Neighboring metal-induced oxidative addition in conjunction with a hydride trap: Formation of [(η5-MeC5H4)Fe(CO)(μ-η 1:-PPh2CH2PPh2)(μ-H)M(CO) 4] (M = W, Mo)

Article abstract of DOI:10.1021/om9608061

The reaction of(η⁴-MeC₅H₅)Fe(CO)₂(η ¹-dppm), 1, with M(CO)₃L₃ produced (η ⁵c?5-I?€a?5C?4)N?a?(€ I?)(i?-c?1:c?1-dppm)(μ-H)M(CO)₄, 3 (L3 = (C₂H

Full text of DOI:10.1021/om9608061

Organometallics 1997, 16, 155-157
155
Neigh bor in g Meta l-In d u ced Oxid a tive Ad d ition in
Con ju n ction w ith a Hyd r id e Tr a p : F or m a tion of
[(η5-MeC5H4)F e(CO)(µ-η1:η1-P P h 2CH2P P h 2)(µ-H)M(CO)4]
(M ) W, Mo)
C. W. Liu, Yuh-Sheng Wen, and Ling-Kang Liu*
Institute of Chemistry, Academia Sinica, Taipei, Taiwan 11529, Republic of China
Received September 23, 1996X
Summary: The reaction of (η4-MeC5H5)Fe(CO)2(η1-dppm),
Sch em e 1
1, with M(CO)3L3 produced (η5-MeC5H4)Fe(CO)(µ-η1:η1-
dppm)(µ-H)M(CO)4, 3 (L3 ) (C2H5CN)3, (THF)3, C7H8;
M ) W, Mo). The novel hydrido-bridged Fe(II)-M(0)
compound was likely formed via the following steps:
coordination of the monodentate dppm to M and then
CO migration from Fe to M with a sequential or
concerted oxidative addition of the endo-C-H bond of
the η4-MeC5H5 ligand to give the (η5-MeC5H4)FeH com-
plex, followed by a trapping of the Fe-H bond by M,
forming a six-membered heterocyclic ring in 3.
Being important in catalytic or stoichiometric reac-
tions,1 the chemistry of organo-transition metal hydrides
has been vigorously pursued for many years. The main
synthetic routes to hydrides are by protonation, from
hydride donors, via oxidative addition, or via â-elimina-
tion.2 The oxidative addition of active hydrogen-
containing species leads to such a formation, silanes
H-SiR3 resulting in silyl hydrides3 and orthometalation
of C-H giving orthometalated hydrides,4 for example.
The intramolecular oxidative addition is key to the facile
loss of hydrogen in (η4-C5H6)Fe(CO)3 to give [(η5-C5H5)-
Fe(CO)2]2, proceeding with an intermediate formation
of (η5-C5H5)Fe(CO)2H.5 Yet (η5-C5H5)Fe(CO)2H in gen-
eral is synthesized independently from the acidification
of (η5-C5H5)Fe(CO)2Na, not directly from (η4-C5H6)Fe-
(CO)3, due to competing and/or consecutive reactions.6
In this communication, we wish to report a clean
activation of endo-C-H bond of η4-cyclopentadiene in
the dppm derivative (η4-MeC5H5)Fe(CO)2(η1-dppm), dppm
) Ph2PCH2PPh2, after its ligation to a M(CO)3 unit (M
) W, a ; M ) Mo, b). The result is a novel hydrido-
bridged heterodimetallic complex, giving the first ex-
ample of a metal (M) inducing an oxidative addition of
C-H of η4-cyclopentadiene on a neighboring metal (Fe)
with the M intervention to finalize in “3c-2e” M-H-
Fe bonding.7
(η4-MeC5H5)Fe(CO)2(η1-dppm), 1, could be prepared
in a reaction of an equimolar amount of (η5-C5H5)Fe-
(CO)2I with MeLi in the presence of dppm at low
temperature,8 following the nucleophilic Cp-ring alky-
lation strategy.9 Compound 1 could be used as a metallo
ligand to construct heterodimetallic complexes in which
the dppm serves as a stabilizing backbone. Examples10
are (η4-MeC5H5)Fe(CO)2(µ-η1:η1-dppm)AuCl and (η5-
MeC5H4)Fe(µ-CO)2(µ-η1:η1-dppm)RhCl2.
X Abstract published in Advance ACS Abstracts, December 15, 1996.
(1) (a) Crabtree, R. H. The Organometallic Chemistry of the Transi-
tion Metals, 2nd ed.; J ohn Wiley & Sons: New York, 1994. (b) Dedieu,
A., Ed. Transition Metal Hydrides; VCH: Weinheim, Germany, 1990.
(c) Kubas, G. J . Acc. Chem. Res. 1988, 21, 120.
(2) Crabtree, R. H. In Encyclopedia of Inorganic Chemistry; King,
R. B., Ed.; J ohn Wiley & Sons: New York, 1994; Vol. 3, pp 1395-
1396.
(3) (a) Schubert, U.; Ackermann, K.; Wo¨rle, B. J . Am. Chem. Soc.
1982, 104, 7378. (b) Fernandez, M. J .; Bailey, P. M.; Bentz, P. O.; Ricci,
J . S.; Koetzle, T. F.; Maitlis, P. M. J . Am. Chem. Soc. 1984, 106, 5458.
(c) Wang, W.-D.; Eisenberg, R. J . Am. Chem. Soc. 1990, 112, 1833.
(4) (a) Bruce, M. I. Angew. Chem., Int. Ed. Engl. 1977, 16, 73. (b)
Constable, E. C. Polyhedron 1984, 3, 1037.
(5) (a) Elschenbroich, C.; Salzer, A. Organometallics, 2nd ed.;
VCH: Weinheim, Germany, 1992; p 199. A few examples of oxidative
addition of η4-cyclopentadiene ligand to a metal: (η5-C5H5)Fe(CO)2H,b-d
(η5-C5H5)Ru(CO)2H,e (η5-C5H5)Os(CO)2H,e (η5-C5H5)Cr(CO)3H,f (η5-
C5H5)Mo(CO)3H,f (η5-C5H5)W(CO)3H,f (η5-C5Me5)Mo(CO)3H,g and (η5-
C5Me5)W(CO)3H.9 (b) Davison, A.; Green, M. L. H.; Wilkinson, G. J .
Chem. Soc. 1961, 3172. (c) Kochhar, R. K.; Pettit, R. J . Organomet.
Chem. 1966, 6, 272. (d) Whitesides, T. H.; Shelly, J . J . Organomet.
Chem. 1975, 92, 215. (e) Humphries, A. P.; Knox, S. A. R. J . Chem.
Soc., Dalton Trans. 1975, 1710. (f) Keppie, S. A.; Lappert, M. F. J .
Chem. Soc. A 1971, 3216. (g) Kubas, G. J .; Wasserman, H. J .; Ryan,
R. R. Organometallics 1985, 4, 2012.
Outlined in Scheme 1, treatment of 1 (0.17 mmol)
with M(CO)5(THF)11 (0.20 mmol) in THF (20 mL) at
ambient temperature for 2 h yielded (η4-MeC5H5)Fe-
(CO)2(µ-η1:η1-dppm)M(CO)5, 2 (2a , 0.15 mmol, 88%
(7) The strategy2 used previously for the synthesis of hydrido-
bridged metal clusters was either an oxidative addition to preformed
cluster compounds or a metal hydride attachment to the second metal
centers.
(8) Liu, L.-K.; Luh, L.-S.; Eke, U. B. Organometallics 1995, 14, 440.
(9) (a) Liu, L.-K.; Luh, L.-S. Organometallics 1994, 13, 2816. (b) Luh,
L.-S.; Liu, L.-K. Bull. Inst. Chem., Acad. Sin. 1994, 41, 39.
(10) Liu, L.-K.; Luh, L.-S.; Wen, Y.-S.; Eke, U. B.; Mesubi, M. A.
Organometallics 1995, 14, 4474.
(6) Shackleton, T. A.; Mackie, S. C.; Fergusson, S. B.; J ohnston, L.
J .; Baird, M. C. Organometallics 1990, 9, 2248 and relevant references
within.
(11) (a) Kolodziej, R. M.; Lee, A. J . Organometallics 1986, 5, 450.
(b) Arndt, L. W.; Darensbourg, M. Y.; Delord, T.; Bancroft, B. T. J .
Am. Chem. Soc. 1986, 108, 2617.
S0276-7333(96)00806-0 CCC: $14.00 © 1997 American Chemical Society

156 Organometallics, Vol. 16, No. 2, 1997
Communications
plexes,14 complex 2a is interestingly the first structur-
ally characterized FeW unit linked by dppm. One close
example is {FeW(µ-CC6H4Me-4)(µ-CO)(µ-dmpm)(CO)2-
[HB(pz)3]}15 (dmpm ) Me2PCH2PMe2, pz ) pyrazolyl)
which has, however, a Fe-W multiple bond [Fe-W )
2.650(1) Å].
When 1 (0.13 mmol) was reacted with M(CO)3(C2H5-
16
CN)3 (0.20 mmol) in THF (20 mL) for 6 h at ambient
temperature, the reaction mixture changed color from
yellow to maroon, the new νCO bands in the IR spectra
being at lower wavenumbers than those of 1 and 2. After
chromatographic workup (silica, 1:4 ethylacetate/n-
hexane), red powders of 3, (η5-MeC5H4)Fe(CO)(µ-η1:η1-
dppm)(µ-H)M(CO)4, were collected (3a , 0.11 mmol, 85%
yield; 3b, 0.11 mmol, 85% yield).17 Compound 3 could
also be obtained in comparable yields from the reaction
F igu r e 1. Thermal ellipsoid drawing (50%) of complex 2a .
The H atoms are omitted for clarity. Selected bond lengths
(Å): Fe-P1 2.206(1), Fe-C2 2.086(5), Fe-C3 2.037(6), Fe-
C4 2.045(5), Fe-C5 2.117(5), Fe-C8 1.763(7), Fe-C9
1.776(6), W-P2 2.551(2), W-C10 2.030(6), W-C11
2.015(8), W-C12 2.045(6), W-C13 2.043(7), W-C14
1.989(7). Selected bond angles (deg): P1-Fe-C8 94.5(2),
P1-Fe-C9 97.6(2), Fe-P1-C7 111.6(2), W-P2-C7
122.6(2), P1-C7-P2 127.7(3).
18
of 1 with either M(CO)3(THF)3 or M(CO)3(η6-C7H8)19
(see Scheme 1). The 1H NMR data for 3a indicated that
the 2:1:2 integration ratios for the η4-MeC5H5 fragment
of 1 disappeared whereas a 4-peak, equal intensity
pattern characteristic of an η5-MeC5H4 connected to a
1
chiral metal center appeared. Also observed in the H
NMR is a doublet of doublets with a tungsten satellite
(J HW ) 37 Hz) centered at δ -16.92, suggesting the
existence of a bridging hydride in 3a .20 The doublet
without tungsten satellite in the 31P NMR spectrum
shifted downfield to δ 83.40. In addition, the J PP
coupling constant of 60 Hz was considerably larger than
that of 2 [24 Hz (2a ), 19 Hz (2b)], suggesting more than
one through-bond connectivity in 3a . Compound 3b was
very similar in spectroscopic data, taking into consid-
eration the difference of W and Mo. Finally the struc-
ture of novel hydrido-bridged complex 3a was confirmed
by a single-crystal X-ray diffraction study.21
yield; 2b, 0.13 mmol, 76% yield), after chromatographic
workup on a silica column using 1:8 ethylacetate/n-
1
hexane as an eluent.12 Complex 2a revealed in its H
NMR spectra the characteristic peaks at δ 4.80 (2H),
2.58 (1H), and 2.07 (2H), consistent with a η4-MeC5H5
bonding mode. In the 31P NMR spectra, a simple AB
pattern was observed with one of them having the
tungsten satellite. Spectroscopically complex 2b be-
haved in a similar way, except for the difference
between W and Mo. Stable in the solid state at ambient
temperature, complex 2 gradually decomposed in chlo-
rinated solvents. The structure of 2a was confirmed by
X-ray crystallography.13 An ORTEP drawing is shown
in Figure 1. The two metal centers are seen linked by
one dppm bridge [Fe‚‚‚W ) 7.035(1) Å]. The torsion
angle of Fe-P‚‚‚P-W is 162.0(1)°. The ring Me group
is exo on the cyclopentadiene from Fe. The coordination
geometry around Fe(0) is a distorted square pyramid
with one of the CO ligands at the apical position. The
second CO ligand is in the basal plane trans to one of
the double bonds of the cyclopentadiene, and the PPh2-
CH2- ligand is trans to the second double bond. An
octahedral geometry around W(0) is revealed. Despite
that the dppm ligand has been broadly used as a
stabilizing backbone to construct heterodimetallic com-
The molecular structure of 3a is shown in Figure 2,
revealing both a hydride bridge and a dppm bridge
between two metal centers. The Fe-H-W vector is
bent at 128.6°, with W-H and Fe-H distances of 1.812
(14) (a) Puddephatt, R. J . Chem. Soc. Rev. 1983, 12, 99. (b) Chaudret,
B.; Delavaux, B.; Poilblanc, R. Coord. Chem. Rev. 1988, 86, 191. (c)
Braunstein, P.; de Meric de Bellefon, C.; Oswald, B. Inorg. Chem. 1993,
32, 1638. (d) Braunstein, P.; Knorr, M.; Strampfer, M.; Dusausoy, Y.;
Bayeul, D.; DeCian, A.; Fischer, J .; Zanello, P. J . Chem. Soc., Dalton
Trans. 1994, 1533.
(15) Green, M.; Howard, J . A. K.; J ames, A. P.; Nunn, C. M.; Stone,
F. G. A. J . Chem. Soc., Dalton Trans. 1986, 1697.
(16) Inorg. Synth. 1990, 28, 29-33.
(17) Spectroscopic and analytical data for 3a : IR (THF) νCO 2010
(s), 1927 (vs), 1890 (sh), 1886 (s), 1855 (s) cm-1 31P NMR (CDCl3) δ
;
83.49 (d, 2+4J PP ) 60 Hz), 13.20 (d, 2+4J PP ) 60 Hz, 1J PW ) 243 Hz); 1H
NMR (CDCl3) δ 7.62-7.00 (m, 20H, Ph), 4.59 (m, 1H), 4.46 (m, 1H),
4.41 (m, 1H), 4.00 (m, 1H) for MeC5H4, 3.65 (m, 1H), 2.78 (m, 1H) for
2
PCH2P, 1.82 (s, 3H, Me), -16.92 (dd, 1H, µ-H, J HP ) 53 Hz, 8 Hz,
1J HW ) 37 Hz); MS (FAB) m/z 846 (M+ + 1). Anal. Calcd for
C36H30FeO5P2W‚1/2Et2O: C, 51.80; H, 3.97. Found: C, 52.13; H, 4.67.
(12) Spectroscopic and analytical data for 2a : IR (n-hexane) νCO 2069
3b: IR (THF) νCO 2015 (s), 1927 (vs), 1900 (sh), 1894 (s), 1859 (s) cm-1
;
(m), 1968 (s), 1941 (b, vs), 1916 (sh) cm-1
;
31P NMR (CDCl3) δ 68.45
31P NMR (CDCl3) δ 81.62 (d,
J
) 61 Hz), 32.25 (d,
J
) 61
2+4
2+4
PP
PP
2
2
1
(d, J PP ) 24 Hz), 10.78 (d, J PP ) 24 Hz, J PW ) 245 Hz); 1H NMR
(CDCl3) δ 7.34-7.17 (m, 20H, Ph), 4.80 (m, 2H, -CHdCHCHMe-),
3.70 (m, 2H, PCH2P), 2.58 (m, 1H, -CHdCHCHMe-), 2.07 (m, 2H,
Hz); 1H NMR (CDCl3) δ 7.58-7.02 (m, 20H, Ph), 4.54 (m, 1H), 4.40
(m, 1H), 4.11 (m, 1H), 4.00 (m, 1H) for MeC5H4, 3.38 (m, 1H), 2.78 (m,
2
1H) for PCH2P, 1.81 (s, 3H, Me), -18.12 (dd, 1H, µ-H, J HP ) 53 Hz,
3
-CHdCHCHMe-), 0.24 (d, 3H, J HH ) 5 Hz, Me); MS (FAB) m/z 901
8 Hz); MS (FAB) m/z 758 (M+). Anal. Calcd for C36H30FeMoO5P2‚1/2-
Et2O: C, 57.87; H, 4.82. Found: C, 57.54; H, 4.41.
(M+). Anal. Calcd for C38H30FeO7P2W: C, 50.70; H, 3.33. Found: C,
50.88; H, 3.33. 2b: IR (n-hexane) νCO 2070 (m), 1968 (s), 1942 (b, vs),
(18) (a) Muetterties, E. L.; Bleeke, J . R.; Sievert, A. C. J . Organomet.
Chem. 1979, 178, 197. (b) Hoff, C. D. J . Organomet. Chem. 1985, 282,
201. (c) Nolan, S. P.; de la Vega, R. L.; Hoff, C. D. Organometallics
1986, 5, 2529.
2
1915 (sh) cm-1
;
31P NMR (CDCl3) δ 69.97 (d, J PP ) 19 Hz), 30.35 (d,
2J PP ) 19 Hz); 1H NMR (CDCl3) δ 7.35-7.14 (m, 20H, Ph), 4.79 (m,
2H, -CHdCHCHMe-), 3.70 (m, 2H, PCH2P), 2.58 (m, 1H,
-CHdCHCHMe-), 2.06 (m, 2H, -CHdCHCHMe-), 0.23 (d, 3H, 3J HH
(19) (a) Abel, E. W.; Bennett, M. A.; Wilkinson, G. Proc. Chem. Soc.
1958, 152. (b) Abel, E. W.; Bennett, M. A.; Burton, R.; Wilkinson, G.
J . Chem. Soc. 1958, 4559. (c) King, R. B.; Fronzaglia, A. Inorg. Chem.
1966, 5, 1837. (d) Kubas, G. J . Inorg. Chem. 1983, 22, 692. (e) Inorg.
Synth. 1990, 27, 4-6.
) 5 Hz, Me); MS (FAB) m/z 814 (M+). Anal. Calcd for C38H30
FeMoO7P2: C, 56.13; H, 3.69. Found: C, 56.20; H, 3.62.
-
(13) Crystallographic data for 2a : C38H30FeO7P2W, fw 900.30,
monoclinic, C2/c, a ) 28.394(4) Å, b ) 13.550(1) Å, c ) 19.447(2) Å, â
) 102.99(1)°, V ) 7290(1) Å3, Z ) 8, F(000) ) 3551, Dcalcd ) 1.641
g‚cm-3; Nonius CAD-4 data, Mo KR radiation, λ ) 0.710 7 Å, µ ) 37.51
cm-1. R ) 0.024, Rw ) 0.026, and GOF ) 1.19 with 79 atoms and 442
parameters for 3578 out of 4756 measured reflections.
(20) (a) The observed J HW is in the range of (µ-H)W2(CO)10- (42 Hz)b
and (µ-H)2W2(CO)82- (30 Hz).c (b) Bau, R.; Teller, R. G.; Kirtley, S. W.;
Koetzle, T. F. Acc. Chem. Res. 1979, 12, 176. (c) Lin, J . T.; Hagen, G.
P.; Ellis, J . E. J . Am. Chem. Soc. 1983, 105, 2296.

Communications
Organometallics, Vol. 16, No. 2, 1997 157
mal Fe-W single bond. The torsion angle of Fe-
P1‚‚‚P2-W, 22.4(1)°, indicates that in 3a the metal
centers are likely attractive whereas in 2a the metal
centers are likely repulsive. If the Fe-H moiety is
considered as a two electron donor to the W(0) center,
an EAN rule fits well on both metal centers in 3a .
The formation of 2 from 1 is not unusual. However,
the formation of 3 from 1 is unexpected. A proposed
reaction pathway is included in Scheme 1, consisting
of coordination of the monodentate dppm to M, the
second metal center, and then CO migration from Fe
to M with a sequential or concerted oxidative addition
of the endo-C-H bond of the η4-MeC5H5 ligand to give
the (η5-MeC5H4)FeH complex that is followed by a
trapping of the Fe-H bond by M, forming a six-
membered ring. The CO migration from one metal
center to another is facile,1a yet it is crucial here to have
the Fe center vacate one site immediately before the
oxidative addition. The attempt to convert 2 to 3 failed
with either oxidative decarbonylation by Me3NO or
photolysis for a long time, only resulting in decomposi-
tion. The reaction of 1 with Mo(CO)4(norbornadiene)24
gave a low yield of 2b (<20%) without giving 3b at all.25
Thus, it seems reasonable to propose that three weakly-
coordinated ligands on the second metal center are
required in order to produce 3 from 1, the first weakly-
coordinated ligand being replaced during the initial
phosphine coordination, the second formally during the
CO relocation from Fe to M, and the third formally
during the formation of “3c-2e” M-H-Fe bond. The
Fe-H moiety is stabilized as a consequence. The
hydride in the 3c-2e bond is derived from cyclopenta-
diene because given various M(CO)3 precursors reacting
with 1, all yield the same product 3. THF as a possible
hydride source has been ruled out because when the
reaction was performed in THF-d8, the hydride reso-
F igu r e 2. Thermal ellipsoid drawing (50%) of complex 3a .
The H atoms except for the bridging hydride are omitted
for clarity. Selected bond lengths (Å): Fe-P1 2.174(4), Fe-
C1 2.107(1), Fe-C2 2.090(1), Fe-C3 2.087(1), Fe-C4
2.074(1), Fe-C5 2.069(1), Fe-C8 1.738(1), Fe-H 1.722,
W-P2 2.504(3), W-C11 1.917(2), W-C12 1.925(1), W-C13
1.985(2), W-C14 1.934(1), W-H 1.812. Selected bond
angles (deg): P1-Fe-C8 92.0(4), Fe-P1-C7 112.9(4),
W-P2-C7 115.3(3), P1-C7-P2 111.9(5), Fe-H-W 128.6.
and 1.722 Å, respectively. To our knowledge, this is the
first structurally characterized, six-membered heterodi-
metallic species bridged by just one hydride and one
dppm. Most of analogous22 heterodimetallic structures
known are bridged by one hydride and two dppm in an
“A-frame” skeleton. In 3a , the Fe(II) center is in a
slightly distorted octahedral bonding environment and
so is the W(0) center. Especially noted are the five CO
ligands (originally two with Fe, three with W) now
redistributed to one with Fe and four with W, the total
remaining unchanged. The Fe-W distance, 3.185(2) Å,
is about 0.2 Å longer than 2.989(2) Å found in [Ph2-
PNPPh2]+[Fe(CO)4(µ-H)W(CO)5]-,11b,23 which has a for-
1
nance could still be recorded in the H NMR spectrum
with no change in intensity; i.e., complex 3 did not
exchange its hydride for the active hydrogen of THF in
the experiment. Works on the above hypothesis and the
reactivity of 3 are currently being undertaken.
Ack n ow led gm en t. Financial support from Aca-
demia Sinica, ROC, is gratefully acknowledged.
(21) Crystallographic data for 3a : C36H30FeO5P2W‚1/2Et2O, fw
881.34, triclinic, P1h, a ) 10.920(6) Å, b ) 11.571(2) Å, c ) 16.516(3) Å,
R ) 89.68(2)°, â ) 75.54(3)°, γ ) 65.24(3)°, V ) 1823(1) Å3, Z ) 2,
F(000) ) 874, Dcalcd ) 1.605 g‚cm-3; Nonius CAD-4 data, Mo KR
radiation, λ ) 0.710 7 Å, µ ) 37.45 cm-1. R ) 0.048, Rw ) 0.056, and
GOF ) 2.52 with 81 atoms and 427 parameters for 3913 out of 4763
measured reflections. The hydride position was found from the final
difference Fourier map. The oxygen atom of the diethyl ether solvate
was located on the crystallographic inversion center, the diethyl ether
being disordered. Currently a neutron diffraction study is being in
progress in order to locate the exact position of hydride.
Su p p or tin g In for m a tion Ava ila ble: For the structures
of (η4-MeC5H5)Fe(CO)2(µ-η1:η1-dppm)W(CO)5, 2a , and (η5-
MeC5H4)Fe(CO)(µ-η1:η1-dppm)(µ-H)W(CO)4, 3a , listings of crys-
tallographic data, positional and isotropic and anisotropic
thermal parameters, and bond distances and angles (13 pages).
Ordering information is given on any current masthead
page.
(22) (a) Delavaux, B.; Chaudret, B.; Dahan, F.; Poilblanc, R. J . Chem.
Soc., Chem. Commun. 1985, 805. (b) Markhm, D. P.; Shaw, B. L.;
Thornton-Pett, M. J . Chem. Soc., Chem. Commun. 1987, 1005. (c)
Antonelli, D. M.; Cowie, M. Inorg. Chem. 1990, 29, 4039.
(23) Arndt, L. W.; Delord, T.; Darensbourg, M. Y. J . Am. Chem. Soc.
1984, 106, 456.
OM9608061
(24) Bennett, M. A.; Pratt, L.; Wilkinson, G. J . Chem. Soc. 1971,
2037.
(25) Only 2b and a trace of Mo(CO)4(dppm) were isolated with a
sizable amount of 1 recovered.