Reactivity and theoretical studies of the unusual phosphaalkenes cis/trans-[Cp2(OC)4Mo2{μ-η1: η2-P(Ph)=C(H)Me}]

Article abstract of DOI:10.1021/om001089k

The title complexes provide rare examples of the coordination of a phosphaalkene to a binuclear transition-metal fragment, and the reactivity of these complexes toward a variety of organic and inorganic reagents is reported. A DFT study suggests that the π=bond of the phosphaalkene moiety is essentially lost on coordination, with both the P=C π and π* orbitals being used in bonding to the dimetal core.

Full text of DOI:10.1021/om001089k

2076
Organometallics 2001, 20, 2076-2087
Rea ctivity a n d Th eor etica l Stu d ies of th e Un u su a l
P h osp h a a lk en es
cis/tr a n s-[Cp 2(OC)4Mo2{µ-η1:η2-P (P h )dC(H)Me}]
Adam J . Bridgeman,† Martin J . Mays,*,‡ and Anthony D. Woods‡
Department of Chemistry, University of Hull, U.K., and Department of Chemistry,
University of Cambridge, Lensfield Road, Cambridge CB2 1EW, U.K.
Received December 27, 2000
The title complexes provide rare examples of the coordination of a phosphaalkene to a
binuclear transition-metal fragment, and the reactivity of these complexes toward a variety
of organic and inorganic reagents is reported. A DFT study suggests that the π-bond of the
phosphaalkene moiety is essentially lost on coordination, with both the PdC π and π* orbitals
being used in bonding to the dimetal core.
In tr od u ction
Phosphaalkenes are currently the subject of intense
study,1-4 the polar nature of the PdC bond meaning
that they are ideal precursors to many phosphorus-
substituted heterocycles. Phosphaalkene-transition-
metal complexes fall into five broad classes (Figure 1);
of these type I has attracted by far the most attention.
There is surprisingly little literature on the reactivity
of phosphaalkenes of types III and V,2 and even less is
known about type IV. To the authors’ knowledge there
are only two known complexes of type IV in which a
phosphaalkene is coordinated to a dinuclear metal
fragment as opposed to two mononuclear centers.5,6
F igu r e 1. The five types of transition-metal-substituted
We recently published a new high-yield synthesis of
the dimolybdenum phosphaalkene complexes cis/ trans
[Cp2(OC)4Mo2{µ-η1:η2-P(Ph)dC(H)Me}] (1),6 and herein
we present the results of a systematic study of the
reactivity of these type IV complexes with metal car-
bonyls and with organic reagents. It is shown that
reaction with metal carbonyls can lead to the formation
of mixed-metal tri- and tetranuclear clusters, in which
the CHMe part of the phosphaalkene moiety has been
eliminated, leaving a phosphinidene capping ligand. The
reaction of 1 with organic reagents also leads to break-
down of the phosphaalkene ligand, although complex-
ation of the PdC bond to a metal fragment has clearly
made it less susceptible to electrophilic attack.
phosphaalkenes.
and also which of the two isomers of 1 is thermody-
namically favored. Unless otherwise stated, however,
the reactivity studies reported here utilize a mixture of
the cis and trans isomers of 1. We have not attempted
to study whether the observed reactions are specific to
one or the other isomer.
Resu lts a n d Discu ssion
P r oton a tion . There have been several documented
reactions involving protonation of transition-metal-
coordinated phosphaalkenes and metallophosphaalk-
enes. Thus, the protonation of the P atom in [Cp-
(OC)3WPdC(SiMe3)2] in which the phosphorus is
σ-bonded to the tungsten was briefly mentioned in a
communication,51 but no X-ray structural data were
given for the product. More recently Hill et al. have
protonated a series of similarly σ-bonded rutheniophos-
phaalkenes7 and Weber has protonated the amino-
substituted metallophosphaalkene [Cp*(CO)2FePdC-
(NMe2)2].8 In all these cases the electrophilic addition
occurs at the phosphorus atom. However, protonation
The results of a DFT study of the isomers trans-
[Cp2(OC)4Mo2{µ-η1:η2-P(Ph)dC(H)Me}] (1a ) and cis-
[Cp2(OC)4Mo2{µ-η1:η2-P(Ph)dC(H)Me}] (1b) reveal how
best to describe the bonding in complexes of this type
* To whom correspondence should be addressed. E-mail:
mjm14@cus.cam.ac.uk.
† University of Hull.
‡ University of Cambridge.
(1) Weber, L. Angew. Chem., Int. Ed. Engl. 1996, 35, 503.
(2) Dillon, K. B.; Mathey, F.; Nixon, J . F. Phosphorus: The Carbon
Copy; Wiley: New York, 1998.
(3) Yoshifuji, M. J . Chem. Soc., Dalton Trans. 1998, 3343.
(4) Nixon, J . F. Chem. Rev. 1988, 88, 1327.
(5) Neumann, B.; Schumann, I.; Stammler, H.-G.; Weber, L. Orga-
nometallics 1995, 14, 1626.
(6) Davies, J . E.; Mays, M. J .; Raithby, P. R.; Woods, A. D. J . Chem.
Soc., Chem. Commun. 1999, 2455.
(7) Arif, A.; Cowley, A. H.; Dartmann, M. J .; Gudat, D.; Hofmockel,
U.; Krebs, B.; Malisch, W.; Niecke, E.; Quashie, S. J . Chem. Soc., Chem.
Commun. 1985, 1687.
(8) Bedford, R. B.; Hill, A. F.; J ones, C. Angew. Chem., Int. Ed. Engl.
1996, 35, 547.
10.1021/om001089k CCC: $20.00 © 2001 American Chemical Society
Publication on Web 04/19/2001

Theoretical Studies of Unusual Phosphaalkenes
Organometallics, Vol. 20, No. 10, 2001 2077
Sch em e 1. Rea ction of 1 w ith HBF 4
of free phosphaalkenes results in addition to the carbon,
as would be expected given the reverse dipole of the Pd
C fragment.9 Furthermore, protonation of phosphaalk-
ene-metal complexes in which the metal is datively
coordinated by a lone pair on the phosphorus (type I,
Figure 1) also results in protonation at the phosphaalk-
ene carbon.2,10 It thus seemed pertinent to attempt the
protonation of 1 to ascertain whether addition of the
proton would occur at the phosphorus or carbon centers.
Addition of a slight excess of ethereal HBF4 to an
acetonitrile solution of 1 led to the formation of a red
solution. Addition of diethyl ether caused precipitation
of red [{Cp(MeCN)4Mo}2(µ-O)]4+ (2) (Scheme 1), which
was then recrystallized by slow evaporation of ether into
an acetonitrile solution of 2 to give moderately air stable
red crystals in low yield.
Figu r e 2. Molecular structureofthecation [{Cp(MeCN)4Mo}2-
(µ-O)]4+ (2).
The outcome of the reaction in acetonitrile is some-
what surprising. Nixon et al. have reported the stepwise
protonation of a coordinated phosphaalkyne to yield an
alkylphosphine,12 and it is proposed that a similar
stepwise double protonation of the phosphaalkene oc-
curs to yield a coordinated alkylphosphine in a dicationic
intermediate. The displacement of the phosphine and
remaining carbonyl groups in 1 by the solvent followed
by Mo-Mo bond cleavage would then yield the inter-
mediate [CpMo(NCMe)4]+. This intermediate is presum-
ably oxidized by adventitious oxygen with concomitant
dimerization to give 2.
Wilkinson et al. reported that protonation of Mo(CO)3-
(NCMe)3 always yielded up to 25% [{(MeCN)5Mo}2(µ-
O)]4+, even under the most rigorous of anaerobic con-
ditions; deliberately allowing air into the reaction vessel
gave yields of 90% of the µ-oxo product.13 It seems likely
that a similar mechanism is operative in the current
case, with the yields of 2 being noticeably higher if a
slight amount of air is allowed into the reaction vessel;
reaction of 1 with 4 equiv of HBF4 in the open air leads
to the formation of 2 in near quantitative yield. The
sample readily decomposes under vacuum, presumably
due to loss of acetonitrile. This decomposition precluded
an accurate microanalysis of 2.
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for [{Cp (MeCN)4Mo}2(µ-O)]4+ (2)
Mo(1)-O(1) 1.873(2) Mo(1)-O(1)-Mo(2)
172.2(1)
79.9(2)
79.8(2)
88.2
Mo(1)-N(1) 2.162(3) O(1)-Mo(1)-N(average)
Mo(1)-N(2) 2.159(3) O(1)-Mo(2)-N(average)
Mo(1)-N(3) 2.161(3) N(cis)-Mo(1)-N(cis)(average)
Mo(1)-N(4) 2.158(3) N(trans)-Mo(1)-N(trans)(average) 159.6
Mo(2)-O(1) 1.889(2) N(cis)-Mo(2)-N(cis)(average) 88.1
Mo(2)-N(5) 2.136(3) N(trans)-Mo(2)-N(trans)(average) 159.6
Mo(2)-N(6) 2.157(3)
Mo(2)-N(7) 2.164(3)
Mo(2)-N(8) 2.156(3)
CN)5Mo}2(µ-O)]4+, contains a perfectly linear Mo-O-
Mo linkage, and the MeCN groups are eclipsed, which
suggests a significant dπ-pπ interaction between the
Mo and O atoms.15
The structure of 2 was confirmed by a single-crystal
X-ray diffraction study. The cationic part of the complex
is shown in Figure 2, and relevant bond lengths and
angles are given in Table 1.
The Mo-O-Mo fragment is not quite linear, with a
bond angle of 172.2(1)°, which may be compared to the
Mo-O-Mo angles of 175.7° in [{Et2NCS2)3Mo}2(µ-
O)]+ 14 and of 180° in [{(MeCN)5Mo}2(µ-O)]4+ 13
Making
.
the approximation that the Mo-O-Mo fragment is
linear allows a calculation of the N-Mo-Mo-N torsion
angles; these vary between 40° and 47°, indicating that
the MeCN groups are staggered. The Mo-O bonds in 2
[1.873(2) and 1.889(2) Å] are longer than the corre-
sponding bonds in Wilkinson’s complex [1.847(3) Å], and
are significantly longer than Mo(IV)dO bond lengths
(range 1.63-1.69 Å).16-18 However, the Mo-O-Mo
separations are appreciably shorter than Mo-O single
bond lengths in other Mo(IV) complexes, and thus some
dπ-pπ interaction between the oxygen lone pair and the
metal d orbitals seems likely. The staggered arrange-
Although molybdenum complexes containing a bridg-
ing oxo group are extremely common, all but two of the
previously documented complexes also contain terminal
ModO or ModS groups. Of the two complexes which
do not, one, [{Et2NCS2)3Mo}2(µ-O)]+, is not strictly
comparable to 2 because it contains two Mo atoms in
different oxidation states.14 The other example, [{(Me-
(9) Laali, K. K.; Neumann, B.; Scheffer, M. H.; Schoeller, W. W.;
Stammler, H.-G.; Sundermann, A.; Weber, L. Organometallics 1999,
18, 4216.
(10) Bickelhaupt, F.; Dam, M. A.; Goede, S. J . Recl. Trav. Chim.
Pays-Bas 1994, 113, 278.
(11) Attali, S.; Caminade, A.-M.; Majoral, J.-P.; Mathieu, R.; Sanchez,
M. Phosphorus Sulfur 1987, 30, 443.
(15) Cotton, F. A.; Wilkinson, G. Advanced Organic Chemistry;
Wiley: New York, 1988; p 466.
(16) Adatia, T.; McPartlin, M.; Mays, M. J .; Morris, M. J .; Raithby,
P. R. J . Chem. Soc., Dalton Trans. 1989, 1555.
(17) Alvarez, C.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A. Organome-
tallics 1997, 16, 1378.
(18) Haymore, B. L.; Nugent, W. A. Chem. Rev. 1980, 31, 123.
(12) Ame´lia, M.; Lemos, N. D. A.; Meidini, M. F.; Nixon, J . F.;
Pombeiro, A. J . L. J . Chem. Soc., Dalton Trans. 1998, 3319.
(13) Wilkinson, G.; Hursthouse, M. B.; McGilligan, B. S.; Motevalli,
M.; Wright, T. C. J . Chem. Soc., Dalton. Trans. 1988, 1737.
(14) Bloomhead, J . A.; Sterns, M.; Young, C. G. J . Chem. Soc., Chem.
Commun. 1981, 1262.

2078 Organometallics, Vol. 20, No. 10, 2001
Bridgeman et al.
Sch em e 2. P r op osed Rea ction P a th w a y Lea d in g
to F or m a tion of 3
ment of the MeCN groups and the bent Mo-O-Mo bond
would suggest that any such dπ-pπ interactions be-
tween the filled oxygen p orbitals and the metal dxz and
dyz orbitals are not optimal.
F igu r e 3. Molecular structure of [Cp2(OC)4Mo2(µ-PPhEt)-
(µ-H)] (3a ) (ORTEP shown to 50% probability).
The Mo atoms are in slightly distorted octahedral
environments, with the equatorial MeCN ligands being
tilted toward the axial O site with an average N-Mo-O
bond angle of 79.80°. The Mo-N bond lengths vary from
2.157(3) to 2.162(3) Å, these being typical distances for
complexes containing acetonitrile ligands coordinated
to molybdenum.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 3a
Mo(1)-Mo(2)
Mo(1)-P(1)
Mo(2)-P(1)
Mo(1)-H(0)
Mo(2)-H(0)
P(1)-C(10)
P(1)-C(12)
3.2775(7)
2.425(1)
2.434(1)
1.8503(5)
1.8471(5)
1.843(3)
1.832(3)
Mo(1)-Mo(2)-P(1)
Mo(1)-Mo(2)-H(0)
Mo(1)-P(1)-C(10)
Mo(1)-P(1)-C(12)
Mo(2)-Mo(1)-H(0)
Mo(2)-P(1)-Mo(1)
H(0)-Mo(1)-P(1)
H(0)-Mo(2)-P(1)
47.47(3)
27.60(1)
114.9(1)
122.6(1)
27.55(1)
84.83(3)
74.48(3)
74.30(3)
Rea ction w ith sBu 3BHLi. Having studied the re-
activity of 1 toward proton sources, it seemed logical to
extend the studies to the reactivity of 1 toward hydride
s
sources. Accordingly L-Selectide (L-Selectide ) Bu3-
lengths and angles being similar to lengths and angles
reported for complexes such as [Cp2(OC)4Mo2(µ-PMe2)-
(µ-H)]22 and [Cp2(OC)4Mo2(µ-PPhH)(µ-H)].23
BHLi) was added dropwise to a solution of 1 in THF at
-78 °C. A deep purple solution was obtained, the crude
infrared spectrum of which was similar to the spectra
of many complexes of the type [Cp2(CO)4M2(µ-PR2)]- (M
) Mo or W),19,20 indicating that an anionic metal
complex of this type was present. Addition of 1 equiv of
HBF4 to the anion, followed by filtration through a silica
pad and removal of the solvent, led to the isolation of
an orange solid, [Cp2(CO)4Mo2(µ-PPhEt)(µ-H)] (3a ), in
high yield. On the basis of these empirical observations,
it is proposed that the initial hydride attack occurs at
the phosphaalkene carbon to yield an intermediate
metal anion, [Cp2(CO)4Mo2(µ-PPhEt)]- (A) (Scheme 2).
Huttner and co-workers have similarly reported that
reaction of [(OC)10Fe3(µ3-η2-RPdCH2)] with H- results
in nucleophilic attack at the phosphaalkene carbon.21
To verify this proposed reaction pathway, the reaction
was repeated but using DCl instead of HBF4 as the
protonating agent. As before an orange solid was
isolated, the 31P NMR spectrum of which clearly shows
a 1:1:1 triplet (2J P-D ) 5.6 Hz). Furthermore, the 2H
NMR spectrum of this complex consists solely of a
doublet at -14.52 ppm, confirming that the product is
[Cp2(CO)4Mo2(µ-PPhEt)(µ-D)] (3b) and that the initial
attack of the hydride is at the phosphaalkene carbon;
no deuteration of the Et group was observed.
The 1H NMR spectrum of 3a consists of two very
broad singlets in the cyclopentadienyl region. Inspection
of the crystal structure clearly indicates that in the solid
state these groups are inequivalent, and it is thus
apparent that the complex is fluxional in solution but
that the process that interconverts the two cyclopenta-
dienyl groups is relatively slow on the NMR time scale
at room temperature, hence giving rise to the two very
broad resonances. Cooling of the sample to -20 °C leads
to a sharpening of the spectrum, giving two very sharp
Cp signals. Warming the sample leads to a gradual
coalescence of the two signals; thus, at 65 °C a single
resonance is observed at 5.02 ppm. The VT 1H NMR
spectra of 3a are shown in Figure 4.
A proposed mechanism for the interconversion of the
cyclopentadienyl groups is shown in Scheme 3. The two
isomers both possess a square pyramidal geometry, and
are interconverted via an intermediate which has a
trigonal bipyramidal geometry (ignoring the metal-
metal bond in all cases). Such a mechanism has been
previously proposed to explain the fluxionality of
[Cp2(OC)4Mo2(µ-PPhH)(µ-H)]23 and [Cp(OC)6MoFe(µ-
AsMe2)]24 as well as of several heterodinuclear manga-
nese-molybdenum complexes.25
The structure of 3a has been confirmed unambigu-
ously by a single-crystal X-ray diffraction study. The
molecular structure of 3a is presented in Figure 3, and
relevant bond lengths and angles are given in Table 2.
There are no unusual features in the structure, all bond
Rea ction w ith P h osp h in es. It was hypothesized
that addition of a two-electron donor to 1 might displace
the η2-coordination of the phosphaalkene. Thus, 1 was
separately reacted with Ph2PH, Ph3P, and (MeO)3P.
Prolonged thermolysis of 1 with Ph2PH led to a signifi-
(19) Davies, J . E.; Mays, M. J .; Raithby, P. R.; Shields, G. P.;
Tompkin, P. K. J . Chem. Soc., Dalton Trans. 1997, 361.
(20) Davies, J . E.; Feeder, N.; Gray, C.A.; Mays, M. J .; Woods, A.
D. J . Chem. Soc., Dalton Trans. 2000, 1695.
(21) Brauer, D. J .; Ciccu, A.; Fischer, J .; Hessler, G.; Stelzer, O.;
Sheldrick, W. S. J . Organomet. Chem. 1993, 462, 111.
(22) Peterson, J . L.; Stewart, R. P. Inorg. Chem. 1980, 19, 186.
(23) Henrick, K.; Horton, A.; McPartlin, M.; Mays, M. J . J . Chem.
Soc., Dalton Trans. 1988, 1083.
(24) Bullock, R. M.; Casey, C. P. J . Organomet. Chem. 1981, 218,
C47.
(25) Bullock, R. M.; Casey, C. P. Organometallics 1984, 3, 1100.

Theoretical Studies of Unusual Phosphaalkenes
Organometallics, Vol. 20, No. 10, 2001 2079
1
F igu r e 4. VT H NMR spectra of [Cp2(OC)4Mo2(µ-PPhEt)(µ-H)] (3a ).
Sch em e 3. P r op osed P a th w a y Lea d in g to
F lu xion a lity of 3
Sch em e 4. P r op osed Rea ction P a th w a y Lea d in g
to F or m a tion of 4
cant amount of decomposition together with the forma-
tion of a new red complex in very low yield, which
initially was not fully characterized.
In contrast, photolysis of a toluene solution of 1 with
Ph2PH yielded green [Cp2(OC)2Mo2(µ-PPh2)(µ-PPhEt)]
(4) in 63% yield. Consideration of this result led to the
realization that the low-yield red product formed on
thermolysis was oxidized 4, [Cp2(OC)(O)Mo2(µ-PPh2)-
(µ-PPhEt)], which exists as a chromatographically in-
separable mixture of the trans-5 and cis-6 isomers. The
oxidation of complexes analogous to 4 is well docu-
mented,26,27 and the hypothesis that in the thermolysis
reaction 5 and 6 are derived from 4 was tested by
stirring a small portion of 4 in dichloromethane. This
led to the formation of 5 and 6 in moderate (40%) yield.
Integration of the 1H NMR spectra suggests that the
isomers are present in a 4:1 ratio.
assumed to substitute a CO group in 1, yielding
intermediate A. It is proposed that oxidative addition
of the datively bound Ph2PH group then occurs, yielding
B, this being followed by reductive elimination to give
the 16-electron intermediate C. Finally, the pendant
phosphide group can coordinate to the second molyb-
denum atom, with concomitant CO elimination and
formation of a metal-metal double bond to give 4.
Similar routes have been proposed to explain the
formation of [Cp(OC)3MoCo{µ-C(CO2Me)dC(H)CO2Me}-
(µ-PPh2)] in the cothermolysis of [Cp(OC)5MoCo(µ-η2-
DMAD)]28 and Ph2PH and to explain the formation of
[Cp2(OC)2Mo2{µ-η3-CHdCHC(O)H}(µ-PPh2)] from [Cp2-
(OC)4Mo2(µ-HCtCH)] and Ph2PH.29 Interestingly, in
A possible course for the reaction leading to 4-6 is
shown below (Scheme 4). The diphenylphosphine is
(26) Adatia, T.; McPartlin, M.; Mays, M. J .; Morris, M. J .; Raithby,
P. R. J . Chem. Soc., Dalton Trans. 1989, 1555.
(27) Alvarez, C.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A. Organome-
tallics 1997, 16, 1378.
(28) Mart´ın, A.; Mays, M. J .; Raithby, P. R.; Solan, G. A. J . Chem.
Soc., Dalton Trans. 1993, 1431.
(29) Doel, G. R.; Feasey, N. D.; Knox, S. A. R.; Orpen, A. G.; Webster,
J . J . Chem. Soc., Chem. Commun. 1986, 542.

2080 Organometallics, Vol. 20, No. 10, 2001
Sch em e 5. P ossible Rea ction P a th w a ys Lea d in g to F or m a tion of 7
Bridgeman et al.
the latter reaction Knox reported that the product was
a result of thermolysis, whereas photolysis resulted in
the simple substitution of a CO group by the phosphine.
The 31P NMR spectrum of 4 consists of two doublets
Insertion of unsaturated hydrocarbons into metal-
carbon bonds is common,31-33 although it is relatively
rare to find such reactions taking place at dimolybde-
num centers; the reaction reported here is also some-
what unusual inasmuch as no carbonyl ligands have
been substituted. In the vast majority of such alkyne
insertion reactions the proposed mechanism involves the
substitution of a carbonyl ligand by the incoming alkyne
followed by carbon-carbon bond formation, or by direct
alkyne coupling without ligand displacement.34,35
There are several examples in the literature of the
coupling of alkynes and metallophosphaalkenes to give
metalloheterocycles, although it must be stressed that
in these cases neither the alkyne nor the PdC double
bond is coordinated to the metal prior to the coupling.1
Cyclization reactions similar to those reported here for
a dinuclear phosphaalkene complex have been reported
previously for dinuclear phosphaalkyne complexes, and
these latter reactions yield a wide variety of metal-
coordinated phosphorus heterocycles.36-38
at 89.10 ppm (2J P-P ) 8.8 Hz) and 84.92 ppm (2J P-P
)
8.8 Hz) which are assigned to the µ-PPh2 and µ-PPhEt
groups, respectively. Oxidation of 4 to yield 5 and 6
causes a downfield shift of the phosphorus resonances,
such downfield shifts on oxidation being commonly
reported; the assignments of the individual resonances
to 5 or 6 are based on a comparison of the 2J P-P coupling
constants with literature values for similar com-
pounds26,27
The 1H NMR spectrum of the mixture of 5 and 6
consists of multiplet resonances between 8.2 and 7.05
ppm, assigned to the phenyl protons. Four distinct
cyclopentadienyl resonances are observed at 5.24, 4.98,
4.82, and 4.80 ppm, the first two resonances being
assigned to the cyclopentadienyl groups of 6 and the
second two to the cyclopentadienyl groups of 5 by
comparison with the spectra of other complexes of this
type.
Attempts to react 1 with Ph3P or (MeO)3P resulted
in the formation of a dark green solution. However, it
was not possible to separate the products by conven-
tional chromatographic methods or to identify any of
them.
Rea ction w ith P h en yla cetylen e. Reaction of un-
coordinated phosphaalkenes with alkynes leads to cy-
clization, and the formation of a wide range of prod-
ucts.1,30 It thus seemed of interest to pursue the
reactivity of 1 toward alkynes, phenylacetylene being
chosen as a representative example.
Photolysis of a toluene solution of 1 with an excess of
HCtCPh using a 400 W UV lamp for 1 h led to the
formation of a purple solution. Separation by TLC led
to the isolation of the orange, crystalline insertion
product [Cp2(OC)4Mo2{µ-PhPC(Me)HC(Ph)dCH}] (7)
(Scheme 5) as a mixture of isomers.
For the reaction reported here three pathways can
be proposed (Scheme 5). The reaction could occur via a
[2+2] cycloaddition of the alkyne to the Mo-C bond
(route i). Alternatively, the phenylacetylene could sub-
stitute a carbonyl group and insert into the Mo-C bond
(route ii); this would yield a 34-electron intermediate
which could then add CO. The reaction was performed
with a N2 purge, so it is unlikely that any of the
(31) Ilg, K.; Werner, H. Organometallics 1999, 18, 5426 and refer-
ences therein.
(32) Otsuka, S.; Nakamura, A. Adv. Organomet. Chem. 1976, 14,
251.
(33) Templeton, J . L. Adv. Organomet. Chem. 1989, 29, 83.
(34) Whitely, M. W. In Comprehensive Organometallic Chemistry;
Abel, W. E., Stone, F. G. A., Wilkinson, G., Eds.; 1995; Vol. 5, Chapter
6.2.
(35) Chisholm, M. H.; Hoffman, D. M.; Huffman, J . C. J . Am. Chem.
Soc. 1984, 106, 6806.
(36) Leininger, S.; Nachbauer, A.; Peters, C.; Preuss, F.; Regitz, M.;
Tabellion, F. Angew. Chem., Int. Ed. Engl. 1998, 37, 1233.
(37) J ohnson, B. F. G.; Nixon, J . F.; Nowotny, M.; Parsons, S. J .
Chem. Soc., Chem. Commun. 1998, 2223.
(38) Dickson, R. S.; Francis, M. D.; Hibbs, D. E.; Hursthouse, M.
B.; J ones, C.; J unk, P. C.; Richards, A. F. Organometallics 1999, 18,
4838.
(30) Mathey, F.; Marinetti, A.; Bauer, S.; Le Floch, P. Pure Appl.
Chem. 1991, 63, 855.

Theoretical Studies of Unusual Phosphaalkenes
Organometallics, Vol. 20, No. 10, 2001 2081
F igu r e 6. Two possible isomers of 7.
recorded for other complexes containing a molybdacy-
clopentene moiety.39-41
The C(24)-C(23) bond separation of 1.347(3) Å is
typical of an uncoordinated CdC double bond but is
somewhat shorter than the value recorded for other
molybdacyclopentenes, in which the alkene is η2-
coordinated to the second metal center.40,41 The bond
angles about C(24) reveal a slight distortion from
idealized sp2 hybridization, with the Mo(1)-C(24)-
C(25) angle being 124.8(3)° rather than 120°, presum-
ably to relieve steric clashes between the MoCp(CO)2
fragment and the phenyl group. As a consequence the
C(23)-C(24)-C(25) and Mo(1)-C(24)-C(23) bond angles
are narrowed somewhat to 116.3(4)° and 118.1(3)°,
respectively. The phosphido group bridges the two
molybdenum atoms symmetrically within experimental
error [P(1)-Mo(1) 2.424(1) Å, P(1)-Mo(2) 2.421(1) Å],
these separations being typical values for these bonds.
The Mo(1)-C(1)-O(1) bond angle of 167.9(4)° suggests
some semibridging character, although the Mo(2)-C(1)
separation of 3.193 Å is somewhat long for such an
interaction.
F igu r e 5. Molecular structure of [Cp2(OC)4Mo2{µ-PhPC-
(Me)HC(Ph)dCH}] (7).
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 7
Mo(1)-Mo(2)
Mo(1)-P(1)
Mo(1)-C(24)
Mo(2)-P(1)
C(24)-C(23)
C(23)-C(22)
3.2309(6)
2.424(1)
2.303(5)
2.421(1)
1.347(7)
1.496(6)
Mo(1)-P(1)-Mo(2)
Mo(1)-C(1)-O(1)
Mo(1)-C(24)-C(23)
Mo(1)-C(24)-C(25)
Mo(2)-Mo(1)-C(24)
P(1)-C(22)-C(23)
C(23)-C(24)-C(25)
83.66(2)
167.9(4)
118.1(3)
124.8(3)
78.5(1)
There are several possible isomers of 7, two of which
are observed in the solution NMR spectra. It seems most
likely that the two isomers are derived from the cis and
trans isomers of 1; these would give rise to R and S
isomers of 7 in the step involving addition of the alkyne
to the phosphaalkene carbon (Figure 6). The crystal
structure is that of the isomer having an S configuration
about C22.
104.3(3)
116.3(4)
substituted CO groups would remain in solution, but
CO groups could be scavenged from decomposition
products formed during the reaction. The modest (50%)
yield would make such a process conceivable. If such a
pathway were followed, then one would expect the yield
to be appreciably higher if the reaction were carried out
under a CO atmosphere, which was not the case.
Finally, a third possible pathway (route iii) involves
displacement of the phosphaalkene from coordination
to the second metal center on the approach of the
alkyne, resulting in a vacant coordination site. Once
coordinated, the alkyne could then add to the phos-
phaalkene moiety, ultimately leading to the formation
of 7.
To characterize 7 unambiguously, a single-crystal
X-ray diffraction study was undertaken. The molecular
structure is shown in Figure 5, and relevant bond
lengths (Å) and angles (deg) are presented in Table 3.
Several complexes with similar structures, but contain-
ing a bridging carbene rather than a phosphido group,
have been previously formed by insertion of alkynes into
MosH39 or ModC bonds, and these serve as useful
structural comparisons.40,41 The Mo(1)-C(24) bond length
of 2.303(5) Å in 7 is somewhat longer than the values
Two double doublets can clearly be seen in the 1H
NMR spectrum of 7 at 1.64 ppm (3J P-H ) 15.65 Hz,
3J H-H ) 7.83 Hz) and at 1.05 ppm (3J P-H ) 13.69 Hz,
3J H-H ) 6.85 Hz), which are assigned to the methyl
group of the S and R isomers, respectively. Two broad
multiplets at 3.90 and 3.60 ppm are assigned to the
P-CH group. Theoretically the resonances due to this
group should each be split into a quartet of double
doublets, but resolution was poor and the individual
coupling constants could not be fully resolved. Two
cyclopentadienyl resonances at 5.13 and 4.88 ppm are
assigned to the inequivalent Cp groups of the S isomer,
and two at 5.30 and 4.98 ppm to those of the R isomer.
A double doublet resonating at 5.86 ppm (3J P-H ) 43.04
Hz, 3J H-H ) 3.91 Hz) is assigned to the CdCH group of
the S isomer. The corresponding resonance of the R
3
isomer is significantly broader, and the J H-H coupling
could not be resolved. The peak is centered at 5.88 ppm
3
with J P-H ) 36.19 Hz. The 31P NMR spectrum of 7
consists of a very broad peak at 226 ppm, which is
presumably due to the overlapping resonances of the
two isomers.
Rea ction w ith Meta l Ca r bon yls. Thermolysis of a
toluene solution of 1 with M3(CO)12 followed by TLC led
(39) Horton, A. D.; Mays, M. J .; Raithby, P. R. J . Chem. Soc., Chem.
Commun. 1985, 247.
(40) Garcia, M. E.; J effrey, J . C.; Sherwood, P.; Stone, F. G. A. J .
Chem. Soc., Dalton Trans. 1988, 2443.
(41) Adams, H.; Gill, L. J .; Morris, M. J . J . Chem. Soc., Dalton Trans.
1998, 2451.

2082 Organometallics, Vol. 20, No. 10, 2001
Bridgeman et al.
F igu r e 7. Molecular structures of [Cp2(OC)7Mo2M(µ3-PPh)], M ) Fe (8), M ) Ru (9) (hydrogen atoms omitted for clarity,
ORTEPs at 50% probability).
Ta ble 4. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 8 a n d 9
Sch em e 6. Rea ction of 1 w ith Meta l Ca r bon yls
8
9
Mo(1)-Fe(1)
Mo(1)-Mo(2)
Mo(1)-P(1)
Mo(2)-Fe(1)
Mo(2)-P(1)
Fe(1)-P(1)
2.8949(4) Mo(1)-Mo(2)
3.1613(2) Mo(1)-Ru(1)
2.3706(6) Mo(1)-P(1)
2.9217(4) Mo(2)-Ru(1)
2.3544(6) Mo(2)-P(1)
2.1461(7) Ru(1)-P(10)
3.1725(8)
2.9687(8)
2.378(1)
2.9958(8)
2.371(1)
2.260(1)
Mo(1)-Fe(1)-Mo(2) 65.84(1)
Mo(1)-Fe(1)-P(1) 53.64(2)
Mo(1)-Mo(2)-Fe(1) 56.67(1)
Mo(1)-Mo(2)-P(1) 48.23(2)
Mo(1)-P(1)-C(18) 127.02(7)
Mo(1)-Ru(1)-Mo(2) 64.26(2)
Mo(1)-Ru(1)-P(1) 51.99(2)
Mo(1)-Mo(2)-Ru(1) 57.45(2)
Mo(1)-Mo(2)-P(1)
Mo(1)-P(1)-Mo(2)
Mo(1)-P(1)-Ru(1)
Mo(1)-P(1)-C(13)
Mo(1)-C(1)-O(1)
Mo(1)-C(2)-O(2)
48.19(3)
83.81(4)
79.55(3)
128.0(1)
166.5(3)
170.9(3)
Mo(1)-C(1)-O(1)
Mo(1)-C(2)-O(2)
Mo(1)-P(1)-Mo(2)
Mo(1)-P(1)-Fe(1)
Mo(2)-Fe(1)-P(1)
167.6(2)
168.3(2)
83.99(2)
79.55(2)
52.70(2)
to the isolation of [Cp2(OC)7Mo2M(µ3-PPh)] (M ) Fe (8),
Ru (9)) each in ca. 35% yield (Scheme 6). It was found
that higher yields of 8 were obtained if a solution of 1
was photolyzed with Fe(CO)5. Due to the difficulties in
preparing Ru(CO)5 this method was not employed for
the preparation of 9.
Mo(2)-Mo(1)-Ru(1) 58.28(2)
Mo(2)-Mo(1)-Fe(1) 57.49(1)
Mo(2)-Mo(1)-P(1)
Mo(2)-Ru(1)-P(1)
Mo(2)-P(1)-Ru(1)
Mo(2)-P(1)-C(13)
Mo(2)-C(6)-O(6)
Ru(1)-Mo(1)-P(1)
Ru(1)-Mo(2)-P(1)
Ru(1)-P(1)-C(13)
48.00(3)
51.34(2)
80.48(3)
137.3(1)
170.9(3)
48.46(3)
48.08(3)
127.4(1)
Mo(2)-Mo(1)-P(1)
Mo(2)-P(1)-Fe(1)
47.79(2)
80.82(3)
Mo(2)-P(1)-C(18) 138.16(7)
Mo(2)-C(4)-O(4)
Fe(1)-Mo(1)-P(1)
Fe(1)-Mo(2)-P(1)
Fe(1)-P(1)-C(18)
171.8(2)
46.81(2)
46.48(2)
127.17(7)
Thermolysis of a toluene solution of 1 with Co2(CO)8
led to the formation of a different type of product,
[Cp2(OC)6Mo2Co2(µ-CO)2{µ3-P(Ph)dC(H)Me}] (10) in
10% yield (Scheme 6). It was found that [(OC)6Co4(µ-
CO)3(η6-PhMe)] was also formed in 30% yield. Com-
plexes of this latter type are well documented, being
formed from prolonged thermolysis of Co2(CO)8 in
aromatic solvents.42 It was found that yields of 10 were
increased by thermolysis of 1 with Co2(CO)8 in nonaro-
matic solvents such as heptane under a CO atmosphere,
although yields were never better than 20%.
Reaction of 1 with other metal carbonyls such as Mn2-
(CO)10, W(CO)6, and [Cp2(OC)2Fe2(µ-CO)2] resulted only
in decomposition.
Complexes 8-10 have been characterized by FAB MS,
microanalysis, and IR, 1H NMR, and 31P NMR spec-
troscopy. Additionally, each complex has been the
subject of a single-crystal X-ray diffraction study.
The molecular structures of 8 and 9 are shown in
Figure 7, and relevant bond lengths (Å) and angles (deg)
are given in Table 4. The Mo2Fe core present in 8 is
somewhat different from that in the related complex
[Cp2(OC)7Mo2Fe{µ3-PMoCp(CO)3}],43 having signifi-
cantly longer bond lengths within the triangular core
[Mo(1)-Fe(1) 2.8949(4) Å, Mo(2)-Fe(1) 2.9217(4) Å,
Mo(1)-Mo(2) 3.1613(2) Å]. As is to be expected the
phosphorus atom caps the triangle asymmetrically with
a short Fe-P separation of 2.1461(7) Å, and somewhat
longer Mo-P separations [Mo(1)-P 2.3706(6) Å, Mo(2)-P
2.3544(6) Å]. All of these distances are significantly
shorter than the corresponding distances in [Cp2(OC)7-
Mo2Fe{µ3-PMoCp(CO)3}], presumably because the P-Ph
group is significantly smaller than the P-MoCp(CO)3
(43) Bridgeman, A. J .; Mays, M. J .; Woods, A. D. Organometallics,
in press.
(42) Bird, P. H.; Fraser, A. R. J . Organomet. Chem. 1974, 33, 103.

Theoretical Studies of Unusual Phosphaalkenes
Organometallics, Vol. 20, No. 10, 2001 2083
group. It thus exerts less steric pressure and can
approach the metal atoms more closely.
The substitution of the Fe(CO)3 group in 8 by the
larger Ru(CO)3 group in 9 leads to a widening of the
M-Mo-Mo bond angles [Ru(1)-Mo(1)-Mo(2) 58.28(2)°,
Ru(1)-Mo(2)-Mo(1) 57.45(2)°, Fe(1)-Mo(1)-Mo(2)
57.49(1)°, Fe(1)-Mo(2)-Mo(1) 56.67(1)°] and a tighten-
ing of the Mo-M-Mo bond angle from 65.84(1)° in 8 to
64.26(2)° in 9. This is to be expected given the longer
Ru-Mo bond length (average 2.9823(8) Å) compared to
the average Fe-Mo separation of 2.9083(8) Å. The Ru-
Mo separations are significantly longer than the dis-
tances of 2.8989(9) and 2.9129(8) Å reported for the
sulfur-capped complex [Cp2(OC)7Mo2Ru(µ3-S)],44 but are
comparable to the distance of 3.031(1) Å reported in
[Cp2(OC)2Mo2Ru(µ3-S){µ-η3-PhCC(H)CPh}{µ3-η3-HC-
C(Ph)CH}].45
In both 8 and 9 the Mo(2)-M separation is 0.03 Å
longer than the Mo(1)-M separation, reflecting the fact
that in each case Mo(1) possesses a semibridging
carbonyl group with C(2)-M separations of 2.801 and
2.802 Å for 8 and 9, respectively. In addition there is
some interaction between C(1) and Mo(2) in each
complex with C(1)-Mo(2) separations of 2.977 and 2.988
Å, respectively. The Ru-P separation of 2.260(1) Å is
consistent with values recorded for other phosphinidine-
capped Ru clusters.46-48
The 31P NMR spectrum of 8 consists of a singlet at
392.37 ppm, and that of 9 consists of a singlet at 349.63
ppm, which are typical of µ3-phosphinidene reso-
nances.49,50
Crystals of 10 suitable for a single-crystal X-ray
diffraction study were grown by slow diffusion of hexane
into a dichloromethane solution of 10 under a nitrogen
atmosphere at 0 °C. The molecular structure of 10 is
shown in Figure 8, and relevant bond lengths (Å) and
angles (deg) are included in Table 5.
Complex 10 is perhaps best viewed as a distorted Co2-
Mo2P trigonal bipyramid with two edges bridged by CO
groups and a third edge bridged by a CHMe group. The
tetrahedral metal core is electron precise, with each
metal atom fulfilling the 18-electron rule, and the
tetrahedron having the expected electron count of 60.
Within the phosphaalkene fragment, the methyl group
lies cis to the phenyl, as highlighted by the torsion angle
C(24)-P(1)-C(25)-C(26) of -48.6°. The P(1)-C(25)
vector is at 147.4° to the Mo(1)-Mo(2) vector, compared
to corresponding angles of 133.1° and 126.8° in 1a and
1b.
F igu r e 8. Molecular structure of [Cp2(OC)6Mo2Co2(µ-CO)2-
{µ3-P(Ph)dC(H)Me}] (10) (ring hydrogens omitted for clar-
ity, ORTEP at 50% probability).
it does fall within the range of Mo-C single bond
lengths. In contrast, the P-Mo(1) separation is very
long, the value of 2.787(1) Å being far greater than the
sum of the covalent radii of Mo and P (2.460 Å), and
well outside the range of singly bonded Mo-P separa-
tions [range 2.40-2.602(3)].51 This can be rationalized
in part by viewing the bonding as involving η2 coordina-
tion of the PdC π system rather than σ-bonding of both
the P and C to the Mo atom.
The phosphorus atom is in a formal +5 oxidation state
and, ignoring the P-Mo(1) bond, can be viewed as being
in a distorted tetrahedral environment. The P(1)-C(25)
bond length of 1.769(4) Å is somewhat longer than the
corresponding bond length in 1a and 1b, but is still
indicative of a degree of multiple bonding and is
comparable to the P-C bond lengths of 1.76(1) and
1.79(1) Å found by Huttner52 and Stelzer53 in other µ3-
phosphaalkenes. By way of contrast, the P(1)-C(24)
single bond length is 1.832(4) Å.
The Co2Mo2 core is, as expected, a distorted tetrahe-
dron. The Co(2)-Mo bond lengths are both shorter than
the Co(1)-Mo bond lengths [Co(1)-Mo(1) 2.7474(7) Å,
Co(1)-Mo(2) 2.7713(6) Å; Co(2)-Mo(1) 2.7367(6) Å,
Co(2)-Mo(2) 2.7104(7) Å], which presumably results
from each of the Co(2)-Mo edges being bridged by a
carbonyl group. All these values fall well within the
range of previously reported Mo-Co bond lengths in
Co2Mo2 tetrahedra [2.695-2.900(3) Å].54-57 The Mo-
The Mo(1)-C(25) separation of 2.280(4) Å is signifi-
cantly shorter than the corresponding separations in 1a
and 1b of 2.382(7) and 2.392(3) Å, respectively, although
(44) Adams, R. D.; Babin, J . E.; Tasi, M. Organometallics 1988, 7,
219.
(45) Adams, R. D.; Babin, J . E.; Tasi, M. Organometallics 1987, 6,
2247.
(46) Bianchi, M.; Frediani, P.; Faggi, C.; Ianelli, S.; Nardelli, M.;
Papaleo, S.; Piccenti, F.; Salvin, A. J . Organomet. Chem. 1997, 536,
123.
(47) Deeming, A. J .; Doherty, S.; Powell, N. I. Inorg. Chim. Acta
1992, 198, 469.
(48) Chi, Y.; Lee, G.-H.; Lin, R.-C.; Peng, S.-M. Inorg. Chem. 1992,
31, 381.
(51) Barre, C.; Kubicki, M. M.; Leblanc, J .-C.; Moı¨se, C. Inorg. Chem.
1990, 29, 5244 and references therein.
(52) Huttner, G.; Knoll, K.; Wasiucionek, M.; Zsolani, L. Angew.
Chem., Int. Ed. Engl. 1984, 23, 739.
(49) Huttner, G.; Natarajan, K.; Scheidsteger, O. J . Organomet.
Chem. 1981, 221, 301.
(50) Huttner, G.; Mohr, G.; Schneider, J .; v. Seyerl, J . J . Organomet.
Chem. 1980, 191, 161.
(53) Brauer, D. J .; Ciccu, A.; Fischer, J .; Hessler, G.; Stelzer, O.;
Sheldrick, W. S. J . Organomet. Chem. 1992, 428, 199.
(54) Davis, R. E.; Kashyap, R. P.; Kerby, M. C.; Kyba, E. P.;
Mountzouris, J . A. Organometallics 1989, 8, 852.

2084 Organometallics, Vol. 20, No. 10, 2001
Ta ble 5. Selected Bon d Len gth s (Å) a n d An gles (d eg) for 10
Bridgeman et al.
Mo(1)-Mo(2)
Mo(1)-Co(1)
Mo(1)-Co(2)
Mo(1)-P(1)
Mo(1)-C(25)
Mo(2)-Co(1)
Mo(2)-Co(2)
Mo(2)-P(1)
Co(1)-Co(2)
Co(1)-P(1)
P(1)-C(25)
P(1)-C(24)
3.0149(5)
2.7474(7)
2.7367(6)
2.787(1)
2.280(4)
2.7713(6)
2.7104(7)
2.371(1)
2.4966(8)
2.185(1)
1.769(4)
1.832(4)
Mo(1)-Co(1)-Mo(2)
Mo(1)-Co(1)-Co(2)
Mo(1)-Co(1)-P(1)
Mo(1)-Mo(2)-Co(2)
Mo(1)-Mo(2)-Co(1)
Mo(1)-Mo(2)-P(1)
Mo(1)-Co(2)-Mo(2)
Mo(1)-Co(2)-Co(1)
Mo(1)-P(1)-C(24)
Mo(1)-P(1)-C(25)
Mo(1)-C(2)-O(2)
Mo(1)-C(25)-P(1)
Mo(1)-C(25)-C(26)
Mo(2)-Mo(1)-Co(1)
Mo(2)-Mo(1)-Co(2)
Mo(2)-Mo(1)-P(1)
66.23(2)
62.70(2)
67.70(3)
56.81(2)
56.51(2)
60.94(3)
67.21(2)
63.14(2)
164.9(1)
54.7(1)
169.4(4)
86.0(2)
120.5(3)
57.27(1)
55.98(2)
48.04(2)
Mo(2)-Mo(1)-C(25)
Mo(2)-Co(1)-Co(2)
Mo(2)-Co(1)-P(1)
Mo(2)-P(1)-C(25)
Mo(2)-P(1)-C(24)
Mo(2)-C(7)-O(7)
Co(1)-Mo(1)-Co(2)
Co(1)-Mo(1)-P(1)
Co(1)-Mo(2)-Co(2)
Co(1)-Mo(2)-P(1)
Co(1)-P(1)-C(24)
Co(1)-P(1)-C(25)
Co(2)-Mo(2)-P(1)
C(24)-P(1)-C(25)
C(26)-C(25)-P(1)
C(25)-Mo(1)-Co(2)
80.6(1)
61.67(2)
55.65(3)
113.1(1)
123.9(1)
168.1(4)
54.16(2)
46.51(2)
54.17(2)
49.55(3)
117.7(1)
109.4(1)
98.58(3)
112.3(2)
117.9(3)
127.9(1)
Mo separation of 3.0149(5) Å is somewhat greater than
that in most Mo2Co2 tetrahedra, but is slightly shorter
than the value of 3.024(1) Å recorded for the unsubsti-
tuted complex [Cp2(OC)7Mo2Co2(µ-CO)3].57 The terminal
CO group on each Mo is actually semibridging [O(7)-
C(7)-Mo(2) 168.1(4)°, O(2)-C(2)-Mo(1) 169.4(4)°] with
calculated separations of 2.941 Å [C(7)-Mo(1)] and
2.697 Å [C(2)-Co(1)].
The 31P NMR spectrum of 10 consists of a singlet at
43.86 ppm, which is significantly upfield from that of
1. Comparisons of the chemical shift may be made to
other cluster-stabilized phosphaalkenes of type V (Fig-
ure 1), the resonance of 10 being significantly upfield
from these values, which are in the range 220-260 ppm,
although all of these other complexes contain a phos-
phaalkene coordinated to a group VIII metal triangle.51
F igu r e 9. Proposed canonical forms of [Cp2(OC)2Fe2{µ-
η1:η2-P(M)dC(H)SMe}].
1
The H NMR spectrum consists of a multiplet at 7.50-
Ta ble 6. Ca lcu la ted Bon d Or d er s a n d Ch a r ge
Den sities for 1a a n d 1b
7.46 ppm which is assigned to the phenyl group. Two
distinct cyclopentadienyl resonances are observed at
5.01 and 4.80 ppm. A broad singlet at 1.52 ppm is
assigned to the PdCH proton, and a double doublet at
1a
1b
1a
1b
P(1)-C(21)
P(1)-Mo(1)
P(1)-Mo(2)
Mo(1)-Mo(2)
C(21)-Mo(2)
Mo(2)-C(4)
Mo(1)-C(4)
0.90
0.88
0.69
0.42
0.65
1.25
0.17
0.95
0.84
0.73
0.41
0.65
1.21
0.18
Mo(1)
Mo(2)
P(1)
C(21)
H(21)
-0.28
-0.05
+0.45
-0.67
-0.36
-0.30
-0.04
+0.44
-0.64
+0.38
3
1.34 ppm (3J P-H ) 19.05 Hz, J H-H ) 6.60 Hz) is
assigned to the PdCMe group.
The IR spectrum contains absorptions at 2073, 2030,
2012, and 1999 cm-1, clearly showing that Co(CO)2
fragments have been introduced. An additional absorp-
tion at 1829 cm-1 confirms the presence of a bridging
carbonyl group.
describe the bonding in such complexes, and these are
shown in Figure 9.
1
DF T Stu d ies of cis/tr a n s-[Cp 2(OC)4Mo2{µ-η :η2-
The DFT analysis suggests that form B most ac-
curately describes the bonding, as can be seen by
inspecting the P-C bond orders (Table 6), which are
indicative only of a single bond interaction. The bond
orders of 0.90 and 0.95 found in 1a and 1b may be
compared to a bond order of 1.88 which was calculated
for the PdC bond in the free phosphaalkene cis-P(Ph)d
C(Me)H. Furthermore, the Mo(1)-P and Mo(2)-C(21)
bond orders are both consistent with a single bond
formulation. An examination of the HOMOs reveals that
they are derived from interaction of the PdC π* orbital
(Figure 10) with an antibonding orbital of the Cp2Mo2-
(CO)4 fragment, reducing the P-C bond order between
P(1) and C(21).
As noted in our preliminary communiation the mo-
lecular structures of 1a and 1b both contain a semibridg-
ing carbonyl group between Mo(1) and C(4);6 this is
highlighted by the DFT results, which show Mo(1)-C(4)
bond orders of 0.17 and 0.18 for 1a and 1b, respectively.
The analysis also reveals that Mo(1) has a good deal of
negative charge buildup, with a charge of -0.28 and
P (P h )dC(H)Me}]. Due to the paucity of complexes
such as 1a and 1b it was decided to undertake a
thorough analysis of these two isomers to describe their
bonding more fully.
The DFT study reveals that cis-1b is in fact the
thermodynamically favored product, being approxi-
mately 35 kJ mol-1 more stable than trans-1a . Modeling
of the transition state for isomerization, which is as-
sumed to involve breaking of the PdC π-bond so that
the p orbitals on the two atoms lie orthogonal to each
other, suggests that the activation barrier to isomer-
ization is about 180 kJ mol-1
.
In the related metallophosphaalkenes [Cp2(OC)2Fe2-
{µ-η1:η2-P(M)dC(H)SMe}] (M ) FeCp(CO)2) Weber5
proposed three canonical forms which could be used to
(55) Kaganovich, V. S.; Mironov, A. V.; Rybinskaya, M. I.; Stovokho-
tov, Y. L.; Struchkov, Y. T. J . Organomet. Chem. 1989, 372, 339.
(56) Curtis, M. D.; Haggerty, B. S.; Rheingold, A. L.; Riaz, U.
Organometallics 1990, 9, 2647.
(57) Curnow, O. J .; Curtis, M. D.; Haggerty, B. S.; Kanf, J . W.;
Rheingold, A. L.; Riaz, U. Organometallics 1995, 14, 5337.

Theoretical Studies of Unusual Phosphaalkenes
Organometallics, Vol. 20, No. 10, 2001 2085
F igu r e 10. Molecular orbital diagram of 1a .
conventional Schlenk line techniques, and solvents freshly
distilled from the appropriate drying agent. NMR spectra were
recorded in CDCl3 using a Bruker DRX 400 spectrometer, with
TMS as an external standard for 1H and 13C spectra and 85%
aqueous H3PO4 as an external standard for 31P spectra.
Infrared spectra were, unless otherwise stated, recorded in
dichloromethane solution in 0.5 mm NaCl solution cells, using
a Perkin-Elmer 1710 Fourier transform spectrometer. FAB
mass spectra were obtained using a Kratos MS 890 instru-
ment, using 3-nitrobenzyl alcohol as a matrix. Preparative TLC
was carried out on 1 mm silica plates prepared at the
University of Cambridge. Column chromatography was per-
formed on Kieselgel 60 (70-230 mesh ASTM). Unless other-
wise stated, all reagents were obtained from commercial
suppliers and used without further purification. [Cp2(OC)4Mo2-
(µ-η1:η2-PhPdCHMe)] was prepared by the literature method.6
Cr ysta l Str u ctu r e Deter m in a tion s. X-ray diffraction
data were collected using a Nonius-Kappa CCD diffractometer,
equipped with an Oxford Cryostream cryostream. Data reduc-
tion and cell refinement were performed with the programs
DENZO58 and COLLECT,59 and multiscan absorption correc-
tions were applied to all intensity data with the program
SORTAV.60 Structures were solved and refined with the
programs SHELXS97 and SHELXL97,61 respectively.
-0.30 in 1a and 1b, respectively; presumably the
semibridging carbonyl is formed to help remove excess
electron density from this center.
There is little difference between the molecular orbital
diagrams of 1a and 1b, so for simplicity’s sake only the
MO diagram of 1a is shown (Figure 10). The major
difference between the two stems from the relative
energies of the orbitals in 1a and 1b, the HOMO being
more stabilized in 1b than 1a . Furthermore, the ener-
gies of the two LUMOs (orbitals 142 and 143) are
-2.709 and -2.113 eV for 1a and -2.562 eV and -2.080
eV for 1b, thus indicating that the HOMO-LUMO
separation is larger for 1b than it is for 1a . Orbital 142
corresponds to the Mo-Mo σ*, which is the LUMO of
the Mo2 fragment, interacting with the P-C π orbital.
Orbital 143 corresponds to the Mo-Mo π* interacting
with the P-C π orbital.
The molecular orbital diagram clearly indicates that
the HOMO is antibonding with respect to both the
metal-metal bond and the PdC π-bond. The fact that
both the PdC π and π* orbitals are involved in bonding
contributions suggests that there is no net π-bonding,
as confirmed by the calculated bond orders (the free
phosphaalkeene has a PdC bond order of 1.86). Ad-
ditionally, as can be seen from inspection of MOs 140-
143, these orbitals contain a significant contribution
from the CO groups, suggesting that these groups
should be labile on photolysis.
Atomic coordinates, bond lengths and angles, and thermal
parameters have been deposited in the Cambridge Crystal-
lographic Data Centre (CCDC). Any request to the CCDC for
this material should quote the full literature citation.
Com p u ta tion a l Deta ils. All DF calculations were per-
formed using the DeFT code written by St-Amant in the linear
(58) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307.
(59) Hooft, R. COLLECT, Nonius BV, Delft, The Netherlands, 1998.
(60) Blessing, R. H. Acta Crystallogr. 1995, A51, 33.
(61) Sheldrick, G. M. SHELXS97 and SHELXL97, University of
Go¨ttingen, Germany.
Exp er im en ta l Section
Unless otherwise stated all experiments were carried out
under an atmosphere of dry, oxygen-free nitrogen, using

2086 Organometallics, Vol. 20, No. 10, 2001
Bridgeman et al.
combination of Gaussian-type orbitals framework.62 The cal-
culations used the local spin density (LSD) approximation of
the correlation part of the exchange-correlation potential of
Vosko et al.63 with the Becke64 and Perdew65 nonlocal correc-
tions for exchange and correlation, respectively. Basis sets of
double-ú quality were used for molybdenum and of triple-ú
quality for all other atoms in all electron treatments. Bond
orders were calculated from the density matrix according to
the prescription suggested by Mayer.66 Molecular orbital plots
were produced using the Molden program.67
P r oton a tion of cis/tr a n s-[Cp 2(OC)4Mo2{µ-η1:η2-P (P h )d
C(H)Me}] (1). To a solution of 1 (250 mg, 0.44 mmol) in
acetonitrile (40 mL) in a vessel open to the air was added 54%
HBF4‚Et2O (0.27 mL, 4 equiv) and the resulting solution
stirred for 30 min, during which time the solution color
changed from brown to red. The reaction mixture was con-
densed to 10 mL and Et2O (25 mL) added to precipitate a red-
brown solid. The solid was washed with Et2O to yield red
[{Cp(MeCN)4Mo}2O][BF4]4 (2) (267 mg, 74%). Crystals suitable
for an X-ray diffraction study were grown by vapor diffusion
of Et2O into an acetronitrile solution of 2 at 0 °C.
to yield a trace of 1 and a trace of red [Cp2(OC)(O)Mo2(µ-PPh2)-
(µ-PPhEt)] as a mixture of cis-6 and trans-5 isomers.
P h otolysis of 1 w ith P h 2P H. Nitrogen was bubbled
through a solution of 1 (150 mg, 0.26 mmol) and Ph2PH (0.1
mL, 2 equiv) in toluene (80 mL), and the mixture was
photolyzed using a 125 W UV lamp for 30 min. The solvent
was removed in vacuo and the residue redissolved in the
minimum amount of CH2Cl2, applied to the base of TLC plates,
and eluted with 3:2 CH2Cl2/hexane to yield green [Cp2(OC)2-
Mo2(µ-PPhEt)(µ-PPh2)] (4) (70 mg, 39%).
IR (ν(CO)): 1863 cm-1. 1H NMR: δ 7.70-7.15 (m, 15H, Ph),
5.39 (s, 5H, Cp), 5.28 (s, 5H, Cp), 3.14 (m, 1H, P-CHH), 2.05
3
3
(m, 1H, P-CHH), 1.31 (dt, J P-H ) 17.39 Hz, J H-H ) 7.41
Hz, 3H, P-CH2-CH3). 31P NMR: δ 89.10 (d, J P-P ) 8.8 Hz,
2
2
µ-PPh2), 84.92 (d, J P-P ) 8.8 Hz, µ-PPhEt). Anal. Calcd for
C
32H30Mo2O2P2: C 54.88, H 4.31, P 8.84. Found: C 55.16, H
4.38, P. 8.76. FAB MS: m/z 700 (M+), M+ C.
-
Oxid a tion of [Cp 2(OC)2Mo2(µ-P P h Et)(µ-P P h 2)] (4). A
solution of 4 (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, and the residue was
dissolved in the minimum amount of CH2Cl2 and applied to
the base of TLC plates. Elution with 3:2 CH2Cl2/hexane yielded
trans-[Cp2(OC)(O)Mo2(µ-PPhEt)(µ-PPh2)] (5) (34 mg, 28%) and
cis-[Cp2(OC)(O)Mo2(µ-PPhH)(µ-PPh2)] (6) (7 mg, 6%).
It should be noted that if a high vacuum was applied to the
sample, it began to decompose substantially, precluding ac-
curate elemental analysis.
IR (ν(CN)): 2159(m), 2154(m) cm-1. 1H NMR: δ 6.21 (s, 10H,
Cp), 2.47 (s, 24H, CH3CN). 13C NMR: δ 132.17 (CtN), 109.77
(Cp), 3.57 (H3CCN). Anal. Calcd for B4C26F16H34Mo2N8O: C
30.80, H 3.38, N 11.0. Found: C 29.02, H 3.33, N 9.55.
Rea ction of 1 w ith LiBsBu 3H. A 1 M solution of LiBsBu3H
in THF (0.52 mL, 1 equiv) was added dropwise at -78 °C to a
solution of 1 (300 mg, 0.52 mmol) in THF (40 mL). The
resulting solution was stirred for 30 min, during which time
the solution changed color from brown to purple. Addition of
54% HBF4‚Et2O caused a color change from purple to orange.
The solvent was removed under reduced pressure and the
residue redissolved in the minimum amount of CH2Cl2. Filtra-
tion through a silica pad yielded orange [Cp2(OC)4Mo2(µ-
PPhEt)(µ-H)] (3a ) (246 mg, 83%).
Da ta Assign ed to 5. IR (ν(CO)): 1847 cm-1 1H NMR: δ
.
8.20-7.05 (m, 15H, Ph), 5.24 (s, 5H, Cp), 4.98 (s, 5H, Cp),
3.16-3.10 (m, PCHH), 2.10-2.00 (m, PCHH), 1.69-1.61 (m,
2
PCH2CH3). 31P NMR: δ 169.86 (d, J P-P ) 6.55 Hz, µ-PPh2),
2
154.7 (d, J P-P ) 6.55 Hz, µ-PPhEt). Anal. Calcd for C31H30
-
Mo2O2P2: C 54.08, H 4.39, P 9.00. Found: C 54.61, H 4.54, P
9.16. FAB MS m/z 691 (M+), M+ - CO.
Da ta Assign ed to 6. IR (ν(CO)): 1831 cm-1 1H NMR: δ
.
8.20-7.05 (m, 15H, Ph), 4.82 (s, 5H, Cp), 4.80 (s, 5H, Cp),
3.16-3.10 (m, PCHH), 2.10-2.00 (m, PCHH), 1.69-1.61 (m,
2
PCH2CH3). 31P NMR: δ 169.43 (d, J P-P ) 5.5 Hz, µ-PPh2),
2
168.96 (d, J P-P ) 5.5 Hz, µ-PPhEt). FAB MS m/z 691 (M+),
M+ - CO.
Crystals suitable for a single-crystal X-ray diffraction study
were grown by slow evaporation of a CH2Cl2/hexane solution
of 3a at 0 °C.
P h otolysis of 1 w ith P h CtCH. Nitrogen was bubbled
through a solution of 1 (300 mg, 0.52 mmol) and PhCtCH
(0.16 mL, 3 equiv) in toluene (200 mL), and the mixture was
photolyzed using a 400 W UV lamp for 1 h. The solvent was
removed in vacuo and the residue redissolved in the minimum
amount of CH2Cl2, applied to the base of TLC plates, and
eluted with 3:2 CH2Cl2/hexane to yield orange [Cp2(OC)4Mo2-
{µ-PhP(C(Me)HC(H)dCPh}] (7) (160 mg, 46%).
Crystals suitable for a single-crystal X-ray diffraction study
were grown by slow evaporation of a CH2Cl2/hexane solution
of 7 at -15 °C.
IR (ν(CO)): 1959(m), 1940(vs), 1882(s), 1875(s) cm-1 1H
.
NMR: δ 7.35-7.00 (m, 5H, Ph), 5.23 (s, br, 5H, Cp), 4.80 (s,
br, 5H, Cp), 3.69 (s, vbr, 2H, P-CH2), 1.40 (d, br, 2J P-H ) 17.56
2
Hz, 3H, P-CH2CH3), -11.60 (d, J P-H ) 37.32 Hz, 1H, µ-H).
13C NMR: δ 224.86 (s, br CO), 199.7 (s, br, CO), 142.96-128.07
1
(m, Ph), 91.45 (s, br, Cp), 30.31 (d, J P-C ) 22.84 Hz, PCH2),
2
12.56 (d, J P-C ) 4.60 Hz, PCH2CH3). 31P NMR: δ 179.61 (s,
µ-PPhEt). Anal. Calcd for C22H21Mo2O4P: C 45.84, H 3.55, P
5.38. Found: C 45.72, H 3.75, P 5.50. FAB MS: m/z 572 (M+),
M+ - nCO (n ) 1-4).
IR (ν(CO)): 2002(w), 1985(vs), 1978(s,sh), 1936(s), 1892(m),
1867(m) cm-1. H NMR: δ
1
3
The reprotonation was also effected by addition of 20% DCl
in D2O (0.1 mL, 1 equiv) to yield [Cp2(OC)4Mo2(µ-PPhEt)(µ-
D)] (3b).
(S isomer) 7.58-7.10 (m, 10H, Ph), 5.86 (dd, J P-H ) 43.04
3
Hz, J H-H ) 3.91 Hz, 1H, CdCH), 5.13 (s, 5H, Cp), 4.88 (s,
3
5H, Cp), 3.90 (m, br, 1H, P-CH), 1.64 (dd, J P-H ) 15.65 Hz,
2
2H NMR: δ -14.52 (d, J P-D ) 5.61 Hz, µ-D). 31P NMR: δ
3J H-H ) 7.83 Hz, 3H, P-C-CH3);
2
(R isomer) 7.58-7.10 (m, 10H, Ph), 5.88 (d, br, 2J P-H ) 36.19
Hz, 1H, CdCH), 5.30 (s, 5H, Cp), 4.98 (s, 5H, Cp), 3.60 (m, br,
179.61 (t, J P-D ) 5.61 Hz, µ-P).
Th er m olysis of 1 w ith P h 2P H. Thermolysis of a solution
of 1 (150 mg, 0.26 mmol) and Ph2PH (0.1 mL, 2 equiv) in
toluene (60 mL) caused a color change from brown to red. The
solvent was removed under reduced pressure, and the residue
was redissolved in the minimum amount of CH2Cl2, applied
to the base of TLC plates, and eluted with 1:1 hexane/CH2Cl2
3
3
1H, P-CH), 1.05 (dd, J P-H ) 13.69 Hz, J H-H ) 6.85 Hz, 3H,
P-C-CH3).
31P NMR: δ 226 (s, vbr, µ-PhP). Anal. Calcd for C30H25
-
Mo2O4P: C 53.59, H 3.75, P 4.61. Found: C 53.06, H 3.70, P
4.66. FAB MS m/z 673 (M+), M+ - nCO (n ) 1, 2), M+ - C
(sample oxidized).
(62) St-Amant, A. DeFT, A FORTRAN program, University of
Ottawa, Canada, 1994.
(63) Vosko, S. H.; Wilk L.; Nusair, M. Can. J . Phys. 1980, 58, 1200.
(64) Becke, A. D. Phys. Rev. A 1988, 38, 3098.
(65) Perdew, J . D. Phys. Rev. B 1986, 33, 8822.
(66) (a) Mayer, I. Chem. Phys. Lett. 1983, 97, 270. (b) Mayer, I. Int.
J . Quantum Chem. 1984, 26, 151.
P h otolysis of 1 w ith F e(CO)5. Nitrogen was bubbled
through a solution of 1 (150 mg, 0.26 mmol) and Fe(CO)5 (0.07
mL, 2 equiv) in toluene (80 mL), and the mixture was
photolyzed using a 125 W UV lamp for 30 min. The solvent
was removed in vacuo and the residue redissolved in the
minimum amount of CH2Cl2, applied to the base of TLC plates,
and eluted with 1:1 hexane/CH2Cl2 to yield a trace of 1 and
[Cp2(OC)7Mo2Fe(µ3-PPh)] (8) (90 mg, 50%).
(67) Schaftenaar G.; Noordik, J . H. Molden:
a pre- and post-
processing program for molecular and electronic structures. J . Comput.-
Aided Mol. Des. 2000, 14, 123.

Theoretical Studies of Unusual Phosphaalkenes
Organometallics, Vol. 20, No. 10, 2001 2087
Crystals suitable for a single-crystal X-ray diffraction study
were grown by slow diffusion of hexane into a CH2Cl2 solution
of 8 at -15 °C.
to the base of TLC plates, and eluted with 1:1 hexane/CH2Cl2
to yield a trace of 1 and [Cp2(OC)6Mo2Co2(µ-CO)2{µ3-P(Ph)d
C(H)Me}] (10) (83 mg, 20%).
Crystals suitable for a single-crystal X-ray diffraction study
were grown by slow diffusion of hexane into a CH2Cl2 solution
of 10 at -15 °C.
IR (ν(CO)): 2069(m), 2012(m), 1996(s), 1988(s,sh), 1938(m),
1874(w) cm-1. 1H NMR: δ 7.57-7.38 (m, 5H, Ph), 5.14 (s, 5H,
Cp). 31P NMR: δ 392.37 (s, µ3-PPh). Anal. Calcd for C23FeH15
-
Mo2O7P: C 40.50, H 2.21, P 4.54. Found: C 40.32, H 2.19, P
4.52. FAB MS m/z 682 (M+), M+ - nCO (n ) 1-5).
Th er m olysis of 1 w ith Ru 3(CO)12. A solution of 1 (150
mg, 0.26 mmol) and Ru3(CO)12 (180 mg, 1 equiv) in toluene
(50 mL) was refluxed for 3 h. The solvent was removed in
vacuo and the residue redissolved in the minimum amount of
CH2Cl2, applied to the base of TLC plates, and eluted with
1:1 hexane/CH2Cl2 to give trans-[Cp2(OC)4Mo2{µ-η1:η2-P(Ph)d
C(H)Me}] (1a ) (9 mg, 6%), cis-[Cp2(OC)4Mo2{µ-η1:η2-P(Ph)d
C(H)Me)] (1b) (27 mg, 18%), and [Cp2(OC)7Mo2Ru(µ3-PPh)] (9)
(66 mg, 35%) as well as several other trace bands and a
decomposition product.
IR (ν(CO)): 2073(m), 2030(vs), 2012(s), 1999(m), 1926(s),
1879(m), 1829(w) cm-1 1H NMR: δ 7.50-7.46 (m, 5H, Ph),
.
5.01 (s, 5H, Cp), 4.80 (s, 5H, Cp), 1.52 (s, br, 1H, PdCH) 1.34
3
3
(dd, J P-H ) 19.05 Hz, J H-H ) 6.60 Hz, 3H, PdCCH3). 31P
NMR: δ 43.86 (s, µ3-PhP)CHMe). Anal. Calcd for C26Co2H19
Mo2O8P: C 38.93, H 2.64, P 5.28. Found: C 38.93, H 2.49, P
3.86. FAB MS m/z 800 (M+), M+ - nCO (n ) 1-8).
-
Ack n ow led gm en t. We are grateful to the EPSRC
for a Quota award to A.D.W. and for financial support
toward the purchase of the diffractometer, and to ICI
for a CASE award to A.D.W. We thank Dr. J . E. Davies
for measuring the diffraction data, and for help with
the X-ray structure solutions.
Crystals suitable for a single-crystal X-ray diffraction study
were grown by slow diffusion of hexane into a CH2Cl2 solution
of 9 at -15 °C.
IR (ν(CO)): 2037(vs), 2026(s), 2002(m), 1954(m), 1845(s),
1
1826(s) cm-1. H NMR: δ 7.84-7.42 (m, 5H, Ph), 5.08 (s, 5H,
Su p p or tin g In for m a tion Ava ila ble: Tables giving the
crystal data and structure refinement, equivalent atomic
coordinates and isotropic displacement parameters, bond
lengths and angles, anisotropic displacement parameters, and
hydrogen coordinates and isotropic displacement parameters
for 2, 4, and 7-10. This material is available free of charge
via the Internet at http://pubs.acs.org.
Cp). 31P NMR: δ 349.63 (s, µ3-PPh). Anal. Calcd for C23H15
-
Mo2O7PRu: C 37.98, H 2.08, P 4.26. Found: C 38.03, H 2.10,
P 4.26. FAB MS m/z 727(M+), M+ - nCO (n ) 1-4).
Th er m olysis of 1 w ith Co2(CO)8. A solution of [Cp2(OC)4-
Mo2{µ-η1:η2-P(Ph)dC(H)Me}] (300 mg, 0.52 mmol) and Co2-
(CO)8 (300 mg, 2 equiv) in heptane (70 mL) was refluxed for 3
h. The solvent was removed under reduced pressure and the
residue redissolved in the minimum amount of CH2Cl2, applied
OM001089K