M-P versus M=M bonds as protonation sites in the organophosphide-bridged complexes [M2Cp2(μ-PR2)(μ- PR′2)(CO)2], (M = Mo, W; R, R′ = Ph, Et, Cy)

Article abstract of DOI:10.1021/ic060544n

The unsaturated complexes [W₂Cp₂(μ-PR ₂)(μ-PR′₂)(CO)₂] (Cp = η⁵-C₅H₅; R = R′ = Ph, Et; R = Et, R′ = Ph) react with HBF₄·OEt₂ at 243 K in dichloromethane solution to give the corresponding complexes [W ₂Cp₂(H)(μ-PR₂)(μ-PR′₂) (CO)₂]BF₄, which contain a terminal hydride ligand. The latter rearrange at room temperature to give [W₂Cp ₂(μ-H)(μ-PR₂)(μ-PR′₂)(CO) ₂]BF₄, which display a bridging hydride and carbonyl ligands arranged parallel to each other (W-W = 2.7589(8) A when R = R′ = Ph). This explains why the removal of a proton from the latter gives first the unstable isomer cis-[W₂Cp₂(μ-PPh ₂)₂(CO)₂]. The molybdenum complex [Mo ₂Cp₂(μ-PPh₂)₂(CO)₂] behaves similarly, and thus the thermally unstable new complexes [Mo ₂Cp₂(H)(μ-PPh₂)₂(CO) ₂]BF₄ and cis-[Mo₂Cp₂(μ-PPh ₂)₂-(CO)₂] could be characterized. In contrast, related dimolybdenum complexes having electron-rich phosphide ligands behave differently. Thus, the complexes [Mo₂Cp₂(μ-PR ₂)₂(CO)₂] (R = Cy, Et) react with HBF ₄·OEt₂ to give first the agostic type phosphine-bridged complexes [Mo₂Cp₂(μ-PR ₂)(μ-κ²-HPR₂)(CO)₂]BF ₄ (Mo-Mo = 2.748(4) A for R = Cy). These complexes experience intramolecular exchange of the agostic H atom between the two inequivalent P positions and at room-temperature reach a proton-catalyzed equilibrium with their hydride-bridged tautomers [ratio agostic/hydride = 10 (R = Cy), 30 (R = Et)]. The mixed-phosphide complex [Mo₂Cp₂(μ-PCy ₂)(μ-PPh₂)(CO)₂] behaves similarly, except that protonation now occurs specifically at the dicyclohexylphosphide ligand [ratio agostic/ hydride = 0.5]. The reaction of the agostic complex [Mo ₂Cp₂(μ-PCy₂)(μ-κ²- HPCy₂)(CO)₂]BF₄ with CN^tBu gave mono- or disubstituted hydride derivatives [Mo₂Cp₂(μ-H) (μ-PCy₂)₂(CO)_2-x(CN^tBu) _x]BF₄ (Mo-Mo = 2.7901(7) A for x = 1). The photochemical removal of a CO ligand from the agostic complex also gives a hydride derivative, the triply bonded complex [Mo₂Cp ₂(H)(μ-PCy₂)₂(CO)]BF₄ (Mo-Mo = 2.537(2) A). Protonation of [Mo₂Cp₂(μ-PCy ₂)₂(μ-CO)] gives the hydroxycarbyne derivative [Mo ₂Cp₂(μ-COH)(μ-PCy₂)₂]BF ₄, which does not transform into its hydride isomer.

Full text of DOI:10.1021/ic060544n

Inorg. Chem. 2006, 45, 6965−6978
M
−
P versus M
Organophosphide-Bridged Complexes [M2Cp2(
(M
Mo, W; R, R′ ) Ph, Et, Cy)†
d
M Bonds as Protonation Sites in the
µ
-PR2)(µ-PR′2)(CO)2],
)
M. Angeles Alvarez,‡ M. Esther Garc´ıa,‡ M. Eugenia Mart´ınez,‡ Alberto Ramos,‡ Miguel A. Ruiz,*,‡
David Sa´ez,‡ and Jacqueline Vaissermann§
Departamento de Qu´ımica Orga´nica e Inorga´nica/IUQOEM, UniVersidad de OViedo,
E-33071 OViedo, Spain, and Laboratoire de Chimie Inorganique et Mate´riaux Mole´culaires,
UniVersite´ P. et M. Curie, 4 Place Jussieu, 75252 Paris, Cedex 05, France
Received March 30, 2006
The unsaturated complexes [W2Cp2(
react with HBF4 OEt2 at 243 K in dichloromethane solution to give the corresponding complexes [W2Cp2(H)(
PR2)( -PR 2)(CO)2]BF4, which contain a terminal hydride ligand. The latter rearrange at room temperature to give
[W2Cp2( -H)( -PR2)( -PR 2)(CO)2]BF4, which display a bridging hydride and carbonyl ligands arranged parallel to
each other (W 2.7589(8) Å when R ′ ) Ph). This explains why the removal of a proton from the latter
gives first the unstable isomer cis-[W2Cp2( -PPh2)2(CO)2]. The molybdenum complex [Mo2Cp2( -PPh2)2(CO)2] behaves
similarly, and thus the thermally unstable new complexes [Mo2Cp2(H)( -PPh2)2(CO)2]BF4 and cis-[Mo2Cp2( -PPh2)2-
(CO)2] could be characterized. In contrast, related dimolybdenum complexes having electron-rich phosphide ligands
behave differently. Thus, the complexes [Mo2Cp2( -PR2)2(CO)2] (R Cy, Et) react with HBF4 OEt2 to give first the
agostic type phosphine-bridged complexes [Mo2Cp2( -PR2)( Mo 2.748(4) Å for R
2-HPR2)(CO)2]BF4 (Mo
µ-PR2)(µ-PR′ ) R′ ) Ph, Et; R ) Et, R′ ) Ph)
2)(CO)2] (Cp ) η5-C5H5; R
‚
µ-
µ
′
µ
µ
µ
′
−W
)
) R
µ
µ
µ
µ
µ
)
‚
µ
µ
-
κ
−
)
)
Cy). These complexes experience intramolecular exchange of the agostic H atom between the two inequivalent P
positions and at room-temperature reach a proton-catalyzed equilibrium with their hydride-bridged tautomers [ratio
agostic/hydride
behaves similarly, except that protonation now occurs specifically at the dicyclohexylphosphide ligand [ratio agostic/
hydride 0.5]. The reaction of the agostic complex [Mo2Cp2( -PCy2)(
2-HPCy2)(CO)2]BF4 with CNtBu gave
mono- or disubstituted hydride derivatives [Mo2Cp2( -H)( Mo 2.7901(7) Å for
-PCy2)2(CO)2 x(CNtBu)x]BF4 (Mo
1). The photochemical removal of a CO ligand from the agostic complex also gives a hydride derivative, the
) 10 (R ) Cy), 30 (R ) Et)]. The mixed-phosphide complex [Mo2Cp2(µ-PCy2)(µ-PPh2)(CO)2]
)
µ
µ-κ
µ
µ
−
)
-
x
)
triply bonded complex [Mo2Cp2(H)(
µ
-PCy2)2(CO)]BF4 (Mo
−Mo
)
2.537(2) Å). Protonation of [Mo2Cp2(
µ-PCy2)2(µ-
CO)] gives the hydroxycarbyne derivative [Mo2Cp2(
µ
-COH)(
µ
-PCy2)2]BF4, which does not transform into its hydride
isomer.
Introduction
pentadienyl or related ligand).1 The presence of positive
charges in this type of molecules greatly increases the
electrophilic character of the dimetal center, which leads to
enhanced reactivity and potential Lewis-acid catalysis, as
shown by our recent studies on the unsaturated cations of
type [M2Cp2(CO)x(µ-L′2)]n+ (M ) Mo, W; x ) 2-4; L′2 )
diphosphine ligand; n ) 1, 2), prepared through chemical
oxidation of the corresponding electron-precise substrates
[M2Cp2(CO)4(µ-L′2)].2 An alternative synthetic approach to
Organometallic compounds having multiple metal-metal
bonds are species of interest due to their high reactivity
toward a great variety of molecules under mild conditions,
as exemplified by the wide chemistry developed around the
unsaturated binuclear complexes [M2L2(CO)x] (L ) cyclo-
* Author to whom correspondence should be addressed: E-mail:
mara@uniovi.es.
† This paper is dedicated to Prof. V. Riera on the occasion of his 70th
birthday.
‡ Universidad de Oviedo.
§ Universite´ P. et M. Curie.
(1) (a) Curtis, M. D. Polyhedron 1987, 6, 759. (b) Winter, M. J. AdV.
Organomet. Chem. 1989, 29, 101.
10.1021/ic060544n CCC: $33.50
Published on Web 07/27/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 17, 2006 6965

Alvarez et al.
related unsaturated cations is the protonation of suitable
precursors having multiple metal-metal bonds. Indeed, the
protonation of a binuclear complex having an M-M bond
usually occurs at the dimetal center and can be considered
as a general synthetic route to hydride-bridged derivatives.3
This approach has been recently used to prepare some
reactive cations having hydride bridges along Ir-Ir, Fe-
Fe, or Ru-Ru double bonds4 as well as W-W triple bonds.5
We thus decided to explore the protonation reactions of the
doubly bonded organophosphide-bridged complexes [M2Cp2-
(µ-PR2)(µ-PR′2)(CO)2] (M ) Mo, W) as a potential prepara-
tive route to unsaturated dimolybdenum or ditungsten cations.
The latter neutral complexes are well-suited substrates for
that purpose, because the groups R and R′ can be chosen so
as to modify the electronic and steric properties of the dimetal
center in a rational way.6 Some time ago Mays et al. reported
that the diphenylphosphide-bridged molybdenum compound
[Mo2Cp2(µ-PPh2)2(CO)2] could be protonated to give the
expected hydride-bridged cation [Mo2Cp2(µ-H)(µ-PPh2)2-
(CO)2]BF4, this being accompanied by a trans to cis
isomerization of the carbonyl ligands.7 With this precedent
at hand we started a prospective study aimed initially to
identify the factors (nature of M, R, and R′) yielding a more
reactive hydride cation suitable for further studies. Unexpect-
edly, we have found that these protonation reactions are more
complex than suspected, as they involve initial H+ attack at
a single metal position (to give a terminal hydride ligand)
or at the metal-phosphorus bond (to give an agostic-type
µ-κ2-HPR2 phosphine bridging ligand), as shown by the
protonation studies on the ditungsten [W2Cp2(µ-PR2)(µ-
PR′2)(CO)2] [R ) R′ ) Ph (1a), Et (1b); R ) Et, R′ ) Ph
(1c)] and dimolybdenum complexes [Mo2Cp2(µ-PR2)(µ-
PR′2)(CO)2] (R ) R′ ) Ph (2a), Et (2b), Cy (2d); R ) Cy,
R′ ) Ph, (2e)] here reported. Phosphine-bridged complexes
exhibiting agostic M-H-P interactions are very rare species,
and only a few palladium complexes of type [Pd2(µ-κ2-
(C2H4)2]+ have been described so far.9 Further interest in
these species stems from the fact that coordination of the
P-H bond of a phosphine ligand to a metal atom weakens
that bond and is expected to result in specific reactivity. It
also represents an intermediate step in the oxidative addition
of P-H bonds of primary and secondary phosphines to
unsaturated dimetal centers.2d,6,10 In this context, the results
here reported provide the first evidence that M-P bonds
compete efficiently with M-M bonds as protonation sites
in organometallic complexes. Moreover, our results provide
the first examples of stable dimolybdenum complexes
displaying agostic P-H bonded bridging phosphines (µ-κ2-
HPR2), which in turn exhibit some novel features: (a)
dynamic behavior in solution involving the intramolecular
exchange of the hydrogen atom between µ-κ2-HPR2 and
µ-PR2 ligands and (b) coexistence in solution with the
corresponding hydride tautomers. Finally, our results clearly
establish that the above tautomerism between agostic and
hydride complexes is governed not only by the nature of
the metal but also by a fine balance between the electronic
and steric properties of the groups around the metal and
phosphorus atoms.
Results and Discussion
The ditungsten and dimolybdenum complexes 1 and 2 are
protonated by different strong acids. The results of these
protonation reactions have been found to be strongly de-
pendent on the nature of the metal groups around phosphorus
and even the ligands coordinated to the dimetal center. The
nature of the external anion also has some influence, as
shown by comparison of the results using HBF4‚OEt2 with
those from selected experiments using strong acids having
noncoordinating (HBAr′4‚2OEt2, Ar′ ) 3,5-C6H3(CF3)2)11 or
coordinating (HCl) anions. We will discuss all these effects
separately.
Protonation of Tungsten Complexes. The ditungsten
substrates 1a-c react with HBF4‚OEt2 rapidly at 243 K in
dichloromethane solution to give cleanly the corresponding
cationic derivatives [W2Cp2(H)(µ-PR2)(µ-PR′2)(CO)2]BF4
(3a-c), displaying a terminal hydride ligand (Scheme 1).
Compounds 3 are thermally unstable, and at room temper-
ature they rearrange to give the corresponding isomers [W2-
Cp2(µ-H)(µ-PR2)(µ-PR′2)(CO)2]BF4 (4a-c), displaying a
bridging hydride and carbonyl ligands in a cis relative
arrangement, as confirmed by spectroscopic (Table 1) and
diffractometric data to be discussed below. Separate experi-
t
HPR2)(µ-PR2)L2]+ (R ) Bu, Cy; L ) phosphine ligand)8
and the platinum complex [Pt2(µ-κ2-HPtBu2)(µ-PtBu2)-
(2) (a) Alvarez, M. A.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.; Bois, C.
Angew. Chem., Int. Ed. Engl. 1993, 32, 1156. (b) Alvarez, M. A.;
Garc´ıa, G.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.; Lanfranchi, M.;
Tiripicchio, A. Organometallics 1999, 18, 4509. (c) Alvarez, M. A.;
Anaya, Y.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.; Vaissermann, J.
Organometallics 2003, 22, 456. (d) Alvarez, M. A.; Anaya, Y.; Garc´ıa,
M. E.; Riera, V.; Ruiz, M. A. Organometallics 2004, 23, 433. (e)
Alvarez, M. A.; Anaya, Y.; Garc´ıa, M. E.; Ruiz, M. A. Organome-
tallics 2004, 23, 3950. (f) Alvarez, M. A.; Anaya, Y.; Garc´ıa, M. E.;
Ruiz, M. A.; Vaissermann, J. Organometallics 2005, 24, 2452.
(3) (a) Moore, D. S.; Robinson, S. D. Chem. Soc. ReV. 1983, 12, 415. (b)
Crabtree, R. H. Organometallic Chemistry of the Transition Metals,
2nd ed.; John Wiley and Sons: New York, 1994; Chapter 13, p 335.
(4) (a) Heinekey, D. M.; Fine, D. A.; Barnhart, D. Organometallics 1997,
16, 2530. (b) Fujita, K.; Nakaguma, H.; Hanasaka, F.; Yamaguchi, R.
Organometallics 2002, 21, 3749. (c) Fujita, K.; Nakaguma, H.;
Hamada, T.; Yamaguchi, R. J. Am. Chem. Soc. 2003, 125, 12368. (d)
Bo¨ttcher, H. C.; Graf, M.; Merzweiler, K.; Wagner, C. J. Organomet.
Chem. 2001, 628, 144.
(8) (a) Albinati, A.; Lianza, F.; Pasquali, M.; Sommovigo, M.; Leoni, P.;
Pregosin, P. S.; Ru¨egger, H. Inorg. Chem. 1991, 30, 25. (b) Leoni,
P.; Pasquali, M.; Sommovigo, M.; Laschi, F.; Zanello, P.; Albinati,
A.; Lianza, F.; Pregosin, P. S.; Ru¨egger, H. Organometallics 1993,
12, 1702. (c) Leoni, P.; Pasquali, M.; Sommovigo, M.; Albinati, A.;
Lianza, F.; Pregosin, P. S.; Ru¨egger, H. Organometallics 1994, 13,
4017. (d) Leoni, P.; Vichi, E.; Leonci, S.; Pasquali, M.; Chiarentin,
E.; Albinati, A. Organometallics 2000, 19, 3062
(9) Leoni, P.; Marchetti, F.; Marchetti, L.; Passarelli, V. Chem. Commun.
2004, 2346.
(10) Alvarez, C. M.; Garc´ıa, M. E.; Ruiz, M. A.; Connelly, N. G.
Organometallics 2004, 23, 4750.
(5) Alvarez, M. A.; Garc´ıa, M. E.; Riera, V.; Ruiz, M. A. Organometallics
1999, 18, 634.
(6) Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.; Rueda, M. T.; Sa´ez, D.
Organometallics 2002, 21, 5515.
(7) Adatia, T.; McPartlin, M.; Mays, M. J.; Morris, M. J.; Raithby, P. R.
J. Chem. Soc., Dalton Trans. 1989, 1555.
(11) (a) Nishida, H.; Takada, N.; Yoshimura, M.; Sonoda, T.; Kobayashi,
H. Bull. Chem. Soc. Jpn. 1984, 57, 2600. (b) Brookhart, M.; Grant,
B.; Volpe, A. F., Jr. Organometallics 1992, 11, 3920.
6966 Inorganic Chemistry, Vol. 45, No. 17, 2006

MsP Wersus MdM Bonds as Protonation Sites
Scheme 1
Spectroscopic data in solution for compounds 4a-c (Table
1 and Experimental Section) indicate that these cations
have all the same structure, consistent with the geometric
features found in the solid state for 4a, which imply
equivalent environments for the cyclopentadienyl or carbonyl
ligands. The almost parallel arrangement of the latter
groups is denoted by the appearance of very strong and
weak (in order of decreasing frequency) C-O stretching
bands in their IR spectra.12 The presence of a bridging
hydride ligand (not located in the X-ray study) is clearly
denoted by the appearance of highly shielded resonances in
1
the H NMR spectra (ca. -15 ppm) displaying identical
(4a,b) or similar (4c) couplings to both phosphorus atoms
and “satellite” lines due to the coupling with two equiv-
alent 183W nuclei. Finally, the phosphide ligands give rise
to quite shielded 31P NMR resonances (ca. 45 ppm upfield
from those in the neutral complexes 1a-c) exhibiting
reduced one-bond coupling to the tungsten nuclei (ca. 220
Hz, to be compared with values of ca. 300 Hz in the neutral
complexes). The latter effect is consistent with the increase
in the coordination number of the tungsten atoms upon
protonation.13 The origin of the strong 31P shielding is not
clear, but it seems to be characteristic of binuclear Mo2 or
W2 cyclopentadienyl cations displaying flat M2P2 cores.
The latter are also characterized by unusually low 2JPP values,
a feature previously found for neutral complexes related to
compounds 1 and 2.6,14 Indeed, this is the case for compound
4c (JPP ) 18 Hz) and the dimolybdenum hydride 10e (see
later).
ments on the bis(diphenylphosphide) complexes proved that
the isomerization 3a/4a was substantially accelerated in the
presence of an excess of acid, so as to be completed in a
few minutes instead of a few hours. Thus we conclude that
the above isomerization is not an intramolecular process but
involves a doubly protonated species, which however could
not be detected by IR or NMR spectroscopy. As it will be
seen later on, similar effects have been found in the
protonation reactions of the dimolybdenum substrates 2.
The different arrangement of the carbonyl ligands in the
hydrides 3 and 4 causes that their deprotonation lead ini-
tially to different neutral isomers. Thus, addition of a strong
base such us DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) to
dichloromethane solutions of compounds 3a-c gave the
corresponding starting trans-dicarbonyls 1a-c as expected.
In contrast, the hydride-bridged 4a gives cleanly the cis-
dicarbonyl cis-[W2Cp2(µ-PPh2)2(CO)2] (5a). This complex
has only a moderate thermal stability and rearranges slowly
in dichloromethane solution to yield the more stable trans-
isomer 1a in ca. 20 h at room temperature. The complexes
having diethylphosphide bridges 4b,c, however, gave directly
the corresponding trans derivatives 1b,c upon reaction with
DBU at room temperature, thus suggesting a strong influence
of the substituents at phosphorus on the rate of cis/trans
isomerization in the neutral dicarbonyls.
Structural Characterization of Compounds 3-4. The
structure of 4a has been determined through an X-ray
diffraction study. A view of the cation is shown in Figure 1,
while the most relevant bond distances and angles are
collected in Table 2. The cation exhibits two CpW(CO)
fragments in an almost eclipsed conformation and bridged
through two quite symmetric diphenylphosphide ligands,
which define a flat W2P2 skeleton. The carbonyl ligands are
almost parallel to each other and essentially perpendicular
to the W2P2 plane. Although the hydride ligand could not
be located in this study, its position can be safely inferred
(see below) to be symmetrically bridging the dimetal center
on the “empty” side of the W2P2 plane, that is, opposite the
carbonyl ligands, thus completing the usual four-legged piano
stool environment around the tungsten atoms. We note finally
that the intermetallic separation is very short, 2.7589(8) Å,
only slightly longer than that measured in the isoelectronic
neutral complex 2a [2.713(1) Å],7 and therefore consistent
with a formal W-W bond of order 2.
The spectroscopic properties of the hydrides 3a-c are
completely different from those of their more stable isomers
just discussed. Their IR spectra display strong and very strong
(in order of decreasing frequency) C-O stretching bands,
thus revealing a transoid arrangement of the carbonyl
ligands.12 Besides, the hydride ligand is now bonded to just
one tungsten atom, as revealed by the intensities of the 183
W
1
“satellite” lines of the corresponding resonances in the H
NMR spectra and their relatively low shielding (11-14 ppm
downfield from their bridged isomers). The terminal coor-
dination of the hydride ligand causes the metal and phos-
phorus atoms to be inequivalent, as denoted by the presence
of two distinct resonances in the 31P NMR spectra. Each of
these resonances displays two quite different 31P-183W
couplings, consistent with the different coordination numbers
of the metal centers. Finally, the hydride ligand in compounds
3 also displays substantially different P-H couplings to the
inequivalent phosphorus nuclei, in agreement with its
terminal coordination, which implies different relative posi-
tions (cis and trans) of the hydride and phosphorus atoms.
2
By considering the general trends for JXY in complexes of
the type [MCpXYL2],13,15 we can assign the large absolute
(12) Braterman, P. S. Metal Carbonyl Spectra; Academic Press: London,
U.K., 1975.
(13) Jameson, C. J. In Phosphorus-31 NMR Spectroscopy in Stereochemical
Analysis; Verkade, J. G., Quin, L. D., Eds.; VCH: Deerfield Beach,
FL, 1987; Chapter 6.
(14) Davies, J. E.; Feeder, N.; Gray, C. A.; Mays, M. J.; Woods, A. D. J.
Chem. Soc., Dalton Trans. 2000, 1965.
(15) Wrackmeyer, B.; Alt, H. G.; Maisel, H. E. J. Organomet. Chem. 1990,
399, 125.
Inorganic Chemistry, Vol. 45, No. 17, 2006 6967

Alvarez et al.
Table 1. Selected IRa and NMRb Data for New Compounds
compound
ν(CO)
δH, (JHP), [JHW
]
δP, [JPW
]
JPP
[W2Cp2(H)(µ-PPh2)2(CO)2]BF4 (3a)
[W2Cp2(H)(µ-PEt2)2(CO)2]BF4 (3b)
[W2Cp2(H)(µ-PEt2)(µ-PPh2)(CO)2]BF4 (3c)
2016 (s), 1923 (vs)
1980 (s), 1931 (vs)
1994 (s), 1828 (vs)
-0.42 (19, 12) [28]c
-3.72 (24, 16) [27]d
-1.26 (24, 16) [24]f
126.6 [387, 185]
101.1 [360.181]c
103.0 [339, 180]
61.4 [317, 178]d
110.4 [367, 198]
71.8 [319, 168]f
-10.0 [225]
8
<10e
<10e
[W2Cp2(µ-H)(µ-PPh2)2(CO)2]BF4 (4a)
[W2Cp2(µ-H)(µ-PEt2)2(CO)2]BF4 (4b)
[W2Cp2(µ-H)(µ-PEt2)(CO)2]BAr’4 (4b′)
[W2Cp2(µ-H)(µ-PEt2)(µ-PPh2)(CO)2]BF4 (4c)
1995 (vs), 1960 (w)
1979 (vs), 1936 (w)
1982 (vs), 1939 (w)
1984 (vs), 1948 (w)
-14.59 (50) [49]
-15.50 (52) [52]g
-16.03 (50) [50]
-14.88 (54, 48) [51]g
-27.0 [215]g
-23.6 [213]
-8.3 (PPh2) [228]
18
-28.5 (PEt2) [209]g
74.3 [335]
158.5, 152.7
68.7
cis-[W2Cp2(µ-PPh2)2(CO)2] (5a)
1926 (vs), 1872 (w)
2003 (s), 1928 (vs)
2010 (s)h
1935 (vs), 1883 (w)
1956 (m, sh), 1915 (vs)
[Mo2Cp2(H)(µ-PPh2)2(CO)2]BF4 (6)
[Mo2Cp2(µ-H)(µ-PPh2)2(CO)2]BF4 (7)
cis-[Mo2Cp2(µ-PPh2)2(CO)2] (8)
-1.88 (32, 30)
-13.35 (56)h
56
145.6
[Mo2Cp2(µ-PEt2)(µ-κ2-HPEt2)(CO)2]BF4 (9b)
-4.22 (103)i
145.0 (br),
91.4 (br, HP)
161.4, 89.7 (HP)d
163.2 (br), 90.2(br)
145.5, 100.4 (HPCy2)g
141.1, 103.5 (HPCy2)c
61.4
<55e
<20e
[Mo2Cp2(µ-PCy2)(µ-κ2-HPCy2)(CO)2]BF4 (9d)
[Mo2Cp2(µ-PCy2)(µ-κ2-HPCy2)(CO)2]BAr’4 (9d′)
[Mo2Cp2(µ-PPh2)(µ-κ2-HPCy2)(CO)2]BF4 (9e)
[Mo2Cp2(µ-PPh2)(µ-κ2-HPCy2)(CO)2]BAr’4 (9e′)
[Mo2Cp2(µ-H)(µ-PEt2)2(CO)2]BF4 (10b)
1931 (m, sh), 1895 (vs)
1931 (m, sh), 1896 (vs)
1959 (m, sh), 1906 (vs)
1907 (vs)
1990 (vs)
1982 (vs)
1983 (vs)
1997 (vs)
1998 (vs), 1962 (w)
2113 (s),j 1942 (vs)
2093 (s),j 2042 (w)j
1838 (s)
-4.80 (134, -5)d
-4.78 (127)i
-4.33 (132, -5)g
-4.68 (132, -5)c
-14.54 (68)
<35e
<10e
12
[Mo2Cp2(µ-H)(µ-PCy2)2(CO)2]BF4 (10d)
[Mo2Cp2(µ-H)(µ-PCy2)2(CO)2]BAr’4 (10d′)
[Mo2Cp2(µ-H) (µ-PCy2)(µ-PPh2)(CO)2]BF4 (10e)
[Mo2Cp2(µ-H) (µ-PCy2)(µ-PPh2)(CO)2]BAr’4 (10e′)
[Mo2Cp2(µ-H)(µ-PCy2)2(CO)(CNtBu)]BF4 (11)
[Mo2Cp2(µ-H)(µ-PCy2)2(CNtBu)2]BF4 (12)
[Mo2Cp2(H)(µ-PCy2)2(CO)]BF4 (13)
-13.54 (58)
78.4
78.5
-13.57 (58)
-13.34 (57, 57)g
-13.47 (57, 57)
-14.74 (43)
84.4 (PCy), 66.3g
84.6 (PCy), 64.
82.5
12
<12e
-16.64 (53)
100.9
-1.60 (45)f
305.2f
[Mo2Cp2(µ-COH)(µ-PCy2)2]BF4 (14)
278.3
a Recorded in dichloromethane solution, unless otherwise stated, ν in cm-1 b Recorded in CD2Cl2 solutions at 290 K and 300.13 (1H) or 121.50 (31P)
.
MHz, unless otherwise stated, δ in ppm relative to internal TMS (1H) or external 85% aqueous H3PO4 (31P); J in Hz. c Recorded at 223 K. d Recorded at
243 K. e Upper limit estimated from the half-width of the lines. f Recorded at 203 K. g Recorded in CDCl3 solution. h Data from ref 7. i False triplet, |JHP
JHP| ) 103. j ν(C-N).
+
Chart 1
Chart 2
Figure 1. ORTEP diagram (30% probability) of the cation in compound
4a, with H atoms and Ph groups (except the C1 atoms) omitted for clarity.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for Compound
4a
Chart 3
W(1)-W(2)
2.7589(8)
2.425(4)
2.421(4)
2.02(2)
1.09(2)
69.4(1)
96.8(5)
92.3(5)
89.2(5)
178.8(15)
W(2)-P(1)
2.422(4)
2.433(4)
2.01(2)
1.11(2)
69.3(1)
90.8(4)
86.2(5)
88.5(4)
176.5(15)
W(1)-P(1)
W(2)-P(2)
W(1)-P(2)
W(2)-C(2)
C(2)-O(2)
W(1)-P(2)-W(2)
C(2)-W(2)-W(1)
C(2)-W(2)-P(1)
C(2)-W(2)-P(1)
W(2)-C(2)-O(2)
W(1)-C(1)
C(1)-O(1)
W(1)-P(1)-W(2)
C(1)-W(1)-W(2)
C(1)-W(1)-P(1)
C(1)-W(1)-P(2)
W(1)-C(1)-O(1)
complex. We can identify it as isomer A on the basis of
selectively 31P-decoupled H NMR experiments. Thus, ir-
1
coupling (20-30 Hz) to that one between the hydride and
the P atom arranged in cis.
In the case of the mixed complex 3c there are two possible
isomers differing in the relative arrangement of the hydride
and phosphide groups (A and B in Chart 1), but only one of
them is present in the dichloromethane solutions of this
radiation of the 71.8 ppm resonance (PEt2 group) caused the
collapse of the smaller P-H splitting (16 Hz) in the hydride
resonance, thus suggesting that these ligands are arranged
in a relative trans position. The reverse (collapse of the larger
splitting) is observed when irradiating the 110.4 ppm
resonance (PPh2 group), thus suggesting that the hydride and
6968 Inorganic Chemistry, Vol. 45, No. 17, 2006

MsP Wersus MdM Bonds as Protonation Sites
Scheme 2
PPh2 ligands are arranged in cis and, therefore, relatively
close to each other. The latter is in agreement with a standard
NOESY 1H-1H experiment performed on 3c at 243 K, which
revealed a positive NOE enhancement between the hydride
atom and the ortho hydrogens of one phenyl ring (δH ) 6.73
ppm) but not between the hydride and any of the ethyl
protons.
A Revision of the Protonation of Compound 2a. As
stated above, some time ago Mays et al. reported that the
dimolybdenum compound 2a could be protonated to give
the hydride bridged cation [Mo2Cp2(µ-H)(µ-PPh2)2(CO)2]BF4
(7) having the same structure as the ditungsten compounds
4a-c just discussed.7 In light of our results on the latter
ditungsten substrates, however, we examined the possibility
that the protonation of 2a could involve intermediate species
related to the terminal hydride complexes 3a-c, and this
proved to be the case. Indeed, HBF4‚OEt2 reacts with 2a at
253 K to give cleanly [Mo2Cp2(H)(µ-PPh2)2(CO)2]BF4 (6),
which at room temperature rearranges to give the hydride-
bridged isomer 7. This isomerization is substantially faster
than that for the ditungsten analogue 3a and is completed in
ca. 20 min when using roughly stoichiometric amounts of
acid (more rapidly when using excess of acid).
The spectroscopic data for 6 are very similar to those for
3a (Table 1 and Experimental Section) except for the
expected changes when replacing tungsten by molybdenum
atoms and need then no detailed comment. The only unusual
feature concerns the H-P couplings of the hydride resonance
with the phosphide ligands, which are roughly the same (ca.
30 Hz), instead of being substantially different, as expected
for cis and trans two-bond P-H couplings (ca. 65 and 25
Hz for cis and trans P-H couplings in mononuclear [MoCp-
(H)(PR3)(CO)2] complexes).16 This unusual result might be
due to specific reinforcement or cancellation effects resulting
from the algebraic sum of two- and three-bond contributions
(i.e. H-Mo-P and H-Mo-Mo-P pathways) to the H-P
coupling.13 On the other hand, our spectroscopic data for 7
are consistent with those reported originally by Mays et al.
except for the 31P chemical shift, reported to be 71.7 ppm in
CDCl3 relative to P(OMe)3 (equivalent to 212.7 ppm relative
to H3PO4).7 The value measured by us for 7 in CD2Cl2
solution is +68.7 ppm (equivalent to -72.3 ppm in the
P(OMe)3 scale), which points to a typographic error in the
originally reported figure.
[Mo2Cp2(µ-PPh2)(µ-PtBu2)(CO)2]6 and need then no further
comment. We note however, that the latter is the only
previous group 6 complex of type [Mo2Cp2(µ-PR2)(µ-PR′2)-
(CO)2] reported to have a cis-dicarbonyl geometry, although
related complexes are thought to be intermediate species in
the carbonylation reactions of the triply bonded compounds
[M2Cp2(µ-PR2)(µ-PR′2)(µ-CO)] to give the corresponding
trans-dicarbonyl derivatives 1 and 2.6
Protonation of Molybdenum Complexes with Electron-
Rich Phosphide Bridges. The dimolybdenum complexes
[Mo2Cp2(µ-PR2)2(CO)2] [R ) Et (2b), Cy (2d)] react with
HBF4‚OEt2 in dichloromethane solutions at 243 K to give,
in a quantitative and reversible way, the corresponding
derivatives [Mo2Cp2(µ-PR2)(µ-κ2-HPR2)(CO)2]BF4 (9b,d),
which contain an agostic type, P-H bonded phosphine
bridging ligand. These complexes rearrange at room tem-
perature so as to reach an equilibrium with the corresponding
hydride-bridged tautomers [Mo2Cp2(µ-H)(µ-PR2)2(CO)2]BF4
(10b,d), which are isostructural to the ditungsten complexes
4a-c discussed above (Scheme 2). The agostic isomers were
the major species in both cases, with the agostic/hydride ratio
being ca. 10 (R ) Cy) and 30 (R ) Et), according to NMR
measurements.
The mixed-phosphide complex [Mo2Cp2(µ-PCy2)(µ-PPh2)-
(CO)2] (2e) reacts with HBF4‚OEt2 in a similar way, to give
first the agostic type derivative (9e) which at room temper-
ature rearranges to reach an equilibrium with its hydride
tautomer 10e. The agostic/hydride ratio is now only 0.5, and
the agostic isomer displays an H-P bond formed specifically
at the cyclohexylphosphide ligand, according to the NMR
data to be discussed below. All this is indicative of a
thermodynamic reluctance of the diphenylphosphide ligand
(relative to the PCy2 or PEt2 groups) to be protonated to give
agostic phosphine-bridged derivatives. By considering the
abundant studies on the steric17 and electronic18 influence
of substituents on phosphine ligands, we can estimate for
the groups involved here that the electron-donor influence
Isomers 6 and 7 behave as their ditungsten analogues upon
deprotonation with DBU in dichloromethane solution, so that
compound 6 gives back the trans-dicarbonyl 2a, while 7 gives
the cis-dicarbonyl cis-[Mo2Cp2(µ-PPh2)2(CO)2] (8). Com-
pound 8 is thermally unstable and rearranges more rapidly
than its ditungsten analogue 5a, to give the more stable trans-
isomer 2a in ca. 1.5 h at room temperature.
Spectroscopic data for the compounds 5a and 8 (Table 1
and Experimental Section) indicate that these complexes are
isostructural to each other and allow their identification as
cis-dicarbonyl complexes. The spectral properties for these
complexes are similar to those previously reported for cis-
(17) (a) Tolman, C. A. Chem. ReV. 1977, 77, 33. (b) Stahl, L.; Ernst, R. D.
J. Am. Chem. Soc. 1987, 109, 5673. (c) Brown, T. L. Inorg. Chem.
1992, 31, 1286. (d) Muller, T. E.; Mingos, D. M. P. Transition Met.
Chem. 1995, 20, 533. (e) Smith, J. M.; Taverner, B. C.; Coville, N. J.
J. Organomet. Chem. 1997, 530, 131 and references therein.
(18) (a) Dias, P. B.; Minas de Piedade, M. E.; Martinho-Simoes, J. A.
Coord. Chem. ReV. 1994, 135, 737 and references therein. (b) Drago,
R. S. Organometallics 1995, 14, 3408.
(16) Faller, J. W.; Anderson, A. S. J. Am. Chem. Soc. 1970, 92, 5852.
Inorganic Chemistry, Vol. 45, No. 17, 2006 6969

Alvarez et al.
Table 3. Selected Bond Lengths (Å) and Angles (deg) for Compound
9d
Mo(1)-Mo(2)
2.748(4)
2.378(7)
2.03(5)
69.1(2)
83.9(11)
85.9(6)
176(4)
Mo(2)-H(1)
1.95
Mo(1)-P(1)
Mo(2)-P(1)
2.464(8)
1.92(4)
1.67
74.8(11)
81.8(7)
171(3)
Mo(1)-C(1)
Mo(2)-C(2)
P(1)-H(1)
C(2)-Mo(2)-Mo(1)
C(2)-Mo(2)-P(1)
Mo(2)-C(2)-O(2)
Mo(1)-P(1)-Mo(2)
C(1)-Mo(1)-Mo(2)
C(1)-Mo(1)-P(1)
Mo(1)-C(1)-O(1)
while the most relevant geometric parameters are collected
in Table 3. The cation is placed on a crystallographic plane
of symmetry containing the metal atoms and carbonyl
ligands, the latter being in a transoid arrangement and slightly
bent over the metal-metal vector (C-Mo-Mo angles ca.
78°). This element of symmetry forces the phosphorus atoms
to be equivalent and the P-H bonded hydrogen atom to be
disordered in two equivalent positions with half occupancy.
These positions were located as bridging the Mo(2)-P(1)
bonds, slightly above the Mo2P2 plane, on a site close to the
cyclopentadienyl ligand bonded to Mo(2). This is in agree-
ment with the substantial elongation of ca. 0.1 Å for the Mo-
(2)-P(1) bonds, relative to the “unbridged” Mo(1)-P(1)
bonds. Obviously, this elongation of the Mo-P bond upon
protonation would be higher in the absence of disorder, and
it can be estimated to be ca. 0.2 Å. Unfortunately, there are
no structural data available for further comparison; in the
case of [Pd2(µ-κ2-HPtBu2)(µ-PtBu2)(PHtBu2)2]+, which is the
only previous related complex crystallographically character-
ized, the agostic H atom could not be located, but the pairs
of Pd-P distances (also related by imposed symmetry)
showed a similar lengthening effect (P-Pd ) 2.311(2) and
2.392(2) Å).8b Finally, the intermetallic separation in 9d is
very short, 2.742(8) Å, a value intermediate between those
measured for compounds 4a (Table 2) and 2a,7 and therefore
consistent with a formal Mo-Mo bond of order 2, as
expected under the EAN formalism by considering the
agostic phosphine ligand as a neutral four-electron donor.
The solid-state structure of 9d suggests that protonation
of the M-P bond in the molybdenum substrates 2b-e takes
place specifically opposite the closer carbonyl ligand. This
is in contrast with the initial protonation of the ditungsten
complexes 1 and the molybdenum substrate 2a, all of which
occur at the metal site and result in cis arrangements of the
carbonyl and hydride ligands (compounds 3a-c and 6). We
trust that this geometric difference can hardly have a steric
origin but surely follows from small differences in the
electron distribution of the corresponding neutral complexes.
Solution Structure of Compounds 9 and 10. The
spectroscopic data for the hydride-bridged isomers 10b-e
(Table 1 and Experimental Section) are comparable to those
for the ditungsten compounds 4a-c or the dimolybdenum
complex 7 and need then no further comments. The data for
isomers 9b-e are essentially consistent with the crystal
structure determined for 9d. For example, the transoid
arrangement of the carbonyl ligands is denoted by the
appearance of medium and very strong (in order of decreas-
ing frequency) C-O stretching bands in their IR spectra,12
ca. 80 cm-1 above those of the corresponding neutral
Figure 2. ORTEP diagram (30% probability) of the cation in compound
9d, with H atoms (except the agostic hydrogen atom) and Cy groups (except
the C1 atoms) omitted for clarity.
on the µ-PR2 ligands would follow the sequence Cy > Et >
Ph, whereas the relative size would decrease in the order
Cy > Ph ≈ Et. Therefore, from the measured equilibrium
ratios in the pairs 9b-e/10b-e we conclude that the agostic
structure is favored over its hydride tautomer for good
electron-donor and small R groups on phosphorus. We note
finally that compounds 9 and 10 represent the first examples
of agostic P-H bonded phosphine complexes being in
equilibrium with their hydride-phosphide tautomers, thus
paralleling the behavior of several κ2-dihydrogen com-
plexes.19 The few Pd and Pt complexes previously reported
to have µ-κ2-HPR2 ligands displayed only agostic type
structures.8
The nature of the phosphide ligands has also an influence
on the rate at which the equilibrium between agostic an
hydride isomers is reached, this following the order (µ-PEt2)2
> (µ-PCy2)2 > (µ-PCy2)(µ-PPh2) under comparable condi-
tions. Besides, this rate is also dependent on the amount of
acid present in the solution. The latter clearly establishes
that the agostic/hydride isomerization is not an intramolecular
process but involves the transient formation of a doubly
protonated species. Unfortunately, no intermediate species
were detected by IR or NMR monitoring of the correspond-
ing reaction mixtures even under quite high concentration
of acid and low temperature. Therefore, we ignore if the
rearrangement of carbonyl ligands required to transform
compounds 9 into 10 occurs at this step or later on. In any
case, in the absence of excess of acid the rate of isomerization
is low, and no significant change in the ratio of isomers is
detected by NMR when cooling the equilibrated dichloro-
methane solutions from 293 K down to 193 K. For the same
reason, rapid crystallization of these solutions (by adding
petroleum ether) gave solid materials shown by IR to contain
mixtures of isomers 9 and 10.
Crystal Structure of the Agostic Complex 9d. Single
crystals of the agostic tautomer could be grown by slow
diffusion of petroleum ether into a dichloromethane solution
of isomers 9d and 10d. The quality of the diffraction data
was low, but the structure could be solved and refined to a
sensible point. A view of the cation is shown in Figure 2,
(19) Kubas, G. J. Metal Dihydrogen and σ-Bond Complexes; Kluwer
Academic/Plenum Press: New York, 2001.
6970 Inorganic Chemistry, Vol. 45, No. 17, 2006

MsP Wersus MdM Bonds as Protonation Sites
Scheme 3. Fluxional Process Proposed for Compounds 9b,d in
Solution
concluded that the two H-P couplings are opposite in sign
(so as to give an averaged triplet with line separations being
half the differencesrather than the sumsof their absolute
values); this is not unusual for one-bond vs two-bond H-P
couplings.13 Finally, from the coalescence temperature of the
outer lines of the agostic H resonance (ca. 278 K) we can
quote an activation barrier of 54.7 ( 0.5 KJ mol-1 for the
corresponding fluxional process.20 From the latter value, in
turn, we can estimate that the coalescence temperature for
the 31P NMR resonances in 9d would be around 340 K if
measured at 162.0 MHz, in agreement with the severe
broadening observed already at room temperature.
As stated above, the protonation of the mixed-phosphide
complex 9e occurs specifically at the PCy2 bridge. This is
deduced on the basis of the 31P chemical shifts. By comparing
the corresponding 31P data for the dicyclohexyl complexes
2d and 9d it is concluded that protonation of the PCy2 bridge
causes a slight shielding on the corresponding nucleus (from
95.4 to 89.7 ppm) and a strong deshielding on the unpro-
tonated bridge (from 95.4 to 161.4 ppm). Therefore, since
the chemical shifts of the PCy2 and PPh2 bridges in 2e are
107.4 and 83.3 ppm, respectively,6 the value of 100.4 ppm
for the HP resonance in 9e denotes that the proton is bonded
Figure 3. Variable-temperature 400.13 MHz 1H NMR spectra of 9d in
CD2Cl2 solution (hydride region): (a) 293 K; (b) 278 K; (c) 258 K; and
(d) 243 K.
substrates 2d,e, as expected. The presence of an agostic-
type Mo-H-P interaction in complexes 9b-e is clearly
1
denoted by the appearance of a considerably shielded H
NMR resonance (δH ca. -4.5 ppm) in each case, which
exhibits a strongly reduced one-bond coupling to phosphorus
[JHP ca. 130 (HPCy2) or 110 Hz (HPEt2)], ca. 50% of the
usual values for comparable “normal” H-P bonds. At the
same time, the corresponding phosphorus resonance is
considerably shielded (by ca. 60-70 ppm) with respect to
that of the remaining phosphide ligand. These spectroscopic
features, shifts, and couplings intermediate between those
corresponding to phosphide (PR2) and secondary phosphine
(HPR2) ligands are similar to those quoted for the previously
reported palladium and platinum complexes having agostic
HPtBu2 or HPCy2 bridges.8,9 The main difference between
the latter and our dimolybdenum complexes concerns their
dynamic behavior in solution. Thus, compounds 9d and 9b
experience intramolecular exchange of the agostic H atom
between both P sites, a process not observed for the related
palladium and platinum complexes. This dynamic rearrange-
ment, which we have studied with some detail for the
dicyclohexyl complex 9d, is denoted by the progressive
broadening, upon increasing the temperature, of the relatively
1
to the PCy2 group. Moreover, since all 31P or H NMR
resonances have normal line widths, we conclude that there
are not dynamic processes under operation in this complex.
Indeed, a rearrangement process similar to that detected for
compounds 9b and 9d (Scheme 3) would now be an
isomerization implying the unfavorable formation of HPPh2
bridges.
The Effect of the External Anion. Selected experiments
were carried out using strong acids having noncoordinating
([H(OEt2)2]BAr′4)11 or coordinating (HCl) anions. The reac-
tion of the former acid with the ditungsten complex 1b at
253 K gave the corresponding hydride derivative [W2Cp2-
(H)(µ-PEt2)2(CO)2](BAr′4) (3b′) (ν(C-O) ) 1982 (s), 1936
(vs) cm-1) which at room temperature rapidly rearranges to
give the hydride-bridged isomer [W2Cp2(µ-H)(µ-PEt2)2(CO)2]-
(BAr′4) (4b′). This behavior is therefore identical to that
observed in the reactions of ditungsten substrates with HBF4‚
OEt2 and need then no further comment. We must note that
no evidence for the involvement of any agostic intermediate
species could be obtained in these reactions.
1
sharp 31P and H NMR resonances observed at 243 K. The
two phosphorus resonances are very broad at 293 K, this
suggesting mutual exchange, while the outer lines of the
hydride resonance have merged into a central broad line
(Figure 3). The inner lines of the hydride resonance are not
affected by the dynamic process, nor are the two cyclo-
pentadienyl resonances of the complex. From all the above
data it can be concluded that the dynamic process under
operation (a) is intramolecular, since H-P couplings are
retained, and (b) involves the migration of the agostic
hydrogen between both phosphorus sites but not between
molybdenum atoms (Scheme 3). In addition, it can be
The reaction of [H(OEt2)2](BAr′4) with the dimolybdenum
compounds 2d and 2e also proceeded as the reactions with
tetrafluoroboric acid, to give first the corresponding agostic
complexes 9d′ or 9e′ which at room temperature reach an
equilibrium with the corresponding hydride tautomers 10d′
and 10e′. However, the agostic/hydride ratios in the equi-
(20) Calculated using the modified Eyring equation ∆G# ) 19.14Tc[9.97
+ log(Tc/∆ν)] (in Jmol-1). See: Gu¨nter, H. NMR Spectroscopy; John
Wiley: Chichester, U.K., 1980; p 243.
Inorganic Chemistry, Vol. 45, No. 17, 2006 6971

Alvarez et al.
librium are now different, ca. 20 and 1 for the (PCy2)2 and
(PCy2)(PPh2) compounds, respectively (to be compared with
ratios of 10 and 0.5 for the tetrafluoroborate salts). From
-
this we conclude that the BAr′4 anion has a modest but
measurable stabilizing effect on the agostic structure, relative
to its isomeric hydride form. This might be due to small
differences in the anion-cation interactions when replacing
-
the weakly coordinating BF4 ion by the almost noncoor-
dinating BAr′4- anion. These differences must be small, since
the spectroscopic properties for the corresponding tetra-
arylborate and tetrafluoroborate salts are essentially the same
(Table 1 and Experimental Section).
The presence of a weakly coordinating anion seems to be
essential for the stability of both the agostic and the hydride
cations, an effect surely related to their unsaturated nature.
Thus, the reaction of compounds 2d or 2e with HCl in
dichloromethane at room temperature seems to give the
corresponding agostic complexes (as their Cl- salts) in a first
stage, as denoted by the presence of C-O stretching bands
at 1934 (m, sh) and 1895 (vs) cm-1 or 1951 (m, sh) and
1907 (vs) cm-1, respectively. However, these complexes
react further at room temperature to give complex mixtures
of products that could not be characterized.
The Effect of Ligands on the Metal Atoms. Having
established the effect of the substituents at phosphorus on
the stability of the agostic phosphine-bridged complexes 9
relative to their hydride-phosphide tautomers 10, we decided
to examine the role of ligands (other than the PR2 bridges)
around the molybdenum atoms. We have done this by
removing a CO ligand from the metal center and by replacing
CO ligands by a slightly better donor such as CNtBu. In both
cases hydride derivatives are invariably formed.
An equilibrium mixture of isomers 9d and 10d reacts
rapidly with CNtBu in dichloromethane solution at room
temperature to give the monosubstituted derivative [Mo2-
Cp2(µ-H)(µ-PCy2)2(CO)(CNtBu)]BF4 (11) in high yield. No
intermediate species could be detected in this reaction.
Besides, further substitution can be forced in the presence
of a second equivalent of isocyanide, by heating the solution
at 313 K for ca. 1.5 h, thus yielding the bis(isocyanide)
derivative [Mo2Cp2(µ-H)(µ-PCy2)2(CNtBu)2]BF4 (12) in good
yield.
Spectroscopic data for 11 and 12 indicate that these
complexes have the same basic structure as the hydride-
bridged dicarbonyls 3a-c, 7, and 10b-e, after replacing one
or two CO ligands by CNtBu. They all show quite shielded
hydride and phosphide NMR resonances. The cis arrange-
ment of the isocyanide ligands in 12 is denoted by the relative
intensities (similar to those found for the cis-dicarbonyls 4a-
c) of the C-N stretching bands present in the IR spectrum.
In the case of compound 11, the structure of the cation has
been confirmed by an X-ray study (Figure 4 and Table 4).
The cation is built up from two CpMo fragments bridged
by dicyclohexylphosphide bridges thus defining an essentially
flat Mo2P2 skeleton. The coordination spheres around the
metal centers are completed by terminal CO and CNR
ligands, almost parallel to each other and roughly perpen-
dicular to the Mo2P2 plane, and by a hydride ligand. This
Figure 4. ORTEP diagram (30% probability) of the cation in compound
11, with H atoms (except the hydride ligand) and Cy or tBu groups (except
the C1 atoms) omitted for clarity.
Table 4. Selected Bond Lengths (Å) and Angles (deg) for Compound
11
Mo(1)-Mo(2)
2.7901(7)
2.428(1)
2.420(1)
2.056(5)
1.87(6)
1.152(6)
70.02(4)
138(2)
96.5(1)
92.9(1)
91.0(1)
175.8(4)
172.7(5)
Mo(2)-P(1)
2.436(1)
2.433(1)
1.967(5)
1.149(6)
1.86(6)
1.454(6)
70.19(4)
129(2)
87.1(1)
86.1(1)
87.1(2)
176.3(4)
Mo(1)-P(1)
Mo(2)-P(2)
Mo(1)-P(2)
Mo(2)-C(1)
Mo(1)-C(2)
C(1)-O(1)
Mo(1)-H(1)
Mo(2)-H(1)
C(2)-N(1)
N(1)-C(3)
Mo(1)-P(1)-Mo(2)
C(2)-Mo(1)-H(1)
C(2)-Mo(1)-Mo(2)
C(2)-Mo(1)-P(1)
C(2)-Mo(1)-P(2)
Mo(1)-C(2)-N(1)
C(2)-N(1)-C(3)
Mo(1)-P(2)-Mo(2)
C(1)-Mo(2)-H(1)
C(1)-Mo(2)-Mo(1)
C(1)-Mo(2)-P(1)
C(1)-Mo(2)-P(2)
Mo(2)-C(1)-O(1)
atom could be satisfactorily refined as bridging the metal
atoms quite symmetrically and arranged trans with respect
to the CO and CNR ligands, thus completing the usual four-
legged piano stool coordination geometry around the molyb-
denum atoms. The intermetallic length in 11 is 2.7901(7)
Å, longer than that in the ditungsten hydride 4a [2.7589(8)
Å], the agostic cation 9d [2.742(8) Å], or the neutral
dicarbonyl 2c [2.713(1) Å],7 all of which are also 32 electron
complexes. This suggests that the isocyanide ligand, being
a better donor than CO, might be causing a significant
lengthening of the intermetallic bond in 11.
The incipient oxidative addition of the P-H bond present
in compound 9d can be driven to full term also by removing
a CO ligand. This cannot be done thermally in an easy way,
since refluxing dichloroethane solutions of isomers 9d and
10d caused no noticeable change after 1 h. However, UV-
visible irradiation of dichloromethane solutions of isomers
9d and 10d for 3.5 h gave the hydride monocarbonyl
complex [Mo2Cp2(H)(µ-PCy2)2(CO)]BF4 (13) with good
yield. The structure of the cation (Figure 5 and Table 5) is
built up from two CpMo moieties symmetrically bridged by
two dicyclohexylphosphide ligands. The coordination spheres
around the metal atoms are completed by terminal hydride
[on Mo(1)] and carbonyl [on Mo(2)] ligands, which are in a
transoid arrangement, but in very different environments. The
hydride ligand, which could be successfully located and its
position refined, is clearly terminal and points away from
the intermetallic region [Mo(2)-Mo(1)-H(1) ) 103(3)°].
In contrast, the carbonyl ligand is bent over the intermetallic
6972 Inorganic Chemistry, Vol. 45, No. 17, 2006

MsP Wersus MdM Bonds as Protonation Sites
analogue of 13 is the unstable methoxycarbyne complex
[Mo2Cp2(µ-COMe)(H)(µ-PCy2)]BF4, prepared recently in our
laboratory through the thermal isomerization of the triply
bonded hydroxycarbyne complex [Mo2Cp2(µ-COH)(µ-
COMe)(µ-PCy2)]BF4.27
The spectroscopic data in solution for 13 (Table 1 and
Experimental Section) are in general agreement with its solid-
state structure. The phosphorus nuclei give rise to a strongly
deshielded 31P NMR resonance (δP ) 305.2 ppm), which
seems to be a spectroscopic characteristic of phosphide-
bridged dimolybdenum or ditungsten cyclopentadienyl com-
plexes with formal triple intermetallic bonds.6 The presence
of a terminal hydride in 13 is denoted by the appearance of
a relatively deshielded hydride resonance (δH ) -1.60 ppm),
to be compared to ca. -15 ppm for the hydride-bridged
complexes 4, 7, and 10-12. On the other hand, the retention
in solution of the semibridging character for the carbonyl
ligand is deduced from its relatively low C-O stretching
frequency (1838 cm-1) and high 13C chemical shift (δC )
Figure 5. ORTEP diagram (30% probability) of the cation in compound
13, with H atoms (except the hydride ligand) and Cy groups (except the C1
atoms) omitted for clarity.
Table 5. Selected Bond Lengths (Å) and Angles (deg) for Compound
13
Mo(1)-Mo(2)
2.534(2)
2.380(4)
2.383(4)
1.65(9)
2.41(1)
64.2(1)
103(3)
80(3)
Mo(2)-P(1)
2.390(4)
2.412(4)
1.94(1)
1.19(1)
63.8(1)
63.5(4)
95.7(4)
94.2(4)
166(1)
Mo(1)-P(1)
Mo(2)-P(2)
Mo(1)-P(2)
Mo(2)-C(1)
C(1)-O(1)
Mo(1)-P(2)-Mo(2)
C(1)-Mo(2)-Mo(1)
C(1)-Mo(2)-P(1)
C(1)-Mo(2)-P(2)
Mo(2)-C(1)-O(1)
Mo(1)-H(1)
Mo(1)-C(1)
Mo(1)-P(1)-Mo(2)
H(1)-Mo(1)-Mo(2)
H(1)-Mo(1)-P(1)
H(1)-Mo(1)-P(2)
1
260.6 ppm). The appearance of a single H or 13C NMR
resonance at room temperature for the inequivalent cyclo-
pentadienyl ligands, however, is indicative of dynamic
behavior. Indeed, although the hydride resonance remains
unchanged on lowering the temperature, the cyclopentadienyl
1H NMR resonance at 5.82 ppm broadens and eventually
splits into two well separated resonances (δH ) 5.92 and
5.78 ppm at 203 K), in agreement with the solid-state
structure. From the corresponding coalescence temperature
(ca. 213 K) we can estimate that the underlying fluxional
process has a low activation barrier of ca. 43 ((1) KJ mol-1,
which we propose to just involve a concerted scrambling of
the CO and H ligands between both metal atoms, perhaps
through a transition state having hydride and carbonyl bridges
(Scheme 4).
73(3)
vector [Mo(1)-Mo(2)-C(1) ) 63.5(4)°] and within bonding
distance to the second metal atom [C(1)-Mo(2) ) 1.94(1)
Å, C(1)‚‚‚Mo(1) ) 2.41(1) Å], while remaining essentially
linear [Mo(2)-C(1)-O(1) ) 166(1)°]. Thus, we can identity
this ligand as a class II linear semibridging carbonyl, in terms
of the classification proposed by Crabtree and Lavin.21
According to the EAN formalism, a triple metal-metal bond
must be formulated for this 30 electron complex cation,
which is in agreement with the very short intermetallic
separation, 2.534(2) Å. The latter value compares well with
those for other triply bonded complexes, such as the neutral
[Mo2Cp2(CO)4] [2.4477(12) Å]22a and [W2Cp2(CO)2(µ-Ph2-
PCH2PPh2)] [2.5144(5) Å].22b We note that the latter
complexes also display linear semibridging carbonyls, a fact
justified by theoretical calculations.23 Similar intermetallic
distances have been found for the phosphide-bridged 30
electron complexes [Mo2Cp2(µ-PPh2)2(µ-CO)] [2.515(2) Å]7
and [Mo2Cp2(µ-H)(µ-PCy2)(CO)2] [2.528(2) Å],24 which
display either bridging or terminal carbonyls, respectively.
Attempts to prepare compound 13 by direct protonation
of the neutral monocarbonyl [Mo2Cp2(µ-PCy2)2(µ-CO)] were
unsuccessful. The latter neutral complex reacts cleanly with
HBF4‚OEt2 to give the corresponding hydroxycarbyne de-
rivative [Mo2Cp2(µ-COH)(µ-PCy2)2]BF4 (14) as expected,28
but the latter does not experience a clean transformation into
its hydride tautomer 13. Instead, stirring dichloromethane
solutions of 14 at room temperature for several hours gave
a mixture of products containing only small amounts of the
hydride 13. The structural characterization of compound 14
can be made easily by comparison of its spectroscopic data
with those of the related diphenylphosphide-bridged ana-
logues [M2Cp2(µ-COX)(µ-PPh2)2]BF4 (M ) Mo, W; X )
H, Me).28 In particular, the presence of the hydroxycarbyne
ligand is denoted by the appearance of characteristic strongly
deshielded 1H (δH ) 12.33 ppm) and 13C (δC ) 368.2 ppm)
NMR resonances as well as the pertinent O-H (3600 cm-1)
and C-O (1262 cm-1) stretching bands in the solid-state IR
spectrum.5,28
Compound 13 is unusual in having its hydride ligand
terminally bound to a metal involved in a triple intermetallic
bond. Usually, these 30 electron complexes display bridging
hydride ligands.5,24-26 In fact, the only reported structural
(21) Crabtree, R. H.; Lavin, M. Inorg. Chem. 1986, 25, 805.
(22) (a) Klinger, R. J.; Butler, W. M.; Curtis, M. D. J. Am. Chem. Soc.
1978, 100, 5034. (b) Alvarez, M. A.; Garc´ıa, M. E.; Riera, V.; Ruiz,
M. A.; Falvello, L. R.; Bois, C. Organometallics 1997, 16, 354.
(23) Simpson, C. Q., II; Hall, M. B. J. Am. Chem. Soc. 1992, 114, 1641.
(24) Alvarez, C. M.; Alvarez, M. A.; Garc´ıa, M. E.; Ramos, A.; Ruiz, M.
A.; Lanfranchi, M.; Tiripicchio, A. Organometallics 2005, 24, 7.
(25) Cotton, F. A.; Walton, R. A. Multiple Bonds Between Metal Atoms,
2nd ed.; Oxford University Press: Oxford, U.K., 1993.
(26) (a) Hoyano, J. K.; Graham, W. A. G. J. Am. Chem. Soc. 1982, 104,
3722. (b) Forrow, W. J.; Knox, S. A. R. J. Chem. Soc., Chem.
Commun. 1984, 679. (c) Kang, B. S.; Koelle, U.; Thewalt, U.
Organometallics 1991, 10, 2569. (d) Suzuki, H. Eur. J. Inorg. Chem.
2002, 1009.
(27) Alvarez, M. A.; Alvarez, C. M.; Garc´ıa, M. E.; Garc´ıa-Vivo´, D.; Ruiz,
M. A. Organometallics 2005, 24, 4122.
(28) Garc´ıa, M. E.; Riera, V.; Rueda, M. T.; Ruiz, M. A.; Halut, S. J. Am.
Chem. Soc. 1999, 121, 1960.
Inorganic Chemistry, Vol. 45, No. 17, 2006 6973

Alvarez et al.
Table 6. Crystal Data for Compounds 4a, 9d, 11, and 13
compound
mol formula
4a‚H2O
9d
11‚CH2Cl2
13‚CH2Cl2
a
C36H33BF4O3P2W2
1030.1
C36H55Mo2O2P2
773.6a
C41H66BCl2F4Mo2NOP2
1000.5
C36H57BCl2F4Mo2OP2
917.4
mol wt
cryst syst
space group
radiation (λ, Å)
a, Å
b, Å
c, Å
tetragonal
I41/a
orthorhombic
Ibam
monoclinic
P21/n
0.71073
16.199(2)
17.829(3)
16.731(2)
90
112.445(2)
90
4466.1(11)
4
1.488
0.802
120
monoclinic
P21/n
0.71069
40.032(10)
40.032(10)
9.257(6))
90
0.71073
17.046(9)
20.151(10)
25.172(12)
90
90
90
8646(7)
8
0.71073
11.539(7)
17.452(10)
19.755(12)
90
92.866(11)
90
3973(4)
4
R, deg
â, deg
90
90
γ, deg
V, Å3
14835(11)
16
1.84
6.47
295
Z
calcd density, g cm-3
absorpt coeff, mm-1
temp, K
1.671
0.893
120
0.679
120
θ range (deg)
index ranges (h,k,l)
1-25
0,47; 0,47;
0, 10
1.56-15.26
0/12; 0/14;
0/18
1.49-28.32
-21,19; 0,23;
0,22
1.56-24.91
-13,13; 0, 20;
0, 23
reflns collected
7161
17344
41607
26302
independent refln
refln with I >2σ(I)
R (data with I >2σ(I))
6500 [Rint ) 0.027]
3560 [I >3σ(I)]
R1 ) 0.0485,
wR2 ) 0.056b
1.034
1069 [Rint ) 0.097]
749
R1 ) 0.1048
wR2 ) 0.2908c,d
1.329
11121 [Rint ) 0.072]
6849
R1 ) 0.0505
wR2 ) 0.1047c,e
1.085
6044
4557
R1 ) 0.0856
wR2 ) 0.1932c,f
0.970
GOF
restraints/ parameters
∆F(max,min), e Å-3
0/435
2.11, -0.95
2/89
1.162, -0.693
36/617
1.783, -1.301
26/369
1.293, -1.250
a BF4- anion and solvent molecule not included (see text). b w ) w′[1-((||Fo|-|Fc||)/6.σ(Fo))2]2 with w′ ) 1/Σr ArTr(X) with 3 coefficients 10.9, -6.36,
2
2
2
and 7.68 for a Chebyshev series, for which X is Fc/Fc(max). c w-1 ) σ2(Fo ) + (aP)2 + (bP), where P ) [max(Fo , 0) + 2Fc ]/3. d a ) 0.200, b ) 0.000.
e a ) 0.0406, b ) 16.0842. f a ) 0.1151, b ) 0.000.
Scheme 4. Fluxional Process Proposed for Compound 13 in
room temperature through proton mediated but again in
different ways. The terminal hydride complexes transform
Solutiona
irreversibly into their hydride-bridged tautomers [M2Cp2(µ-
H)(µ-PR2)(µ-PR′2)(CO)2]+, this being accompanied by a trans
to cis rearrangement of the carbonyl ligands. In contrast, the
agostic cations reach an equilibrium with their hydride-
bridged tautomers, with the former being favored (higher
equilibrium ratios) for phosphide ligands having better donor
and smaller R groups around phosphorus, to yield the
sequence PEt2 > PCy2 . PPh2. The external anion has a
a Substituents on phosphorus and charge were omitted.
modest but measurable influence on the above equilibria,
with the agostic cation being somewhat favored for the
-
noncoordinating BAr′4- anion, when compared to the BF4
Concluding Remarks
salts. In contrast, coordinating anions as Cl- lead to complete
Although the protonation reactions of the doubly bonded
decomposition of the above unsaturated cations. The ligands
phosphide-bridged complexes [M2Cp2(µ-PR2)(µ-PR′2)(CO)2]
around the metal atoms also affect dramatically the above
(M d Mo, W; R, R′ ) Ph, Et, Cy) eventually give the
agostic/hydride equilibria, so that replacing CO by CNtBu
hydride-bridged cations [M2Cp2(µ-H)(µ-PR2)(µ-PR′2)(CO)2]+
ligands yields exclusively hydride derivatives, an effect that
as it might have been anticipated, our experiments prove that
can be rationalized as a result of the increased electron
the double metal-metal bond never is the initial site of
density at the metal centers. Finally, removal of a CO ligand
proton attack. Instead, protonation occurs first at either the
also yields a hydride derivative, an effect that now can be
M-P bonds having higher electron density (PEt2 and PCy2
bridges favored over PPh2 bridges), to give phosphine-
bridged complexes [Mo2Cp2(µ-κ2-HPR2)(µ-PR′2)(CO)2]+ dis-
attributed to the coordinative unsaturation thus generated at
the dimetal center, which is expected to facilitate any
oxidative addition process.
playing agostic-type M-H-P interactions (when M ) Mo
and R ) Et, Cy), or at the metal site, to give hydride cations
Experimental Section
[M2Cp2(H)(µ-PR2)(µ-PR′2)(CO)2]+ having terminal M-H
bonds (when M ) Mo and R ) Ph or when M ) W,
irrespective of the nature of R). These different pathways
are possibly governed by electronic rather than steric factors.
In a second step, the above unsaturated cations rearrange at
General Procedures and Starting Materials. All manipulations
and reactions were carried out under a nitrogen (99.995%)
atmosphere using standard Schlenk techniques. Solvents were
purified according to literature procedures and distilled prior to
6974 Inorganic Chemistry, Vol. 45, No. 17, 2006

MsP Wersus MdM Bonds as Protonation Sites
use.29 Petroleum ether refers to that fraction distilling in the range
65-70 °C. Compounds [M2Cp2(µ-PR2)(µ-PR′2)(CO)2] (M ) Mo,
W; R, R′ ) Cy, Ph, Et),6 [Mo2Cp2(µ-CO)(µ-PCy2)2],6 [Mo2Cp2-
(µ-PPh2)2(CO)2],7 and [H(OEt2)2](BAr′4),11 were prepared as de-
scribed previously, and all other reagents were obtained from the
usual commercial suppliers and used as received, unless otherwise
stated. Photochemical experiments were performed using jacketed
Pyrex Schlenk tubes, cooled by tap water (ca. 285 K). A 400 W
mercury lamp (Applied Photophysics) placed ca. 1 cm away from
the Schlenk tube was used for these experiments. Chromatographic
separations were carried out using jacketed columns cooled by tap
water. Commercial aluminum oxide (activity I, 150 mesh) was
degassed under vacuum prior to use. The latter was mixed under
nitrogen with the appropriate amount of water to reach the activity
desired. Filtrations were performed using diatomaceous earth. IR
stretching frequencies of CO ligands were measured in solution
and are referred to as ν(CO) (solvent). Nuclear magnetic resonance
(NMR) spectra were routinely recorded at 300.13 (1H), 121.50
(31P{1H}), or 75.47 MHz (13C{1H}) at 290 K in CD2Cl2 solutions
unless otherwise stated. Chemical shifts (δ) are given in ppm,
relative to internal tetramethylsilane (1H, 13C) or external 85%
aqueous H3PO4 solutions (31P). Coupling constants (J) are given
in Hertz.
of dichloromethane/petroleum ether (1/2). The resulting residue was
dissolved in dichloromethane and filtered. Removal of solvent from
the filtrate gave compound 4a as a dark-brown microcrystalline
solid (0.025 g, 74%). The crystals used in the X-ray study were
grown by slow diffusion of petroleum ether into a concentrated
solution of the complex in dichloromethane at 253 K and were
found to contain a molecule of water, presumably arising from
adventitious moisture in the solvent during crystallization. Anal.
Calcd for C36H33BF4O3P2W2 (4a‚H2O): C, 41.98; H, 3.23. Found:
1
C, 42.15; H, 3.30. H NMR δ 7.73-6.85 (m, 20H, Ph), 5.52 (s,
10H, Cp), -14.59 (t, JHP ) 50, JHW ) 49, 1H, µ-H). 13C{1H} NMR
(100.63 MHz) δ 226.4 (s, CO), 142.3 [d, JCP ) 45, C1(Ph)], 137.6-
128.0 (m, Ph), 89.0 (s, Cp).
Preparation of [W2Cp2(µ-H)(µ-PEt2)2(CO)2]BF4 (4b). A
dichloromethane solution (5 mL) of compound 1b (0.015 g, 0.020
mmol) was stirred at room temperature with HBF4‚OEt2 (4 µL of
a 54% solution in Et2O, 0.029 mmol) for 5 min to give a yellow-
orange solution. Solvent was then removed in a vacuum, and the
residue was washed with petroleum ether (3 × 5 mL) and dried
under vacuum to give compound 4b as a yellow solid (0.014 g,
83%). Anal. Calcd for C21H33BCl2F4O2P2W2(4b‚CH2Cl2): C, 27.88;
1
H, 3.68. Found: C, 27.99; H, 3.88. H NMR (CDCl3) δ 5.56 (s,
10H, Cp), 2.61, 2.46 (2 × m, 2 × 4H, PCH2), 1.38, 1.35 (2 × dt,
JHP ) 18, JHH ) 8, 2 × 6H, CH3), -15.50 (t, JHP ) 52, JHW ) 52,
1H, µ-H).
Preparation of Solutions of [W2Cp2(H)(µ-PPh2)2(CO)2]BF4
(3a). In a typical experiment, a dichloromethane (3 mL) or CD2-
Cl2 (0.5 mL) solution of compound 1a (0.030 g, 0.033 mmol) was
treated at 243 K with HBF4‚OEt2 (8 µL of a 54% solution in Et2O,
0.060 mmol) to give a dark-yellow solution shown (by NMR) to
contain essentially pure compound 2. 1H NMR (400.13 MHz, 223
K) δ 8.08-6.65 (m, 20H, Ph), 5.53, 4.70 (2 × s, 2 × 5H, Cp),
-0.42 (dd, JHP ) 19, 12, JHW ) 28, 1H, W-H). 13C{1H} NMR
(100.63 MHz, 223 K) δ 228.9 (s, CO), 201.8 (d, JCP ) 14, CO),
148.1 [d, JCP ) 57, C1(Ph)], 143.5 [d, JCP ) 47, C1(Ph)], 140.4 [d,
JCP ) 61, C1(Ph)], 136.0 [d, JCP ) 55, C1(Ph)], 135.2, 134.6 [2 ×
d, JCP ) 11, 2 × C2(Ph)], 133.3, 132.8 [2 × d, JCP ) 12, 2 ×
C2(Ph)], 131.6-128.5 (m, Ph), 93.7, 90.1 (2 × s, Cp).
Preparation of [W2Cp2(µ-H)(µ-PEt2)(µ-PPh2)(CO)2]BF4 (4c).
The procedure is identical to that described for compound 4b but
using compound 1c (0.022 g, 0.027 mmol), 4 µL of the HBF4
solution (0.029 mmol), and a reaction time of 10 h. Compound 4c
was obtained as a yellow solid (0.021 g, 86%). The complex can
be crystallized by slow diffusion of a layer of toluene into a
dichloromethane solution of the complex at 253 K. Anal. Calcd
for C35H39BF4O2P2W2 (4c‚C7H8): C, 41.70; H, 3.90. Found: C,
41.35; H, 3.38. 1H NMR (CDCl3) δ 7.74-6.70 (m, 10H, Ph), 5.57
(s, 10H, Cp), 2.84, 2.47 (2 × quint, JHP ) JHH ) 8, 2 × 2H, PCH2),
1.45-1.28 (m, 6H, CH3), -14.88 (dd, JHP ) 54, 48, JHW ) 51,
1H, µ-H).
Preparation of Solutions of [W2Cp2(H)(µ-PEt2)2(CO)2]BF4
(3b). The procedure is identical to that described for 3a but using
compound 1b (0.010 g, 0.014 mmol) and 4 µL of the HBF4 solution
Preparation of cis-[W2Cp2(µ-PPh2)2(CO)2] (5a). A dichloro-
methane solution (5 mL) of compound 4a (0.030 g, 0.030 mmol)
was stirred at 263 K with DBU (1,8-diazabicyclo[5.4.0]undec-7-
ene, 4 µL, 0.031 mmol) for 1 min to give a pale green solution.
Solvent was then removed in vacuum, and the residue was
chromatographed on alumina (activity IV) at 285 K. Elution with
dichloromethane/petroleum ether (2/1) gave a green fraction.
Removal of solvents from the latter fraction yielded compound 5a
as a green microcrystalline solid (0.020 g, 72%). Anal. Calcd for
1
(0.029 mmol). H NMR (400.13 MHz, 183 K) δ 5.64, 5.59 (2 ×
s, 2 × 5H, Cp), 3.28 (m, 4H, PCH2), 2.34, 1.63 (2 × m, 2 × 1H,
PCH2), 1.69 (dt, JHP ) 15, JHH ) 7, 3H, CH3), 1.42 (m, 6H, CH3),
1.11 (m, 2H, PCH2), 0.85 (dt, JHP ) 20, JHH ) 7, 3H, CH3), -3.79
(dd, JHP ) 27, 16, JHW ) 27, 1H, H-W).
Preparation of Solutions of [W2Cp2(H)(µ-PEt2)(µ-PPh2)(CO)2]-
BF4 (3c). The procedure is identical to that described for 1b but
using compound 1c (0.010 g, 0.012 mmol) and 4 µL of the HBF4
1
C36H30O2P2W2: C, 46.75; H, 3.27. Found: C, 46.66; H, 3.19. H
NMR (223 K) δ 7.42-6.48 (m, 20H, Ph), 5.65 (s, 10H, Cp). 13C-
{1H} NMR (100.63 MHz, 223 K) δ 234.5 (s, CO), 144.7-127.4
(m, Ph), 91.7 (s, Cp).
1
solution (0.029 mmol) instead. H NMR (400.13 MHz, 190 K) δ
7.85 (dd, JHP ) 12, JHH ) 8, 2H, o-Ph), 7.69 (false t, JHH ≈ 7, 2H,
m-Ph), 7.59 (t, JHH ) 7, 1H, p-Ph), 7.35 (false t, JHH ) 7, 2H,
m-Ph), 7.28 (t, JHH ≈ 7 1H, p-Ph), 6.73 (d, JHP ) 13, JHH ) 8, 2H,
o-Ph), 5.56, 5.25 (2 × s, 2 × 5H, Cp), 3.48, 3.31 (2 × m, 2 × 2H,
PCH2), 1.73 (dt, JHP ) 17, JHH ) 7, 3H, CH3), 1.55 (m, 3H, CH3),
-1.26 (dd, JHP ) 24, 16, JHW ) 24, 1H, H-W).
Preparation of [W2Cp2(µ-H)(µ-PPh2)2(CO)2]BF4 (4a). A
dichloromethane solution (5 mL) of compound 1a (0.030 g, 0.033
mmol) was stirred at room temperature with HBF4‚OEt2 (8 µL of
a 54% solution in Et2O, 0.060 mmol) for 4 h to give a brown
solution. Solvent was then removed in a vacuum, and the residue
was washed with petroleum ether (3 × 3 mL) and then with 3 mL
Preparation of Solutions of [Mo2Cp2(H)(µ-PPh2)2(CO)2]BF4
(6). The procedure is identical to that described for 3a butusing
compound 2a (0.020 g, 0.027 mmol). This gives a green-yellow
solution shown (by NMR) to contain essentially pure compound
6. 1H NMR δ 7.42-6.79 (m, 20 H, Ph), 5.33, 4.83 (2 × s, br, 2 ×
5H, Cp), -1.88 (dd, JHP ) 32, 30, 1H, Mo-H).
Preparation of cis-[Mo2Cp2(µ-PPh2)2(CO)2] (8). The procedure
is identical to that described for 5a but using compound 7 (0.020
g, 0.024 mmol). After similar workup, compound 8 was obtained
as a green microcrystalline solid (0.014 g, 78%). Anal. Calcd for
C36H30Mo2O2P2: C, 57.77; H, 4.04. Found: C, 57.83; H, 4.07. 1H
NMR (400.13 MHz, 223 K) δ 8.05-6.42 (m, 20H, Ph), 4.91 (s,
10H, Cp).
(29) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals; Pergamon Press: Oxford, U.K., 1988.
Inorganic Chemistry, Vol. 45, No. 17, 2006 6975

Alvarez et al.
Preparation of Compounds [Mo2Cp2(µ-PCy2)(µ-κ2-HPCy2)-
(CO)2]BF4 (9d) and [Mo2Cp2(µ-H)(µ-PCy2)2(CO)2]BF4 (10d).
A green solution of compound 2d (0.040 g, 0.052 mmol) in
dichloromethane (6 mL) was stirred with HBF4‚OEt2 (16 µL of a
54% Et2O solution, 0.12 mmol) for 30 min to afford a yellow-
greenish solution shown (by NMR) to be an equilibrium mixture
of compounds 9d and 10d (10:1). The solvent was then removed
under vacuum, and the residue was washed with petroleum ether
(3 × 5 mL) to give a yellow-greenish microcrystalline solid (0.040
g, 89%) of compound 9d contaminated with a small amount of its
isomer 10d. Anal. Calcd for C36H55BF4Mo2O2P2: C, 50.26; H, 6.44.
solution of the complex at 253 K. Anal. Calcd for C41H66BCl2F4-
Mo2NOP2 (11‚CH2Cl2): C, 49.22; H, 6.65; N, 1.40. Found: C,
1
48.71, H, 6.83; N, 1.65. H NMR δ 5.56, 5.14 (2 × s, 2 × 5H,
Cp), 2.80-0.30 (m, 44H, Cy), 1.36 (s, 9H, tBu), -14.74 (t, JHP
43, 1H, µ-H).
)
Preparation of [Mo2Cp2(µ-H)(µ-PCy2)2(CNtBu)2]BF4 (12). A
dichloromethane solution of isomers 9d and 10d was prepared “in
situ” as described above from compound 2d (0.035 g, 0.045 mmol)
and HBF4‚OEt2 (16 µL of a 54% solution in Et2O, 0.116). Neat
CNtBu (12 µL, 0.104 mmol) was then added, and the mixture was
heated at 313 K for 1.5 h to give a red solution which was filtered.
Workup of the filtrate as described for 11 gave compound 12 as
an orange solid (0.030 g, 70%). Anal. Calcd for C44H73BF4-
Mo2N2P2: C, 54.44; H, 7.58; N, 2.89. Found: C, 54.02; H, 7.98;
1
Found: C, 49.83; H, 6.15. Spectroscopic data for 9d: H NMR
(293 K) δ 5.63, 5.61 (2 × s, br, 2 × 5H, Cp), 2.60-1.00 (m, 44H,
1
Cy), -4.73 (m, |JPH + JPH| ) 129, 1H, µ-HP). H NMR (400.13
1
MHz, 243 K) δ 5.66, 5.63 (2 × s, 2 × 5H, Cp), 2.80-0.80 (m,
44H, Cy), -4.80 (dd, JPH ) 134, -5, 1H, µ-HP). 31P{1H} NMR
(121.52 MHz, 293K) δ 162.8 (br, µ-PCy2), 89.9 (br, µ-HPCy2).
31P NMR (162.00 MHz, 243K) δ 161.4 (s, µ-PCy2), 89.7 (br d,
JPH ) 134, µ-HPCy2). The crystals used in the X-ray study of isomer
9d were grown at 253 K by slow diffusion of layers of petroleum
ether and toluene into a solution of the complex in dichloromethane.
Spectroscopic data for 10d: 1H NMR δ 5.60 (s, 10H, Cp), -13.54
(t, JPH ) 58, 1H, µ-H), other resonances obscured by those of the
major isomer.
N, 3.02. H NMR δ 5.06 (s, 10H, Cp), 1.77-1.26 (m, 44H, Cy),
t
1.35 (s, 18H, Bu), -16.64 (t, JHP ) 53, 1H, µ-H).
Preparation of [Mo2Cp2(H)(µ-PCy2)2(CO)]BF4 (13). An equi-
librium mixture of isomers 9d and 10d in dichloromethane (8 mL),
prepared as described above, was irradiated with UV-visible light
at 285 K for 3.5 h to give a red solution. Solvent was then removed
under vacuum, and the residue was washed with petroleum ether
(3 × 5 mL) to give compound 13 as a red microcrystalline solid
(0.035 g, 90%). The crystals used in the X-ray diffraction study
were grown by slow diffusion of a layer of toluene into a
concentrated solution of the complex in dichloromethane at 253 K
and were found to contain a dichloromethane molecule. Anal. Calcd
for C36H57BCl2F4Mo2OP2 (13‚CH2Cl2): C, 47.14; H, 6.26. Found:
Preparation of Compounds [Mo2Cp2(µ-PEt2)(µ-κ2-HPEt2)-
(CO)2]BF4 (9b) and [Mo2Cp2(µ-H)(µ-PEt2)2(CO)2]BF4 (10b). The
procedure is identical to that described for 9d and 10d but using
compound 2b (0.020 g, 0.038 mmol) instead. After 10 min, a green
solution is obtained shown (by NMR) to be an equilibrium mixture
of compounds 9b and 10b (30:1). Workup as above gave a green
oily residue which could not be converted into a microcrystalline
solid. Spectroscopic data for 9b: 1H NMR δ 5.56, 5.50 (2 × s, 2
× 5H, Cp), 3.02, 1.78 (2 × m, 2 × 4H, PCH2), 1.44-0.88 (m,
12H, CH3), -4.22 (m, |JHP + JHP| ) 103, 1H, µ-HP). Spectroscopic
data for 10b: 1H NMR δ -14.54 (t, JHP ) 68, 1H, µ-H), other
resonances for this very minor isomer obscured by those of the
major isomer.
1
C, 46.65; H, 6.07. H NMR (400.13 MHz) δ 5.82 (s, 10H, Cp),
2.34-0.58 (m, 44H, Cy), -1.41 (t, JHP ) 44, 1H, Mo-H). 1H NMR
(400.13 MHz, 223 K) δ 5.84 (s, br, 10H, Cp), 2.54-0.58 (m, 44H,
1
Cy), -1.55 (t, JHP ) 44, 1H, Mo-H). H NMR (400.13 MHz,
CD2Cl2, 203 K) δ 5.93, 5.78 (2 × s, 2 × 5H, Cp), 2.36-0.43 (m,
44H, Cy), -1.60 (t, JPH ) 44, 1H, Mo-H). 13C{1H} NMR δ 260.6
(t, JCP ) 7, CO), 93.5 (s, Cp), 53.3, 46.7 [2 × s, br, 2 × C1(Cy)],
33.7, 32.8 [2 × s, 2 × C2(Cy)], 28.1, 27.1 [2 × false t, |JCP + JCP′|
) 12, 2 × C3(Cy)], 26.0, 25.8 [2 × s, 2 × C4(Cy)]. 31P{1H} NMR
(CDCl3) δ 306.2 (s, µ-PCy2).
Preparation of Compounds [Mo2Cp2(µ-PPh2)(µ-κ2-HPCy2)-
(CO)2]BF4 (9e) and [Mo2Cp2(µ-H)(µ-PCy2)(µ-PPh2) (CO)2]BF4
(10e). The procedure is identical to that described for 9d but using
compound 2e (0.020 g, 0.026 mmol) instead. After 40 min, a green
solution is obtained, shown (by NMR) to be an equilibrium mixture
of compounds 9e and 10e (1:2). Workup as for 9d gave a mixture
of the isomers as a green-yellowish powder (0.018 g, 81%). Anal.
Calcd for C36H34BF4Mo2O2P2: C, 50.96; H, 5.11. Found: C, 50.59;
H, 4.29. Spectroscopic data for 9e: 31P NMR (CDCl3) δ 145.4 (s,
br, µ-PPh2), 100.3 (d, br, JPH ≈ 135, µ-HPCy2). 1H NMR (CDCl3)
δ 7.75-7.41 (m, 10H, Ph), 5.56, 5.54 (2 × s, 2 × 5H, Cp), 2.04-
1.24 (m, 22H, Cy), -4.33 (dd, JHP ) 132, -5, 1H, µ-HP).
Spectroscopic data for 10e: 1H NMR (CDCl3) δ 7.75-7.41 (m,
10H, Ph), 5.51 (s, 10H, Cp), 2.04-1.24 (m, 22H, Cy), -13.34 (t,
JHP ) 57, 1H, µ-H).
Preparation of [Mo2Cp2(µ-H)(µ-PCy2)2(CO)(CNtBu)]BF4 (11).
A dichloromethane solution of compounds 9d and 10d was prepared
“in situ” as described above from compound 2d (0.035 g, 0.045
mmol) and HBF4‚OEt2 (16 µL of a 54% solution in Et2O, 0.116
mmol). CNtBu (2 mL of a 0.05 M solution in petroleum ether, 0.1
mmol) was then added, and the mixture was stirred for 1 min to
give a red solution. The solvent was then removed under vacuum,
and the residue was washed with petroleum ether (3 × 5 mL) to
give compound 11 as an orange microcrystalline solid (0.035 g,
85%). The crystals used in the X-ray study of 11 were grown by
slow diffusion of a layer of diethyl ether into a dichloromethane
Preparation of [Mo2Cp2(µ-COH)(µ-PCy2)2]BF4 (14). A toluene
solution (6 mL) of [Mo2Cp2(µ-PCy2)2(µ-CO)] (0.015 g, 0.020
mmol) was stirred at room temperature with HBF4‚OEt2 (16 µL of
a 54% solution in Et2O, 0.109 mmol), whereby a deep rose solid
rapidly precipitated from the solution. After discarding the solution,
this solid was washed with diethyl ether (2 × 4 mL) and then with
petroleum ether/diethyl ether (3 × 4 mL of a 1:1 mixture) to give
compound 14 as a red-rose microcrystalline solid (0.015 g, 88%).
Anal. Calcd for C35H55BF4Mo2OP2: C, 50.50; H, 6.66. Found: C,
50.29; H, 8.42. IR (Nujol mull): 3600 [w, ν(O-H)], 1262 [m, ν-
(C-O)]. 1H NMR (400.13 MHz, 223 K) δ 12.33 (s, br, 1H,
µ-COH), 6.02 (s, 10H, Cp), 2.12-0.22 (m, 44H, Cy). 13C{1H} NMR
(100.63 MHz, 223 K) δ 368.2 (s, br, µ-COH), 93.8 (s, Cp), 52.0,
43.6 [2 × s, br, 2 × C1(Cy)], 34.2, 29.6 [2 × s, 2 × C2(Cy)], 27.4,
27.2 [2 × d, JHP ) 15, 2 × C3(Cy)], 25.8, 25.75 [2 × s, 2 × C4(Cy)].
Preparation of [W2Cp2(µ-H)(µ-PEt2)2(CO)2]BAr′4 (4b′). The
procedure is identical to that described for 4b but using compound
1b (0.022 g, 0.030 mmol) and [H(OEt2)2](BAr′4) (0.030 g, 0.030
mmol) instead. After workup as described for 4b, compound 4b′
was obtained as a yellow solid (0.035 g, 77%). Anal. Calcd for
C48H33BF24O2P2W3: C, 37.48; H, 2.16. Found: C, 37.86; H, 2.49.
1H NMR δ 7.73 (s, 8H, Ar′), 7.57 (s, 4H, Ar′), 5.47 (s, 10H, Cp),
2.68, 2.50 (2 × m, 2 × 4H, PCH2), 1.41, 0.69 (2 × m, 2 × 6H,
CH3), -16.03 (t, JHP ) 50, JHW ) 50, 1H, µ-H).
Preparation of Solutions of Compounds [Mo2Cp2(µ-PCy2)-
(µ-κ2-HPCy2)(CO)2]BAr′4 (9d′) and [Mo2Cp2(µ-H)(µ-PCy2)2-
6976 Inorganic Chemistry, Vol. 45, No. 17, 2006

MsP Wersus MdM Bonds as Protonation Sites
(CO)2]BAr′4 (10d′). In a typical experiment, solid [H(OEt2)2]-
(BAr′4) (0.028 g, 0.028 mmol) was added to a dichloromethane (3
mL) or CD2Cl2 (0.5 mL) solution of compound 2d (0.010 g, 0.014
mmol), whereupon the solution turned yellow-greenish. This was
shown (by NMR) to be an equilibrium mixture (ca. 20:1) of
integration by the software SAINT,33 and a multiscan absorption
correction was applied with SADABS.34 The structure was solved
by Patterson interpretation and phase expansion using DIRDIF35
and refined with full-matrix least squares on F2 using SHELXL97.36
The resolution process shows one-half of the cation in the
asymmetric unit and was placed on a plane of symmetry, so that
the structure of the cation is imposed to have a symmetry plane
that does not correspond to the molecular symmetry. Due to the
low quality of the diffraction data, only the heavy atoms could be
refined anisotropically, as the temperature factors for the remaining
non-H atoms were persistently nonpositive definites. One of the
cyclohexyl groups appeared heavily disordered, but it was not
possible to model the different orientations of this group properly,
and only the strongest peaks were retained. All hydrogen atoms
were fixed at calculated positions and refined isotropically, except
for the agostic hydrogen atom. The latter could not be located in
the final difference map; therefore, possible positions were inves-
tigated by a potential energy minima search using the program
HYDEX.37 Only one minimum was found around the P(1)-Mo-
(2) bond, at approximately 1.67 Å from P(1) and 1.95 Å from the
Mo(2) atom, in agreement with the proposed structure in solution.
Nevertheless, this hydrogen atom had to be fixed at this position
to reach a satisfactory refinement. During refinement, the anion
could not be satisfactorily solved, and a possible molecule of a
nonidentified solvent was found to be present in the asymmetric
unit. Therefore, the SQUEEZE38 program, as implemented in
PLATON,39 was used to model the corresponding electron densities.
1
compounds 9d′ and 10d′. Spectroscopic data for 9d′: H NMR δ
7.72 (s, 8H, Ar′), 7.56 (s, 4H, Ar′), 5.62, 5.57 (2 × s, 2 × 5H, Cp),
2.37-1.26 (m, 44H, Cy), -4.78 (m, |JHP + JHP| ) 127, 1H, µ-HP).
Spectroscopic data for 10d′: 1H NMR δ 5.56 (s, 10H, Cp), -13.57
(t, JHP ) 58, µ-H), other resonances of this very minor isomer
obscured by those of the major isomer.
Preparation of Solutions of Compounds [Mo2Cp2(µ-PPh2)-
(µ-κ2-HPCy2)(CO)2]BAr′4 (9e′) and [Mo2Cp2(µ-H)(µ-PCy2)(µ-
PPh2)(CO)2]BAr′4 (10e′). The procedure is identical to that
described for compounds 9d′ and 10d′ but using compound 2e
(0.010 g, 0.013 mmol) and solid [H(OEt2)2](BAr′4) (0.053 g, 0.052
mmol). If the reaction is carried out at 253 K, a green solution is
immediately formed shown (by NMR at 223 K) to contain
essentially pure compound 9e′. Upon standing this solution at room
temperature for 5 h, an equilibrium mixture (1:1 by NMR) of
compounds 9e′ and 10e′ is obtained. Spectroscopic data for 9e′:
1H NMR (400.13 MHz, 223 K): δ 7.72 (s, 8H, Ar′), 7.56 (s, 4H,
Ar′), 7.48-7.25 (m, 10H, Ph), 5.71, 5.59 (2 × s, 2 × 5H, Cp),
1.93-1.40 (m, 22H, Cy), -4.68 (dd, JHP ) 132, -5), 1H, µ-HP).
Spectroscopic data for 10e′: 1H NMR δ 7.74 (s, 8H, Ar′), 7.57 (s,
4H, Ar′), 7.57-7.21 (m, 10H, Ph), 5.48 (s, 10H, Cp), 2.33-1.22
(m, 22H, Cy), -13.47 (t, JHP ) 57, 1H, µ-H).
After convergence, the strongest residual peaks (1.17-0.96 e A-3
)
X-ray Structure Determination of Compound 4a. A suitable
crystal of 4a (0.25 × 0.25 × 0.6 mm) was stuck on a glass fiber
and mounted on an Enraf-Nonius MACH-3 automatic diffracto-
meter. Accurate cell dimensions and orientation matrix were
obtained by least-squares refinements of 25 accurately centered
reflections. No significant variations were observed in the intensities
of two checked reflections during data collection. The data were
corrected for Lorentz and polarization effects. Computations were
performed by using the PC version of CRYSTALS.30 Scattering
factors and corrections for anomalous absorption were taken from
ref 31. The structure was solved by direct methods (SHELXS),32
completed by Fourier techniques, and refined by full-matrix least-
squares. An empirical absorption correction based on psi-scan curve
was applied (Tmin ) 0.95, Tmax ) 1). All non-hydrogen atoms were
anisotropically refined. The C-bonded hydrogen atoms were
introduced in calculated positions and were allocated an overall
isotropic thermal parameter. The complex crystallized with a
molecule of water.
X-ray Structure Determination of Compound 9d. Data were
collected on a Smart-CCD-1000 Bruker diffractometer using
graphite-monochromated Mo KR radiation at 120 K. Cell dimen-
sions and orientation matrixes were initially determined from least-
squares refinements on reflections measured in 3 sets of 30
exposures collected in 3 diferent ω regions and eventually refined
against all reflections. The software SMART33 was used for
collecting frames of data, indexing reflections, and determining
lattice parameters. The collected frames were then processed for
were located around the disordered cyclohexyl group.
X-ray Structure Determination of Compound 11. Collection
of data, structure solution, and refinements were done as described
for 9d. For compound 11 one of the cyclohexyl groups and the
dichloromethane molecule were found disordered in two positions,
with occupancy factors of 0.7/0.3 and 0.6/0.4, respectively. All non-
hydrogen atoms were refined anisotropically, except C(35b) and
C(36b) atoms (involved in the disorder) which were refined
isotropically because they were persistently nonpositive definites.
Most hydrogen atoms were located in the Fourier map, but only
some of them were refined (the hydride bridging ligand, the
aromatic hydrogens, and the methine H(17), H (23) and H(29)
atoms). All the hydrogen atoms were given an overall isotropic
thermal parameter.
X-ray Structure Determination of Compound 13. Collection
of data, structure solution, and refinements were done as described
for 9d. Twinning was found to occur in the crystal, and the program
GEMINI40 was used to determine the twin law, the cell dimensions,
and orientation matrixes before data reduction. Non-H atoms were
refined anisotropically except for a number of C atoms in the cation
and all atoms in the anion and dichloromethane molecule, which
were refined isotropically because some of their temperature factors
(34) Sheldrick, G. M. SADABS, Program for Empirical Absorption
Correction; University of Go¨ttingen: Go¨ttingen, Germany, 1996.
(35) Beurkens, P. T.; Admiraal, G.; Beurkens, G.; Bosman, W. P.; Garc´ıa-
Granda, S.; Gould, R. O.; Smits, J. M. M.; Smykalla, C. The DIRDIF
Program System; Technical Report of the Crystallographic Laboratory;
University of Nijmegen: Nijmegen, The Netherlands, 1999.
(36) Sheldrick, G. M. SHELXL97: Program for the Refinement of Crystal
Structures; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(37) Orpen, A. G. J. Chem. Soc., Dalton Trans. 1980, 2509.
(38) Van der Sluis, P.; Spek, A. L. Acta Crystallogr., Sect. A 1990, A46,
194.
(30) Watkin, D. J.; Prout, C. K.; Carruthers, J. R.; Betteridge, P. W. Crystals
Issue 10; Chemical Crystallography Laboratory, University of Ox-
ford: U.K., 1996.
(31) Cromer, D. T. International Tables for X-ray Crystallography; Kynoch
Press: Birmingham, U.K., 1974; Vol. IV.
(32) Sheldrick, G. M. SHELXS 86, Program for Crystal Structures Solution;
University of Go¨ttingen: Go¨ttingen, Germany, 1986.
(33) SMART & SAINT Software Reference Manuals, Version 5.051
(Windows NT Version); Bruker Analytical X-ray Instruments: Madi-
son, WI, 1998.
(39) (a) Spek, A. L. Acta Crystallogr., Sect. A 1990, A46, C34. (b) Spek,
A. L. PLATON, A Multipurpose Crystallographic Tool; Utrecht
University: Utrecht, The Netherlands, 1998.
(40) GEMINI, Twinning Solution Program Suite; Version 1.0; copyright
2000, 1999, Bruker AXS Inc.: Madison, WI 53711.
Inorganic Chemistry, Vol. 45, No. 17, 2006 6977

Alvarez et al.
-
were persistently nonpositive definites. Both the BF4 anion and
Acknowledgment. The authors thank the MECD of Spain
for Ph.D. grants (to D.S. and A.R.) and the MCYT for
financial support (Project BQU2003-05471).
the CH2Cl2 molecule were found to be highly disordered, and both
were modelized in two positions (occupancy factors ) 0.7/0.3 and
0.6/0.4, respectively) while applying restraints on the B-F or C-Cl
bond lengths and F-B-F or Cl-C-Cl angles. Because of the low
quality of the diffraction data only some of the hydrogen atoms
were found in Fourier maps, so all hydrogen atoms were fixed at
calculated geometric positions in the last least-squares refinements,
except for H(1), which could be located in the Fourier maps and
its position was refined satisfactorily. All hydrogen atoms were
given an overall isotropic thermal parameter.
Supporting Information Available: Crystallographic data for
the structural analysis of compounds 4a, 9d, 11, and 13 in the CIF
file format. This material is available free of charge via the Internet
at http://pubs.acs.org.
IC060544N
6978 Inorganic Chemistry, Vol. 45, No. 17, 2006