Chemistry of Highly Electrophilic Binuclear Cations. 1. Oxidation Reactions of [M2(γ5-C5H5) 2(CO)4(μ-Ph2PCH2PPh2)] (M = Mo, W) with [FeCp2]X (X = BF4, PF6)

Article abstract of DOI:10.1021/om990135h

Oxidation of the title compounds with 2 equiv of [FeCp₂]BF₄ in dichloromethane leads to the tetracarbonylic fluoro complexes [M₂Cp₂(μ-F)(CO)₄(μ-dppm)]BF₄ in high yields (dppm = Ph₂PCH₂PPh₂). By contrast, the analogous reaction with [FeCp₂]PF₆ gives the tricarbonylic fluoro derivatives [M₂Cp₂(μ-F)(μ-CO)(CO)₂(μ-dppm)]PF ₆. Separate experiments revealed that the latter cations cannot be obtained through decarbonylation of the former fluoro complexes. By carrying out the [FeCp₂]PF₆ oxidations in the presence of halide ions X^- (X = Cl, Br, I), the corresponding halo derivatives [M₂Cp₂(μ-X)(μ-CO)(CO)₂(μ-dppm)]PF ₆ are formed in good yields. All above species are derived from the unsaturated dications [M₂Cp₂(μ-CO)₂(CO) ₂-(μ-dppm)]²⁺, which are the initial products of the removal of two electrons from the title compounds. Despite its high reactivity, the tungsten dication can be isolated as a solid, thanks to its low solubility in dichloromethane, and has been shown to react with other donor molecules such as acetate ions or methanol, to give tricarbonylic derivatives [W₂Cp₂(μ-Y)-(μ-CO)(CO) ₂(μ-dppm)]PF₆ (Y = O₂CMe, OMe), which display structures comparable to those of the corresponding halogeno complexes. The structure of both tungsten fluoro complexes has been determined by X-ray diffraction methods, that on the tetracarbonylic compound revealing the presence of a weak H-bonding interaction between the BF₄^- counterion and a methylenic hydrogen in the diphosphine ligand. The reaction pathways likely operative in the oxidation of the title compounds are analyzed in light of the experimental findings and the critical role played by the BF₄^- or PF₆^- counterions.

Full text of DOI:10.1021/om990135h

Organometallics 1999, 18, 4509-4517
4509
Ch em istr y of High ly Electr op h ilic Bin u clea r Ca tion s. 1.
Oxid a tion Rea ction s of
[M2(η5-C5H5)2(CO)4(µ-P h 2P CH2P P h 2)] (M ) Mo, W) w ith
[F eCp 2]X (X ) BF 4, P F 6)
M. Angeles Alvarez, Gema Garc´ıa, M. Esther Garc´ıa, Victor Riera, and
Miguel A. Ruiz*,†
Departamento Quı´mica Orga´nica e Inorga´nica/ IUQOEM, Universidad de Oviedo,
E-33071 Oviedo, Spain
Maurizio Lanfranchi and Antonio Tiripicchio
Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica,
Centro di Studio per la Strutturistica Diffrattometrica del CNR, Universita` di Parma,
Viale delle Scienze 78, I-43100 Parma, Italy
Received February 24, 1999
Oxidation of the title compounds with 2 equiv of [FeCp2]BF4 in dichloromethane leads to
the tetracarbonylic fluoro complexes [M2Cp2(µ-F)(CO)4(µ-dppm)]BF4 in high yields (dppm )
Ph2PCH2PPh2). By contrast, the analogous reaction with [FeCp2]PF6 gives the tricarbonylic
fluoro derivatives [M2Cp2(µ-F)(µ-CO)(CO)2(µ-dppm)]PF6. Separate experiments revealed that
the latter cations cannot be obtained through decarbonylation of the former fluoro complexes.
By carrying out the [FeCp2]PF6 oxidations in the presence of halide ions X- (X ) Cl, Br, I),
the corresponding halo derivatives [M2Cp2(µ-X)(µ-CO)(CO)2(µ-dppm)]PF6 are formed in good
yields. All above species are derived from the unsaturated dications [M2Cp2(µ-CO)2(CO)2-
(µ-dppm)]2+, which are the initial products of the removal of two electrons from the title
compounds. Despite its high reactivity, the tungsten dication can be isolated as a solid, thanks
to its low solubility in dichloromethane, and has been shown to react with other donor
molecules such as acetate ions or methanol, to give tricarbonylic derivatives [W2Cp2(µ-Y)-
(µ-CO)(CO)2(µ-dppm)]PF6 (Y ) O2CMe, OMe), which display structures comparable to those
of the corresponding halogeno complexes. The structure of both tungsten fluoro complexes
has been determined by X-ray diffraction methods, that on the tetracarbonylic compound
revealing the presence of a weak H-bonding interaction between the BF4- counterion and a
methylenic hydrogen in the diphosphine ligand. The reaction pathways likely operative in
the oxidation of the title compounds are analyzed in light of the experimental findings and
-
-
the critical role played by the BF4 or PF6 counterions.
In tr od u ction
plexes having this chemical behavior are being exten-
sively studied because of their proven or potential
catalytic applications in a number of organic reactions.
For example, there is a large number of mononuclear
transition metal complexes that act as Lewis acid
catalysts in different aldol additions and cycloaddition
reactions.3,4 Perhaps the most prominent example is
provided by the dicyclopentadienyl group 4 metal-alkyl
complexes, which are excellent catalysts for alkene
polymerization.5 The latter process is one of high
Organometallic transition metal dimers with formal
metal-metal bond orders of 2 or higher constitute a very
interesting group of species, mainly due to their high
reactivity toward a great variety of molecules under
mild conditions.1 Electrophilicity is perhaps their most
characteristic property, and this is expected to be
enhanced when the molecule carries a neat positive
charge. Examples of this type of cation are however very
scarce, they being generally synthesized through redox
reactions,2 and their chemistry has been therefore little
explored. Further interest in these species comes from
the fact that they are expected to behave as transition
metal-based Lewis acids. In fact, mononuclear com-
(3) For recent reviews on the subject see for example: (a) Mahrwald,
R. Chem. Rev. 1999, 99, 1095. (b) Nelson, S. G. Tetrahedron: Asym-
metry 1998, 9, 357. (c) Lautens, M.; Klute, W.; Tam, W. Chem. Rev.
1996, 96, 49. (d) Ojima, I.; Tzamarioudaki, M.; Li, Z.; Donovan, R. J .
Chem. Rev. 1996, 96 (6), 635.
(4) For recent work on the subject see for example: (a) Evans, D.
A.; Rovis, T.; Kozlowski, M. C.; Tedrow, J . S. J . Am. Chem. Soc. 1999,
121, 1994. (b) Ku¨ndig, E. P.; Sandan, C. M.; Bernardinelli, G. Angew.
Chem., Int. Ed. Engl. 1999, 38, 1220. (c) Park, D. H.; Kim, S. H.; Kim,
S. M.; Kim, J . D.; Kim, Y. H. J . Chem. Soc., Chem. Commun. 1999,
963. (d) Hollis, T. K.; Robinson, N. P.; Bosnich, B. Organometallics
1992, 11, 2745.
† E-mail: mara@sauron.quimica.uniovi.es.
(1) (a) Curtis, M. D. Polyhedron 1987, 6, 759. (b) Winter, M. J . Adv.
Organomet. Chem. 1989, 29, 101, and references therein.
(2) (a) Connelly, N. G. Chem. Soc. Rev. 1989, 18, 153, and references
therein. (b) Connelly, N. G.; Geiger, W. E. Adv. Organomet. Chem.
1985, 24, 87.
(5) J ordan, R. J . Adv. Organomet. Chem. 1991, 32, 325.
10.1021/om990135h CCC: $18.00 © 1999 American Chemical Society
Publication on Web 10/07/1999

4510 Organometallics, Vol. 18, No. 22, 1999
Alvarez et al.
Sch em e 1. Mech a n ism for th e Oxid a tion
known and “innocent” one-electron-oxidizing species in
organometallic chemistry.15 This cation has been previ-
ously used in the selective oxidation of compounds
containing metal-metal bonds.8,16 Although the men-
tioned counteranions can be classified as “noncoordi-
nating” species, there are however examples where they
can act as ligands.17-19 In fact, our preliminary studies
on the reaction of 1b with [FeCp2]PF6 showed that the
unsaturated species initially formed, [W2Cp2(µ-CO)2-
(CO)2(µ-dppm)][PF6]2 (2b), was able to abstract a fluo-
ride ion from the counterion.20 As will be next discussed,
the oxidation products of compounds 1a ,b are highly
electrophilic and interact in different ways with their
counterions to give fluoro derivatives unless a competi-
tor ligand is present, in which case coordination of the
latter preferentially occurs.
Rea ction s of [M2Cp 2(CO)6] (M ) Mo, W)12
industrial importance, and the search for new types of
complexes displaying improved catalytic performance
still continues.6 Although most of the current research
is concentrated on mononuclear complexes, multiply
bonded binuclear cations meet in principle the require-
ments for this sort of catalytic activity, that is, Lewis
acidity and coordinative unsaturation.3,5,6 As an ex-
ample, the dication [Ru2H2(CO)4(µ-L4)]2+ (L4 ) tetra-
dentate P-donor ligand) has been found to be a good
precatalyst for the hydroformilation of 1-alkenes.7 Thus,
exploring and understanding the chemistry of binuclear
unsaturated cations not only is a matter of academic
interest but also can lead to some useful applications.
Removal of one or more electrons from a singly
metal-metal bonded dimetallic complex is the most
straightforward route for multiply metal-metal bonded
cations. Very often, however, the reactivity of the
product is so high that the system further evolves so as
to reduce the electronic unsaturation generated. Typical
secondary processes are solvent coordination or ligand
rearrangements.8,9 The latter processes can be some-
times avoided by the use of bridging ligands which
increase the stability of the unsaturated cation. This is
the case, for example, of the 33-electron dimers
[W2(µ-PPh2)2(CO)6(PPh2H)2]+ 10 and [Mo2(µ-C5H4PPh2)2-
(CO)4]+,11 where the diphenylphosphido or cyclopenta-
dienyl(diphenyl)phosphine bridging ligands no doubt
play a determinant stabilizing role. The latter complex
is prepared through oxidation of neutral dimer [Mo2(µ-
C5H4PPh2)2(CO)4], but removal of two electrons leads
to decomposition. For comparison, the oxidation of the
unbridged hexacarbonyls [M2Cp2(CO)6] (M ) Mo, W),
studied by electrochemical methods,12 leads to the
disruption of the dimetallic unit even at the monocation
step (Scheme 1).
Resu lts a n d Discu ssion
Oxid a tion of Com p ou n d s 1 w ith [F eCp 2]BF 4.
Compounds 1a ,b react rapidly with 2 equiv of [FeCp2]-
BF4 in dichloromethane at temperatures of ca. -25 °C
to give with good yield the fluoro derivatives [M2Cp2-
(µ-F)(CO)4(µ-dppm)]BF4 (3a ,b). The reaction conditions
are critical. Thus, the use of lower temperatures or 1
equiv of oxidant leads to the formation of the mono-
nuclear cations [MCp(CO)2(dppm)]+. The molybdenum
cation has been previously detected by us,13b and the
tungsten one can be identified by comparison of its IR
and NMR spectra21 with those of the molybdenum
analogue13 and related species.8b,16a,22 On the other
hand, if the reaction on 1a is carried out at room
temperature, we have observed that a mixture of the
corresponding complexes 3a and some tricarbonyl [Mo2-
Cp2(µ-F)(µ-CO)(CO)2(µ-dppm)]PF6 (4a , see later) is ob-
tained. These observations have mechanistic implica-
tions, as will be discussed later on.
The structure of the dichloromethane solvate of the
tungsten compound 3b has been determined by an X-ray
study. A view of structure of 3b is shown in the Figure
1 together with the atom-numbering system. Selected
bond distances and angles are given in Table 2. The
cation is made up of two cis-W(CO)2Cp fragments joined
by symmetrical dppm and fluoride bridges. The local
geometry around each metal atom is of the usual four
legged “piano stool” type. The overall conformation of
the molecule is of the syn type, with the Cp ligands
In this paper we report our full studies on the
chemical oxidation of the dppm-bridged complexes [M2-
Cp2(CO)4(µ-dppm)] (1a ,b) [M ) Mo (a ),13 W (b);14 Cp )
η5-C5H5; dppm ) Ph2PCH2PPh2] using the BF4 and
-
-
PF6 salts of the ferricenium cation [FeCp2]+, a well-
(14) (a) Alvarez, M. A.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.; Bois,
C.; J eannin, Y. J . Am. Chem. Soc. 1993, 115, 3786. (b) Alvarez, M. A.;
Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.; Falvello, L. R.; Bois, C.
Organometallics 1997, 16, 354.
(15) Connelly, N. G.; Geiger, W. E. Chem. Rev. 1996, 96, 877.
(16) (a) Schumann, H. J . Organomet. Chem. 1986, 304, 341. (b)
North, T. E.; Thoden, J . B.; Spencer, B.; Dahl, L. F. Organometallics
1993, 12, 1299.
(6) (a) Gibson, V.; Wass, D. Chem. Br. 1999, 7, 21. (b) J anas, Z.;
J erzykiewicz, L. B.; Richards, R. L.; Sobota, P. J . Chem. Soc., Chem.
Commun. 1999, 1105.
(7) Matthews, R. C.; Howell, D. K.; Peng, W.-J .; Train, S. G.;
Treleaven, W. D.; Stanley, G. G. Angew. Chem., Int. Ed. Engl. 1996,
35, 2253.
(8) (a) Schumann, H. J . Organomet. Chem. 1985, 290, C34. (b)
Schumann, H. J . Organomet. Chem. 1987, 323, 193.
(9) (a) Connelly, N. G.; Forrow, N. J .; Gracey, B. J .; Knox, S. A. R.;
Orpen, A. G. J . Chem. Soc., Chem. Commun. 1985, 14. (b) Ogino, H.;
Tobita, H.; Inomata, S.; Shinoi, M. J . Chem. Soc., Chem. Commun.
1988, 586.
(10) Keiter, R. L.; Keiter, E. A.; Rust, M. S.; Miller, D. R.; Sherman,
E. O.; Cooper, D. E. Organometallics 1992, 11, 487.
(11) Brumas-Soula, B.; de Montauzon, D.; Poilblanc, R. New J .
Chem. 1995, 19, 757.
(12) Kadish, K. M.; Lacombe, D. A.; Anderson, J . E. Inorg. Chem.
1986, 25, 2246.
(13) (a) Riera, V.; Ruiz, M. A.; Villafan˜e, F.; J eannin, Y.; Bois, C. J .
Organomet. Chem. 1988, 345, C4. (b) Riera, V.; Ruiz, M. A.; Villafan˜e,
F. Organometallics 1992, 11, 2854.
(17) (a) Albano, P.; Aresta, M.; Manassero, M. Inorg. Chem. 1980,
19, 1069. (b) Honeychuck, R. V.; Hersh. W. H. Inorg. Chem. 1989, 28,
2869. (c) Hersh, W. H. Inorg. Chem. 1990, 29, 713. (d) Bachmann, M.
Angew. Chem., Int. Ed. Engl. 1992, 31, 1181. (e) Green, J .; Sinn, E.;
Woodward, S.; Butcher, R. Polyhedron 1993, 12, 991.
(18) (a) Strauss, S. H. Chem. Rev. 1993, 93, 927. (b) Seppelt, K.
Angew. Chem., Int. Ed. Engl. 1993, 32, 1025.
(19) Beck, W.; Su¨nkel, K. Chem. Rev. 1988, 88, 1405.
(20) 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.
(21) ν(CO)(CH2Cl2): 1978 (vs), 1915 (s) cm-1
-32.5 (s, J PW ) 206).
.
31P{1H} (CD2Cl2) δ
(22) (a) Treichel, P. M.; Barnett, K. W.; Shubkin, R. L. J . Organomet.
Chem. 1967, 7, 449. (b) Schumann, H.; Enemark, J . H.; Laberre, M.
J .; Bruck, M.; Wexler, P. Polyhedron 1991, 10, 665.

Highly Electrophilic Binuclear Cations
Organometallics, Vol. 18, No. 22, 1999 4511
Ta ble 1. IR a n d 31P {1H} NMR Da ta for New Com p ou n d s
b
c
compd
νst(CO)a/cm-1
δP (J PW
)
J PP
[W2Cp2(µ-CO)2(CO)2(µ-dppm)](PF6)2 (2b)
[Mo2Cp2(µ-F)(CO)4(µ-dppm)]BF4 (3a )
2024 (s), 1980 (w), 1864 (s), 1814 (vs)d
1983 (vs), 1906 (m), 1886 (s)
1973 (vs), 1960 (sh), 1893 (m), 1868 (m)
1980 (vs), 1920 (w), 1726 (s)
1969 (vs), 1907 (w), 1681 (s)
1982 (vs), 1918 (w), 1723 (s)
1973 (vs), 1911 (w), 1678 (m)
1980 (vs), 1905 (w), 1719 (s)
1971 (vs), 1907 (w), 1674 (m)
1980 (vs), 1905 (m), 1714 (m)
1971 (vs), 1908 (w), 1671 (m)
1975 (vs), 1888 (w), 1663 (m)k
1963 (vs), 1896 (w), 1674 (m)
54.3e,f
[W2Cp2(µ-F)(CO)4(µ-dppm)]BF4 (3b)
38.0 (308)g
48.7h
[Mo2Cp2(µ-F)(µ-CO)(CO)2(µ-dppm)]PF6 (4a )
[W2Cp2(µ-F)(µ-CO)(CO)2(µ-dppm)]PF6 (4b)
[Mo2Cp2(µ-Cl)(µ-CO)(CO)2(µ-dppm)]PF6 (5a )
[W2Cp2(µ-Cl)(µ-CO)(CO)2(µ-dppm)]PF6 (5b)
[Mo2Cp2(µ-Br)(µ-CO)(CO)2(µ-dppm)]PF6 (6a )
[W2Cp2(µ-Br)(µ-CO)(CO)2(µ-dppm)]PF6 (6b)
[Mo2Cp2(µ-I)(µ-CO)(CO)2(µ-dppm)]PF6 (7a )
[W2Cp2(µ-I)(µ-CO)(CO)2(µ-dppm)]PF6 (7b)
[W2Cp2(µ-O2CCH3)(µ-CO)(CO)2(µ-dppm)]PF6 (8)
[W2Cp2(µ-OCH3)(µ-CO)(CO)2(µ-dppm)]PF6 (9)
55.1 (257, -59)i,j
99
83
83
46.0e,i
31.1 (214, -17)
45.5i
27.9 (215, -18)e
45.2i
22.3 (218, -18)
37.9 (235, -20)e
39.1 (214, -17)e
80
114
96
a
b
Recorded in CH2Cl2 solution unless otherwise stated. Recorded at 121.50 MHz and 291 K in CD2Cl2 solution, unless otherwise
stated; δ in ppm relative to external 85% aqueous H3PO4; J in hertz. c PP and PW coupling constants are obtained from the 183W “satellite”
lines (see ref 10b). In Nujol mull. νst(PF) 846 (vs, br) cm-1 e Recorded at 81.02 MHz. J PF ) 44 Hz. Recorded at 161.98 MHz, J PF ) 56
.
d
f
g
h
i
j
k
Hz, isomer syn. Recorded at 233 K; J PF ) 22 Hz. Recorded in acetone-d6. J PF ) 29 Hz.
ν
asym(OCO): 1556 (m) cm-1 in CH2Cl2; 1543
(m) cm-1 in Nujol mull.
Ch a r t 1
The six-membered ring formed by the two bridges
with the two W atoms adopts a twist-boat conformation,
with the methylenic carbon on the same side of the
fluoride bridge. The F(5) atom of the tetrafluoborate ion
is involved in three weak interactions with the H(152)
methylenic proton [H(152)‚‚‚F(5) ) 2.50(1) Å], with the
H(21) of a phenyl group [H(21)‚‚‚F(5) ) 2.49(1) Å] and
with the H(14) from a Cp ring [H(14)‚‚‚F(5) ) 2.41(2)
Å]. These interactions, slightly shorter than the sum of
van der Waals radii (2.60 Å),23 could be retained in
solution, as will be discussed next. Although we are not
aware of any previously reported H-bonding interactions
involving the methylenic group of the dppm ligand, we
can quote the complex [Ru2Cp2(µ-CH2)(µ-CO)(CO)-
(CF2dCFCF3)],24 where a significantly shorter H‚‚‚F
separation (2.23 Å) was found between a methylenic
proton and a F atom in the coordinated olefin.
F igu r e 1. ORTEP view of the structure of the complex
3b together with the atomic numbering scheme. The
ellipsoids for the atoms are drawn at the 30% probability
level.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p ou n d 3b
W(2)-F(1)
W(2)-P(2)
W(2)-C(3)
W(2)-C(4)
P(2)-C(15)
2.127(6)
2.489(2)
1.965(11)
1.972(11)
1.857(9)
W(1)-F(1)
W(1)-P(1)
W(1)-C(1)
W(1)-C(2)
P(1)-C(15)
2.125(6)
2.481(2)
1.979(10)
1.940(10)
1.845(10)
Spectroscopic data for compounds 3a ,b indicate that
both species are isostructural and also that the solid-
state structure found for 3b is retained in solution. The
syn geometry of the molecule (Chart 1) is revealed by
the appearance of nonequivalent methylenic protons in
the 1H NMR spectra. For both compounds, the more
shielded methylenic resonance exhibits a large coupling
to the bridging fluoride (4J FH ) 10-13 Hz) and is
significantly broader than the other one. For compari-
P(1)-C(15)-P(2)
P(1)-W(1)-F(1)
P(1)-W(1)-C(2)
F(1)-W(1)-C(1)
C(1)-W(1)-C(2)
120.2(5)
79.8(1)
80.2(3)
86.3(3)
74.9(4)
W(1)-F(1)-W(2)
P(2)-W(2)-F(1)
P(2)-W(2)-C(4)
F(1)-W(2)-C(3)
C(3)-W(2)-C(4)
155.8(3)
77.2(2)
81.0(3)
85.5(4)
74.8(4)
placed on the same side of the average plane defined
by the W and P atoms (Chart 1), as found for the
hydridocomplex [Mo2Cp2(µ-H)(CO)4(µ-dppm)]+.13 On the
basis of the EAN rule, the bond order for the cation in
3b must be 0, in agreement with the long intermetallic
separation of 4.158(1) Å. This allows the fluoride anion
to display a large W-F-W angle of 155.8(3)°. Although
comparable carbonylic fluoro compounds are not avail-
able, the tendency of the fluoride ligand to adopt a linear
bridging mode in classical coordination complexes is
well-known, thus maximizing its donor ability though
π-donation.
4
son, J HF ) 3.7 Hz for the trans ethylimido fluoro
complex [W(F)(NEt)(dppe)2]BF4.25 We interpret the
unusual broadening effect as derived from the presence
in solution of some H-bonding interaction between this
proton and the tetrafluoroborate counterion, as found
(23) Richmond, T. G. Coord. Chem. Rev. 1990, 105, 221.
(24) Howard, J . A. K.; Knox, S. A. R.; Terrill, N. J .; Yates, M. I. J .
Chem. Soc., Chem. Commun. 1989, 640.
(25) Field, L. D.; J ones, N. G.; Turner, P. Organometallics 1998, 17,
2394.

4512 Organometallics, Vol. 18, No. 22, 1999
Alvarez et al.
Ta ble 3. 19F {1H} NMR Da ta for New Com p ou n d s
Sch em e 2. Rea ctivity of Com p ou n d s 2 a s P F 6-
Sa lts
a
δ/ppm (J FP
)
compd
anion
-150.6 (s)
-152.2 (s)
-72.6 (d, J FP ) 715)
-71.7 (d, J FP ) 710)
µ-F
3a
-645.3 (t, 44)
-674.8 (t, 56)b
-480.1 (t, 22)
-523.8 (t, 29)
3b
4a
4bc
a
Measured at 188.30 MHz in CD2Cl2 solutions at 291 K unless
otherwise indicated; chemical shifts relative to CFCl3; coupling
b
constants in hertz. J FW ) 51. c Measured in acetone-d6.
in the solid state. On the other hand, the large F-H
coupling detected is indicative of a strong binding of the
fluorine ligand. This might also contribute to the strong
shielding observed for this ligand in the 19F NMR
spectra of compounds 3. The observed chemical shifts
(ca. -645 and -675 ppm, Table 3) are among the lowest
ones reported for transition metal fluoro complexes.
Compounds 3 are structurally related to the molyb-
denum cations [Mo2Cp2(µ-X)(CO)4(µ-dppm)]+ (X ) H, I),
prepared through reaction of H+ or I2 on compound 1a .13
However, the latter cations display two isomers in
solution (syn and anti, Chart 1). On the basis of the size
and electronegativity of F (as compared with H or I)
there would be no apparent reason for the existence of
a single, syn isomer in the case of fluoro complexes 3.
When examining by 31P NMR spectroscopy at -30 °C
the crude reaction mixture in the case of 3b, we noted,
in addition to the resonance of the final product, the
presence of a doublet at 26.8 ppm (J PF ) 44 Hz, intensity
ca. 10% relative to the main resonance), which irrevers-
ibly disappears on leaving the solution at room temper-
ature for a couple of minutes. In agreement with this,
small changes were also detected in the IR spectra of
the corresponding reaction mixtures. For example, a
crude solution of the tungsten compound, just after
being prepared from 1b and [FeCp2]BF4 at -30 °C,
exhibits just three CO-stretching bands at 1973 (vs),
1892 (m), and 1868 (m) cm-1, but after a few minutes a
fourth band at 1960 (m, sh) cm-1 is clearly appreciated,
while the two bands at lower frequency invert their
relative intensities. We interpret all the above observa-
tions by assuming that the reaction of compounds 1 with
[FeCp2]BF4 initially generates both syn and anti iso-
mers, but the latter rapidly transform into the former
ones. The reason for the higher stability of the syn
isomers for complexes 3 is not clear, but might be due
to a more favorable H-interaction with the tetrafluo-
roborate counterion. As has been discussed for the solid
structure of 3b, the syn geometry allows one of the
methylenic protons to point away from the molecule,
thus facilitating such an interaction. For an anti geom-
etry, however, the NMR data on the above-mentioned
cations [Mo2Cp2(µ-X)(CO)4(µ-dppm)]+ (chemical equiva-
lence of methylenic protons, low couplings to bridging
hydrido atom)13b suggest that both methylenic protons
might be less exposed to the molecular surroundings.
Oxid a tion of Com p ou n d s 1 w ith [F eCp 2]P F 6. The
result of the title reaction has been found to be strongly
dependent not only on experimental conditions but also
on the dimetal substrate. Two equivalents of oxidant is
also required, otherwise the side reaction yielding the
mononuclear cations [MCp(CO)2(dppm)]+ becomes com-
petitive, as found in the oxidations using [FeCp2]BF4.
For this reason, compounds 1 were usually added to a
solution containing the ferricenium cation, so that defect
of oxidant was avoided during reaction. Temperature
is also a critical parameter in the reactions of the
tungsten substrate 1b in dichloromethane using 2 equiv
of oxidant. At low temperatures (ca. -60 °C) the
mononuclear cation is preferentially formed. On the
other hand, when the reaction is carried out at room
temperature, the tricarbonyl fluoro derivative [W2Cp2-
(µ-F)(µ-CO)(CO)2(µ-dppm)] (4b) is obtained in high yield
(we note here that a small amount of tetracarbonylic
3b is detected in the latter reaction when working at
elevated concentrations of reactants). Finally, by work-
ing in the range -20 to -10 °C, clean and nearly
quantitative precipitation of [W2Cp2(µ-CO)2(CO)2-
(µ-dppm)](PF6)2 (2b) occurs. The molybdenum substrate
1a behaves in a similar way, except that the corre-
sponding dication 2a cannot be isolated or even de-
tected.
The unsaturated dication 2b is stable only in the solid
state. It can be stored at -10 °C for several weeks or
handled at room temperature for short periods of time.
However, fast cation-anion reaction occurs in solution
even at low temperatures (for example, acetone at -40
°C) to give cleanly the tricarbonyl fluoro derivate 4b
(Scheme 2). Obviously then, isolation of 2b is possible
just because of its very low solubility in dichloro-
methane. This circumstance is apparently not met for
the dimolybdenum analogue 2a and, hence, our inability
to even detect that complex in the reactions under
discussion. However, the formation of the fluoro complex
4a and related halogeno derivatives (see later) strongly
suggests that cation 2a is also the initial product of the
oxidation of 1a with [FeCp2]PF6.
The structure proposed for compound 2b in just based
-
on its IR spectrum. The latter gives no indication of PF6
interaction with the cation. Thus, a single and strong

Highly Electrophilic Binuclear Cations
Organometallics, Vol. 18, No. 22, 1999 4513
Ch a r t 2
P-F stretch is found at 854 cm-1, as expected for a free
PF6 ion.19 It is known that coordination of this anion,
-
by the lowering of local symmetry implied, causes the
splitting of this band (for example, [MoCp(FPF5)(CO)3]
exhibits P-F stretching bands at 879, 810, and 739
cm-1).19 Moreover, should PF6 coordination to the
-
cation be present in 2b, the νst(CO) bands of the latter
would shift to values comparable to those of the tetra-
carbonylic fluoro derivatives 3, a circumstance not met
either. In fact, the CO stretching bands of 2a are much
higher in frequency than those of 3 or 4, in agreement
with the presence of a higher positive charge in the
molecule. These bands are grouped in two sets, which
we assign to terminal C-O stretches (2024 (s), 1980 (w)
cm-1) and bridging ones (1864 (s), 1814 (vs) cm-1). From
their relative intensities26 it can be deduced that the
terminal carbonyls are almost parallel to each other (as
found for compounds 4), while the bridging CO groups
must define an angle somewhat larger than 90°. The
implied geometry would be then not much different from
the tricarbonylfluoro complex 4b (to be discussed next)
after replacement of fluoride by carbonyl at the bridging
position (Chart 2). From our limited data, however, we
cannot rule out that semibridging carbonyls (instead of
fully bridging ones) might actually be present in com-
pound 2b.
F igu r e 2. ORTEP view of the structure of the complex
4b together with the atomic numbering scheme. The
ellipsoids for the atoms are drawn at the 30% probability
level.
Ta ble 4. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p ou n d 4b
W(1)-W(2)
W(2)-P(2)
W(2)-F(1)
W(2)-C(2)
W(2)-C(3)
P(1)-C(14)
2.945(1)
2.510(3)
2.091(5)
1.953(11)
2.128(11)
1.815(9)
W(1)-P(1)
W(1)-F(1)
W(1)-C(1)
W(1)-C(3)
P(2)-C(14)
2.506(3)
2.107(5)
1.934(11)
2.127(10)
1.821(9)
P(1)-W(1)-F(1)
F(1)-W(1)-C(3)
C(1)-W(1)-C(3)
P(1)-W(1)-C(1)
W(2)-W(1)-P(1)
W(2)-W(1)-F(1)
W(2)-W(1)-C(1)
W(2)-W(1)-C(3)
W(1)-C(3)-W(2)
P(1)-C(14)-P(2)
77.9(1)
73.8(3)
86.3(4)
85.7(3)
90.8(1)
45.2(1)
86.4(4)
46.2(3)
87.6(4)
112.7(5)
P(2)-W(2)-F(1)
F(1)-W(2)-C(3)
C(2)-W(2)-C(3)
P(2)-W(2)-C(2)
W(1)-W(2)-P(2)
W(1)-W(2)-F(1)
W(1)-W(2)-C(2)
W(1)-W(2)-C(3)
W(1)-F(1)-W(2)
82.7(1)
74.1(3)
87.6(4)
83.5(3)
90.7(1)
45.7(1)
93.2(3)
46.2(3)
89.1(2)
The structure of the tricarbonylic fluoro complex 4b
has been determined by an X-ray study. A view of the
structure of the cation of 4b is shown in Figure 2
together with the atom-numbering system. Selected
bond distances and angles are given in Table 4. The
structure of the cation is very similar to that of its
analogous chlorocomplex 5b.20 Apart from the expected
differences in the structural parameters involving the
halide bridge, all other bond distances and angles are
similar, except for the intermetallic distance, which falls
from 3.040(3) Å (for 5b) to 2.945(1) Å (for 4b). These
values are not themselves unusual for cyclopenta-
dienylic cations having single metal-metal bonds (for
rare, so structural comparisons are not possible. In fact,
we are aware of just one other related fluorocarbonylic
complex structurally characterized. In [Mn3(µ2-F)-
(µ3-OEt)2(CO)9] the fluoro ligand bridges two manganese
atoms separated by only 2.829(7) Å (Mn-F-Mn )
93(1)°).29 However, the presence of a metal-metal bond
in this trimetallic 52-valence-electron compound is
doubtful.
The geometry around the tungsten atoms in 4b is of
the “four-legged piano stool” type, with the bridging CO
trans to the dppm bridge and the bridging halide trans
to the terminal carbonyls. The overall structure of the
cation is again of the syn type, so that the terminal
carbonyls are almost parallel to each other. Although
the bridging dppm ligand adopts a nearly eclipsed
conformation, as found for 3b, the methylenic carbon
now points away from the fluoride bridge.
example, 3.001(2)
Å for [Mo2Cp2(µ-CH2PPh2)(µ-I)-
(µ-PPh2)(CO)2]+ or 3.008(2) Å for [Mo2Cp2(µ-StBu)2-
(CO)4]2+).27,28 However, the ca. 0.1 Å shortening in the
W-W length from 5b to 4b cannot be exclusively a
geometrical consequence of the necessarily shorter W-F
lengths (relative to W-Cl ones), as, for example, the
resulting W-F-W angle (89.1(2)°) is already quite acute
if we recall the general tendency of fluoride for linear
bridges. Unfortunately, organometallic complexes hav-
ing bridging fluorides across metal-metal bonds are
Spectroscopic data in solution for the fluoro complexes
4 are consistent with the solid-state structure of 4b. The
nearly parallel positioning of the terminal carbonyls
gives rise to strong and weak (in order of decreasing
frequency) C-O stretching bands, as predicted.26 On the
(26) Braterman, P. S. Metal Carbonyl Spectra; Academic Press:
London, 1975.
(27) Villafan˜e, F.; Riera, V.; Ruiz, M. A.; Bois, C.; J eannin, Y. J .
Organomet. Chem. 1989, 375, C23-C26.
(28) Courtot-Coupez, J .; Gue´guen, M.; Guerchais, J . E.; Pe´tillon, F.
Y.; Talarmin, J .; Mercier, R. J . Organomet. Chem. 1986, 312, 81.
(29) Abel, E. W.; Towle, I. D. H.; Cameron, T. S.; Cordes, R. E. J .
Chem. Soc., Dalton Trans. 1979, 1943.

4514 Organometallics, Vol. 18, No. 22, 1999
Alvarez et al.
other hand, the bridging carbonyl gives rise to the
expected low-frequency C-O stretch (ca. 1700 cm-1) and
highly deshielded 13C NMR resonance (ca. 300 ppm),
which in the molybdenum complex exhibits coupling to
the bridging fluorine nucleus. Lack of symmetry relating
both sides of the M2P2 pseudoplane is indicated by the
appearance of nonequivalent methylenic protons, which
now show no coupling to the bridging fluorine. The
latter gives in turn a highly shielded 19F NMR reso-
nance (Table 3). Noticeably, no F-W coupling is detect-
able for the tungsten complex 4b (to be compared with
a value of 51 Hz for the tetracarbonyl 3b). We regard
this fact as accidental, perhaps due to a mutual cancel-
lation of the one-bond and two-bond contributions
(usually of opposite signs) to the tungsten-fluorine
coupling in complex 4b (this possibility is obviously to
be excluded for the tetracarbonyl 3b, which lacks a
W-W bond). A final unusual spectroscopic detail con-
cerns the 31P shielding of complexes 4. Phosphorus
chemical shifts for molybdenum complexes are usually
higher than those for the corresponding tungsten com-
plexes. Indeed, this is the case for all compounds here
reported, the difference being around 15-20 ppm. In
contrast, the chemical shift of 4b is ca. 7 ppm higher
than that of its molybdenum analogue 4a . At present
we cannot offer a satisfactory explanation for this
anomaly.
methoxycomplex 9, the use of NaOMe caused substan-
tial electron transfer (i.e., formation of 1b), and dry
MeOH proved to be a much more convenient source of
the methoxide ion. Thus, rather than a simple cation-
anion reaction, coordination of methanol to unsaturated
2b followed by proton ejection from the resulting di-
cationic intermediate seems to be a more likely reaction
pathway in this reaction.
Spectroscopic data in solution for complexes 5-9
(Table 1 and Experimental Section) indicate that these
species have the same structure as the fluoro derivatives
4 and need then no further comments in general. We
just note that 31P chemical shifts increase with the
electronegativity of the donor X (I < Br < Cl < O < F).
The C-O stretching frequencies are much less sensitive
to the nature of X and cannot be correlated in this way.
In the case of compound 8, the presence of the acetate
1
ligand is denoted by a H resonance at 1.15 ppm and a
13C resonance at 188.8 ppm. The latter is in the region
observed for other organometallic dimers having bridg-
ing acetate groups.32a,b The coordination mode of the
bridging acetate group through both oxygen atoms
(µ-η2) rather than coordination through a single oxygen
atom (µ-η1) is derived from the solid-state IR spectrum
of 8. This exhibits a strong band at 1543 cm-1 (Nujol
mull), which can be assigned to the asymmetric O-C-O
stretch of the ligand.33 This value is similar to those
observed for other carbonylic complexes containing an
M2(µ-η2-O2CMe) moiety,32 whereas a µ-η1 coordination
of the ligand would give rise to a C-O stretch some 100
cm-1 higher in fequency.32c
The formation of the fluoro derivatives 4 implies a
-
fluoride abstraction from PF6 by the unsaturated
dications 2. Although several examples of mononuclear
complexes experiencing such a process have been de-
scribed,30 precedents involving binuclear complexes
seem to be restricted to the F- abstraction observed in
the oxidation of [Fe2(µ-SMe)2(CO)4(PMe3)2] with
AgPF6.31 Attempts to detect intermediate species in the
transformation 2b/4b, which also requires CO elimina-
tion, were however unsuccessful. 31P or 19F NMR
monitoring of the reaction mixtures did not show new
resonances, so we could not determine the fate of the
“reacted” PF6-, which presumably is evolved as PF5.
Rea ction P a th w a ys in th e Oxid a tion of Com -
p ou n d s 1. Through the preceding sections, we have
shown that the nature of products resulting from
oxidation of compounds 1 with [FeCp2]X (X ) BF4, PF6)
is strongly dependent on the nature of reactants and
experimental conditions, particularly stoichiometry and
temperature. The use of a defect of oxidant (less than 2
equiv) or very low temperatures leads to the mono-
nuclear cations [MCp(CO)2(dppm)]+. Fluoride abstrac-
-
tion from X- finally occurs in all cases, with BF4
Ha lid e a n d Rela ted Der iva tives of Com p ou n d s
2. From the preceding sections it is clear that the
unsaturated cations 2 are highly acidic species able to
extract a fluoride anion from its own counterion. Cations
2 are also good oxidants, and we have found a number
of reagents that just promote electron transfer to give
back the parent neutral dimers 1. This occurs, for
example, in the reactions of 2b with KOH, LiCtCPh,
H2O, or RSH. However, the high acidity of cations 2 (as
PF6- salts) can be put to good synthetic use by reacting
them with bases more resistant to oxidation. This is the
case of the halide anions and some oxygen donors as
the acetate of methoxide anions. In this way, the
compounds of general formula [M2Cp2(µ-X)(µ-CO)(CO)2-
(µ-dppm)]PF6 [X ) Cl (5), Br (6), I (7), O2CMe (8), OMe
(9)] have been obtained in good yield (Scheme 2). The
synthetic procedure is simple. For molybdenum deriva-
tives, the neutral complex 1a is oxidized with [FeCp2]-
PF6 in the presence of X-. For tungsten derivatives, a
suspension of compound 2b in dichloromethane is
reacted with the appropriate X- salt. In the case of the
promoting the formation of tetracarbonylic derivatives
3 and PF6 favoring that of the tricarbonyls 4. From
-
separate experiments we have found that 3 and 4 cannot
be interconverted. In fact, compounds 3 could not be
transformed into 4 by either thermal or photochemical
decarbonylation, and compounds 4 were found in turn
to be unreactive toward CO at room temperature.
Therefore, we conclude that compounds 3 and 4 are
formed though different reaction pathways. Attempts
to gain complementary information from CV experi-
ments were unsuccessful, the cyclic voltammograms
being too complex and irreversible to be interpreted.
Despite this, we can rationalize the experimental find-
ings by considering the reaction pathways illustrated
in Scheme 3.
In the first place, our data indicate that reaction of
compounds 1 with [FeCp2]+ occurs in all cases through
(32) (a) Frauenhoff, G. R.; Wilson, S. R.; Shapley, J . R. Inorg. Chem.
1991, 30, 78. (b) Esteruelas, M. A.; Lahuerta, O.; Modrego, J .;
Nu¨rnberg, O.; Oro, L. A.; Rodriguez, L.; Sola, E.; Werner, H. Organo-
metallics 1993, 12, 266. (c) Garc´ıa Alonso, F. J .; Garc´ıa Sanz, M.; Liu,
X. Y.; Oliveira, A.; Ruiz, M. A.; Riera, V.; Bois, C. J . Organomet. Chem.
1996, 511, 93.
(30) Doherty, N. M.; Hoffman, N. W. Chem. Rev. 1991, 91, 553.
(31) Mathieu, R.; Poilblanc, R.; Lemoine, P.; Gross, M. J . Organomet.
Chem. 1979, 165, 243.
(33) Nakamoto, K. Infrared and Raman Spectra of Inorganic and
Coordination Compounds, 4th ed.; Wiley: New York, 1986; p 231.

Highly Electrophilic Binuclear Cations
Organometallics, Vol. 18, No. 22, 1999 4515
Sch em e 3. Rea ction P a th w a ys P r op osed for th e
Oxid a tion of Com p ou n d s 1 w ith [F eCp 2]X (X- )
BF 4-, P F 6-; P -P ) d p p m )
atoms to give intermediates C and D, respectively.
Examples of this type of complexes are well estab-
lished.19 Clearly, intermediates C and D must be in turn
precursors of compounds 3 and 4, respectively. Both
processes require F- abstraction from either BF4 or
-
PF6-, but this must occur at a different step. At this
point we can just put forward a somewhat speculative
explanation for this difference. We propose that, being
sterically more demanding, the bonded hexafluorophos-
phate tends to lose first a PF5 molecule to give inter-
mediates F . Loss of CO from the latter, possibly induced
by the labilizing effect of the terminal fluoro ligand,
would give finally the tricarbonyls 4. By contrast, the
smaller sized tetrafluoroborate ligand might survive
enough in the coordination sphere of the metals so as
to move into a coordinatively more sensible bridging
position (E) before boron trifluoride elimination. Loss
of BF3 from the latter intermediate would then give the
tetracarbonyls 3.
Although somewhat speculative, the reaction path-
ways just proposed are consistent with the experimental
finding that the unsaturated cations 2 invariably give
tricarbonylic products in the presence of halide ions.
Because of the presence of bridging carbonyls in com-
pound 2, initial attack of halide on these substrates is
expected to occur at a single metal center, thus giving
an intermediate similar to F , which afterward would
experience an analogous decarbonylation to yield com-
plexes 5-7.
In summary we have shown that, in addition to
experimental conditions, the nature of the counterions
has a critical role in the fate of the highly electrophilic
unsaturated cations 2. It can be anticipated that the
use of [FeCp2]+ salts having “weakly coordinating”
-
-
anions different from BF4 or PF6 might have a
dramatic influence on the course of the oxidation
reactions of compounds 1. Studies in that direction are
currently in progress in our laboratory.
one-electron steps. Removal of the first electron would
give the 33-electron radical A. Although we have not
been able to isolate this intermediate, we note that if
compounds 1 are reacted with 1 equiv of [FeCp2]X at
ca. -60 °C, a deep green solution is formed. The latter
turns to yellow in a few minutes at that temperature,
or instantaneously if warmed, and the IR spectrum
shows then the C-O bands of the corresponding mono-
nuclear cations [MCp(CO)2(dppm)]+ (B). We note here
that the 33-electron radical [W2(µ-PPh2)2(CO)6(PPh2H)2]+
also exhibits a green color.10
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 procedures34 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)]13 and
[W2Cp2(CO)4(µ-dppm)]14b were prepared as reported before.
Reagents [FeCp2]PF6 and [FeCp2]BF4 were prepared according
to literature procedures.15 All other reagents were purchased
from the usual commercial suppliers and used as received.
Low-temperature reactions were performed using jacketed
Schlenk tubes, refrigerated by a closed 2-propanol circuit kept
at the desired temperature with a cryostat. Filtrations were
carried out using dry diatomaceous earth under nitrogen.
NMR spectra were recorded at 300.13 (1H), 188.31 (19F{1H}),
121.50 (31P{1H}), or 75.47 MHz (13C{1H}) at room temperature,
unless otherwise indicated. Chemical shifts (δ) are given in
ppm, relative to internal TMS (1H, 13C) or CFCl3 (19F) 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 (Hz). 13C{1H} NMR
spectra were routinely recorded on solutions containing a small
amount of tris(acetylacetonato)chromium(III) as a relaxation
reagent.
It seems clear, then, that radical A is the main
precursor of the mononuclear species B, possibly through
a process similar to that proposed for [M2Cp2(CO)6]
(Scheme 1).12 If a second equivalent of [FeCp2]+ is
present, radical A can be further oxidized to give the
unsaturated dications 2. This second step is slower than
the former and competes with the decomposition leading
to B, being dominant at temperatures above ca. -30 °C.
However, the unsaturated cations 2 are only stable for
-
the combination M ) W, X ) PF6 due to its low
solubility in dichloromethane. For the other combina-
tions, or at higher temperatures in any case, cations 2
react with the corresponding counterion X, but different
reaction pathways must then appear for either BF4- or
-
PF6
.
It is reasonable to assume that either anion would
coordinate to cations 2 through one of their fluorine
(34) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals; Pergamon Press: Oxford, U.K., 1988.

4516 Organometallics, Vol. 18, No. 22, 1999
Alvarez et al.
Syn th esis of [W2Cp 2(CO)4(µ-d p p m )](P F 6)2 (2b). Com-
pound 1b (0.066 g, 0.06 mmol) was added slowly to a dichlo-
romethane solution (16 mL) containing [FeCp2]PF6 (0.040 g,
0.12 mmol) at -15 °C, whereupon a black-violet microcrys-
talline powder precipitated immediately. The solution was
syringed off, and the solid was washed with dichloromethane
(2 × 6 mL) at -10 °C and dried in vacuo, yielding 0.075 g
(0.058 mmol, 88%) of compound 2. Satisfactory microanalytical
data could not be obtained for this air-sensitive complex, which
is also unstable in solution (see Results and Discussion
section).
Syn th esis of [Mo2Cp2(µ-F)(CO)4(µ-dppm )]BF4 (3a). Com-
pound 1a (0.049 g, 0.06 mmol) was added slowly to a dichlo-
romethane solution (10 mL) containing [FeCp2]BF4 (0.033 g,
0.12 mmol) at -30 °C, and the mixture was stirred for 5 min
to give a violet solution. Solvent was then removed under
vacuum, and the residue was washed with toluene (2 × 4 mL)
and petroleum ether (3 × 3 mL) and then extracted with a
mixture of CH2Cl2/toluene (1:1) and filtered. Removal of
solvents from the filtrate gave compound 3a (0.048 g, 87%) as
a violet solid. Anal. Calcd for C39H32BF5Mo2O4P2: C, 50.67;
H, 3.49. Found: C, 50.65; H, 3.46. 1H NMR (200.13 MHz, CD2-
Cl2): δ 7.70-7.05 (m, 20H, Ph), 5.25 (s, 10H, Cp), 3.64 (dt, J HH
) 13, J HP ) 9, 1H, CH2), 2.96 (tt, br, J HP ) 17, J HH ) 13, J HF
) 13, 1H, CH2).
164, CO), 134.8-128.3 (Ph), 94.8 (s, Cp), 27.4 (t, J CP ) 21,
CH2).
Syn th esis of [Mo2(µ-Cl)Cp 2(µ-CO)(CO)2(µ-d p p m )]P F 6
(5a ). A dichloromethane solution (10 mL) containing 0.049 g
(0.06 mmol) of 1a and 0.025 g (0.06 mmol) of [AsPh4]Cl was
added very slowly to another solution containing 0.040 g (0.12
mmol) of [FeCp2]PF6 in 10 mL of dichloromethane. The
mixture was stirred at room temperature for 15 min and then
the solvent removed under vacuum. The residue was afterward
washed with petroleum ether (4 × 4 mL), extracted with a
mixture of toluene/THF (1:1), and filtered. Removal of solvents
under vacuum gave compound 5a as a greenish solid (0.055
g, 95%). Anal. Calcd for C38H32ClF6Mo2O3P3: C, 47.01; H, 3.32.
1
Found: C, 46.98; H, 3.30. H NMR (200.13 MHz, acetone-d6):
δ 7.67-7.01 (m, 20H, Ph), 5.32 (s, 10H, Cp), 4.45 (dt, J HH
)
13, J HP ) 12, 1H, CH2), 3.15 (dt, J HH ) 13, J HP ) 10, 1H, CH2).
13C{1H} NMR (50.32 MHz, acetone-d6): δ 295.8 (s, µ-CO), 242.6
(AXX′, |J CP + J CP′| ) 16, CO), 138.5-126.1 (Ph), 96.3 (s, Cp);
the CH2 resonance for this complex was obscured by those from
the solvent.
Syn th esis of [W2(µ-Cl)Cp2(µ-CO)(CO)2(µ-dppm )]P F6 (5b).
Solid [AsPh4]Cl (0.016 g, 0.038 mml) was added to a suspension
of compound 2 (0.050 g (0.038 mmol) in dichloromethane (3
mL) at -30 °C, and the mixture was stirred for 3 min to give
a brown-orange solution, which was afterward allowed to reach
room temperature for 30 min. Solvent was then removed under
vacuum, and the residue was washed with petroleum ether
(3 × 3 mL), extracted with EtOH, and filtered. Removal of
solvent from the filtrate under vacuum gave compound 5b as
Syn th esis of [W2Cp 2(µ-F )(CO)4(µ-d p p m )]BF 4 (3b). The
procedure is completely analogous to that described for 3a but
using compound 1b (0.049 g, 0.06 mmol) instead. In this way,
compound 3b is isolated as a violet powder (0.070 g, 90%).
Single crystals suitable for the X-ray diffraction study were
grown by slow diffusion of a concentrated dichloromethane
solution of the complex into a layer of toluene at -20 °C. They
were shown (by NMR and X-ray) to contain one molecule of
dichloromethane per molecule of complex. Anal. Calcd for
a brown-orange solid (0.038 g, 86%). Anal. Calcd for C38H32
-
1
ClF6O3P3W2: C, 39.80; H, 2.81. Found: C, 39.79; H, 2.81. H
NMR (CD2Cl2): δ 7.95-7.15 (m, 20H, Ph), 5.15 (s, 10H, Cp),
4.50 (dt, J HH ) 13, J HP ) 11, 1H, CH2), 3.06 (dt, J HH ) 13, J HP
) 10, 1H, CH2). 13C{1H} NMR (CD2Cl2): δ 294.5 (s, µ-CO),
229.0 (s, CO), 137.5-127.1 (m, Ph), 94.0 (s, Cp), 36.0 (t, J CP
24, CH2).
)
C
40H34BCl2F5O4P2W2 (3b‚CH2Cl2): C, 40.55; H, 2.89. Found:
C, 40.60; H, 2.81. 1H NMR (400.13 MHz, CD2Cl2): δ 7.65-
7.02 (m, 20H, Ph), 5.43 (s, 10H, Cp), 3.69 (dt, J HH ) 13, J HP
)
Syn th esis of [Mo2(µ-Br )Cp 2(µ-CO)(CO)2(µ-d p p m )]P F 6
(6a ). The procedure is completely analogous to that described
for 5a , except that [PPh4]Br (0.025 g, 0.06 mmol) was used
instead, and the extraction was carried out using a toluene/
THF (2:1) mixture. In this way, compound 6a (0.054 g, 90%)
was obtained as an orange solid. Anal. Calcd for C38H32BrF6-
Mo2O3P3: C, 44.95; H, 3.18. Found: C, 44.93; H, 3.15. 1H NMR
(acetone-d6): δ 7.70-7.16 (m, 20H, Ph), 5.31 (s, 10H, Cp), 4.73
10, 1H, CH2), 2.25 (m br, CH2, 1H). 1H{31P} NMR (400.13 MHz,
CD2Cl2): δ 3.69 (d, J HH ) 13, 1H, CH2), 2.26 (dd br, J HH ) 13,
J HF ) 10, 1H, CH2). 19F NMR (CD2Cl2): δ - 152.2 (s, BF4-),
-674.8 [dt, J FP ) 56, J FH ) 10, µ-F). 13C{1H,31P} NMR (100.61
MHz, CD2Cl2): δ 246.2 (s, CO), 246.0 (d, J CF ) 19, CO), 132.0-
129.3 (Ph), 95.8 (s, Cp), 16.9 (s, CH2).
Syn th esis of [Mo2Cp2(µ-F)(µ-CO)(CO)2(µ-dppm )]P F6 (4a).
Compound 1a (0.049 g,0.06 mmol) was added slowly to a
dichloromethane solution (20 mL) containing [FeCp2]PF6
(0.040 g, 0.12 mmol) at room temperature, and the mixture
was stirred for 15 min to give a green solution. Solvent was
then removed under vacuum, and the residue was washed with
toluene (4 × 4 mL), extracted with dichloromethane, and
filtered. Removal of the solvent from the filtrate under vacuum
yielded compound 4a (0.048 g, 85%) as a green solid. Anal.
Calcd for C38H32F7Mo2O3P3: C, 47.82; H, 3.38. Found: C, 48.05;
(dt, J HH ) 13, J HP ) 12, 1H, CH2), 3.15 (dt, J HH ) 13, J HP
)
10, 1H, CH2). 13C{1H} NMR (acetone-d6): δ 294.3 (s, µ-CO),
240.1 (s br, CO), 138.5-127.0 (m, Ph), 95.8 (s, Cp), 31.3 (t, J CP
) 21, CH2).
Syn th esis of [W2(µ-Br )Cp2(µ-CO)(CO)2(µ-dppm )]P F6 (6b).
The procedure is completely analogous to that described for
5b, except that [PPh4]Br (0.016 g, 0.038 mmol) was used
instead. The brown-yellow reaction mixture was stirred with
water several times (5 × 5 mL) and the organic phase then
filtered through MgSO4 and diatomaceous earth. Solvent was
removed under vacuum from the filtrate, and the residue was
washed with toluene (3 × 3 mL) and dried under vacuum, to
give compound 6b as a brown powder (0.038 g, 84%). Anal.
Calcd for C38H32BrF6O3P3W2: C, 38.32; H, 2.71. Found: C,
1
H, 3.40. H NMR (CD2Cl2, 233 K): δ 7.48-6.88 (m, 20H, Ph),
5.11 (s, 10H, Cp), 3.02 (dt, J HH ) 11, J HP ) 10, 1H, CH2), 2.70
[dt, J HH ) 11, J HP ) 6, 1H, CH2). 13C{1H} NMR (CD2Cl2): δ
297.4 (d, J CF ) 11, µ-CO), 245.5 (s br, CO), 137.2-124.5 (Ph),
96.1 (s, Cp), 22.7 (t, J CP ) 16, CH2).
1
38.32; H, 2.71. H NMR (CD2Cl2): δ 7.96-7.17 (m, 20H, Ph),
Syn th esis of [W2Cp2(µ-F)(µ-CO)(CO)2(µ-dppm )]P F6 (4b).
The procedure is completely analogous to that described for
4a except that compound 1b (0.066 g, 0.06 mmol) was used
instead. In this way, compound 4b was isolated as a green
powder (0.064 g, 85%). The crystals used in the X-ray study
were grown by slow diffusion of a concentrated dichloro-
methane solution of the complex into a layer of petroleum
ether. Anal. Calcd for C38H32F7O3P3W2: C, 40.38; H, 2.85.
Found: C, 40.43; H, 2.84. IR (Nujol mull): νst(CO) 1973 (vs),
1913 (m), 1674 (vs); ν(PF) 854 (vs br) cm-1. 1H NMR (acetone-
d6): δ 7.75-7.06 (m, 20H, Ph), 5.40 (s, 10H, Cp), 3.98 (dt, J HH
) 13, J HP ) 12, 1H, CH2), 3.38 (dt, J HH ) 13, J HP 10, 1H, CH2).
5.19 (s, 10H, Cp), 4.88 (dt, J HH ) 13, J HP ) 11, 1H, CH2), 3.06
(dt, J HH ) 13, J HP ) 10, 1H, CH2). 13C{1H} NMR (CD2Cl2): δ
290.8 (s, µ-CO), 226.5 (AXX′, |J CP + J CP′| ) 8, CO), 136.0-
128.5 (m, Ph), 92.6 (s, Cp), 37.7 (t, J CP ) 24, CH2).
Syn th esis of [Mo2Cp2(µ-I)(µ-CO)(CO)2(µ-dppm )]P F6 (7a).
The procedure is completely analogous to that described for
5a , except that [NtBu4]I (0.022 g, 0.06 mmol) was used instead.
Compound 7a (0.053 g, 84%) was thus obtained as a brown
powder. Anal. Calcd for C38H32F6IMo2O3P3: C, 42.96; H, 3.03.
1
Found: C, 42.94; H, 3.11. H NMR (acetone-d6): δ 7.70-7.14
(m, 20H, Ph), 5.30 (s, 10H, Cp), 5.13 (dt, J HH ) 14, J HP ) 12,
1H, CH2), 3.16 [dt, J HH ) 14, J HP ) 10, 1H, CH2].
13C{1H} NMR (CD2Cl2): δ 304.1 (s, µ-CO), 232.9 (s br, J CW
)

Highly Electrophilic Binuclear Cations
Organometallics, Vol. 18, No. 22, 1999 4517
Ta ble 5. Exp er im en ta l Da ta for th e X-r a y
Diffr a ction Stu d ies
Syn th esis of [W2Cp 2(µ-I)(µ-CO)(CO)2(µ-d p p m )]P F 6 (7b).
The procedure is completely analogous to that described for
5b, except that [NtBu4]I (0.014 g (0.038 mmol) was used
instead. Solvent was removed under vacuum from the reaction
mixture, and the residue was extracted with a toluene/THF
(3:1) mixture (5 × 4 mL) and filtered. Removal of solvent from
the filtrate under vacuum gave compound 7b as a brown-
orange solid, which was washed with petroleum ether (3 × 3
mL) (0.041 g, 85%). Anal. Calcd for C38H32F6IO3P3W2: C, 36.86;
H, 2.60. Found: C, 36.86; H, 2.61. 1H NMR (400.13 MHz, CD2-
Cl2): δ 7.62-7.11 (m, 20H, Ph), 5.24 (dt, J HH ) 14, J HP ) 11,
1H, CH2), 5.20 (s, 10H, Cp), 3.06 (dt, J HH ) 14, J HP ) 10, 1H,
CH2). 13C{1H} NMR (CD2Cl2): δ 316.2 (s, µ-CO), 222.4 (AXX′,
|J CP + J CP′| ) 9, CO), 138.2-129.1 (Ph), 91.9 (s, Cp), 40.6 (t,
J CP ) 25, CH2).
3b‚CH2Cl2
4b
mol formula
mol wt
cryst syst
space group
radiation (λ, Å)
a, Å
C40H34BCl2F5O4P2W2 C38H32F7O3P3W2
1185.06
triclinic
P1h
1130.28
monoclinic
P21/n
graphite-monochromated (Mo KR, 0.71073)
11.256(2)
19.221(3)
11.092(2)
97.86(1)
114.38(1)
101.43(1)
2077.2(7)
2
10.961(2)
b, Å
c, Å
18.787(3)
18.055(3)
R, deg
90
91.85(1)
â, deg
γ, deg
90
3716(1)
4
V, Å3
Z
Syn th esis of [W2Cp 2(µ-O2CMe)(µ-CO)(CO)2(µ-d p p m )]-
P F 6 (8). Solid Na[MeCO2] (0.010 g, 0,12 mmol) was added to
a suspension of compound 2 (0.050 g, 0.038 mmol) in dichlo-
romethane (3 mL) at -15 °C, and the mixture was stirred for
1 h to give a dark orange solution, which was filtered. Solvent
was then removed under vacuum from the filtrate and the
residue washed with petroleum ether (3 × 3 mL) to give
compound 8 as a brown orange powder (0.039 g, 88%). Anal.
Calcd for C40H35F6O5P3W2: C, 41.05; H, 3.01. Found: C, 40.99;
F(000)
1136
2160
cryst size, mm
µ(Cu KR), cm-1
diffractometer
scan type
scan speed, deg/min 3-12
θ range, deg
std reflctn
no. of reflctns measd (h, (k, l
total no. of unique
data
0.12 × 0.21 × 0.30
0.15 × 0.24 × 0.35
58.01
63.88
Philips PW 1100
θ/2θ
Philips PW 1100
θ/2θ
3-12
3-24
3-27
one measd after 100 reflctns
(h, k, l
5863
9058
1
H, 3.07. H NMR (400.13 MHz, acetone-d6): δ 7.70-7.14 (m,
20H, Ph), 5.54 (dt, J HH ) 15, J HP ) 10, 1H, CH2), 5.37 (s, 10H,
Cp), 4.13 (dt, J HH ) 15, J HP ) 11, 1H, CH2), 1.15 (s, 3H, Me).
13C{1H} NMR (100.61 MHz, CD2Cl2): δ 300.1 (s br, µ-CO),
232.6 (s, J CW ) 142, CO), 188.8 [s, µ-OOCMe], 136.3-128.8
(Ph), 96.1 (s, Cp), 42.4 (t, J CP ) 26, CH2), 21.5 (s, Me).
Syn th esis of [W2Cp 2(µ-OMe)(µ-CO)(CO)2(µ-d p p m )]P F 6
(9). Dry MeOH (0.5 mL) was added to a suspension of
compound 2 (0.050 g, 0.038 mmol) in dichloromethane (3 mL)
at -30 °C, and the mixture stirred for 5 min to give a brown-
yellow solution. Solvents were then removed under vacuum,
and the residue was washed with toluene (2 × 5 mL), extracted
with dichloromethane, and filtered. Removal of solvent from
the filtrate under vacuum gave compound 9 as a brown-orange
solid, which was washed with petroleum ether (3 × 3 mL)
(0.037 g, 85%). Anal. Calcd for C39H35F6O4P3W2: C, 41.01; H,
3.09. Found: C, 40.66; H, 3.03. 1H NMR (200.13 MHz, CD2-
Cl2): δ 7.55-6.94 (m, 20H, Ph), 5.09 (s, 10H, Cp), 4.00 (s, 3H,
unique obsd data
[I > 2σ(I)]
Ra
6137
3066
0.0397
0.0482
0.0281
0.0338
b
Rw
a
b
R ) ∑||Fo| - |Fc||/∑|Fo|. Rw ) [∑w(|Fo| - |Fc|)2/∑w(Fo)2]1/2
.
at their calculated positions (C-H ) 0.96 Å) and refined
“riding” on the corresponding carbon atoms. The final cycles
of refinement were carried out on the basis of 493 (3b‚CH2-
Cl2) and 360 (4b) variables; after the last cycles, no parameters
shifted by more than 0.2 (3b‚CH2Cl2) and 0.8 (4b) esd. The
highest remaining peak in the final difference map was
equivalent to about 1.8 (3b‚CH2Cl2) and 0.6 (4b) e/Å3. A
2
-1
weighting scheme w ) K[s2(Fo) + gFo
]
was used in the last
cycles of refinement with K ) 1.096 and g ) 0.0009 (3b‚CH2-
Cl2) and K ) 0.199 and g ) 0.0022 (4b) at convergence. Final
R and Rw values were 0.0397 and 0.0482 (3b‚CH2Cl2) and
0.0281 and 0.0338 (4b), respectively. Atomic scattering factors,
corrected for anomalous dispersion, were taken from ref 36.
The SHELX-76 and SHELXS-86 systems of computer pro-
grams were used.37 All calculations were carried out on the
GOULD POWERNODE 6040 of the Centro di Studio per la
Strutturistica Diffrattometrica del CNR, Parma.
OMe), 3.69 (dt, J HH ) 13, J HP ) 11, 1H, CH2), 2.84 (dt, J HH
)
13, J HP ) 9, 1H, CH2). 13C{1H} NMR (CD2Cl2): δ 302.3 (br,
µ-CO), 231.0 (s, CO), 134.0-127.3 (Ph), 92.2 (s, Cp), 80.6 (s,
OMe), 27.8 (t, J CP ) 22, CH2).
Cr ysta l Str u ctu r e Deter m in a tion s of Com p lexes 3b‚
CH2Cl2 a n d 4b. Selected crystallographic data for both
compounds are listed in Table 5. Data were collected at room
temperature on a Philips PW 1100 single-crystal diffractome-
ter using graphite-monochromated Mo KR radiation. All
reflections with θ in the range 3-27° (3b‚CH2Cl2) and 3-24°
(4b) were measured. The intensities were corrected for Lorentz
and polarization effects. A correction for absorption was
applied (maximum and minimum values for the transmission
factors were 1.000 and 0.706 (3b‚CH2Cl2) and 1.000 and 0.740
(4b)).35 Only the observed reflections were used in the struc-
ture solution and refinement.
Both structures were solved by Patterson and Fourier
methods and refined by full-matrix least-squares first with
isotropic and then with anisotropic thermal parameters in the
last cycles for all the non hydrogen atoms excepting the C and
Cl atoms of the CH2Cl2 solvate molecules for 3b and the phenyl
carbon atoms of dppm for 4b. All hydrogen atoms were placed
Ack n ow led gm en t. We thank the DGICYT of Spain
for financial support (Project PB91-0678) and the FICYT
of Asturias (Spain) for a grant to M.A.A.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates, anisotropic thermal parameters, and bond lengths
and angles for compounds 3b and 4b. This material is
available free of charge via the Internet at http://pubs.acs.org.
Tables of observed and calculated structure factors may be
obtained from the authors.
OM990135H
(36) International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, England, 1974; Vol IV.
(37) Sheldrick, G. M. SHELX-76, Program for crystal structure
determination; University of Cambridge: England, 1976. SHELXS-
86, Program for the solution of crystal structures, University of
Go¨ttingen, 1986.
(35) Walker, N.; Stuart, D. Acta Crystallogr., Sect. A 1983, 39, 158.
Ugozzoli, F. Comput. Chem. 1987, 11, 109.