Chemistry of unsaturated group 6 metal complexes with bridging hydroxy and methoxycarbyne ligands. 6. C-E bond formation and C-O bond cleavage processes in the reactions of [Mo2(η5-C5H 5)2(μ-COMe)(μ-PCy2)(μ-CO)] with several p -block elements (E) and their hydride derivatives

Article abstract of DOI:10.1021/om100117a

The unsaturated complex [Mo₂Cp₂(μ-COMe)(μ- PCy₂)(μ-CO)] (1) reacts with several HER_n molecules (HER_n = HSPh, HPHPh, HSnPh₃) in toluene at 263-288 K to give the corresponding derivatives [Mo₂Cp₂(μ-ER _n)(μ-PCy₂)(CO)₂]. A related reaction takes place in toluene at 263 K with the diphosphite (EtO)₂POP(OEt) ₂ to give a mixture of the diethoxyphosphide derivatives [Mo ₂Cp₂(μ-PCy₂){μ-P(OEt)₂}(CO) ₂] and [Mo₂Cp(η⁵-C₅H ₄CH₂Ph)(μ-PCy₂){μ-P(OEt) ₂}(CO)₂], the latter incorporating a benzyl group from the solvent, and with iodine (in dichloromethane at room temperature) to give first the iodide complex [Mo₂Cp₂(μ-I)(μ-PCy ₂)(CO)₂] and then the triiodide derivative [Mo ₂Cp₂(μ-I)I₂(μ-PCy₂)(CO) ₂]. In all of the above reactions, neat demethylation of the methoxycarbyne ligand takes place. In contrast, the silanes HSiPh₃ and H₂SiPh₂ (unreactive toward 1 in refluxing toluene) react slowly under visible-UV irradiation at room temperature to give in good yields the novel complexes [Mo₂Cp₂{μ-C(2-C ₆H₄SiPh₂OMe)}(μ-PCy₂)(μ-CO)] and [Mo₂Cp₂(μ-CSiPh₂OMe)(μ-PCy ₂)(μ-CO)], having arylcarbyne and silylcarbyne ligands, respectively, the latter resulting from the overall elimination of H₂ and insertion of Ph₂SiC₆H₄ and SiPh ₂ fragments, respectively, into the strong C-OMe bond of the carbyne ligand. The reactions of 1 with elemental selenium and sulfur involve the incorporation of three to four chalcogen atoms to the dimetal center under mild conditions, to give respectively the carbene-seleniolate derivative [Mo ₂Cp₂{μ-C(OMe)C(O)Se}(μ-PCy₂)(μ-Se ₂)] and the O-methyldithiocarbonate [Mo₂Cp ₂(μ-PCy₂){μ-S₂C(OMe)}(S)₂], the latter derived from an unexpected coupling of two sulfur atoms to the carbyne ligand.

Full text of DOI:10.1021/om100117a

Organometallics 2010, 29, 2157–2165 2157
DOI: 10.1021/om100117a
Chemistry of Unsaturated Group 6 Metal Complexes with
Bridging Hydroxy and Methoxycarbyne Ligands. 6. C-E Bond
Formation and C-O Bond Cleavage Processes in the Reactions of
[Mo2(η5-C5H5)2( μ-COMe)( μ-PCy2)( μ-CO)] with Several p-Block
Elements (E) and Their Hydride Derivatives
ꢀ
M. Esther Garcıa, Daniel Garcıa-Vivo, and Miguel A. Ruiz*
´
ꢀ
Departamento de Quımica Organica e Inorganica/IUQOEM, Universidad de Oviedo, E-33071 Oviedo, Spain
ꢀ
Received February 12, 2010
The unsaturated complex [Mo2Cp2( μ-COMe)( μ-PCy2)( μ-CO)] (1) reacts with several HERn molecules
(HERn = HSPh, HPHPh, HSnPh3) in toluene at 263-288 K to give the corresponding derivatives
[Mo2Cp2( μ-ERn)( μ-PCy2)(CO)2]. A related reaction takes place in toluene at 263 K with the diphosphite
(EtO)2POP(OEt)2 to give a mixture of the diethoxyphosphide derivatives [Mo2Cp2( μ-PCy2){μ-P(OEt)2}-
(CO)2] and [Mo2Cp(η5-C5H4CH2Ph)( μ-PCy2){μ-P(OEt)2}(CO)2], the latter incorporating a benzyl group
from the solvent, and with iodine (in dichloromethane at room temperature) to give first the iodide complex
[Mo2Cp2( μ-I)( μ-PCy2)(CO)2] and then the triiodide derivative [Mo2Cp2( μ-I)I2( μ-PCy2)(CO)2]. In all of
the above reactions, neat demethylation of the methoxycarbyne ligand takes place. In contrast, the silanes
HSiPh3 and H2SiPh2 (unreactive toward 1 in refluxing toluene) react slowly under visible-UV irradiation
at room temperature to give in good yields the novel complexes [Mo2Cp2{μ-C(2-C6H4SiPh2OMe)}-
( μ-PCy2)( μ-CO)] and [Mo2Cp2( μ-CSiPh2OMe)( μ-PCy2)( μ-CO)], having arylcarbyne and silylcarbyne
ligands, respectively, the latter resulting from the overall elimination of H2 and insertion of Ph2SiC6H4 and
SiPh2 fragments, respectively, into the strong C-OMe bond of the carbyne ligand. The reactions of 1 with
elemental selenium and sulfur involve the incorporation of three to four chalcogen atoms to the dimetal
center under mild conditions, to give respectively the carbene-seleniolate derivative [Mo2Cp2{μ-C(OMe)-
C(O)Se}( μ-PCy2)( μ-Se2)] and the O-methyldithiocarbonate [Mo2Cp2( μ-PCy2){μ-S2C(OMe)}(S)2], the
latter derived from an unexpected coupling of two sulfur atoms to the carbyne ligand.
Introduction
alkyne metathesis.3 In contrast, the chemistry of alkoxycar-
byne complexes is considerably less developed,4 especially in
the case of binuclear compounds having multiple metal-
metal bonds. We thus initiated a systematic study of the
reactivity of such unsaturated species using group 6 metal
substrates, focused first on cationic binuclear complexes
The chemistry of carbyne complexes is a well-developed
field within organometallic science. These complexes usually
display a high reactivity derived from the multiple nature of
their metal-carbon bonds in either the terminal or the μ2-
bridging coordination modes, which can be further increased
in the latter case by the presence of multiple metal-metal
bonds (Chart 1),1 and they are also involved in several
industrial processes of interest such as the Fischer-Tropsch
synthesis of hydrocarbons from syngas (CO þ H2)2 and
(3) For some recent reviews see: (a) Schrock, R. R.; Czekelius, C.
Adv. Synth. Catal. 2007, 349, 55. (b) Mori, M.; Kitamura, K. In Compre-
hensive Organometallic Chemistry III; Crabtree, R. H.; Mingos, D. M. P.,
Eds.; Elsevier: Oxford, U.K., 2007; Vol 11, Chapter 8. (c) Mortreux, A.;
Coutelier, O. J. Mol. Catal. A 2006, 254, 96. (d) Schrock, R. R. Chem.
Commun. 2005, 2773.
(4) For some studies of reactivity of alkoxycarbyne-bridged com-
pounds see: (a) Hersh, W. H.; Fong, R. H. Organometallics 2005, 24,
4179. (b) Peters, J. C.; Odon, A. L.; Cummins, C. C. Chem. Commun. 1997,
1995. (c) Bronk, B. S.; Protasiewicz, J. D.; Pence, L. E.; Lippard, S. J.
Organometallics 1995, 14, 2177. (d) Seyferth, D.; Ruschke, D. P.; Davis, W.
H. Organometallics 1994, 13, 4695. (e) Chi, Y.; Chuang, S. H.; Chen,
B.-F.; Peng, S.-M.; Lee, G.-H. J. Chem. Soc., Dalton Trans. 1990, 3033.
(f) Friedman, A. E.; Ford, P. C. J. Am. Chem. Soc. 1989, 111, 551. (g)
Keister, J. B. Polyhedron 1988, 7, 847. (h) Friedman, A. E.; Ford, P. C. J. Am.
Chem. Soc. 1986, 108, 7851. (i) Farrugia, L. J.; Miles, A. D.; Stone, F. G. A.
J. Chem. Soc., Dalton Trans. 1985, 2437. (j) Beanan, L. R.; Keister, J. B.
Organometallics 1985, 4, 1713. (k) Nuel, D.; Dahan, F.; Mathieu, R. J. Am.
Chem. Soc. 1985, 107, 1658. (l) Shapley, J. R.; Yeh, W.-Y.; Churchill, M. R.;
Li, Y.-J. Organometallics 1985, 4, 1898. (m) Green, M.; Mead, K. A.; Mills,
R. M.; Salter, I. D.; Stone, F. G. A.; Woodward, P. J. J. Chem. Soc., Chem.
Commun. 1982, 51.
*To whom correspondence should be addressed. E-mail: mara@
uniovi.es.
(1) See for example: (a) Stone, F. G. A. Leaving no Stone Unturned.
Pathways in Organometallic Chemistry; American Chemical Society:
Washington, DC, 1993. (b) Fischer, H.; Hoffmann, P.; Kreissl, F. R.; Schrock,
R. R.; Schubert, U.; Weiss, K. Carbyne Complexes; VCH: Weinheim,
Germany, 1988. (c) Mays, A.; Hoffmeister, H. Adv. Organomet. Chem.
1991, 32, 259. (d) Angelici, R. J.; Heesook, K. P. Adv. Organomet. Chem.
1987, 27, 51. (e) Stone, F. G. A. Angew. Chem., Int. Ed. Engl. 1984, 23, 89.
(2) (a) Maitlis, P. M.; Zanotti, V. Chem. Commun. 2009, 1619. (b) Cho,
H.-G.; Lester, A. J. Phys. Chem. A 2006, 110, 3886. (c) Marsh, A. L.;
Becraft, K. A.; Somorjai, G. A. J. Phys. Chem. B 2005, 109, 13619.
(d) Maitlis, P. M. J. Organomet. Chem. 2004, 689, 4366. (e) Maitlis, P. M.
J. Mol. Catal. A 2003, 204-205, 55. (f) Dry, M. E. Catal. Today 2002, 71,
227.
r
2010 American Chemical Society
Published on Web 04/08/2010
pubs.acs.org/Organometallics

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Esther Garcıa et al.
2158 Organometallics, Vol. 29, No. 9, 2010
Chart 1
Chart 2
Scheme 1. Reactivity of the Methoxycarbyne Complex 1
reactivity of 1, reported as a communication,11 revealed that
there are also reactions in which either C-O bond cleavage or
other substantial modifications in the methoxycarbyne ligand
of compound 1 might take place, which are not possible for
alkyl- or arylcarbyne complexes. In this paper we report full
details of these reactions, ranging from those taking place
between 1 and several p-block elements (chalcogens, iodine) to
those with some hydride derivatives of the former elements
(HERn), such as thiols, primary phosphines, or silanes. As will
be discussed below, these reactions may involve inter alia
several processes modifying the methoxycarbyne ligand exten-
sively, such as overall demethylation, C-E and C-C bond
formation at the bridgehead C atom, and insertion into the
C-OMe bond, with some of these reactions being almost
unprecedented in the chemistry of carbyne complexes.
with 32- and 30-electron counts5,6 and then on an electron-
richer species, the neutral 30-electron complex [Mo2Cp2( μ-
COMe)( μ-PCy2)( μ-CO)] (1) (Cp=η5-C5H5).7 In line with
the increased electron density of the latter, we have found
that 1 can be easily protonated or alkylated at the oxygen
atom of its bridging carbonyl ligand in a charge-controlled
process, to give the corresponding cations having new hy-
droxy- or alkoxycarbyne groups, respectively,8 while the
electron density accumulated at the Mo2C triangle, having
π (metal-carbyne)-bonding character, seems well-suited for
the complex to act as a base under conditions of orbital
control, with this enabling compound 1 to act as a useful
building block for the rational synthesis of heterometallic
clusters upon the addition of different coordinatively un-
saturated metal fragments (Scheme 1).9 On the other hand,
compound 1 can also behave as an acceptor molecule, as
expected for an unsaturated (30-electron) complex, and thus
reacts readily with CO to give the electron-precise derivative
[Mo2Cp2( μ-COMe)( μ-PCy2)(CO)3].10 In all these reactions,
the methoxycarbyne ligand remains unperturbed, except for
changes in its coordination mode (e.g., from μ2 to μ3), and
behaves much in the same way as an alkyl- or arylcarbyne
ligand would. However, our preliminary experiments on the
Results and Discussion
Reactions with Small Molecules Having E-H Bonds (E =
O, S, N, P, Si, Sn). Compound 1 was found to be unreactive
at room temperature or even under forcing thermal condi-
tions (several hours in refluxing toluene solution) toward
simple alcohols (PhOH), amines (PhNH2), and silanes
(Ph3SiH, Ph2SiH2). A very slow reaction (ca. 20% conver-
sion after 4 h) was observed with the stannane Ph3SnH in
refluxing toluene to give the known stannyl-bridged complex
[Mo2Cp2( μ-SnPh3)( μ-PCy2)(CO)2],12 with this obviously
having no practical use. In contrast, the thiol PhSH reacts
with 1 at a reasonable rate (completion after ca. 6 h at 353 K)
to give with good yield the known thiolate-bridged derivative
[Mo2Cp2( μ-PCy2)( μ-SPh) (CO)2] (2),13 whereas the primary
phosphine PhPH2 reacts analogously (but more slowly) to
give the novel phenylphosphide-bridged derivative [Mo2-
Cp2( μ-PCy2)( μ-PHPh)(CO)2] (3) (Chart 2). In all of the
above reactions the methoxycarbyne ligand of 1 has been
demethylated, presumably by formation of methane with the
hydrogen atom of the incoming reagent. Obviously, the
strength of the corresponding E-H bond being cleaved is a
critical factor determining the feasibility of these reactions.
Since the corresponding order of bond energy (in kJ mol-1) is
O (459) . N (386) > S (363) >P (322) = Si (318) . Sn
(<214),14 the failure of 1 to react with amines and alcohols
can be thus easily explained. However, the slow (Sn) or
negligible (Si) thermal reactivity of stannanes and silanes,
respectively, in spite of their low E-H bond strengths,
suggests that the presence of electron pairs on E might be
relevant for the reaction to proceed at a significant rate, a
matter to be discussed later on.
(5) (a) Alvarez, M. A.; Garcıa, M. E.; Riera, V.; Ruiz, M. A.; Robert,
F. Organometallics 2002, 21, 1177. (b) Alvarez, M. A.; García, M. E.; Riera,
V.; Ruiz, M. A. Organometallics 1999, 18, 634. (c) Alvarez, M. A.; Bois, C.;
García, M. E.; Riera, V.; Ruiz, M. A. Angew. Chem., Int. Ed. Engl. 1996, 35,
102.
ꢀ
(6) (a) Garcıa, M. E.; Garcıa-Vivo, D.; Ruiz, M. A.; Herson, P.
ꢀ
Organometallics 2008, 27, 3879. (b) García, M. E.; García-Vivo, D.; Ruiz,
M. A. Organometallics 2008, 27, 543. (c) Alvarez, C. M.; Alvarez, M. A.;
ꢀ
García, M. E.; García-Vivo, D.; Ruiz, M. A. Organometallics 2005, 24, 4122.
(d) García, M. E.; Riera, V.; Rueda, M. T.; Ruiz, M. A.; Halut, S. J. Am.
Chem. Soc. 1999, 121, 1960.
ꢀ
(7) (a) Garcıa, M. E.; Melon, S.; Ramos, A.; Ruiz, M. A. Dalton
ꢀ
Trans. 2009, 8171. (b) García, M. E.; Melon, S.; Ramos, A.; Riera, V.; Ruiz,
M. A.; Belletti, D.; Graiff, C.; Tiripicchio, A. Organometallics 2003, 22,
1983.
ꢀ
ꢀ
(8) Garcıa, M. E.; Garcıa-Vivo, D.; Ruiz, M. A.; Aullon, G.; Alvarez,
(12) (a) Alvarez, M. A.; Garcıa, M. E.; Ramos, A.; Ruiz, M. A.
Organometallics 2006, 25, 5374. (b) Alvarez, M. A.; García, M. E.; Ramos,
A.; Ruiz, M. A. J. Organomet. Chem. 2009, 695, 36.
S. Organometallics 2007, 26, 4930.
ꢀ
(9) Garcıa, M. E.; Garcıa-Vivo, D.; Ruiz, M. A. Organometallics
2009, 28, 4385.
(10) Garcıa, M. E.; Garcıa-Vivo, D.; Ruiz, M. A.; Aullon, G.;
Alvarez, S. Organometallics 2007, 26, 5912.
ꢀ
(11) Garcıa, M. E.; Garcıa-Vivo, D.; Ruiz, M. A. Organometallics
(13) Alvarez, C. M.; Alvarez, M. A.; Alonso, M.; Garcıa, M. E.;
Rueda, M. T.; Ruiz, M. A. Inorg. Chem. 2006, 45, 9593.
(14) Huheey, J. E.; Keiter, E. A.; Keiter, R. L. Inorganic Chemistry:
Principles of Structure and Reactivity, 4th ed.; HarperCollins College
Publishers: New York, 1993.
ꢀ
ꢀ
2008, 27, 169.

Article
Organometallics, Vol. 29, No. 9, 2010 2159
Table 1. Selected IRa and NMRb Data for New Complexes
ν(CO)
compound
δ(P)
228.5
δ( μ-C) [JCP]
[Mo2Cp2( μ-COMe)( μ-PCy2)( μ-CO)] (1)c
[Mo2Cp2 ( μ-PCy2)( μ-PHPh)(CO)2] (3)
[Mo2Cp2( μ-PCy2){μ-P(OEt)2}(CO)2] (4a)
[Mo2Cp(η5-C5H4CH2Ph)( μ-PCy2){μ-P(OEt)2}(CO)2] (4b)
[Mo2Cp2{μ-C(2-C6H4SiPh2OMe)}( μ-PCy2)( μ-CO)] (5)
[Mo2Cp2( μ-CSiPh2OMe)( μ-PCy2)( μ-CO)] (6)
[Mo2Cp2( μ-PCy2){μ-S2C(OMe)}(S)2] (7)
1674 (s)
352.0 [15], 305 [9]
1868 (m, sh), 1836 (vs)
1876 (m, sh), 1848 (vs)
1873 (w, sh), 1845 (vs)
1683 (s)
113.6, 28.5d
352.1, 119.5e
349.5, 117.3e
223.6
386.2, 300.8 [6]
417.9 [13], 302.3 [8]
225.9 f
1687 (s)
230.7
84.2f
181.3
[Mo2Cp2{μ-C(OMe)C(O)Se}( μ-PCy2)( μ-Se2)] (8)
[Mo2Cp2( μ-I)I2( μ-PCy2)(CO)2] (10)
1646 (m)
1932 (vs), 1909 (m)g
134.8 [17]
159.9h
a Recorded in dichloromethane solution, ν(CO) in cm-1 for carbonyl groups. b Recorded in CD2Cl2 solutions at 290 K and 121.50 (31P) or 75.48 (13C)
MHz, unless otherwise stated; δ in ppm relative to internal TMS (13C) or external 85% aqueous H3PO4 (31P), J in Hz. c Data taken from ref 7. d In CDCl3
solution, with the more deshielded resonance arising from the PCy2 ligand; JPP = 8. e The more shielded resonance arises from the PCy2 ligand; JPP = 19.
f Averaged resonances at 290 K in CDCl3 solution (see text). g In THF solution. h In C6D6 solution.
The spectroscopic data for 3 (Table 1) are comparable to
those of 2 and to those of different bis(phosphide) complexes
trans-[M2Cp2( μ-PR2)( μ-PR02)(CO)2] (M=Mo, W; R, R0 =
Ph, Cy, Et, H, etc.) previously described by us and others.15,16
Chart 3
The latter are characterized by displaying relatively shielded 31
P
NMR resonances and C-O stretching bands of weak and
strong intensities (in order of decreasing frequency), as ex-
pected for transoid M2(CO)2 oscillators.17 In addition, we
note that the presence of the PPhH bridge in 3 now makes
the two cyclopentadienyl groups inequivalent, as observed in
The formation of compounds 4a,b implies once more a
demethylation of the methoxycarbyne ligand, perhaps in-
volving the formation of P(OEt)2(OMe) and/or P(O)Me-
(OEt)2. Although we have not investigated this in detail, we
note that the 31P NMR spectra of the crude reaction mixtures
exhibit several resonances at ca. 140 ppm and at ca. 0 ppm
that might correspond to species of the type P(OEt)2(OR)
and P(O)(OEt)2R, respectively, according to their chemical
shifts.18
Reaction Pathways in the Demethylation of the Carbyne
Ligand in Compound 1. In general terms, the C-O bond of
the alkyl group of a bridging alkoxycarbyne ligand in a
neutral complex is strong enough to remain unperturbed
under most reaction conditions and is not expected to be
cleaved easily. Actually, there are only a limited number of
precedents involving the rupture of that bond. These include
the migration of the alkyl group to the carbon atom under
thermal or photochemical activation to give the correspond-
ing acyl-bridged isomers,4d,f,h and to the metal atom, also
under thermal activation, to give alkyl complexes.4a,19 The
demethylation reactions observed for compound 1 thus
represent a different way (eventual methane elimination)
for inducing the cleavage of the Me-O bond of a methoxy-
carbyne ligand.
1
the corresponding H NMR spectrum, with the latter also
displaying a characteristic (strongly coupled to phosphorus)
P-H resonance at 6.25 ppm (1JPH = 367 Hz; see Experimental
Section).
Reactions with Other P-Donors. Since two CO molecules
are easily added to compound 1 (Scheme 1), it might have
been anticipated that 1 should add easily different phosphine
or diphosphine ligands. In fact, it is somewhat surprising that
the reaction with PPhH2 would proceed very slowly, as noted
above. Actually, the presence of a P-H bond (thus providing
a path for demethylation) seems to be of relevance since no
reaction took place at all between complex 1 and several
good P-donors such as P(OMe)3 or Me2PCH2PMe2 after
several hours in refluxing toluene. A slow reaction, however,
was observed with the diphosphite (EtO)2POP(OEt)2 (24 h at
363 K for completion), to give not the simple addition product
but unexpectedly a mixture of two diethoxyphosphide-bridged
derivatives, [Mo2Cp2( μ-PCy2){μ-P(OEt)2}(CO)2] (4a) and
[Mo2Cp(η5-C5H4CH2Ph)( μ-PCy2){μ-P(OEt)2}(CO)2] (4b) in
a ca. 2:5 ratio (Chart 3).
Compound 4a has been recently reported by us to be the
main product in the reaction of the anion [Mo2Cp2( μ-PCy2)( μ-
CO)2]- with ClP(OEt)2.12b As for the major product 4b, the
corresponding spectroscopic data are indeed very similar to
those of 4a (Table 1 and Experimental Section) except for the
As noted above, the reactions of 1 with HERn molecules
resulting in the loss of the Me group are rather slow. Yet, we
have detected no intermediate species by IR or 31P NMR
monitoring of the corresponding reactions, which are neces-
sarily complex and multistep in nature. As also noted, the
presence of an electron pair on E seems to have a beneficial
effect on the reaction rate. We thus propose, in agreement
with the unsaturated nature of 1, that the first step would be
just the coordination (even if weak) of the H-ERn molecule
cyclopentadienyl resonances. In fact, both the 1H and the 13
C
NMR spectra reveal that compound 4b has one benzyl-sub-
stituted cyclopentadienyl ligand, clearly denoted by the appear-
ance of five inequivalent 13C resonances for the carbon atoms
of the ring, and four distinct resonances for the corresponding
protons, all of this in agreement with the lack of symmetry
introduced by the presence of two different bridging phosphide
ligands.
(18) Tebby, J. C. In Phosphorus-31 NMR Spectroscopy in Stereo-
chemical Analysis; Verkade, J. G.; Quin, L. D., Eds.; VCH: New York, 1987;
Chapter 1.
ꢀ
(15) Garcıa, M. E.; Riera, V.; Ruiz, M. A.; Rueda, M. T.; Saez, D.
Organometallics 2002, 21, 5515.
(19) (a) Idmoumad, H.; Liu, C. H.; Hersh, W. H. Organometallics
1995, 14, 4051. (b) Fong, R. H.; Liu, C. H.; Idmoumad, H.; Hersh, W. H.
Organometallics 1993, 12, 503. (c) Wang, B.; Hersh, W. H.; Rheingold, A. L.
Organometallics 1993, 12, 1319. (d) Fong, R. H.; Hersh, W. H. Organo-
metallics 1985, 4, 1468.
(16) Adatia, A.; McPartlin, M.; Mays, M. J.; Morris, M. J.; Raithby,
P. R. J. Chem. Soc., Dalton Trans. 1989, 1555.
(17) Braterman, P. S. Metal Carbonyl Spectra; Academic Press:
London, U.K., 1975.

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Esther Garcıa et al.
2160 Organometallics, Vol. 29, No. 9, 2010
Scheme 2. Proposed Pathways for the Reactions of 1 with
H-ERn Moleculesa
proceed because, in the absence of added reagents, com-
pound 1 does not undergo any methyl migration process (to
give its isomer [Mo2Cp2( μ-CH3)( μ-PCy2)(CO)2]) either in
refluxing toluene or under photochemical activation.7a
The reaction of 1 with the diphosphite (EtO)2POP(OEt)2
to give 4a can be understood along the same lines just
discussed, if we allow the backbone P-O bond of this ligand
to play the role of the E-H bond in the reactions with HERn
molecules. This requires the oxidative addition of the back-
bone P-O bond of the diphosphite to the metal center (to
yield diethoxyphosphide and diethylphosphonate groups)
after coordination, a process possible at unsaturated dimo-
lybdenum and ditungsten complexes, as shown by previous
work from our laboratory.21 The final step (C to 4a) now
would involve the reductive elimination of the methyl and
phosphonate groups in the form of either P(OEt)2(OMe) or
P(O)Me(OEt)2, two molecules possibly present in the crude
reaction mixtures, as noted above.
The formation of 4b, having the same structure as 4a but with
a benzyl-substituted cyclopentadienyl ligand, is much more
difficult to explain, and we will not dare to give any hypothetical
sequence of elemental steps. We must note, however, that recent
work from our laboratory has shown that the unsaturated
benzyl-bridged complex [Mo2Cp2( μ-CH2Ph)( μ-PCy2)(CO)2]
reacts with CO to give the hydride [Mo2Cp(η5-C5H4CH2Ph)-
( μ-H)( μ-PCy2)(CO)4], having a benzyl-substituted cyclopenta-
dienyl ligand, thus accomplishing an overall H/CH2Ph
exchange at one of the cyclopentadienyl rings of the complex.22
Therefore, we can conceive that a toluene molecule might
become coordinated at some intermediate step of the reaction
of 1 with the diphosphite and then converted into benzyl and
hydride ligands after oxidative addition, thus initiating a se-
quence yielding a (η5-C5H4CH2Ph) group, as observed for the
mentioned benzyl complex. A separate experiment showed that
no detectable (by 1H and 31P NMR) modification of compound
1 took place after heating a toluene solution of this complex at
373 K for 24 h, thus confirming that the presence of the
diphosphite is compulsory for the incorporation of the benzyl
group at the Cp ring in these substrates.
Photochemical Reactions with Silanes. Although Ph3SiH
and Ph2SiH2 fail to react with compound 1 in refluxing
toluene, they do it slowly under visible-UV irradiation at
room temperature to give in good yields the novel complexes
[Mo2Cp2{μ-C(2-C6H4SiPh2OMe)}( μ-PCy2)( μ-CO)] (5) and
[Mo2Cp2( μ-CSiPh2OMe)( μ-PCy2)( μ-CO)] (6), having aryl-
carbyne and silylcarbyne ligands, respectively (Chart 4).
Some other minor products are formed in the above reac-
tions, but they could not be purified nor properly character-
ized. Moreover, even when the extensive rearrangement
needed to give the above products requires several elemental
steps to take place, no clear intermediates could be identified
in these reactions through IR or 31P NMR monitoring of the
corresponding mixtures. Compound 1 also reacted with the
primary silane (n-Hex)SiH3 under comparable conditions,
but the reaction was much less selective and no pure products
could be isolated nor properly characterized in that case.
The structure of the arylcarbyne complex 5 was con-
firmed through a single-crystal X-ray study and is shown
in Figure 1.11 The coordination environment of the dimetal
a Mo-Mo = Mo2Cp2( μ-PCy2); ERn = SPh, PHPh, SnPh3.
to the metal center through the electron pair of E or, when
this is not possible (Si, Sn), through the E-H bond, to give
32-electron intermediates (A or A0, respectively, Scheme 2).
The reduced donor ability of an E-H bond (compared with a
nonbonding electron pair on E) would explain the very slow
rate of the HSnPh3 reaction in spite of the very weak H-Sn
bond to be eventually cleaved. The strength of the E-H bond
would actually be a determinant factor for the next step, the
oxidative addition of this bond to the unsaturated inter-
mediates A (or A0) to give a hydride intermediate B. This
would occur less easily for the stronger E-H bonds, thus
justifying the failure of 1 to react with phenol and phenyla-
mine, while the failure of silanes to react with 1 would follow
from the combined effect of the low coordination ability and
relatively high strength of the Si-H bond. In any case, we
note that these oxidative addition reactions are not uncom-
mon at unsaturated dimetal centers. For instance, the reac-
tion of primary and secondary phosphines has been used
extensively to synthesize phosphide-bridged dimolybdenum
and ditungsten cyclopentadienyl complexes,15,20 and we
have reported recently that HSnPh3 undergoes a fast Sn-H
cleavage at room temperature when reacting with the un-
saturated hydride [Mo2Cp2( μ-H)( μ-PCy2)(CO)2].12a Inter-
mediates B now would evolve through Me migration to the
metal to give methyl-hydride derivatives C, then undergo the
reductive elimination of methane to yield the corresponding
ERn-bridged derivatives finally isolated. As noted above,
there are precedents of methyl migrations to the metal in
alkoxycarbyne complexes. In our case, however, the eventual
CH4 elimination seems to be critical for this migration to
(20) (a) Jones, R. A.; Schwab, S. T.; Stuart, A. L.; Whittlesey, B. R.;
Wright, T. C. Polyhedron 1985, 4, 1689. (b) Henrick, K.; McPartlin, M.;
Horton, A. D.; Mays, M. J. J. Chem. Soc., Dalton Trans. 1988, 1083.
€
(c) Ebsworth, E. A. V.; Mcintosh, A. P.; Schroder, M. J. Organomet. Chem.
(21) Alvarez, M. A.; Alvarez, C.; Garcıa, M. E.; Riera, V.; Ruiz,
M. A.; Bois, C. Organometallics 1997, 16, 2581.
(22) Alvarez, M. A.; Garcıa, M. E.; Martınez, M. E.; Ramos, A.;
1986, 312, C41. (d) Woodward, S.; Curtis, M. D. J. Organomet. Chem.
1992, 439, 319. (e) Alvarez, M. A.; Anaya, Y.; García, M. E.; Riera, V.; Ruiz,
M. A. Organometallics 2004, 23, 433.
Ruiz, M. A. Organometallics 2009, 28, 6293.

Article
Organometallics, Vol. 29, No. 9, 2010 2161
Scheme 3. Proposed Pathways for the Reactions of 1 with
Silanesa
Figure 1. ORTEP drawing of compound 5, with H atoms and
cyclohexyl rings (except the C1 atoms) omitted for clarity (repro-
˚
duced from ref 11). Selected bond lengths (A): Mo(1)-Mo(2) =
2.469(1), Mo(1)-P(1)=2.393(1), Mo(2)-P(1)=2.396(1), Mo(1)-
C(1)=2.119(2), Mo(2)-C(1)=2.081(2), Mo(1)-C(2)=1.980(2),
Mo(2)-C(2) = 2.002(2).
Chart 4
center is very similar to that of the isoelectronic ethoxycar-
byne complex [Mo2Cp2( μ-COEt)( μ-PCy2)( μ-CO)]7a and al-
most identical to that of the benzylidyne complex [Mo2-
Cp2( μ-CPh)( μ-PCy2)( μ-CO)] recently reported by us,23 and
therefore does not need to be discussed in detail. We just note
a Mo-Mo = Mo2Cp2( μ-PCy2).
˚
the very short intermetallic separation of 2.469(1) A, con-
sistent with the triple bond proposed for all these molecules
NMR resonance at 386.2 ppm (5) and 417.9 ppm (6), as
expected. Note the progressive deshielding of the carbyne
13C nucleus as we move from alkoxycarbyne to arylcarbyne
and then to silylcarbyne ligands. This trend is also found for
mononuclear complexes24 and can be related to the increased
electron density at the bridgehead carbon atom in that
sequence, also reflected in the concomitant reduction of
electronic charge at the dimetal center, as indicated by the
relative C-O stretching frequencies of the bridging carbonyl in
these complexes (1 < 5 < 6, Table 1). The nature of the
substituent of the carbyne ligand in compounds 5 and 6 is
readily apparent from the corresponding 1H and NMR data
(see Experimental Section) and deserves no specific comments.
Pathways in the Photochemical Reactions of Silanes with
Compound 1. As noted above, no intermediates could be
identified in the necessarily complex rearrangements con-
necting the methoxycarbyne complex 1 with their aryl- or
silylcarbyne derivatives 5 and 6. Yet we can outline sensible
steps to justify the formation of these products (Scheme 3).
For this we propose that, under photochemical activation,
on the basis of the EAN formalism and DFT calculations,8
˚
and the quite short Mo-C(carbyne) lengths of ca. 1.99 A,
consistent with the formal bond order (1.5) in a carbyne
ligand symmetrically bridging two metal atoms. The SiPh2-
(OMe) group placed at the ortho position of the phenyl
substituent of the carbyne ligand introduces no significant
distortions in the molecule and displays unnoticeable inter-
atomic distances.
Spectroscopic data for 5 and 6 in solution are similar to
each other except for the resonances corresponding to the
respective substituents at the carbyne ligand and are consis-
tent with the structure found in the crystal for 5. Moreover
they are not very different from those of the methoxycarbyne
precursor 1 (Table 1). All these complexes are characterized
by a relatively deshielded 31P NMR resonance and by a low-
frequency C-O stretching band corresponding to the brid-
ging carbonyl, as also found for the isoelectronic phosphide
complexes of the type [M2Cp2( μ-PR2)( μ-PR02)( μ-CO)].15,16
The carbyne ligand is identified by a strongly deshielded 13
C
(24) Mann, B. E.; Taylor, B. F. 13C NMR Data for Organometallic
Compounds; Academic Press: London, U.K., 1981.
ꢀ
(23) Alvarez, M. A.; Garcıa, M. E.; Martınez, M. E.; Menendez, S.;
Ruiz, M. A. Organometallics 2010, 29, 710.

´
Esther Garcıa et al.
2162 Organometallics, Vol. 29, No. 9, 2010
the weak initial adduct of type A0 proposed for the thermal
reactions would now undergo a double oxidative addition,
first of H-Si bonds (to give the corresponding intermediates
of type B) and then of an H-C(Ph) bond (reaction with
HSiPh3) or a second H-Si bond (reaction with H2SiPh2), thus
providing an irreversible path for H2 elimination, eventually
introducing SiPh2(C6H4) and SiPh2 fragments in the molecule,
respectively. In the latter case, the silylene intermediate E thus
generated might undergo a Si-C coupling analogous to the
methylene-carbyne coupling reactions previously observed
for other arylcarbyne- and methoxycarbyne-bridged com-
plexes.25,5a This leads to an intermediate F that would yield
the final product 6 through a 1,2-shift of the OMe group from
C to Si atoms, thermodynamically favored by the much higher
strength of the Si-O over the Si-C bond.14 We have shown
recently that a related 1,2-shift (from C to C) takes place
instantaneously at the ketenyl intermediate [Mo2Cp2{μ-C-
(OMe)CO}( μ-PCy2)(CO)2] to give the carboxycarbyne deri-
vative [Mo2Cp2{μ-CC(O)OMe}( μ-PCy2)(CO)2].6b
Figure 2. ORTEP drawing of compound 8, with H atoms and
cyclohexyl rings (except the C1 atoms) omitted for clarity (repro-
In the reaction with HSiPh3, the ortho-metalated silyl inter-
mediate H generated after H2 elimination might evolve through
C-C coupling to the carbyne ligand (preferred over Si-C
coupling due to the higher strength of the C-C bond) to give a
silyl-carbene intermediate I, which might rearrange into the
silylcarbyne product 5 through migration of the methoxyl
group from C to Si via the dimetal center, something facilitated
by the electronic and coordinative unsaturation of the latter.
Once again, the formation of a very strong Si-O bond would
provide a significant driving force for this rearrangement.
Irrespectively of the actual sequence of elemental steps
connecting the methoxycarbyne compound 1 with the aryl
and silylcarbyne derivatives 5 and 6, it should be remarked
that it is the quite strong MeO-C(carbyne) bond (the one
having some degree of π-bonding component)8,10 that is the
bond to be cleaved in these reactions. This is a very unusual
process for an alkoxycarbyne ligand, only observed pre-
viously in a few instances, upon reaction either with a strong
reducing agent such as Na (to give a carbide ligand)4b or with
molecules able to remove in some way the methoxyl group
such us BH35b,c or H24e (to give a methylidyne ligand). Inter-
estingly, the removal of a methoxyl group from a bridging
methoxycarbene ligand using strong acids such as Me3Oþ or
BBr3 has been successfully used previously for the synthesis
of several carbyne-bridged binuclear complexes.26 Clearly,
silicon plays in our reactions the role of an “intramolecular
extractor” of the methoxyl group by virtue of the strong
Si-O bond thus formed. Besides all this, we should note that
the formation of compounds 5 and 6 implies the overall
insertion of ylidene- or diyl-type fragments into the strong
C-OMe bond of an alkoxycarbyne ligand, a process having,
to our knowledge, no precedent in the literature.
˚
duced from ref 11). Selected bond lengths (A) and angles (deg):
Mo(1)-Mo(2) = 2.709(1), Mo(1)-P = 2.414(1), Mo(2)-P =
2.431(1), Mo(1)-C(1) = 2.194(5), Mo(2)-C(1) = 2.223(5), Mo-
(1)-Se(3) = 2.596(1), Mo(2)-Se(3) = 2.591(1), Mo(1)-Se(1) =
2.541(1),Mo(2)-Se(2) = 2.539(1), Se(1)-Se(2) = 2.309(1), Se(3)-
C(3) = 2.009(5), C(3)-O(3) = 1.198(6), C(3)-C(1) = 1.433(7);
Mo(1)-Se(1)-Se(2) = 93.7(1).
Chart 5
O-methyldithiocarbonate [Mo2Cp2( μ-PCy2){μ-S2C(OMe)}-
(S)2] (7) and the carbene-seleniolate derivative [Mo2Cp2-
{μ-C(OMe)C(O)Se}( μ-PCy2)( μ-Se2)] (8) with good yields
(Chart 5). Attempts to obtain products derived from the
incorporation of just one or two chalcogen atoms to the
unsaturated dimetal center of complex 1 were unsuccessful.
The structure of the selenium derivative 8 was confirmed
through a single-crystal X-ray study and is shown in Figure 2.11
The molecule displays two cyclopentadienylmolybdenum
fragments symmetrically bridged by dicyclohexylphosphide,
κ1:κ1-diselenide, and carbene-seleniolate ligands, the latter
derived from the coupling of the methoxycarbyne and carbo-
nyl ligands to a selenium atom, thus resembling the behavior
of heterodinuclear arylcarbyne-bridged complexes toward
elemental oxygen and sulfur.27 The intermetallic length in 8
is quite short considering the size of the bridging atoms
Reactions with Group 16 Elements. We have noted pre-
viously that compound 1 is oxygen-sensitive, giving the oxo
derivative cis-[Mo2Cp2( μ-COMe)( μ-PCy2)(O)(CO)] upon
brief exposure to air.7a Thus it was not surprising that this
complex would react with elemental sulfur and selenium
under mild conditions. These reactions, however, unexpect-
edly involve the incorporation of three to four chalco-
gen atoms to the dimetal center, to give respectively the
˚
(2.709(1) A), this being consistent with the formulation
of a double Mo-Mo bond for this molecule under the
(25) Garcıa, M. E.; Tran-Huy, N. H.; Jeffery, J. C.; Sherwood, P.;
Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1987, 2201.
(26) (a) Howard, J. A. K.; Jeffery, J. C.; Laguna, M.; Navarro, R.;
Stone, F. G. A. J. Chem. Soc., Chem. Commun. 1979, 1170. (b) Chen, J.;
Wang, R. Coord. Chem. Rev. 2002, 231, 109.
(27) Byrne, P. G.; Garcıa, M. E.; Jeffery, J. C.; Sherwood, P.; Stone,
F. G. A. J. Chem. Soc., Dalton Trans. 1987, 1215, and references therein.

Article
Organometallics, Vol. 29, No. 9, 2010 2163
EAN formalism, if single Mo-Se bonds are assumed for the
apparently equivalent cyclohexyl rings, which suggests the
operation of dynamic effects. This was confirmed by vari-
able-temperature 1H and 31P NMR measurements revealing
that, on lowering the temperature, the single phosphorus or
cyclopentadienyl resonances of 7 eventually split into two
resonances with ca. 2:1 relative intensities in each case (see
Experimental Section). Thus it is clear that compound 7
exists in solution as an equilibrium mixture of two isomers.
Both of them have similar spectroscopic properties (equiva-
lent Cp and Cy rings, related by a C2 rotation) and therefore
are proposed to have the remaining sulfur atoms as terminal
ligands placed in a transoid arrangement (Chart 5). The
difference between both isomers would just lie in the coordi-
nation mode of the dithiocarbonate ligand, bridging the
dimetal center through one (7A) or both (7B) sulfur atoms,
although we do not know which of them is the major isomer
in solution (arbitrarily chosen as A). In any case, these iso-
mers are formally 32-electron complexes, isostructural with
the dicarbonyls of the type trans-[Mo2Cp2( μ-PR2)( μ-PR02)-
(CO)2], and accordingly they exhibit comparatively shielded
31P NMR resonances at ca. 84.2 ppm (cf. 95.4 ppm for the
complex with R=R0=Cy).15
The isomerism proposed for compound 7 in solution is well
established for carboxylate complexes, and we have previously
reported a comparable equilibrium for formate-bridged com-
plexes at dimanganese centers.33 In the case of the alkyldi-
thiocarbonate and related ligands, the bridging coordination
modes proposed for compound 7 are comparatively rare, and
we can quote just one example of such isomerism for metal-
metal bonded complexes, this being reported for the trinuclear
cluster [Os3( μ-H){μ-S2C(OEt)}(CO)10]. In that case, however,
no interconversion takes place in solution and the isomers
could be separated from each other using conventional chro-
matographic techniques.34
˚
diselenide ligand, and the Se-Se length of 2.309(1) A is very
similar to the values found for comparable diselenide com-
1
1
28
˚
plexes (e.g., 2.307(1) A for [V2Cp*2( μ-S)2( μ-κ :κ -Se2]).
˚
However, the Mo-Se lengths for this ligand in 8 (ca. 2.54 A)
are ca. 0.05 A shorter than those involving the bridging
˚
˚
seleniolate atom Se(3) and ca. 0.1 A shorter than the single-
bond W-Se lengths in the triselenide-bridged complex
[W2Cp2( μ-κ1:κ1-Se3)(CO)6].29 All of this points to the presence
of some multiplicity in the corresponding Se-Mo bonds in 8
(pπ-dπ donation), which would somewhat reduce the
strength of the intermetallic interaction. We should note that
no other dimolybdenum complex having a κ1:κ1-diselenido
bridging ligand appears to have been reported previously.
These ligands are more often found in the κ2:κ2-bridging
mode,30 but in the case of 8 this mode must be disfavored
because it would lead to an electronic and coordinative over-
saturation of the dimetal center. Finally we note that the
˚
Mo-C(1) lengths of ca. 2.20 A can be considered normal for
a single bond in bridging carbene and related hydrocarbyl
˚
ligands (e.g., ca. 2.22 A in [W2Cp2{μ-C( p-tol)C(O)C( p-tol)}-
(CO)4]31 and ca. 2.20 A in the cation [W2Cp2( μ-CH2)-
˚
{μ-C(OMe)CH2}(CO)2( μ-Ph2PCH2PPh2)]þ).5a
The spectroscopic data in solution for 8 (Table 1 and
Experimental Section) are consistent with the structure
found in the crystal, effectively implying the chemical
equivalence of both metal fragments in solution. The former
carbyne atom gives rise now to a much more shielded 13C
NMR resonance (124.8 ppm), as expected for a bridging
carbene-like ligand, while the coupling of the former carbo-
nyl ligand to the C(OMe) group is denoted by the substantial
shielding (compared to a Mo-bound ligand) of its 13C
resonance (δC 177.7 ppm) and decreased C-O stretching
frequency (1646 cm-1).
The structure of the sulfur derivative 7 is substantially
different from that of the selenium compound just discussed.
Although all attempts to obtain suitable crystals for an X-ray
analysis of this complex were unsuccessful, the essential
structural details can be obtained unambiguously from the
spectrometric and spectroscopic data available (Table 1 and
Experimental Section). In the first place, the presence of four
S atoms in the molecule is firmly established by the micro-
analytical data and the mass spectrum of the complex, the
latter displaying the corresponding molecular ion as well as
those derived from the loss of COMeS and COMeS2 frag-
ments from the latter. This is suggestive of the presence of an
O-methyldithiocarbonate (or xanthate) ligand ( μ-S2COMe),
in turn consistent with the appearance of a resonance at
225.9 ppm in the corresponding 13C NMR spectrum when
recorded at room temperature. Indeed, that chemical shift is
comparable to those of different molybdenum complexes
having unidentated or chelating alkyldithiocarbonate liga-
nds (in the range ca. 190-240 ppm).32 This spectrum, how-
ever, displays anomalously broad resonances for the C1 (δC
41.3 ppm) and C2 (δC 27.7 and 25.5 ppm) carbons of two
The formation of 7 implies the coupling of two sulfur
atoms and a bridging carbyne ligand to give a dithiocar-
boxylate-type ligand. As far as we know, such a process has
been observed previously only for terminal alkyl- or arylcar-
byne ligands.35 We can quote, however, examples of the
addition of a single sulfur atom to several heterometallic
arylcarbyne-bridged complexes, to give the correspond-
ing thioacyl-bridged derivatives.27,36 Finally we note that
the formation of 7 also requires the elimination of a
CO ligand and the addition of two more sulfur atoms
as terminal ligands. This is not unexpected for the reaction
of a triply bonded dimolybdenum complex with elemental
sulfur and is reminiscent of the behavior of some isoelec-
tronic [M2L2(CO)4] complexes (L = Cp or related ligand;
M = Mo, W).37
Reactions with Iodine. Compound 1 reacts rapidly with
iodine in dichloromethane at room temperature. When one
equivalent of iodine is added, a mixture of the known iodide
complex [Mo2Cp2( μ-I)( μ-PCy2)(CO)2] (9)7a and the new
triiodide complex [Mo2Cp2( μ-I)I2( μ-PCy2)(CO)2] (10) is
(33) Garcıa-Alonso, F. J.; Garcıa-Sanz, M.; Liu, X. Y.; Oliveira, A.;
Ruiz, M. A.; Riera, V.; Bois, C. J. Organomet. Chem. 1996, 511, 93.
(34) Arce, A. J.; Deeming, A. J.; Donovan-Mtunzi, S.; Kabir, S. E.
J. Chem. Soc., Dalton Trans. 1985, 2479.
(35) (a) Gill, D. S.; Gree, M.; Marsden, K.; Moore, I.; Orpen, A. G.;
Stone, F. G. A.; Williams, I. D.; Woodward, P. J. Chem. Soc., Dalton
Trans. 1984, 1343. (b) Kreissl, F. R.; Ulrich, N. J. Organomet. Chem. 1989,
361, C30.
(28) Herberhold, M.; Kuhnlein, M.; Schrepfermann, M.; Ziegler,
M. L.; Nuber, B. J. Organomet. Chem. 1990, 398, 259.
€
(29) Jones, P. G.; Thone, C. Inorg. Chem. 1996, 35, 6625.
(30) Adams, R. D.; Kwon, O. S. Inorg. Chem. 2003, 42, 6175.
(31) Sheridan, J. B.; Geoffroy, G. L.; Rheingold, A. L. Organome-
tallics 1986, 5, 1514.
(32) (a) Yih, K. H.; Lee, G. H. J. Organomet. Chem. 2008, 693, 3303.
(b) Montilla, F.; Pastor, A.; Galindo, A. J. Organomet. Chem. 1999,
587, 127.
(36) Hill, A. F.; Nasir, B. A.; Stone, F. G. A. Polyhedron 1989, 8, 179.
(37) (a) Curtis, M. D. Polyhedron 1987, 6, 759. (b) Winter, M. J. Adv.
Organomet. Chem. 1989, 29, 101.

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Esther Garcıa et al.
2164 Organometallics, Vol. 29, No. 9, 2010
Chart 6
and SiPh2, respectively, into the strong C-OMe bond of the
carbyne ligand, with silicon playing here the role of “intramole-
cular extractor” of the methoxyl group by virtue of the strong
Si-O bond thus formed. All the above reactions involve the
cleavage of C-O bonds and are therefore exclusive of alkoxy-
carbyne ligands. The reactions of 1 with selenium and sulfur still
reveal other unusual transformations of the methoxycarbyne
ligand. Thus, along with the expected incorporation of chalco-
genide or dichalcogenide ligands to the unsaturated dimetal
center, additional chalcogen atoms can couple to the methoxy-
carbyne ligand (formation of the O-methyldithiocarbonate
ligand μ-S2C(OMe)) or induce the coupling of a CO ligand
(formation of the carbene-seleniolate ligand μ-C(OMe)C(O)Se).
obtained (Chart 6), with the former being an intermediate
for the latter. Thus, the addition of a second equivalent of
iodine to the above mixture completes the formation of
the triiodide complex 10, which could be isolated in the
conventional way and characterized by spectroscopic
methods.
The IR spectrum of 10 displays two C-O stretching bands of
strong and medium relative intensities in order of decreasing
frequency (Table 1), this indicating a relative arrangement of the
two CO ligands of the molecule defining an angle smaller than
90°.17 This is only compatible with a cisoid arrangement of the
CpMo(CO)I fragments of the molecule. On the other hand, the
1H and 13C NMR data reveal the chemical inequivalence of
these metal fragments, with the carbonyl resonances exhibiting
very different coupling to the phosphorus atoms. By recalling
that for complexes of type [MoCpXYL2] it is well established
Experimental Section
General Procedures and Starting Materials. All manipulations
and reactions were carried out under a nitrogen (99.995%) atmo-
sphere using standard Schlenk techniques. Solvents were purified
according to literature procedures and distilled prior to their use.39
Petroleum ether refers to that fraction distilling in the range
338-343 K. Compound 1 was prepared as described previously.7
All other reagents were obtained from the usual commercial
suppliers and used as received. Photochemical experiments were
performed using jacketed quartz or Pyrex Schlenk tubes, cooled by
tap water (ca. 288 K) or by a closed 2-propanol circuit, kept at the
desired temperature with a cryostat. A 400 W mercury lamp placed
ca. 1 cm away from the Schlenk tube was used for all these
experiments. Chromatographic separations were carried out using
jacketed columns. Commercial aluminum oxide (activity I, 150
mesh) was degassed under vacuum prior to use. The latter was
mixed under nitrogen with the appropriate amount of water to
reach the activity desired. Filtrations were carried out using diato-
maceous earth. IR C-O stretching frequencies were measured in
solution, are referred to as ν(CO), and are given in wavenumber
units (cm-1). Nuclear magnetic resonance (NMR) spectra were
routinely recorded at 300.13 (1H), 121.50 (31P{1H}), or 75.47 MHz
(13C{1H}) at 290 K in CD2Cl2 solutions unless otherwise stated.
Chemical shifts (δ) are given in ppm, relative to internal tetra-
methylsilane (1H, 13C) or external 85% aqueous H3PO4 (31P).
Coupling constants (J) are given in Hz.
2
that JXY coupling constants increase algebraically with the
X-Mo-Y angle, and being usually negative at acute angles,38
we can safely assign the more strongly coupled resonance
(δ 241.7 ppm, JCP = 11 Hz) to a carbonyl ligand cis to the phos-
phide bridge, whereas the other resonance (δ 236.7 ppm, JCP ca.
0 Hz) is assigned to a carbonyl trans to that bridge (Chart 6).
The formation of the triiodide complex 10 in the reaction of 1
with iodine can be understood in similar terms to those discussed
for the reactions with H-ERn molecules (Scheme 2) if we let the
I-I bond here play a role comparable to that of the H-E bonds
there, with the difference that now the nucleophile would be the
carbyne complex. The reaction would thus be initiated by the
nucleophilic attack of the latter complex to the iodine molecule,
this eventually resulting in the formation of the iodide-bridged
complex 9 and methyl iodide, thus accomplishing once more the
neat demethylation of the carbyne ligand. However, compound
9 is still a cordinatively and electronically unsaturated species.
Then it is not unexpected that this complex in turn reacts rapidly
with a second molecule of iodine to give complex 10, the product
of the oxidative addition of iodine across a double metal bond to
give an electron-precise derivative.
Preparation of [Mo2Cp2( μ-PCy2)( μ-SPh)(CO)2] (2). Com-
pound 1(0.050 g, 0.085 mmol) and PhSH (30 μL, 0.292 mmol) were
heated in toluene (10 mL) at 353 K for 6 h to give a green solution,
which was filtered. Removal of the solvent from the filtrate under
vacuum gave a residue, which was crystallized by slow diffusion of a
layer of petroleum ether into a dichloromethane solution of the
product to yield compound 2 as a dark green microcrystalline solid
(0.046 g, 83%). Microanalytical and spectroscopic data for this
product were identical to those previously reported by us for
complex 2 using a different synthetic route.13
Concluding Remarks
The electronic and coordinative unsaturation of the methoxy-
carbyne complex 1 facilitates the approach of different H-ERn
molecules to the dimetal center, eventually accomplishing a full
demethylation of the carbyne ligand (presumably through for-
mation of methane) and formation of the corresponding deriva-
tive [Mo2Cp2( μ-ERn)( μ-PCy2)(CO)2]. The reactions with iodine
and the diphosphite (EtO)2POP(OEt)2 to yield [Mo2Cp2( μ-I)( μ-
PCy2)(CO)2] and [Mo2Cp2( μ-PCy2){μ-P(OEt)2}(CO)2] can be
interpreted analogously, with the I-I and backbone P-O bonds
in the latter reactions playing a role analogous to the H-E bonds
in the former ones. In contrast, the photochemical reactions of the
silanes HSiPh3 and H2SiPh2 with 1do not involve demethylation,
but dehydrogenation and insertion of the fragments Ph2SiC6H4
Preparation of [Mo2Cp2( μ-PCy2)( μ-PHPh)(CO)2] (3). Com-
pound 1(0.050 g, 0.085 mmol) and PH2Ph(20μL, 0.182 mmol) were
refluxed in toluene (10 mL) for 12 h to give a green solution. The
solvent was then removed under vacuum, the residue was extracted
with dichloromethane-petroleum ether (1:9), and the extracts were
chromatographed on alumina (activity IV) at 288 K. Elution with
dichloromethane-petroleum ether (1:2) gave a green fraction, which
yielded, after removal of solvents under vacuum, compound 3 as a
dark green solid (0.044 g, 75%). Anal. Calcd for C30H38Mo2O2P2:C,
52.64; H, 5.60. Found: C, 52.35; H, 5.20. 1H NMR (CDCl3): δ 7.59
(m, Ph, 2H), 7.35-7.22 (m, Ph, 3H), 6.25 (dd, JHH = 367, 2, P-H,
1H), 5.35, 5.33 (2d, Cp, 2 ꢀ 5H), 2.40-1.10 (m, Cy, 22H).
Reaction of Compound 1 with (EtO)2POP(OEt)2. A toluene
solution (20 mL) of compound 1 (0.100 g, 0.169 mmol) and
(EtO)2POP(OEt)2 (120 μL, 0.491 mmol) was placed into a
(38) (a) Jameson, C. J. In Phosphorus-31 NMR Spectroscopy in
Stereochemical Analysis; Verkade, J. G.; Quin, L. D., Eds.; VCH: New
York, 1987; Chapter 6. (b) Wrackmeyer, B.; Alt, H. G.; Maisel, H. E.
J. Organomet. Chem. 1990, 399, 125.
(39) Armarego, W. L. F.; Chai, C. Purification of Laboratory Che-
micals, 5th ed.; Butterworth-Heinemann: Oxford, U.K., 2003.

Article
Organometallics, Vol. 29, No. 9, 2010 2165
Schlenk tube equipped with a Young’s valve, and the mixture
was heated at 363 K for 24 h to give a brown solution. The solvent
was then removed under vacuum, the residue was extracted with
dichloromethane-petroleum ether (1:5), and the extracts were
chromatographed on alumina (activity II) at 243 K. Elution with
dichloromethane-petroleum ether (1:4) gave first a yellowish-green
fraction and then an orange fraction. Removal of solvents from the
first fraction gave complex [Mo2Cp2( μ-PCy2){μ-P(OEt)2}(CO)2]
(4a) as a yellowish-green solid (0.024 g, 20%). Spectroscopic data
for this product were identical to those previously reported by us for
complex 4a using a different synthetic route.12b Removal of solvents
from the second fraction gave an orange solid shown (by NMR)
to contain the complex [Mo2Cp(η5-C5H4CH2Ph)( μ-PCy2){μ-P-
(OEt)2}(CO)2] (4b) contaminated with small and variable amounts
of an uncharacterized species (0.065 g, ca. 50%). All attempts to
further separate or purify this solid were unsuccessful and resulted in
its progressive decomposition. Spectroscopic data for compound 4b:
1H NMR (400.13 MHz): δ 7.30-7.15 (m, Ph, 5H), 5.89, 5.82 (2 m,
br, C5H4, 2 ꢀ 1H), 5.43 (s, Cp, 5H), 5.16, 4.77 (2 m, C5H4, 2 ꢀ 1H),
4.27, 4.03 (2 m, OCH2, 2 ꢀ 2H), 3.21, 3.10 (AB, JHH = 15, CH2Ph,
2 ꢀ 1H), 1.38 (t, JHH = 7, Me, 6H), 2.40-1.10 (m, Cy, 22H).
13C{1H} NMR (100.62 MHz): δ 236.2, 232.9 (2s, br, MoCO), 141.7
[s, C1(Ph)], 128.8 [s, C2 and C3(Ph)], 126.5 [s, C4(Ph)], 110.7 [s,
C1(C5H4)], 90.6, 89.4, 85.2, 85.0 [4s, C2-5(C5H4)], 88.3 (s, Cp), 65.72
(d, JCP = 9, OCH2), 65.70 (d, JCP = 10, OCH2), 47.9 [d, JCP = 20,
C1(Cy)], 44.0 [d, JCP = 17, C1(Cy)], 35.9, 35.0, 34.4 [3s, br, C2(Cy)],
34.7, 33.4 [2s, C2(Cy) andCH2Ph], 28.5 [d, JCP = 12, 2C3(Cy)], 28.4
[d, JCP = 10, C3(Cy)], 28.3 [d, JCP = 11, C3(Cy)], 26.7, 26.6 [2s,
C4(Cy)], 17.4 (s, Me), 17.3 [d, JCP = 3, Me].
Preparation of [Mo2Cp2{μ-C(2-C6H4SiPh2OMe)}( μ-PCy2)-
( μ-CO)] (5). Neat SiHPh3 (0.090 g, 0.346 mmol) was added to a
toluene solution (15 mL) of compound 1 (0.040 g, 0.068 mmol), and
the mixture was exposed to visible-UV radiation in a quartz
Schlenk tube at 288 K for 3.5 h to give a brown mixture. The
solvent was then removed under vacuum, the residue was extracted
with dichloromethane-petroleum ether (1:4), and the extracts were
chromatographed through an alumina column (activity IV) at 288
K. Elution with dichloromethane-petroleum ether (1:3) gave a
brown fraction containing an uncharacterized mixture of silane
derivatives and then an orange fraction. Removal of solvents from
the latter fraction gave compound 5 as an orange powder (0.030 g,
52%). Anal. Calcd for C43H49Mo2O2PSi: C, 60.85; H, 5.82. Found:
C, 60.63; H, 5.65. 1H NMR: δ 7.50-7.30 (m, Ph, 10H), 7.12 (m,
C6H4, 2H), 6.83 (m, C6H4, 1H), 6.69 (m, C6H4, 1H), 5.60 (s, Cp,
10H), 3.14 (s, OMe, 3H), 1.60-0.30 (m, Cy, 22H). 13C{1H} NMR:
δ 386.2 (s, br, μ-CC6H4), 300.8 (d, JCP = 6, μ-CO), 173.4 [s,
C1(C6H4)], 136.5 [s, C2(C6H4)], 135.9 [s, C1(Ph)], 135.8 [s, C2(Ph)],
130.1 [s, C4(Ph)], 128.2 [s, C3(Ph)], 128.7, 121.6, 121.3, 120.5 [4s,
C3-6(C6H4)], 95.8 (s, Cp), 52.1 (s, OMe), 46.5 [d, JCP = 18, C1(Cy)],
42.3 [d, JCP = 19, C1(Cy)], 33.4, 32.5[2s, C2(Cy)], 27.7[d, JCP = 12,
C3(Cy)], 27.4 [d, JCP = 11, C3(Cy)], 26.2, 23.0 [2s, C4(Cy)].
Preparation of [Mo2Cp2( μ-PCy2){μ-S2C(OMe)}(S)2] (7). So-
lid sulfur (0.022 g, 0.086 mmol of S8) was added to a dichloro-
methane solution (10 mL) of compound 1 (0.050 g, 0.085 mmol),
and the mixture was refluxed for 2 h to give a purple solution. The
solvent was then removed under vacuum, the residue was extracted
with dichloromethane-petroleum ether (1:5), and the extracts
were chromatographed through an alumina column (activity IV)
at 288 K. Elution with dichloromethane-petroleum ether (1:3)
gave a deep-rose fraction, which gave, after removal of solvents,
compound 7as a deep-rose powder (0.048 g, 82%). Anal. Calcd for
C24H35Mo2OPS4: C, 41.74; H, 5.11; S, 18.57. Found: C, 42.04; H,
1
5.40; S, 17.80. H NMR (CDCl3): δ 6.37 (s, Cp, 10H), 3.82 (s,
OMe, 3H), 1.60-0.90 (m, Cy, 22H). 13C{1H} NMR (CDCl3): δ
225.9 (s, μ-S2C), 96.5 (s, Cp), 66.3 (s, OMe), 41.3 [d, br, JCP = 15,
C1(Cy)], 34.0, 33.1 [2s, br, C2(Cy)], 27.7, 25.5[2d,JCP =8, C3(Cy)],
25.5 [s, 2C4(Cy)]. 1H NMR (CD2Cl2, 223 K): δ 6.41 (s, Cp, 10H,
isomer A), 6.40 (s, Cp, 10H, isomer B), 3.81 (s, OMe, 3H, iso-
mer A), 3.80 (s, OMe, 3H, isomer B), 1.60-0.80 (m, Cy, 22H, iso-
mers A and B). Ratio A/B = 2. 31P{1H} NMR (CD2Cl2, 223 K):
δ 83.9 (s, μ-P, isomer A), 83.7 (s, μ-P, isomer B). SI-MS (m/z):
689.8 (Mþ), 614.9 (Mþ - COMeS), 582.9 (Mþ - COMeS2), 417.7
(Mþ - COMeS - PCy2).
Preparation of [Mo2Cp2{μ-C(OMe)C(O)Se}( μ-PCy2)( μ-Se2)]
(8). Gray selenium (0.055 g, 0.696 mmol) was added to a
dichloromethane solution (10 mL) of compound 1 (0.050 g,
0.085 mmol), and the mixture was stirred for 2.5 h to give a
greenish-blue solution. The solvent was then removed under
vacuum, the residue was extracted with dichloromethane-
petroleum ether (1:5), and the extracts were chromatographed
through an alumina column (activity IV) at 288 K. Elution with
dichloromethane-petroleum ether (1:4) gave a blue fraction
containing a small amount of an uncharacterized com-
pound. Elution with a 1:2 mixture gave a dark green fraction,
yielding, after removal of solvents, compound 8 as a green
powder (0.040 g, 57%). Anal. Calcd for C27.33H37.66Mo2-
O2PSe3 (3 1/3C7H8): C, 38.26; H, 4.42. Found: C, 38.18;
3
H, 4.34. 1H NMR: δ 5.89 (s, Cp, 10H), 3.43 (s, OMe, 3H),
2.30-0.90 (m, Cy, 22H). 13C{1H} NMR: δ 177.7 (s, CdO),
134.8 (d, JCP=17, COMe), 94.8 (s, Cp), 58.9 (s, OMe), 48.3 [d,
JCP = 18, C1(Cy)], 40.4 [d, JCP = 13, C1(Cy)], 34.6 [d,
JCP = 3, C2(Cy)], 34.2 [d, JCP = 4, C2(Cy)], 29.0 [d, JCP
=
11, C3(Cy)], 27.7 [d, JCP = 9, C3(Cy)], 26.7, 26.6 [2s, C4(Cy)].
SI-MS (m/z): 828.6 (Mþ), 799.6 (Mþ - CO), 756.6 (Mþ
CO - COMe).
-
Preparation of [Mo2Cp2( μ-I)I2( μ-PCy2)(CO)2] (10). Solid
iodine (0.043 g, 0.167 mmol) was added to a tetrahydrofuran
solution of compound 1 (0.050 g, 0.085 mmol), and the mixture
was stirred for 15 min to give an orange solution. The solvent was
then removed under vacuum, the residue was extracted with
dichloromethane-petroleum ether (1:5), and the extracts were
filtered. Removal of the solvents from the filtrate under vacuum
gave compound 10 as an orange powder (0.074 g, 91%). Anal.
Calcd for C24H32I3Mo2O2P: C, 30.15; H, 3.37. Found: C, 30.26; H,
3.46. 1HNMR(C6D6):δ5.41, 5.12 (2s, Cp, 2 ꢀ5H), 2.95, 2.53 (2 m,
Cy, 2 ꢀ 1H), 1.80-0.70 (m, Cy, 20H). 13C{1H} NMR (C6D6):
δ 241.7 (d, JCP = 11, ΜοCO), 236.7 (s, MoCO), 98.1, 91.6 (2s, Cp),
48.7 [d, JCP = 11, C1(Cy)], 47.8 [d, JCP = 13, C1(Cy)], 36.3, 30.8
Preparation of [Mo2Cp2( μ-CSiPh2OMe)( μ-PCy2)( μ-CO)]
(6). Neat SiH2Ph2 (70 μL, 0.380 mmol) was added to a toluene
solution (15 mL) of compound 1 (0.040 g, 0.068 mmol), and the
mixture was exposed to visible-UV radiation in a quartz Schlenk
tube at 288 K for 2.5 h to give a brown mixture. The solvent was
then removed under vacuum, the residue was extracted with
dichloromethane-petroleum ether (1:5), and the extracts were
chromatographed through an alumina column (activity IV) at
253 K. Elution withdichloromethane-petroleumether(1:1) gave
a orange fraction, which yielded, after removal of solvents under
vacuum, compound 6 as an orange powder (0.030 g, 57%). Anal.
Calcd for C37H45Mo2O2PSi: C, 57.51; H, 5.87. Found: C, 57.64;
H, 5.98. 1H NMR: δ 7.40-7.10 (m, Ph, 10H), 5.71 (s, Cp, 10H),
3.41 (s, OMe, 3H), 1.90-0.30 (m, Cy, 22H). 13C{1H} NMR: δ
417.9 (d, JCP = 13, μ-CSi), 302.3 (d, JCP = 8, μ-CO), 136.6 [s,
C1(Ph)], 135.5 [s, C2(Ph)], 129.6 [s, C4(Ph)], 127.9 [s, C3(Ph)],
95.6 (s, Cp), 51.7 (s, OMe), 42.3 [d, JCP = 17, C1(Cy)], 42.2 [d,
[2d, JCP = 5, C2(Cy)], 32.9, 32.2 [2s, C2(Cy)], 28.0, 26.5 [2d, JCP
=
9, C3(Cy)], 27.6 [d, JCP = 8, C3(Cy)], 27.4 [d, JCP = 12, C3(Cy)],
25.6, 26.1 [2s, C4(Cy)].
Acknowledgment. We thank the MEC of Spain for a
grant (to D.G.V.) and the DGI for financial support
(Project CTQ2006-01207).
Supporting Information Available: A CIF file giving the
crystallographic data for the structural analysis of compounds
5 and 8. This material is available free of charge via the Internet
at http://pubs.acs.org.
J
CP = 18, C1(Cy)], 33.5, 33.0 [2s, C2(Cy)], 27.5, 27.4 [2d, JCP
12, C3(Cy)], 26.2 [s, 2C4(Cy)].
=