A versatile and unprecedented triply bonded dimolybdenum carbonyl anion

Article abstract of DOI:10.1021/om030150t

Chemical reduction of [Mo₂Cp₂(μ-Cl) (μ-PA₂)-(CO)₂] (A = Cy, Ph, OEt) gives the corresponding alkaline metal salts of the triply bonded anions [Mo₂-Cp₂(μ-PA₂) (μ-CO)₂]^-, which exhibit both molybdenum and oxygen nucleophilic sites. The PCy₂ anion reacts easily with NH₄⁺, [AuCl(PR₃)], or MeI to give unsaturated dicarbonyls [Mo₂Cp₂(μ-X)(μ-PA₂) (CO)₂] (X = H, AuPR₃, Me), while [Me₃O]BF₄ gives the methoxycarbyne [Mo₂Cp₂(μ-COMe)(μ-PCy₂)(μ-CO)] and allyl chloride rearranges to give the unsaturated alkenyl complex [Mo₂-Cp₂(μ-PCy₂)(μ-CMeCH₂) (CO)₂].

Full text of DOI:10.1021/om030150t

© Copyright 2003
Volume 22, Number 10, May 12, 2003
American Chemical Society
Communications
A Ver sa tile a n d Un p r eced en ted Tr ip ly Bon d ed
Dim olybd en u m Ca r bon yl An ion
M. Esther Garc´ıa,† Sonia Melo´n,† Alberto Ramos,† V´ıctor Riera,†
Miguel A. Ruiz,*,† Daniele Belletti,‡ Claudia Graiff,‡ and Antonio Tiripicchio‡
Departamento de Quı´mica Orga´nica e Inorga´nica/ IUQOEM, Universidad de Oviedo,
33071 Oviedo, Spain, and Dipartimento di Chimica Generale ed Inorganica,
Chimica Analitica, Chimica Fisica, Universita` di Parma, Parco Area delle Science 17/ A,
I-43100 Parma, Italy
Received March 3, 2003
Summary: Chemical reduction of [Mo2Cp2(µ-Cl)(µ-PA2)-
(CO)2] (A ) Cy, Ph, OEt) gives the corresponding
alkaline metal salts of the triply bonded anions [Mo2-
Cp2(µ-PA2)(µ-CO)2]-, which exhibit both molybdenum
and oxygen nucleophilic sites. The PCy2 anion reacts
easily with NH4+, [AuCl(PR3)], or MeI to give unsatur-
ated dicarbonyls [Mo2Cp2(µ-X)(µ-PA2)(CO)2] (X ) H,
AuPR3, Me), while [Me3O]BF4 gives the methoxycarbyne
[Mo2Cp2(µ-COMe)(µ-PCy2)(µ-CO)] and allyl chloride re-
arranges to give the unsaturated alkenyl complex [Mo2-
Cp2(µ-PCy2)(µ-CMeCH2)(CO)2].
(BO ) 1.5),2 dihydrides [M2(µ-H)2(CO)8]2- (BO ) 2;
M ) Cr, Mo, W),3 the phosphido complex [Fe2(µ-PPh2)-
(CO)6]- (BO ) 2),4 and the diphosphine-bridged
[Mn2(CO)6(µ-Ph2PCH2PPh2)]2- (BO ) 2).5 The unusual
combination of a negative charge and a double M-M
bond in these substrates provides these anions with a
remarkably wide synthetic potential.4,5 We here report
the synthesis of the very reactive dimolybdenum anions
[Mo2Cp2(µ-PA2)(µ-CO)2]- (2a -c) [A ) Cy (a ), Ph (b),
OEt (c)]. To our knowledge, these 30 e- species are the
first examples of transition-metal carbonyl anions dis-
playing a triple intermetallic bond. Moreover, their high
reactivity gives a unique opportunity to explore the
chemistry of binuclear anions under a highly unsatur-
ated metal environment. As shown below, these anions
allow the synthesis of unsaturated derivatives that
cannot be prepared through other routes, and they also
promote unusual coordination modes or rearrangements
in the incoming electrophile, always under mild condi-
tions.
Transition-metal carbonyl anions are very useful
reagents in organometallic synthesis. This is mainly due
to their nucleophilicity, which allows these molecules
to react with a great variety of electrophiles, thus
forming new M-E bonds (E ) H, C, p-element, d-
element, etc.).1 Although a large number of mononuclear
and polynuclear species are known, the number of
metal-metal bonded binuclear anions is comparatively
low, and only a few of them exhibit M-M bond orders
(BO) higher than one. In fact, examples of the latter are
restricted to the paramagnetic [Fe2(µ-PtBu2)2(CO)5]-
(2) Van der Linden, J . G. M.; Heck, J .; Walter, B.; Bottcher, H.-C.
Inorg. Chim. Acta 1995, 217, 29.
(3) Lin, J . T.; Hagen, G. P.; Ellis, J . E. J . Am. Chem. Soc. 1983,
105, 2296, and references therein.
(4) Seyferth, D.; Brewer, K. S.; Wood, T. G.; Cowie, M.; Hilts, R. W.
Organometallics 1992, 11, 2570.
* Corresponding author. E-mail: mara@sauron.quimica.uniovi.es.
† Universidad de Oviedo.
‡ Universita` di Parma.
(1) Reviews: (a) Cotton, F. A.; Wilkinson, G. Advanced Inorganic
Chemistry, 5th ed.; Wiley: New York, 1988; Chapter 22. (b) Ellis, J .
E. Adv. Organomet. Chem. 1990, 31, 1, and references therein.
(5) (a) Liu, X. Y.; Riera, V.; Ruiz, M. A.; Bois, C. Organometallics
2001, 20, 3007. (b) Liu, X. Y.; Riera, V.; Ruiz, M. A. Organometallics
1994, 13, 2925.
10.1021/om030150t CCC: $25.00 © 2003 American Chemical Society
Publication on Web 04/12/2003

1984 Organometallics, Vol. 22, No. 10, 2003
Communications
Sch em e 1
Tetrahydrofuran solutions of anions 2a -c are easily
generated in a two-step reaction. First, the new chloro
complexes [Mo2Cp2(µ-Cl)(µ-PA2)(CO)2] (1a -c) are syn-
thesized through the oxidative addition of the corre-
sponding ClPA2 on [Mo2Cp2(CO)6] in refluxing toluene
(Cy, Ph) or diglyme (OEt) (eq 1).6
Complexes 1 are structurally related to the mixed-
phosphido compounds [M2Cp2(µ-PR2)(µ-PR′R′′)(CO)2],7
but they are much more unstable and could not be
isolated. In a second step, tetrahydrofuran solutions of
the crude compounds 1 are reacted with several reduc-
ing agents such as Li[BHEt3], Na(Hg), or K[BH(sBu)3]
to give the corresponding alkaline metal salts of anions
2a -c. Although these complexes could not be isolated,
IR and 31P NMR data of the corresponding reaction
mixtures indicated the presence of single major species
in each case,8 so these crude solutions could be used for
further studies. The IR spectra of anions 2 clearly reveal
the presence of two bridging carbonyls. These spectra
are sensitive to the nature of the alkaline counterion,
an indication of ion-pair effects,9 yet to be studied.
Cp2(µ-Me)(µ-PCy2)(CO)2] (4),13 whereas reaction of 2a
with [Me3O]BF4 gives the methoxycarbyne [Mo2Cp2(µ-
COMe)(µ-PCy2)(µ-CO)] (5).14 Although NMR data for 4
down to 193 K indicate the presence of a symmetric
methyl group, we propose for this compound a fluxional
monohapto agostic ligand instead. This is supported by
the 31P chemical shift of 4, with a value characteristic
of doubly bonded complexes of the type [M2Cp2(µ-PR2)-
(µ-X)(CO)2] (M ) Mo, W; X ) three-electron ligand).7 A
number of related agostic complexes have been de-
scribed, but none of them seem to involve a bridging
methyl across a double M-M bond. It is to be seen
whether this will enhance the reactivity of the methyl
ligand, for example with respect to C-C coupling
reactions.
Compound 5 retains the most significant structural
features present in the parent anion 2, that is, the triple
Mo-Mo bond and the bridging carbonyls. This has been
confirmed through an X-ray study on the ethoxycarbyne
5′, which can be conveniently prepared from 2a and
Et2SO4 (Figure 1).15,16 Indeed, compound 5′ displays a
Mo-Mo distance (2.4793(15) and 2.4772(11) Å in the
two crystallographically independent molecules) com-
The high synthetic potential of the unsaturated
anions 2 is illustrated through the reactions of 2a (Li+
salt) shown in Scheme 1. As expected, this anion is
easily protonated by [NH4]PF6 to give the corresponding
hydride [Mo2Cp2(µ-H)(µ-PCy2)(CO)2] (3).10 Compound 3
is a rare example of a metal carbonyl displaying a
bridging H ligand across a triple M-M bond. Precedents
for this 30 e- compound are restricted to the monocar-
bonyls [M2Cp*2(µ-H)(µ-CO)] (M ) Ru,11a,b Os11c) and the
cations [W2Cp2(µ-H)(CO)2(µ-R2PCH2PR2)]+ (R ) Me,
Ph).12 More importantly, our initial studies indicate that
hydride 3 is very reactive toward a great variety of small
molecules.
The reactions of 2a with other electrophiles reveal
that not only the metal atoms but also the O (carbonyl)
atoms are nucleophilic sites of the anion. For example,
reaction of 2a with MeI gives the methyl complex [Mo2-
(6) Selected spectroscopic data for compounds 1: ν(CO) (toluene):
1844(vs) cm-1 (1a ); 1859(vs) cm-1 (1b). ν(CO) (diglyme): 1890(m, sh),
1867(vs) cm-1 (1c). 31P{1H} NMR (81.03 MHz): δ 155.6 ppm (1a , C6D6);
135.3 ppm (1b, CH2Cl2), 329.2 ppm (1c, CH2Cl2).
(7) Garc´ıa, M. E.; Riera, V.; Rueda, M. T.; Ruiz, M. A.; Sa´ez, D.
Organometallics 2002, 21, 5515.
(8) Selected spectroscopic data for compounds 2: ν(CO) (THF):
1588(m), 1562(vs) cm-1 (2a , Li+ salt); 1644(m), 1604(vs), 1593(s, sh)
cm-1 (2b, Na+ salt); 1605(m), 1570(vs) cm-1 (2c, Li+ salt). 31P{1H} NMR
(121.50 MHz, THF): δ 209.8 ppm(2a ); 334.8 ppm(2c).
(13) Selected data for 4: ν(CO) (CH2Cl2): 1854(w, sh), 1815(s) cm-1
.
)
1H NMR (300.13 MHz, CD2Cl2): δ 5.16 (s, 10H, Cp), -0.77 (d, J HP
2.5, J HC ) 124, 3H, µ-Me) ppm. 31P{1H} NMR (121.49 MHz, CD2Cl2):
δ 153.3 (s, µ-P) ppm. 13C{1H} NMR (100.61 MHz, CD2Cl2): δ 249.6 (d,
J CP ) 15, CO), 89.4 (s, Cp), -44.3 (d, J CP ) 2.5, µ-Me) ppm.
(14) Selected data for 5: ν(CO) (CH2Cl2): 1674(s) cm-1 1H NMR
.
(300.13 MHz, CD2Cl2): δ 5.75 (s, 10H, Cp), 3.74 (s, 3H, OMe) ppm.
31P{1H} NMR (121.52 MHz, CD2Cl2): δ 228.5 (s, µ-P) ppm. 13C{1H}
NMR (100.63 MHz, CD2Cl2, 213 K): δ 352.0 (d, J CP ) 15, µ-COMe),
305.0 (d, J CP ) 9, µ-CO), 93.5 (s, Cp), 66.4 (s, OMe) ppm.
(9) Darensbourg, M. Y. Prog. Inorg. Chem. 1985, 33, 221
(10) Selected data for 3: ν(CO) (THF): 1871(w, sh), 1837(s) cm-1
.
)
(15) Selected data for 5′: ν(CO) (CH2Cl2) 1672(s) cm-1 1H NMR
.
1H NMR (300.13 MHz, CD2Cl2): δ 5.09 (s, 10H, Cp), -6.94 (d, J HP
(200.13 MHz, CD2Cl2): δ 5.72 (s, 10H, Cp), 3.92 (q, J HH ) 7, 2H, OCH2),
1.28 (t, J HH ) 7, 3H, CH3) ppm. 31P{1H} NMR (81.04 MHz, CD2Cl2):
δ 227.8 (s, µ-P) ppm. 13C{1H} NMR (100.63 MHz, CD2Cl2): δ 351.0 (d,
J CP ) 15, µ-COEt), 303.5 (d, J CP ) 9, µ-CO), 93.6 (s, Cp), 76.3 (s, OCH2)
ppm.
11, 1H, µ-H) ppm. 31P{1H} NMR (121.50 MHz, CD2Cl2): δ 232.3 (s,
µ-P) ppm.
(11) (a) Forrow, N. J .; Knox, S. A. R. J . Chem. Soc., Chem.
Commun.1984, 679. (b) Kang, B. S.; Koelle, U.; Thewalt, U. Organo-
metallics 1991, 10, 2569. (c) Hoyano, J . K.; Graham, W. A. G. J . Am.
Chem. Soc. 1982, 104, 3722.
(12) (a) Alvarez, M. A.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.
Organometallics 1999, 18, 634. (b) Alvarez, M. A.; Garc´ıa, M. E.; Riera,
V.; Ruiz, M. A.; Bois, C. Angew. Chem., Int. Ed. Engl. 1996, 35, 102.
(16) X-ray data for 5′: red crystals, Mo2PO2C26H37, fw 604.41,
triclinic, (P1h), a ) 17.489(5) Å, b ) 15.118(5) Å, c ) 10.254(5) Å, R )
91.75(5)°, â ) 92.51(5)°, γ ) 72.57(5)°, V ) 2583.7(17) Å3, Z ) 4, T )
293 K, R1 ) 0.0551 [for I > 2σ(I)], wR2 ) 0.1481 (all data), GOF )
0.851.

Communications
Organometallics, Vol. 22, No. 10, 2003 1985
shift in the original allyl group at some stage of the
reaction. Noticeably, this unexpected rearrangement is
opposite the 1,2-shift (alkenyl to allyl) proposed to occur
during the photolysis of alkynes at Mn2 or MnMo
centers.20 Compound 6 exists in solution as a mixture
of cis- and trans-dicarbonyl isomers,7 as deduced from
its IR spectrum. Interestingly, these isomers intercon-
vert rapidly on the NMR time scale, a process not
detected previously in the related alkenyl complexes
[Mo2Cp2(µ-CMeCHMe)(µ-SR)(CO)2].21
Other synthetic uses of anion 2a are illustrated
through the reactions with ClP(OEt)2 and [AuCl{P(p-
tol)3}], which lead to the unsaturated mixed-phosphido
complex [Mo2Cp2(µ-PCy2){µ-P(OEt)2}(CO)2] (7)22 and the
unstable heterometallic cluster [Mo2AuCp2(µ-PCy2)-
(CO)2{P(p-tol)3}] (8), respectively.23
In summary, we have shown that the triply bonded
anion 2a is quite reactive toward a great variety of
electrophiles under mild conditions, thus leading to
unsaturated molecules that are not accessible through
conventional preparative routes. Anion 2a displays both
Mo and O nucleophilic sites, and the presence of the
triple Mo-Mo bond might have a critical influence on
the coordination mode or rearrangements in the incom-
ing electrophile. We are further exploring the synthetic
potential of anions 2 and some of their unsaturated
derivatives.
F igu r e 1. View of the molecular structure of compound
5′.
parable to those found for related triply bonded neutral
complexes such as [Mo2Cp2(CO)4]17a or [Mo2Cp2(µ-PPh2)2-
(µ-CO)].17b Interatomic distances within the ethoxycar-
byne ligand are similar to those in the cation [W2Cp2(µ-
COMe)(µ-PPh2)2]+.18 These two complexes are the only
known examples of COR ligands across triple M-M
bonds to be structurally characterized and have a
considerable synthetic potential derived from the si-
multaneous presence of M-M and M-C multiple bonds.
The unsaturated nature of the dimetal center in 2a
might promote some unusual rearrangements in the
incoming electrophile. For example, 2a reacts readily
at room temperature with allyl chloride to give the
alkenyl derivative [Mo2Cp2{µ-η1:η2-C(Me)dCH2}(µ-PCy2)-
(CO)2] (6) as sole product.19 This requires a 2,1-H atom
Ack n ow led gm en t. The authors thank the MECD
of Spain for a grant (to A.R.) and MCYT and FICYT for
financial support.
Su p p or tin g In for m a tion Ava ila ble: Experimental pro-
cedures for new complexes and crystallographic data for 5′.
This material is available free of charge via the Internet at
http://pubs.acs.org.
OM030150T
(20) Horton, A. D.; Kemball, A. C.; Mays, M. J . J . Chem. Soc., Dalton
Trans. 1988, 2953.
(21) Schollhammer, P.; Pe´tillon, F. Y.; Poder-Guillon, S.; Talarmin,
J .; Muir, K. W.; Yufit, D. S. J . Organomet. Chem. 1996, 513, 181.
(17) (a) Klinger, R. J .; Butler, W. M.; Curtis, M. D. J . Am. Chem.
Soc. 1978, 100, 5034. (b) Adatia, T.; McPartlin, M.; Mays, M. J .; Morris,
M. J .; Raithby, P. R. J . Chem. Soc., Dalton Trans. 1989, 1555.
(18) Garc´ıa, M. E.; Riera, V.; Rueda, M. T.; Ruiz, M. A.; Halut, S. J .
Am. Chem. Soc. 1999, 121, 1960.
(22) Selected data for 7: ν(CO) (CH2Cl2) 1875(w, sh), 1848(s) cm-1
.
1H NMR (300.13 MHz, CD2Cl2): δ 5.40 (s, 10H, Cp), 4.28, 3.98 (2 × m,
2 × 2H, OCH2), 1.37 (t, J HH ) 7, 6H, CH3). 31P{1H} NMR (121.49 MHz,
CD2Cl2): δ 351.1 [d, J PP ) 19, µ-P(OEt)2], 119.5 (d, J PP ) 19, µ-PCy2)
ppm.
(19) Selected data for 6: ν(CO) (petroleum ether) 1888(vs), 1838(s),
1808(vs) cm-1
.
1H NMR (300.13 MHz, CD2Cl2): δ 5.36, 5.31 (2 × s, 2
× 5H, Cp), 5.07, 4.68 (2 x d, J HH ) 2.6, 2 × 1H, CH2), 2.27 (s, 3H, Me)
ppm. 31P{1H} NMR (121.52 MHz, CD2Cl2): δ 131.2 (s, µ-P) ppm.
13C{1H} NMR (100.63 MHz, CD2Cl2, 213 K): δ 250.0 (d, J CP ) 14, CO),
237.9 (d, J CP ) 13, CO), 174.6 (s, CdCH2), 90.0, 89.0 (2 × s, Cp), 79.3
(s, CdCH2), 38.7 (s, Me) ppm.
(23) Selected data for 8: ν(CO) (CH2Cl2): 1765 cm-1 1H NMR
.
(200.13 MHz, CD2Cl2): δ 7.60-7.10 (m, 12H, p-C6H4CH3), 4.89 (s, 10H,
Cp), 2.33 (s, 9H, CH3) ppm. 31P{1H} NMR (81.04 MHz, CD2Cl2): δ 213.9
(s, µ-PCy2), 63.3 [s, AuP(p-tol)3] ppm.