Chemistry of highly electrophilic binuclear cations. 4. synthesis and reactivity of the dinuclear radicals [M2(η5-C 5H5)2(μ-CO)2(CO) 2(μ-L2)][B{3,5-C6H

Article abstract of DOI:10.1021/om049763b

The synthesis and reactivity of the dinuclear radicals [M ₂(η⁵-C₅H₅)₂ (μ-CO)₂(CO)₂(μ-L₂)][B{3,5-C₆ H₃(CF₃)₂}₄](

Full text of DOI:10.1021/om049763b

3950
Organometallics 2004, 23, 3950-3962
Ch em istr y of High ly Electr op h ilic Bin u clea r Ca tion s. 4.
Syn th esis a n d Rea ctivity of th e Din u clea r Ra d ica ls
[M2(η5-C5H5)2(µ-CO)2(CO)2(µ-L2)][B{3,5-C6H3(CF 3)2}4] (M )
Mo, W; L2 ) P h 2P CH2P P h 2, Me2P CH2P Me2,
(EtO)2P OP (OEt)2)
M. Angeles Alvarez, Yvonne Anaya, M. Esther Garc´ıa, and Miguel A. Ruiz*
Departamento de Quı´mica Orga´nica e Inorga´nica/ IUQOEM, Universidad de Oviedo,
E-33071 Oviedo, Spain
Received April 2, 2004
Oxidation of the compounds [M2Cp2(CO)4(µ-L2)] (M ) Mo, W; Cp ) η5-C5H5; L2
Ph2PCH2PPh2 (dppm), Me2PCH2PMe2 (dmpm), (EtO)2POP(OEt)2 (tedip)) with [FeCp2](BAr′4)
(Ar′ ) 3,5-C6H3(CF3)2) gives the corresponding tetracarbonyl radicals [M2Cp2(µ-CO)2(CO)2-
(µ-L2)](BAr′4). The stability of these paramagnetic complexes depends on the ligand and the
metal. Thus, the dmpm complexes are stable in solution for reasonable periods of time,
whereas the dppm complexes experience spontaneous decarbonylation at room temperature
to give the radicals [Mo2Cp2(µ-CO)2(µ-dppm)](BAr′4) and [W2Cp2(µ-CO)(CO)2(µ-dppm)](BAr′4).
The tedip-bridged derivatives are the most unstable radicals, with the ditungsten cation
experiencing rapid hydrogen atom capture to give the hydride complex [W2Cp2(µ-H)(CO)4-
(µ-tedip)](BAr′4). The complexes [M2Cp2(µ-CO)2(CO)2(µ-L2)](BAr′4) react with NO to give the
binuclear nitrosyl derivatives [M2Cp2(CO)4(NO)(µ-L2)](BAr′4) (M ) Mo, W; L2 ) dmpm,
tedip) and [Mo2Cp2(µ-CO)(CO)2(NO)(µ-dmpm)](BAr′4). Some mononuclear products such as
[MCp(CO)2(OPMe2CH2PMe2)](BAr′4) were identified in these reaction mixtures. The diphos-
phine-bridged dimolybdenum radicals are reactive toward small molecules containing H-E
bonds (with E ) N, P, O, S) under mild conditions. Thus, reaction of [Mo2Cp2(µ-CO)2(CO)2-
(µ-dppm)](BAr′4) with water at room temperature yields the hydroxo complexes [Mo2Cp2-
(µ-OH)(CO)2(µ-dppm)](BAr′4) and [Mo2Cp2(µ-H)(µ-OH)(CO)2(µ-dppm)](BAr′4)(OH), while reac-
tions with HSPh give mixtures of cis-[Mo2Cp2(µ-SPh)(µ-CO)(CO)2(µ-L2)](BAr′4), cis-[Mo2Cp2-
(µ-SPh)(CO)2(µ-dppm)](BAr′4), and cis-[Mo2Cp2(µ-H)(µ-SPh)(CO)2(µ-dppm)](BAr′4)(SPh), with
their relative amounts depending on the diphosphine and experimental conditions. The
tricarbonyls cis-[Mo2Cp2(µ-SPh)(µ-CO)(CO)2(µ-L2)](BAr′4) rearrange to the corresponding
trans isomers upon exposure to UV-visible light, and the dppm derivative even experiences
a reversible decarbonylation to give trans-[Mo2Cp2(µ-SPh)(CO)2(µ-dppm)](BAr′4). cis- and
trans-dicarbonyls [Mo2Cp2(µ-SPh)(CO)2(µ-dppm)](BAr′4) are protonated by HBF4‚OEt2
with retention of geometry to yield the corresponding hydride derivatives cis- and trans-
[Mo2Cp2(µ-H)(µ-SPh)(CO)2(µ-dppm)](BAr′4)(BF4). Deprotonation of the latter with 1,8-
diazabicyclo[5.4.0]undec-7-ene (DBU) is not reversible, as it gives in both cases the cis isomer,
which suggest the operation of a reduction/dehydrogenation reaction pathway. The structures
of the new complexes are analyzed on the basis of the corresponding IR and NMR (1H, 31P,
13C) data, and the reaction pathways operative in the reactions with H2O and HSPh are
discussed on the basis of the available data and some additional experiments.
)
In tr od u ction
ruption of the dimetallic unit to give the corresponding
mononuclear cations [MCp(CO)2(dppm)]+. In contrast,
if a second equivalent of [FeCp2]X is present, the
transient dinuclear radical is rapidly oxidized to give
the unsaturated and highly electrophilic dications
[M2Cp2(CO)4(µ-dppm)]2+, which experience a fast fluo-
ride abstraction process with their own counterions. In
a later work2 we reported the use of [FeCp2](BAr′4)
(Ar′ ) 3,5-C6H3(CF3)2) as an oxidizing reagent on the
above tungsten tetracarbonyl 2a . Currently, the (BAr′4)-
In the first part of this series1 we have shown that
one-electron oxidation of the neutral complexes
[M2Cp2(CO)4(µ-dppm)] (M ) Mo (1a ), W (2a ); Cp )
η5-C5H5; dppm ) Ph2PCH2PPh2) with [FeCp2]X (X )
BF4, PF6) leads presumably to the 33-electron radicals
[M2Cp2(CO)4(µ-dppm)]+, which rapidly evolve with dis-
* To whom correspondence should be addressed. E-mail: mara@
fq.uniovi.es.
(1) (a) Alvarez, M. A.; Garc´ıa, G.; Garc´ıa, M. E.; Riera, V.; Ruiz, M.
A.; Lanfranchi, M.; Tiripicchio, A. Organometallics 1999, 18, 4509. (b)
Alvarez, M. A.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.; Bois, C.; J eannin,
Y. Angew. Chem., Int. Ed. Engl. 1993, 32, 1156.
(2) Alvarez, M. A.; Anaya, Y.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.;
Vaissermann, J . Organometallics 2003, 22, 456.
10.1021/om049763b CCC: $27.50 © 2004 American Chemical Society
Publication on Web 06/29/2004

Highly Electrophilic Binuclear Cations
Organometallics, Vol. 23, No. 16, 2004 3951
Sch em e 1. Oxid a tion Rea ction s of th e
d p p m -Br id ged Ditu n gsten Com p lex 2a 2
Ch a r t 1
which then evolve in different ways depending on the
metal and bridging ligand. Noticeably, both the dppm-
and dmpm-bridged dimolybdenum radicals proved to be
isolable products and, therefore, suitable for reactivity
studies. Despite the general relevance of organometallic
radicals,8,9 there are still only a few metal-metal-
bonded binuclear radicals that can be isolated, particu-
larly those with electron counts below 34, and their
chemistry thus remains little explored.10 We therefore
decided to study in some detail the behavior of these
33-electron dimolybdenum radicals. In this paper we
present our results on their reactions toward classical
radical traps as NO and simple donor molecules having
H-E bonds (E ) O, S, N, P) such as phosphines, thiols,
water, or amines. These paramagnetic cations are also
very reactive toward 1-alkynes, and the results of these
reactions will be reported separately.
anion3 is being used extensively as a quite efficient and
inert counterion for reactive cations.4 In our case, the
use of a more inert and noncoordinating counterion
allowed the stabilization of the 33- and 31-electron
paramagnetic species [W2Cp2(CO)x(µ-dppm)]+ (x ) 3, 4).
Moreover, further oxidation of the latter radicals al-
lowed the isolation of the unsaturated tricarbonyl
complex [W2Cp2(µ-CO)(CO)2(µ-dppm)](BAr′4)2 (Scheme
1).2 Metal-metal bond orders higher than 1 should be
formulated for all the above cations on the basis of the
EAN rule. For example, a triple intermetallic bond is
formulated for the dipositive tricarbonyl cation. This is
in agreement with its highly electrophilic behavior5 and
with the very short intermetallic distance (2.599(1) Å)
found for its isoelectronic derivative [W2Cp2(µ-CO)(CO)-
{P(OMe)3}(µ-dppm)](BAr′4)2.2
Due to our interest in the relatively little explored
chemistry of organometallic cations having multiple
intermetallic bonds, we decided to examine in more
detail the above oxidation reactions by analyzing the
role played by not only the metals but also the ligands.
For this reason, we have studied the oxidation reactions
of the related tungsten substrates [W2Cp2(CO)4(µ-L2)]
(2b,c), having more efficient binucleating bridging
ligands such as the diphosphine Me2PCH2PMe2 (dmpm)6
or diphosphite (EtO)2POP(OEt)2 (tedip).7 The effect of
the metal has been examined by studying the oxida-
tion reactions of the related dimolybdenum complexes
[Mo2Cp2(CO)4(µ-L2)] (L2 ) dppm (1a ), dmpm (1b), tedip
(1c)). As will be shown, two-electron oxidation does not
occur on complexes 1a -c or 2b,c when using [FeCp2]-
(BAr′4) as oxidant. Instead, the paramagnetic cations
[M2Cp2(µ-CO)2(CO)2(µ-L2)]+ are formed in all cases,
Resu lts a n d Discu ssion
On e-E lect r on Oxid a t ion of t h e Com p lexes
[M2Cp 2(CO)4(µ-L2)]. As found previously for the dppm-
bridged ditungsten complex 2a ,2 all of the dimolybde-
num compounds 1a -c and the tedip and dmpm ditung-
sten complexes 2b,c react rapidly with 1 equiv of
[FeCp2](BAr′4) in dichloromethane at room temperature
(L2 ) dppm, dmpm) or -20 °C (L2 ) tedip) to give
quantitatively the green cationic tetracarbonyl radicals
[M2Cp2(µ-CO)2(CO)2(µ-L2)](BAr′4) (3, 4) (Chart 1). Sur-
prisingly, no further reaction was observed between the
above cations and a second equivalent of [FeCp2](BAr′4).
This is in contrast with the behavior of the ditungsten
radical 4a , which experiences further oxidation to give
the tricarbonyl complex [W2Cp2(µ-CO)(CO)2(µ-dppm)]-
(BAr′4)2, as noted above (Scheme 1).2 The stability of
the paramagnetic complexes 3 and 4 is moderate or low
(see later), and only the dmpm-bridged dimolybdenum
complex 3b could be properly isolated as a crystalline
solid. Despite this, satisfactory IR spectra (Table 1)
(3) Nishida, H.; Takada, N.; Yoshimura, M.; Sonoda, T.; Kobayashi,
H. Bull. Chem. Soc. J pn. 1984, 57, 2600.
(4) For some recent work, see for example: (a) J imenez-Tenorio, M.;
Puerta, M. C.; Salcedo, I.; Valerga, P.; Costa, S. I.; Gomes, P. T.;
Mereiter, K. Chem. Commun. 2003, 1168. (b) Leatherman, M. D.;
Svejda, S. A.; J ohnson, L. K.; Brookhart, M. J . Am. Chem. Soc. 2003,
125, 3068. (c) Norris, C. M.; Reinartz, S.; White, P. S.; Templeton, J .
L. Organometallics 2002, 21, 5649. (d) Taw, F. L.; Mellows, H.; White,
P. S.; Hollander, F. J .; Bergman, R. G.; Brookhart, M.; Heinekey, D.
M. J . Am. Chem. Soc. 2002, 124, 5100. (e) Voges, M. H.; Bullock, R.
M. Dalton 2002, 757.
(8) (a) Paramagnetic Organometallic Species in Activation/ Selectiv-
ity, Catalysis; Chanon, M., J ulliard, M., Poite, J . C., Eds.; Kluwer
Academic: Dordrecht, The Netherlands, 1989. (b) Organometallic
Radical Processes; Trogler, W. C., Ed.; Elsevier: Amsterdam, 1990.
(c) Astruc, D. Electron Transfer and Radical Processes in Transition-
Metal Chemistry; VCH: New York, 1995.
(5) Alvarez, M. A.; Anaya, Y.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.
Organometallics 2004, 23, 433.
(6) Alvarez, M. A.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.; Falvello, L.
R.; Bois, C. Organometallics 1997, 16, 354.
(7) Alvarez, M. A.; Alvarez, C.; Garc´ıa, M. E.; Riera, V.; Ruiz, M.
A.; Vaissermann, J . Organometallics 1997, 16, 2581.
(9) (a) Ward, M. D. Chem. Soc. Rev. 1995, 24, 121. (b) Astruc, D.
Acc. Chem. Res. 1997, 30, 383.
(10) Garc´ıa, M. E.; Riera, V.; Rueda, M. T.; Ruiz, M. A.; Lanfranchi,
M.; Tiripicchio, A. J . Am. Chem. Soc. 1999, 121, 4060.

3952 Organometallics, Vol. 23, No. 16, 2004
Ta ble 1. IR a n d 31P {1H} NMR Da ta for New Com p ou n d s
Alvarez et al.
b
compd
νst(CO)a/cm-1
δ(P) (J PW
)
J PP
[Mo2Cp2(µ-CO)2(CO)2(µ-dppm)](BAr′4) (3a )
[Mo2Cp2(µ-CO)2(CO)2(µ-dmpm)](BAr′4) (3b)
[Mo2Cp2(µ-CO)2(CO)2(µ-tedip)](BAr′4) (3c)
[W2Cp2(µ-CO)2(CO)2(µ-dppm)](BAr′4) (4a )
1978 (vs), 1922 (w), 1780 (w), 1718 (m)
1975 (vs), 1920 (w), 1772 (w), 1709 (m)
2006 (vs), 1782 (w), 1728 (m)
1969 (vs), 1909 (w), 1747 (w), 1674 (m)
1967 (vs), 1907 (w), 1737 (w), 1668 (m)
1812 (w, sh), 1782 (vs)
[W2Cp2(µ-CO)2(CO)2(µ-dmpm)](BAr′4) (4b)
[Mo2Cp2(µ-CO)2(µ-dppm)](BAr′4) (5)
[W2Cp2(µ-H)(CO)4(µ-tedip)](BAr′4) (6)
1993 (m), 1974 (vs), 1910 (s)
122.9,c 118.9d
33.2, 21.5
194.0, 137.6
14.8 (176), -3.0 (467)
34.2, 22.8
38.2, 17.7
84.0, 33.5
90.8, 7.4 (280)
-65.2 (204)
28.9, 20.1
55.1c
[Mo2Cp2(CO)4(NO)(µ-dmpm)](BAr′4) (7b)
2061 (s), 2002 (m), 1965 (vs), 1926 (m)e
2070 (s), 2010 (m), 1987 (vs), 1941 (m)f
2056 (s), 1988 (m), 1953 (vs), 1914 (m)g
1992 (s), 1879 (m, br), 1746 (s)h
2061 (s), 2001 (m), 1966 (vs)
19
71
20
70
19
34
31
[Mo2Cp2(CO)4(NO)(µ-tedip)](BAr′4) (7c)
[W2Cp2(CO)4(NO)(µ-dmpm)](BAr′4) (8)
[Mo2Cp2(µ-CO)(CO)2(NO)(µ-dmpm)](BAr′4) (9)
[MoCp(CO)3{κ1-Me2PCH2P(O)Me2}](BAr′4) (10)
[MoCp(CO)2(κ2-OPMe2CH2PMe2)](BAr′4) (11)
[WCp(CO)2(κ2-OPMe2CH2PMe2)](BAr′4) (12)
[WCp(CO)2(κ2-dmpm)](BAr′4) (13)
1989 (vs), 1911 (m)
1985 (vs), 1917 (m)
1862 (vs)
1985 (s), 1971 (vs), 1904 (s)
1986 (s), 1968 (vs), 1898 (s)
1941 (vs), 1872 (w)
1996 (vs), 1943 (w)
1995 (vs), 1942 (w)
1981 (vs), 1926 (w), 1710 (m)
1975 (vs), 1923 (w), 1710 (m)
1952 (vs), 1884 (w)
[MoCp{NH2(p-tol)}(CO)(κ2-dppm)](BAr′4) (14)
[Mo2Cp2(µ-H)(CO)4(µ-dppm)](BAr′4) (15a )
71
[Mo2Cp2(µ-H)(CO)4(µ-dmpm)](BAr′4) (15b)
[Mo2Cp2(µ-OH)(CO)2(µ-dppm)](BAr′4) (16)
[Mo2Cp2(µ-H)(µ-OH)(CO)2(µ-dppm)](BAr′4)(BF4) (17′)
[Mo2Cp2(µ-H)(µ-OH)(CO)2(µ-dppm)](BAr′4)(I) (17′′)
cis-[Mo2Cp2(µ-SPh)(µ-CO)(CO)2(µ-dppm)](BAr′4) (18a )
cis-[Mo2Cp2(µ-SPh)(µ-CO)(CO)2(µ-dmpm)](BAr′4) (18b)
cis-[Mo2Cp2(µ-SPh)(CO)2(µ-dppm)](BAr′4) (19)
cis-[Mo2Cp2(µ-H)(µ-SPh)(CO)2(µ-dppm)](BAr′4)(BF4) (20′)
trans-[Mo2Cp2(µ-SPh)(µ-CO)(CO)2(µ-dppm)](BAr′4) (21a )
trans-[Mo2Cp2(µ-SPh)(µ-CO)(CO)2(µ-dmpm)](BAr′4) (21b)
trans-[Mo2Cp2(µ-SPh)(CO)2(µ-dppm)](BAr′4) (22)
trans-[Mo2Cp2(µ-H)(µ-SPh)(CO)2(µ-dppm)](BAr′4)(BF4) (23)
22.1,c 19.0d
33.0
38.7
38.8
44.1
25.2
19.4, 18.1i
29.9
1996 (vs), 1936 (w)
1966 (vs), 1906 (w), 1707 (m)
1962 (vs), 1902 (w), 1709 (m)
1939 (vs), 1861 (w)
35.4
31.0
43.4
39.6
2010 (vs), 1964 (w)
a
b
Recorded in CH2Cl2 solution. Recorded at 121.50 MHz and 291 K in CD2Cl2 solution, unless otherwise stated. δ values are in ppm
relative to external 85% aqueous H3PO4; J values are in hertz. c Data for anti isomer. Data for syn isomer. νst(NO) 1609 (m). νst(NO)
1640 (m). νst(NO) 1588 (m). νst(NO) 1651 (s). Endo and exo conformers respectively (see text); exo:endo ) 3.
d
e
f
g
h
i
could be obtained for all of these cations, except for the
tedip-bridged 4c.
lated electron-precise cations with a higher number of
bridging atoms tend to exhibit intermetallic separations
shorter than the above neutral species, around 3 Å. For
example, this value in the chloro complex [W2Cp2(µ-Cl)-
(µ-CO)(CO)2(µ-dppm)](PF6) is 3.040(3) Å,1 similar to
those found in the dimolybdenum cations [Mo2Cp2-
(µ-I)(µ-CH2PPh2)(µ-PPh2)(CO)2]+ (3.001(2) Å)13 and
[Mo2Cp2(µ-StBu)2(CO)4]2+ (3.008(2) Å).14 All these data
support our view that the intermetallic bonding interac-
tion in cation 3b is stronger than that in the neutral
precursor, in agreement with the formal bond order of
1.5 that should be formulated for all compounds 3 and
4 on the basis of the EAN rule. In solution, compound
3b exhibits a magnetic susceptibility (measured in
CD2Cl2 by the Evans method)15 corresponding to an
effective magnetic moment of about 1.1 µB, thus con-
firming its paramagnetic nature. This value is lower
than the spin-only figure expected for a molecule with
one unpaired electron (µeff ) 1.73 µB), which may be
attributed to partial decomposition of the complex
during measurement, although the presence of some
intermolecular radical-radical interactions in solution
cannot be excluded.
IR data in solution for compounds 3 and 4 indicate
that all these cations are isostructual and exhibit two
bridging and two terminal carbonyl ligands, the latter
being almost parallel to each other. This geometry
(Chart 1) has been previously identified for the radical
4a 2 and thus needs no further comments. We only note
that the C-O stretching bands of complex 3c are
considerably shifted to higher frequencies compared to
those of 3a , as expected from the stronger acceptor
character of the tedip ligand relative to dppm, whereas
differences between dppm and dmpm compounds are
much smaller. This parallels the differences in stability
of these species, which seem to increase with the
electron-donor strength of the bridging phosphorus
ligand (see later). In fact, we could not obtain a
completely clean IR spectrum for 3c (an expected weak
asymmetric CO stretching band is masked by those
arising from decomposition products). The green solu-
tions of 4c decompose even more rapidly, and no reliable
IR data could be obtained for this complex.
Compound 3b is stable enough to be crystallized.
Unfortunately, its structure could not be properly solved
through an X-ray study because of the progressive
degradation of the crystals in the X-ray beam. De-
spite this, a value of 2.985 Å for the Mo-Mo distance
could be estimated from the available diffraction data.
This value is substantially shorter than those found
in the electron-precise compounds 1a (3.27(1) Å)11 or
[Mo2Cp2(CO)4(µ-tBuPHCH2PHtBu)] (3.2109(4) Å).12 Re-
Evolu tion of Ra d ica ls 3 a n d 4 in Dich lor o-
m eth a n e Solu tion . The stability of compounds 3 and
4 is strongly dependent on the bridging ligand L2 and,
to a lesser extent, on the metal (Scheme 2). Thus, the
dmpm complexes 3b and 4b (those with the smallest
and strongest donor bridge) do not undergo any evolu-
tion in solution at room temperature for several hours.
(13) Riera, V.; Ruiz, M. A.; Villafan˜e, F.; Bois, C.; J eannin, Y. J .
Organomet. Chem. 1989, 375, C23.
(11) Azam, K. A.; Deeming, A. J .; Felix, M. S. B.; Bates, P. A.;
Hurthouse, M. B. Polyhedron 1988, 7, 1793.
(12) Brauer, D. J .; Hasselkuss, G.; Stelzer, O. J . Organomet. Chem.
1987, 321, 339.
(14) Courtot-Coupez, J .; Gue´guen, M.; Guerchais, J . E.; Pe´tillon, F.
Y.; Talarmin, J .; Mercier, R. J . Organomet. Chem. 1986, 312, 81.
(15) (a) Evans, J . J . Am. Chem. Soc. 1960, 2003. (b) Grant, D. H. J .
Chem. Educ. 1995, 72, 39.

Highly Electrophilic Binuclear Cations
Organometallics, Vol. 23, No. 16, 2004 3953
Sch em e 2. Sp on ta n eou s Evolu tion in Solu tion of
th e P a r a m a gn etic Com p lexes 3 a n d 4
Ch a r t 2
these radicals is very low, especially for the tungsten
derivative, and their solutions cannot be handled at
room temperature even briefly. Second, the spontaneous
evolution of these solutions is different from that of the
dppm derivatives just discussed. The dimolybdenum
radical 3c evolves to give a mixture of products which
could not be identified, while the tungsten derivative
4c evolves rapidly by hydrogen abstraction (possibly
from traces of water present or even from the solvent)
to give the hydride complex [W2Cp2(µ-H)(CO)4(µ-tedip)]-
(BAr′4) (6) as the major product. In a separate experi-
ment, we have verified that addition of water to a
freshly prepared solution of 4c gives this hydride
complex more rapidly, in higher yield. This reaction thus
suggests that the unpaired electron density in 4c is
mainly located at the dimetal center, in strong contrast
with the case for the 31-electron complex [W2Cp2(µ-CO)-
(CO)2(µ-dppm)](BAr′4). The latter cation abstracts hy-
drogen from water (Scheme 2) to give the hydroxycar-
byne [W2Cp2(µ-COH)(CO)2(µ-dppm)](BAr′4),19 a behavior
suggesting significant delocalization of the unpaired
electron density on the π orbitals involving the bridging
CO ligand.2
In contrast, the dppm derivatives experience facile
decarbonylation at room temperature. We have previ-
ously shown that the ditungsten compound 4a decar-
bonylates spontaneously to give the 31-electron radical
[W2Cp2(µ-CO)(CO)2(µ-dppm)](BAr′4).2 We have now found
that its dimolybdenum analogue 3a experiences double
decarbonylation at room temperature to give the 29-
electron dicarbonyl [Mo2Cp2(µ-CO)2(µ-dppm)](BAr′4) (5),
with a formal intermetallic bond order of 3.5 according
to the EAN rule (Chart 1). The IR spectrum of cation 5
in CH2Cl2 exhibits two bands in the CO stretching
region with relative intensities (Table 1) indicative of a
trans arrangement.16 In fact, this spectrum is quite
similar to that for the dicarbonyl complex [W2Cp2-
(µ-CO)2(µ-dppm)],6,17 but shifted ca. 50 cm-1 to higher
frequencies, as expected due to reduction of the electron
density at the dimetallic center. The X-ray structure of
the neutral complex showed the presence of type II
linear semibridging carbonyls, in terms of the structural
classification of semibridging carbonyls proposed by
Crabtree and Lavin.18 Except for the metal-metal
distance, the geometry of radical 5 should then be very
similar to that for [W2Cp2(µ-CO)2(µ-dppm)]. To our
knowledge, compound 5 is the first carbonyl complex
with an intermetallic formal bond order of 3.5. Unfor-
tunately, all attempts to obtain compound 5 as a pure
crystalline material were unsuccessful, due to the
progressive decomposition of its solutions during ma-
nipulation, crystallization, etc.
IR and NMR data for complex 6 (Table 1 and
Experimental Section) indicate a close structural rela-
tionship with the cations [Mo2Cp2(µ-H)(CO)4(µ-dppm)]+ 20
and [W2Cp2(µ-H)(CO)4(µ-L2)]+ (L2 ) dppm, dmpm),21
previously prepared by us. The structures in solution
for these hydrides, which typically exist in solution as
a mixture of syn and anti isomers, have been extensively
discussed and thus need no further comment. We note
only that the 31P{1H} NMR data for 6 reveal also the
existence of both anti (122.9 ppm) and syn (118 ppm)
isomers20,21 (assigned on the basis of their relative
chemical shifts) (Chart 2). This is also verified by the
1
appearance of two triplet hydride resonances in the H
NMR spectra, at -21.76 ppm (J HP ) 35 Hz) for the syn
isomer and -23.39 ppm (J HP ) 37 Hz) for the anti
isomer. The remarkable aspect of the process leading
to complex 6 is that this hydride species could not be
obtained by the conventional route: that is, by direct
protonation of the neutral substrate [W2Cp2(CO)4-
(µ-tedip)].7 Thus, the “radical route” is currently the only
synthetic way to this diphosphite-bridged hydride com-
plex.
The tedip-bridged radicals 3c and 4c behave in quite
a different way with respect to their diphosphine-
bridged analogues. In the first place, the stability of
In summary, we have found that the chemical behav-
ior of the paramagnetic cations 3 and 4 is strongly
(19) Alvarez, M. A.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.; Robert, F.
Organometallics 2002, 21, 1177.
(16) Braterman, P. S. Metal Carbonyl Spectra; Academic Press:
London, 1975.
(17) Alvarez, M. A.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.; Bois, C.;
J eannin, Y. J . Am. Chem. Soc. 1993, 115, 3786.
(18) Crabtree, R. H.; Lavin, M. Inorg. Chem. 1986, 25, 805.
(20) Riera, V.; Ruiz, M. A.; Villafan˜e, F. Organometallics 1992, 11,
2854.
(21) (a) Alvarez, M. A.; Bois, C.; Garc´ıa, M. E.; Riera, V.; Ruiz, M.
A. Angew. Chem., Int. Ed. Engl. 1996, 35, 102. (b) Alvarez, M. A.;
Garc´ıa, M. E.; Riera, V.; Ruiz, M. A. Organometallics 1999, 18, 634.

3954 Organometallics, Vol. 23, No. 16, 2004
Alvarez et al.
Ch a r t 3
Ch a r t 5
directly responsible for the implied phosphine oxidation,
this being caused instead by the action of NO2 (gener-
ated in situ through the rapid oxidation of NO by traces
of O2 present). Indeed, reaction of 7b with NO2 gives
selectively 10, while 9 failed to react with NO2. Thus,
we conclude that complex 10 is formed from 7b, through
a degradation process involving oxygen atom transfer
from NO2 to one of the phosphorus atoms of the
diphosphine. This behavior of NO2 as an oxygen atom
transfer reagent has been reported before.23
Ch a r t 4
Reactions of radicals 3c and 4b with NO were car-
ried out at low temperature. The tedip-bridged sub-
strate gave the corresponding tetracarbonyl derivative
[Mo2Cp2(CO)4(NO)(µ-tedip)](BAr′4) (7c) as a single prod-
uct, while the ditungsten radical gave the analogous
species [W2Cp2(CO)4(NO)(µ-dmpm)](BAr′4) (8), along
with a small amount of the mononuclear dicarbonyl
compound [WCp(CO)2(κ2-OPMe2CH2PMe2)](BAr′4) (12).
In a separate experiment we have verified that the
molybdenum tricarbonyl complex 10 loses a CO mol-
ecule in refluxing toluene to give the similar chelate
compound [MoCp(CO)2(κ2-OPMe2CH2PMe2)](BAr′4) (11),
isostructural with 12 (Chart 4). It is thus quite unlikely
that the hypothetical tricarbonyl compound [WCp(CO)3-
{κ1-Me2PCH2P(O)Me2}](BAr′4) (analogous to 10) is ever
formed, as it should be more resistant to decarbonyla-
tion (to yield dicarbonyl 12) than its molybdenum
analogue. Instead, it seems that mononuclear tricarbo-
nyls and dicarbonyls arise from different degradation
processes.
The origin of the binuclear tricarbonyl complex 9,
formally a CO-loss product of tetracarbonyl 7b, is not
obvious, either. In fact, decarbonylation of compound 7b
does not occur in refluxing toluene but is only ac-
complished under UV light irradiation. From this we
conclude that tetracarbonyl 7b is not a precursor of
tricarbonyl 9 in the reactions of radical 3b with NO,
even at room temperature. As a result, we assume that
there must be a reaction pathway involving decarbony-
lation of radical 3b prior to its reaction with NO. We
must also note that decarbonylation is not an easy
process either for the tedip-bridged tetracarbonyl 7c or
the ditungsten nitrosyl 8. In fact, no reaction is observed
in refluxing toluene solutions of the above complexes,
whereas UV photolysis leads to a generalized decom-
position of the Mo compound and degradation to the
mononuclear cation [WCp(CO)2(κ2-dmpm)](BAr′4) (13)
for the ditungsten substrate (Chart 5).
dependent on the nature of the bridging phosphorus
ligands and, to a lesser extent, on the metal. Those
radicals having the tetraethylpyrophosphite bridge are
the most reactive, and the ditungsten complex experi-
ences spontaneous capture of a hydrogen atom to give
the corresponding hydride-bridged derivative. The dppm-
bridged radicals experience spontaneous single (W) or
double (Mo) decarbonylation to give highly unsaturated
31- and 29-electron derivatives (Scheme 2). Finally,
those radicals with the strongest donor and least bulky
ligand (dmpm) are the most stable ones and can stand
in dichloromethane solutions at room temperature over
a few hours without noticeable decomposition.
Rea ction s of Ra d ica ls 3 a n d 4 tow a r d NO. As
expected, radicals 3 and 4 are very reactive toward NO,
even at low temperature. Although we have used diluted
NO (5% in dinitrogen) in order to achieve a better
control of the reaction, not all of these reactions led to
stable binuclear products. Reactions of the dppm de-
rivatives (3a and 4a ) as well as the tungsten complex
4c produced highly unstable species that would decom-
pose even at low temperature to give complex mixtures
of products. In contrast, when NO (5%) was gently
bubbled through a dichloromethane solution of 3b at
room temperature, a mixture of the nitrosyl complexes
[Mo2Cp2(CO)4(NO)(µ-dmpm)](BAr′4) (7b) and [Mo2Cp2-
(µ-CO)(CO)2(NO)(µ-dmpm)](BAr′4) (9) was formed rap-
idly (Chart 3), with their relative amounts being some-
what dependent on experimental conditions such as
concentration of the radical solution and gas flux.
Control of these conditions was also important in order
to minimize the formation of the mononuclear species
[MoCp(CO)2(NO)],22 formed as a side product in all these
reactions. Attempts to improve the selectivity of the
above reaction were unsuccessful. For example, reaction
of NO with 3b at -60 °C gave lower yields of 7b and 9
because of the formation of the mononuclear tricarbonyl
[MoCp(CO)3{κ1-Me2PCH2P(O)Me2}](BAr′4) (10) as an
additional side product (Chart 4). We have verified
through some separate experiments that oxygen is not
Str u ctu r al Ch ar acter ization of Com pou n ds 7-13.
IR and NMR spectroscopic data for compounds 7b,c and
8 allow us to establish that they are isostructural with
(23) (a) Feltham, R. D.; Kriege, J . C. J . Am. Chem. Soc. 1979, 101,
5064. (b) Bhaduri, S. A.; Bratt, I.; J ohnson, B. F. G.; Khair, A.; Segal,
J . A.; Walters, R. J . Chem. Soc., Dalton Trans. 1981, 234. (c) Grundy,
K. R.; Laing, K. R.; Roper, W. R. J . Chem. Soc., Chem. Commun. 1970,
1500.
(22) Seddon, D.; Kita, W. G.; Bray, J .; McCleverty, J . A. Inorg. Synth.
1976, 16, 24.

Highly Electrophilic Binuclear Cations
Organometallics, Vol. 23, No. 16, 2004 3955
each other and give full support to the structure
proposed for them (Chart 3). Frequencies and relative
intensities of the bands in the IR spectra (Table 1) are
indicative of a terminal coordination of the carbonyl16
and nitrosyl24 ligands. The presence of a “Mo(CO)3”
fragment follows from comparison with the IR spectra
of the related mononuclear cations [(η5-C5R5)Mo(CO)3L]+
(R ) H, Me; L ) PPh3, P(OMe)3, P(OEt)3).25 The
arrangement of the carbonyl ligands is further con-
firmed in the 13C{1H} NMR spectra, which exhibit two
distinct resonances for the inequivalent cyclopentadi-
enyl ligands and four doublet resonances in the region
of terminal carbonyls. The 31P{1H} NMR spectra further
confirm the strong differences in the chemical environ-
ments around the inequivalent metal centers. This is
dramatically illustrated by the value of the 183W-31P
couplings in the ditungsten complex 8, where the metal
atom bearing the NO ligand exhibits a P-W coupling
of 467 Hz, to be compared with a value of just 176 Hz
for the metal atom with the higher coordination number.
The IR spectrum of compound 9 exhibits just two
bands in the region of terminal C-O stretches with
relative intensities characteristic of cis-M(CO)2 oscilla-
tors, a further band at 1746 cm-1, indicative of the
presence of a bridging CO ligand, and a fourth band at
1651 cm-1 in the usual region for N-O stretches of
terminal nitrosyl ligands. In agreement with this, the
carbonyl groups give rise to three distinct 13C reso-
nances, one of them very deshielded (δ 287.1 ppm), as
expected for a bridging carbonyl. Other resonances
1). We note finally that the 31P-183W coupling of 280
Hz in compound 12 is considerably higher than expected
for a four-legged pianoo-stool geometry (for example,
J PW ) 176 Hz for compound 8). We interpret this as an
indication of the weak donor efficiency of the oxygen
atom of the diphosphine monoxide. The hemilability of
chelated diphosphine monoxides is not unusual, and it
actually makes these molecules relevant ligands in
homogeneous catalysis.26b
Rea ctivity of Dim olybd en u m Ra d ica ls 3a ,b to-
w a r d Liga n d s Ha vin g E-H Bon d s (E ) O, S, N, P ).
As we have stated in the Introduction, the reactivity of
binuclear organometallic radicals has been relatively
little explored to date. From the extensive studies
carried out on mononuclear complexes, it could be
anticipated that binuclear radicals should also react
with ligands bearing E-H bonds (E ) O, S, N, P) by
experiencing either H atom or E fragment abstraction.8
Preliminary experiments showed that the ditungsten
radical 4b was deceptively unreactive toward these
types of molecules. The diphosphine-bridged molybde-
num radicals 3a ,b, however, did react with these simple
molecules, although the products formed were found to
be strongly dependent on both the incoming molecule
and the bridging diphosphine, as discussed below.
Rea ction s w ith P HP h 2 a n d NH2(p-tol). Com-
pounds 3a ,b react with stoichiometric amounts of
PHPh2 to give a mixture of compounds which could not
be characterized. All attempts at separation or purifica-
tion of these products lead to their decomposition. A
similar result was obtained in the reaction of 3b with
NH2(p-tol). In contrast with this, reaction of the dppm-
bridged radical 3a with NH2(p-tol) gives the mono-
nuclear complex [MoCp{NH2(p-tol)}(CO)(κ2-dppm)](BAr′4)
(14) as the major product (Chart 5), along with small
amounts of the hydride [Mo2Cp2(µ-H)(CO)4(µ-dppm)]-
(BAr′4) (15a ), which probably results from hydrogen
abstraction from the amine molecule. Characterization
of the mononuclear cation 14 is straightforward on the
basis of its IR and NMR data (Table 1 and Experi-
mental Section), and by comparison with the corre-
sponding data of the related complex [MoCp(CO)-
(NCMe)(κ2-dppm)](BF4).27
Spectroscopic data for compound 15a indicate that the
cation is identical with that present in the tetrafluo-
roborate salt [Mo2Cp2(µ-H)(CO)4(µ-dppm)](BF4).20 There
is, however, a significant difference to be noted. While
the BF4- salt of this hydride complex exists in solution
as an equilibrium mixture of syn and anti isomers
(Chart 2), compound 15a exists in solution exclusively
as the anti isomer. Thus, it is concluded that anion/
cation interactions (expected to be essentially absent in
the case of 15a ) are relevant in order to determine the
thermodynamic stability of the possible isomers in these
binuclear cations.
Rea ction s w ith H2O a n d MeOH. Compound 3a
reacts with an excess of water to give a mixture of the
hydroxo derivatives [Mo2Cp2(µ-OH)(CO)2(µ-dppm)](BAr′4)
(16) and [Mo2Cp2(µ-H)(µ-OH)(CO)2(µ-dppm)](BAr′4)(OH)
(17) (Chart 6). In a separate experiment we have
verified that 16 reacts with water to yield the hydride
complex 17. This suggests that complex 16 is the initial
1
present in the H and 13C NMR spectra are in agree-
ment with the asymmetric structure proposed for this
cation (Chart 3).
The structural characterization of the mononuclear
cations 10-13 is quite straightforward on the basis of
their IR and NMR spectra (Table 1 and Experimental
Section). The tricarbonyl complex 10 exhibits an IR
spectrum similar to that of the “M(CO)3” fragment in
complex 7b. The presence of a monooxidized dmpm
ligand coordinated through just a single phosphorus
atom is clearly indicated by the 31P NMR spectrum,
which exhibits two doublets, one of them (δ 38.2 ppm)
appearing at a chemical shift close to those of free
alkylphosphine oxides.26 The vacant site generated by
removal of CO in tricarbonyl 10 is occupied by the
oxygen atom of the monooxidized diphosphine, thus
generating a stable five-membered chelate ring (Chart
4). The retention of this oxygen atom after decarbony-
lation of 10 is supported by the mass spectrum of
compound 11, which exhibits the expected parent peak
at m/z 371. Finally, coordination of this oxygen atom to
the metal is derived by comparison of the 31P spectra of
compounds 11 and 12, which exhibit similar shifts for
the O-bonded P atoms (ca. 90 ppm), while the metal-
bonded P atoms exhibit a chemical shift substantially
higher when bound to Mo instead of W atoms (Table
(24) Richter-Addo, G. B.; Legzdins, P. Metal Nitrosyls; Oxford
University Press: Oxford, U.K., 1992.
(25) (a) Leoni, P.; Aquilini, E.; Pasquali, M.; Marchetti, F. J . Chem.
Soc., Dalton Trans. 1988, 329. (b) Gibson, D. H.; Owens, K.; Ong, T.-
S. J . Am. Chem. Soc. 1984, 106, 1125. (c) Gibson, D. H.; Owens, K.;
Mandal, S. K.; Sattich, W. E.; Franco, J . O. Organometallics 1989, 8,
498.
(26) (a) Tebby, J . C. In Phosphorus-31 NMR Spectroscopy in Ster-
eochemical Analysis; Verkade, J . G., Quin, L. D., Eds.; VCH: Wein-
heim, Germany, 1987; Chapter 1. (b) Grushin, V. V. Chem. Rev. 2004,
104, 1629.
(27) Riera, V.; Ruiz, M. A.; Villafan˜e, F.; Bois, C.; J eannin, Y. J .
Organomet. Chem. 1990, 382, 407.

3956 Organometallics, Vol. 23, No. 16, 2004
Alvarez et al.
Ch a r t 6
cis/trans nomenclature used here corresponds to the
relative position of the thiolate and diphosphine bridges).
The exact composition of the above mixture was found
to be substantially dependent on the experimental
conditions. Thus, the use of a large excess of SHPh led
to tricarbonyl 18a as the major product, while the use
of stoichiometric amounts of thiol caused a significant
increase of the dicarbonyl products 19 and 20. An
increase of the 20/19 ratio was also observed when using
an excess of reagent, which is due to partial protonation
of 19 by the thiol, as shown by separate experiments.
IR monitoring of the reaction with excess thiol revealed
the rapid formation of the intermediate A, which then
evolves to the tricarbonyl 18a finally isolated. This
intermediate species exhibits high-frequency C-O bands
(2024 (m), 1930 (s) and 1881 (m) cm-1) and gives no
detectable resonance in the 31P NMR spectrum; there-
fore, it is assumed to be a paramagnetic intermediate
having terminal CO and SHPh ligands (see later). In
an attempt to obtain dicarbonyl 19 in a more selective
way, we carried out the reaction of dicarbonyl radical 5
with an excess of SHPh. Surprisingly, the expected
dicarbonyl 19 is still formed along with some tricarbonyl
18b, which suggests that partial decomposition of some
of the reaction intermediates occurs under these experi-
mental conditions.
product formed, which would result from loss of two
CO ligands in 3a (to give dicarbonyl 5) followed by
rapid addition of an OH radical to the dimetallic cen-
ter. In agreement with this, we have found that radi-
cal 5 reacts with water to give the same mixture of
hydroxo derivatives. The dipositive hydride complex 17
could not be isolated as a pure solid from the above
mixtures, while chromatography of these mixtures on
alumina led to their deprotonation to yield 16. How-
ever, this hydride cation could be easily identified
by comparison of its IR and 31P NMR signals with those
of the mixed salts having BAr′4 and BF4 (17′) or
I- (17′′) counterions. These products could be ob-
tained quantitatively by reacting compound 16 with
HBF4.Et2O or I2, respectively, thus paralleling the
chemical behavior of the isoelectronic phosphide-bridged
ditungsten complexes [W2Cp2(µ-PR2)(CO)2(µ-dppm)]-
(BAr′4).5 Hydroxo compounds 16 and 17 are closely
related to the thiolate complexes 19 and 20, respectively
(Chart 6); therefore, their structures will be discussed
later.
Radical 3a also reacts with MeOH, but in this case a
mixture of products was obtained which could not be
separated. As for the dmpm-bridged radical 3b, no
reaction was observed with either H2O or MeOH at
room temperature. These results suggest that tetracar-
bonyl radicals 3a ,b are not reactive enough to cleave
the relatively strong O-H bonds of water or alcohols,
this being accomplished in the dppm substrate only
after decarbonylation. Thiols have comparatively weaker
S-H bonds, and indeed they react more readily with
both the dppm- and dmpm-bridged radicals 3a ,b, as
discussed next.
The influence of the diphosphine bridge on the reac-
tion products is significant. This is illustrated by the
observation that the dmpm-bridged radical 3b reacts
with SHPh to give the tricarbonyl cis-[Mo2Cp2(µ-SPh)-
(µ-CO)(CO)2(µ-dmpm)](BAr′4) (18b ), along with small
amounts of the H-abstraction product [Mo2Cp2(µ-H)-
(CO)4(µ-dmpm)](BAr′4) (15b), a tetracarbonyl hydride
complex similar to compounds 6 and 15c. Although we
have not isolated this minor compound, analysis of its
IR spectrum and of the corresponding NMR data (Table
1 and Experimental Section) allow us to establish that
this hydride complex is isostructural with compounds
[Mo2Cp2(µ-H)(CO)4(µ-dppm)](BF4)20 and [W2Cp2(µ-H)-
(CO)4(µ-dmpm)](BF4),21b previously prepared in our
laboratory through protonation of the corresponding
neutral precursors. As found for these hydride com-
plexes, compound 15b also exists in solution as a
mixture of syn and anti isomers (Chart 2). The struc-
tures and spectroscopic characterization of these types
of isomers have been discussed previously in detail and
thus need no further comment.20,21b
-
-
It is interesting to remark that reactions of radicals
3a ,b with thiophenol involve the incorporation of the
bridging thiolate specifically in a cis position with
respect to the bridging diphosphine. Isomerization to
the trans isomers is possible in some cases, but only
under photochemical conditions. Thus, UV-visible light
irradiation of tricarbonyls 18a ,b in THF gives in good
yield the corresponding isomers trans-[Mo2Cp2(µ-SPh)-
(µ-CO)(CO)2(µ-L2)](BAr′4) (L2 ) dppm (21a ), dmpm
(21b)). This result strongly contrasts with that of the
related compounds cis- and trans-[W2Cp2(µ-SPh)(µ-CO)-
(CO)2(µ-dppm)](BAr′4), which could not be intercon-
verted by either heating or irradiating with UV-vis-
ible light.5 In any case, we note that the trans iso-
mers 21 are thermally unstable and progressively revert
to the cis isomers in solution at room temperature
(Scheme 3).
Rea ction s w ith Th iols. When a slight excess of
SHPh is added to a solution of 3a , a mixture of the
thiolate derivatives cis-[Mo2Cp2(µ-SPh)(µ-CO)(CO)2-
(µ-dppm)](BAr′4)
(18a ),
cis-[Mo2Cp2(µ-SPh)(CO)2-
(µ-dppm)](BAr′4) (19), and cis-[Mo2Cp2(µ-H)(µ-SPh)-
(CO)2(µ-dppm)](BAr′4)(SPh) (20) is obtained (the

Highly Electrophilic Binuclear Cations
Organometallics, Vol. 23, No. 16, 2004 3957
electron-precise species.28 The formation of unsaturated
species such as cations 19 and 20 at room temperature
is thus remarkable and can be attributed to the high
reactivity of organometallic radicals compared to that
of diamagnetic species. Finally, we should also note that
the hydride complexes 17, 20, and 23 belong to a quite
scarce family of organometallic complexes displaying a
bridging hydride across a molybdenum-molybdenum
double bond. In fact, we can only quote two other 32-
electron dimolybdenum hydrides, these being the anion
[Mo2(µ-H)2(CO)8]2- and the phosphide-bridged cation
[Mo2Cp2(µ-H)(µ-PPh2)2(CO)2]+.29
Sch em e 3. Ch em ica l Rela tion sh ip s betw een th e
Th iola te Com p lexes 18-23a
St r u ct u r a l Ch a r a ct er iza t ion of Com p ou n d s
16-23. Analysis of the IR and NMR data for the
tricarbonyl complexes 18 (cis isomers) and 21 (trans
isomers) reveals that these cations are isostructural
with the ditungsten compounds [W2Cp2(µ-X)(µ-CO)-
(CO)2(µ-dppm)](BAr′4) (X ) I,2 SPh5), which also exhibit
cis and trans isomers. The structure and spectroscopic
properties of the latter complexes have been discussed
in detail previously and thus need no further comments.
We note only that the general trend observed for the
a
Terminal CO and Cp ligands are omitted for clarity; P-P
) dmpm, dppm.
31P shifts exhibited for the dppm-bridged cations (δ(Pcis
)
Prolonged photolysis of the dmpm-bridged tricarbonyl
21b causes its progressive decomposition. In contrast,
the dppm-bridged 21a still loses a CO molecule to yield
the dicarbonyl trans-[Mo2Cp2(µ-SPh)(CO)2(µ-dppm)]-
(BAr′4) (22). As expected, this unsaturated species reacts
with CO rapidly to give almost quantitatively the
electron-precise tricarbonyl complex 21a . Compound 22
is an unstable molecule, and in solution at room
temperature it progressively transforms into its cis
isomer 19 (rapidly upon attempts at chromatography
on alumina). Surprisingly, the cis isomer is not particu-
larly reactive, as it does not react with CO or experience
any isomerization under UV-visible irradiation.
Although formally unsaturated and cationic, dicar-
bonyls 19 and 22 are electron-rich species. As stated
above, compound 19 reacts with excess SHPh to give
20. In fact, an equilibrium mixture of 19 and 20 is
obtained in this way, due to the relatively weak acid
strength of thiol. As expected, complete protonation is
accomplished by using a strong acid such as HBF4‚OEt2.
Thus, compounds 19 and 22 react quantitatively with
HBF4‚OEt2 to give the corresponding hydrides cis-
[Mo2Cp2(µ-H)(µ-SPh)(CO)2(µ-dppm)](BAr′4)(BF4) (20′) and
trans-[Mo2Cp2(µ-H)(µ-SPh)(CO)2(µ-dppm)](BAr′4)(BF4)
(23), respectively. This means that proton addition to
the metal-metal bond in these substrates occurs with
retention of the relative position of the bridging ligands.
In contrast with this, deprotonation of hydrides 20′ and
23 with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) gives
in both cases the cis isomer 19 (the most stable form).
A similar behavior has been observed during the depro-
tonation process of the related trans phosphide hydride
complexes [W2Cp2(µ-H)(µ-PR2)(CO)2(µ-dppm)](BAr′4)2 (R
) Ph, Cy) with DBU.5 There we could prove that
reaction with DBU was not a simple deprotonation
process but, rather, an unexpected reduction followed
by a dehydrogenation/isomerization reaction to yield
finally the cis “deprotonated” isomer. All transforma-
tions relating the thiolate derivatives 18-23 are sum-
marized in Scheme 3. Although a large number of
thiolate-bridged dimolybdenum cyclopentadienyl com-
plexes have been described so far, most of them are
> δ(Ptrans)) does not hold for the dmpm derivatives 18b
and 21b (Table 1).
All dicarbonyl complexes exhibit a similar pattern for
their C-O stretching bands (strong and weak, in order
of decreasing frequency; Table 1), this being indicative
of CO ligands arranged almost parallel with each
other.16 The hydride-hydroxo or hydride-thiolate com-
plexes 17, 20, and 23 are isostructural with the cis and
trans isomers of the ditungsten phosphide complexes
[W2Cp2(µ-H)(µ-PR2)(CO)2(µ-dppm)](BAr′4)2.5 For the lat-
ter we have found that the cis isomers give rise to an
hydride resonance appearing at a quite unusually high
field (ca. +3 ppm), which we have attributed to the high
magnetic anisotropy of the double metal-metal bond.
Complexes 17′ and 20′ exhibit very deshielded hydride
resonances at 6.10 (t, J PH ) 4 Hz) and 5.70 ppm (t, J PH
) 4 Hz) and are thus identified as cis isomers. This
implies a relative arrangement of the hydride ligand
trans to the diphosphine bridge, in agreement with the
low P-H coupling measured. In contrast, complex 23
gives rise to a hydride resonance at -3.33 ppm (t, J PH
) 4 Hz) and is thus identified as a trans isomer. This
implies a relative arrangement of the hydrido ligand cis
to the diphosphine bridge, which should yield a P-H
coupling close to 20 Hz, rather than the low value
measured for this complex. We have found previously
this effect in the mentioned ditungsten complexes,
which seems to be mainly due to ion pairing between
the hydride and the BF4- anion.5 Ion pairing effects are
obviously present in our hydroxo and thiolate hydrides,
as revealed, for example, by the differences in the
-
hydride chemical shifts between compounds 17′ (BF4
salt, δ 6.10 ppm) and 17′′ (I- salt, δ 4.52 ppm).
The green deprotonated products 16 and 19 are
isostructural with the ditungsten phosphide complexes
cis-[W2Cp2(µ-PR2)(CO)2(µ-dppm)](BAr′4) and share with
them similar spectroscopic properties. In contrast, the
(28) Pe´tillon, F. Y.; Schollhammer, P.; Talarmin, J .; Muir, K. W.
Coord. Chem. Rev. 1998, 178-180, 203.
(29) (a) Lin, J . T.; Hagen, G. P.; Ellis, J . E. J . Am. Chem. Soc. 1983,
105, 2296. (b) Adatia, T.; McPartlin, M.; Mays, M. J .; Morris, M. J .;
Raithby, P. R. J . Chem. Soc., Dalton Trans. 1989, 1555.

3958 Organometallics, Vol. 23, No. 16, 2004
Alvarez et al.
Sch em e 4. Rea ction P a th w a ys in th e Rea ction s of
Dim olybd en u m Ra d ica ls 3a ,b w ith H2O a n d
Th iop h en ola
F igu r e 1. Schematic projections of the structures proposed
for the conformers present in the solutions of dicarbonyl
19 along the intermetallic bond (Cp ligands and organic
residues on P atoms omitted for clarity).
trans isomer 22 has no phosphide-bridged equivalent.
Complex 22 is characterized by lower C-O stretching
bands than its cis isomer, as found for tricarbonyls 21
and 18. Although two conformers are possible for all
these thiolate compounds, just a single conformer is
detected by NMR in each case, with the exception of the
cis isomer 19, which exists in solution as a mixture of
two conformers having slightly different NMR proper-
ties but identical ν(CO) bands. These conformers are
present in the relative amounts 3:1, and they are
thought to arise from the two possible arrangements of
the phenyl group of the thiolate bridge with respect to
the bridging diphosphine (labeled endo and exo in
Figure 1).
The presence of the hydroxo bridge in complex 16 is
1
denoted by a relatively shielded H NMR resonance at
ca. 0.7 ppm. This chemical shift, somewhat dependent
upon the concentration of the solution and other ex-
perimental conditions, falls in a region similar to that
found for other hydroxo-bridged organometallic com-
plexes such as, for example, the dimanganese hydride
[Mn2(µ-H)(µ-OH)(CO)6(µ-dppm)] (δ -1.4 ppm)30 and the
dimolybdenum cations [Mo2Cp2(µ-OH)(µ-SMe)3]+ (δ -1.1
ppm).31 In contrast, the hydroxo ligand in the dipositive
cations 17 exhibits a considerably more deshielded
resonance, located at 6.33 ppm for the iodide salt 17′′.
This resonance could not be located in the BF4- salt 17′,
it being possibly hidden by the phenyl resonances of the
complex. The implied changes in chemical shifts denote
the presence of significant interactions of the external
anion not only with the hydride ligand, as stated above,
but also with the hydroxo group. It is interesting to
compare the hydride and hydroxo proton shifts for 17′
and for the electron-precise dipositive cation [Mo2Cp2-
(µ-η5:η5-C10H4)(µ-H)(µ-OH)](PF6)2,32 perhaps the only
comparable hydride-hydroxo dimolybdenum complex
previously described. While the hydroxo resonance for
the latter fulvalene complex (δ 7.23 ppm) displays a
similar chemical shift, the hydride resonance (δ -11.15
ppm) appears in the “normal” hydride region and lacks
then the unusual deshielding observed for 17′ (δ 6.10
ppm). This is again considered to be further evidence
of the strong deshielding effect that double metal-metal
bonds can exert on bridging hydrides in these unsatur-
ated complexes.
a
Cp ligands are omitted for clarity; P-P ) dmpm, dppm;
M ) Mo; E-H ) H2O, SHPh.
mainly to dicarbonyl or tricarbonyl derivatives and are
strongly dependent on the bridging diphosphine present
in the starting material. The results obtained can be
rationalized by assuming the operation of two main
reaction pathways, as depicted in Scheme 4. The route
to tetra- or tricarbonyl derivatives would be rapidly
initiated by direct reaction of radicals 3a ,b with the
molecule H-E (water or thiol), to give the tetracarbonyl
intermediate A. This is presumably the intermediate
species detected by IR spectroscopy in the reaction of
3a with SHPh. This species could then experience two
processes, either the extrusion of an SPh group (possibly
as S2Ph2, minor pathway) to give the hydride 15b or
dehydrogenation to yield the second intermediate B (not
detected). Our data, however, do not allow us to exclude
the direct H-abstraction reaction from SHPh as a
possible route leading to hydride 15b. Intermediate B
could in turn evolve in two different ways, either by
Rea ction P a th w a ys in th e F or m a tion of Com -
p ou n d s 16-20. As discussed in the preceding sections,
the reactions of radicals 3a ,b with water and thiols lead
(30) Garc´ıa Alonso, F. J .; Garc´ıa Sanz, M.; Riera, V. J . Organomet.
Chem. 1991, 421, C12.
(31) Schollhammer, P.; Le He´nanf, M.; Le Roy-Le Floch, C.; Pe´tillon,
F. Y.; Talarmin, J .; Muir, K. W. Dalton 2001, 1573.
(32) (a) Berry, M.; Cooper, J .; Green, M. L. H.; Simpson, S. J . J .
Chem. Soc., Dalton Trans. 1980, 29. (b) Calhorda, M. J .; Carrondo, M.
A. A. F.; Dias, A. R.; Felix, V.; Galvao, A. M.; Garcia, M. H.; Matias, P.
M.; Villa de Brito, M. J . J . Organomet. Chem. 1993, 453, 231.

Highly Electrophilic Binuclear Cations
Organometallics, Vol. 23, No. 16, 2004 3959
rearrangement of the E group into a bridging position
(not observed) or through decarbonylation followed by
rearrangement to the bridging mode, thus yielding
tricarbonyls 18a ,b.
cals are quite reactive toward simple ligands having
E-H bonds (E ) O, S, N, P). H atom abstraction is not
a prevalent process for these radicals. Instead, two main
reaction pathways seem to be operative in the reactions
with H2O or thiols, one of them leading to the tricar-
bonyl derivatives [Mo2Cp2(µ-SR)(µ-CO)(CO)2(µ-L2)](BAr′4)
and the second one (thought to involve the 29-electron
dicarbonyl [Mo2Cp2(µ-CO)2(µ-dppm)](BAr′4)) leading to
unsaturated [Mo2Cp2(µ-E)(CO)2(µ-dppm)](BAr′4) deriva-
tives (E ) OH, SPh). The latter are basic enough to be
partially protonated by the reagent in excess to give the
hydride derivatives [Mo2Cp2(µ-H)(µ-E)(CO)2(µ-L2)](BAr′4)-
(E). All these reactions are stereospecific, as the corre-
sponding products are generated exclusively with the
bridging E group occupying a position cis relative to the
diphosphine ligand.
In summary, we have shown that it should be possible
to achieve a fine-tuning of the reactivity of binuclear
organometallic radicals by proper adjustment of the
steric and electronic properties of the bridging ligands.
For example, the reactions of these paramagnetic
complexes with simple molecules having E-H bonds
could be directed specifically so as to generate either
new M-E or M-H bonds.
The formation of dicarbonyl products is only observed
for the dppm derivatives and is thus proposed to be
initiated by the slow decarbonylation of 3a to give
dicarbonyl 5, which then would react with H-E to give
(after some rearrangements) dicarbonyls 16 and 19. Due
to the presence of an excess of H-E, these unsaturated
species would be partially protonated, as denoted by
separate experiments. In this way, the formation of
mixtures 16/17 and 19/20 is thus explained. This
reaction pathway is not available for the dmpm deriva-
tives (because radical 3b does not evolve CO at room
temperature) and is also the dominant route when E )
OH. Moreover, we note that the slow step in this
reaction pathway would be the formation of dicarbonyl
5, thus yielding a rate roughly independent of the
concentration of thiol, whereas the formation of inter-
mediate A is expected to be first order in the concentra-
tion of reagent. This explains the prevalent formation
of tricarbonyl 18a at large thiol concentration.
To gain further understanding of the elements gov-
erning the above reaction pathways, we carried out
reactions of radicals 3a ,b with a slightly bulkier thiol,
2-methylbenzenethiol. Surprisingly, both 3a and 3b
react with this thiol to give the corresponding tricarbo-
nyl thiolate complexes of type 18, but no dicarbonyl
compounds. This gives indirect support to the proposal
that dicarbonyl 5 is the main species responsible for the
formation of dicarbonyls 19. Were the presence of thiol
critical in the pathway to the dicarbonyl complexes,
their relative amount in the final mixtures should have
been increased when using the bulkier thiol, as the
latter would have favored the necessary decarbonylation
steps.
Exp er im en ta l Section
Gen er a l Com m en ts. All reactions were carried out under
an atmosphere of nitrogen. Solvents were purified according
to standard procedures33 and distilled under nitrogen prior to
use. Petroleum ether refers to that fraction distilling in the
range 65-70 °C. The compounds [Mo2Cp2(CO)4(µ-dppm)],20
[M2Cp2(CO)4(µ-tedip)] (M ) Mo, W),7 [W2Cp2(CO)4(µ-L2)] (L2
) dppm, dmpm),6 [FeCp2]BAr′4,34 and [Mo2Cp2(CO)4]35 were
prepared according to the literature procedures. All other
reagents were purchased from the usual commercial suppliers
and used as received. Low-temperature reactions and photo-
chemical experiments were performed using jacketed Schlenk
tubes, refrigerated by a closed 2-propanol circuit kept at the
desired temperature with a cryostat, or by tap water. Filtra-
tions were carried out using dry diatomaceous earth under
nitrogen. Low-temperature chromatographic separations were
carried out analogously using jacketed columns. Aluminum
oxide (alumina, activity I, 150 mesh, from Aldrich) 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.
NMR spectra were recorded at 300.13 (1H), 121.50 (31P{1H}),
or 75.47 MHz (13C{1H}) in CD2Cl2 at room temperature, unless
otherwise indicated. Chemical shifts (δ) are given in ppm,
relative to internal TMS (1H, 13C) or external 85% H3PO4
aqueous solution (31P), with positive values for frequencies
higher than that of the reference. Coupling constants (J ) are
given in hertz. 13C{1H} NMR spectra were routinely recorded
on solutions containing a small amount of tris(acetylaceto-
nato)chromium(III) as a relaxation reagent.
Con clu d in g Rem a r k s. By using the inert and non-
coordinating BAr′4- anion as a counterion, the new 33-
electron organometallic radicals [M2Cp2(µ-CO)2(CO)2-
(µ-L2)](BAr′4) can be synthesized as products of moder-
ate to low stability, the latter following the order M )
Mo > W and L2 ) dmpm > dppm > tedip. The reactivity
of these paramagnetic cations is strongly modulated by
the nature of the bridging phosphorus ligand and, to a
lesser extent, by the metal. Thus, an increase in the
electron-withdrawing power of that ligand (dmpm <
dppm < tedip) seems to favor H-atom capture processes
by the radical. On the other hand, an increase in the
steric demands of that ligand (dmpm < tedip < dppm)
clearly favors the spontaneous decarbonylation of these
radicals, and this is also easier for molybdenum than
for tungsten compounds, as found in diamagnetic car-
bonyl complexes. In this way, the observation that the
dppm-bridged radicals experience spontaneous decar-
bonylation at room temperature to cleanly give 31-elec-
tron [W2Cp2(µ-CO)(CO)2(µ-dppm)](BAr′4) or 29-electron
[Mo2Cp2(µ-CO)2(µ-dppm)](BAr′4) derivatives is thus jus-
tified.
Syn th esis of [Mo2Cp 2(CO)4(µ-d m p m )] (1b). This proce-
dure represents a modification of a method previously reported
for this complex,12 which gives enhanced yields. dmpm (0.157
mL, 1 mmol) was added slowly to a diglyme solution (25 mL)
containing [Mo2Cp2(CO)4] (ca. 0.434 g, 1 mmol) at 0 °C, and
the mixture was stirred for 20 min at room temperature. The
resulting red solution was filtered, using dichloromethane (3
The tetracarbonyl radicals can be trapped by NO to
give stable binuclear nitrosyl derivatives of the type
[M2Cp2(CO)4(NO)(µ-L2)](BAr′4), which cannot be ob-
tained from conventional (diamagnetic) precursors. In
addition, the diphosphine-bridged dimolybdenum radi-
(33) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals; Pergamon Press: Oxford, U.K., 1988.
(34) Cha´vez, I.; Alvarez-Carena, A.; Molins, E.; Roig, A.; Maniuk-
iewicz, W.; Arancibia, A.; Arancibia, V.; Brand, H.; Manr´ıquez, J . M.
J . Organomet. Chem. 2000, 601, 126.
(35) Curtis, M. D.; Hay, M. S. Inorg. Synth. 1990, 28, 152.

3960 Organometallics, Vol. 23, No. 16, 2004
Alvarez et al.
× 10 mL) to remove any product retained in the filtration pad,
and the filtrate was then evaporated under vacuum until ca.
25 mL. Addition of petroleum ether (30 mL) and crystallization
at -20 °C for 24 h gave compound 1b as dark red crystals,
which were separated from the solution, washed with petro-
leum ether, and dried under vacuum (0.322 g, 66%). The
mother liquor was chromatographed on alumina (activity II,
10 × 2.5 cm) at -10 °C. Elution with dichloromethane/
petroleum ether gave a rose and then a red fraction. Removal
of solvents from the latter gave an additional 0.088 g (18%) of
compound 1b as a red microcrystalline powder (overall yield
84%).
P r ep a r a tion of Solu tion s of [Mo2Cp 2(µ-CO)2(CO)2-
(µ-d p p m )](BAr ′4) (3a ). Compound 1a (0.035 g, 0.043 mmol)
was added slowly to a well-stirred CH2Cl2 solution (8 mL) of
[FeCp2](BAr′4) (0.045 g, 0.043 mmol) to give instantaneously
a green brownish solution containing virtually pure compound
3a . This compound is unstable and experiences spontaneous
decarbonylation in solution at room temperature to give
compound 5.
P r ep a r a tion of [Mo2Cp 2(µ-CO)2(CO)2(µ-d m p m )](BAr ′4)
(3b). Compound 1b (0.035 g, 0.061 mmol) was added slowly
to a well-stirred CH2Cl2 solution (8 mL) of [FeCp2](BAr′4)
(0.064 g, 0.061 mmol) to give instantaneously a green solution
containing virtually pure compound 3b, which was filtered.
Solvent was then removed under vacuum from the filtrate, and
the residue was washed with petroleum ether (3 × 10 mL) to
give compound 3b as a dark green microcrystalline powder
(0.078 g, 90%). The crystals used in the X-ray study were
grown by slow diffusion of a concentrated dichloromethane
solution of the complex into a layer of petroleum ether. Anal.
Calcd for C53H40BCl4F24Mo2O4P2 (3b‚2CH2Cl2): C, 39.70; H,
2.51. Found: C, 39.72; H, 2.49. µeff (CD2Cl2, Evans method):
1.1 µB.
P r ep a r a tion of Solu tion s of [Mo2Cp 2(µ-CO)2(CO)2-
(µ-ted ip )](BAr ′4) (3c). Compound 1c (0.035 g, 0.051 mmol)
was added slowly to a well-stirred CH2Cl2 solution (8 mL) of
[FeCp2](BAr′4) (0.053 g, 0.051 mmol) at -20 °C to give almost
instantaneously a green solution containing compound 3c as
the major species. This compound is quite unstable and decom-
poses in solution within a few minutes at room temperature.
P r ep a r a tion of Solu tion s of [W2Cp 2(µ-CO)2(CO)2-
(µ-d m p m )](BAr ′4) (4b). Compound 2b (0.035 g, 0.047 mmol)
was added slowly to a well-stirred CH2Cl2 solution (8 mL) of
[FeCp2](BAr′4) (0.049 g, 0.047 mmol) to give instantaneously
a green solution containing virtually pure compound 4b.
Attempts to isolate this compound as a crystalline material
led to its progressive decomposition.
P r ep a r a tion of [Mo2Cp 2(µ-CO)2(µ-d p p m )](BAr ′4) (5). A
dichloromethane solution (8 mL) of compound 3a (ca 0.050 g,
0.030 mmol), prepared in situ as described above, was stirred
at 15 °C for 90 min, while nitrogen was bubbled through the
solution gently. The brown resulting solution was then filtered.
Solvent was then removed from the filtrate under vacuum to
give a brown residue, which was washed with petroleum ether
(2 × 10 mL) and dried under vacuum to give 0.034 g (0.035 g,
70%) of compound 5 as a brown solid. All attempts to further
purify this air-sensitive product resulted in its progressive
decomposition.
P r ep a r a tion of [W2Cp 2(µ-H)(CO)4(µ-ted ip )](BAr ′4) (6).
Compound 2c (0.044 g, 0.051 mmol) was slowly added to a
well-stirred CH2Cl2 solution (8 mL) of [FeCp2](BAr′4) (0.053
g, 0.051 mmol) at 0 °C. Water (4 µL, 0.222 mmol) was
immediately added, and the mixture was stirred at room
temperature, whereby the solution rapidly changed from green
to brown to give a mixture containing 6 as the major product,
along with smaller quantities of other unidentified species.
Solvent was then removed from the solution, and the residue
was chromatographed on alumina (activity IV, 10 × 2.5 cm)
at -20 °C. Elution with dichloromethane/petroleum ether
(1:4) gave a yellow fraction containing ferrocene. Elution with
dichloromethane/petroleum ether (4:1) gave an orange fraction
containing syn and anti isomers of compound 6 in an 1:4 ratio.
Removal of solvents yielded compound 6 as an orange solid
(0.026 g, 30%). Anal. Calcd for C54H43BF24O9P2W2: C, 37.44;
H, 2.50. Found: C, 37.26; H, 2.45. 1H NMR: δ 7.73 (s, 8H,
Ar′), 7.56 (s, 4H, Ar′), 5.56 (s, 8H, Cp, isomer anti), 5.32 (s,
2H, Cp, isomer syn), 4.19-3.84 (m, 8H, OCH2), 1.47-1.31 (m,
12H, Me), -21.76 (t, J HP ) 35, 0.2H, µ-H, isomer syn), -23.39
(t, J HP ) 37, J HW ) 42, 0.8H, µ-H, isomer anti).
Rea ction of Com p ou n d 3b w ith NO. Nitrogen monoxide
(5% in N2) was gently bubbled through a dichloromethane
solution (8 mL) of compound 3b (0.057 g, 0.040 mmol) for 5
min, whereupon the color of the solution changed from green
to orange. Solvent was then removed from the solution, and
the residue was chromatographed on an alumina column
(activity IV, 10 × 2.5 cm) at -20 °C. Elution with dichlo-
romethane/petroleum ether (1:4) gave a yellow fraction con-
taining ferrocene and [MoCp(CO)2(NO)]. Elution with dichlo-
romethane/petroleum ether (2:3) gave an orange fraction
containing variable amounts (ca. 0.015 g, 20-30%) of the
reasonably pure compound [Mo2Cp2(µ-CO)(CO)2(NO)(µ-dmpm)]-
(BAr′4) (9). Attempts at crystallization of this crude product
resulted in its progressive decomposition. Another orange
fraction was eluted with dichloromethane, from which
variable amounts (ca. 0.020 g, 30-40%) of the compound
[Mo2Cp2(CO)4(NO)(µ-dmpm)](BAr′4) (7b) were obtained by
removal of solvents under vacuum. Spectroscopic data for 9
are as follows. 1H NMR (200.13 MHz): δ 7.74 (s, 8H, Ar′), 7.59
(s, 4H, Ar′), 5.51 (d, J HP ) 1, 5H, Cp), 5.32 (d, J HP ) 1, 5H,
Cp), 2.59 (dt, J HH ) 14, J HP ) 11, 1H, CH2), 1.83 (d, J HP ) 8,
3H, Me), 1.76 (d, J HP ) 9, 3H, Me), 1.74 (d, J HP ) 8, 3H, Me),
1.71 (d, J HP ) 9, 3H, Me). The resonance of the second
methylenic proton was obscured by those of methyl groups.
13C{1H} NMR (100.61 MHz, 213 K): δ 287.1 (s, µ-CO), 237.6
(d, J CP ) 20, CO), 221.6 (d, J CP ) 23, CO), 162.1 (q, J CB ) 50,
i-C(Ar′)), 135.0 (s, o-C(Ar′)), 128.9 (q, J CF ) 32, m-C(Ar′)), 124.8
(q, J CF ) 272, CF3), 117.9 (s, p-C(Ar′)), 102.8, 95.8 (2 × s, 2 ×
Cp), 33.0 (t, J CP ) 28, CH2), 22.4-17.3 (m, 4 × Me). Data for
7b are as follows. Anal. Calcd for C51H36BF24Mo2NO5P2: C,
1
41.86; H, 2.48; N, 0.96. Found: C, 41.67; H, 2.39; N, 0.98. H
NMR (200.13 MHz): δ 7.73 (s, 8H, Ar′), 7.58 (s, 4H, Ar′), 5.68
(d, J HP ) 1, 5H, Cp), 5.44 (d, J HP ) 1, 5H, Cp), 2.53, 2.28 (2 ×
m, 2 × 1H, CH2), 2.12 (d, J HP ) 10, 3H, Me), 2.09 (d, J HP ) 10,
3H, Me), 1.75 (d, J HP ) 8, 3H, Me), 1.58 (d, J HP ) 7, 3H, Me).
13C{1H} NMR: δ 242.8 (d, J CP ) 11, CO), 224.9 (d, J CP ) 6,
CO), 224.5 (d, J CP ) 6, CO), 223.5 (d, J CP ) 5, CO), 162.2 (q,
J CB ) 50, i-C(Ar′)), 135.3 (s, o-C(Ar′)), 129.3 (q, J CF ) 32,
m-C(Ar′)), 125.1 (q, J CF ) 272, CF3), 118.0 (s, p-C(Ar′)), 94.5,
93.5 (2 × s, 2 × Cp), 39.5 (d, J CP ) 26, CH2), 24.6 (d, J CP
)
26, Me), 24.5 (d, J CP ) 27, Me), 19.1, 19.0 (2 × d, J CP ) 33, 2
× Me).
P r ep a r a tion of [Mo2Cp 2(CO)4(NO)(µ-ted ip )](BAr ′4) (7c).
Nitrogen monoxide (5% in N2) was gently bubbled through a
freshly prepared dichloromethane solution (8 mL) of compound
3c (0.053 g, 0.034 mmol) at -60 °C for 5 min, whereupon the
color of the solution changed from green to orange. Solvent
was then removed from the solution, and the residue was
chromatographed on an alumina column (activity IV, 10 × 2.5
cm) at -20 °C. Elution with dichloromethane/petroleum
ether (1:4) gave an orange fraction containing ferrocene and
[MoCp(CO)2(NO)]. Elution with dichloromethane/petroleum
ether (3:2) gave an orange fraction. Removal of solvents
from the latter under vacuum yielded compound 7c as an
orange microcrystalline powder (0.042 g, 78%). Anal. Calcd for
C
54H42BF24Mo2NO10P2: C, 40.91; H, 2.67; N, 0.88. Found: C,
1
40.63; H, 2.52; N, 0.91. H NMR: δ 7.72 (s, 8H, Ar′), 7.57 (s,
4H, Ar′), 5.75, 5.53 (2 × s, 2 × 5H, Cp), 4.21, 4.03 (2 × m, 2 ×
4H, OCH2), 1.41, 1.40, 1.35, 1.33 (4 × t, J HH ) 7, 4 × 3H, Me).
13C{1H} NMR (100.61 MHz): δ 237.8 (d, J CP ) 17, CO), 224.4
(d, J CP ) 4, CO), 223.2 (d, J CP ) 3, CO), 222.8 (d, J CP ) 3,
CO), 162.5 (q, J CB ) 50, i-C(Ar′)), 135.5 (s, o-C(Ar′)), 129.6 (q,

Highly Electrophilic Binuclear Cations
Organometallics, Vol. 23, No. 16, 2004 3961
J CF ) 32, m-C(Ar′)), 125.3 (q, J CF ) 272, CF3), 118.2 (s,
p-C(Ar′)), 94.9, 93.7 (2 × s, 2 × Cp), 67.2, 67.1 (2 × d, J CP ) 9,
2 × OCH2), 64.3 (s, 2 × OCH2), 16.6 (d, J CP ) 6, 2 × Me), 16.2
(d, J CP ) 7, 2 × Me).
(8 mL) of compound 3a (0.051 g, 0.030 mmol), and the mixture
was stirred for 30 min to give a brown solution containing
compounds 14 and 15a (ca. 3:1). Solvent was then removed
from the solution, and the residue was chromatographed on
an alumina column (activity IV, 10 × 2.5 cm) at -10 °C.
Elution with dichloromethane/petroleum ether (1:4) gave a
yellow fraction containing small quantities of unidentified
species. Elution with dichloromethane/petroleum ether
(3:2) gave an orange fraction containing the hydride complex
15a . This product was not isolated, due to the small amount
obtained, but could be identified spectroscopically from solution
data. Another orange fraction was eluted with dichloromethane.
Removal of solvents from the latter and washing of the residue
with petroleum ether gave compound 14 as an orange powder
(0.030 g, 64%). Data for 14 are as follows. Anal. Calcd for
C70H48BF24MoNOP2: C, 54.46; H, 3.13; N, 0.91. Found: C,
Rea ction of Com p ou n d 4b w ith NO. Nitrogen monoxide
(5% in N2) was gently bubbled through a dichloromethane
solution (8 mL) of compound 4b (0.076 g, 0.047 mmol) at -70
°C for 5 min, whereupon the color of the solution changed from
green to orange. The IR and 31P{1H} NMR spectra of the
reaction mixture indicated the presence of the compound
[W2Cp2(CO)4(NO)(µ-dmpm)](BAr′4) (8) as the major product,
along with small amounts of the complex [WCp(CO)2-
(κ2-Me2PCH2P(O)Me2)](BAr′4) (12). Workup as described for 7c
yielded compound 8 (0.062 g, 81%) as a yellow microcrystalline
solid. Compound 12 decomposed during chromatography and
could not be isolated from the reaction mixture. Data for 8
are as follows. Anal. Calcd for C51H36BF24NO5P2W2: C, 37.37;
1
54.30; H, 3.01; N, 0.95. H NMR: δ 7.73 (s, 8H, Ar′), 7.55 (s,
1
4H, Ar′), 7.52-7.20 (m, 20H, Ph), 7.03 (m, 4H, C6H4), 4.92 (d,
J HP ) 3, 5H, Cp), 4.66, 4.50 (ABMX, 2 × m, 2H, CH2), 4.03
(dd, J HH ) 11, J HP ) 5, 1H, NH2), 3.74 (br d, J HH ) 11, 1H,
H, 2.21; N, 0.85. Found: C, 37.40; H, 2.22; N, 0.86. H NMR:
δ 7.72 (s, 8H, Ar′), 7.57 (s, 4H, Ar′), 5.82 (d, J HP ) 0.4, 5H,
Cp), 5.52 (d, J HP ) 1, 5H, Cp), 2.76 (m, ABMX, J HH ) 15, J HP
) 9, 1H, CH2), 2.52 (m, ABMX, J HH ) 15, J HP ) 9, 1H, CH2),
2.23 (d, J HP ) 10, 3H, Me), 2.22 (d, J HP ) 11, 3H, Me), 1.90 (d,
J HP ) 8, 3H, Me), 1.74 (d, J HP ) 7, 3H, Me). 13C{1H} NMR: δ
1
NH2), 2.25 (s, 3H, Me). Data for 15a are as follows. H NMR:
δ 7.73 (s, 8H, Ar′), 7.56 (s, 4H, Ar′), 7.46-6.98 (m, 20H, Ph),
4.97 (s, 10H, Cp), 3.73 (td, J HP ) 11, J HH ) 2, 2H, CH2), -18.58
(tt, J HP ) 34, J HH ) 2, 1H, µ-H).
235.7 (d, J CP ) 3, CO), 214.8 (d, J CP ) 5, CO), 214.5 (d, J CP
)
5, CO), 210.7 (d, J CP ) 4, CO), 162.5 (q, J CB ) 50, i-C(Ar′)),
135.6 (s, o-C(Ar′)), 129.6 (q, J CF ) 32, m-C(Ar′)), 125.4 (q, J CF
) 272, CF3), 118.3 (s, p-C(Ar′)), 93.3, 92.1 (2 × s, 2 × Cp), 39.8
(d, J CP ) 28, CH2), 25.9 (d, J CP ) 31, Me), 25.4 (d, J CP ) 34,
Me), 19.3 (d, J CP ) 36, 2 × Me).
P r epar ation of Solu tion s of [MoCp(CO)3{K1-Me2P CH2P -
(O)Me2}](BAr ′4) (10). A dichloromethane solution (8 mL) of
compound 7b (0.030 g, 0.020 mmol) was transferred to a
Schlenk tube containing NO2 and NO (prepared “in situ” by
mixing NO with air). After 5 min of stirring the color of the
solution changed from orange to yellow, due to the formation
of compound 10 as the major product. This complex could not
be isolated as a pure solid, and the corresponding spectroscopic
data were obtained from the filtered reaction mixtures. 1H
NMR: δ 7.72 (s, 8H, Ar′), 7.57 (s, 4H, Ar′), 5.77 (s, 5H, Cp),
2.38 (t, J HP ) 11, 2H, CH2), 2.07 (d, J HP ) 11, 6H, Me), 1.65
(d, J HP ) 13, 6H, Me).
P r epar ation of [MoCp(CO)2(K2-OP Me2CH2P Me2)](BAr ′4)
(11). A toluene solution (5 mL) of the crude mixture containing
compound 10 (generated as described above) was refluxed for
30 min, and the solvent was removed under vacuum. The
residue was then dissolved in dichloromethane and chromato-
graphed on alumina (activity IV, 10 × 2.5 cm) at -10 °C. After
washing of the column with petroleum ether, elution with
dichloromethane gave an orange fraction. Removal of solvents
from the latter under vacuum yielded compound 11 (0.018 g,
72%) as an orange microcrystalline powder. Anal. Calcd for
C
44H31BF24MoO3P2: C, 42.88; H, 2.54. Found: C, 42.60; H,
2.35. MS (electrospray; m/z): 371 [M]+, 343 [M - CO]+, 315
[M - 2CO]+. H NMR (200.13 MHz): δ 7.73 (s, 8H, Ar′), 7.57
1
(s, 4H, Ar′), 5.54 (s, 5H, Cp), 3.54 (m, 1H, CH2), 2.19 (dd, J HP
) 10, 9, 1H, CH2), 2.08 (d, J HP ) 9, 3H, Me), 1.86 (d, J HP ) 8,
3H, Me), 1.68 (d, J HP ) 13, 3H, Me), 1.51 (d, J HP ) 12, 3H,
Me).
P h otoch em ica l Decom p osition of Com p ou n d 8. A tet-
rahydrofuran solution (5 mL) of compound 8 (0.045 g, 0.027
mmol) was irradiated with UV-visible light at 15 °C for 5 min.
The resulting brown solution was filtered and the solvent
removed from the filtrate under vacuum. The residue was
washed with petroleum ether (2 × 5 mL) and dried under
vacuum to give compound 13 (0.011 g, 30%) as a brown solid.
1H NMR: δ 7.72 (s, 8H, Ar′), 7.57 (s, 4H, Ar′), 5.55 (s, 5H,
P reparation of cis-[Mo2Cp2(µ-SP h)(µ-CO)(CO)2(µ-dppm)]-
(BAr ′4) (18a ). A large excess of SHPh (33 µL, 7.5 mmol) was
added to a CH2Cl2 solution (8 mL) of compound 3a (0.051 g,
0.030 mmol), and the mixture was stirred for 3 h to give a
brown solution. The solvent was removed under vacuumm, and
the residue was then dissolved in dichloromethane and the
solution chromatographed on an alumina column (activity IV,
10 × 2.5 cm) at -10 °C. After washing of the column with
petroleum ether, elution with dichloromethane/petroleum
ether (3:2) gave an orange fraction. Removal of solvents from
the latter under vacuum yielded compound 18a (0.047 g, 89%)
as a brownish orange microcrystalline powder. Anal. Calcd for
Cp), 4.39 (dt, J HH ) 15, J HP ) 11, 1H, CH2), 3.97 (dt, J HH
)
15, J HP ) 11, 1H, CH2), 1.92, 1.84 (2 × false t, A3A′3XX′, |J HP
+ J HP′|) 11, 2 × 6H, Me).
R ea ct ion of Com p ou n d 3a w it h NH2(p -t ol). Solid
NH2(p-tol) (0.005 g, 0.04 mmol) was added to a CH2Cl2 solution
C
76H49BF24Mo2O3P2S: C, 51.78; H, 2.80. Found: C, 51.70; H,

3962 Organometallics, Vol. 23, No. 16, 2004
Alvarez et al.
1
2.63. H NMR (200.13 MHz): δ 7.72 (s, 8H, Ar′), 7.56 (s, 4H,
solution changed instantaneously to green. The sol-
vent was then removed under vacuum and the residue
washed with Et2O/petroleum ether (1:3; 3 × 10 mL) to give
compound 20′ (0.045 g, 92%) as a green solid. Anal. Calcd for
Ar′), 7.48-7.11 (m, 25H, Ph), 4.75 (s, 10H, Cp), 4.06 (dt, J HH
) 13, J HP ) 11, 1H, CH2), 2.97 (dt, J HH ) 13, J HP ) 10, 1H,
CH2).
Preparation of cis-[Mo2Cp2(µ-SPh)(µ-CO)(CO)2(µ-dmpm)]-
(BAr ′4) (18b). An excess of SHPh (50 µL, 7.9 mmol) was added
to a CH2Cl2 solution (8 mL) of compound 3b (0.057 g, 0.040
mmol), and the mixture was stirred for 70 min to give a brown
solution. Workup as for 18a (elution with dichloromethane/
petroleum ether (2:1)) yielded compound 18b (0.051 g, 85%)
as a brown microcrystalline powder. Elution with dichlo-
romethane gave an orange fraction containing small amounts
(<5%) of compound 15b, which was not isolated. Data for 18b
are as follows. Anal. Calcd for C56H41BF24Mo2O3P2S: C, 44.41;
H, 2.73. Found: C, 44.60; H, 2.69. 1H NMR: δ 7.73 (s, 8H,
Ar′), 7.57 (s, 4H, Ar′), 7.57-7.13 (m, 5H, Ph), 4.88
(s, 10H, Cp), 2.36 (dt, J HH ) 14, J HP ) 11, 1H, CH2), 1.68,
1.62 (2 × false t, A3A′3XX′, |J HP + J HP′| ) 6, 2 × 6H, Me), 1.21
(dt, J HH ) 14, J HP ) 11, 1H, CH2). Data for 15b are as fol-
lows. 1H NMR (200 MHz): anti isomer, δ 5.44 (s, 10H, Cp),
2.44 (td, J HP ) 10, J HH ) 1.5, 2H, CH2), 1.69 (m, A3A′3XX′,
|J HP + J HP′|) 8.5, 12H, Me), -19.71(tt, J HP ) 32, J HH ) 1.5,
1H, µ-H; syn isomer, δ 5.39 (s, 10H, Cp), 1.61 (m, A3A′3XX′,
|J HP + J HP′|) 8, 6H, Me), -17.45(td, J HP ) 30, J HH ) 2.5, 1H,
µ-H), other resonances for this isomer were obscured by those
from the major isomer. anti:syn ) 3.
C
75H50B2F28Mo2O2P2S: C, 49.42; H, 2.77. Found: C, 49.09; H,
2.53. 1H NMR: δ 7.73 (s, 8H, Ar′), 7.56 (s, 4H, Ar′), 7.47-7.10
(m, 25H, Ph), 5.70 (t, J HP ) 4, 1H, µ-H), 5.50 (false t, |J HP
J HP′| ) 2.2, 10H, Cp), 4.06 (m, 2H, CH2).
+
P r ep a r a tion of Solu tion s of tr a n s-[Mo2Cp 2(µ-SP h )-
(µ-CO)(CO)2(µ-d p p m )](BAr ′4) (21a ). A tetrahydrofuran solu-
tion (5 mL) of compound 18a (0.030 g, 0.017 mmol) was
irradiated with UV-visible light at 15 °C for 15 min. The
resulting orange solution contains compound 21a as the major
product. This complex could not be isolated as a pure material,
due to its progressive isomerization to the starting compound
18a .
P r ep a r a tion of Solu tion s of tr a n s-[Mo2Cp 2(µ-SP h )-
(µ-CO)(CO)2(µ-d m p m )](BAr ′4) (21b). A tetrahydrofuran so-
lution (8 mL) of compound 18b (0.025 g, 0.017 mmol) was
irradiated with UV-visible light at 15 °C for 10 min. Solvent
was then removed from the resulting brown solution, and the
residue was washed with petroleum ether to give an orange
solid containing essentially pure compound 21b. All attempts
to further purify this product led to its progressive isomeriza-
1
tion to the starting compound 18b. H NMR (200.13 MHz): δ
7.72 (s, 8H, Ar′), 7.57 (s, 4H, Ar′), 7.32-7.17 (m, 5H, Ph), 5.25
P h otoch em ica l Deca r bon yla tion of Com p ou n d 18a . A
tetrahydrofuran solution (5 mL) of compound 18a (0.030 g,
0.017 mmol) was irradiated with UV-visible light at 15 °C
for 40 min while gently bubbling nitrogen through the solution.
The resulting orange solution was shown at this point to
contain the compound trans-[Mo2Cp2(µ-SPh)(CO)2(µ-dppm)]-
(BAr′4) (22) as the major product. Workup as for 18a (elution
with dichloromethane/petroleum ether (4:1)) yielded 0.017 g
(57%) of a yellow microcrystalline solid containing two con-
formers (exo and endo) of the compound cis-[Mo2Cp2(µ-SPh)-
(CO)2(µ-dppm)](BAr′4) (19) in a 3:1 ratio. Compound 22 could
not be isolated as a pure solid, and all manipulations led to
its progressive transformation into 19. Data for 19 are as
follows. Anal. Calcd for C75H49BF24Mo2O2P2S: C, 51.92; H,
(false t, |J HP + J HP′| ) 2, 10H, Cp), 2.87 (dt, J HH ) 14, J HP
)
11, 1H, CH2), 1.82 (br m, 1H, CH2), 1.59-1.53 (m, 12H, Me).
Preparation of tra ns-[Mo2Cp2(µ-H)(µ-SPh)(CO)2(µ-dppm)]-
(BAr ′4)(BF 4) (23). A dichloromethane solution (5 mL) of
compound 22 (0.034 g, 0.020 mmol) was treated with HBF4‚
OEt2 (4 µL of a 85% solution in Et2O, 0.034 mmol). The orange
solution changed instantaneously to green. The solvent was
then removed under vacuum and the residue washed with
Et2O/petroleum ether (1:3; 3 × 10 mL) to give compound 23
1
(0.032 g, 91%) as a green solid. H NMR: δ 7.73 (s, 8H, Ar′),
7.56 (s, 4H, Ar′), 7.47-7.10 (m, 25H, Ph), 5.50 (false t, |J HP
+
J HP′| ) 2.2, 10H, Cp), 4.06 (m, 2H, CH2), -3.33 (t, J HP ) 4,
1H, µ-H).
1
2.85. Found: C, 51.81; H, 2.75. H NMR: δ 7.73 (s, 8H, Ar′),
7.56 (s, 4H, Ar′), 7.51-7.02 (m, 25H, Ph), 5.29 (m, AA′XX′,
Ack n ow led gm en t. We thank the Ministerio de
Ciencia y Tecnolog´ıa of Spain for financial support
(Projects BQU2000-0944 and BQU2003-05471) and the
Agencia Espan˜ola de Cooperacio´n Iberoamericana and
FICYT of Asturias (Project GE-EXP-01-09) for grants
to Y.A.
|J HP + J HP′| ) 2.3, Cp, endo conformer), 5.15 (false t, |J HP
+
J HP′| ) 2.3, Cp, exo conformer), 3.50 (m, 2H, CH2, conformers
exo and endo).
P reparation of cis-[Mo2Cp2(µ-H)(µ-SP h)(CO)2(µ-dppm)]-
(BAr ′4)(BF 4) (20′). A dichloromethane solution (5 mL) of
compound 19 (0.047 g, 0.027 mmol) was treated with HBF4‚
OEt2 (4 µL of a 85% solution in Et2O, 0.034 mmol). The yellow
OM049763B