Synthesis, structure, and reactivity of ansa-rhenocene complexes

Article abstract of DOI:10.1021/om9810145

Complexes of rhenocene (Cp₂Re) with substitution at the cyclopentadienyl rings have been prepared from Cp₂Re-Me by dilithitation of the Cp rings followed by reaction with Me₂-SiCl₂ or Cl(SiMe₂)₂Cl to afford ansa-bridged species. Protonation of the resulting neutral Re methyl complexes gives thermally labile methyl hydride complexes. The thermal stability of the methyl hydride complex with a single silicon atom in the ansa bridge is enhanced with respect to the unbridged analogues.

Full text of DOI:10.1021/om9810145

3070
Organometallics 1999, 18, 3070-3074
Syn th esis, Str u ctu r e, a n d Rea ctivity of a n sa -Rh en ocen e
Com p lexes
D. Michael Heinekey* and Catherine E. Radzewich
Department of Chemistry, Box 351700, University of Washington,
Seattle, Washington 98195-1700
Received December 14, 1998
Complexes of rhenocene (Cp2Re) with substitution at the cyclopentadienyl rings have been
prepared from Cp2Re-Me by dilithitation of the Cp rings followed by reaction with Me2-
SiCl2 or Cl(SiMe2)2Cl to afford ansa-bridged species. Protonation of the resulting neutral Re
methyl complexes gives thermally labile methyl hydride complexes. The thermal stability
of the methyl hydride complex with a single silicon atom in the ansa bridge is enhanced
with respect to the unbridged analogues.
In tr od u ction
reactivity of this 16-electron fragment and the difficulty
of finding an unreactive solvent for this chemistry is
indicated by our recent observation that chemically
generated Cp2Re+ reacts with methylene chloride even
at low temperatures to afford [Cp2Re(CH2Cl)Cl]+.6 To-
bita and co-workers have recently demonstrated the
utility of rhenocene cation for activation of C-H bonds
of benzene by the in situ photolysis of [Cp2Re(NCCH3)]-
[BF4] in acetone in the presence of benzene.7 The
resulting phenyl hydride cation, [Cp2Re(C6H5)H]+, is
stable in the solid state and undergoes gradual decom-
position in solution. Similar results were obtained for
thiophene, but the prospects for generality of this
interesting C-H bond activation chemistry are not
encouraging, since the rhenocene alkyl hydride com-
plexes are known to be quite thermally unstable in
solution, decomposing at or below 0 °C by elimination
of alkane.8
To facilitate the investigation of C-H activation of a
greater variety of substrates by “Cp2Re+” and related
fragments, the stability of the products should be
increased. We have previously reported that the thermal
stability of cationic rhenocene derivatives can be in-
creased by utilization of less nucleophilic anions, such
as (BAr′4)-; (Ar′ ) 3,5-(CF3)2C6H3).6 On the basis of the
observations of Green and co-workers, we expect that
further improvements in thermal stability of rhenocene
derivatives can be achieved by the incorporation of an
ansa bridge between the Cp rings. In this paper, we
report the synthesis and structural characterization of
ansa-bridged metallocenes of rhenium and a prelimi-
nary exploration of their thermal stability.
There is considerable current interest in ansa-bridged
metallocene complexes due to their utility in the ca-
talysis of stereoregular olefin polymerization reactions.1
The importance of the ansa bridge in the preparation
of novel metallocene-based polymers has been investi-
gated by Manners.2 On a more fundamental level,
several groups have recently reported ansa-bridged
metallocene complexes which show interesting changes
in structure or reactivity compared to the corresponding
unbridged metallocene complexes.3 Parkin and co-
workers have recently reported changes in reactivity
and structure between several ansa-bridged zirconium
complexes and the Cp* parent complexes.4 Green and
co-workers have investigated the influence of the ansa
bridge on several group 6 metallocene complexes and
have noted dramatic reactivity differences in compari-
son to the unbridged analogues, most notably in the
facility of reductive elimination from alkyl hydride
complexes.5 For example, the presence of an ansa bridge
in the alkyl hydride complex (η5-C5H4-CMe2-η5-C5H4)W-
(H)CH3 makes elimination of methane significantly
slower than in the unbridged parent compound.
In comparison to other metallocenes of the d-block,
there are very few reports of rhenocene derivatives. By
analogy to the well-known chemistry of photogenerated
tungstenocene (Cp2W), an interesting chemistry of the
rhenocene cation “Cp2Re+” can be anticipated. The high
(1) Cf.: Brintzinger, H. H.; Fischer, D.; Mulhaupt, R.; Rieger, B.;
Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143-1170;
Kaminsky, W. Catal. Today 1994, 20, 257-271.
(2) Manners, I. Can. J . Chem. 1998, 76, 371-381 and references
therein.
(3) A recent review details selected examples of the reactivity, orbital
descriptions, and structural characteristics of bent metallocenes and
ansa-bridged metallocenes: Green, J . C. Chem. Soc. Rev. 1998, 27,
263-271.
Resu lts
Reaction of Cp2ReCH3 (1)9 with 2 equiv of nBuLi in
THF at 0 °C affords a dilithiated species which was
(4) Lee, H.; Desrosiers, P. J .; Guzei, I.; Rheingold, A. L.; Parkin, G.
J . Am. Chem. Soc. 1998, 120, 3255-3256.
(5) (a) Conway, S. L. J .; Dijkstra, T.; Doerrer, L. H.; Green, J . C.;
Green, M. L. H.; Stephens, A. H. H. J . Chem. Soc., Dalton Trans. 1998,
2689-2695. (b) Chernega, A.; Cook, J .; Green, M. L. H.; Labella, L.;
Simpson, S. J .; Souter, J .; Stephens, A. H. H. J . Chem. Soc., Dalton
Trans. 1997, 3225-3243. (c) Labella, L.; Chernega, A.; Green. M. L.
H. J . Chem. Soc., Dalton Trans. 1995, 395-402. (d) Labella, L.;
Chernega, A.; Green. M. L. H. J . Organomet. Chem. 1995, 485, C18-
C21.
(6) Heinekey, D. M.; Radzewich, C. E. Organometallics 1998, 17,
51-58.
(7) Tobita, H.; Hashidzume, K.; Endo, K.; Ogino, H. Organometallics
1998, 17, 3405-3407.
(8) Gould, G. L.; Heinkey, D. M. J . Am. Chem. Soc. 1989, 111, 5502-
5504.
(9) Heinekey, D. M.; Gould, G. L. Organometallics 1991, 10, 2977-
2979.
10.1021/om9810145 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 07/07/1999

ansa-Rhenocene Complexes
Organometallics, Vol. 18, No. 16, 1999 3071
Ta ble 1. Selected Bon d Dista n ces a n d An gles for 2
Distances, Å
Re-C(1)
Re-C(4)
Re-C(6)
Si-C(3)
C(3)-C(4)
C(5)-C(6)
C(3)-C(7)
2.117(24)
2.213(16)
2.253(17)
1.880(13)
1.473(18)
1.427(20)
1.439(20)
Re-C(3)
Re-C(5)
Re-C(7)
Si-C(2)
C(4)-C(5)
C(6)-C(7)
2.193(12)
2.262(11)
2.212(19)
1.841(13)
1.373(22)
1.457(22)
Angles, deg
C(3)-Si-C(3a)
C(3)-C(7)-C(6)
C(5)-C(6)-C(7)
C(4)-C(5)-C(6)
92.9(8)
C(2)-Si-C(2a)
112.2(9)
107.9(13)
107.1(11)
107.2(12) C(3)-C(4)-C(5)
107.0(14) C(4)-C(3)-C(7)
110.7(13) Cpcnt-M-Cpcnt (R) 145.2(16)
Cpnorm-M-Cpnorm 140.0(15) between Cp planes
(â) (γ)
40.0(4)
F igu r e 1. ORTEP representation of (η5-C5H4-SiMe2-η5-
C5H4)ReCH3 (2). Thermal ellipsoids are shown at 50%
probability. Hydrogen atoms have been omitted for clarity.
collection and solution procedures are summarized in
the Experimental Section.
Sch em e 1
Attempts to extend the derivatization of the dilithi-
ated intermediate to carbon bridges were not successful.
Reaction with methylene chloride, methylene bromide,
methylene ditosylate, and a variety of other halocarbons
and ditosylates led to no tractable products.
Addition of 1 equiv of [H(Et2O)2]B(Ar′)4 to complexes
1-4 gives clean formation of cationic methyl hydride
complexes 5-8. The methyl hydride cations have been
characterized by 1H NMR spectroscopy at 250 K in both
CD2Cl2 and CD3CN. The 1H and 13C NMR spectra of
the Si-bridged ansa complexes 6-8 are observed to have
decreased symmetry compared to the corresponding
1
neutral methyl complexes. The H NMR spectra of the
cyclopentadienyl rings exhibit four broad resonances
due to the four chemically inequivalent protons on each
ring, although the two rings are still equivalent to each
other. Two resonances are observed for the methyl
groups of the silicon bridge, which become inequivalent
with one group cisoid to the rhenium methyl group and
the other cisoid to the hydride.
immediately derivatized to give ansa-bridged complexes
in good yield (Scheme 1). When the dilithiated inter-
mediate was treated with a slight excess of Me2SiCl2,
dark orange crystals of {η5-C5H4-SiMe2-η5-C5H4}-
ReCH3 (2) were isolated in 84% yield after removal of
1
the volatiles followed by sublimation. The H and 13C
Colorless solutions of 5-8 were prepared and moni-
tored by 1H NMR spectroscopy from 250 K to room
temperature. At 250 K complexes 5-8 were indefinitely
stable, and 13C NMR spectra of complexes 5 and 6 were
obtained at this temperature without noticeable decom-
position. As the solutions were warmed to 0 °C, rapid
reaction occurred for complexes 5, 7, and 8. The solu-
tions became dark orange, and the elimination of
methane was observed in the 1H NMR spectra. Complex
6 was observed to be stable at 0 °C, and decomposition
was only evident when the sample was allowed to stand
at room temperature: t1/2 ) 2 h.
NMR spectra of 2 are consistent with a Cp2ReCH3
complex containing a bridging -(Si(CH3)2)- group. The
1H NMR spectrum of the cyclopentadienyl region reveals
two doublet of doublet resonances (δ 4.82 and 4.21),
consistent with the expected AA′BB′ spin system (J HH
) 1.6 and 1.9 Hz). The 13C NMR spectrum of the
cyclopentadienyl region contains two doublet resonances
(δ 83.7 and 75.0) which exhibit a large one-bond CH
1
coupling (1J CH ) 180 Hz). The H NMR chemical shifts
for the 3,4- and 2,5-positions of the cyclopentadienyl
rings were assigned by NOE effects between the cyclo-
pentadienyl and methyl groups. The 13C NMR reso-
nances were assigned by selective 1H decoupling ex-
periments.
Discu ssion
The procedure used for the synthesis of 2 can be
extended to the synthesis of rhenocene derivatives with
an ansa bridge containing a two-silicon bridge, (η5-
C5H4-SiMe2-SiMe2-η5-C5H4)ReCH3 (3), and a deriva-
tive containing two SiMe3 substituents, (Me3Si-η5-
C5H4)2ReCH3 (4). Complexes 3 and 4 are isolated as
pure solids by sublimation and characterized by 1H and
13C NMR spectroscopy, which gave spectra similar to
those of complex 2.
The most common synthetic routes to ansa-bridged
metallocene complexes employ a ligand having two
cyclopentadienyl rings joined by a bridging group. A
dianionic form of the ligand is reacted with an appropri-
ate metal salt. While this approach is satisfactory, yields
are variable and rarely completely satisfactory. A
promising alternative to the salt elimination reaction
has been reported by J ordan and co-workers10 and by
Collins and co-workers.11 This approach uses the ap-
The molecular structure of complex 2 was confirmed
by X-ray crystallography. An ORTEP diagram of the
structure is shown in Figure 1. A table of relevant bond
distances and angles is given in Table 1. The data
(10) Diamond, G. M.; J ordan, R. F.; Petersen, J . L. J . Am. Chem.
Soc. 1996, 118, 8024-8033.
(11) Gauthier, W. J .; Corrigan, J . F.; Taylor, N. J .; Collins, S.
Macromolecules 1995, 28, 3771-3778.

3072 Organometallics, Vol. 18, No. 16, 1999
Heinekey and Radzewich
propriate dicyclopentadiene and a metal amide complex.
Liberation of amine provides the driving force for the
reactions, which afford both chiral and achiral ansa-
metallocene complexes in excellent yield.
In part due to the lack of a readily available Re(III)
precursor, synthetic entries to conventional rhenocene
chemistry employ reaction of the cyclopentadienyl anion
with either ReCl4(THF)2 or ReCl5.9 Yields of Cp2ReH
are modest, and our attempts to extend this approach
to ansa-bridged complexes were unsuccessful.
of the unbridged complexes but fall within the range of
140-158° observed for the crystallographically charac-
terized rhenocene derivatives.16 This is consistent with
the bending angles for group 4 metallocenes reported
by Corey and co-workers.15 The bending angles for
structures with a single SiMe2 bridge are 3-4° smaller
than the unbridged metallocenes, while the structures
with a single CMe2 bridge are 10-13° smaller than the
unbridged metallocenes. The difference between the R
and â angles for 2 is 5°, which indicates a slight shift
in the angle of the Re to Cp centroid compared to that
of Re to the normal of the cyclopentadienyl plane. There
is a slight distortion of ring C to Re bond lengths,
indicating a subtle shift toward an η3 structure. The
Re-C(3) bond distance is the shortest, and the longest
Re-C bond distances are to the two carbons which are
further from the Si bridge. The most dramatic effect that
the SiMe2 bridge has upon the structure is the bending
of the angle that Si-C(3) makes with the plane of the
cyclopentadienyl ring. An unbridged substituent on the
Cp ring, such as H or a SiMe3 group, normally is found
to point slightly away from the other Cp ring. In
complex 2, the constraints of the bridge cause the SiMe2
moiety to be shifted significantly toward the metal atom.
We have previously studied methane elimination from
the methyl hydride complex 5 resulting from protona-
tion of complex 1 with various acids. On the basis of
our observation6 that the thermal stability of certain
cationic rhenocene derivatives is dependent on the
nature of the counterion, with the greatest stability
achieved with B(Ar′)4 , protonation of 1 with [H(Et2O)2]B-
(Ar′)4 was investigated. The rate of methane elimination
from the methyl hydride complex 5 is found to be
independent of the counterion. This is consistent with
our earlier investigation of the mechanism of this
reaction, which was found to proceed by rate-determin-
ing dissociation of methane.8
An alternative methodology starts from unbridged
metallocene complexes, which are then derivatized to
ansa complexes. The metalation of cyclopentadienyl
complexes by nBuLi has been reported by several
groups.12 Consistent with our synthetic goals, there have
been reports of metalation of sandwich complexes fol-
lowed by addition of dialkyldichlorosilane to generate
ansa-bridged complexes.13,14 Since Cp2Re-H is known
to react with alkyllithium reagents to give lithiation at
the metal,9 alkyl derivatives such as Cp2Re-CH3 present
a better starting point for this chemistry.
Dilithiation of Cp2Re-CH3 gives a very reactive
material, which was not isolated. Formulation of this
intermediate as (η5-C5H4Li)2Re-CH3 was confirmed by
the formation of complexes 2-4 by reaction with various
chlorosilanes. The ansa-bridged species are obtained in
a state of high purity as very air-sensitive orange
crystals by sublimation of the reaction residues. The 1H
and 13C NMR data are consistent with the structures
depicted in Scheme 1. Retention of the methyl group
bound directly to Re is indicated by the high-field
resonance in both the 1H and 13C NMR spectra. The
presence of the bridge connecting the two rings in
complexes 2 and 3 is indicated by the reduced symmetry
of the Cp rings and appropriate resonances for the Si-
bound methyl groups.
The molecular structure of complex 2 was confirmed
by X-ray crystallography. No X-ray structure of Cp2-
ReCH3 has been reported, but comparison of complex 2
to several other unbridged rhenocene complexes is
possible. It is important to clearly define the bond angles
involved in comparing various structures, since some
confusion exists in the literature on this point. We adopt
the definitions of Corey and co-workers15 as defined in
the following diagram:
Motivated by the recent work of Green and co-
workers,5 who report that ansa-metallocene complexes
of Mo and W alkyl hydrides are significantly stabilized
with respect to the unsubstituted analogues, we antici-
pated that the alkyl hydride complexes of ansa-bridged
rhenocene such as 6 and 7 would have enhanced
thermal stability. Complex 8, which has two SiMe3
substituents, serves as a good comparison to evaluate
purely inductive effects of silicon substitution.
The reactivity differences among complexes 5, 7, and
8 are subtle, but it appears that the single Si ansa
bridge in complex 6 significantly increases the thermal
stability of the methyl hydride complexes toward meth-
ane elimination. Complex 6 was observed to be stable
at 0 °C, and decomposition was only evident when the
sample was allowed to stand at room temperature; t1/2
(16) (a) [(η5-C5H5)2ReH2][BF4], â ) 145.7: Welter, J . J . Ph.D. Thesis,
University of Illinois at Urbana-Champaign, 1980. (b) [(η5-C5H5)2-
ReBr2][BF4], â ) 139.5: Prout, K.; Cameron, T. S.; Forder, R. A.;
Critchley, S. R.; Denton, B.; Rees, G. V. Acta Crystallogr. 1974, B30,
2290-2304. (c) (η5-C5H5)2ReCl, R ) 147.6: Apostolidis, C.; Kanella-
kopulos, B.; Maier, R.; Rebizant, J .; Siegler, M. J . Organomet. Chem.
1991, 409, 243-254. (d) (η5-C5H5)2ReCuCl2, R ) 150.1, â ) 147.5:
Ishchenko, V. M.; Bulychev, B. M.; Soloveichik, G. L.; Bel’sky, V. K.;
Ellert, O. G. Polyhedron 1984, 3, 771-774. (e) [(η5-C5H5)2ReHCuI]2, R
) 158.0: Bel’sky, V. K.; Ischenko, V. M.; Bulychev, B. M.; Soloveichik,
G. L. Polyhedron 1984, 3, 749-752. (f) [(η5-C5H5)2Re[η1-(E)-C(CO2Me)d
CH(CO2Me)], â ) 146.2; [(η5-C5H5)2Re[η1-(Z)-C(CO2Me)dCH(CO2Me)],
â ) 146.8: Herberich, G. E.; Barlage, W. Organometallics 1987, 6,
1924-1930.
The Cp-M-Cp bending angles (R and â) of complex 2
are approximately 5° smaller than the bending angles
(12) Rausch, M. D.; Ogasa, M.; Rogers, R. D.; Rollins, A. N.
Organometallics 1991, 10, 2084-2086 and references therein.
(13) Manners, I. Adv. Organomet. Chem. 1995, 37, 131-168.
(14) (a) Wrighton, M. S.; Palazzotto, M. C.; Bocarsly, A. B.; Bolts,
J . M.; Fischer, A. B.; Nadjo, L. J . Am. Chem. Soc. 1978, 100, 7264-
7271. (b) Fischer, A. B.; Kinney, J . B.; Staley, R. H.; Wrighton, M. S.
J . Am. Chem. Soc. 1979, 101, 6501-6510.
(15) Shaltout, R. M.; Corey, J . Y.; Rath, N. P. J . Organomet. Chem.
1995, 503, 205-212.

ansa-Rhenocene Complexes
Organometallics, Vol. 18, No. 16, 1999 3073
dried over silica gel which was activated by heating to 300 °C
under vacuum.
) 2 h. Complexes 5, 7, and 8 eliminate methane too
rapidly at room temperature to allow observation at this
temperature. Green and co-workers have observed a
more drastic reactivity difference between Cp2W(CH3)H
and ansa-(Me2C)Cp2W(CH3)H. The parent compounds
have been shown to reductively eliminate methane at
40 °C, while the ansa complexes show no reactivity up
to 150 °C.5 Green et al. have proposed that this reactiv-
ity difference is the result of the ability of the “Cp2W”
intermediate to attain a parallel structure following
reductive elimination of methane and the inability of
“ansa-Cp2W” to attain a parallel structure. This is
consistent with the results that we have observed and
suggests that the unbridged complexes, 5 and 8, achieve
a parallel ring structure during the transition state of
methane reductive elimination. Complex 7, which con-
tains the double Si bridge, does not constrain the
geometry to a bent metallocene and the reactivity is
therefore similar to that of the unbridged species. While
complex 6 does appear to be more thermally stable than
the other complexes, the stability is unfortunately still
inadequate for isolation at room temperature.
1H and 13C NMR spectra were recorded on Bruker AC-200,
AF-300, and WM-500 spectrometers. Samples were contained
in sealed or Teflon-valved tubes at ambient probe temperature
1
unless otherwise indicated. H and 13C NMR chemical shifts
(δ) are referenced to the deuterated solvent relative to SiMe4.
Unless otherwise noted, all NMR spectra were recorded in CD2-
Cl2. In complexes 5-8, resonances due to the B(Ar′)4 anion
1
are listed only for complex 5. The H and 13C resonances due
to this anion are identical in all complexes reported here. The
cyclopentadienyl protons of rhenocene complexes have been
observed to relax slowly, and a relaxation delay of 120 s is
required to observe appropriate integrals. Elemental analyses
were performed by Canadian Microanalytical Service Ltd.,
Delta, Canada.
(η5-C5H4-SiMe2-η5-C5H4)Re-CH3 (2). A small glass ves-
sel with an 8 mm Kontes valve was charged with Cp2ReCH3
(274 mg, 0.83 mmol). THF (20 mL) was vacuum-transferred
to the vessel and warmed to 0 °C. Under an argon flow, 2 equiv
n
of BuLi (1.03 mL, 1.6 M, 1.65 mmol) was added via syringe.
The solution was stirred at 0 °C for 45 min. Under an argon
flow, Me2SiCl2 (101 µL, 0.83 mmol) was added via syringe and
the mixture was stirred at 0 °C for 15 min. The solvent was
removed in vacuo. Sublimation of the residue affords 320 mg
of dark orange crystals (84%). 1H NMR: δ 4.82 (d of d, 4H,
J HH ) 1.6, J HH ) 2.0 Hz, η5-C5H4), 4.21 (d of d, 4H, J HH ) 1.6,
J HH ) 2.0, η5-C5H4), 0.28 (s, 3H, ReCH3), 0.18 (s, 6H, Si(CH3)2).
13C NMR (CD2Cl2): δ 83.7 (d of quart, J CH ) 180, J CH ) 6.6
Hz, η5-C5H4), 75.0 (d of quart, J CH ) 183, J CH ) 7, η5-C5H4),
28 (s, η5-C5H4), -5.2 (quart, J CH ) 121, Si(CH3)2), -34.0 (quart,
J CH ) 127, ReCH3). Anal. Calcd for C13H17ReSi: C, 40.29; H,
4.42. Found: C, 40.31; H, 4.61.
We anticipate that ansa-rhenocene alkyl hydride
complexes with a more constrained structure, such as
that provided by a single carbon bridge, may be isolable
at room temperature. Synthetic efforts directed toward
this goal are continuing.
Con clu sion s
(η5-C5H4-SiMe2-SiMe2-η5-C5H4)Re-CH3 (3). The pro-
cedure used for complex 2 was followed. To the dilithiated
intermediate generated from 50 mg of Cp2ReCH3 in THF
solution was added 1 equiv of ClSiMe2-SiMe2Cl. After removal
A high-yield synthesis for the first ansa-bridged
complexes of rhenocene has been developed. The addi-
tion of Me2SiCl2 or (Me2Si)2Cl2 to a THF solution of (η5-
C5H4Li)2ReCH3 generates ansa-bridged complexes with
one or two silicon dimethyl groups, respectively. The
structure of (η5-C5H4-SiMe2-η5-C5H4)ReCH3 was con-
firmed by X-ray diffraction. Rhenocene methyl hydride
complexes have been generated by protonation and
characterized at low temperature by NMR spectroscopy.
Methane elimination from these complexes occurs below
ambient temperature, although [(η5-C5H4-SiMe2-η5-
C5H4)Re(CH3)H]B(Ar′)4 has been observed to be more
stable at room temperature than analogous unbridged
complexes. This increased stability is attributed to the
ansa bridge, which restricts formation of the favored
transition state for reductive elimination.
of the solvent, 58 mg of complex 3 was obtained in 56% yield
1
by sublimation (56% yield). H NMR: δ 4.42 (“t”, 4H, J HH
)
1.7 Hz, η5-C5H4), 4.37 (“t”, 4H, J HH ) 1.7, η5-C5H4), 0.36 (s,
3H, ReCH3), 0.25 (s, 12H, Si(CH3)2). 13C NMR: δ 83.91 (d of
q, J CH ) 181, J CH ) 7 Hz, η5-C5H4), 71.24 (d of q, J CH ) 180,
J CH ) 7, η5-C5H4), 75.01 (s, η5-C5H4), -1.4 (q, J CH ) 121, (Si-
(CH3)2)2), -36.77 (q, J CH ) 129, ReCH3). Anal. Calcd for C15H23
ReSi2: C, 40.42; H, 5.20. Found: C, 40.41; H, 5.15.
-
(Me3Si-η5-C5H4)2Re-CH3 (4). This compound was pre-
pared as described above, but the dilithiated intermediate
prepared from 120 mg of Cp2ReCH3 was reacted with an excess
of trimethylsilyl chloride, which was added to the reaction
mixture by vacuum transfer at -78 °C. The solution was
slowly warmed to room temperature, and the volatiles were
removed in vacuo. The solid was sublimed at 60 °C under
dynamic vacuum to give 150 mg of 4 as an orange solid (87%).
1H NMR: δ 4.52 (“t”, 4H, J HH ) 1.9, η5-C5H4), 3.52 (“t”, 4H,
J HH ) 1.9, η5-C5H4), 0.19 (s, 18H, Si(CH3)3), 0.18 (s, 3H,
ReCH3). 13C NMR: δ 83.9 (d of q, J CH ) 176, J CH ) 8, η5-C5H4),
68.7 (d of q, J CH ) 180, J CH ) 6, η5-C5H4), 0.58 (q, J CH ) 119,
Si(CH3)3), -36.3 (quart, J CH ) 128, ReCH3). Anal. Calcd for
Exp er im en ta l Section
All manipulations were conducted with rigorous exclusion
of air and water using standard high-vacuum Schlenk and
drybox techniques. Chlorinated solvents were distilled from
CaH2. Hydrocarbon solvents were distilled from Na/K ben-
zophenone ketyl. Deuterated solvents (Cambridge Isotope
Laboratories) were dried and stored in the same manner as
their protio analogues. All solvents were vacuum-transferred
immediately prior to use. Reagent grade chemicals were used
as received unless stated otherwise. ReCl4(THF)2,17 Cp2-
ReCH3,9 and [H(Et2O)2]B(Ar′)418 were prepared using literature
procedures. Me3SiCl was used as received from Aldrich. (Me2-
Si)2Cl2 (Gelest) and Me2SiCl2 (Aldrich) were degassed and
C
17H29ReSi2: C, 42.92; H, 6.14. Found: C, 42.94; H, 6.05.
[(η5-C5H5)2Re(CH3)H][B(Ar ′)4] (5). A sealable NMR tube
was charged with (η5-C5H5)2ReCH3 (1; 6 mg, 0.018 mmol) and
[H(Et2O)2][B(Ar′)4] (18.3 mg, 0.018 mmol). Methylene chloride-
d2 (0.5 mL) was vacuum-transferred into the tube. The tube
1
was kept at -78 °C until it was placed in the NMR probe. H
NMR (CD2Cl2, 250 K): δ 7.74 (m, 8H, o-B(Ar′)4); 7.58 (m, 4H,
p-B(Ar′)4); 5.30 (s, 10H, η5-C5H5); 0.53 (s, 3H, Re-CH3); -11.88
(s, 1H, Re-H). 13C{1H} NMR (CD2Cl2, 250 K): δ 162.2 (quart,
1
1J CB ) 50 Hz, B(Ar′)4 ipso); 135.2 (d, J CH ) 159, o-B(Ar′)4);
(17) Allen, E. A.; J ohnson, N. P.; Rosevear, D. T.; Wilkinson, G. J .
Chem. Soc. A 1969, 788-791.
(18) Brookhart, M.; Grant, B.; Volpe, A. F., J r. Organometallics 1992,
11, 3920-3922.
2
1
129.3 (quart, J CF ) 30, m-B(Ar′)4); 125.0 (quart, J CF ) 272,
1
3
B(Ar′)4 CF3); 118.0 (d of t, J CH ) 166, J CF ) 4, p-B(Ar′)4);
84.0 (η5-C5H5); -40.1 (Re-CH3).

3074 Organometallics, Vol. 18, No. 16, 1999
Heinekey and Radzewich
[(η5-C5H4-SiMe2-η5-C5H4)Re(CH3)H][B(Ar ′)4] (6). A seal-
able NMR tube was charged with {η5-C5H4-Si(CH3)2-η5-
C5H4}ReCH3 (2; 8 mg, 0.021 mmol) and [H(Et2O)2][B(Ar′)4] (21
mg, 0.021 mmol). CD2Cl2 was vacuum-transferred to the tube.
The tube was kept at -78 °C until it was placed in the NMR
probe. 1H NMR (CD2Cl2, 250 K): 5.81 (s, 2H, η5-C5H4); 5.72
(s, 2H, η5-C5H4); 5.32 (s, 2H, η5-C5H4); 4.92 (s, 2H, η5-C5H4);
0.53 (s, 3H, Re-CH3); 0.35 (s, 3H, Si-CH3); 0.30 (s, 3H, Si-
CH3); -10.47 (s, 1H, Re-H). 13C{1H} NMR (250 K): 114.7 (η5-
C5H4); 89.5 (η5-C5H4); 84.4 (η5-C5H4); 73.5 (η5-C5H4); 49.5 (ipso
η5-C5H5); -6.3 (SiCH3); -6.4 (SiCH3); -41.0 (ReCH3).
stream at 183 K on an Enraf-Nonius CAD4 diffractometer
using Mo KR radiation with a graphite monochromator (λ )
0.710 73 Å). An orientation matrix was determined from 20
reflections in the range 24° e 2θ g 32°. Monoclinic symmetry
(space group C2/c) was indicated on the basis of systematic
absences. The cell parameters are a ) 11.242(2) Å, b ) 14.118-
(3) Å, c ) 7.885(2) Å, â ) 108.19(3)°, V ) 1188.9(4) Å3 (Z ) 4).
A high-ø reflection was scanned to provide for an absorption
correction, reducing the equivalency disagreement from 9% to
3%. The decay was negligible. Reduction of the data was
carried out using XCAD4, and all further work was carried
out using the Siemens version of SHELX. The structure was
solved primarily from the Patterson map, as refinement on
the Re was obtained. The weighting scheme required a
correction of 0.005. Hydrogens were introduced by calculation.
The methyl carbon attached to the Re atom showed a large
ellipsoid, and by modeling disorder of the hydrogens bonded
to the carbon, it was considerably reduced. A final R value of
6.3% with a GOF of 1.14 was obtained (data/parameter ) 981/
71).
[{η5-C5H4-SiMe2-SiMe2-η5-C5H4}Re(CH3)H][B(Ar ′)4] (7).
A sealable NMR tube was charged with (η5-C5H4-SiMe2-
SiMe2-η5-C5H4)ReCH3 (3; 3 mg, 0.0067 mmol) and [H(Et2O)2]-
[B(Ar′)4] (6.8 mg, 0.0067 mmol). CD2Cl2 was vacuum-trans-
ferred to the tube. The tube was kept at -78 °C until it was
1
placed in the NMR probe. H NMR (250 K): 5.44 (s, 2H, η5-
C5H4); 5.38 (s, 2H, η5-C5H4); 5.32 (s, 2H, η5-C5H4); 4.31 (s, 2H,
η5-C5H4); 0.63 (s, 3H, Re-CH3); 0.42 (s, 6H, Si-CH3); 0.40 (s,
6H, Si-CH3); -12.00 (s, 1 H, Re-H).
[(Me3Si-η5-C5H4)2Re(CH3)H][B(Ar ′)4] (8). A sealable NMR
tube was charged with {(CH3)3Si-η5-C5H4}2Re(CH3)ReCH3 (4;
12 mg, 0.025 mmol) and [H(Et2O)2][B(Ar′)4] (26 mg, 0.025
mmol). CD2Cl2 was vacuum-transferred to the tube. The tube
Ack n ow led gm en t. We thank the Petroleum Re-
search Fund, administered by the American Chemical
Society, for support of this work. C.E.R. is grateful to
the University of Washington for a Ritter Fellowship.
We thank Dr. David Barnhart for assistance with X-ray
crystallography.
1
was kept at -78 °C until it was placed in the NMR probe. H
NMR (250 K): 5.58 (br, 2H, η5-C5H4), 5.41 (br, 2H, η5-C5H4),
4.79 (m, 4H, η5-C5H4), 0.40 (s, 3H, ReCH3), 0.25 (s, 18H, Si-
(CH3)3), -12.1 (s,1H, Re-H).
X-r a y Str u ctu r e Deter m in a tion for (η5-C5H4-Si(CH3)2-
η5-C5H4)ReCH3 (2). Crystals were generated upon sublima-
tion of the crude reaction material at 50 °C to a probe cooled
with ice water under dynamic vacuum. An orange needle of
dimensions 0.15 × 0.20 × 0.35 mm was placed in a nitrogen
Su p p or tin g In for m a tion Ava ila ble: Details of the struc-
ture determination for complex 2. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM9810145