The reactions of the anions [Cp2(CO)4Mo2(u-PRR')]- (R, R' = H, Ph) towards chloroarsines and chlorophosphines; synthesis of complexes containing both bridging phosphide and arsenido groups

Article abstract of DOI:10.1039/b001193m

Deprotonation of the complexes [CpCOMoμ-PR'R'Xμ-H)] (R1 and R2 = H or Ph; Cp = cyclopentadienyl) in THF yields the related anions [Cp₂(CO)4Mo₂(μ-PR'R2)r. The reactivity of these anions towards Ph2PCl, (EtO)2PCl, Ph₂AsCl and Me₂AsCl has been investigated. The outcome of the reactions with chlorophosphines depends on the nature of the substituents on the bridging phosphido ligand. Thus reaction of [Cp₂(CO)4Mo₂(μ-PH2)]~ with Ph2PCl yields [Cp₂(CO)4Mo₂{μ-P(H)PPh₂}(μ-H)], whereas the analogous reaction with [Cp₂(CO)4Mo₂(μ-PPhR)]~ yields [Cp₂(CO),Mo₂(μ-PPh₂)(μ-PPhR)] (R = H, .v = 4; R = Ph, x = 2). Thermolysis of [Cp₂(CO)4Mo₂(μ-PPhH)(μ-PPh₂)J in toluene yields [Cp₂(CO)2Mo₂(μ-PPhH)(μ-PPh₂)] and [Cp₂(CO)(O)Mo₂(μ-PPhH)(μ-PPh₂)]. In contrast, the reaction of [Cp₂(CO)4Mo₂(μ-PR'R2)]~ with chloroarsines is not dependent on the nature of the R groups either on the phosphorus or arsenic atoms, yielding [Cp₂(CO)4Mo₂(μ-PR'R2)(μ-AsR32)] in all cases. These complexes are the first example of transition metal compounds containing both a bridging phosphido and a bridging arsenide group. The crystal structures of [Cp₂(CO)4Mo₂{μ-P(H)PPh₂}(μ-H)], [Cp₂(CO)4Mo₂(μ-PPhH){μ-P(OEt)2}], and [Cp₂(CO)4)Mo₂(μ-PH2)(μ-AsMe2)] are reported. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b001193m

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The reactions of the anions [Cp2(CO)4Mo2(ꢀ-PRRЈ)]؊ (R, RЈ ؍ H,
Ph) towards chloroarsines and chlorophosphines; synthesis of
complexes containing both bridging phosphido and arsenido groups
John E. Davies, Neil Feeder, Caspar A. Gray, Martin J. Mays* and Anthony D. Woods
Department of Chemistry, Lensfield Road, Cambridge, UK CB2 1EW.
E-mail: mjm14@cus.cam.ac.uk
Received 14th February 2000, Accepted 6th April 2000
Deprotonation of the complexes [Cp2(CO)4Mo2(µ-PR1R2)(µ-H)] (R1 and R2 = H or Ph; Cp = cyclopentadienyl) in
THF yields the related anions [Cp2(CO)4Mo2(µ-PR1R2)]Ϫ. The reactivity of these anions towards Ph2PCl, (EtO)2PCl,
Ph2AsCl and Me2AsCl has been investigated. The outcome of the reactions with chlorophosphines depends on the
nature of the substituents on the bridging phosphido ligand. Thus reaction of [Cp2(CO)4Mo2(µ-PH2)]Ϫ with Ph2PCl
yields [Cp2(CO)4Mo2{µ-P(H)PPh2}(µ-H)], whereas the analogous reaction with [Cp2(CO)4Mo2(µ-PPhR)]Ϫ yields
[Cp2(CO)xMo2(µ-PPh2)(µ-PPhR)] (R = H, x = 4; R = Ph, x = 2). Thermolysis of [Cp2(CO)4Mo2(µ-PPhH)(µ-PPh2)] in
toluene yields [Cp2(CO)2Mo2(µ-PPhH)(µ-PPh2)] and [Cp2(CO)(O)Mo2(µ-PPhH)(µ-PPh2)]. In contrast, the reaction
of [Cp2(CO)4Mo2(µ-PR1R2)]Ϫ with chloroarsines is not dependent on the nature of the R groups either on the
phosphorus or arsenic atoms, yielding [Cp2(CO)4Mo2(µ-PR1R2)(µ-AsR3 )] in all cases. These complexes are the first
2
example of transition metal compounds containing both a bridging phosphido and a bridging arsenido group. The
crystal structures of [Cp2(CO)4Mo2{µ-P(H)PPh2}(µ-H)], [Cp2(CO)4Mo2(µ-PPhH){µ-P(OEt)2}], and
[Cp2(CO)4)Mo2(µ-PH2)(µ-AsMe2)] are reported.
temperature proceeds somewhat more slowly, giving [Cp2-
(CO)4Mo2(µ-PPhH)(µ-PPh2)] 8 in high (70–80%) yield. The
reaction with 6 at room temperature again proceeds differently,
giving [Cp2(CO)2Mo2(µ-PPh2)2] 10 in moderate (50–60%) yield
Introduction
The chemistry of dinuclear complexes containing bridging
phosphido groups has been the subject of much study.1,2 The
reactions of anionic complexes of this type, which should be
(Scheme 1).
more nucleophilic than related uncharged species, have, how-
A possible set of reaction pathways leading to the formation
ever, received less attention.3–5
Herein we report the results of the nucleophilic reactions of a
series of dinuclear anionic complexes [Cp2(CO)4Mo2(µ-
of the observed products is shown in Scheme 2. It is proposed
that in each case the first step in the reaction is attack of the
anionic metal centre present in 4–6 on the electrophilic phos-
PR1R2)]Ϫ (R1, R2 = H, Ph) with Ph2PCl, (EtO)2PCl, Ph2AsCl and
phorus atom to give the neutral intermediate A in which the
Me2AsCl. It has been found that the nature of the R substitu-
PPh2 unit is terminally bonded to one of the metal centres.
ents on the µ-phosphido group in the anions has a strong effect
on the product distribution obtained from reaction with
Ph2PCl, but that there is no such effect on reaction with R2AsCl
Reaction from then on can follow one of two pathways. When
the anion is [Cp2(CO)4Mo2(µ-PH2)]Ϫ 4 reductive elimination
with the formation of a P–P bond presumably occurs to give the
34-electron intermediate B. Subsequent oxidative addition of a
(R = Me or Ph). We also report on attempts to decarbonylate
the series of complexes [Cp2(CO)4Mo2(µ-PR1R2)(µ-AsR3 )] (R1
2
P–H bond in a manner similar to that reported by Hartung
and R2 = H or Ph; R3 = Me or Ph); here again the product
et al.6 would then regenerate a bridging hydride and phosphido
distribution appears to be dependent on the nature of the R
substituents on the µ-phosphido group.
group to give 7.
In the reactions involving 5 and 6 the reductive elimination
step leading to P–P bond formation does not occur, perhaps for
steric reasons. It may be that the transition state required for
reductive elimination is unattainable due to steric clashes of
the bulky phenyl groups on each phosphorus atom. Instead, the
terminally-bonded phosphide phosphorus atom in intermedi-
ate A (Scheme 2) donates its lone pair to the second metal
centre, causing metal–metal bond cleavage, to yield [Cp2(CO)4-
Mo2(µ-PPhR)(µ-PPh2)].
In the case of 5 (R = Ph) reaction stops at this point and
[Cp2(CO)4Mo2(µ-PPhH)(µ-PPh2)] 8 is obtained. The spectro-
scopic characterisation of 8 did not define the structure
unambiguously; the NMR data do not distinguish between
the two possible structural isomers [Cp2(CO)4Mo2(µ-PPhH)-
(µ-PPh2)] and [Cp2(CO)4Mo2(η1 :η1-PPhHPPh2)]. In order to
characterise the new complex unambiguously a single crystal
X-ray analysis was clearly needed, but no crystals suitable for
such an analysis could be grown. Hence 5 was also reacted with
Results and discussion
(a) Reaction of deprotonated [Cp2(CO)4Mo2(ꢀ-PR1R2)(ꢀ-H)]
(R1 ؍ R2 ؍ H 1; R1 ؍ H, R2 ؍ Ph 2; R1 ؍ R2 ؍ Ph 3) with
Ph2PCl
Deprotonation of a solution of 1 or 2 in THF using a slight
n
excess of BuLi proceeds rapidly at Ϫ78 ЊC to yield a purple
solution of the corresponding anions [Cp2(CO)4Mo2(µ-PHR)]Ϫ
(R = H 4 or Ph 5). In contrast, deprotonation of 3 is somewhat
n
slower, requiring stirring of a THF solution of 3 with BuLi
at room temperature for 1 h to yield green [Cp2(CO)4Mo2-
(µ-PPh2)]Ϫ 6.
Complex 4 reacts rapidly with Ph2PCl at Ϫ78 ЊC giving
[Cp2(CO)4Mo2{µ-P(H)PPh2}(µ-H)] 7 in low (10–20%) yield in
addition to unreacted starting material and decomposition
products. The analogous reaction of 5 with Ph2PCl at room
DOI: 10.1039/b001193m
J. Chem. Soc., Dalton Trans., 2000, 1695–1702
This journal is © The Royal Society of Chemistry 2000
1695

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Scheme 1 Reactivity of 1–3 towards nBuLi and Ph2PCl.
Scheme 2 Proposed reaction pathway for the formation of 7–11 from 4–6 and Ph2PCl. (i) Ph2PCl; (ii) reductive elimination; (iii) oxidative addition;
(iv) decarbonylation.
(EtO)2PCl to yield [Cp2(CO)4Mo2(µ-PPhH){µ-P(OEt)2}] 9 the
structure of which was elucidated by a single crystal X-ray
diffraction study (see below).
In the reaction of 6 with Ph2PCl, which gives the known
compound [Cp2(CO)2Mo2(µ-PPh2)2] 10, it is assumed that
[Cp2(CO)4Mo2(µ-PPh2)2] is first formed as an intermediate and
that decarbonylation then occurs. Complex 10, which is the sole
product of the reaction, was identified by comparison of its
1H, 31P NMR and IR spectroscopic data with the literature
values.7,8 In a previous study it was found that thermolysis of
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Table 1 Selected bond lengths (Å) and angles (Њ) for complexes 7 and 9
7
9
Mo(1)–P(1)
Mo(1)–H(100)
Mo(1)–Mo(2)
Mo(2)–H(100)
Mo(2)–P(1)
P(1)–H(1)
P(1)–P(2)
P(2)–C(1)
P(2)–C(7)
2.419(2)
1.76(6)
3.278(1)
1.82(6)
2.407(2)
1.299
2.188(2)
1.853(6)
1.848(7)
Mo(1)–P(1)
Mo(1)–P(2)
Mo(2)–P(1)
Mo(2)–P(2)
P(1)–C(15)
P(1)–H(100)
P(2)–O(10)
P(2)–O(11)
2.5290(9)
2.4801(9)
2.5047(9)
2.4967(8)
1.825(3)
1.29(3)
1.637(2)
1.635(2)
Mo(1)–Mo(2)–H(100) 23(2)
Mo(1)–P(1)–Mo(2) 107.32(3)
Mo(1)–P(2)–Mo(2) 109.12(3)
Mo(1)–Mo(2)–P(1)
Mo(1)–P(1)–H(1)
Mo(1)–P(1)–P(2)
Mo(1)–P(1)–Mo(2)
Mo(2)–P(1)–H(1)
Mo(2)–P(1)–P(2)
Mo(2)–Mo(1)–P(1)
P(1)–H(100)–Mo(1)
P(1)–H(100)–Mo(2)
P(1)–P(2)–C(1)
47.38(4)
108.9
119.96(8)
85.56(5)
108.9
122.47(9)
47.06(4)
70(2)
70(2)
103.3(2)
98.7(2)
Mo(1)–P(1)–H(100) 105.9(1)
Mo(1)–P(1)–C(15) 117.62(1)
Mo(1)–P(2)–O(10) 119.18(9)
Mo(1)–P(2)–O(11) 106.77(8)
Fig. 1 Molecular structure of [Cp2(CO)4Mo2{µ-P(H)PPh2}(µ-H)] 7.
[Cp(CO)3Mo(PPh2)] also led directly to the formation of 10,
suggesting that decarbonylation of the assumed intermediate
[Cp2(CO)4Mo2(µ-PPh2)2] is facile.8
Mo(2)–P(1)–H(100) 117.4(1)
Mo(2)–P(1)–C(15) 115.71(1)
Mo(2)–P(2)–O(10) 102.39(8)
Mo(2)–P(2)–O(11) 118.24(9)
These observations prompted us to investigate whether 8
could be converted to an analogue of 10. Overnight thermolysis
of a solution of 8 in toluene did indeed yield [Cp2(CO)2Mo2-
(µ-PPhH)(µ-PPh2)] 11 as the sole product in near quantitative
yield. During the conversion of 8 to 11 a faint red band was
sometimes noticed on the TLC plate, especially when the sol-
vent was removed on a rotary evaporator rather than on a
vacuum line prior to separation. It seemed likely that this red
complex was an oxo complex derived from replacement of a
carbonyl ligand in 11 by an oxygen atom since such reactions
are well documented.8,9 Accordingly, a small portion of 11 in
dichloromethane was stirred in an open vessel for several hours
leading to a colour change from green to blue. A small amount
each of two new red complexes was then obtained after TLC, in
addition to several ionic products which were inseparable and
not fully characterised. It was found that the yield of the two
red complexes was considerably increased by carrying out the
reaction in a sealed, air-filled vessel rather than in the open air.
The new red complexes were assigned on the basis of spectro-
scopic data (see below) as trans- and cis-[Cp2(CO)(O)Mo2-
(µ-PPhH)(µ-PPh2)] 12 (trans) and 13 (cis).
P(1)–P(2)–C(7)
constant is more typical of a one-bond interaction than a two-
bond one,10 and initially led us to speculate that 8 had the
formula [Cp2(CO)4Mo2(η1 :η1-PPhHPPh2)], but the presence of
1
such a P–P bond was not compatible with the observed H
NMR spectrum, which suggests a 1JP-H and a 3JP-H interaction.14
Additionally, the observed resonances in the 31P NMR spec-
trum have very different 31P chemical shifts from that of the
diphosphane ligand in the known complex [(CO)4Co2-
{µ-C2(CO2Me)2}(µ-P2Ph4)].15 The observed shifts are more
typical of phosphido groups bridging two non-bonded metal
centres;16 thus the upfield shift of the two resonances as com-
pared to those of 7 and 1–3 reflects the opening of the Mo–P–
Mo angle caused by the absence of a metal–metal bond.12
Although bis-phosphido bridged complexes are common there
are few examples of complexes which contain two inequivalent
phosphido bridges and therefore there is little information on
2
the P–P coupling in such systems.17 The range of quoted JP-P
coupling constants varies from 5 to 160 Hz, but it should be
noted that in all these reported cases a metal–metal bond is
present which will affect the geometry at the phosphorus atom
and therefore the coupling constant. Additionally, Grim has
shown that the most important term in determining the magni-
tude of the geminal phosphorus coupling for the complexes
[(CO)4Mo(DPPM)] is the through-metal term,18 and clearly
the presence of a metal–metal bond will alter the degree of
through-metal coupling.
(b) Characterisation of complexes 7–13
1
Complexes 7–13 have been characterised by H, 31P NMR, IR
spectroscopy and FAB MS. In addition 7 and 9 have each been
the subject of a single crystal X-ray diffraction study.
The 31P NMR spectrum of 7 exhibits two doublets at δ 105.49
and Ϫ9.23 which are assigned respectively to the bridging
phosphorus atom (µ-PHPPh2) and to the uncoordinated phos-
phorus atom (µ-PHPPh2). The observed 1JP-P coupling of 314.3
Hz is typical of a one-bond interaction.10 The presence of a
bridging hydride was confirmed by a doublet resonance at
δ Ϫ12.61 (2JP-H = 36 Hz) in the 1H NMR spectrum.
In the 1H NMR spectrum of 8 a doublet of doublets at δ 5.31
integrating to 1 proton is assigned to the P–H proton. Both the
3
1JP-H coupling constant of 322.6 Hz and the JP-H constant of
7.9 Hz are in the expected range.14 Two resonances at δ 5.40 and
4.89, each integrating to 5 protons, are assigned to the non-
equivalent cyclopentadienyl groups.
The molecular structure of 7 is shown in Fig. 1, with selected
bond lengths and angles being listed in Table 1. The Mo(1)–
P(1)–Mo(2) angle of 85.56(5)Њ is typical of metal–phosphorus–
metal systems in which a metal–metal single bond is present
between the two metal centres.1,11 Additionally, this small M–P–
M bond angle is as expected in the light of 31P NMR data for
related three-membered phosphacycles: the smaller the M–P–
M bond angle, the more downfield is the phosphorus resonance
in the 31P NMR spectrum.12 The two MoPH planes lie at an
angle of 171.5Њ to each other, indicating a slight deviation from
planarity of the Mo2PH core. The recorded P(1)–P(2) bond
length of 2.188(2) Å falls within the range of documented
phosphorus–phosphorus single bond lengths.13
The 31P NMR spectrum of 9 shows two doublets at δ 195.79
2
and Ϫ142.43 with a JP-P of 413.9 Hz, again this coupling is
unusually high. The 1H NMR spectrum shows that the two OEt
groups are in different environments, as confirmed by the single
crystal X-ray analysis (see below).
The molecular structure of 9 is shown in Fig. 2 and selected
bond lengths and angles are listed in Table 1. The Mo(1)–P(1)–
Mo(2) and Mo(1)–P(2)–Mo(2) bond angles of 107.32(3) and
109.12(3)Њ respectively are typical for phosphido-bridged metal
complexes in which there is no metal–metal bond.16,17 The two
MoP2 planes lie at an angle of 31.6Њ to each other, indicating a
highly folded butterfly structure. The two phosphorus atoms
bridge the metal atoms unsymmetrically, with P(1) approaching
The 31P NMR spectrum of 8 exhibits two doublets at
δ Ϫ91.33 and Ϫ142.17 with 2JP-P of 309 Hz. This P–P coupling
J. Chem. Soc., Dalton Trans., 2000, 1695–1702
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The NMR spectroscopic data do not allow any formal
differentiation between the trans and cis isomers 12 and 13.
However assignment is made by comparison of the spectro-
scopic data with those of the known complexes trans-[Cp2-
(CO)(O)Mo2(µ-PPh2)2] and cis-[Cp2(CO)(O)Mo2(µ-PPh2)2]. In
these known complexes it was found that the trans isomer had
the higher 31P NMR shift, and additionally the higher carbonyl
stretching frequency.8 In the present case it was found that the
31P NMR spectra showed two doublets for each isomer, which
had moved downfield by ca. 60 ppm compared to the parent
complex 11; a similar shift on formation of such oxo species has
1
been previously reported.8,9 In the H NMR spectra it is again
only possible to locate one half of the double doublet corre-
sponding to the P–H proton. A 1H coupled 31P NMR spectrum
again confirmed the presence of the P–H proton. It is interest-
1
ing to note that the trans isomer 12 has a slightly higher JP-H
coupling constant of 367.8 Hz, as compared to 337.6 Hz for the
cis isomer 13. The carbonyl stretching frequencies of 1845 and
1822 cmϪ1 for 12 and 13 respectively are very low for terminal
carbonyl groups. This drop reflects the increased electron
density at the Mo centres caused by loss of a carbonyl group.
Fig. 2 Molecular structure of [Cp2(CO)4Mo2(µ-PPhH){µ-P(OEt)2}] 9.
Mo(2) more closely, whereas P(2) approaches Mo(1). Addition-
ally, the molybdenum–phosphorus bond lengths to the bridging
(EtO)2P ligand [Mo(1)–P(2) 2.4801(9) Å; Mo(2)–P(2) 2.4967(8)
Å] are significantly shorter than the corresponding bond
lengths to the phenylphosphido ligand [Mo(1)–P(1) 2.5290(9)
Å; Mo(2)–P(1) 2.5047(9) Å], reflecting the fact that the (EtO)2P
group is a better σ-donor and π-acid than the phenylphosphido
group.
(c) Reaction of 4–6 with chloroarsines
Reaction of 4–6 with the chloroarsine Me2AsCl proceeds
rapidly at Ϫ78 ЊC to yield [Cp2(CO)4Mo2(µ-PR1R2)(µ-AsMe2)]
(R1 = R2 = H 14; R1 = H,R2 = Ph 15; R1 = R2 = Ph 16) as the
sole isolable product in high (65–80%) yield. The outcome of
these reactions showed no dependence on the substituents on
the µ-phosphido group. In order to determine whether or not
the lack of other products analogous to those obtained in the
reaction with Ph2PCl was associated with the lower steric
demands of the less bulky methyl groups the series of reactions
was repeated using Ph2AsCl. Again only one product was
obtained in each case, affording the complexes [Cp2(CO)4-
Mo2(µ-PR1R2)(µ-AsPh2)] 17–19 (R1 = R2 = H 17; R1 = H, R2 =
Ph 18; R1 = R2 = Ph 19).
It is assumed that the initial reaction of 4–6 with R2AsCl
yields one intermediate [Cp2(CO)4Mo2(µ-PR1R2)(σ-AsR2)],
similar to intermediate A in Scheme 1. In contrast to the course
of the reaction with Ph2PCl, reductive elimination at one of the
metal centres to form a phosphorus–arsenic bond does not
occur, even with the less sterically bulky Me2AsCl. This is pre-
sumably because arsenic–phosphorus bonds of the type which
would be formed are relatively weak. Instead the terminally
bound arsenic atom donates its lone pair to the second metal
centre, forming a bridging arsenido group with concomitant
metal–metal bond scission.
The 31P NMR spectrum of 11 shows two double resonances
at δ 96.78 and 34.84; these are assigned as µ-PPh2 and µ-PPhH
respectively and are significantly downfield from those of the
2
parent complex 8. Furthermore the JP-P of 8.9 Hz is greatly
reduced from the corresponding P–P coupling of 309 Hz
recorded for 8. The M–P–M angle of 69Њ in 10 may be com-
pared with the average angle of 108Њ in 9 and it is plausible to
assume that such a decrease in angle also occurs on conversion
of 8 to 11, thus accounting for the downfield shift in the phos-
phorus resonances. Surprisingly there is little precedent in the
literature for the observed decrease in the P–P coupling con-
stant which accompanies the formation of the multiple metal–
metal bond in 11. To the authors’ knowledge there exists only
one other case in which metal–metal bonds of differing order
are supported by inequivalent phosphido bridging ligands.
The complexes [(CO)6Fe2(µ-PtBu2)(µ-PPh2)] and [(CO)5Fe2(µ-
PtBu2)(µ-PPh2)], which contain a single and double metal–
2
metal bond respectively, show very similar JP-P coupling
constants of 29.5 and 56.9 Hz.19 However, it should be noted
that these two complexes contain a similar Fe2P2 core geometry:
both are essentially planar with the P2Fe planes lying respec-
tively at an angle of 178 and 169Њ to each other, whereas in the
present case 8 and 9 are butterfly type complexes and 10 and 11
possess planar Mo2P2 cores. This flattening of the core is pre-
sumably necessary to allow the large degree of metal–metal
interaction present in 10 and 11.
To the authors’ knowledge complexes 14–19 represent the
first known examples of complexes in which two metal centres
are bridged by both a phosphido and arsenido group. One
related complex containing a phosphinidine ligand and an
arsenido group, [Cp(CO)8MoCo2(µ3-PtBu)(µ-AsMe2)] has pre-
viously been obtained by Vahrenkamp from the reaction of
[(CO)9Co3(µ3-PtBu)] with [Cp(CO)3Mo(AsMe2)].20 The Co2Mo
triangle in this complex is capped by a PtBu group, and a
Co–Mo edge is bridged by the arsenido group.
1
The H NMR spectrum of 11 exhibits a multiplet at δ 7.69–
7.18 which is assigned to phenyl protons, as well as to half of
the double doublet due to the P–H proton; the observable part
of this double doublet resonates at δ 5.87 (3JP-H = 2.1 Hz). In
order to be sure that the P–H proton was correctly assigned a
31P NMR spectrum with proton coupling was recorded. This
(d) Characterisation of complexes 14–19
1
clearly shows a JP-H coupling of 369.3 Hz for the phosphorus
Complexes 14–19 have been characterised by 1H NMR, 31P
NMR, IR spectroscopy, by FAB MS spectrometry and by C,H
microanalysis. The presence of a large amount of arsenic in the
sample precluded microanalytical results for phosphorus being
obtained.
Complex 14 has been the subject of a single crystal X-ray
diffraction study and the molecular structure of 14 is shown in
Fig. 3 with bond lengths and angles being listed in Table 2. The
Mo2AsP core is best described as a butterfly structure with no
hinge As–P bond; the two MoPAs planes lie at an angle of 145Њ
to each other. The Mo ؒ ؒ ؒ Mo separation of 4.12 Å clearly
atom resonating at δ 34.84. Two Cp signals are observed in the
1H NMR spectrum at δ 5.36 and 5.33. There are two possible
isomers for 11 in which the Cp rings either lie mutually cis or
trans, but only two Cp signals were observed in solution. The
geometry of 11 is therefore assumed to be identical to that of 10
in which the Cp rings are located trans to each other.8 The
infrared spectrum of 11 shows one carbonyl stretch at 1871
cmϪ1, indicating a large amount of electron density at the metal
centres, and an associated high degree of metal–ligand back-
bonding.
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Table 2 Selected bond lengths (Å) and angles (Њ) for 14
Mo(1)–As(1)
Mo(1)–P(1)
Mo(2)–P(1)
2.610(3)
2.497(7)
2.512(7)
Mo(2)–As(1)
As(1)–C(5)
As(1)–C(6)
2.597(3)
1.94(2)
1.97(2)
Mo(1)–As(1)–Mo(2)
Mo(1)–P(1)–Mo(2)
Mo(1)–As(1)–C(5)
Mo(2)–As(1)–C(5)
C(5)–As(1)–C(6)
104.60(1)
110.7(3)
109.0(8)
115.4(8)
98.8(1)
Mo(1)–As(1)–C(6)
Mo(2)–As(1)–C(6)
As(1)–Mo(1)–P(1)
As(1)–Mo(2)–P(1)
117.6(7)
112.0(7)
64.3(2)
64.3(2)
Scheme 3 Reactivity of 1–3 towards nBuLi and R2AsCl (R = Me or
Ph).
Fig. 3 Molecular structure of [Cp2(CO)4Mo2(µ-PH2)(µ-AsMe2)] 14.
gradual colour change from orange to dark green after which
spot TLC revealed the presence of three new products. How-
ever, attempts to separate these products by preparative TLC
using either silica or alumina plates led to substantial decom-
position and to the reformation of starting material. In the case
of reaction with 18 it was possible to isolate a trace amount of a
new red complex. The infrared spectrum of this new complex
revealed only one absorption in the carbonyl region at 1832
cmϪ1, and on this basis the complex is tentatively formulated
as [Cp2(CO)(O)Mo2(µ-PPhH)(µ-AsPh2)] 20 although a full
spectroscopic analysis could not be undertaken due to the low
yield.
By contrast thermolysis of a toluene solution of 19 led to the
formation of a green solution after several hours and chrom-
atographic separation of the products was possible. Three
new complexes [Cp2(CO)2Mo2(µ-PPh2)(µ-AsPh2)] 21 (60–70%
yield), trans-[Cp2(CO)(O)Mo2(µ-PPh2)(µ-AsPh2)] 22 (2–3%
yield) and cis-[Cp2(CO)(O)Mo2(µ-PPh2)(µ-AsPh2)] 23 (2–3%
yield) were obtained.
represents a non-bonding interaction, and the two Cp groups
are arranged trans to the Mo–Mo vector. The Mo–As–Mo and
Mo–P–Mo bond angles of 104.6(1) and 110.7(3)Њ are typical for
ligand-bridged complexes in which there is no metal–metal
bond between the two metal centres.21,16 The two Mo–As separ-
ations (Mo(1)–As(1) 2.610(3); Mo(2)–As(1) 2.597(3) Å) are
almost identical within experimental error as are the two P–Mo
separations (Mo(1)–P(1) 2.497(7); Mo(2)–P(1) 2.512(7) Å).
The 1H NMR spectrum of 14 shows one resonance at δ 5.30
integrating to 10 protons which is assigned to the Cp groups. A
doublet at δ 2.22 (1JP-H 299.8 Hz) is assigned to the P–H protons
and a singlet resonance at δ 1.52 integrating to 6 protons
is assigned to the AsMe2 protons. Likewise, the 1H NMR
spectrum of 16 exhibits only one methyl resonance at δ 1.58
thus indicating that these complexes are fluxional. A wing
flapping mechanism, similar to that proposed by Keller and
Vahrenkamp,21 would result in the two methyl groups of AsMe2
becoming equivalent in both 14 and 16, likewise the R groups
of the PR2 moiety would also become equivalent on the NMR
It has been previously shown that decarbonylation of bis-
phosphido-bridged molybdenum complexes is dependent on
the steric properties of the R groups on the bridging ligand.
Thus Hayter’s compound [Cp2(CO)4Mo2(µ-PMe2)2] was not
reported to decarbonylate7,8 and Heck has shown that [(η5 :η5-
C5H4SiMe2C5H4)(CO)4Mo2(µ-PMe2)] loses only one carbonyl
ligand on heating to yield [(η5 :η5-C5H4SiMe2C5H4)(CO)3-
Mo2(µ-PMe2)].22 Furthermore Böttcher et al. reported that the
1
timescale. In the H NMR spectrum of 15 two methyl reson-
ances are observed at δ 1.58 and 1.57 reflecting the fact that
even with wing flapping fluxionality the two methyl groups are
always in different environments due to the two different sub-
stituents on the µ-phosphido group. Complexes 15 and 18 both
exhibit two Cp signals, which indicates that the Cp groups lie
trans to each other in solution. It is reasonable to assume that
this holds true for 14, 16, 17 and 19, and indicates that the
solution structure of 14 is the same as its solid state structure.
The 31P NMR spectra of 14–19 all show a very upfield singlet
resonance, which reflects the large M–P–M bond angle in these
butterfly complexes, and also suggests an increased electron
density at the phosphorus atom as compared to the related bis-
phosphido-bridged species which show similar M–P–M bond
angles but whose phosphorus resonances have a less upfield
chemical shift.
bis-phosphido-bridged di-iron clusters [(CO)6Fe2(µ-PR1 )-
2
(µ-PR2 )] would decarbonylate to give [(CO)5Fe2(µ-PR1 )-
2
2
(µ-PR2 )], complexes which contain a formal iron–iron double
2
bond, only when both R1 and R2 were bulky groups such as tBu
and Ph.19 These observations go some way towards explaining
why no new products were obtained in the thermolysis reac-
tions of 14–17. However, as previously shown, complex 8
decarbonylates on reflux to give 11. Accordingly if steric influ-
ences were the sole determining factor it might be expected that
18 would also decarbonylate to yield stable products.
Decarbonylation of bis-arsenido-bridged complexes has been
less well explored than decarbonylation of phosphido-bridged
analogues. The complex [Cp2(CO)4Mo2(µ-AsMe2)2] was not
reported to decarbonylate,7 nor were the complexes [(CO)8-
Re2(µ-AsPh2)2] or [(CO)4Ir2(µ-AstBu2)2],23 all having been
formed under conditions which might have been expected to
(e) Attempted decarbonylation of 14–19
Complexes 14–19 were thermolysed to determine whether
or not they would undergo decarbonylation in a similar way to
the analogous bis-phosphido-bridged complexes (Scheme 3).
Thermolysis of solutions of 14–18 for several days caused a
J. Chem. Soc., Dalton Trans., 2000, 1695–1702
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Table 3 Crystallographic data for the complexes 7, 9 and 14a
Compound
7
9
14
Formula
M
C26H22Mo2O4P2
652.26
C24H26Mo2O6P2
664.27
C16H18AsMo2O4P
572.07
Crystal system
Space group
Monoclinic
P21/n
Monoclinic
P21/c
Orthorhombic
P212121
a/Å
b/Å
c/Å
14.222(6)
10.378(4)
17.861(6)
104.16(3)
2556.1(16)
4
9.7396(5)
17.1917(7)
15.346(1)
97.401(3)
2548.1(2)
4
10.9454(4)
21.547(6)
8.022(5)
β/Њ
V/Å3
1891.8(15)
4
3.162
Z
µ/mmϪ1
1.137
1.147
Reflections collected
Independent reflections
4674
4484
7464
4492
3954
3002
Rint = 0.0407
R1 = 0.0438
wR2 = 0.1008
R1 = 0.0660
wR2 = 0.1109
Rint = 0.0265
R1 = 0.0307
wR2 = 0.0637
R1 = 0.0496
wR2 = 0.0705
Rint = 0.1010
R1 = 0.0814
wR2 = 0.1652
R1 = 0.1662
wR2 = 0.2083
Final R indices [I > 2σ(I)]
R indices (all data)
a Data in common: graphite-monochromated Mo-Kα radiation, λ = 0.71073 Å; T = 180(2) K.
lead to decarbonylation. A series of complexes [(CO)xMMЈ-
(µ-AsMe2)2] (M, MЈ = Fe, x = 6; M, MЈ = Cr, Mo, x = 8;
M = Fe, MЈ = Cr, Mo, x = 7) which already formally contain
one metal–metal bond were likewise not reported to decarb-
onylate.24 It is concluded that decarbonylation of bis-
arsenido-bridged complexes is difficult to achieve even when
the R substituents at the bridging arsenido ligands are very
bulky groups. It may be that decarbonylation is more
difficult for complexes containing a µ-AsR2 group than a µ-PR2
group because of the fact that the former is a poor π-acid
ligand.
Preparative TLC was carried out on 1 mm silica plates pre-
pared at the University of Cambridge. Column chromato-
graphy was performed on Kieselgel 60 (70–230 mesh).
Unless otherwise stated, all reagents were obtained
from commercial suppliers and used without further purifi-
cation. 1–3,1,3 Me2AsCl25,26 and Ph2AsCl27 were prepared by
the literature method.
Crystal structure determinations
Data for 7 and 14 were collected by the ω/2θ scan method on a
Rigaku AFC7R four-circle diffractometer. Data for the com-
plex 9 were collected on a Nonius Kappa CCD diffractometer.
All data were collected at 180(2) K using an Oxford Cryostream
cooling apparatus.
For 7 the P–H hydrogen atom was initially placed in a calcu-
lated position (P–H 1.29 Å) and allowed to ride on the phos-
phorus atom with an isotropic displacement parameter fixed at
U = 0.10 Å2.
For 14 the crystals were of poor quality and the data are poor
(Rint = 0.10). For this structure the light atoms (C,O) were
refined with isotropic temperature factors. The P–H protons
were not located in the final difference map: coordinates for
these two atoms are not included in the table of atomic
coordinates.
The decarbonylation of 19 leads to a large increase in the
amount of electron density present at the metal centres, this
being reflected in the unusually low stretching frequency of the
remaining terminal carbonyl ligands which occurs between
1847 and 1821 cmϪ1
.
We therefore propose that decarbonylation will only occur,
and lead to stable products, in mixed arsenido and phosphido
bridged complexes if both the bridging phosphido and arsenido
groups are good π-acids, as is the case in 19. The nature of the
substituents at the bridging phosphido group is especially
important in any event since bridging arsenides are significantly
poorer π-acids than bridging phosphides. Thus in the present
series of reactions decarbonylation only leads to stable prod-
ucts when sufficient electron density can be removed from the
metal centres by the co-ligands.
Table 3 shows crystallographic data for complexes 7, 9 and
14.
The 31P NMR spectra of 20–23 all show a considerable
downfield shift compared to the starting complex 19, which
indicates that the M–P–M bond angle has been decreased con-
siderably in 20–23, this being necessary to allow the metals to
approach within bonding distance. The 1H NMR spectra of 21,
22 contain multiplet peaks due to the phenyl protons as well as
two resonances due to the inequivalent Cp rings.
CCDC reference number 186/1930.
Seehttp://www.rsc.org/suppdata/dt/b0/b001193m/forcrystal-
lographic files in .cif format.
(i) Reaction of [Cp2(CO)4Mo2(ꢀ-PHR)(ꢀ-H)] with nBuLi
A solution of [Cp2(CO)4Mo2(µ-PHR)(µ-H)] (R = H 1, R = Ph
2) (300 mg, 0.64 mmol 1, 300 mg, 0.57 mmol 2) in THF (60 ml)
was cooled to Ϫ78 ЊC and 1.1 equiv. of 1.6 M nBuLi in hexane
(0.45 ml 1; 0.4 ml 2) was added dropwise over 5 minutes
during which time the solution turned a deep purple to give
[Cp2(CO)4Mo2(µ-PHR)]Ϫ (R = H 4, R = Ph 5). In each case in
Experimental
Unless otherwise stated all experiments were carried out under
an atmosphere of dry, oxygen-free nitrogen, using conventional
Schlenk line techniques, and solvents freshly distilled from the
appropriate drying agent. NMR spectra were, unless otherwise
stated, recorded using a Bruker DRX 250 spectrometer, with
1
situ H NMR spectroscopy revealed that no bridging hydride
was present. The solutions were used with no further purifi-
cation or spectroscopic analysis.
SiMe4 as an external standard for 1H spectra, and H3PO4 for 31
P
spectra; all spectra were recorded in CDCl3. Infrared spectra
were, unless otherwise stated, recorded in hexane solution in 0.5
mm NaCl solution cells, using a Perkin-Elmer 1710 Fourier-
Transform spectrometer. FAB mass spectra were obtained
using a Kratos Concept instrument, with 3-nitrobenzyl alcohol
as a matrix.
(ii) Reaction of [Cp2(CO)4Mo2(ꢀ-PPh2)(ꢀ-H)] with nBuLi
To a solution of [Cp2(CO)4Mo2(µ-PPh2)(µ-H)] 3 (300 mg, 0.5
mmol) in THF (60 ml) was added 1.1 equiv. of 1.6 M nBuLi in
hexane (0.35 ml) over 5 minutes. The solution was stirred at
room temperature for 1 h during which time the solution turned
1700
J. Chem. Soc., Dalton Trans., 2000, 1695–1702

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a deep green to give [Cp2(CO)4Mo2(µ-PPh2)]Ϫ 6 as the sole
product. The solution was used with no further purification or
spectroscopic analysis.
δ 7.69–7.18 [m, 15H, Ph], 6.60 [dd, 1J(PH) 369.3, 3J(PH) 2.1 Hz,
1H, PH], 5.36 [s, 5H, Cp], 5.33 [s, 5H, Cp]; 31P, δ 96.78 [d, 2J(PP)
2
8.9, µ-PPh2], 34.84 [d, J(PP) 8.9 Hz, µ-PPhH]; m/z 673(Mϩ),
644 (Mϩ Ϫ CO), 615 (Mϩ Ϫ 2CO) (Found: C 53.05, H 4.12, P
8.73; C30H26Mo2O2P2 requires C 53.26, H 3.88, P 9.16%).
(iii) Reaction of 4–6 with Ph2PCl
A solution of the metal anion (300 mg, 0.64 mmol 4; 300 mg,
0.57 mmol 5; 300 mg, 0.5 mmol 6) in THF (60 ml) was cooled
to Ϫ78 ЊC and Ph2PCl (1.1 equiv.) was added dropwise over
5 minutes.
(vi) Oxidation of 11
A solution of 11 (100 mg, 0.15 mmol) in CH2Cl2 was stirred in a
sealed, air filled flask for 4 h, during which time the solution
turned brown. The solvent was removed, the residue was
dissolved in the minimum CH2Cl2 and applied to the base of
TLC plates. Elution with 3:2 CH2Cl2 :hexane yielded trans-
[Cp2(CO)(O)Mo2(µ-PPhH)(µ-PPh2)] (29 mg, 32%) 12 and
cis-[Cp2(CO)(O)Mo2(µ-PPhH)(µ-PPh2)] (10 mg, 10%) 13.
For 4. The solution was then stirred for 30 minutes, during
which time the solution turned a dark brown. The solvent was
removed in vacuo, and the residue was dissolved in the mini-
mum CH2Cl2 and applied to the base of TLC plates. Elution
with 1:1 CH2Cl2 :hexane yielded a trace of starting material 1
and [Cp2(CO)4Mo2{µ-P(H)PPh2}(µ-H)] 7 (83 mg, 20%). Suit-
able crystals for single X-ray diffraction were grown by slow
For 12. νmax
(CH2Cl2)/cmϪ1 (CO) 1845; NMR: 1H, δ 8.36–7.11
1 3
˜
[m, 15H, Ph], 6.83 [dd, J(PH) 367.8, J(PH) 1.9 Hz, 1H, PH],
5.24 [s, 5H, Cp], 4.82 [s, 5H, Cp]; 31P, δ 173.55 [d, J(PP) 6.54,
2
evaporation of a CH2Cl2 :hexane solution of 7 at Ϫ20 ЊC.
µ-PPh2], 102.54 [d, J(PP) 6.54 Hz, µ-PPhH]; m/z 661(Mϩ)
2
1
ν˜ max
(CH2Cl2)/cmϪ1 (CO) 1933(vs), 1872(s); NMR: H, δ 7.88–
1
2
(Found: C 52.46, H 4.03, P 8.81; C29H26Mo2O2P2 requires C
51.5, H 3.87, P 9.16%).
7.07 [m, 10H, Ph], 5.54 [dd, J(PH) 320, J(PH) 10.2, 1H,
3
µ-PH], 5.11 [s, 5H, Cp], 4.69 [d, J(PH) 1.38, 5H, Cp], Ϫ12.61
[dd, J(PH) 36, J(PH) 1 Hz, 1H, µ-H]; 31P, δ 105.49 [d, J(PP)
2
3
1
For 13. νmax
(CH2Cl2)/cmϪ1 (CO) 1822; NMR: 1H, δ 8.32–7.15
1 2
˜
1
314.3, µ-PHPPh2], Ϫ9.23 [d, J(PP) 314.3 Hz, µ-PHPPh2]; m/z
664 (Mϩ), 578 (Mϩ Ϫ 3CO) (Found: C 46.75, H 3.31, P 9.19;
[m, 15H, Ph], 6.41 [dd, J(PH) 337.6, J(PH) 1.2 Hz, 1H, PH],
5.02 [s, 5H, Cp], 4.91 [s, 5H, Cp]; 31P, δ 172.19 [d, J(PP) 5.47,
2
C26H22Mo2O4P2 requires C 47.57, H 3.38, P 9.44%).
µ-PPh2], 95.95 [d, 2J(PP) 5.47 Hz, µ-PPhH]; m/z 661(Mϩ);
microanalysis for 13 was not recorded.
For 5. The solution was allowed to warm to RT and stirred
overnight. The solvent was removed in vacuo, the residue was
dissolved in the minimum CH2Cl2 and applied to the base of
TLCplates. Elutionwith1:1CH2Cl2 :hexaneyielded[Cp2(CO)4-
Mo2(µ-PPhH)(µ-PPh2)] 8 (330 mg, 80%) as the sole isolable
(vii) Reaction of 4–6 with R2AsCl
A solution of the metal anion (300 mg, 0.64 mmol 4; 300 mg,
0.57 mmol 5; 300 mg, 0.5 mmol 6) in THF (60 ml) was cooled to
Ϫ78 ЊC and R2AsCl (R = Me or Ph 0.9 equiv.) was added
dropwise over 5 minutes. The resulting mixture was stirred for a
further 1/2 h at Ϫ78 ЊC during which time the solution colour
changed from purple to a clear orange. The solution was then
filtered through a silica pad and washed with a small amount of
hexane. After removal of solvent in vacuo the residue was dis-
solved in the minimum CH2Cl2 and applied to the base of TLC
plates.
product. νmax
˜
/cmϪ1 (CO) 1954(m), 1942(vs), 1879(s), 1867(m);
1
NMR: 1H, δ 7.6–7.2 [m, 15H, Ph], 5.31 [dd, J(PH) 322.6,
3J(PH) 7.9 Hz, 1H, PH], 5.40 [s, 5H, Cp], 4.89 [s, 5H, Cp]; 31P,
2
2
δ Ϫ91.33 [d, J(PP) 309, µ-PPh2], Ϫ142.17 [d, J(PP) 309 Hz,
µ-PPhH]; m/z 730 (Mϩ), 673 (Mϩ Ϫ 2CO) (Found: C 52.06,
H 3.79, P 7.54; C32H26Mo2O4P2 requires C 52.46, H 3.58, P
8.46%).
For 6. A similar procedure was followed as for 5 to yield
[Cp2(CO)4Mo2(µ-PPh2)2] 10 (224 mg, 60%). Spectroscopic data
were in accordance with literature values.8
For 4. Elution with 1:1 CH2Cl2 :hexane yielded a trace of
starting material 1 and [Cp2(CO)2Mo2(µ-PH2)(µ-AsMe2)] 14
(249 mg, 68%) or [Cp2(CO)2Mo2(µ-PH2)(µ-AsPh2)] 17 (329 mg,
74%). Slow evaporation of a CH2Cl2 :hexane solution of 14 at
0 ЊC yielded crystals suitable for an X-ray diffraction analysis.
(iv) Reaction of 5 with (EtO)2PCl
Using an identical procedure to that for the reaction of 5 with
Ph2PCl reaction of 5 with 1.1 equiv. of (EtO)2PCl gave
[Cp2(CO)4Mo2(µ-PPhH){µ-P(OEt)2}] 9 (242 mg, 64%) as the
sole isolable product. Suitable crystals for single X-ray diffrac-
tion were grown by slow evaporation of a CH2Cl2 :hexane solu-
14: νmax
˜
(CH2Cl2)/cmϪ1 (CO) 1929(vs), 1857(s); NMR: 1H,
1
δ 5.30 [s, 10H, Cp], 2.22 [d, J(PH) 299.8 Hz, 2H, µ-PH2],
1.52 [s, 6H, AsCH3]; 31P, δ Ϫ249.44 [s, µ-PH2]; m/z 572 (Mϩ),
544 (Mϩ Ϫ CO) (Found: C 33.38, H 3.05; AsC16H18Mo2O4P
requires C 33.34, H 3.15%).
tion of 9 at Ϫ20 ЊC. νmax
/cmϪ1 (CO) 1962(s), 1941(vs), 1890(s),
˜
17: νmax
/cmϪ1 (CO) 1956(m), 1945(vs), 1887(s), 1872(s);
˜
1
1871(s); NMR: H (400 MHz), δ 7.71–7.3 [m, 5H, Ph], 5.37 [s,
NMR: 1H, δ 7.83–7.28 [m, 10H, Ph], 5.15 [s, 10H, Cp], 3.85 [d,
1J(PH) 355.6 Hz, 1H, PH]; 31P, δ Ϫ240.04 [s, µ-PH2]; m/z 806
(Mϩ), 750 (Mϩ Ϫ 2CO) (Found: C 45.64, H 3.29; AsC26H22-
Mo2O4P requires C 44.58, H 3.17%).
1
3
5H, Cp], 5.06 [s, 5H, Cp], 3.92 [dd, J(PH) 312.7, J(PH) 19.5,
3
3
1H, PH], 4.09 [qd, J(HH) 6.9, J(PH) 3.3, 2H, POCH2], 3.79
[qd, 3J(HH) 7, 3J(PH) 2.7, 2H, POCH2], 1.42 [t, 3J(HH) 7, 3H,
POCH2CH3], 1.35 [t, J(HH) 6.9 Hz, 3H, POCH2CH3]; 31P,
3
δ 195.79 [d, 2J(PP) 413.9, µ-P(OEt)2], Ϫ142.43 [d, 2J(PP) 413.9
Hz, µ-PPhH]; m/z 668 (Mϩ), 640 (Mϩ Ϫ CO), 612 (Mϩ Ϫ 2CO)
(Found: C 43.10, H 3.92, P 9.06; C24H26Mo2O6P2 requires C
43.12, H 3.92, P 9.27%).
For 5. Elution with 3:2 CH2Cl2 :hexane yielded a trace of
starting material 2 and [Cp2(CO)2Mo2(µ-PPhH)(µ-AsMe2)] 15
(284 mg, 77%) or [Cp2(CO)2Mo2(µ-PPhH)(µ-AsPh2)] 18 (352
mg, 80%).
(v) Thermolysis of 8
1
15. νmax
˜
/cmϪ1 (CO) 1952(m), 1938(vs), 1882(s), 1866(m); H,
A solution of 8 (200 mg, 0.27 mmol) in toluene (60 ml) was
refluxed for 16 h during which time the solution colour changed
from orange to green. The solvent was removed in vacuo, the
residue was dissolved in the minimum CH2Cl2 and applied to
the base of TLC plates. Elution with 3:2 CH2Cl2 :hexane
yielded [Cp2(CO)2Mo2(µ-PPhH)(µ-PPh2)] 11 (155 mg, 90%) as
δ 7.56–7.22 [m, 5H, Ph], 5.28 [s, 5H, Cp], 5.24 [s, 5H, Cp], 4.61
1
[d, J(PH) 309 Hz, 1H, PH], 1.58 [s, AsCH3], 1.57 [s, AsCH3];
31P, δ Ϫ199.53 [s, µ-PPhH]; m/z 652(Mϩ), 591 (Mϩ Ϫ 2CO)
(Found: C 39.21, H 3.34; AsC22H22Mo2O4P2 requires C 40.5, H
3.40%).
18: νmax
/cmϪ1 (CO) 1957(s), 1942(vs), 1886(vs), 1867(s);
˜
1
the sole product. νmax
˜
(CH2Cl2)/cmϪ1 (CO) 1871. NMR: 1H,
NMR: H, δ 7.8–7.2 [m, 15H, Ph], 5.47 [s, 5H, Cp], 5.42 [d,
J. Chem. Soc., Dalton Trans., 2000, 1695–1702 1701

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1J(PH) 316.4 Hz, 1H, PH], 4.96 [s, 5H, Cp]; 31P, δ Ϫ157.5 [s,
µ-PPhH]; m/z 775 (Mϩ), 719 (Mϩ Ϫ 2CO) (Found: C 49.71, H
3.63; AsC32H26Mo2O4P requires C 49.49, H 3.38%).
3 J. E. Davies, M. J. Mays, E. J. Pook, P. R. Raithby and P. K.
Tomplin, J. Chem. Soc., Dalton Trans., 1997, 3282; J. E. Davies,
L. C. Kerr, M. J. Mays, P. R. Raithby, P. K. Tompkin and A. D.
Woods, Angew. Chem., Int. Ed., 1998, 37, 1428.
4 M. E. Garcia, V. Riera, M. T. Rueda, M. A. Ruiz, M. Lanfracuchi
and A. Tiripicchio, J. Am. Chem. Soc., 1999, 16, 4061.
5 H. Egold, U. Flörke, H.-J. Haupt and M. Schwefer, Inorg. Chem.,
1995, 34, 292.
6 U. Baumeister, H.-C. Böttcher, H. Hartung, A. Krug, F. Rosche and
B. Walther, Polyhedron, 1992, 11, 1563.
7 R. G. Hayter, Inorg. Chem.,1963, 2, 1031.
For 6. Elution with 3:2 CH2Cl2 :hexane yielded starting
material 3 (18 mg, 6%) and [Cp2(CO)2Mo2(µ-PPh2)(µ-AsMe2)]
16 (257 mg, 71%) or a trace of starting material and
[Cp2(CO)2Mo2(µ-PPh2)(µ-AsPh2)] 19 (313 mg, 74%).
16: νmax
/cmϪ1 (CO) 1946(m), 1936(vs), 1873(s), 1864(m);
˜
NMR: 1H, δ 7.57–7.22 [m, 10H, Ph], 5.07 [s, 10H, Cp], 1.58 [s,
6H, AsCH3]; 31P, δ Ϫ120.64 [s, µ-PPh2]; m/z 724 (Mϩ), 696
(Mϩ Ϫ CO), 670 (Mϩ Ϫ 2CO) (Found: C 45.45, H 3.53;
AsC28H26Mo2O4P requires C 46.16, H 3.6%).
8 T. Adatia, M. McPartlin, M. J. Mays, M. J. Morris and P. R.
Raithby, J. Chem. Soc., Dalton Trans., 1989, 1555.
9 C. Alvarez, M. E. García, V. Riera and M. A. Ruiz, Organometallics,
1997, 16, 1378; H. Adams, N. A. Bailey, M. N. Bancroft, A. P.
Bisson and M. J. Morris, J. Organomet. Chem., 1997, 542, 197.
10 V. Caliman, P. B. Hitchcock and J. F. Nixon, J. Chem. Soc.,
Chem. Commun., 1995, 1663; E. M. Holt, R. B. King and F.-J. Wu,
J. Am. Chem. Soc., 1987, 109, 7764; R. E. Davis, R. B. King,
E. P. Kyba, J. S. McKennis and B. Sheikh, Organometallics, 1985, 4,
994.
19: νmax
/cmϪ1 (CO) 1964(m), 1949(vs), 1881(s), 1867(m);
˜
1
NMR: H, δ 7.72–7.10 [m, 20H, Ph], 4.95 [s, 10H, Cp]; 31P,
δ Ϫ120.37 [s, µ-PPh2]; m/z 820 (Mϩ Ϫ CO), 795 (Mϩ Ϫ 2CO),
767 (Mϩ Ϫ 3CO) (Found: C 53.96, H 3.70; AsC38H30Mo2O4P
requires C 53.53, H 3.55%).
11 R. E. Davies, K. L. Hassett, E. P. Kyba, J. D. Mather and
J. S. McKennis, J. Am. Chem. Soc., 1984, 106, 5371; J. E. Davies,
M. J. Mays, P. R. Raithby, G. P. Shields and P. K. Tompkin, Chem.
Commun., 1997, 361.
12 P. E. Garrou, Chem. Rev., 1981, 81, 229; C. Barré, P. Boudot,
M. M. Kubicki and C. Moïse, Inorg. Chem., 1995, 34, 289;
A. J. Carty, F. Hartstock and N. J. Taylor, Inorg, Chem., 1982, 21,
2349.
13 O. J. Scherer, M. Ehses and G. Wolmerhäuser, Angew. Chem., Int.
Ed., 1998, 37, 507; R. Appel, C. Carger and F. Knoch, J. Organomet.
Chem., 1985, 297, 21.
14 E. M. Holt, R. B. King and F.-J. Wu, J. Am. Chem. Soc., 1988, 110,
2775.
(viii) Thermolysis of 18 and 19
A solution of 18 or 19 (200 mg, 0.27 mmol 18; 200 mg, 0.23
mmol 19) in toluene (60 ml) was refluxed for 16 h during which
time the solution colour turned from orange to a dark green.
The solvent was removed in vacuo and the residue dissolved in
the minimum CH2Cl2 and applied to the base of TLC plates.
For 18. Substantial decomposition occurred on the TLC
plates and only one red product was obtained in trace yield.
This is tentatively formulated by comparison of its colour and
carbonyl stretching frequency as [Cp2(CO)(O)Mo2(µ-PPhH)-
15 D. Braga, A. J. M. Caffyn, G. Conole, M. J. Mays, M. McPartlin,
H. R. Powell, P. Sabatino and G. A. Solan, J. Chem. Soc., Dalton
Trans., 1991, 3103.
(µ-AsPh2)] 20. νmax
(CH2Cl2)/cmϪ1 (CO) 1832.
˜
16 U. Flörke and H.-J. Haupter, Acta Crystallogr., Sect. C, 1993, 49,
374; S. C. Goel, M. Y. Chiang, D. J. Rauscher and W. E. Buhro,
J. Am. Chem. Soc., 1993, 115, 160; P. Braunstein, D. Matt, O. Bars,
M. Lour, D. Grandjean, J. Fischer and A. Mistschler, J. Organomet.
Chem., 1981, 213, 79.
17 H.-C. Böttcher, C. Bruhn, M. Graf and K. Merzweiler, J. Organo-
met. Chem., 1998, 553, 371; S. Bambirra, H. Hartung, A. Krug,
H.-C. Böttcher and B. Walther, Organometallics, 1994, 13, 172;
H. Werber, B. Klingert and A. L. Rheingold, Organometallics, 1988,
7, 911; S. Attali, F. Dahan, R. Mathieu, A. M. Caminadi
and J.-P. Majoral, J. Am. Chem. Soc., 1988, 110, 1990; D. Belletti,
A. Tiripicchio, M. Tiripicchio-Camellini and E. Sappa, J. Chem.
Soc., Dalton Trans., 1990, 702; H.-C. Böttcher, H. Hartung and
A. Krug, Polyhedron, 1995, 14, 901.
18 R. C. Barth, J. Del Gaudio, S. O. Grim and J. D. Mitchell, Inorg.
Chem., 1977, 16, 1776.
19 U. Baumeister, H.-C. Böttcher, H. Hartung, P. G. Jones, A. Krug,
C. Mealli, A. Möckel and B. Walther, Organometallics, 1992, 11,
1542.
20 M. Müller and H. Vahrenkamp, Chem. Ber., 1983, 116, 2748.
21 G. Conole, J. E Davies, J. D. King, M. J. Mays, M. McPartlin,
H. R. Powell and P. R. Raithby, J. Organomet. Chem., 1999,
585, 141; E. Keller and H. Vahrenkamp, Chem. Ber., 1979, 112,
1991.
For 19. Elution with 3:2 CH2Cl2 :hexane led to the isolation
of 3 new complexes with decreasing Rf: [Cp2(CO)2Mo2(µ-PPh2)-
(µ-AsPh2)] 21, trans-[Cp2(CO)(O)Mo2(µ-PPh2)(µ-AsPh2)] 22,
cis-[ Cp2(CO)(O)Mo2(µ-PPh2)(µ-AsPh2)] 23.
1
21: νmax
˜
(CH2Cl2)/cmϪ1 (CO) 1847(br, s); NMR: H, δ 7.68–
7.19 [m, 20H, Ph], 5.37 [s, 10H, Cp]; 31P, δ 92.25 [s, µ-PPh2];
m/z 796 (Mϩ), 768 (Mϩ Ϫ CO) (Found: C 53.87, H 3.67;
AsC36H30Mo2O2P requires C 54.28, H 3.8%).
1
22: νmax
˜
(CH2Cl2)/cmϪ1 (CO) 1821(br, s); NMR: H, δ 8.05–
7.15 [m, 20H, Ph], 5.05 [d, J(PH) 1.47, 5H, Cp], 4.91 [d, J(PH)
1.13 Hz, 5H, Cp]; 31P, δ 172.58 [s, µ-PPh2]; m/z 784 (Mϩ), 756
(Mϩ Ϫ CO) (Found: C 53.48, H 3.83; AsC35H30Mo2O2P requires
C 53.58, H 3.86%).
1
23: νmax
˜
(CH2Cl2)/cmϪ1 (CO) 1842(s); NMR: H, δ 8.05–7.15
[m, 20H, Ph], 5.20 [d, J(PH) 0.2 Hz, 5H, Cp], 4.90 [s, 5H, Cp];
31P, δ 168.71; m/z 784 (Mϩ), 756 (Mϩ Ϫ CO) (Found: C 53.61, H
3.91; AsC35H30Mo2O2P requires C 53.58, H 3.86%).
Acknowledgements
22 J. Heck, J. Organomet. Chem., 1986, 311, C5.
We thank the EPSRC for a quota award to A. D. W. and ICI for
a CASE award to A. D. W. EPSRC support for the purchase of
the Nonius Kappa CCD diffractometers is also gratefully
acknowledged.
23 E. Gross, C. Burschka and W. Malisch, Chem. Ber., 1986, 119, 38;
A.-J. DiMaio, S. J. Geib and A. L. Rheingold, J. Organomet. Chem.,
1987, 335, 97; R. A. Jones and B. R. Whittlesey, J. Am. Chem. Soc.,
1985, 107, 1078; A. M. Arif, R. A. Jones, M. H. Seeberger,
B. R. Whittlesey and T. C. Wright, Inorg. Chem., 1986, 25, 3943;
A. M. Arif, D. E. Heaton, R. A. Jones, K. B. Kidd, T. C. Wright,
B. R. Whittlesey, J. L. Atwood, W. E. Hunter and H. Zhang, Inorg.
Chem., 1987, 26, 4065.
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1702
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