023
5053
β/Њ
V/Å3
Z
µ/mmϪ1
Reflections collected
Independent reflections
[R(int) = 0.0662]
0.0460, 0.1013
0.0650, 0.1081
[R(int) = 0.1183]
0.0487, 0.1181
0.0589, 0.1266
Final R1, wR2 [I > 2σ(I)]
(all data)
and refined with a riding model (including torsional freedom
for methyl groups) and with Uiso constrained to be 1.2 (1.5 for
methyl groups) times Ueq of the carrier atom. Refinement con-
verged at the final R values shown with allowance for the ther-
mal anisotropy of all non-hydrogen atoms. Weighting schemes
2
2
w = 1/[σ2(Fo ) ϩ (0.0633P)2 ϩ 0.00P] (for 3) and 1/[σ2(Fo ) ϩ
(0.1102 P)2 ϩ 25.74 P] (for 7b) where P = (Fo2 ϩ 2 Fc2)/3 were
used in the latter stages of refinement. Complex scattering
factors were taken from the program package SHELXTL16 as
implemented on the Viglen pentium computer.
11 G. Conole, K. A. Hill, M. McPartlin, M. J. Mays and M. J. Morris,
J. Chem. Soc., Chem. Commun., 1989, 688.
12 H. Adams, L. J. Gill and M. J. Morris, Organometallics, 1996, 15,
464.
CCDC reference number 186/2094.
See http://www.rsc.org/suppdata/dt/b0/b004210m/ for crys-
tallographic files in .cif format.
13 H. Adams, N. A. Bailey, L. J. Gill, M. J. Morris and F. A.
Wildgoose, J. Chem. Soc., Dalton Trans., 1996, 1437.
14 W. I. Bailey, Jr., M. H. Chisholm, F. A. Cotton and L. A. Rankel,
J. Am. Chem. Soc., 1978, 100, 5764.
15 W. Kuchen and H. Buchwald, Chem. Ber., 1958, 91, 2871.
16 SHELXTL, An integrated system for solving and refining crystal
structures from diffraction data (Revision 5.1), Bruker AXS
Ltd., Madison, WI, 1997.
Acknowledgements
We thank the SERC (now the EPSRC) for postdoctoral support
J. Chem. Soc., Dalton Trans., 2000, 2983–2989
2989