Oxidative additions of coordinated ligands at unsaturated molybdenum and tungsten diphosphine-bridged carbonyl dimers. 1. Decarbonylation reactions of [W2(η5-C5H5) 2(CO)4(μ-R2PCH2PR2)] (R = Ph, Me)

Article abstract of DOI:10.1021/om960714b

The new complexes [W₂Cp₂(CO)₄(μ-L₂)] (Cp = η⁵-C₅H₅; L₂ = Ph₂PCH₂PPh₂ (dppm), Me₂PCH₂PMe₂ (dmpm)) have been prepared from [W₂Cp₂(CO)₄] and the corresponding diphosphine at room temperature. Decarbonylation of the dppm complex in refluxing n-octane gives the triply bonded compound [W₂Cp₂(CO)₂(μ-dppm)] as the major product, along with a small amount of the oxo complex [W₂Cp₂(μ-CH₂PPh ₂)(O)(μ-PPh₂)(CO)], which results from a P-C(sp³) cleavage in the dppm ligand. Both compounds (as their dibenzene and toluene solvates, respectively) have been characterized through single-crystal X-ray studies. The analysis of the dicarbonyl complex, carried out at 200 K, reveals the presence of linear semibridging carbonyls experiencing an incipient dynamic disorder that at higher temperatures might be observed as a fully developed disorder of each carbonyl between its two asymmetric dispositions. The latter is consistent with a structure determination carried out previously on the same compound at 291 K and with its dynamic behavior in solution. This air-sensitive complex adds oxygen readily to give the W(I)-W(V) oxo derivative [W₂Cp₂(O)₂(CO)₂(η ¹-dppm)]. Photochemical decarbonylation of [W₂Cp₂(CO)₄(μ-L₂)] proceeds via the hydrido cyclopentadienylidene complexes [W₂(μ-η¹:η⁵-C₅H ₄)Cp(μ-H)(CO)₃(μ-L₂)] to finally give the corresponding dicarbonyls [W₂Cp₂(CO)₂(μ-L₂)]. The latter react readily with ^tBuNC at room temperature or below to give [W₂Cp₂(μ-η¹:η²-CN ^tBu)(CO)₂(μ-L₂)], which, when L₂ = dppm, isomerizes at room temperature to give [W₂(μ-η¹:η⁵-C₅H ₄)Cp(μ-H)(CN^tBu)(CO)₂-(μ-dppm)].

Full text of DOI:10.1021/om960714b

354
Organometallics 1997, 16, 354-364
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. 1.
Deca r bon yla tion Rea ction s of
[W2(η5-C5H5)2(CO)4(µ-R2P CH2P R2)] (R ) P h , Me)†
M. Angeles Alvarez, M. Esther Garc´ıa, V´ıctor Riera, and Miguel A. Ruiz*,‡
Departamento de Qu´ımica Orga´nica e Inorga´nica/ IUQOEM, Universidad de Oviedo,
33071 Oviedo, Spain
Larry R. Falvello
Departamento de Quı´mica Inorga´nica, Universidad de Zaragoza, 50009 Zaragoza, Spain
Claudette Bois
Laboratoire de Chimie des Me´taux de Transition, UACNRS 419, Universite´ P. et M. Curie,
4 Place J ussieu, 75252 Paris, cedex 05, France
Received August 20, 1996X
The new complexes [W2Cp2(CO)4(µ-L2)] (Cp ) η5-C5H5; L2 ) Ph2PCH2PPh2 (dppm),
Me2PCH2PMe2 (dmpm)) have been prepared from [W2Cp2(CO)4] and the corresponding
diphosphine at room temperature. Decarbonylation of the dppm complex in refluxing
n-octane gives the triply bonded compound [W2Cp2(CO)2(µ-dppm)] as the major product, along
with a small amount of the oxo complex [W2Cp2(µ-CH2PPh2)(O)(µ-PPh2)(CO)], which results
from a P-C(sp3) cleavage in the dppm ligand. Both compounds (as their dibenzene and
toluene solvates, respectively) have been characterized through single-crystal X-ray studies.
The analysis of the dicarbonyl complex, carried out at 200 K, reveals the presence of linear
semibridging carbonyls experiencing an incipient dynamic disorder that at higher temper-
atures might be observed as a fully developed disorder of each carbonyl between its two
asymmetric dispositions. The latter is consistent with a structure determination carried
out previously on the same compound at 291 K and with its dynamic behavior in solution.
This air-sensitive complex adds oxygen readily to give the W(I)-W(V) oxo derivative
[W2Cp2(O)2(CO)2(η1-dppm)]. Photochemical decarbonylation of [W2Cp2(CO)4(µ-L2)] proceeds
via the hydrido cyclopentadienylidene complexes [W2(µ-η1:η5-C5H4)Cp(µ-H)(CO)3(µ-L2)] to
finally give the corresponding dicarbonyls [W2Cp2(CO)2(µ-L2)]. The latter react readily with
tBuNC at room temperature or below to give [W2Cp2(µ-η1:η2-CNtBu)(CO)2(µ-L2)], which, when
L2 ) dppm, isomerizes at room temperature to give [W2(µ-η1:η5-C5H4)Cp(µ-H)(CNtBu)(CO)2-
(µ-dppm)].
In tr od u ction
precise dimers [M2Cp2(CO)4(µ-dppm)] (M ) Mo, W).
Unexpectedly, our initial results revealed that removal
of CO from these substrates involved significant activa-
tion of the coordinated ligands. Thus, thermal decar-
bonylation on the molybdenum complex yielded [Mo2-
Cp2(µ-CH2PPh2)(µ-PPh2)(CO)2] as a result of a P-C(sp3)
bond oxidative addition of the dppm ligand.4 In con-
trast, decarbonylation on the ditungsten dimer yielded
the triply bonded [W2Cp2(CO)2(µ-dppm)] via the cyclo-
pentadienylidene hydride [W2(µ-H)(µ-η1:η5-C5H4)Cp-
(CO)3(µ-dppm)], a product resulting from a reversible
C-H oxidative addition of the cyclopentadienyl ligand.5
The unsaturated complexes [M2Cp2(CO)4] (M ) Cr,
Mo, W; Cp ) η5-C5H5) are well-known to be formed
through decarbonylation reactions from the correspond-
ing hexacarbonylic precursors, this being induced by
photochemical or thermal methods.1 Interest in these
triply bonded dimers arises mainly from their high
reactivity toward many different sorts of molecules,1,2
but the molecular and electronic structure of these
species has also attracted considerable attention.1,3 In
an attempt to synthesize related complexes bridged by
the dppm ligand (dppm ) Ph2PCH2PPh2), we started a
study on decarbonylation reactions of the electron-
Given the general interest of both C-P6 and C-H7
activation processes, we decided to examine in more
detail the above decarbonylation reactions, as well as
† Dedicated to Prof. R. Uso´n on the occasion of his 70th birthday.
‡ E-mail: mara@sauron.quimica.uniovi.es.
X Abstract published in Advance ACS Abstracts, December 1, 1996.
(1) Winter, M. J . Adv. Organomet. Chem. 1989, 29, 101 and
references therein.
(4) Riera, V.; Ruiz, M. A.; Villafan˜e, F.; Bois, C.; J eannin, Y. J .
Organomet. Chem. 1989, 375, C23.
(5) Alvarez, M. A.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.; Bois, C.;
J eannin, Y. J . Am. Chem. Soc. 1993, 115, 3786.
(6) (a) Chaudret, B.; Delavaux, B.; Poilblanc, R. Coord. Chem, Rev.
1988, 86, 191. (b) Garrou, P. E. Chem. Rev. 1985, 85, 171.
(2) Curtis, M. D. Polyhedron 1987, 6, 759 and references therein.
(3) Simpson, C. Q., II; Hall, M. B. J . Am. Chem. Soc. 1992, 114,
1641 and references therein.
S0276-7333(96)00714-5 CCC: $14.00 © 1997 American Chemical Society

[W2(η5-C5H5)2(CO)4(µ-R2PCH2PR2)]
Organometallics, Vol. 16, No. 3, 1997 355
Ta ble 1. IR a n d 31P {1H} NMR Da ta for New Com p ou n d s
b
compd
νst(CO)a/cm-1
δ(P) (J PW
)
J PP
[W2Cp2(CO)4(µ-dppm)] (1a )
1911 (ms), 1876 (vs)
1838 (m), 1816 (ms)c
1858 (vs), 1800 (s)c
1730 (s)
11.1 (338, -7) [isomer A]
-0.6 (343, -2) [isomer B]
-31.9 (224, -3) [isomer A]
27.2 (421, 11)
112d
73d
55e
68f
63
15
82
69
[W2Cp2(CO)4(µ-dmpm)] (1b)
[W2Cp2(CO)2(µ-dppm)] (2a )
[W2Cp2(CO)2(µ-dmpm)] (2b)
1733 (s)
-21.0 (432, 8)
[W2Cp2(µ-CH2PPh2)(O)(µ-PPh2)(CO)] (3)
1793g
138.5 (358, 248), -2.0 (315, 66)
23.5 (295, 25), -26.3
37.7 (244, 7), 22.8 (300)
-2.3, -16.5
[W2Cp2(O)2(CO)2(η1-dppm)] (4)
1888 (w), 1815 (vs)h
1931 (vs), 1851 (s), 1755 (m)
1923 (vs), 1845 (s), 1781 (m)
1822 (s), 1723 (vs)i
1816 (s), 1760 (vs)j
1814 (vs), 1748 (vs)k
[W2(µ-C5H4)Cp(µ-H)(CO)3(µ-dppm)] (5a )
[W2(µ-C5H4)Cp(µ-H)(CO)3(µ-dmpm)] (5b)
[W2Cp2(µ-η1:η2-CNtBu)(CO)2(µ-dppm)] (6a )
[W2Cp2(µ-η1:η2-CNtBu)(CO)2(µ-dmpm)] (6b)
[W2(µ-C5H4)Cp(µ-H)(CNtBu)(CO)2(µ-dppm)] (7)
52
10.9, 3.5
-26.8, -32.9
37.6 (247, 8), 22.5 (306)
83e
70
70e
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 and J in hertz. For compounds 1 and 2, PP and PW coupling constants are obtained
d
from the 183W “satellite” lines (see note on ref 9). c Toluene solution. 233 K; A:B ratio 0.5 (this ratio increases to ca. 2 at 291 K). e C6D6
g
h
solution. f 223 K. Petroleum ether solution; νst(W-O) 923 (m) cm-1 in Nujol mull. νst(W-O) 942 (m), 899 (m) cm-1 in Nujol mull.
Toluene solution; νst(C-N) 1623 (m) cm-1
.
νst(C-N) 1613 (w) cm-1
.
CH2Cl2 solution; νst(C-N) 2089 (m), 2047 (m) cm-1
.
i
j
k
Ch a r t 1
Ch a r t 2
those of the related substrates [Mo2Cp′2(CO)4(µ-dppm)]
(Cp′ ) η5-C5H4Me) and [W2Cp2(CO)4(µ-dmpm)] (dmpm
) Me2PCH2PMe2). In this way we have attempted to
gain more insight about the role played by not only the
metals but also the ligands, in determining whether
multiple M-M bond formation and C-H or P-C cleav-
age will occur during decarbonylation of these tetra-
carbonyl complexes. In this paper we present the full
results of our studies on the ditungsten compounds,
while those on the molybdenum analogues will be
discussed in a separate paper.
for [Mo2Cp2(CO)4(µ-dmpm)] and related complexes
bridged by alkyl-substituted diphosphines.10 Therefore,
1b should have the structure determined crystallo-
graphically for [Mo2Cp2(CO)4(µ-HtBuPCH2PtBuH)],10
which we have labeled as isomer A. In contrast, the
dppm complex 1a displays two isomers in solution
(labeled A and B), again as found for its molybdenum
analogue.8,11 Both isomers have a symmetry element
which makes the phosphorus atoms, cyclopentadienyl
ligands, and methylenic protons equivalent (Table 1 and
Experimental Section). The relative abundance of these
isomers is temperature-dependent, so that the isomer
exhibiting the more shielded 31P resonance (B) prevails
at low temperature. On the basis of the above data we
conclude that, contrary to our earlier proposal for
[Mo2Cp2(CO)4(µ-dppm)],8 and in agreement with that
one of Azam et al. on the same complex,11 the structures
of isomers A and B in solution are adequately repre-
sented by those determined crystallographically for
[Mo2Cp2(CO)4(µ-HtBuPCH2PtBuH)]10 (isomer A) and
[Mo2Cp2(CO)4(µ-dppm)]11 (isomer B).
Th er m a l Deca r bon yla tion s. Loss of CO in the
dppm complex 1a occurs smoothly in refluxing toluene
or n-octane to give the triply bonded complex [W2Cp2-
(CO)2(µ-dppm)] (2a ) in high yield, along with a small
amount of the oxo compound [W2Cp2(µ-CH2PPh2)(O)(µ-
PPh2)(CO)] (3). The dmpm complex 1b turned out to
be more resistant to decarbonylation. Thus, no reaction
was observed in refluxing toluene, while a rather
generalized decomposition of the starting substrate was
observed in refluxing diglyme.
Resu lts a n d Discu ssion
Sta r tin g Su bstr a tes. We have shown previously
that the room-temperature reaction of dppm with the
triply bonded dimer [Mo2Cp2(CO)4] gives [Mo2Cp2(CO)4-
(µ-dppm)] in high yield.8 This method also provides an
efficient synthesis for the related ditungsten complexes
[W2Cp2(CO)4(µ-L2)] (1a ,b: a , L2 ) dppm; b, L2 ) dmpm).
Spectroscopic data in solution for complexes 1a ,b
indicate that they are isostructural with their molyb-
denum analogues. Thus, 1b displays a single isomer
in solution, characterized by a singlet in the 31P NMR
spectrum9 and just two νst(CO) bands (Table 1), as found
(7) (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.
(8) Riera, V.; Ruiz, M. A.; Villafan˜e, F. Organometallics 1992, 11,
2854.
(9) In a diphosphine-bridged ditungsten complex having chemically
equivalent phosphorus atoms, the 31P NMR subspectrum corresponding
to the isotopomer having a single 183W nucleus (ca. 24% natural
abundance) can be described as derived from an AA′X spin system (A
) P; X ) W). Analysis of this subspectrum by the method of the
effective Larmor frequencies allows the calculation of J AX and J A′X (and
their relative sign), while |J AA′| is measured directly in the subspec-
trum. See for example: Gu¨nther, H. NMR Spectroscopy; Wiley:
Chichester, U.K., 1980; p 160.
In order to establish the origin of the side product 3,
we first noted that the triply bonded 2a experienced no
(10) Brauer, D. J .; Hasselkuss, G.; Stelzer, O. J . Organomet. Chem.
1987, 321, 339.
(11) Azam, K. A.; Deeming, A. J .; Felix, M. S. B.; Bates, P. A.;
Hursthouse, M. B. Polyhedron 1988, 7, 1793.

356 Organometallics, Vol. 16, No. 3, 1997
Alvarez et al.
Ch a r t 3
significant alteration in refluxing toluene or n-octane
for several hours. A separate experiment showed that
compound 3 is not formed by the action of oxygen on
2a . Thus, when 2a is exposed to low amounts of
dioxygen, the mixed-valence compound [W2Cp2(O)2-
(CO)2(η1-dppm)] (4) is formed in good yield. Moreover,
the prolonged exposure of this product to higher amounts
of oxygen leads only to decomposition. Therefore, it
seems very likely for 3 to be derived from small amounts
of the P-C cleavage product [W2Cp2(µ-CH2PPh2)(µ-
PPh2)(CO)2] (not detected), which, being highly air-
sensitive as its dimolybdenum analogue is,12 would react
rapidly with trace amounts of oxygen present in the
reaction mixture.
The structures of compounds 2a and 3 have been
confirmed through X-ray diffraction studies (see below),
while that proposed for 4 is firmly supported on spec-
troscopic evidence. Thus, the IR spectrum of 4 shows
νst(CO) bands at 1880 (w) and 1815 (vs) cm-1, with a
pattern indicative of a transoid M(CO)2 oscillator.13 In
agreement with this, a single carbonyl resonance at
227.1 ppm is present in the 13C NMR spectrum. In
addition, two medium-intensity bands at 942 and 899
cm-1 are observed in the solid-state IR spectrum of 4
(Nujol mull). These can be attributed respectively to
the asymmetric and symmetric W-O stretches of a
cisoid W(O)2 oscillator by comparison with the data for
the mononuclear complexes [MCp(O)2R] (M ) Mo, W;
R ) Me, CH2SiMe3).14 In agreement with this asym-
F igu r e 1. ORTEP diagram of the molecular structure of
[W2Cp2(µ-CH2PPh2)(O)(µ-PPh2)(CO)] (3). Ellipsoids repre-
sent 30% probability. Labels for phenyl carbon atoms are
omitted for clarity.
(PR3)X] complexes.16 Finally, the presence of a single
metal-metal bond linking the WCp(CO)2(η1-dppm) and
WCp(O)2 fragments (17e and 15e, respectively) is sup-
ported by the observation of P-W coupling (25 Hz)
between dppm and the tungsten atom to which this
ligand is not bonded.
Compound 4 is a rare example of a W(I)-W(V)
dimer17 and is strongly related to [W2(C5Me5)2(O)2-
(CO)3],18 the only other W(I)-W(V) complex which
seems to have been described previously. Interestingly,
both compounds are formed by oxidative addition of O2
at a single metal center in triply bonded ditungsten
precursors. In both cases, the O2 addition is ac-
companied by CO transfer to the other metal center and
ejection of one ligand (i.e. decoordination of the dppm
ligand in the case of 4) to leave a 16 e W(V) center.
Str u ctu r e of Com p ou n d 3. The molecular struc-
ture of the oxo complex 3 is shown in Figure 1. The
ditungsten metal core is bridged by phosphido and
phosphinomethyl ligands, almost lying in the same
plane (the angle between the plane W(1)W(2)P(1) and
the least-squares plane W(2)W(2)C(2)P(2) is 13.4°). The
tungsten atoms also bear a cyclopentadienyl and ter-
minal carbonyl (on W(1)) or oxygen (on W(2)) ligands.
By considering the Cp groups as occupying a single
coordination position, we can then describe the local
environments around the metal atoms in 3 as distorted
tetrahedral, with the Cp (or CO and O) ligands placed
at opposite sides of the approximate plane defined by
the bridging groups. Distortion from a tetrahedral
1
metric distribution of CO and O ligands, the H and 13C
NMR spectra of 4 reveal the presence of two Cp ligands
with quite different chemical shifts. Then, the lower-
field cyclopentadienylic resonances (δH 6.02; δC 109.1
ppm) presumably correspond to that ligand bonded to
the W(O)2 moiety. Besides, there is a dppm ligand
coordinated through a single phosphorus atom, as
clearly indicated by the 31P NMR spectrum of 4, which
shows two doublets, one of them (δ -26.3 ppm) at a
chemical shift close to that of the free ligand, displaying
no 183W-P coupling. The appearance of the methylenic
1H resonance exhibiting small coupling with one of the
phosphorus atoms (J HP ) 9 and 2 Hz for 4) is also
characteristic of complexes having the η1-dppm ligand.15
The coordination of the dppm ligand to the W(CO)2
rather than the W(O)2 moiety is indicated by the
observation of P-H coupling in the higher field Cp
resonance (δH 5.50 ppm, J HP ) 1 Hz), which is a
characteristic feature of mononuclear trans-[MCp(CO)2-
(12) Riera, V.; Ruiz, M. A.; Villafan˜e, F.; Bois, C. J eannin, Y.
Organometallics 1993, 12, 124.
(13) Braterman, P. S. Metal Carbonyl Spectra; Academic Press:
London, 1975.
(14) Legzdins, P.; Phillips, E. C.; Sa´nchez, L. Organometallics 1989,
8, 940.
(16) Barnett, K. W.; Slocum, D. W. J . Organomet. Chem. 1972, 44,
1.
(17) Herberhold, M.; J in, G. X. Angew. Chem., Int. Ed. Engl. 1994,
33, 964.
(15) Riera, V.; Ruiz, M. A.; Villafan˜e, F.; Bois, C.; J eannin. Y. J .
Organomet. Chem. 1990, 382, 407.
(18) Alt, H. G.; Hayen, H. I.; Rogers, R. D. J . Chem. Soc., Chem.
Commun. 1987, 1795.

[W2(η5-C5H5)2(CO)4(µ-R2PCH2PR2)]
Organometallics, Vol. 16, No. 3, 1997 357
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p ou n d 3a
oxo ligand has been recognized to display a measurable
trans influence on cyclopentadienyl ligands,12,22,25 this
does not seem to be the case in 3, where a rather
generalized lengthening effect on all bonds involving the
W(IV) atom seems to occur instead.
Spectroscopic data in solution for compound 3 (Table
1 and Experimental Section) are consistent with its
solid-state structure. Moreover, they are comparable
to those exhibited by its molybdenum analogue, which
we have discussed previously in detail,12 and thus need
no further comments.
W(1)-W(2)
W(1)-P(1)
W(1)-P(2)
W(1)-C(1)
W(1)-C(10)
W(1)-C(11)
W(1)-C(12)
W(1)-C(13)
W(1)-C(14)
W(1)-Cp(1)
2.9500(7)
2.323(3)
2.380(3)
1.93(1)
2.32(1)
2.35(1)
2.36(2)
2.32(2)
2.31(2)
2.01
P(2)-C(2)
1.76(1)
2.425(3)
2.21(1)
1.703(9)
2.42(1)
2.44(1)
2.41(1)
2.42(1)
2.36(1)
2.09
W(2)-P(1)
W(2)-C(2)
W(2)-O(2)
W(2)-C(20)
W(2)-C(21)
W(2)-C(22)
W(2)-C(23)
W(2)-C(24)
W(2)-Cp(2)
P(1)-W(1)-P(2)
C(1)-W(1)-W(2)
Cp(1)-W(1)-W(2)
114.8(1)
75.3(4)
164.8
P(1)-W(2)-C(2)
O(2)-W(2)-W(1)
Cp(2)-W(2)-W(1)
126.1(4)
112.1(3)
131.4
Solu t ion a n d Solid -St a t e St r u ct u r e of Com -
p ou n d 2a . Spectroscopic data in solution for 2a reveal
a high symmetry for this molecule. Thus, its 31P and
1H NMR spectra show the chemical equivalence of each
pair of phosphorus atoms and cyclopentadienyl groups
or methylenic protons, respectively. The carbonyl ligands
are also equivalent and give rise to a single νst(CO) band
at a low frequency (1730 cm-1) and a single 13C
resonance with a chemical shift somewhat higher than
those in the parent complex 1a . The latter values
suggest some bridging character for the CO ligands in
compound 2a but do not allow a safe distinction among
the different possibilities (linear semibridging, bent
semibridging or even symmetrical bridging).26
Compounds 2 are diphosphine-substituted derivatives
of the triply bonded dimers [M2L2(CO)4] (M ) Cr, Mo,
W; L ) Cp or related ligand). All crystal structure
studies available on these dimers have revealed the
presence of linear semibridging carbonyls, a fact justi-
fied by theoretical calculations.3 Thus, a linear semi-
bridging coordination for the carbonyl ligands would be
the most sensible proposal in the case of complexes 2.
In contrast, however, we noted that the 13C NMR
resonance of 2a at room temperature exhibited 183W
“satellite” lines having ca. 24% of the total signal
intensity, instead of the expected ca. 14% value. This
situation remained unchanged down to 183 K. From
the latter it was concluded that either a more symmetric
coordination mode of the CO ligands was present
(perhaps induced by the presence of the diphosphine
ligand) or a rapid scrambling of semibridging carbonyls
was underway (therefore yielding an average structure).
In order to solve this uncertainty, an X-ray diffraction
study was undertaken.
In the first instance, a room-temperature study on
2a ‚2C7H8 was carried out.5 From these data, the
carbonyl ligands appeared to be bent semibridging, but
the thermal parameters of the carbonyl ligands were
rather high, especially those of the carbon atoms. An
analogous situation had been found previously in the
structures of the related dimers [Mo2L2(CO)4] (L )
C5H5,27a C5H4Me27b). In the first case, the structure was
successfully refined as a molecule having linear semi-
bridging carbonyls and being disordered in two different
orientations,27a and the same was assumed for the
methylcyclopentadienyl complex.27b On this basis, the
hypothesis of a static disorder in the carbonyls for
complex 2a was a plausible one. However, the possibil-
ity of a dynamic disorder of these ligands, a common
a
Cp(1) and Cp(2) are the centroids of the cyclopentadienyl rings.
environment is more severe around W(1), so that the
corresponding Cp ligand centroid is placed close to the
intermetallic vector (Cp(1)-W(1)-W(2) ) 164.8°, to be
compared with 131.4° for Cp(2)-W(2)-W(1)). This
possibly minimizes unfavorable repulsions between
Cp(1) and the phenyl rings in the phosphinomethyl
ligand. In addition, the carbonyl ligand leans over the
metal-metal vector (C(1)-W(1)-W(2) ) 75.3(4)°), a fact
which we interpret as a geometrical consequence of the
Cp(1) arrangement, since the W(2)-C(1) separation (ca.
3.09 Å) is too large to denote any semibridging interac-
tion. This effect has been previously observed in the
related tetranuclear derivative [{Mo2Cp2(µ-CH2PPh2)-
(µ-OPPh2)(µ-O)(CO)}2(µ-O)].12
As for the phosphinomethyl ligand in 3, the P(2)-
C(2) distance of 1.76(1) Å is among the shortest found
for this type of group19,20 and therefore is indicative of
a P-C bond order higher than 1 (for internal compari-
son, the P(2)-C(phenyl) distances are 1.85(1) and
1.82(1) Å). This has been previously rationalized by
Klein et al. by invoking the contribution of a resonance
form of the type H2CdPR2 for this sort of ligand.21
Overall, the structure of 3 is similar to those found
for the isoelectronic molybdenum complexes [Mo2Cp2-
(O)(µ-PPh2)(µ-X)(CO)] (X ) PPh2,22 CHdCHPh23 ). The
structures of these three 32e, M(II)-M(IV) species seem
to be characterized by (a) a relatively large (for a formal
double bond) intermetallic distance, which is 2.9500(7)
Å for 3, and (b) an asymmetric coordination of the
phosphido ligand, found closer to the metal atom bear-
ing the carbonyl ligand (i.e. W(1)-P(1) ) 2.323(3) Å but
W(2)-P(1) ) 2.425(3) Å in 3). In our complex we also
note significantly longer W-C distances for the Cp
ligand bonded to the W(IV) center (averaged values are
2.33 and 2.41 Å for Cp(1) and Cp(2) ligands, respec-
tively; see Table 2). All the above lengthenings can be
attributed mostly to the presence of the strongly bound
oxo ligand in 3, which displays a W-O distance (1.703(9)
Å) typical for double bonds.24 Although the terminal
(19) Doherty, N. M.; Hogarth, G.; Knox, S. A. R.; Macpherson, F.
M.; Morton, D. A. V.; Orpen, A. G. Inorg. Chim. Acta 1992, 198-200,
257.
(20) Chau, C. N.; Yu, Y. F.; Wojcicki, A.; Calligaris, M.; Nardin, G.;
Balducci, G. Organometallics 1987, 6, 308 and references therein.
(21) Klein, H. F.; Wenninger, J .; Schubert, U. Z. Naturforsch., B:
Anorg. Chem., Org. Chem. 1979, 34B, 1391.
(22) Adatia, T.; McPartlin, M.; Mays, M. J .; Morris, M. J .; Raithby,
P. R. J . Chem. Soc., Dalton Trans. 1989, 1555.
(23) Endrick, K.; Korswagen, R.; Zahn, T.; Ziegler, M. L. Angew.
Chem., Int. Ed. Engl. 1982, 21, 919.
(25) Herrmann, W. A.; Herdtweck, E.; Flo¨el, M.; Kulpe, J .; Ku¨st-
hardt, U.; Okuda, J . Polyhedron 1987, 6, 1165.
(26) Crabtree, R. H.; Lavin, M. Inorg. Chem. 1986, 25, 805.
(27) (a) Klinger, R. J .; Butler, W. M.; Curtis, M. D. J . Am. Chem.
Soc. 1978, 100, 5034. (b) Huang, J . S.; Dahl, L. F. J . Organomet. Chem.
1983, 243, 57.
(24) Bottomley, F.; Sutin, L. Adv. Organomet. Chem. 1988, 28, 339.

358 Organometallics, Vol. 16, No. 3, 1997
Alvarez et al.
Figu r e 3. Schematic representation of the carbonyl scram-
bling proposed for compound 2a in the solid state.
proposed. This is indicated by noting that the largest
principal displacement29 for C(1) is nearly parallel to
the W(1)-W(2) vector; the angle is 14(9)°. For C(2), the
largest principal displacement is tilted 48(15)° from the
direction of the intermetallic vector but remains near
the plane of W(1), W(2), and C(2). The RMS displace-
ments of C(1) and C(2) (ca. 0.22 Å) in the direction of
the W(1)-W(2) vector are slightly larger than those of
the corresponding oxygen atoms in the same direction
(ca. 0.20 Å).
F igu r e 2. ORTEP diagram of the molecular structure of
[W2Cp2(CO)2(µ-dppm)] (2a ) determined at 200 K. Ellipsoids
represent 50% probability. Labels for phenyl and cyclo-
pentadienyl carbon atoms are omitted for clarity.
In order to examine more closely the information (and
its level of credibility) derived from displacement pa-
rameters, we carried out several analyses of overall
motion of the molecule, using the so-called TLS analy-
sis.30,31 Excellent fits to the anisotropic thermal pa-
rameters of the structure of 2a were obtained, which
lends credence to the notion that useful information can
be derived from the atomic displacements. In the more
sophisticated model, rotations of each C5H5 moiety about
the vector joining its centroid to the nearest W atom,
libration of the dppm ligand about the P-P vector, and
rotation of the C(20), ..., C(25) and C(32), ..., C(37)
phenyl groups about their respective P-C bonds was
allowed. This gave the best residuals, Rw ) 0.041 for
all Uij values and Rw ) 0.030 for the diagonal elements,
with a quality of fit of 1.44.
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p ou n d 2a a t 200 K
W(1)-W(2)
W(1)-C(2)
W(2)-C(1)
W(2)-P(2)
2.5144(5)
2.432(8)
2.458(7)
2.403(2)
W(1)-C(1)
W(2)-C(2)
W(1)-P(1)
1.976(8)
1.964(9)
2.414(2)
W(1)-C(1)-O(1)
C(1)-W(1)-W(2)
C(1)-W(1)-P(1)
166.2(6)
65.1(2)
92.0(2)
W(2)-C(2)-O(2)
C(2)-W(2)-W(1)
C(2)-W(2)-P(2)
167.1(7)
64.4(2)
87.8(2)
situation in solution, could not be excluded either.
Therefore, a low-temperature study (200 K) was under-
taken. Crystals of 2a were now obtained as a benzene
solvate in order to minimize additional problems derived
from disorder in the solvent molecules.
The structure of 2a at 200 K is shown in Figure 2.
Selected bond distances and angles are given in Table
3 and are almost the same as those determined at 291
K, except for the data involving the carbonyl ligands.
The latter now display M-C lengths and M-C-O or
C-M-M angles characteristic of type II linear semibridg-
ing carbonyls,26 as expected for a triply bonded dimer.3
In agreement with this, the intermetallic distance is
quite short, 2.5144(5) Å, a value only ca. 0.01 Å longer
than those found in the related dimers [W2L2(CO)4] (L
) C5H4CO2Et,28a CpCo{P(O)(OEt)2}328b).
The abnormally high displacement parameters for the
carbon atoms in the CO groups found in the room-
temperature study have been largely diminished at 200
K, so as to reach almost normal values. Therefore, we
can safely conclude that the disorder observed in the
291 K structure of 2a is not of a static nature but of a
dynamic one. We propose it to be analogous to the
carbonyl scrambling commonly observed in solution for
many di- and polynuclear metal carbonyls (Figure 3).
Of course, this process should be much faster in solution,
and therefore it is not surprising for the carbonyls of
2a to give an averaged 13C NMR resonance even at 183
K.
We also examined the differences in mean-square
displacement amplitudes (∆MSDA) between bonded and
nonbonded atom pairs. Each value is the difference of
the MSDA of two atoms along the vector joining them.
For bonded atoms, according to the principles underly-
ing the “rigid bond test”, this difference should be small,
because the stretching of a covalent bond has an
amplitude which is small compared to other factors that
give rise to atomic displacement in a crystal.32 For
2a ‚2C6H6, most of the bonded atoms pairs fall in line
with the above predictions, when compared to atom
pairs from different groups. For example, the RMS
values of ∆MSDA for all atom pairs within all of the
phenyl groups is 47 × 10-4 Å2, while the RMS value of
∆MSDA for carbon atom pairs between phenyl groups
is 92 × 10-4 Å2. The Cp rings show comparable effects.
However, the W-C(O) ∆MSDA values stand in contrast,
with a difference of 105 × 10-4 Å2 for W(1)-C(1) and
276 × 10-4 Å2 for W(2)-C(2). The ∆MSDA values for
C(1)-O(1) (120 × 10-4 Å2) and for C(2)-O(2) (302 ×
10-4 Å2) are even more pronounced, especially since the
(29) Busing, W. R.; Martin, K. O.; Levy, H. A. ORFEE: A crystal-
lographic Function-and-Error Program; Oak Ridge National Labora-
tory, Oak Ridge, TN, 1971.
(30) Schomaker, V.; Trueblood, K. N. Acta Crystallogr. 1968, B24,
63.
The anisotropic displacement parameters of the C(car-
bonyl) atoms in the 200 K structure appear to suggest
a slightly disproportionate displacement parallel to the
W-W vector, in agreement with the dynamic process
(31) (a) Dunitz, J . D.; Schomaker, V.; Trueblood, K. N. J . Phys.
Chem. 1988, 92, 856. (b) Program THMA11: Trueblood, K. N. Private
communication, 1992. (c) The residuals for the displacement parameter
analysis are defined as: Rw ) [Σw(Uij,obs - Uij,calc)2/Σw(Uij,obs)2]1/2 and
(28) (a) Song, L. C.; Wang, J . Q.; Zhao, W. J .; Hu, Q. M.; Fang, Y.
Q.; Zhang, S. J .; Wang, R. J .; Wang, H. G. J . Organomet. Chem. 1993,
453, 105. (b) Klau¨l, W.; Mu¨ller, A.; Herbst, R.; Egert, E. Organo-
metallics 1987, 6, 1824.
quality of fit ) [Σ{(Uij,obs - Uij,calc)/σ(Uij,obs)}2]1/2[Σ(Nobs - Nparam)]-1/2
(32) Hirshfeld, F. L. Acta Crystallogr. 1976, A32, 239.
.

[W2(η5-C5H5)2(CO)4(µ-R2PCH2PR2)]
Organometallics, Vol. 16, No. 3, 1997 359
discussed in detail,34 or the dimolybdenum compound
[Mo2(µ-η1:η5-C5H4)Cp2(CO)3].35 The same comment ap-
plies to the 13C NMR resonances of this ligand. As for
the carbonyl groups, they give rise to three distinct 13C
resonances and C-O stretching bands, at frequencies
compatible with a terminal coordination of these groups.
The formation of compounds 5 from 1 requires the
intramolecular oxidative addition of a C-H bond of a
cyclopentadienyl ligand, itself an unusual observation.5
Even more interestingly, it should be noted that the
process is reversible, so that the Cp ligand is regener-
ated through reductive elimination between the C5H4
and hydrido ligands in compounds 5. This can occur
either through decarbonylation (to give 2) or carbonyl-
ation, which occurs instantaneously at room tempera-
ture to regenerate the starting substrates 1. To our
knowledge, reversibility in the C-H oxidative addition
of a cyclopentadienyl ligand has never been directly
observed with now. However, it has been postulated
so as to explain the dynamic behavior of the cluster
[Mo3(µ-η1:η5-C5H4)Cp2(CO)6]34 or the H/D exchange in
the cation [MRh(µ-η1:η5-C5H4)Cp(µ-H)2H(PR3)2]+ (M )
Mo, W).36 In addition, there are a few examples of
transformation of a bridging cyclopentadienylidene
ligand into a Cp group by reaction with external
reagents such as H2,37 NaOH,38a HCl,38b and HPPh2.39
The C-H cleavage process leading to complexes 5
does not require photochemical activation. In fact,
complex 5a can be also detected as an intermediate
species in the thermal decarbonylation of 1a . Therefore,
it seems that the electronic and coordinative unsatura-
tion generated at the ditungsten center by loss of a CO
molecule in complexes 1 might just be the driving force
for this C-H cleavage process. To check this hypoth-
esis, we examined some reactions of the triply bonded
compounds 2 with some simple ligands (L′) with the
purpose of generating reactive unsaturated species of
the type [W2Cp2(CO)2(L′)(µ-L2)].
Ch a r t 4
carbonyl C-O bond should be as rigid as any other in
this structure.
Taken together, all of the evidence from the displace-
ment parameters indicate the presence of “nonrigid”
effects in the bridging carbonyl ligands of 2a even at
200 K. We conclude that there is a slight dynamic
disorder present in these bridges. The effect is more
pronounced for C(2)-O(2), perhaps due to the proximity
of the bridgehead methylene group of the dppm ligand.
The displacement parameters suggest a shift in the
direction of a bent semibridging geometry. This con-
formational coordinate shift has been explored in a good
deal of detail26,33 and is understood to involve very little
change in the energy of the molecule. To our knowledge,
this is the first time that a dynamic disorder involving
semibridging carbonyls has been directly observed in
the solid state.
P h otoch em ica l Deca r bon yla tion s. UV-visible
light irradiation of compounds 1 in toluene at 15 °C (1a )
or 0 °C (1b) gives the triply bonded dimers 2a ,b in good
yields. This represents an alternative way of preparing
the dppm compound 2a but is the only satisfactory route
to the highly air-sensitive dmpm compound 2b. IR and
13C NMR data for 2b are comparable to those of 2a , and
hence these two compounds are assumed to be iso-
structural.
IR monitoring of the above reactions reveal in each
case the presence of tricarbonylic intermediates which
have been identified as the corresponding hydrido
cyclopentadienylidene complexes [W2(µ-η1:η5-C5H4)Cp-
(µ-H)(CO)3(µ-L2)] (5a ,b). Compound 5a can be obtained
selectively by carrying out the photolysis reaction on 1a
at -15 °C, but the dmpm complex 5b was always
obtained along with some dicarbonyl 2b even at -20
°C. These hydrido complexes are air-sensitive species
and display only a moderated thermal stability, espe-
cially the dmpm compound. Separate experiments
showed that compounds 5 transform into the corre-
sponding dicarbonyls 2 after photolysis at 15 °C (5a ) or
0 °C (5b).
Structural characterization of compounds 5 is firmly
supported by spectroscopic data (Table 1 and Experi-
mental Section) and the solid-state structure of com-
pound 7 (see below), which is formally derived from 5a .
The presence of the bridging hydride is clearly indicated
by the appearance of a highly shielded NMR resonance
(at ca. -13.5 ppm) which exhibits comparable couplings
to both phosphorus (ca. 30-40 Hz) and tungsten (ca.
40-50 Hz) atoms of these molecules. The bridging
cyclopentadienylidene ligand gives rise to a character-
istic set of four multiplets in the 1H NMR spectrum,
similar to those found for the trinuclear species [M2M′(µ-
η1:η5-C5H4)Cp2(CO)6] (M, M′ ) Mo, W), which we have
Rea ction of Com p ou n d s 2 w ith tBu NC. Com-
pounds 2 react almost instantaneously with CO at
atmospheric pressure to regenerate the tetracarbonylic
precursors 1. No intermediates could be detected in
these fast reactions, so we turned our attention to
simple ligands that were easier to use in stoichiometric
amounts. Surprisingly, no reaction was observed be-
tween 2 and PR3 (R ) Me, Ph) or P(OMe)3 at room
temperature under stoichiometric conditions, but a
smooth reaction is observed with tBuNC, a ligand
having electronic properties closer to CO than do
phosphines.
t
Compound 2a reacts readily with BuNC at 0 °C to
give [W2Cp2(µ-η1:η2-CNtBu)(CO)2(µ-dppm)] (6a ) in good
yield. The latter isomerizes smoothly at room temper-
(34) Alvarez, M. A.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.; Bois, C.;
J eannin, Y. J . Am. Chem. Soc. 1995, 117, 1324.
(35) Berry, M.; Cooper, N. J .; Green, M. L. H.; Simpson, S. J . J .
Chem. Soc., Dalton Trans. 1980, 29.
(36) (a) Alcock, N. W.; Howarth, O. W.; Moore, P.; Morris, G. E. J .
Chem. Soc., Chem. Commun. 1979, 1160. (b) Howarth, O. W.; McAteer,
C. H.; Moore, P.; Morris, G. E.; Alcock, N. W. J . Chem. Soc., Dalton
Trans. 1982, 541.
(37) (a) Casey, C. P. J . Organomet. Chem. 1990, 400, 205. (b)
Hoxmeier, R. J .; Blickensderfer, J . R.; Kaesz, K. D. Inorg. Chem. 1979,
18, 3453.
(38) (a) Bashkin, J .; Green, M. L. H.; Poveda, M. L.; Prout, K. J .
Chem. Soc., Dalton Trans. 1982, 2485. (b) Barral, M. C.; Green, M. L.
H.; J imenez, R. J . Chem. Soc., Dalton Trans. 1982, 2495.
(39) Gell, K. I.; Harris, T. V.; Schwartz, J . Inorg. Chem. 1981, 20,
481.
(33) Cotton, F. A. Prog. Inorg. Chem. 1976, 21, 1.

360 Organometallics, Vol. 16, No. 3, 1997
Alvarez et al.
Ch a r t 5
ature to yield the hydrido cyclopentadienylidene com-
plex [W2(µ-η1:η5-C5H4)Cp(µ-H)(CNtBu)(CO)2(µ-dppm)]
(7). The dmpm complex 2b reacts analogously to give
6b as the initial product. This species, however, does
not yield a cyclopentadienylidene complex at room
temperature but just experiences a slow, unspecific
decomposition process instead.
The structural characterization of complexes 6 is
based on spectroscopic and microanalytical data. The
single isocyanide ligand binds the dimetal center in a
σ,π fashion, as deduced from the very low C-N stretch-
ing frequencies (ca. 1610-1620 cm-1) and high 13C NMR
chemical shifts (ca. 215 ppm). These values compare
well with those of the related complexes [W2Cp2(µ-η1:
η2-CNtBu)(CO)4] (R ) tBu, Ph, Me)40 and [Mo2Cp2(µ-η1:
η2-CNtBu)(CO)3(η1-dppm)].15
The molecular structure of compound 7 has been
determined through an X-ray study5 and is shown in
Figure 4, along with some relevant bond lengths and
angles. The ditungsten center is bridged by dppm and
cyclopentadienylidene groups. The hydrido ligand could
not be located in this study. Finally, the coordination
spheres are completed by terminal cyclopentadienyl and
carbonyl (on W(1)) or terminal carbonyl and isocyanide
ligands (on W(2)). The intermetallic distance (3.179(2)
Å) is comparable to that found for [W2Cp2(CO)6] (3.222(1)
Å),41 in agreement with the single W-W bond proposed
for 7 on the basis of the 18e rule. The coordination of
the cyclopentadienylidene ligand is best described as
µ-η1:η5 on the basis of (a) the absence of significant
distortions in the C5 ring, with regard to C-C and W-C
lengths, and (b) the relatively large value for the W(1)-
C(40) separation, 2.18(3) Å, as expected for a W-C(sp2)
single bond, which excludes a significant “carbenoid”
contribution37,42 to that bond.
The terminal isocyanide ligand in 7 adopts a slightly
bent conformation (C(4)-N(1)-C(5) ) 156.7(39)°). This
is not unusual for isocyanide ligands43 and can be
reflected in the appearance of more than one C-N
stretch in the IR spectrum.43c In fact, the IR spectrum
of 7 in dichloromethane solution exhibits two medium-
intensity bands at 2089 and 2047 cm-1, which can be
interpreted along these lines. Other spectroscopic data
of compound 7 in solution are in agreement with its
F igu r e 4. ORTEP diagram of the molecular structure of
[W2(µ-η1:η5-C5H4)Cp(µ-H)(CNtBu)(CO)2(µ-dppm)] (7).5 El-
lipsoids represent 30% probability. Labels for phenyl,
cyclopentadienyl, and methyl carbon atoms are omitted for
clarity. Selected distances (Å): W(1)-W(2) ) 3.179(2),
W(1)-C(1) ) 1.80(5), W(1)-C(40) ) 2.18(3), W(2)-C(2) )
1.99(4), W(2)-C(4) ) 2.09(3), W(2)-C(40) ) 2.22(3). Se-
lected angles (deg): W(2)-C(4)-N(1) ) 176.4(32), C(4)-
N(1)-C(5) ) 156.7(39), C(1)-W(1)-W(2) ) 95.4(15), C(2)-
W(2)-W(1) ) 103.5(11), C(4)-W(2)-W(1) ) 164.6(9).
crystal structure. Moreover, the 1H NMR and 13C NMR
resonances of the C5H4 ligand are similar to those of
the tricarbonylic complexes 5. The same applies to the
hydrido resonance of 7, which also appears at a low
chemical shift (-13.28 ppm) and exhibits comparable
couplings to both phosphorus (32 and 22 Hz) and
tungsten (40 and 50 Hz) atoms of the molecule. Thus,
although it was not located in the X-ray study, it is
reasonable to assume a bridging (even if asymmetric)
coordination mode for this hydrido ligand.
The formation of compound 7 proves that the oxida-
tive addition of C-H cyclopentadienyl bonds in these
ditungsten complexes does not require photochemical
activation. It does not require strong thermal activation
either, as it can proceed easily at room temperature.
This C-H cleavage process leads to the electronic
saturation of the ditungsten center just as µ-η1:η2
coordination of CNR or CO ligands can do. A delicate
balance among different factors seems to define the most
favored option from a thermodynamic point of view.
Thus, in our complexes, C-H oxidative addition is
preferred over µ-η1:η2 coordination of CNtBu (or CO) in
the case of dppm, but not for the related dmpm system,
where the µ-η1:η2-CNtBu complex fails to experience the
C-H cleavage process.
Rea ction P a th w a ys in th e Deca r bon yla tion of
Com p lexes 1. The results discussed above allow us to
propose a general mechanism which gives a satisfactory
picture of the decarbonylation processes experienced by
the ditungsten complexes 1 and the products obtained
thereof (Scheme 1).
(40) (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.
Ejection of a CO molecule from 1, by either heating
or photolysis, would yield the tricarbonylic intermediate
A, probably having a µ-η1:η2-CO ligand in its most stable
form. This follows from comparison with the isoelec-
tronic compounds [M2Cp2(µ-η1:η2-CO)(CO)4] (M ) Mo,
W) and the isocyanide-bridged complexes 6. The former
pentacarbonylic species have been characterized in PVC
(41) Adams, R. D.; Collins, D. M.; Cotton, F. A. Inorg. Chem. 1974,
13, 1086.
(42) Herrmann, W. A.; Kriechbaum, G.; Bauer, C.; Guggolz, E.;
Ziegler, M. L. Angew. Chem., Int. Ed. Engl. 1981, 20, 815.
(43) (a) Nakamoto, K. Infrared and Raman Spectra of Inorganic and
Coordination Compounds, 4th ed.; Wiley: New York, 1986; Chapter
1. (b) Malatesta, L.; Bonati, F. Isocyanide Complexes of Metals; Wiley:
New York, 1969; Chapter 2. (c) Singleton, E.; Oosthuizen, H. E. Adv.
Organomet. Chem. 1983, 22, 209.

[W2(η5-C5H5)2(CO)4(µ-R2PCH2PR2)]
Organometallics, Vol. 16, No. 3, 1997 361
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 1
(P -C-P ) d p p m , d m p m )
ence a P-C cleavage process, slower than the former,
leading to C and then to 3. Apparently, this minor
reaction pathway is fully suppressed at low tempera-
tures (i.e. photochemical decarbonylations). Thus, even
when it is relatively facilitated at high temperatures,
it seems that P-C cleavage of the dppm ligand does not
occur fast enough so as to provide a significant pathway
in our ditungsten system. Finally, the notable influence
of the diphosphine ligand on the above processes is
difficult to define, since the thermal decarbonylation of
the dmpm complex 1b leads to a generalized decomposi-
tion of the binuclear substrate. From our limited data,
however, it can be seen that replacement of dppm by
dmpm decreases the stability of the complexes in
general, particularly that of the C-H cleavage products,
and makes them much more air-sensitive.
Exp er im en ta l Section
Gen er a l Com m en ts. All manipulations and reactions
were carried out under a nitrogen (99.9995%) atmosphere,
using standard Schlenk techniques. Solvents were purified
according to literature procedures45 and distilled prior to use.
Petroleum ether refers to that fraction distilling in the range
65-70 °C, and diglyme refers to bis(2-methoxyethyl)ether. The
compounds [W2Cp2(CO)4]46 and dppm47 were prepared as
described previously. All other reagents were obtained from
the usual commercial suppliers and used as received. Photo-
chemical experiments were performed using jacketed Pyrex
or quartz Schlenk tubes, refrigerated by a closed 2-propanol
circuit kept at the desired temperature with a cryostat or by
tap water. A 400 W mercury lamp (Applied Photophysics),
placed ca. 1 cm away from the Schlenk tube, was used for these
experiments. Low-temperature chromatographic separations
were carried out analogously using jacketed columns. Com-
mercial aluminum oxide (Aldrich, activity I, 150 mesh) was
degassed under vacuum prior to use. The latter was mixed
afterward under nitrogen with the appropriate amount of
water to reach the activity desired. Filtrations were carried
out using diatomaceous earth. NMR spectra were routinely
recorded at 300.13 (1H), 121.50 (31P{1H}), or 75.47 MHz
(13C{1H}). Chemical shifts (δ) are given in ppm, relative to
internal TMS (1H, 13C) or external 85% H3PO4 aqueous solution
(31P). Coupling constants (J ) are given in hertz.
or frozen-gas matrixes44 as primary products in the
photolysis of the hexacarbonylic complexes [M2Cp2-
(CO)6]. Intermediate A would then experience two
major processes, either loss of a second CO molecule (to
yield 2) or a reversible C-H oxidative addition (to yield
5), possibly via the agostic intermediate B. The trans-
formation A/5 is equivalent to the isomerization 6a /7
discussed above and presumably is very fast, as no
spectroscopic evidence for the presence of A or B in the
corresponding reaction mixtures has been obtained.
Moreover, because of the fact that 5 gives either 1 or 2
(through carbonylation or decarbonylation reactions,
respectively), it is also likely that the latter reactions
occur via intermediate A, in other words, that the
transformation A/5 is reversible.
P r ep a r a tion of [W2Cp 2(CO)4(µ-d p p m )] (1a ). A dichloro-
methane solution (8 mL) containing dppm (0.384 g, 1 mmol)
was added slowly to a diglyme solution (25 mL) containing
[W2Cp2(CO)4] (ca. 0.610 g, 1 mmol) at 0 °C, and the mixture
was stirred for 10 min. The resulting solution was filtered,
using dichloromethane (3 × 10 mL) to remove any product
retained in the filtration pad, and then evaporated under
vacuum to ca. 25 mL. Addition of petroleum ether (30 mL)
and crystallization at -20 °C for 1 day gave compound 1a as
dark red crystals, which were separated from the solution,
washed with petroleum ether, and dried under vacuum (0.746
g, 75%). Anal. Calcd for C39H32O4P2W2 (1a ): C, 47.11; H, 3.24.
Found: C, 47.13; H, 3.37. 1H NMR (CD2Cl2, 233 K): δ 7.93-
6.84 (m, 20H, Ph), 5.61 (t, J HP ) 9, 2H, CH2, isomer A), 4.98
(t, J HP ) 8, 2H, CH2, isomer B), 5.35 (s, 10H, Cp, isomer B),
4.57 (s, 10H, Cp, isomer A); ratio A:B ) 0.5. 13C{1H} NMR
(CD2Cl2, 203 K): δ 235.9, 226.6 (2 × m, CO), 140.1-126.5 (Ph),
90.3 (s, Cp, isomer B), 88.8 (s, Cp, isomer A), 70.0 (br, CH2,
isomer B).
Because of the reversibility of all mutual transforma-
tions involving complexes 1, 2, and 5, the nature of the
products obtained in the decarbonylation of compounds
1 is then mainly dictated by the extent of loss of CO,
not by the method used to achieve it. Thus, the
tricarbonyl 5a is detected as an intermediate species
in the formation of dicarbonyl 2a by either thermal or
photochemical decarbonylation of 1a . A different situ-
ation is found with respect to the oxo complex 3, a minor
product in the thermal decarbonylation of 1a . As we
have said above, we trust it is formed from the P-C
cleavage product [W2Cp2(µ-CH2PPh2)(µ-PPh2)(CO)2] (C
in Scheme 1). We recall here that the dimolybdenum
analogue of C is the major product obtained in the
thermal decarbonylation of [Mo2Cp2(CO)4(µ-dppm)].4
Because of the fact that 2 does not experience itself any
P-C cleavage process on heating, we conclude that the
product distribution in the thermal treatment of 1a is
controlled kinetically. Thus, as an alternative to the
simple decarbonylation, intermediate A would experi-
P r ep a r a tion of [W2Cp 2(CO)4(µ-d m p m )] (1b). By a pro-
cedure identical with that described for 1a but using dmpm
(45) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals; Pergamon Press: Oxford, U.K., 1988.
(46) Curtis, M. D.; Fotinos, N. A.; Messerle, L.; Sattelberger, A. P.
Inorg. Chem. 1983, 22, 1559.
(44) (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. J . Chem. Soc., Dalton Trans. 1990, 2825.
(47) Agiar, A. M.; Beisler, J . J . Org. Chem. 1964, 29, 1660.

362 Organometallics, Vol. 16, No. 3, 1997
Alvarez et al.
(0.15 mL, 1 mmol) instead of dppm, compound 1b is isolated
as a red microcrystalline solid which is partially soluble in
petroleum ether (0.420 g, 56%). Anal. Calcd for C19H24O4P2W2
(1b): C, 30.56; H, 3.22. Found: C, 30.52; H, 3.25. 1H NMR
(C6D6, 291 K): δ 4.9 (s, 10H, Cp), 2.35 (t, J HP ) 8, 2H, CH2),
1.50 [AA′(XX′)3, |J HP + J HP′| ) 8, 6H, Me], 1.30 [AA′(XX′)3, |J HP
+ J HP′| ) 7, 6H, Me]. 13C{1H} NMR (C6D6, 291 K): δ 237.4
[AA′X, |J CP + J CP′| ) 20, CO], 230.9 [AA′X, |J CP + J CP′| ) 12,
resulting yellow-orange solution was evaporated under vacuum,
and the residue was extracted with toluene (5 × 5 mL) and
the extract filtered. Removal of solvent from the filtrate and
washing of the residue with petroleum ether (5 mL) yielded
compound 4 as an orange-brown powder (0.041 g, 80%). Anal.
Calcd for C37H32O4P2W2 (4): C, 45.80; H, 3.35. Found: C,
45.77; H, 3.30. 1H NMR (CD2Cl2, 291 K): δ 7.41-7.24 (m, 20H,
Ph), 6.02 (s, 5H, Cp), 5.50 (d, J HP ) 1, 5H, Cp), 3.75 (dd, J HP
) 9, 2, 2H, CH2). 13C{1H} NMR (CD2Cl2, 291 K): δ 227.1 (d,
J CP ) 17, 2 × CO), 133.5-128.5 (Ph), 109.1 (s, Cp), 92.5 (s,
Cp), 35.4 (t, J CP ) 30, CH2).
CO], 90.1 (s, Cp), 47.9 (t, J CP ) 38, CH2), 23.7 [AA′X, |J CP
+
J CP′| ) 24, 2 × Me], 23.5 [AA′X, |J CP + J CP′| ) 44, 2 × Me].
P r ep a r a tion of [W2Cp 2(CO)2(µ-d p p m )] (2a ). Meth od A.
A toluene solution (25 mL) of compound 1a (0.100 g, 0.1 mol)
was irradiated with UV-visible light at 15 °C for 5 h while
nitrogen was bubbled gently through the solution. The result-
ing mixture was then filtered and concentrated under vacuum
to ca. 5 mL. Addition of petroleum ether (20 mL) and
crystallization at -20 °C overnight gave compound 2a as an
air-sensitive black-green microcrystalline powder, which was
isolated from the solution by the usual methods (0.080 g, 85%).
P r epar ation of [W2(µ-η1:η5-C5H4)Cp(µ-H)(CO)3(µ-dppm )]
(5a ). A tetrahydrofuran solution (25 mL) of compound 1a
(0.100 g, 0.1 mmol) was irradiated in a quartz Schlenk tube
with UV-visible light at 0 °C for 2 h while nitrogen was
bubbled gently through the solution. Workup of the resulting
yellow-brown mixture as described for 4 gave compound 5a
as
a brown powder (0.092 g, 95%). Anal. Calcd for
C
38H32O3P2W2 (5a ): C, 47.23; H, 3.34. Found: C, 47.28; H,
Anal. Calcd for
C
37H32O2P2W2 (2a ): C, 47.36; H, 3.48.
3.50. 1H NMR (CD2Cl2, 291 K): δ 7.80-6.80 (m, 20H, Ph),
5.74, 5.30, 5.14, 4.58 (4 × m, 4 × 1H, C5H4), 5.19 (d, J HP ) 1,
5H, Cp), 4.82 (dtd, J HH ) 13, J HP ) 11, J HH ) 2, 1H, CH2),
3.94 (dt, J HH ) 13, J HP ) 10, 1H, CH2), -13.35 (ddd, J HP ) 37,
26, J HH ) 2, J HW ) 51, 41, 1H, µ-H). 13C{1H} NMR (CD2Cl2,
243 K): δ 246.8 (d, J CP ) 9, CO), 239.4 (d, J CP ) 17, CO), 231.1
(s, J CW ) 167, CO), 172.5 [s, J CW ) 81, µ-C(C5H4)], 141.0 -128.0
(Ph), 115.6 (s, C5H4), 105.2 (d, J CP ) 5, C5H4), 88.5 (s, Cp),
84.0 (s, C5H4), 79.4 (s, C5H4). 13C{1H} NMR (C6D6, 291 K): δ
55.0 (m, CH2); other resonances similar to those measured in
CD2Cl2.
P r epar ation of [W2(µ-η1:η5-C5H4)Cp(µ-H)(CO)3(µ-dm pm )]
(5b). A toluene solution (30 mL) of compound 1b (0.100 g,
0.13 mmol) was treated as described for 5a at -20 °C for 2 h.
Similar workup yielded a brown solid shown (by NMR) to
contain compound 5b along with significant amounts of 2b.
Typical 5b:2b ratios obtained were ca. 3:1. All attempts to
separate these compounds resulted in decomposition of the
mixture. Spectroscopic data for 5b: 1H NMR (400.13 MHz,
toluene-d8, 291 K) δ 5.66, 4.93, 4.80, 4.76 (4 × m, 4 × 1H,
C5H4), 4.81 (d, J HP ) 1, 5H, Cp), 2.02 (m, 2H, CH2), 1.36, 1.33,
1.04, 0.84 (4 × d, J HP ) 8, 4 × 3H, Me), -13.98 (ddt, J HP ) 30,
27, J HH ) 2, 1H, µ-H).
Found: C, 47.24; H, 3.57. 1H NMR (CD2Cl2, 223 K): δ 7.50-
7.13 (m, 20H, Ph), 6.13 (t, J HP ) 11, 2H, CH2), 4.61 (s, 10H,
Cp). 13C{1H} NMR (CD2Cl2, 223 K): δ 240.7 (s, J CW ) 131,
CO), 138.8-125.6 (Ph), 88.2 (s, Cp), 69.7 (t, J CP ) 28, CH2).
The crystals used in the 200 K X-ray study on 2a were grown
by slow diffusion of a concentrated dichloromethane solution
of the complex into a layer of benzene.
P r ep a r a tion of [W2Cp 2(CO)2(µ-d m p m )] (2b). A tetrahy-
drofuran solution (30 mL) of compound 1b (0.100 g, 0.13 mmol)
was irradiated in a quartz Schlenk tube with UV-visible light
at 0 °C for 3 h while nitrogen was bubbled gently through the
solution. The resulting mixture was filtered and the solvent
removed under vacuum. The residue was washed with
petroleum ether (2 × 5 mL) and dried under vacuum to give
compound 2b as a brown powder (0.065 g, 70%). Satisfactory
microanalytical data for this complex could not be obtained,
due to its high air sensitivity. 1H NMR (CD2Cl2, 291 K): δ
4.95 (t, J HP ) 11, 2H, CH2), 4.89 (s, 10H, Cp), 1.78 [AA′(XX′)3,
|J HP + J HP′| ) 8, 12H, Me]. 13C{1H} NMR (CD2Cl2, 291 K): δ
239.4 (s, CO), 86.4 (s, Cp), 79.0 (t, J CP ) 31, CH2), 24.9 [AA′X,
|J CP + J CP′| ) 37, Me].
Th er m a l Deca r bon yla tion of 1a (Meth od B for P r ep a -
r a tion of 2a ). An n-octane solution (12 mL) of compound 1a
(0.100 g, 0.1 mmol) was refluxed for 1.5 h while nitrogen was
bubbled gently through the solution, which gradually acquired
an olive green color. The mixture was then cooled to room
temperature, whereby black-green crystals were formed. These
were separated from the solution, washed with toluene (5 mL)
and petroleum ether (5 mL), and then dried under vacuum to
yield 0.084 g of compound 2a (89%). The solution and washing
liquids were mixed and the solvents removed under vacuum.
The resulting residue was then dissolved in dichloromethane
(3 mL) and chromatographed on an aluminum oxide column
(activity III, 15 × 2.5 cm) at 15 °C. After the column was
washed with petroleum ether, elution with dichloromethane-
petroleum ether (1:1) gave a brown fraction. Removal of
solvents from the latter under vacuum yielded [W2Cp2(µ-
CH2PPh2)(O)(µ-PPh2)(CO)] (3) as a brown powder (ca. 0.005
g, 5%). Anal. Calcd for C36H32O2P2W2 (3): C, 46.65; H, 3.46.
Found: C, 46.04; H, 3.40. 1H NMR (CD2Cl2, 291 K): δ 7.85-
7.15 (m, 20H, Ph), 5.59 (d, J HP ) 1, 5H, Cp), 4.64 (t, J HP ) 2,
5H, Cp), 3.84 (dt, J HH ) 12, J HP ) 6, 1H, CH2), 2.51 (dd, J HH
) 12, J HP ) 9, 1H, CH2). 13C{1H} NMR (CD2Cl2, 291 K): δ
227.0 (d, J CP ) 5, CO), 135.6-127.5 (Ph), 107.5 (s, Cp), 85.8
(s, Cp), -3.1 (d, J CP ) 3, CH2). The crystals used in the X-ray
study on 3 were grown by slow diffusion of a concentrated
dichloromethane solution of the complex into a layer of toluene
and petroleum ether.
P r ep a r a tion of [W2Cp 2(µ-η1:η2-CNtBu )(CO)2(µ-d p p m )]
(6a ). tBuNC (6 µL, 0.05 mmol) was added to a tetrahydrofuran
solution (8 mL) of compound 2a (0.050 g, 0.05 mmol) at 0 °C,
and the mixture was stirred at that temperature for 30 min
to give an orange-brown solution. Solvent was then removed
under vacuum and the residue washed with petroleum ether
(3 × 3 mL) at 0 °C and dried under vacuum to give compound
6a as a brown powder (0.049 g, 87%). Anal. Calcd for C42H41
-
NO2P2W2 (6a ): C, 49.39; H, 4.05; N, 1.37. Found: C, 49.35;
H, 4.16; N, 1.40. 1H NMR (CD2Cl2, 291 K): δ 7.90-6.80 (m,
20H, Ph), 6.20 (m, 1H, CH2), 6.00 (m, 1H, CH2), 4.75 (s, 5H,
Cp), 4.33 (s, 5H, Cp), 2.11 (s, 9H, CH3). 13C{1H} NMR (50.32
MHz, CD2Cl2, 233 K): δ 254.1 (d, J CP ) 20, CO), 230.8 (d, J CP
) 9, CO), 212.4 (s br, µ-CNR), 146.0-127.0 (Ph), 92.2 (s, Cp),
89.1 (s, Cp), 76.0 (dd, J CP ) 32, 26, CH2), 57.9 [s, CNC(CH3)3],
30.9 (s, CH3).
P r ep a r a tion of [W2Cp 2(µ-η1:η2-CNtBu )(CO)2(µ-d m p m )]
(6b). tBuNC (11 µL, 0.09 mmol) was added to a tetrahydro-
furan solution (30 mL) of compound 2b (ca. 0.065 g, 0.09 mmol)
prepared “in situ” as described above, and the mixture was
stirred at room temperature for 10 min to give an orange
solution. Workup as for 6a gave essentially pure compound
6b as an orange-brown powder (0.065 g, 89%). Satisfactory
microanalytical data could not be obtained for this complex
due to its progressive decomposition during all attempts to
crystallize it. 1H NMR (200.13 MHz, toluene-d8, 291 K): δ
4.98 (d, J HP ) 1, 5H, Cp), 4.79 (d, J HP ) 1, 5H, Cp), 3.47 (ddd,
P r ep a r a tion of [W2Cp 2(O)2(CO)2(η1-d p p m )] (4). A tet-
rahydrofuran solution (10 mL) of compound 2a (0.05 g, 0.053
mmol) was treated with air (6.1 mL, 0.053 mmol of O2) under
nitrogen and stirred at room temperature for 30 min. The
J HP ) 15, 5, J HH ) 12, 1H, CH2), 3.09 (ddd, J HP ) 15, 4, J HH
)
12, 1H, CH2), 1.71, 1.69 (2 × d, J HP ) 9, 2 × 3H, PCH3), 1.20
[s, 9H, CNC(CH3)3], 1.10 (d, J HP ) 8, 3H, PCH3), 1.00 (d, J HP

[W2(η5-C5H5)2(CO)4(µ-R2PCH2PR2)]
Organometallics, Vol. 16, No. 3, 1997 363
Ta ble 4. Exp er im en ta l Da ta for th e X-r a y Diffr a ction Stu d ies
2a ‚2C6H6
3‚C7H8
mol formula
mol wt
color
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
C49H44O2P2W2
1094.48
dark purple
orthorhombic
P212121
26.412(4)
14.440(2)
11.023(2)
90
90
90
4204(1)
4
1.729
C43H40O2P2W2
1018.5
dark brown
triclinic
P1h
10.807(5)
14.142(5)
14.820(5)
117.23(3)
106.70(3)
96.99(3)
1842(3)
2
Z
D
calcd, g cm-3
1.84
orientation rflns: no.; range (2θ), deg
30; 23.9-35.9
25; 22-24
F(000)
2128
984
µ, cm-1
59.0
65.0
transmissn factors: max, min
temp, K
cryst size, mm
diffractometer
radiation
monochromator
scan type
scan width, deg
θ range, deg
std rflns
0.82, 0.44
200.0 ( 0.2
0.52 × 0.38 × 0.35
Stoe AED-2
Mo KR
291
0.35 × 0.35 × 0.20
Nonius CAD4
Mo KR
graphite
ω-θ
graphite
ω-2θ
1.08
2-25
3
0.8 + 0.34 tan θ
1-25
2
no. of measd rflns
no. of rflns used
no. of rflns with Fo g 2σ(Fo
no. of refined parameters
4388
6069
3545 (I g 3σ(I))
4144 (Rint ) 0.0201)
4032
558
2
2
)
388
no. of restraints
R
61
0.0214a
0.0528c
1.067, 1.058
0.002, 0.099
0.82, -1.05
0.036b
0.041d
Rw
QOF: unrestr,e restrf
mean, max |shift/esd|, final cycle
largest diff peak, e/Å3
-0.67, -1.28
a
2
b
2
R ) ∑(|Fo| - |Fc|)/ ∑|Fo|; value for data having Fo g 2σ(Fo2). R ) ∑(|Fo| - |Fc|)/ ∑|Fo|. c Rw ) [∑w(Fo - Fc2)2/∑w(Fo2)2]1/2, with w )
[σ2(Fo2) + (g1P)2 + g2P]-1, with P ) [max(Fo2;0) + 2Fc2]/3; g1 and g2 values used were 0.0273 and 4.93, respectively. Rw ) [∑w(|Fo| -
d
|Fc|)2/∑w(Fo)2]1/2, with w ) 1. e Quality of fit (QOF) ) [∑w(Fo2 - Fc2)2/(Nobservns - Nparam)]1/2
.
f Restrained QOF ) [{∑w(Fo2 - Fc2)2 + ∑w(Ytarget
- Ycalc)2}/(Nreflns + Nrestraints - Nparam)]1/2
.
) 7, 3H, PCH3). 13C{1H} NMR (100.61 MHz, CD2Cl2, 200 K):
δ 255.2 (d, J CP ) 19, CO), 227.6 (d, J CP ) 10, CO), 217.2 (d,
J CP ) 8, µ-CNR), 90.2 (s, Cp), 86.8 (s, Cp), 72.6 (t, J CP ) 28,
CH2), 57.4 [s, CNC(CH3)3], 30.3 (s, CH3), 27.8, 25.2, 21.4, 19.5
(4 × d, PCH3).
with epoxy, mounted at the end of a glass fiber, and placed in
a nitrogen gas cold stream on the diffractometer. Routine
procedures were used to determine unit-cell dimensions, lattice
type, and Laue symmetry. These were verified by normal-
beam axial photography of a, b, and c, of three face diagonals,
and of the body diagonal of the cell. The cell dimensions and
other crystal data are given, along with data collection
parameters, in Table 4. The learned-profile method48 of
deriving intensities was used during data collection. Absorp-
tion corrections were based on 10 full ψ-scans of reflections
with diffractometer angle ø near 90°, along with 160 measure-
ments comprising all of the symmetry equivalents of each of
20 reflections with general indices.49 A power failure during
the course of data collection, which left the low-temperature
device disabled for ca. 70 min, did not lead to any significant
changes in the learned-profile parameters, the unit cell, or the
orientation matrix, all of which were redetermined following
the failure. Three monitor reflections, which were measured
periodically during data collection, did not vary significantly.
P r epar ation of [W2(µ-η1:η5-C5H4)Cp(µ-H)(CNtBu )(CO)2(µ-
d p p m )] (7). tBuNC (6 µL, 0.05 mmol) was added to a
tetrahydrofuran solution (8 mL) of compound 2a (0.05 g, 0.05
mmol), and the mixture was stirred at room temperature for
3 h. Solvent was then removed from the resulting yellow-
brown solution, and the residue was extracted with toluene
and the extract filtered. Removal of solvent from the filtrate
and washing of the residue with petroleum ether (3 × 3 mL)
gave compound 7 as a brown powder (0.047 g, 84%). Suitable
crystals for the X-ray study were grown by slow diffusion of a
concentrated dichloromethane solution of the complex into a
layer of petroleum ether. They were shown (by NMR and
X-ray) to contain 0.5 CH2Cl2 per molecule of complex. Anal.
Calcd for C42.5H42ClNO2P2W2 (7‚0.5CH2Cl2): C, 47.98; H, 3.98;
N, 1.32. Found: C, 47.73; H, 4.00; N, 1.32. 1H NMR (CD2Cl2,
291 K): δ 7.50-7.00 (m, 20H, Ph), 5.85, 5.04, 4.94, 4.47 (4 ×
m, 4 × 1H, C5H4), 5.06 (d, J HP ) 1, 5H, Cp), 4.87 (m, 1H, CH2),
4.03 (dt, J HH ) 13, J HP ) 10, 1H, CH2), 1.12 (s, 9H, CH3),
-13.28 (ddd, J HP ) 37, 22, J HH ) 1, J HW ) 50, 40, 1H, µ-H).
13C{1H}NMR (CD2Cl2, 291 K): δ 246.8 (d, J CP ) 17, CO), 236.3
(s, J CW ) 176, CO), 181.4 (d, J CP ) 21, CNR), 159.7 [s,
µ-C(C5H4)], 115.2 (d, J CP ) 2, C5H4), 103.1 (d, J CP ) 6, C5H4),
88.6 (s, Cp), 87.8 (s, Cp), 77.4 (d, J CP ) 2, C5H4), 58.9 [s,
CNC(CH3)3], 55.7 (dd, J CP ) 40, 25, CH2), 31.1 (s, CH3).
X-r a y Str u ctu r e Deter m in a tion for 2a ‚2C6H6 a t 200 K.
Da ta Collection . A block-shaped purple crystal was covered
Str u ctu r e Solu tion a n d Refin em en t. The structure was
solved by direct methods. All unique data were used in the
development and refinement of the structure,50 which was
2
refined on Fo
. Thirty of the 32 H atoms of the dinuclear
complex were located in Fourier maps, and the other two were
(48) Clegg, W. Acta Crystallogr. 1981, A37, 22.
(49) Calculations were carried out on a local area VAXcluster (VAX/
VMS V5.5) with the program REDU4 Rev. 7.03 (Stoe) for data
reduction and with the commercial package SHELXTL-PLUS Release
4.21/V (1990, Siemens Analytical X-ray Instruments, Inc.); least-
squares calculations were done on a Hewlett-Packard 715/50 (HP-UX
V9.0).

364 Organometallics, Vol. 16, No. 3, 1997
Alvarez et al.
initially placed at idealized positions, as were the hydrogen
atoms of two interstitial benzene sites. Positional parameters
of the H atoms of the main molecule were refined independ-
ently, but with similarity restraints51 placed on the C-H
distances of a given chemical fragment (for example, within a
given phenyl group). For one of the benzene moieties, which
was not disordered, the hydrogens were treated as riding
atoms. The second benzene group was disordered over two
sites, both in the same plane, related by a rotational displace-
ment. The congeners were treated as half-occupied, variable-
metric rigid groups, with hydrogen atoms in idealized posi-
tions. All non-hydrogen atoms in the structure were refined
anisotropically, except for the carbon atoms of the disordered
benzene site, which were isotropic with similarity restraints
between the Uiso values of nearest atoms from the two groups.
All hydrogen atoms on the asymmetric unit were assigned
isotropic displacement parameters equal to 1.2 times the
isotropic or equivalent isotropic displacement parameters of
their respective parent carbon atoms. The enantiomorph was
chosen by use of the Flack parameter,52 which had a value of
-0.01(1) for the enantiomorph reported here.
Difference maps showed a toluene molecule which was
refined as a rigid group, with an isotropic overall thermal
parameter. Other non-hydrogen atoms were anisotropically
refined. Not all hydrogen atoms could be found on difference
maps; therefore, they were geometrically located, except those
of the toluene molecule, which were not introduced. Scattering
factors were taken from CRYSTALS and corrected from
anomalous dispersion. Further details of the data collection
and crystallographic analysis are given in Table 4.
Ack n ow led gm en t. We thank the DGICYT of Spain
for financial support (Project PB91-0678) and the FICYT
of Asturias (Spain) for a grant to M.A.A. We also thank
Dr. A. G. Orpen (University of Bristol, Bristol, U.K.) for
useful comments on the crystal structure of compound
2a determined at room temperature.
Su p p or tin g In for m a tion Ava ila ble: ORTEP diagrams
of the molecular structures for compounds 2a and 3 showing
the full atom-numbering scheme (Figures S1 and S2) and
atomic coordinates for non-hydrogen atoms (Tables S1 and S5)
and for hydrogen atoms (Tables S2 and S6), anisotropic
thermal parameters (Tables S3 and S7), and interatomic
distances and angles (Tables S4 and S8) for both structure
determinations (11 pages). Ordering information is given on
any current masthead page. Tables of observed and calculated
structure factors may be also obtained from the authors on
request.
X-r a y Str u ctu r e Deter m in a tion for 3‚C7H8. The struc-
ture was solved by direct methods and subsequent Fourier
maps. An absorption correction was applied with the program
DIFABS53 from CRYSTALS.54 Refinements were carried out
by least-squares methods in three blocks.
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