Synthesis and reactivity of the cationic methylene complex [Cp2Re=CH2]+

Article abstract of DOI:10.1021/om970706a

Reaction of Cp₂ReCH₂R (R = H, CH₃) (Cp = η⁵-C₅H₅) with [Ph₃C]B(Ar′)₄ (Ar′ = 3,5-CF₃)₂C₆H₃) generates carbene complexes [Cp<

Full text of DOI:10.1021/om970706a

Organometallics 1998, 17, 51-58
51
Syn th esis a n d Rea ctivity of th e Ca tion ic Meth ylen e
Com p lex [Cp 2RedCH2]+
D. M. Heinekey* and Catherine E. Radzewich
Department of Chemistry, Box 351700, University of Washington,
Seattle, Washington 98195-1700
Received August 11, 1997X
Reaction of Cp2ReCH2R (R ) H, CH3) (Cp ) η5-C5H5) with [Ph3C]B(Ar′)4 (Ar′ )
3,5-CF3)2C6H3) generates carbene complexes [Cp2RedCH2]B(Ar′)4 (1) and [Cp2RedCH-
(CH3)]B(Ar′)4 (3). Complex 1 is thermally robust and is only observed to decompose to [Cp2-
Re(C2H4)]+ and [Cp2Re(NCCD3)]+ upon prolonged thermolysis in acetonitrile-d3 or upon
-
-
addition of BF4 or PF6 salts. The formation of 1 is also observed upon reaction of [Cp2-
Re(CH3)H]B(Ar′)4 with CH2Cl2 at 0 °C to give [Cp2Re(CH2Cl)Cl]B(Ar′)4 (2) followed by
treatment with Mg. The electrophilic nature of 1 is confirmed by adduct formation with
PPh3, pyridine, and CNtBu. Complex 1 reacts with halogens by 1,2-addition across the Re-C
double bond to form halomethyl halide complexes [Cp2Re(CH2X)X]B(Ar′)4 (X ) Cl, Br, I).
Reaction of 1 with pyridine N-oxide gives the formaldehyde complex [Cp2Re(η2-H2CdO)]B-
(Ar′)4. The formaldehyde ligand can be displaced in solution by reaction with PPh3,
acetonitrile, or methylene chloride. Complex 1 reacts with sulfur-atom donor reagents to
give the thioformaldehyde complex [Cp2Re(η2-H2CdS)]B(Ar′)4. Reaction of 1 with N2CHSiMe3
generates the olefin complex [Cp2Re(η2-H2CdCHSiMe3)]B(Ar′)4.
In tr od u ction
formation of a phosphine adduct.4 Related methylene
complexes of group VI metallocenes are not known, but
Cp2WdCHPh has been isolated and structurally char-
acterized.5
Despite the extensive development of the chemistry
of metal carbene complexes, few examples of bound
methylene, the simplest type of carbene complex, have
been completely characterized. The first methylene
complex was synthesized by Schrock in 1975 via depro-
tonation of [Cp2TaMe2]+ to give Cp2TaCH3(dCH2).1 The
number of isolable methylene complexes has grown
slowly since this time.2 Several synthetic routes have
been observed to produce methylene complexes. In
addition to proton abstraction from a cationic methyl
group, a common route is hydride abstraction from a
methyl group using [Ph3C]+.
Stucky and co-workers have reported that the reaction
of [Ph3C]BF4 with Cp2ReCH3 led to an unstable meth-
1
ylene complex by abstraction of an R hydride.6 The H
NMR resonances for [Cp2ReCH2]BF4 were quickly re-
placed by signals assigned to the ethylene complex, [Cp2-
Re(C2H4)]BF4. Reaction of Cp2ReCH2CH3 with [Ph3C]-
BF4 also affords [Cp2Re(C2H4)]BF4, proposed to result
from â-hydride abstraction from the ethyl group, al-
though labeling studies were not performed to confirm
the site of hydride abstraction.
A very important example of a methylene complex
which is not isolable is provided by Cp2TiCH2. This
titanium methylene complex is very reactive,3 and has
only been characterized by indirect methods, including
We have found that reaction of [Ph3C]B(Ar′)4 (Ar′ )
3,5-(CF3)2C6H3)7 with Cp2ReCH3 leads to a stable,
cationic methylene complex [Cp2ReCH2]B(Ar′)4. Addi-
tion of [Ph3C]B(Ar′)4 to Cp2ReCH2CH3 leads to hydride
abstraction from the R carbon to generate an ethylidene
complex [Cp2ReCH(CH3)]B(Ar′)4. The thermal stability
of these complexes is greatly increased with use of the
non-nucleophilic and noncoordinating anion B(Ar′)4.7-11
X Abstract published in Advance ACS Abstracts, December 15, 1997.
(1) (a) Schrock, R. R. J . Am. Chem. Soc. 1975, 97, 6577-6578. (b)
Guggenberger, L. J .; Schrock, R. R. J . Am. Chem. Soc. 1975, 97, 6578-
6579. (c) Schrock, R. R.; Sharp, P. R. J . Am. Chem. Soc. 1978, 100,
2389-2399.
(2) Some representative examples are as follows. (a) [Cp*Re-
(NO)(PPh3)CH2]+: Patton, A. T.; Strouse, C. E.; Knobler, C. B.; Gladysz,
J . A. J . Am. Chem. Soc. 1983, 105, 5804-5811. (b) [Cp*Fe(dppe)CH2]+:
Roger, C.; Lapinte, C. J . Chem. Soc., Chem. Commun. 1989, 1598-
1600. (c) [Tp*W(PhC2CH3)CH2]+: Gunnoe, T. B.; White, P. S.; Tem-
pleton, J . L.; Casarrubios, L. J . Am. Chem. Soc. 1997, 119, 3171-3172.
(d) [N(SiMe2CH2PPh3)2]IrCH2: Fryzuk, M. D.; Gao, X.; J oshi, K.;
MacNeil, P. A.; Massey, R. L. J . Am. Chem. Soc. 1993, 115, 10581-
10590. (e) (PPh3)2Ru(Cl)(NO)CH2: Burrell, A. K.; Clark, G. R.; Rickard,
C. E. F.; Roper, W. R.; Wright, A. H. J . Chem. Soc., Dalton Trans.
1991, 609-614. (f) (PPh3)2Os(Cl)(NO)CH2: Hill, A. F.; Roper, W. R.;
Waters, J . M.; Wright, A. H. J . Am. Chem. Soc. 1983, 105, 5939-5940.
(g) (PCy3)2Ru(Cl)2CH2: Schwab, P.; Grubbs, R. H.; Ziller, J . W. J . Am.
Chem. Soc. 1996, 118, 100-110.
(4) Meinhardt, J . D.; Anslyn, E. V.; Grubbs, R. H. Organometallics
1989, 8, 583-589.
(5) Marsella, J . A.; Folting, K.; Huffman, J . C.; Caulton, K. G. J .
Am. Chem. Soc. 1981, 103, 5596-5598.
(6) (a) Welter, J . J . Ph.D. Thesis, University of Illinois at Urbana-
Champaign, 1980. (b) Mink, R. I.; Welter, J . J .; Young, P. R.; Stucky,
G. D. J . Am. Chem. Soc. 1979, 101, 6928-6933.
(7) Bahr, S. R.; Boudjouk, P. J . Org. Chem. 1992, 57, 5545-5547.
(8) For reviews of weakly coordinating anions, see: (a) Strauss, S.
H. Chemtracts: Inorg. Chem. 1994, 6, 1-13. (b) Strauss, S. H. Chem.
Rev. 1993, 93, 927-942. (c) Seppelt, K. Angew. Chem., Int. Ed. Engl.
1993, 32, 1025-1027. (c) Bochman, M. Angew. Chem., Int. Ed. Engl.
1992, 31, 1181-1182. (d) Beck, W.; Sunkel, K. Chem. Rev. 1988, 88,
1405-1421.
(3) Brown-Wensley, K. A.; Buchwald, S. L.; Cannizzo, L.; Clawson,
L.; Ho, S.; Meinhart, D.; Stille, J . R.; Straus, D.; Grubbs, R. H. Pure
Appl. Chem. 1983, 55, 1733-1744.
S0276-7333(97)00706-1 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 01/05/1998

52 Organometallics, Vol. 17, No. 1, 1998
Heinekey and Radzewich
Sch em e 1
The electrophilic nature of the methylene complex is
confirmed by reactions with various nucleophiles, lead-
ing to several new complexes of rhenocene.
Resu lts
P r ep a r a t ion a n d Ch a r a ct er iza t ion of [Cp 2-
RedCH2]+ (1). A solution of Cp2ReCH3 in methylene
chloride reacts rapidly with [Ph3C]B(Ar′)4 to form [Cp2-
RedCH2]B(Ar′)4 (1) and Ph3CH (eq 1). Complex 1 is
Re(NCCH3)]B(Ar′)4 at room temperature by loss of
methane.12
Gen er a tion of Com p lex 1 fr om Meth ylen e Ch lo-
r id e. Consistent with previous reports,12,13 the proto-
nation of Cp2ReCH3 with [H(Et2O)2]B(Ar′)4 results in
the formation of [Cp2Re(CH3)H]B(Ar′)4, which has been
precipitated from solution by addition of pentane and
isolated by filtration (97% yield). Complex 1 has been
1
characterized by H and 13C NMR spectroscopy as well
as by elemental analysis. The downfield resonances
1
characterized by H and 13C NMR spectroscopy at 250
1
observed in the H and 13C NMR spectra are particu-
K (Scheme 1). Warming a solution of the methyl
hydride complex to room temperature in methylene
chloride results in methane elimination and the forma-
tion of [Cp2Re(CH2Cl)Cl]B(Ar′)4 (2). Confirmation of the
structure of 2 was obtained by 1H and 13C NMR
spectroscopy as well as by generating the compound by
larly indicative of the formation of a transition-metal
carbene complex. The H NMR spectrum of 1 in CD2-
1
Cl2 shows two resonances for the cation; a singlet for
the 10 equivalent cyclopentadienyl protons at 5.60 ppm
and a singlet for the two protons of the carbene ligand
at 13.19 ppm. The carbon resonance of the carbene
ligand appears at 247.7 ppm as a triplet due to coupling
1
another route (vide infra). The H NMR spectrum of 2
1
shows a single Cp resonance at 6.02 ppm and a
resonance at 4.40 ppm which integrates for two protons.
The 13C NMR resonance for Re-CH2Cl appears as a
triplet at δ 11.5 (J CH ) 163 Hz). Complex 2 reacts with
Mg turnings to generate 1.
P r ep a r a tion a n d Ch a r a cter iza tion of [Cp 2ReCH-
(CH3)]B(Ar ′)4 (3). Cp2ReCH2CH3 reacts rapidly with
[Ph3C]B(Ar′)4 in methylene chloride to form [Cp2RedCH-
(CH3)]B(Ar′)4 (3) and Ph3CH (eq 3). Complex 3 is
of the two equivalent protons with J CH ) 152 Hz.
Contrary to the extreme air sensitivity of the alkyl
complexes of rhenocene, 1 is air stable in the solid state
and in solution, showing little decoloration over several
days. Complex 1 was formed as a tetraphenylborate
salt upon reaction of Cp2ReCH3 with [Ph3C]BPh4 in
CH2Cl2 and isolated as a pink solid. Complex 1-BP h 4
is thermally stable, but its low solubility in CH2Cl2
makes it inconvenient for the synthesis of further
derivatives.
Reaction of Cp2ReCH3 with [Cp2Fe]B(Ar′)4 at room
temperature in acetonitrile-d3 affords a 50/50 mixture
of the methylene complex 1 and [Cp2Re(NCCH3)]B(Ar′)4
(eq 2). Monitoring the reaction at low temperature by
isolated by precipitation with pentane followed by
filtration to give a pale orange solid in 94% yield. The
1H and 13C NMR spectra indicate the formation of an
ethylidene complex and a small amount (<5%) of the
previously reported ethylene complex.6 The 1H NMR
spectrum of 3 in CD2Cl2 reveals a doublet at 1.53 ppm
for the methyl group of the ethylidene ligand and a
quartet at 13.82 ppm for the carbene proton (3J HH ) 8
Hz). The cyclopentadienyl resonances are observed as
two singlets at 5.56 and 5.51 ppm. The 13C NMR
spectrum of 3 exhibits a doublet at 266.0 ppm for the
carbene carbon with a one-bond CH coupling constant
of 143 Hz. A quartet is observed for the methyl carbon
1H NMR spectroscopy indicates the formation of [Cp2-
Re(CH3)H]B(Ar′)4, which then proceeds to generate [Cp2-
(9) Brookhart, M.; Grant, B.; Volpe, A. F., J r. Organometallics 1992,
11, 3920-3922.
(10) (a) Golden, J . H.; Mutolo, P. F.; Lobkovsky, E. B.; DiSalvo, F.
J . Inorg. Chem. 1994, 33, 5374-5375. (b) Hayashi, Y.; Rhode, J . J .;
Corey, E. J . J . Am. Chem. Soc. 1996, 118, 5502-5503.
(11) Hughes, R. P.; Lindner, D. C.; Rheingold, A. L.; Yap, G. P. A.
Inorg. Chem. 1997, 36, 1726-1727.
(12) Gould, G. L.; Heinekey, D. M. J . Am. Chem. Soc. 1989, 111,
5502-5504.
(13) Heinekey, D. M.; Gould, G. L. Organometallics 1991, 10, 2977-
2979.

Synthesis and Reactivity of [Cp2RedCH2]+
Organometallics, Vol. 17, No. 1, 1998 53
of the ethylidene ligand at 45.0 ppm with a one-bond
CH coupling constant of 128 Hz.
13C NMR data are consistent with the formation of the
phosphine-ylide complex [Cp2Re(CH2PPh3)]B(Ar′)4 (4).
The 1H and 13C resonances of the methylene ligand have
shifted considerably to higher field at 2.58 and -32.7
Sta bility of Ca r ben e Com p lexes 1 a n d 3. Com-
plex 1-B(Ar′)4 has been found to be indefinitely stable
as a solid, and no decomposition has been observed in
CD2Cl2 at room temperature. Complexes 1 and 3 were
heated in CD2Cl2 at 40 °C and monitored periodically
by 1H NMR spectroscopy. Gradual formation of complex
product mixtures was observed over 2 weeks. The
thermolysis of 1 and 3 in CD3CN led to cleaner reac-
tions. Complete disappearance of starting material was
observed after 2 weeks at 55 °C. The two main products
identified by their 1H NMR spectra are [Cp2Re-
1
ppm, respectively. The methylene resonance in the H
NMR appears as a doublet due to a 31P coupling of 10.8
Hz. The methylene resonance in the 13C NMR spectrum
appears as a doublet of triplets due to 31P and 1H
coupling (J CP ) 25.6 Hz, J CH ) 126.2 Hz).
Addition of 3 equiv of pyridine to 1 in CD2Cl2 resulted
in the formation of a pyridine-ylide complex [Cp2Re-
1
(CH2NC5H5)]B(Ar′)4 (5). The H NMR resonance of the
methylene protons was shifted to 5.86 ppm, and a
singlet for the cyclopentadienyl protons was observed
at 4.51 ppm. Attempts to isolate this complex as a solid
were unsuccessful. When pentane was added to a
methylene chloride solution of 5, a pale peach solid
6
12
(C2H4)]B(Ar′)4 and [Cp2Re(NCCD3)]B(Ar′)4 (eq 4).
1
precipitated. The H NMR spectrum of the solid dis-
solved in CD2Cl2 gave broadened resonances for the
cyclopentadienyl and the methylene protons, which were
intermediate between those due to 5 and [Cp2ReCH2]+
(1). Addition of excess pyridine to the solution resulted
1
in conversion back to the sharp H NMR resonances of
5 as noted above.
t
Addition of BuNC to a CH2Cl2 solution of 1 gives a
pale orange solution from which [Cp2ReCH2CNtBu]B-
(Ar′)4 (6) is isolated in 86% yield. The 1H NMR
resonance of the methylene protons was observed at
1.64 ppm, and the carbon resonance was observed as a
triplet (J CH ) 164 Hz) at -31.8 ppm in the 13C NMR
spectrum. An IR spectrum of 6 as a Nujol mull
exhibited a strong band at 1780 cm-1, which is consis-
tent with a ketenimine structure with a CN double
bond.
We find that complex 1 does not react with CO, CH3-
CN, PhNCO, CO2, or CS2. Complex 1 also fails to
undergo any reaction with olefins such as ethylene or
styrene to generate cyclopropanes.
The reaction of Cp2ReCH3 with [Ph3C]BF4 in CD2Cl2
forms several unidentifiable products, and no evidence
for the carbene complex was observed. The reaction is
much cleaner in CD3CN and shows almost exclusive
formation of [Cp2ReCH2]BF4 as well as a small amount
of [Cp2Re(NCCD3)]BF4. The carbene complex undergoes
complete conversion to [Cp2Re(C2H4)]BF4 and [Cp2Re-
(NCCD3)]BF4 after 24 h at room temperature.
In either CD2Cl2 or CD3CN, the reaction of Cp2ReCH2-
CH3 with [Ph3C]BF4 gives [Cp2Re(C2H4)]+ immediately.
Minor amounts of the carbene complex (3) are observed
Complex 2 can also be formed by the reaction of [Cp2-
ReCH2]B(Ar′)4 (1) with Cl2 in CH2Cl2. [Cp2Re(CH2X)X]B-
(Ar′)4 (X ) Br (7) I (8)) are formed upon addition of Br2
or I2 to a CH2Cl2 solution of 1. Complexes 2, 7, and 8
have been isolated by recrystallization from CH2Cl2/
pentane and completely characterized by 1H and 13C
NMR spectroscopy and elemental analysis. The 1H and
13C NMR resonances of the methylene group are ob-
served to shift to higher field as the halogens become
less electronegative, consistent with prior reports.14
[Cp2ReCH2]B(Ar′)4 (1) reacts cleanly with pyridine
N-oxide (pyO) to form [Cp2Re(η2-CH2O)]B(Ar′)4 (9) in
CH2Cl2. Complex 9 was isolated as a pale orange solid
in 93% yield by crystallization from CH2Cl2/pentane
1
in the initial H NMR spectrum. The reaction in CD3-
CN leads to fewer side products, and [Cp2Re(NCCD3)]+
is also formed as a major product. [Cp2ReCH(CH3)]BF4
is cleanly generated when the reaction is monitored at
low temperature, but the complex isomerizes to the
ethylene complex at room temperature. Addition of 1,8-
bis(dimethylamino)naphthalene to solutions of [Cp2-
ReCH(CH3)]B(Ar′)4 does not inhibit isomerization to the
ethylene complex.
Addition of BF4- or PF6- salts to CD3CN solutions of
1-B(Ar′)4 induces decomposition, which is similar to the
outcome of the [Ph3C]BF4 reactions. Complex 1 was
allowed to react with either excess [NH4]BF4, [NH4]PF6,
or NaBF4 in CD3CN. The reactions with the ammonium
salts were rapid, presumably due to greater solubility
in CD3CN. Clean formation of [Cp2Re(C2H4)]BF4, [Cp2-
Re(NCCD3)]BF4, and a small amount of free ethylene
(δ 5.4) was observed. The reaction with NH4BF4 affords
the ethylene and acetonitrile products in a 50/50 ratio
while the NaBF4 reaction gave 33/66, respectively.
Rea ctivity of [Cp 2ReCH2]B(Ar ′)4 (1). Addition of
1 equiv of PPh3 to a solution of 1 in methylene chloride
results in an immediate color change from pink to pale
orange (Scheme 2). A crystalline solid is precipitated
1
followed by filtration. The H NMR spectrum shows a
single Cp resonance at 5.49 ppm and a resonance at 3.69
ppm for the methylene protons. The 13C NMR reso-
nance of the formaldehyde ligand was located at 46.2
ppm.
The formaldehyde ligand can be displaced by reaction
with solvent or nucleophiles. Heating a solution of 9
in CD3CN at 55 °C for several days eventually led to
the formation of [Cp2ReNCCD3]+. Complex 9 reacts
similarly with CD2Cl2 to form [Cp2Re(CD2Cl)Cl]+ (2)
(14) Hubbard, J . L.; McVicar, W. K. Organometallics 1990, 9, 2683-
2694.
1
in 90% yield by addition of pentane. The H, 31P, and

54 Organometallics, Vol. 17, No. 1, 1998
Heinekey and Radzewich
Sch em e 2
after several days at 55 °C. A solution of 9 and PPh3
in CD2Cl2 slowly forms [Cp2RePPh3]+ 15 after 1 week
at room temperature.
two cyclopentadienyl resonances at 5.13 and 5.10 ppm,
indicating hindered rotation of the olefin ligand.
Heating complex 1 with excess sulfur in CD2Cl2 for 3
h at 50 °C leads to the clean formation of a thioform-
aldehyde complex. [Cp2Re(η2-CH2S)]B(Ar′)4 (10) can be
more conveniently formed by reaction of 1 with excess
ethylene sulfide at room temperature. A bright orange/
yellow solid is isolated in 89% yield by crystallization
Discu ssion
Syn th esis a n d Ch a r a cter iza tion of Com p lexes 1
a n d 3. Reaction of Cp2ReCH3 with [Ph3C]B(Ar′)4
generates the stable methylene complex in nearly
quantitative yield. The abstraction of an R hydride from
a neutral metal alkyl with trityl cation is well-known,
with several examples reported by Gladysz and co-
workers in the preparation of cationic rhenium carbene
complexes of the general formula [CpRe(NO)(PPh3)-
(dCHR)]+.16
1
from CH2Cl2/pentane. The H NMR spectrum shows a
cyclopentadienyl resonance at 5.47 ppm and a methyl-
ene resonance for the thioformaldehyde ligand at 3.41
ppm. The 13C NMR spectrum exhibits a triplet at 13.7
1
ppm for CH2S with J CH ) 168 Hz.
The phosphonium-ylide complex [Cp2ReCH2PPh3]+ (4)
reacts rapidly with excess ethylene sulfide to form
complex 10 and SPPh3. Addition of SPPh3 to complex
1 produces equal amounts of complexes 4 and 10. The
thioformaldehyde ligand of 10 is not displaced by PPh3
but reacts rapidly to form [Cp2ReCH2PPh3]+ and
SdPPh3.
Hydride abstraction by trityl cation has been proposed
to proceed by an initial electron transfer from the metal
alkyl complex followed by a hydrogen-atom transfer for
complexes which are electron rich and easily oxi-
dized.17,18 Cooper has provided clear evidence for this
mechanism by the isolation and characterization of
stable radical cations, [Cp2W(CH3)(C2H5)]•+, which react
Addition of N2CHSiMe3 (2 M in hexanes) to a meth-
ylene chloride solution of complex 1 results in a color
change from pink to light tan, accompanied by rapid
evolution of N2. The olefin complex [Cp2Re(CH2d
CHSiMe3)]B(Ar′)4 (11) is isolated in 69% yield by
crystallization from a concentrated CH2Cl2 solution
(16) (a) Kiel, W. A.; Lin, G.-Y.; Gladysz, J . A. J . Am. Chem. Soc.
1980, 102, 3299-3301. (b) Tam, W.; Lin, G.-Y.; Wong, W.-K.; Kiel, W.
A.; Wong, V. K.; Gladysz, J . A. J . Am. Chem. Soc. 1982, 104, 141-
152. (c) Kiel, W. A.; Lin, G.-Y.; Constable, A. G.; McCormick, F. B.;
Strouse, C. E.; Eisenstein, O.; Gladysz, J . A. J . Am. Chem. Soc. 1982,
104, 4865-4878. (d) Kiel, W. A.; Lin, G.-Y.; Bodner, G. S.; Gladysz, J .
A. J . Am. Chem. Soc. 1983, 105, 4958-4972. (e) Patton, A. T.; Strouse,
C. E.; Knobler, C. B.; Gladysz, J . A. J . Am. Chem. Soc. 1983, 105,
5804-5811. (f) Georgiou, S.; Gladysz, J . A. Tetrahedron 1986, 42,
1109-1116.
1
layered with pentane. The H NMR spectrum exhibits
(15) Baudry, D.; Ephritikhine, M. J . Organomet. Chem. 1980, 195,
213-222.

Synthesis and Reactivity of [Cp2RedCH2]+
Organometallics, Vol. 17, No. 1, 1998 55
further with Ph3C• by hydrogen-atom abstraction to
generate a carbene complex.17
complex which then rapidly inserts into a C-H bond of
the Cp ligand to generate [(η5-C5H4Me)Cr(NO)2]+.28
Caulton has recently reported the formation of a known
methlylene compound RudCH2(PCy3)2Cl22g by reaction
of Ru(H2)2H2(PCy3)2 with CH2Cl2 (with loss of 3 equiv
of dihydrogen).29 We find that reaction of complex 2
with Mg turnings affords the methylene complex 1
In order to investigate the possibility of an initial
electron transfer in the formation of complex 1, we
investigated the reactivity of Cp2ReCH3 with [Cp2Fe]+.19
The reaction of [Cp2Fe]B(Ar′)4 with Cp2ReCH3 at low
temperature in acetonitrile-d3 generates complex 1,
[Cp2Re(CH3)H]+, and Cp2Fe. We propose that initial
electron transfer affords the 17-electron radical cation
[Cp2ReCH3]•+. Rapid proton transfer to Cp2ReCH3 leads
to [Cp2Re(CH3)H]+ and Cp2ReCH2, which is rapidly
oxidized to afford complex 1. This result demonstrates
the utility of a chemical oxidant to generate carbene
complexes (in a 50% yield) when reacted with electron-
rich metal alkyl complexes.
1
quantitatively by H NMR. While this preparation is
less convenient than the trityl abstraction procedure,
it serves to verify the formulation of complex 2 as a
chloromethyl chloride. Additional confirmation is pro-
vided by the reaction of complex 1 with elemental
chlorine, which leads to clean formation of the chloro-
methyl chloride complex 2.
The reaction of Cp2ReCH2CH3 with [Ph3C]B(Ar′)4
results almost exclusively in abstraction of an R hydride.
A small amount (<5%) of the [Cp2Re(η2-C2H4)]B(Ar′)4
complex is formed as a result of â-hydride abstraction.
The ratio between the ethylidene and the ethylene
complexes does not change upon standing at room
temperature for 1 week. Gladysz and co-workers ob-
served a similar ratio of R vs â-hydride abstraction for
CpRe(NO)(PPh3)2(CH2CH3) with a greater percentage
of â hydride abstraction occurring for higher alkyls.30
Sta bility of th e Ca r ben e Com p lexes: An ion Ef-
fects. Stucky and co-workers have previously described
the reactivity of Cp2ReCH3 and Cp2ReCH2CH3 with
[Ph3C]BF4.6 In both cases, the main product was
identified as [Cp2Re(C2H4)]BF4. Formation of a ther-
mally unstable methylene complex by R-hydride ab-
straction from Cp2ReCH3 was suggested, while a stable
ethylene complex was thought to be formed by â-hydride
abstraction from Cp2ReCH2CH3. In contrast to these
results, we find that [Cp2ReCH2]+ (1) and [Cp2ReCH-
(CH3)]+ (3) are readily isolable and thermally robust
when the counterion employed is B(Ar′)4. Acetonitrile
An independent preparation of complex 1 is provided
by dehalogenation of the chloromethyl chloride complex
2. Complex 2 is generated by the oxidative addition of
CH2Cl2 upon loss of methane from the thermally
unstable [Cp2Re(CH3)H]+. Complex 2 can only be
isolated using the B(Ar′)4 anion. The synthesis of
chloromethyl chloride complexes have been reported by
several groups. Typically, these complexes are formed
via oxidative addition of CH2Cl2 to a coordinatively
unsaturated metal complex.20-24 A different approach
has been taken by Hubbard and co-workers, who have
reported the stepwise addition of diazomethane to
Cp*Ru(NO)Cl2 to generate the chloromethyl chloride
complex and the bis(chloromethyl) complex.25
Cp*Ru(NO)(CH2Cl)Cl has been shown to form poly-
methylene upon thermolysis or photolysis, and Cp*Ru-
(NO)(CH2Cl)(CH2Cl) extrudes ethylene with the dichlo-
ride Cp*Ru(NO)Cl2 formed as the final product. In
contrast, complex 2 is thermally robust. Thermolysis
of complex 2 did not result in any conversion to the
known26 [Cp2ReCl2]+.
-
solutions of complex 1 react with added BF4- and PF6
The displacement of the halide from halomethyl
ligands is a common synthetic technique to generate
such complexes as cationic ylides by reaction with a
phosphine or to generate hydroxymethyl and alkoxy-
methyl complexes by reaction with water or alcohols.14,27
Hubbard has reported the dehalogenation of CpCr(NO)2-
CH2Cl with Ag+ to generate a very reactive methylene
salts while undergoing relatively clean conversion to the
corresponding ethylene complex [Cp2ReC2H4]+ and [Cp2-
Re(CH3CN)]+. These results are consistent with the
operation of a bimolecular coupling mechanism. In
several previous reports, complexes of the type LnMdCH2
have been observed to form the corresponding ethylene
complexes in 50% yield, with the other 50% of the metal
complex decomposing or forming a solvent-stabilized
complex. The mechanism of this reaction has been
studied by Gladysz and co-workers for [CpRe(NO)-
(PPh3)(CH2)]BF4 and was shown to proceed through a
bimolecular coupling.31 Consistent with this, the bulkier
complex, [Cp*Re(NO)(PPh3)(CH2)]BF4, is considerably
more stable than the Cp complex.16e Direct evidence
for the bimolecular decomposition pathway is provided
in one case by the isolation of a 1,3-dimetallacyclobutane
complex from a reaction thought to produce “Cp2-
TidCH2”.32
(17) (a) Hayes, J . C.; Cooper, N. J . J . Am. Chem. Soc. 1982, 104,
5570-5572. (b) Hayes, J . C.; Cooper, N. J . Organometallic Com-
pounds: Synthesis, Structure and Theory; Texas A&M University
Press: College Station, TX, 1983; p 353. (c) Hayes, J . C.; J ernakoff,
P.; Miller, G. A.; Cooper, N. J . Pure Appl. Chem. 1984, 56, 25-33. (d)
Asaro, M. F.; Cooper, S. R.; Cooper, N. J . J . Am. Chem. Soc. 1986,
108, 5187-5193.
(18) (a) Asaro, M. F.; Bodner, G. S.; Gladysz, J . A.; Cooper, S. R.;
Cooper, N. J . Organometallics 1985, 4, 1020-1024. (b) Bodner, G. S.;
Gladysz, J . A.; Nielson, M. F.; Parker, V. D. J . Am. Chem. Soc. 1987,
109, 1757-1764. (c) Bodner, G. S.; Gladysz, J . A.; Nielson, M. F.;
Parker, V. D. Organometallics 1987, 6, 1628-1633.
(19) Connelly, N. G.; Geiger, W. E. Chem. Rev. 1996, 96, 877-910.
(20) Chang, J .; Bergman, R. G. J . Am. Chem. Soc. 1987, 109, 4298-
4304.
(21) Olson, W. L.; Nagaki, D. A.; Dahl, L. F. Organometallics 1986,
5, 630-634.
(27) (a) Werner, H. Pure Appl. Chem. 1982, 54 , 177-188. (b)
Werner, H. Angew. Chem., Int. Ed. Engl. 1983, 22, 927-949. (c) Paul,
W.; Werner, H. Chem. Ber. 1985, 118, 3032-3040. (d) Werner, H.;
Hofmann, L.; Feser, R.; Paul, W. J . Organomet. Chem. 1985, 281, 317-
347.
(22) Scherer, O. J .; J ungmann, H. J . Organomet. Chem. 1981, 208,
153-159.
(23) Labinger, J . A.; Osborn, J . A.; Coville, N. J . Inorg. Chem. 1980,
3236-3243.
(28) Hubbard, J . L.; McVicar, W. K. J . Am. Chem. Soc. 1986, 108,
6422-6424.
(24) Young, G. B.; Whitesides, G. M. J . Am. Chem. Soc. 1978, 100,
5808-5815.
(29) Olivan, M.; Caulton, K. G. Chem. Commun. 1997, 1733-1734.
(30) Roger, C.; Bodner, G. S.; Hatton, W. G.; Gladysz, J . A.
Organometallics 1991, 10, 3266-3274.
(25) Hubbard, J . L.; Morneau, A.; Burns, R. M.; Nadeau, O. W. J .
Am. Chem. Soc. 1991, 113, 9180-9184.
(26) Gowik, P.; Kapotke, T.; Tornieporth-Oetting, I. Chem. Ber. 1989,
122, 2273-2274.
(31) Merrifield, J . H.; Lin, G.-Y.; Kiel, W. A.; Gladysz, J . A. J . Am.
Chem. Soc. 1983, 105, 5811-5819.

56 Organometallics, Vol. 17, No. 1, 1998
Heinekey and Radzewich
Sch em e 3
and B, and although the barrier is not directly related
to the strength of the π bond, the π contribution from
structure B is likely negligible.34 Caulton and co-
workers have synthesized Cp2WdCH(CH3), which also
1
shows inequivalent cyclopentadienyl rings by H NMR
spectroscopy and have confirmed this arrangement with
a crystal structure of Cp2WdCH(Ph).5
Rea ctivity of Com p lex 1. Complex 1 displays
electrophilic reactivity, as expected for a cationic meth-
ylene complex. The addition of PPh3 to 1 forms a stable
ylide complex, while pyridine forms a less stable ylide
complex that reversibly dissociates pyridine in solution.
Complex 1 shows no reaction in the presence of a large
excess of dimethyl sulfide. In a similar system, Gladysz
and co-workers have found that isolable ylide complexes
can be generated by reaction of [CpRe(NO)(PPh3)CH2]+
Several complexes of the form LnMCH(CH3) have also
been observed to form the corresponding ethylene
complexes upon decomposition. This reaction has been
proposed to proceed via a 1,2-hydrogen shift. A bimo-
lecular coupling reaction similar to those observed from
methylene complexes would produce 2-butene. In our
case, we find that complex 3 in acetonitrile isomerizes
t
with PPh3, NC5H5, and SMe2.16b,35 With Bu isonitrile,
-
to the ethylene complex in the presence of added BF4
we find that complex 1 forms an adduct which we
formulate as the ketenimine complex 6 based primarily
on the IR spectrum, which is consistent with a signifi-
cant decrease in the CN bond order.
Complex 1 reacts with elemental chlorine to give the
chloromethyl chloride complex 2. This novel reaction
has precedent in the work of Roper and co-workers who
report that Os(dCH2)(PPh3)2(NO)(Cl) reacts with chlo-
rine to form a chloromethyl chloride complex, Os(CH2-
Cl)(PPh3)2(NO)Cl2.2f
and PF6- salts. Gladysz and co-workers have explored
the conversion of [CpRe(NO)(PPh3)(CHR)]BF4 com-
plexes to the corresponding olefin complexes.30 In this
case, a solvent-coordinated species would not be ex-
pected to form.
We propose that the larger anions such as B(Ar′)4 and
BPh4 hinder the bimolecular coupling reaction of com-
plex 1. This interpretation is speculative, since we have
not observed any 1H or 13C NMR evidence which
suggests any interaction between the anions and the
methylene complex. Presumably, complexes such as 1
form tight ion pairs with anions such as B(Ar′)4, which
would not be effectively separated by solvent. Caulton
and co-workers have recently reported the structure of
an η2-CH2Cl2 adduct of [RuH(CO)(PtBu2Me)2]B(Ar′)4 in
which the hydrogens of the dichloromethane ligand are
observed to have a hydrogen-bond interaction with the
phenyl rings of the anion, forming an overall ion pair.33
On the basis of the observation that complex 3 is also
stabilized with the B(Ar′)4 anion, we consider it possible
that the 1,2-hydrogen shift to afford the olefin complex
could be assisted by a bimolecular reaction.
Str u ctu r e of th e Car ben e Com plexes. The equiva-
lent protons of the methylene ligand in complex 1 do
not give an indication of the alignment of the methylene
ligand nor the barrier to rotation. Additional informa-
tion about the structure of the carbene complex can be
gained from an unsymmetrical carbene ligand. The
observation of two inequivalent Cp resonances in the
1H and 13C NMR spectra of [Cp2ReCH(CH3)]B(Ar′)4 (3)
indicates that the methyl group is aligned with one Cp
while the hydrogen of the carbene ligand is aligned with
the other Cp (structure A; Scheme 3).
Our preparation of a bound formaldehyde ligand is
similar to that reported by Gladysz and co-workers
using reaction of a nucleophilic oxygen-atom donor with
an electrophilic methylene complex.36 Oxygen-atom
donors react with complex 1 to give the formaldehyde
complex 9, which is characterized as an η2-CH2O
structure based on the high-field 13C NMR resonance
of the formaldehyde ligand at 46.2 ppm. The IR spectra
of [Cp2RedCH2]B(Ar′)4 and [Cp2Re(η2-H2CdO)]B(Ar′)4
were compared, but a band for νCO could not be located
in the expected region between 1300-1000 cm-1, which
was obscured by bands from the anion. In closely
related complexes, an intense νCO band was observed
in the IR spectrum for Cp2V(η2-H2CdO) at 1160 cm-1
and for Cp2Mo(η2-H2CdO) at 1155 cm-1 37
The lack of
.
a CO stretch in the IR spectrum between 1400 and 1600
cm-1 rules out an end-bound formaldehyde ligand.
Reports from the groups of Gladysz and Grubbs note
that thioformaldehyde complexes can be formed by the
reaction of methylene complexes with several different
sulfur-donor reagents; cyclohexene sulfide, styrene sul-
fide, SdPPh3, and S8.38,39 Consistent with this, we find
that methylene complex 1 reacts with various sulfur-
The rotation of the carbene ligand must be slow on
the NMR time scale in order to observe this inequiva-
lence. A sample of [Cp2RedCH(CH3)]B(Ar′)4 in CD3NO2
was heated to 63 °C at 200 MHz. No coalescence of the
cyclopentadienyl resonances was observed, and the
resonances remain quite sharp at this temperature. A
minimum barrier for the rotation about the rhenium-
carbon double bond is calculated as ∆Gq g 17.7 kcal/
mol. This large barrier to rotation is formally a reflec-
tion of the difference in energy between conformers A
(34) For a discussion of bonding for metallocene carbene complexes,
see: Hofmann, P. Transition Metal Carbene Complexes; Verlag Che-
mie: Weinheim, Germany, 1983; pp 141-143.
(35) McCormick, F. B.; Gleason, W. B.; Zhao, X.; Heah, P. C.;
Gladysz, J . A. Organometallics 1986, 5, 1778-1785.
(36) (a) Buhro, W. E.; Georgiou, S.; Fernandez, J . M.; Patton, A. T.;
Strouse, C. E.; Gladysz, J . A. Organometallics 1986, 5, 956-965. (b)
Buhro, W. E.; Patton, A. T.; Strouse, C. E.; Gladysz, J . A.; McCormick,
F. B.; Etter, M. C. J . Am. Chem. Soc. 1983, 105, 1056-1058.
(37) (a) Gambarotta, S.; Floriani, C.; Chiesi-Villa, A.; Guastini, C.
J . Am. Chem. Soc. 1985, 107, 2985-2986. (b) Herberich, G. E.; Okuda,
J . Angew. Chem., Int. Ed. Engl. 1985, 24, 402. (c) Gambarotta, S.;
Floriani, C.; Chiesi-Villa, A.; Guastini, C. J . Am. Chem. Soc. 1982, 104,
2019-2020.
(38) Buhro, W. E.; Etter, M. C.; Georgiou, S.; Gladysz, J . A.;
McCormick, F. B. Organometallics 1987, 6, 1150-1156.
(39) Park, J . W.; Henling, L. M.; Schaefer, W. P.; Grubbs, R. H.
Organometallics 1990, 9, 1650-1656.
(32) Ott, K. C.; Grubbs, R. H. J . Am. Chem. Soc. 1981, 103, 5922-
5923.
(33) Huang, D.; Huffman, J . C.; Bollinger, J . C.; Eisentstein, O.;
Caulton, K. G. J . Am. Chem. Soc. 1997, 119, 7398-7399.

Synthesis and Reactivity of [Cp2RedCH2]+
Organometallics, Vol. 17, No. 1, 1998 57
1
(t, J CH ) 152 Hz, Re-CH2), 162.2 (quart, J CB ) 49.8 Hz,
atom sources to afford the thioformaldehyde complex
[Cp2Re(η2-H2CdS)]B(Ar′)4 (10). Reactivity studies of
complexes 9 and 10 with nucleophiles are in agreement
with the observations of Gladysz and co-workers that
the thioformaldehyde ligand is less labile than the
formaldehyde ligand.
B(Ar′)4 ipso), 135.2 (d, 1J CH ) 158.9 Hz, o-B(Ar′)4), 129.3 (quart,
2J CF ) 30.1 Hz, m-B(Ar′)4), 125.0 (quart, J CF ) 272.3 Hz,
1
1
3
B(Ar′)4 CF3), 117.9 (d of t, J CH ) 165.9 Hz, J CF ) 3.6 Hz,
1
2
p-B(Ar′)4), 86.4 (d of quint, J CH ) 188 Hz, J CH ) 7 Hz, Cp).
Anal. Calcd for C43H24BF24Re: C, 43.27; H, 2.03. Found: C,
1
-
43.19; H, 2.06. The H and 13C NMR resonances for B(Ar′)4
are identical with those reported for complex 1 and have been
omitted from the spectral characterization of subsequent
complexes.
[Cp 2ReCH2]BP h 4 (1-BP h 4). The preparation of 1-BP h 4 is
similar to that for 1-B(Ar ′)4. Cp2ReCH3 (76.5 mg, 0.231 mmol)
is reacted with [Ph3C]BPh4 (130 mg, 0.231 mmol) in CH2Cl2
followed by precipitation with pentane. The pink solid was
collected in 80% yield (120 mg). 1H NMR (CD2Cl2): 12.95 (s,
2H, Re-CH2), 7.4-6.8 (m, BPh4), 5.29 (s, 10H, Cp).
[Cp 2Re(CH3)H]B(Ar ′)4. A sealable NMR tube was charged
with Cp2ReCH3 (6 mg, 0.018 mmol) and [H(Et2O)2]B(Ar′)4 (18.3
mg, 0.018 mmol). CD2Cl2 (0.5 mL) was vacuum transferred
to the tube. The tube was sealed and kept at -78 °C until it
was placed in the NMR probe. 1H NMR (CD2Cl2, 250 K): 5.30
(s, 10 H, Cp), 0.53 (s, 3 H, Re-CH3), -11.88 (s, 1 H, Re-H).
13C{1H} NMR (CD2Cl2): 84.0 (Cp), -40.1 (Re-CH3).
[Cp 2Re(CH2Cl)Cl]B(Ar ′)4 (2). Meth od A. A small glass
vessel with an 8 mm Kontes valve was charged with Cp2ReCH3
(50 mg, 0.151 mmol) and [H(Et2O)2]B(Ar′)4 (153 mg, 0.151
mmol). Methylene chloride (10 mL) is vacuum transferred to
the flask, and the solution is stirred at room temperature for
30 min. The red solution is reduced in volume to 3 mL, and
pentane (10 mL) is vacuum transferred to the flask. An oil
separates from the solvent, but after stirring for 30 min at 0
°C, a precipitate forms. The peach-colored solid is dried under
dynamic vacuum. Yield: 180 mg (94%). 1H NMR (CD2Cl2):
6.02 (s, 10 H, η5-C5H5), 4.40 (s, 2 H, Re-CH2Cl). 13C NMR
(CD2Cl2): 98.6 (d of quint, 1J CH ) 191.4 Hz, J CH ) 6.3 Hz, Cp),
Con clu sion
A convenient preparation of cationic rhenocene car-
bene complexes using hydride abstraction from the
neutral alkyls has been demonstrated. The stability of
the carbene complexes is dramatically increased by the
use of unreactive tetraphenylborate counteranions. The
carbene ligand has a high barrier to rotation and
exhibits reactivity consistent with electrophilic charac-
ter of the carbene carbon.
Exp er im en ta l Section
Gen er a l P r oced u r es. Manipulations were conducted with
rigorous exclusion of air and water. Solid samples were
handled and stored under argon in Vacuum Atmosphere or
Braun inert-atmosphere boxes. Solution samples were handled
using standard high-vacuum or Schlenk techniques. Chlori-
nated solvents were distilled from CaH2. Hydrocarbon sol-
vents were distilled from Na/K benzophenone ketyl. Deuter-
ated solvents (Cambridge Isotope Labs) were dried and stored
in the same manner as their protio analogs. All solvents were
vacuum-transferred immediately prior to use. Reagent grade
chemicals were used as received unless stated otherwise. Cp2-
ReCH3,13 Cp2ReCH2CH3,13 [Ph3C]B(Ar′)4,7 [Ph3C]BPh4,40 [H-
41
(Et2O)2]B(Ar′)4,9 and SPPh3 were prepared using literature
methods. tBuNC (Strem) was degassed and stored under
argon. Pyridine N-oxide (pyO) (Aldrich) was sublimed prior
to use and stored under argon. Ethylene sulfide was degassed
and stored under vacuum in a vessel equipped with a Teflon
needle valve.
11.5 (t, J CH ) 163.1 Hz, Re-CH2Cl). Anal. Calcd for C43H24
BCl2F24Re: C, 40.84; H, 1.91. Found: C, 40.65; H, 2.02.
-
Meth od B. A sealable NMR tube was charged with
complex 1 (5 mg, 0.004 mmol). Methylene chloride-d2 (0.5 mL)
was vacuum transferred to the tube. The solution was briefly
purged with chlorine gas, and the color changed from bright
pink to yellow. After 3 freeze-pump-thaw cycles, the tube
was sealed. 1H NMR (CD2Cl2): 6.02 (s, 10 H, Cp); 4.40 (s, 2
H, Re-CH2Cl).
[Cp 2ReCH(CH3)]B(Ar ′)4 (3). The preparation of compound
3 is similar to that for 1-B(Ar ′)4. Cp2ReCH2CH3 (50 mg, 0.145
mmol) is reacted with [Ph3C]B(Ar′)4 (160 mg, 0.145 mmol) in
CH2Cl2 followed by precipitation with pentane. The pale
orange solid was collected in 94% yield (164 mg). 1H NMR
(CD2Cl2): 13.82 (quart, 1 H, J HH ) 7.9 Hz, RedCH(CH3)), 5.56
(s, 5 H, Cp), 5.51 (s, 5 H, Cp), 1.53 (d, 3 H, J HH ) 8.1 Hz,
RedCH(CH3)). 13C NMR (CD2Cl2): 266.0 (d, J CH ) 143 Hz,
RedCH(CH3)), 86.0 (d of quint, J CH ) 187 Hz, J CH ) 6 Hz,
Cp), 85.6 (d of quint, J CH ) 187 Hz, J CH ) 6 Hz, Cp), 45.0
(quart, J CH ) 128 Hz, RedCH(CH3)).
[Cp 2F e]B(Ar ′)4. Ferrocene (0.625 g, 3.36 mmol) was dis-
solved in 12.5 mL of H2SO4. The dark blue solution was stirred
for 2 h then added to 185 mL of H2O and filtered. The solution
was sparged with Ar in a Schlenk flask, and NaB(Ar′)4 (1 g,
1.13 mmol) was added. After 24 h of stirring, a light blue
precipitate was collected by filtration, rinsed with H2O, and
dried under dynamic vacuum. Yield: 0.892 g (76%). 1H NMR
(acetone-d6): 28 (s, 10 H, Cp2Fe+), 7.8 (s, 4 H, p-B(Ar′)4), 7.7
(s, 8 H, o-B(Ar′)4).
[Cp 2ReCH2P P h 3]B(Ar ′)4 (4). A small glass vessel with an
8 mm Kontes valve was charged with 1 (50 mg, 0.0419 mmol)
and PPh3 (11 mg, 0.0419 mmol). Dichloromethane (15 mL)
was vacuum transferred to the vessel, and the solution was
stirred for 10 min. The solvent volume was reduced to 2 mL,
and 10 mL of pentane was vacuum transferred to the vessel
to give a pale orange precipitate. The solvent was removed
1H, 13C, and 31P NMR spectra were recorded on Bruker AC-
200 (200.133 MHz 1H, 81.015 MHz 31P), AF-300 (300.117 MHz
1H, 75.465 MHz 13C), and WM-500 (500.136 MHz 1H) spec-
trometers. 1H and 13C NMR chemical shifts (δ) are referenced
to the internal residual proton or natural abundance 13C
resonances of the deuterated solvent relative to TMS. 31P
NMR chemical shifts (δ) are reported in parts per million
relative to 85% H3PO4 (external standard). The cyclopenta-
dienyl protons of rhenocene complexes have been observed to
relax slowly, and a relaxation delay of 120 s is required to
observe appropriate integrals. All NMR-tube reactions were
conducted in flame sealed tubes or J . Young screw-cap tubes.
Elemental analyses were performed by Canadian Microana-
lytical Service Ltd., Delta, B.C.
[Cp 2ReCH2]B(Ar ′)4 (1). A 20 mL round-bottom flask was
charged with Cp2ReCH3 (250 mg, 0.754 mmol) and [Ph3C]B-
(Ar′)4 (835 mg, 0.754 mmol) and attached to a swivel -frit
apparatus. The swivel frit was attached to a vacuum line, and
10 mL of CH2Cl2 was vacuum transferred at -78 °C. The red
solution was warmed to room temperature and stirred for a
few minutes. The solvent volume was reduced under vacuum
to 4 mL. Pentane (10-15 mL) was vacuum transferred to the
solution to give a pink solid with a yellow solution. The solid
was collected on the frit and rinsed by condensation of the
filtrate solvent, which was repeated 5 times. The pink, air-
stable solid was collected in 97% yield (870 mg). 1H NMR (CD2-
Cl2): 13.19 (s, 2 H, Re-CH2), 7.74 (m, 8 H, o-B(Ar′)4), 7.58 (m,
4 H, p-B(Ar′)4), 5.60 (s, 10 H, Cp). 13C NMR (CD2Cl2): 247.7
(40) Straus, D. A.; Zhang, C.; Tilley, T. D. J . Organomet. Chem.
1989, 369, C13-C17.
(41) Seyferth, D.; Welch, D. E. J . Organomet. Chem. 1964, 2, 1-7.

58 Organometallics, Vol. 17, No. 1, 1998
Heinekey and Radzewich
by cannula, and the solid was dried under dynamic vacuum.
The pale orange solid was collected in 90% yield (55 mg). 1H
NMR (CD2Cl2): 7.4-7.9 (m, 15 H, PPh3), 4.16 (s, 10 H,Cp),
2.58 (d, 2 H, J PH ) 10.8 Hz, Re-CH2). 31P{sel 1H} NMR (CD2-
Cl2): 32.6 (t, PPh3). 13C NMR (CD2Cl2): 134.5 (s, p-PPh3),
134.3 (d, J CP ) 8.9 Hz, o-PPh3), 129.9 (d, J CP ) 163 Hz,
m-PPh3), 123.5 (d, J CP ) 81.3 Hz, ipso PPh3), 73.7 (d of quint,
1J CH ) 182.2 Hz, J CH ) 6.5 Hz, Cp), -32.7 (d of t, J CP ) 25.6
was warmed to room temperature and stirred for a few
minutes. The solvent volume was reduced under vacuum to
2 mL. Pentane (10 mL) was vacuum transferred to the
solution to give an orange precipitate. The solid was collected
on the frit and rinsed 5 times by condensation of the filtrate
solvent. The pale orange solid was collected in 93% yield (99
mg). 1H NMR (CD2Cl2): 5.49 (s, 10 H, Cp), 3.69 (s, 2 H, Re-
1
(H2CdO)). 13C NMR (CD2Cl2): 88.4 (d of quint, J CH ) 189
Hz, J CH ) 126.2 Hz, Re-CH2). Anal. Calcd for C61H39BF24
-
Hz, J CH ) 6.7 Hz, Cp), 46.2 (t, J CH ) 178.7 Hz, H2CO). Anal.
Calcd for C43H24BF24ORe: C, 42.70; H, 2.00. Found: C, 42.57;
H, 1.99.
PRe: C, 50.32; H, 2.70. Found: C, 49.48; H, 2.68.
Rea ction of [Cp 2ReCH2)]B(Ar ′)4 w ith P yr id in e. A seal-
able NMR tube was charged with compound 1 (5 mg, 0.004
mmol). Methylene chloride-d2 (0.5 mL) was vacuum trans-
ferred to the tube. Under an argon flow, excess pyridine (1
µL, 0.013 mmol) was added via a gas-tight syringe. The
solution was degassed by 3 freeze-pump-thaw cycles, and
the tube was sealed. 1H NMR (CD2Cl2): 8.6 and 7.2 (m, free
and coordinated NC5H5), 5.86 (br, 2 H, Re-CH2-), 4.51 (s, 10
H, Cp).
Rea ction of [Cp 2Re(H2CdO)]B(Ar ′)4 w ith P P h 3.
A
sealable NMR tube was charged with [Cp2Re(H2CdO)]B(Ar′)4
(4 mg, 0.003 mmol) and PPh3 (1 mg, 0.004 mmol). Methylene
chloride-d2 (0.5 mL) was vacuum transferred to the tube and
sealed. After 1 week at room temperature, the starting
material had been completely consumed. 1H NMR (CD2Cl2):
9.65 (s, free CH2O), 7.7-7.3 (m, Re-PPh3), 4.53 (d, J HP ) 3.83
Hz, Cp). 31P{1H} NMR (CD2Cl2): 23.1 (s, Re-PPh3).
[Cp 2Re(H2CdS)]B(Ar ′)4 (10). A 20 mL round-bottom flask
was charged with 1 (80 mg, 0.067 mmol) and attached to a
swivel-frit apparatus. The swivel frit was attached to a
vacuum line, and 5 mL of CH2Cl2 was vacuum transferred at
-78 °C. The pink solution was exposed to 120 Torr of ethylene
sulfide, and the color began turning orange. The solution was
degassed by a freeze-pump-thaw cycle and again exposed to
ethylene sulfide. Pentane (10 mL) was vacuum transferred
to the solution to give a bright yellow/orange precipitate. The
solid was collected on the frit and rinsed by condensation of
the filtrate solvent which was repeated 5 times. The solid was
collected in 89% yield (82 mg). 1H NMR (CD2Cl2): 5.47 (s, 10
H, Cp), 3.41 (s, 2 H, Re(H2CdS)). 13C NMR (CD2Cl2): 88.2 (d
of quint, 1J CH ) 189 Hz, J CH ) 6.4 Hz, Cp), 13.7 (t, J CH ) 168.4
Hz, H2CS). Anal. Calcd for C43H24BF24ReS: C, 42.14; H, 1.97.
Found: C, 42.19; H, 1.97.
[Cp 2ReCH2CNtBu ]B(Ar ′)4 (6). A small glass vessel with
an 8 mm Kontes valve was charged with 1 (60 mg, 0.0503
mmol). Dichloromethane (15 mL) was vacuum transferred to
the vessel. Under an argon flow, CNtBu (6 µL, 0.0503 mmol)
was added via a gas-tight syringe. The solution was stirred
for 10 min, and the solvent volume was reduced to 2 mL.
Pentane (10 mL) was vacuum transferred to the vessel to give
a
pale orange precipitate. The solvent was removed by
cannula, and the pale orange solid was dried under vacuum.
Yield: 55 mg, 86%. 1H NMR (CD2Cl2): 5.15 (s, 10 H,Cp), 1.64
(s, 2 H, Re-CH2), 1.26 (s, 9 H, CNtBu). 13C NMR (CD2Cl2):
1
158.5 (s, CNtBu), 84.0 (d of quint, J CH ) 188 Hz, J CH ) 6.4
Hz, Cp), 28.8 (quart, J CH ) 125.9 Hz, CNtBu), -31.8 (t, J CH
)
163.8, Re-CH2). IR (cm-1, Nujol, νCN): 1780. Anal. Calcd
for C48H33BF24NRe: C, 45.16; H, 2.60; N, 1.10. Found: C,
44.82; H, 2.55; N, 1.15.
[Cp 2Re(CH2Br )Br ]B(Ar ′)4 (7). A small glass vessel with
an 8 mm Kontes valve was charged with 1 (60 mg, 0.0503
mmol). Dichloromethane (10 mL) was vacuum transferred to
the vessel. The solution was titrated with a Br2/CH2Cl2
solution until the pink color of the carbene complex was
discharged. The solution was stirred for 10 min and the
volatiles were removed under vacuum. The peach-colored solid
was recrystallized from CH2Cl2 and pentane and isolated in
81% yield (55 mg). 1H NMR (CD2Cl2): 6.06 (s, 10 H, Cp), 4.26
(s, 2 H, Re-CH2Br). 13C NMR (CD2Cl2): 98.1 (d of quint, 1J CH
) 191.8 Hz, J CH ) 6.1 Hz, Cp), -5.58 (t, J CH ) 162.4 Hz, Re-
CH2Br). Anal. Calcd for C43H24BBr2F24Re: C, 38.16; H, 1.79.
Found: C, 37.95; H, 1.80.
[Cp 2Re(CH2I)I]B(Ar ′)4 (8). A small glass vessel with an
8 mm Kontes valve was charged with 1 (60 mg, 0.0503 mmol).
CH2Cl2 (10 mL) was vacuum transferred to the vessel. Under
an argon flow, I2 (17 mg, 0.067 mmol) was added to give a
deep red solution. The volatiles were removed under vacuum,
and the solid was recrystallized from CH2Cl2/pentane. The
product was isolated as a light green solid (63 mg, 86%). 1H
Rea ction of [Cp 2Re(CH2)]B(Ar ′)4 w ith Su lfu r . A seal-
able NMR tube was charged with [Cp2ReCH2]B(Ar′)4 (5 mg,
0.004 mmol) and excess sulfur. Methylene chloride-d2 (0.5 mL)
was vacuum transferred to the tube, which was sealed. An
initial 1H NMR spectrum showed no reaction. After the
mixture was heated at 50 °C for 3 h, the color changed from
pink to orange. 1H NMR (CD2Cl2): 5.47 (s, 10 H, Cp), 3.41 (s,
2 H, (H2CdS)).
[Cp 2Re(CH2CH(SiMe3))]B(Ar ′)4. A small glass vessel
with an 8 mm Kontes valve was charged with 1 (100 mg,
0.0838 mmol). CH2Cl2(10 mL) was vacuum transferred to the
vessel. Under an argon flow, N2CHSiMe3 (45 µL, 2 M, 0.0838
mmol) was added via a gas-tight syringe. The solution was
stirred for 10 min, and the solvent volume was reduced to 2
mL. Pentane (10 mL) was vacuum transferred to the vessel
to give a pale tan precipitate. The solvent was removed by
cannula, and the solid was dried under vacuum. Yield: 74
mg, 69%. 1H NMR (CD2Cl2): 5.13 (s, Cp), 5.10 (s, Cp), 2.67 (d
of d, J HH ) 12.1, 3.8 Hz, CHZHE), 2.24 (d of d, J HH ) 15.5, 4.0
Hz, CHZHE), 1.73 (d of d, J HH ) 15.1, 12.1 Hz, CHSiMe3), 0.18
(s, SiMe3).
NMR (CD2Cl2): 6.06 (s, 10 H, Cp), 3.84 (s, 2 H, Re-CH2I). 13
C
1
NMR (CD2Cl2): 96.18 (d of quint, J CH ) 191.4 Hz, J CH ) 6.2
Hz, Cp), -44.0 (t, J CH ) 158.8 Hz, Re-CH2I). Anal. Calcd
for C43H24BF24I2Re: C, 35.68; H, 1.67. Found: C, 35.57; H,
1.57.
Ack n ow led gm en t. This research was supported by
the Department of Energy, Office of Basic Energy
Science. C.E.R. is grateful to the University of Wash-
ington for a Ritter Fellowship. We thank Professor
George L. Gould for helpful discussions.
[Cp 2Re(H2CdO)]B(Ar ′)4 (9). A 20 mL round-bottom flask
was charged with 1 (105 mg, 0.088 mmol) and C5H5NO (8 mg,
0.088 mmol) and attached to a swivel-frit apparatus. The
swivel frit was attached to a vacuum line, and 10 mL of CH2-
Cl2 was vacuum transferred at -78 °C. The orange solution
OM970706A