Oxidative additions of coordinated ligands at unsaturated molybdenum and tungsten diphosphine-bridged carbonyl dimers. 2. Decarbonylation reactions of [Mo2(η5-C5H4R) 2(CO)4(μ-Ph2PCH2PPh2)] (R = H, Me)

Article abstract of DOI:10.1021/om9607154

Decarbonylation of the dimolybdenum complexes [Mo₂(η⁵-C₅H₄R) ₂(CO)₄(μ-dppm)] (R = H, Me, dppm = Ph₂PCH₂PPh₂) occurs readily upon heating in tetrahydrofuran or toluene solution to afford with good yield the phosphido complexes [Mo₂(η⁵-C₅H₄R) ₂(μ-CH₂PPh₂)(μ-PPh₂)(CO) ₂], which arise from an irreversible P-C(sp³) bond cleavage in the backbone of the dppm ligand. Other minor products in these reactions are the oxo complexes [Mo₂(η⁵-C₅H₄R) ₂(μ-CH₂PPh₂)(O)(μ-PPh₂)(CO)], which are formed by the action of oxygen on the former dicarbonyl compounds, and the triply-bonded complexes [Mo₂(η⁵-C₅H₄R) ₂(CO)₂(μ-dppm)], in which the dppm ligand remains intact. By contrast, photochemical decarbonylation of the parent tetracarbonyl complexes at 10°C yields the triply-bonded dicarbonyls as major products, along with a small amount of the monocarbonyl complexes [Mo₂(η⁵-C₅H₄R) ₂(μ-CH₂PPh₂)(μ-PPh ₂)(μ-CO)]. Separate experiments show that the latter compounds are formed from [Mo₂(η⁵-C₅H₄R) ₂(μ-CH₂PPh₂)(μ-PPh₂)(CO) ₂] under photolytic conditions, this reaction being reversible. Thus it is concluded that the P-C(sp³) cleavage of the dppm ligand is fairly well suppressed at ambient temperatures or below. The reactions of all the above unsaturated species with CN^tBu proceed rapidly at room temperature. In this way, the new isocyanide derivatives [Mo₂(η⁵-C₅H₄Me) ₂(μ-CH₂PPh₂)(μ-PPh₂)(CN ^tBu)(μ-CO)(CO)], [Mo₂(η⁵-C₅H₅) ₂(μ-CH₂PPh₂)(μ-PPh₂)(CN ^tBu)(CO)], and[Mo₂(ηC₅-C₅H₄R) ₂(μ-η¹,η²-CN^tBu)(CO) ₂(μ-dppm)] have been prepared. All of them are formed in good yields as single isomers but have a rather low stability. Reaction of the monocarbonyl derivative with atmospheric oxygen gives the oxo complex [Mo₂(η⁵-C₅H₅) ₂(μ-CH₂PPh₂)(μ-O)(μ-OPPh ₂)(CN^tBu)(CO)], which is also obtained as a single isomer. In marked contrast to their ditungsten analogues, the isocyanide-bridged compounds [Mo₂(η⁵-C₅H₄R) ₂(μ-η¹,η²-CN^tBu)(CO) ₂(μ-dppm)] do not experience C-H bond cleavages in their cyclopentadienylic rings to a significant extent.

Full text of DOI:10.1021/om9607154

624
Organometallics 1997, 16, 624-631
Oxid a tive Ad d ition s of Coor d in a ted Liga n d s a t
Un sa tu r a ted Molybd en u m a n d Tu n gsten
Dip h osp h in e-Br id ged Ca r bon yl Dim er s. 2.
Deca r bon yla tion Rea ction s of
[Mo2(η5-C5H4R)2(CO)4(µ-P h 2P CH2P P h 2)] (R ) H, Me)
Gema Garc´ıa, M. Esther Garc´ıa, Sonia Melo´n, V´ıctor Riera, and Miguel A. Ruiz*
Departamento de Qu´ımica Orga´nica e Inorga´nica/ IUQOEM, Universidad de Oviedo,
E-33071 Oviedo, Spain
Fernando Villafan˜e
Departamento de Quı´mica Inorga´nica, Universidad de Valladolid, E-47005 Valladolid, Spain
Received August 20, 1996X
Decarbonylation of the dimolybdenum complexes [Mo2(η5-C5H4R)2(CO)4(µ-dppm)] (R ) H,
Me, dppm ) Ph2PCH2PPh2) occurs readily upon heating in tetrahydrofuran or toluene
solution to afford with good yield the phosphido complexes [Mo2(η5-C5H4R)2(µ-CH2PPh2)(µ-
PPh2)(CO)2], which arise from an irreversible P-C(sp3) bond cleavage in the backbone of
the dppm ligand. Other minor products in these reactions are the oxo complexes [Mo2(η5-
C5H4R)2(µ-CH2PPh2)(O)(µ-PPh2)(CO)], which are formed by the action of oxygen on the former
dicarbonyl compounds, and the triply-bonded complexes [Mo2(η5-C5H4R)2(CO)2(µ-dppm)], in
which the dppm ligand remains intact. By contrast, photochemical decarbonylation of the
parent tetracarbonyl complexes at 10 °C yields the triply-bonded dicarbonyls as major
products, along with a small amount of the monocarbonyl complexes [Mo2(η5-C5H4R)2(µ-
CH2PPh2)(µ-PPh2)(µ-CO)]. Separate experiments show that the latter compounds are formed
from [Mo2(η5-C5H4R)2(µ-CH2PPh2)(µ-PPh2)(CO)2] under photolytic conditions, this reaction
being reversible. Thus it is concluded that the P-C(sp3) cleavage of the dppm ligand is
fairly well suppressed at ambient temperatures or below. The reactions of all the above
unsaturated species with CNtBu proceed rapidly at room temperature. In this way, the
new isocyanide derivatives [Mo2(η5-C5H4Me)2(µ-CH2PPh2)(µ-PPh2)(CNtBu)(µ-CO)(CO)], [Mo2(η5-
C5H5)2(µ-CH2PPh2)(µ-PPh2)(CNtBu)(CO)], and [Mo2(η5-C5H4R)2(µ-η1,η2-CNtBu)(CO)2(µ-dppm)]
have been prepared. All of them are formed in good yields as single isomers but have a
rather low stability. Reaction of the monocarbonyl derivative with atmospheric oxygen gives
the oxo complex [Mo2(η5-C5H5)2(µ-CH2PPh2)(µ-O)(µ-OPPh2)(CNtBu)(CO)], which is also
obtained as a single isomer. In marked contrast to their ditungsten analogues, the
isocyanide-bridged compounds [Mo2(η5-C5H4R)2(µ-η1,η2-CNtBu)(CO)2(µ-dppm)] do not experi-
ence C-H bond cleavages in their cyclopentadienylic rings to a significant extent.
In tr od u ction
(2a ).2 In view of the general interest of C-P3 and C-H4
activation processes we decided to examine in more
detail the decarbonylation reactions of the dimolybde-
num compound 1a and to extend these studies to its
methylcyclopentadienyl analogue [Mo2Cp′2(CO)4(µ-dppm)]
(1b) (Cp′ ) η5-C5H4Me).
In the first part of this series we have shown that
decarbonylation of the ditungsten complex [W2Cp2(CO)4-
(µ-dppm)] (Cp ) η5-C5H5; dppm ) Ph2PCH2PPh2) leads
mainly to the triply-bonded species [W2Cp2(CO)2(µ-
dppm)].1 This can be accomplished either thermally or
photochemically and occurs via the hydrido cyclopen-
tadienylidene complex [W2(µ-η1,η5-C5H4)Cp(µ-H)(CO)3-
(µ-dppm)], a product derived from the intramolecular
cleavage of a C-H bond in the cyclopentadienyl ligand,
which turns out to be reversible. The above results are
in marked contrast with our preliminary decarbonyla-
tion studies on the related dimolybdenum complex [Mo2-
Cp2(CO)4(µ-dppm)] (1a ), which showed that P-C(sp3)
bond cleavage of the dppm ligand was the dominant
process under thermolytic conditions, this leading to the
unsaturated species [Mo2Cp2(µ-CH2PPh2)(µ-PPh2)(CO)2]
Resu lts a n d Discu ssion
Sta r tin g Su bstr a tes. The synthesis of compound 1a
has been previously described.5 The methylcyclopen-
(2) Riera, V.; Ruiz, M. A.; Villafan˜e, F.; Bois, C.; J eannin, Y. J .
Organomet. Chem. 1989, 375, C23.
(3) (a) Chaudret, B.; Delavaux, B.; Poilblanc, R. Coord. Chem. Rev.
1988, 86, 191. (b) Garrou, P. E. Chem. Rev. 1985, 85, 171.
(4) (a) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987; p 295. (b) Crabtree,
R. H. Angew. Chem., Int. Ed. Engl. 1993, 32, 789. (c) Ryabov, A. D.
Chem. Rev. 1990, 90, 403. (d) J ones, W. D.; Feher, F. J . Acc. Chem.
Res. 1989, 22, 91. (e) Crabtree, R. H. Chem. Rev. 1985, 85, 245. (f)
Brookhart, M.; Green, M. L. H. J . Organomet. Chem. 1983, 250, 395.
(5) Riera, V.; Ruiz, M. A.; Villafan˜e, F. Organometallics 1992, 11,
2854.
X Abstract published in Advance ACS Abstracts, J anuary 1, 1997.
(1) (a) Part 1: Alvarez, M. A.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.;
Falvello, L. R.; Bois, C. Organometallics, in press. (b) Alvarez, M. A.;
Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.; Bois, C.; J eannin, Y. J . Am. Chem.
Soc. 1993, 115, 3786.
S0276-7333(96)00715-7 CCC: $14.00 © 1997 American Chemical Society

Mo and W Diphosphine-Bridged Carbonyl Dimers
Organometallics, Vol. 16, No. 4, 1997 625
Ta ble 1. IR a n d 31P {1H} NMR Da ta for New Com p ou n d s
compd
νst(CO)a/cm-1
δ(P)b
J PP
[Mo2Cp′2(CO)4(µ-dppm)] (1b)
1842 (m), 1822 (ms)
1913 (ms), 1874 (vs)c
1835 (m, sh), 1807 (s)c
1833 (m, sh), 1796 (s)c
1787 (s)c,g
46.5 (br, isomer A)
34.8 (br, isomer B)d
92.1, 46.8e
[Mo2Cp2(µ-CH2PPh2)(µ-PPh2)(CO)2] (2a )
[Mo2Cp′2(µ-CH2PPh2)(µ-PPh2)(CO)2] (2b)
[Mo2Cp′2(µ-CH2PPh2)(O)(µ-PPh2)(CO)] (3b)
[Mo2Cp2(CO)2(µ-dppm)] (4a )
16
16
3
94.0, 46.6f
198.8, 39.6e
57.9
1739 (s)
1735 (s)
1674 (s)
1669 (s)
[Mo2Cp′2(CO)2(µ-dppm)] (4b)
58.0
[Mo2Cp2(µ-CH2PPh2)(µ-PPh2)(µ-CO)] (5a )
[Mo2Cp′2(µ-CH2PPh2)(µ-PPh2)(µ-CO)] (5b)
[Mo2Cp2(µ-η1,η2-CNtBu)(CO)2(µ-dppm)] (6a )
[Mo2Cp′2(µ-η1,η2-CNtBu)(CO)2(µ-dppm)] (6b)
[Mo2Cp2(µ-η1,η2-CNtBu)(CNtBu)(CO)2(η1-dppm)] (7)
206.0, 20.4f
16
16
84
84
84
83
2
207.1, 21.7e
53.5, 37.7f
1825 (s), 1788 (vs)h
1825 (s), 1788 (vs)i
1836 (s), 1805 (vs)
52.4, 35.5
72.8, -25.0 (isomer A)
72.5, -25.1 (isomer B)k
104.8, 67.5m
103.4, 58.7o
107.6, 58.9
[Mo2Cp′2(µ-CH2PPh2)(µ-PPh2)(CNtBu)(µ-CO)(CO)] (8)
[Mo2Cp2(µ-CH2PPh2)(µ-PPh2)(CNtBu)(CO)] (9)
1833 (s, br), 1685 (m)l
1760 (vs)n
8
187
[Mo2Cp2(µ-CH2PPh2)(µ-OPPh2)(µ-O)(CNtBu)(CO)] (10)
1815 (vs)c,p
a
b
Recorded in THF solution unless otherwise stated. Recorded at 121.50 MHz and 291 K in CD2Cl2 solution unless otherwise stated;
δ in ppm relative to external 85% aqueous H3PO4; J in hertz. c Toluene solution. Recorded at 161.98 MHz; ratio B:A ca. 5; this ratio
d
increases to ca. 20 at 233 K. e C6D6 solution. f Toluene-d8 solution. νst(Mo-O) ) 907 cm-1 in KBr disk. νst(CN) ) 1666 (w), 1636 cm-1
g
h
(w). Dichloromethane solution; νst(CN) ) 1655 (w), 1636 (w). νst(CN) ) 2120 (w), 1651 (w), 1619 cm-1 (w). Ratio A:B ca. 1. νst(CN) )
i
j
k
l
2130 (s). 253 K. νst(CN) ) 2040 cm-1 (s). o 213 K. νst(CN) ) 2112 cm-1 (s).
m
n
p
Ch a r t 1
Ch a r t 2
angle of the methylcyclopentadienyl ligand, relative to
the unsubstituted ring, the difference being estimated
as ca. 10°.8 The above modifications have clear struc-
tural consequences. For example, the ratio between
isomers B and A in CD2Cl2 solution at 291 K increases
from ca. 2 (for 1a ) to ca. 5 (for 1b), a change that can be
mostly attributed to steric factors by recalling that the
B:A isomer ratio for the ditungsten complex [W2Cp2-
(CO)4(µ-dppm)] is ca. 0.5 under the same conditions.
However, in spite of this marked structural effect, the
presence of the methylcyclopentadienyl ligand induces
only a quite modest influence on the decarbonylation
reactions of these dimetallic substrates, as will be next
discussed.
Th er m al Decar bon ylation of Com pou n ds 1. Com-
plex 1a is readily decarbonylated in tetrahydrofuran at
60 °C to give the unsaturated complex [Mo2Cp2(µ-CH2-
PPh2)(µ-PPh2)(CO)2)] (2a ) (Chart 2) in high yield, along
with trace amounts of the oxo compound [Mo2Cp2(µ-
CH2PPh2)(O)(µ-PPh2)(CO)] (3a ) and the triply-bonded
complex [Mo2Cp2(CO)2(µ-dppm)] (4a ). Compound 3a is
probably formed during manipulation of the reaction
mixture. This follows from the previous observation
that 3a is a major product in the reaction of 2a with
molecular oxygen.9 On the other hand, the relative
amounts between isomers 2a and 4a could not be sig-
nificantly modified by changing the reaction conditions
(solvent, temperature, etc.). Moreover, pure samples of
compounds 2a or 4a did not show noticeable transfor-
mations upon heating under the above conditions.
The methylcyclopentadienyl complex 1b behaves analo-
gously, affording the P-C cleavage product 2b in high
tadienyl complex 1b is analogously prepared by addition
of dppm to the triply-bonded dimer [Mo2Cp′2(CO)4]. As
found for 1a , complex 1b displays two isomers in
solution (labeled A and B, Table 1), with their ratio
being temperature and solvent dependent. Because of
the relatively fast exchange between isomers (on the
NMR time scale) sharp NMR resonances for 1b could
only be obtained at low temperature, where isomer B
is the dominant species present (ratio B:A ca. 10 at 253
1
K in CD2Cl2 solution). Its H NMR spectrum showed
the chemical equivalence of the methylenic protons of
the dppm ligand, in agreement with the data previously
obtained for [W2Cp2(CO)4(µ-dppm)].1 Thus we conclude
that, contrary to our earlier proposal for 1a ,5 and in
agreement with that of Azam et al. on the same
complex,6 the structures of isomers A and B in solution
are adequately represented by those determined crys-
tallographically for [Mo2Cp2(CO)4(µ-HtBuPCH2PtBuH)]7
(isomer A) and for 1a 6 (isomer B) (Chart 1).
The presence of the methylcyclopentadienyl ligand in
1b increases both the electron density and steric hin-
drance at the dimolybdenum center, when compared
with the cyclopentadienyl complex 1a . The former effect
is reflected in the average νst(CO) frequencies, decreas-
ing in toluene solution from 1869 cm-1 (1a ) to 1860 cm-1
(1b), the latter value being the same as that found for
the ditungsten complex [W2Cp2(CO)4(µ-dppm)].1 As will
be seen later, this does not translate into similar
chemical behaviors for 1b and the ditungsten complex.
On the other hand, changes in the steric hindrance at
the dimetal center are expected due to the higher cone
(6) Azam, K. A.; Deeming, A. J .; Felix, M. S. B.; Bates, P. A.;
Hursthouse, M. B. Polyhedron 1988, 7, 1793.
(7) Brauer, D. J .; Hasselkuss, G.; Stelzer, O. J . Organomet. Chem.
1987, 321, 339.
(8) Coville, N. J .; du Plooy, K. E.; Pickl, W. Coord. Chem. Rev. 1992,
116, 1.
(9) Riera, V.; Ruiz, M. A.; Villafan˜e, F.; Bois, C.; J eannin, Y.
Organometallics 1993, 12, 124.

626 Organometallics, Vol. 16, No. 4, 1997
Garc´ıa et al.
Ch a r t 3
yield, along with small amounts of 3b and 4b. However,
IR monitoring of the reaction (either in toluene or THF)
shows in this case additional νst(CO) bands at 1969,
1908, 1890, 1780, and 1743 cm-1, which can be at-
tributed to [MoCp′(CO)2(dppm)][MoCp′(CO)3] by com-
parison to its cyclopentadienyl analogue.5 The forma-
tion of this side product, not observed during decar-
bonylation of 1a , might reflect the increase in the steric
pressure at the dimetal center introduced by the me-
thylcyclopentadienyl ligands.
Spectroscopic data for the oxo complex 3b are entirely
analogous to that for 3a , which we have discussed
previously in detail,9 and need then no further comment.
The structure has been confirmed through an X-ray
study on the ditungsten analogue [W2Cp2(µ-CH2PPh2)-
(O)(µ-PPh2)(CO)].1 The proposed structure for the di-
carbonyls 2 is based on that of the latter oxo complex,
after replacing the terminal oxo ligand by a carbonyl.
This results in a trans arrangement of both carbonyls
in the molecule, relative to the average plane defined
by the metal atoms and bridging ligands. In agreement
with this proposal, the IR spectra of compounds 2
exhibit the νst(CO) pattern expected for such a relative
arrangement (medium and strong intensities, in order
of decreasing frequency).10 The phosphinomethyl ligand
in complexes 2 is characterized by a 31P NMR resonance
in a region similar to that of the dppm complexes 1,
while its CH2 group gives characteristic low-field 1H and
13C NMR resonances, as expected from its coordination
to a transition-metal atom. The phosphido ligands in
compounds 2 give rise to a more deshielded resonance
as expected.11 The corresponding chemical shifts (ca.
90 ppm) are similar to that found for the isoelectronic
bis(phosphido) complex [Mo2Cp2(µ-PPh2)2(CO)2].12 Yet,
these shifts can be considered somewhat low for a
diphenylphosphido bridge at a metal-metal-bonded
binuclear complex. Because of the unsaturated nature
of compounds 2, the intermetallic distance is expected
to be short, thus leading to relatively low Mo-P-Mo
bond angles. This in turn could cause a shielding
effect on the 31P resonance of the phosphido bridge, as
it has been previously found for binuclear group 8
complexes.11,13
P h otoch em ica l Deca r bon yla tion of Com p ou n d s
1. Compounds 1a ,b are slowly decarbonylated by the
action of UV light in tetrahydrofuran at 10 °C to give
the triply-bonded dicarbonyl complexes 4a ,b in high
yield, along with small amounts of the monocarbonyl
species [Mo2L2(µ-CH2PPh2)(µ-PPh2)(µ-CO)] (5a , L ) Cp;
5b, L ) Cp′). Noticeably, the dicarbonyl complexes 2
were completely absent in these reaction mixtures.
Separate experiments showed that compounds 4 and
5 arise from different reaction pathways. Thus, pure
samples of compounds 4 gave no detectable amounts of
the corresponding complexes 5 after prolonged exposure
to the UV light. On the other hand, compounds 5 can
be obtained almost quantitatively upon UV photolysis
of the dicarbonyl compounds 2. Moreover, the photo-
chemical transformation from 2 to 5 was found to occur
faster than that one from 1 to 4. Thus it is concluded
that, contrary to the thermolytic experiments, the
photochemical decarbonylation of compounds 1 leads
mainly to the dppm-bridged dicarbonyls 4 (Chart 3) and
only to small amounts of the P-C cleavage products 2
which, being rapidly decarbonylated under the experi-
mental conditions, are observed as their monocarbonyl
derivatives 5. From the above data it seems that
formation of the P-C cleavage products (2 or 5) is fairly
suppressed at low temperatures. However, full sup-
pression of the P-C cleavage process could not be
reached, because the photochemical decarbonylation of
compounds 1 below 0 °C becomes too slow to be effective
in a preparative sense.
Spectroscopic data for compounds 4 indicate a close
structural relationship to the ditungsten triply-bonded
complex [W2Cp2(CO)2(µ-dppm)].1 The crystal structure
of the latter revealed the presence of linear semibridging
carbonyls experiencing an incipient dynamic disorder,
which in solution was observed in the form of a rapid
scrambling of the carbonyl ligands between both metal
centers. This seems to be also the case for the dimo-
lybdenum compounds 4, as far as the structure in
solution is concerned. Thus, the IR spectra of complexes
4 display a single νst(CO) band at ca. 1740 cm-1 and a
single 13C NMR resonance for the carbonyl ligands at
ca. 254 ppm (to be compared to 1730 cm-1 and 241 ppm
for the ditungsten complex).
The structural characterization of the monocarbonyl
complexes 5 is firmly supported on their spectroscopic
data. The bridging nature of the single carbonyl ligand
in these molecules is clearly indicated by their low νst-
(CO) values (ca. 1670 cm-1) and high 13C NMR chemical
shifts (ca. 305 ppm). The phosphinomethyl ligand gives
rise to the expected 31P, 13C, or 1H NMR resonances,
not very different from those exhibited by their dicar-
bonyl precursors 2. However, the 31P NMR chemical
shift of the phosphido group in compounds 5 (ca. 207
ppm) is ca. 110 ppm higher than those found for
compounds 2. The bis(phosphido) complex [Mo2Cp2(µ-
PPh2)2(µ-CO)], which is isoelectronic to 5, has been
shown to display a similar 31P NMR chemical shift (ca.
198 ppm) and a very short intermetallic distance (2.515-
(2) Å).12 Thus, the dramatic differences in the 31P NMR
shifts found for compounds 2 and 5 can be hardly
explained only on the basis of geometrical grounds.
Therefore, it is likely that the differences in the formal
bond orders for the above species (double vs triple
metal-metal bond) have a significant influence on the
shielding of the phosphido group.
(10) Braterman, P. S. Metal Carbonyl Spectra; Academic Press:
London, 1975.
(11) Carty, A. J .; MacLaughin, S. A.; Nucciarone, D. In Phosphorus-
31 NMR Spectroscopy in Stereochemical Analysis; Verkade, J . G., Quin,
L. D., Eds.; VCH: New York, 1987; Chapter 16.
(12) Adatia, T.; McPartlin, M.; Mays, M. J .; Morris, M. J .; Raithby,
P. R. J . Chem. Soc., Dalton Trans. 1989, 1555.
(13) Carty, A. J .; Fyfe, C. A.; Lettinga, M.; J ohnson, S.; Randall, L.
H. Inorg. Chem. 1989, 28, 4120.
Rea ction s of Com p ou n d s 4 w ith CO a n d CNtBu .
As we have said above, the formation of the triply-
bonded complex [W2Cp2(CO)2(µ-dppm)] from [W2Cp2-
(CO)4(µ-dppm)] proceeds through the hydrido cyclopen-

Mo and W Diphosphine-Bridged Carbonyl Dimers
Organometallics, Vol. 16, No. 4, 1997 627
Ch a r t 4
F igu r e 1. Proposed structures for the isomers detected
in the solutions of complex 7 (PsP ) dppm).
could well correspond to a hydrido cyclopentadienyli-
dene complex analogous to the above mentioned ditung-
sten compound. However, no conditions could be found
for increasing the relative amount of this minor species.
Compound 6a reacts slowly with an excess of CNtBu
at room temperature to afford the bis(isocyanide) com-
plex [Mo2Cp2(µ-η1,η2-CNtBu)(CNtBu)(CO)2(η1-dppm)] (7).
Although the crude reaction mixture contained no other
organometallic products in significant amounts (as
shown by IR and 31P NMR spectroscopy), all attempts
to isolate this complex as a pure solid sample were
unsuccessful. In fact, rapid decomposition of this spe-
cies takes place when the excess isocyanide ligand is
removed. The methylcyclopentadienyl compound 6b
reacts analogously with an excess of CNtBu, but the
product was even less stable and no further attempts
were made to characterize it.
The retention of the η1,η2-bridging isocyanide in
complex 7 is clearly indicated by the presence of C-N
stretching bands at 1651 and 1619 cm-1, while the new
terminal isocyanide ligand gives rise to a characteristic
C-N stretch at 2120 cm-1. The 31P{1H} NMR spectrum
of complex 7 suggests the presence of two similar
isomers, they being present in a ca. 1:1 ratio. Each of
these isomers (labeled A and B in Table 1) gives rise to
two doublets, one of them at ca. 70 ppm and the other
one at ca. -25 ppm, the latter being very close to the
chemical shift of the free dppm ligand. These data are
clearly indicative of the presence of unidentate dppm
ligand and are similar to those measured for [Mo2Cp2(µ-
η1,η2-CNtBu)(CO)3(η1-dppm)].15 In fact, the structure of
compound 7 can be derived from the molecular structure
of the above tricarbonyl complex,15 after replacing one
carbonyl by a terminal CNtBu ligand. As the latter
complex presents no isomers in solution, those isomers
observed for compound 7 then probably arise from the
two possible coordination positions of the terminal
isocyanide relative to the bridging one, at the metal
atom not bearing the phosphorus ligand (Figure 1).
The formation of compound 7 from 6a implies that
coordination of the second CNtBu ligand causes a Mo-P
cleavage process. This is somewhat unexpected con-
sidering the lability of the bridging isocyanide ligand
in 6 and the fact that the related complexes [Mo2Cp2(µ-
η1,η2-CNR)(CO)4] (R ) tBu, Ph, Me) transform into [Mo2-
Cp2(CNR)2(CO)4] upon reaction with CNR.14a Thus,
formation of complex 7 rather than its dppm-bridged
isomer [Mo2Cp2(CNtBu)2(CO)2(µ-dppm)] might have an
steric origin, as the relatively bulky dppm ligand thus
occupies a less space-demanding position.
tadienylidene complex [W2(µ-η1,η5-C5H4)Cp(µ-H)(CO)3(µ-
dppm)]. In the case of our dimolybdenum complexes,
no intermediates were detected during the formation
of dicarbonyls 4. In an attempt to reach these presumed
intermediates we examined the reactions of 4 with CO
and CNtBu.
Complexes 4 are rapidly carbonylated at room tem-
perature or below to regenerate the parent tetracarbo-
nyls 1. Unfortunately, no intermediates were detected
in these reactions either. However, the reactions of
compounds 4 with CNtBu proceed at a somewhat lower
rate, which allows a stoichiometric control of the reac-
tion. When 1 equiv of CNtBu is used, the isocyanide-
bridged species [Mo2L2(µ-η1,η2-CNtBu)(CO)2(µ-dppm)]
(6a , L ) Cp; 6b, L ) Cp′) (Chart 4) are formed in good
yields. The structural characterization of compounds
6 is straightforward by comparison of their spectroscopic
data with those of the ditungsten analogue [W2Cp2(µ-
η1,η2-CNtBu)(CO)2(µ-dppm)]1 or the related species [W2-
t
Cp2(µ-η1,η2-CNR)(CO)4] (R ) Bu, Ph, Me)14 and [Mo2-
Cp2(µ-η1,η2-CNtBu)(CO)3(η1-dppm)].15 In particular, the
coordination of the isocyanide ligand in a σ, π fashion
is deduced from the low C-N stretching frequencies (ca.
1670-1640 cm-1) and high 13C NMR chemical shifts
(223 ppm for 6a ). We must note that for compounds 6
two C-N stretches (instead of a single one) are observed
in the IR spectrum. This has been found sometimes for
either terminal16 or bridging15 isocyanide ligands and
might be attributed to the presence of more than one
conformer for these molecules.
The ditungsten analogue of compounds 6 was found
to isomerize at room temperature to yield the corre-
sponding hydrido cyclopentadienylidene complex [W2-
(µ-η1,η5-C5H4)Cp(µ-H)(CO)2(CNtBu)(µ-dppm)].1 Indeed
complexes 6 also have only a moderate stability; how-
ever they do not experience C-H(cyclopentadienyl)
cleavage processes at a significant extent. Instead, the
isocyanide ligand dissociates rather easily (for example
during the usual purification steps) so that the corre-
sponding dicarbonyls 4 are regenerated. In spite of this,
1
we note that the H NMR spectra of crude samples of
the methylcyclopentadienyl complex 6b denote the
presence of small amounts of a species having a hydrido
resonance at -12.35 ppm (dd, J PH ) 41, 26 Hz). This
(14) (a) Adams, H.; Bailey, N. A.; Bannister, C.; Faers, M. A.;
Fedorko, P.; Osborn, V. A.; Winter, M. J . J . Chem. Soc., Dalton Trans.
1987, 341. (b) Adams, R. D.; Katahira, D. A.; Wang, L. W. Organo-
metallics 1982, 1, 231.
(15) Riera, V.; Ruiz, M. A.; Villafan˜e, F.; Bois, C.; J eannin, Y. J .
Organomet. Chem. 1990, 382, 407.
Rea ction s of Com p ou n d s 2 a n d 5 w ith CO a n d
CNtBu . In order to trace back the decarbonylation
pathway leading from compounds 1 to 2 or 5, we decided
to study the carbonylation reactions of the latter un-
saturated species. This also should give us information
about the reversibility of the P-C cleavage process
(16) (a) Singleton, E.; Oosthuizen, H. E. Adv. Organomet. Chem.
1983, 22, 209. (b) Harris, G. W.; Albers, M. D.; Boeyens, J . C. A.;
Coville, N. J . Organometallics 1983, 2, 609. (c) Riera, V.; Ruiz, J .;
J eannin, Y.; Philoche-Levisalles, M. J . Chem. Soc., Dalton Trans. 1988,
1591. (d) Mart´ınez de Ilarduya, J . M.; Otero, A.; Royo, P. J . Organomet.
Chem. 1988, 340, 187.

628 Organometallics, Vol. 16, No. 4, 1997
Garc´ıa et al.
Ch a r t 5
Ch a r t 6
5a reacts rapidly with 1 equiv of CNtBu to give cleanly
[Mo2Cp2(µ-CH2PPh2)(µ-PPh2)(CNtBu)(CO)] (9) (Chart 6),
which is isoelectronic to complexes 2. The 31P NMR
spectrum of 9 is similar to that of 2a as expected, while
its IR spectrum denotes the presence of terminal iso-
cyanide (νst(CN) ) 2040 cm-1) and carbonyl (νst(CO) )
1760 cm-1) ligands. However, complex 9 is extremely
air sensitive, so we could not assign unambiguously its
1H NMR resonances nor obtain an informative 13C NMR
spectrum. Thus, direct identification of the coordination
position of the isocyanide ligand in this species could
not be achieved.
responsible for the formation of these products. Once
again, CNtBu was also used as a model for CO when
the latter gave not enough information.
As expected, the triply-bonded monocarbonyls 5 react
rapidly with CO (1 atm) at room temperature to give
quantitatively the corresponding dicarbonyls 2. Sur-
prisingly, however, the reaction does not proceed any
further under these conditions, in spite of the formal
unsaturation of complexes 2. We noticed that toluene
solutions of 2a changed from brown to pink upon
exposure to a higher CO pressure (ca. 2-3 atm), but
the change was reversed as soon as the pressure was
released.
Reaction of complex 9 with molecular oxygen gives
with good yield the oxo derivative [Mo2Cp2(µ-CH2PPh2)-
(µ-O)(µ-OPPh2)(CNtBu)(CO)] (10). This complex is iso-
electronic and presumably isostructural to the dicarbo-
nyl compound [Mo2Cp2(µ-CH2PPh2)(µ-O)(µ-OPPh2)(CO)2].9
In fact, 1H, 31P, and 13C NMR data for these two species
are very similar and need then no further discussion.
The location of the terminal isocyanide in 10 is deter-
mined on the basis of the observed P-C couplings.
Thus, the terminal carbonyl gives rise to a doublet of
In an attempt to model the carbonylation reaction of
dicarbonyls 2 we reacted 2b with 1 equiv of CNtBu, this
ligand being a better electron donor than CO. That
reaction proceeds rapidly in THF at 0 °C to give almost
quantitatively the isocyanide complex [Mo2Cp′2(µ-
CH2PPh2)(µ-PPh2)(CNtBu)(µ-CO)(CO)] (8) (Chart 5).
Compound 8 can be isolated as an essentially pure solid,
but attempts to further purify it led to its progressive
(crystallization) or complete (chromatography) decom-
position. The oxo complex 3b was found as a major
species in these attempts, which suggests that the
isocyanide ligand in 8 is labile.
doublets in the 13C NMR spectrum at 254.1 ppm (J PC
)
17, 14 Hz), which safely places it on the molybdenum
atom bearing both phosphorus atoms of the molecule.
Therefore, the isocyanide ligand in 10 must be located
at the metal atom bearing the CH2- and O-ends of the
bridging groups. This is consistent with the fact that
this ligand gives rise to a singlet 13C NMR resonance
at 174.4 ppm, because at that position there are only
three-bond pathways connecting the isocyanide carbon
with any of the phosphorus atoms of the molecule, and
this is expected to result in very small P-C couplings.
On the other hand, as there is no reason to anticipate
a change in the location of the terminal isocyanide
ligand when going from 9 to 10, it is assumed that
this ligand in compound 9 is also bonded to the metal
atom bearing the C- and O-ends of the bridging phos-
phorus ligands (Chart 6), in agreement with the initial
expectations.
1
The spectroscopic data for 8 show H and 31P NMR
resonances for the phosphido and phosphinomethyl
groups not very different from those of 2b. The IR
spectrum of 8 clearly indicates that the isocyanide
ligand adopts a terminal coordination mode (νst(CN) )
2130 cm-1) while one of the carbonyls has moved into a
bridging position (νst(CO) ) 1685 cm-1). This is further
corroborated in the 13C NMR spectrum, which shows
respectively low (163.2 ppm) and high (294.4 ppm)
chemical shifts for the coordinated carbon atoms of these
ligands. In addition, the terminal carbonyl (δc ) 256.6
ppm) is equally coupled to both phosphorus atoms (J PC
) 16 Hz) while the coordinated carbon of the isocyanide
ligand is just coupled to a single phosphorus atom. This
strongly suggests that the isocyanide ligand is bonded
to the molybdenum atom bearing the C-end of the
phosphinomethyl group.
The regiospecific addition of CNtBu to 2b can be
attributed to both electronic and steric factors. In the
first place, the PPh2 group of the phosphinomethyl
ligand is clearly more space-demanding than its CH2
group. On the other hand, the former group is also
likely to be a somewhat better donor. Thus, coordina-
tion of CNtBu at the CH2-bonded molybdenum atom in
compounds 2 would be favored because this metal atom
is both the less crowded and also somewhat electron
poorer in the dimetal center.
The formation of the oxo complex 10 requires the
addition of an oxygen atom to the double metal-metal
bond in 9 and insertion of a second oxygen in a
P(phosphido)-metal bond, specifically in that metal
atom bonded to the CH2 group of the phosphinomethyl
ligand. This insertion pattern parallels that found for
the reactions of 2a with molecular oxygen9 and can be
understood on grounds similar to the ones used above
to rationalize the reactions of complexes 2 or 5 toward
CNtBu. As a result, the phosphido group is transformed
into a bridging phosphidoxo (µ-OPPh2) ligand. Prece-
dents for this insertion reactions are scarce, but some
examples are available from studies on group 9 metal
dimethylphosphido complexes.17 Alternatively, P-C
The above considerations should apply for the mono-
carbonyl compounds 5, so we would predict that
CNtBu should bind this molecule at the CH2-bonded
molybdenum atom. Unfortunately, direct verification
of this hypothesis was not possible. Indeed, complex
(17) (a) Klingert, B.; Rheingold, A. L.; Werner, H. Inorg. Chem. 1988,
27, 1354. (b) Klingert, B.; Werner, H. J . Organomet. Chem. 1983, 252,
C47.

Mo and W Diphosphine-Bridged Carbonyl Dimers
Organometallics, Vol. 16, No. 4, 1997 629
Sch em e 1. P r op osed Rea ction P a th w a ys in th e
Deca r bon yla tion Rea ction s of Com p ou n d s 1a
tural to the isocyanide complex 8 and would easily
decarbonylate further to yield the dicarbonyls 2. We
recall here that complexes 2 give no stable CO adducts
(i.e. intermediates B) and that compound 8 easily gives
up the isocyanide ligand. Thus, the equilibrium B/2 +
CO seems to be shifted far to the right under the
experimental conditions examined. Finally, compounds
2 would lose under photochemical activation (but not
upon heating) a further CO molecule to yield the
monocarbonyls 5, as it has been demonstrated through
separate experiments.
From our data it is clear that processes a and b can
occur both under thermal or photochemical conditions
but at different extents. We recall here that the
corresponding products, 4 and 2 (or 5), do not intercon-
vert under these conditions, so the product distribution
is kinetically controlled. Thus, P-C cleavage of the
backbone of the dppm ligand becomes dominant (faster)
at high temperatures (thermal decarbonylations in the
range 65-110 °C) while it is fairly well suppressed at
low temperatures (photochemical decarbonylations at
10 °C or below). This is not surprising, as the vast
majority of observed P-C cleavage processes in phos-
phine ligands occur upon heating.3 This is also the case
for the P-C(sp3) cleavages occurring on the diiron
complexes [Fe2(µ-CO)(CO)6(µ-R2PCH2PR2)],20 which are
entirely analogous to the ones here reported.
In the light of our previous studies on the ditungsten
analogues of 1,1 we would have expected to observe the
products of a third reaction pathway starting from
intermediate A, that is the intramolecular C-H (Cp)
oxidative addition leading to the hydride [Mo2(µ-η1,η5-
C5H3R)(η5-C5H4R)(µ-H)(CO)3(µ-dppm)] (R ) H, Me).
However, as we have said above, we have obtained only
weak evidence for the presence of this type of product,
which in any case are formed in very small amounts.
This stands in contrast to the behavior of the ditungsten
system, where the C-H cleavage process can be entirely
dominant. There is no clear explanation for that
significant difference when moving from molybdenum
to tungsten. In our studies on the photochemical
decarbonylations of [M2Cp2(CO)6] (M ) Mo, W) we have
established that C-H (Cp) cleavages invariably occur
to yield the trinuclear clusters [M3(µ-η1,η5-C5H4)Cp2-
(CO)6].21 From these studies we concluded that the
cyclopentadienylidene ligand has a marked thermody-
namic preference to form σ bonds to tungsten rather
than to molybdenum atoms. So this thermodynamic
effect could be in part responsible for the evolution of
the dimolybdenum intermediate A not through the C-H
cleavage pathway. Another effect working in favor of
the P-C cleavage pathway is the fact that the trans-
formation A into B seems to be irreversible, while the
C-H cleavage of the cyclopentadienylic ring is expected
to be reversible.1
a
L ) C5H4R; R ) H, Me; P-C-P ) Ph2PCH2PPh2.
cleavage reactions in tertiary phosphine oxides also
represent a potential synthetic route for this sort of
complex.18
Rea ction P a th w a ys in th e Deca r bon yla tion of
Com p ou n d s 1. We have shown above that, depending
on the particular reaction conditions, the decarbonyla-
tion reactions of complexes 1 can lead to one or several
of the products 2, 4, and 5, the results being rather
insensitive to the nature of the cyclopentadienylic ring
(Cp or Cp′). In addition, the reactions of these unsatur-
ated products with CO and CNtBu provide complemen-
tary information about the nature and structure of the
intermediates likely involved. All these data allow us
to propose a general mechanism which gives a satisfac-
tory explanation of the decarbonylation reactions expe-
rienced by the dimolybdenum complexes 1 (Scheme 1).
As proposed for the ditungsten analogues of com-
pounds 1, the first step would be the ejection of a CO
molecule to yield a tricarbonyl intermediate A. The
latter would probably have a µ-η1,η2-CO ligand, by
analogy with the related compounds [M2Cp2(µ-η1,η2-
CO)(CO)4], which have been detected in PVC or frozen
gas matrixes as primary products in the photolysis of
the hexacarbonyl complexes [M2Cp2(CO)6].19 Interme-
diate A is also isostructural to the isocyanide-bridged
complexes 6 and would experience two major pro-
cesses: (a) a reversible further decarbonylation, yielding
the triply-bonded complexes 4 or (b) an intramolecular
but irreversible P-C(sp3) oxidative addition of the dppm
ligand to yield intermediate B. The latter is isostruc-
The above considerations allow us to partially under-
stand why the dimolybdenum systems evolve through
P-C rather than C-H bond cleavage pathways. How-
ever, it remains unclear why the P-C cleavage of the
(20) (a) Doherty, N. M.; Hogarth, G.; Knox, S. A. R.; Macpherson,
K. A.; Melchior, F.; Morton, D. A. V.; Orpen, A. G. Inorg. Chim. Acta
1992, 198-200, 257. (b) Doherty, N. M.; Hogarth, G.; Knox, S. A. R.;
Macpherson, K. A.; Melchior, F.; Orpen, A. G. J . Chem. Soc., Chem.
Commun. 1986, 540.
(21) Alvarez, M. A.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.; Bois, C.;
J eannin, Y. J . Am. Chem. Soc. 1995, 117, 1324.
(18) Fogg, D. E.; Taylor, N. J .; Meyer, A.; Carty, A. J . Organome-
tallics 1987, 6, 2252.
(19) (a) Hooker, R. H.; Rest, A. J . J . Organomet. Chem. 1983, 254,
C25. (b) Hooker, R. H.; Rest, A. J . J . Chem. Soc., Dalton Trans. 1990,
1221. (c) Baker, M. L.; Bloyce, P. E.; Campen, A. K.; Rest, A. J .;
Bitterwolf, T. E. Ibid. 1990, 2825.

630 Organometallics, Vol. 16, No. 4, 1997
Garc´ıa et al.
fraction yielded complex 2b as a dark-brown, very air-sensitive
microcrystalline powder (0.150 g, 80%). 1H NMR (200.13 MHz,
toluene-d8): δ 8.1-7.1 (20H, Ph), 5.33, 5.22, 5.07, 4.95, 4.85,
4.50, 4.45, 4.07 (8 × m, 8 × 1H, C5H4), 2.53 (dd, J HH ) 11, J PH
) 4, 1H, CH2), 1.84 (ddd, J HH ) 11, J PH ) 17, 3, 1H, CH2),
1.43, 0.98 (2 × s, 2 × 3H, Me).
backbone of the dppm ligand remains a relatively
efficient process for the dimolybdenum complex 1 even
at 10 °C (photochemical decarbonylations) while for the
ditungsten analogues this process is almost absent
under all decarbonylation conditions examined (thermal
or photochemical). Further experiments on the mixed-
metal (MoW) analogues of the tetracarbonyl species 1
are currently under way, which are expected to provide
some useful complementary information concerning this
matter.
Elution with toluene gave a violet fraction which yielded,
after removal of solvents under vacuum, the oxo complex 3a
as a dark violet powder (0.010 g, 5%). Anal. Calcd for C38H36
-
Mo2O2P2, 3b: C, 58.63; H, 4.66. Found: C, 58.35; H, 4.51. 1H
NMR (C6D6): δ 8.0-7.0 (20H, Ph), 5.78, 5.18, 5.00, 4.82, 4.65,
4.37, 4.17, 4.12 (8 × m, 8 × 1H, C5H4), 3.13 (td, J HH ) 11, J PH
) 11, 4, 1H, CH2), 2.29 (dd, J HH ) 11, J PH ) 6, 1H, CH2), 1.80,
1.55 (2 × s, 2 × 3H, Me).
Exp er im en ta l Section
Finally, elution with toluene-dichloromethane (4:1) gave
a green fraction which, after similar workup, yielded complex
4b as a green powder (0.015 g, 8%).
Gen er a l Com m en ts. The general experimental techniques
and manipulation procedures are described in ref 1a. The
compounds 1a ,5 [Mo2Cp′2(CO)4],22 and dppm23 were prepared
as described previously. NMR spectra were recorded at 291
K and 300.13 (1H), 121.50 (31P{1H}), or 75.47 MHz (13C{1H}),
unless otherwise stated. Chemical shifts are given in ppm,
relative to internal TMS (1H, 13C) or external 85% H3PO4
aqueous solution (31P). Coupling constants (J ) are given in
hertz. Complexes 2, 4a , 5, and 9 are highly air-sensitive, and
satisfactory elemental analyses could not be obtained in these
cases.
P r ep a r a tion of [Mo2Cp ′2(CO)4(µ-d p p m )] (1b). The pro-
cedure is totally analogous to that described for 1a 5 but using
[Mo2Cp′2(CO)4] instead of [Mo2Cp2(CO)4]. Typical yields on a
5 mmol scale were about 85%. Anal. Calcd for C42H38Cl2-
Mo2O4P2, 1b‚CH2Cl2: C, 54.16; H, 4.11. Found: C, 54.63; H,
4.47. 1H NMR (400.13 MHz, CD2Cl2, 243 K): δ 7.8-7.1 (Ph),
5.53, 5.29, 5.04, 4.96 (4 × m, 4 × 2H, C5H4, isomer B), 4.37 (t,
J PH ) 8, 2H, CH2, isomer B), 2.04 (s, 6H, Me, isomer B), 5.04,
4.98, 3.82, 3.56 (4 × m, 4 × 2H, C5H4, isomer A), 5.28 (t, J PH
) 8, 2H, CH2, isomer A), 1.62 (s, 6H, Me, isomer A). Ratio
B:A ca. 15.
P r epar ation of [Mo2Cp2(µ-CH2P P h 2)(µ-P P h 2)(CO)2] (2a).
A tetrahydrofuran (THF) solution (30 mL) of 1a (0.819 g, 1.0
mmol) was stirred at 60 °C for 6 h to give a dark brown
solution. The solvent was then removed under vacuum and
the residue dissolved in toluene and chromatographed at 10
°C on an alumina column (activity 4, 10 × 3 cm) prepared in
petroleum ether. Elution with the latter solvent gave a pink
fraction containing trace amounts of unidentified species as
well as some [Mo2Cp2(CO)6]. Elution with toluene gave a
brown fraction. Removal of solvents under vacuum from the
latter and washing of the residue with petroleum ether yielded
complex 2a as a brown, very air-sensitive powder (0.580 g,
76%). 1H NMR (C6D6): δ 8.0-7.1 (20H, Ph), 4.81 (s, 5H, Cp),
4.75 (s, 5H, Cp), 2.61 (dd, J HH ) 11, J HP ) 4, 1H, CH2), 1.99
(ddd, J HH ) 11, J HP ) 17, 3, 1H, CH2). 13C{1H} NMR (C6D6):
δ 233.0 (t, J PC ) 14, CO), 231.6 (dd, J PC ) 18, 3, CO), 148.0 -
127.8 (Ph), 91.4, 89.8 (2 × s, Cp), 1.0 (d, J PC ) 8, CH2).
Further elution with toluene gave a violet fraction contain-
ing a small amount of the oxo complex 3a . Finally, elution
with toluene-dichloromethane (2:1) gave a green band which,
after similar workup, yielded complex 4a as a green powder
(0.040 g, 5%).
P r epar ation of [Mo2Cp′2(µ-CH2P P h 2)(µ-P P h 2)(CO)2] (2b).
A toluene solution (15 mL) of 1b (0.200 g, 0.24 mmol) was
stirred at 110 °C for 45 min while bubbling nitrogen gently
through the solution. The resulting brown mixture was
concentrated under vacuum to ca. 5 mL and then chromato-
graphed at 10 °C on an alumina column (activity 3.5, 20 × 2.5
cm) prepared in petroleum ether. Elution with the latter
solvent gave a pink fraction containing a small amount of [Mo2-
Cp′2(CO)6]. Elution with toluene-petroleum ether (7:3) gave
a brown fraction. Removal of solvents under vacuum from this
P r ep a r a tion of [Mo2Cp 2(CO)2(µ-d p p m )] (4a ). A THF
solution (15 mL) of compound 1a (0.082 g, 0.1 mmol) was
photolyzed with visible-UV light in a quartz Schlenk tube at
10 °C for 5 h, while bubbling nitrogen gently through the
solution. Solvent was then removed under vacuum from the
dark green resulting solution, and the residue was washed
with toluene-petroleum ether (1:1, 2 × 8 mL) to remove a
small amount of compound 5a in the reaction mixture. The
washed residue was dissolved in THF and filtered. Removal
of solvent under vacuum from the filtrate yielded compound
4a as dark green, very air-sensitive solid (0.061 g, 80%). 1H
NMR (200.13 MHz, CD2Cl2): δ 7.50-7.10 (20H, Ph), 5.29 (t,
J HP ) 10, 2H, CH2), 4.51 (s, 10H, Cp). 13C{1H} NMR (50.32
MHz, CD2Cl2): δ 254.2 (t, J CP ) 5, CO), 138.4 (false t, J CP
+
J CP′ ) 45, C1[Ph]), 133.0 (false t, J CP + J CP′ ) 12, Ph), 129.8 (s,
C4[Ph]), 128.3 (false t, J CP + J CP′ ) 10, Ph), 89.1 (s, Cp), 63.7
(t, J PC ) 22, CH2).
P r ep a r a tion of [Mo2Cp ′2(CO)2(µ-d p p m )] (4b). Complex
1b (0.150 mg, 0.18 mmol) was photolyzed as described above
during 6 h. After removal of the solvent under vacuum, the
residue was dissolved in the minimum amount of toluene and
chromatographed at 10 °C on an alumina column (activity 3.5,
20 × 2.5 cm) prepared in petroleum ether. Elution with
toluene-dichloromethane (5:1) gave a green fraction which
yielded, after removal of solvents under vacuum, complex 4b
as a dark green, air-sensitive microcrystalline solid (0.105 g,
75%). Elution with toluene-dichloromethane (3:1) gave a gray
fraction which yielded, after similar workup, complex 5b as a
dark gray microcrystalline solid (0.020 g, 15%). Anal. Calcd
for C39H36Mo2O2P2, 4b: C, 59.25; H, 4.59. Found: C, 58.53;
H, 4.74. 1H NMR (200.13 MHz, CD2Cl2): δ 7.5-7.1 (20H, Ph),
5.29 (t, J PH ) 10, 2H, CH2), 4.50, 3.93 (2 × m, 2 × 4H, C5H4),
2.01 (s, 6H, Me). 13C{1H} NMR (100.61 MHz, CD2Cl2): δ 254.6
(s, br, CO), 138.3 (false t, J CP + J CP′ ) 46, C1[Ph]), 133.0 (false
t, J CP + J CP′ ) 12, Ph), 129.1 (s, C4[Ph]), 128.2 (false t, J CP
+
J CP′ ) 9, Ph), 105.6 (s, C1[C5H4]), 89.6, 87.8 (2 × s, C5H4), 63.7
(t, J PC ) 22, CH2), 14.4 (s, Me).
P r ep a r a t ion of [Mo2Cp 2(µ-CH2P P h 2)(µ-P P h 2)(µ-CO)]
(5a ). Complex 2a (0.077 g, 0.1 mmol) was photolyzed as
described above for 1 h to give a black-blue solution. Solvent
was then removed under vacuum, the residue extracted with
toluene-petroleum ether (1:1) (2 × 10 mL) and filtered.
Removal of solvents from the filtrate yielded complex 5a as a
highly air-sensitive solid (0.070 g, 95%). 1H NMR (toluene-
d8): δ 7.23-6.70 (20H, Ph), 5.27 (d, J HP ) 1, 5H, Cp), 4.97 (s,
5H, Cp), 0.03 (ddd, J HH ) 11, J PH ) 6, 1, 1H, CH2), -0.42 (dd,
J HH ) 11, J PH ) 8, 1H, CH2). 13C{1H} NMR (toluene-d8): δ
304.5 (t, J PC ) 16, µ-CO), 153.6-124.4 (Ph), 95.8, 94.1 (2 × s,
Cp), and -13.4 (s, CH2).
P r ep a r a t ion of [Mo2Cp ′2(µ-CH2P P h 2)(µ-P P h 2)(µ-CO)]
(5b). Complex 2b (0.065 g, 0.08 mmol) was photolyzed as
described above for 75 min to give a black solution. Workup
as described for 5a yielded compound 5b as a dark-gray, highly
air-sensitive solid (0.057 g, 90%). 1H NMR (C6D6): δ 7.3-6.8
(20H, Ph), 5.50, 5.18, 4.93, 4.76, 4.42 (5 × m, 5 × 1H, C5H4),
(22) Curtis, M. D.; Klinger, R. J . J . Organomet. Chem. 1978, 161,
23.
(23) Agiar, A. M.; Beisler, J . J . Org. Chem. 1964, 29, 1660.

Mo and W Diphosphine-Bridged Carbonyl Dimers
Organometallics, Vol. 16, No. 4, 1997 631
5.10-5.05 (m, 3H, C5H4), 1.82, 1.79 (2 × s, 2 × 3H, Me), -0.06
(ddd, J HH ) 11, J PH ) 6, 1, 1H, CH2), -0.40 (dd, J HH ) 11, J PH
) 8, 1H, CH2). 13C{1H} NMR (toluene-d8): δ 305.7 (br, µ-CO),
153.5-125.5 (Ph), 111.8, 108.7 (2 × s, C1[C5H4]), 96.7, 95.6,
95.5, 94.9, 94.7, 93.1, 92.0, 91.8 (8 × s, C5H4), 14.4, 13.7 (2 ×
s, Me), -9.5 (s, CH2).
Removal of solvents under vacuum from the filtrate and
washing of the residue with petroleum ether (2 × 5 mL) yielded
essentially pure compound 8 as an orange powder (0.080 g,
85%). Further purification of this compound could not be
achieved (see Discussion). 1H NMR (400.13 MHz, CD2Cl2, 253
K): δ 7.7-6.9 (20H, Ph), 4.81, 4.76, 4.47, 4.39, 4.36, 4.31, 3.60,
3.35 (8 × m, 8 × 1H, C5H4), 1.92, 1.85 (2 × s, 2 × 3H, Me),
P r ep a r a tion of [Mo2Cp 2(µ-η1,η2-CNtBu )(CO)2(µ-d p p m )]
(6a ). A THF solution (8 mL) of compound 4a (0.038 g, 0.05
mmol) was stirred with CNtBu (6 µL, 0.05 mmol) at room
temperature for 5 min, whereupon its color changed from green
to red-brown. Solvent was then removed under vacuum at 0
°C and the residue dissolved in toluene (10 mL) and filtered.
Removal of solvent under vacuum from the filtrate at 0 °C
and washing of the residue with petroleum ether at the same
temperature (2 × 3 mL) yielded compound 6a as a brown solid
(0.039 g, 92%). Anal. Calcd for C42H41Mo2NO2P2, 6a : C, 59.65;
H, 4.89; N, 1.66. Found: C, 60.15; H, 4.91; N, 1.82. 1H NMR
(200.13 MHz, toluene-d8): δ 8.40-6.80 (20H, Ph), 5.48 (t, J PH
) 9, 2H, CH2), 4.60 (d, J HP ) 2, 5H, Cp), 4.22 (s, 5H, Cp), 1.39
1.37 (t, J HH ) J PH ) 11, 1H, CH2), 0.62 (dd, J HH ) 11, J PH
)
t
9, 1H, CH2), 0.54 (s, 9H, Bu). 13C{1H} NMR (100.61 MHz,
CD2Cl2, 233 K): δ 294.4 (d, J PC ) 23, µ-CO), 256.6 (t, J PC
)
16, CO), 163.2 [d, J CP ) 13, CNC(CH3)3], 150.9-124.9 (Ph),
105.5, 104.4 (2 × s, C1[C5H4]), 96.8, 96.0, 93.2, 91.4, 88.8, 88.4,
88.2, 87.0 (8 × s, C5H4), 55.1 [s, CNC(CH3)3], 27.9 [s, CNC-
(CH3)3], 13.7, 12.4 (2 × s, C5H4CH3), -14.6 (s, CH2).
P r ep a r a tion of [Mo2Cp 2(µ-CH2P P h 2)(µ-P P h 2)(CNtBu )-
(CO)] (9). A THF solution (10 mL) of compound 5a (0.052 g,
0.07 mmol) was stirred with CNtBu (8 µL, 0.07 mmol) at 10
°C for 5 min to give a brown-red solution. Solvent was then
removed under vacuum and the residue extracted with toluene
(2 × 8 mL) and filtered. Removal of solvent from the filtrate
under vacuum and washing of the residue with petroleum
ether (3 × 3 mL) at 0 °C gave compound 9 as a highly air-
sensitive brown powder (0.050 g, 90%).
(s, 9H, Me). 13C{1H} NMR (CD2Cl2, 238 K): δ 261.9 (d, J PC
)
29, CO), 241.5 (d, J PC ) 15, CO), 223.1 (s, µ-CNCMe3), 145.0-
127.0 (Ph), 93.4, 90.6 (2 × s, Cp), 59.0 (s, µ-CNCMe3), 31.2 (s,
Me). The resonance due to the CH2 group is obscured by that
one from the solvent.
P r epar ation of [Mo2Cp2(µ-CH2P P h 2)(µ-O)(µ-OP P h 2)(CNt-
Bu )(CO)] (10). A THF solution (15 mL) of compound 9 (0.070
g, 0.095 mmol) was treated with air (11 mL, ca. 0.1 mmol of
O2) under nitrogen and stirred for 10 min to give a brown
solution. Solvent was then removed under vacuum and the
residue washed with petroleum ether (4 × 4 mL), extracted
with toluene (2 × 8 mL), and filtered. Removal of solvent from
the filtrate yielded compound 10 as a brown powder (0.057 g,
70%). Anal. Calcd for C41H41Mo2NO3P2, 10: C, 57.96; H, 4.86,
N, 1.65. Found: C, 57.52; H, 4.62; N, 1.50. 1H NMR (200.13
MHz, toluene-d8): δ 7.9-6.9 (20H, Ph), 4.84 (s, 5H, Cp), 4.77
(t, J HP ) 2, 5H, Cp), 2.27 (dd, J HH ) 11, J PH ) 8, 1H, CH2),
1.32 (s, 9H, Me), -0.25 (t, J HH ) J PH ) 11, 1H, CH2). 13C{1H}
NMR (50.32 MHz, CD2Cl2, 243 K): δ 254.1 (dd, J PC ) 17, 14,
CO), 174.4 (s, CNCMe3), 148.5-128.0 (Ph), 96.2, 94.4 (2 × s,
Cp), 58.8 (s, CNCMe3), 31.1 (s, Me), 0.2 (s, CH2).
P r ep a r a tion of [Mo2Cp ′2(µ-η1,η2-CNtBu )(CO)2(µ-d p p m )]
(6b). The procedure is completely analogous to that described
for 6a but using dichloromethane as solvent. This compound
was found to decompose in solution or in the solid state
(especially under vacuum) more rapidly than complex 6a so
that a satisfactory 1H NMR spectrum or elemental analysis
could not be obtained.
P r ep a r a tion of Solu tion s of [MO2Cp 2(µ-η1,η2-CNtBu )-
(CNtBu )(CO)2(η1-d p p m )] (7). A THF (8 mL) solution of
complex 6a (0.043 g, 0.05 mmol) was stirred with CNtBu (18
µL 0.15 mmol) at room temperature for 24 h to afford a brown
solution. The latter was shown (by 31P NMR) to contain only
two (presumably) isomers of 7 in a ca. 1:1 ratio (see Discus-
sion). Decomposition of these species rapidly occurs when the
excess isocyanide is removed from the solution (vacuum,
crystallization, etc.).
P r ep a r a tion of [Mo2Cp ′2(µ-CH2P P h 2)(µ-P P h 2)(CNtBu )-
(µ-CO)(CO)] (8). A THF solution (12 mL) of compound 2b
(0.085 g, 0.1 mmol) was stirred with CNtBu (13 µL, 0.1 mmol)
at 0 °C for 10 min to give an orange solution which was filtered.
Ack n ow led gm en t. We thank the DGICYT of Spain
for financial support (Project PB91-0678).
OM9607154