Synthesis and X-ray structure of the rhenium methyl complex trans-Cp*Re(CO)2(Me)I and a study of the products of photolysis of the rhenium alkyl methyl and dimethyl complexes Cp*Re(CO)2(Me)R (R = Ph, p-Tolyl, Me) under CO

Article abstract of DOI:10.1021/om980688c

Reaction of Cp*Re(CO)₂I₂ with methylcopper affords cis-Cp*Re(CO)₂(Me)I, which converts to the trans isomer on prolonged reaction or in the presence of neutral alumina. The X-ray structure of the trans isomer has been determined. The related chloro complexes Cp*Re-(CO)₂(Me)Cl and Cp*Re(CO)₂(p-tolyl)Cl are formed in the photolyses of compounds 3 and 1 (below) in CCl₄. Photolysis of Cp*Re(CO)₂(Me)R (R = p-tolyl (1), Ph (2), Me (3)) in the presence of CO has been carried out in hydrocarbons, CCl₄, and benzene-d₆. In hydrocarbons, 1 and 2 produce Cp*Re(CO)₃, CH₄, and either toluene or benzene, respectively; 3 produces Cp*Re-(CO)₃ and CH₄. In benzene-d₆ 1 gave CH₃D and toluene-4-d, and 3 gave mainly CH₃D. These results are consistent with a general scheme involving successive homolysis of the metal-methyl and metal-aryl bonds to give methyl and aryl radicals that abstract H or D from the solvent and carbonylation of the rhenium dicarbonyl fragment. Products known or expected to arise from further photolysis of Cp*Re(CO)₃ in benzene-d₆, such as Cp*₂Re₂(CO)₃, Cp*₂Re₂(CO)₅, and Cp*Re(CO)₂(η²-C₆D₆), were also found. Photolysis of 1 in CCl₄ in the presence or absence of CO gave CH₃Cl and Cp*Re(CO)₂(p-tolyl)Cl, but no p-chlorotoluene, indicating the preferential homolysis of the Re-Me bond and the rapid scavenging of the subsequent radicals by the chlorinated solvent. Photolysis of the dimethyl complex 3 gave CH₃Cl and some evidence of a small amount of Cp*Re(CO)₂(Me)Cl, but the major rhenium product was Cp*Re(CO)₂Cl₂, consistent with the more facile homolysis of both Re-Me bonds in 3. Production of small amounts of CH₂D₂ (in benzene-d₆) and CH₄ and CH₂Cl₂ (in CCl₄) are discussed in terms of a competing pathway. Notably, in none of these photolyses were there observed other than trace amounts of products such as p-xylene, which would be expected to be major products if reductive elimination were to occur.

Full text of DOI:10.1021/om980688c

Organometallics 1999, 18, 339-347
339
Syn th esis a n d X-r a y Str u ctu r e of th e Rh en iu m Meth yl
Com p lex tr a n s-Cp *Re(CO)2(Me)I a n d a Stu d y of th e
P r od u cts of P h otolysis of th e Rh en iu m Alk yl Meth yl a n d
Dim eth yl Com p lexes Cp *Re(CO)2(Me)R (R ) P h , p-Tolyl,
Me) u n d er CO
Carmen Leiva,† A. Hugo Klahn,‡ Fernando Godoy,‡ Adriana Toro,‡
Victor Manriquez,§ Oscar Wittke,§ and Derek Sutton*,†
Department of Chemistry, Simon Fraser University,
Burnaby, British Columbia V5A 1S6, Canada, Instituto de Quimica, Universidad Catolica de
Valparaiso, Casilla 4059, Valparaiso, Chile, and Departmento de Quimica, Facultad de
Ciencias, Universidad de Chile, Casilla 653, Santiago, Chile
Received August 12, 1998
Reaction of Cp*Re(CO)2I2 with methylcopper affords cis-Cp*Re(CO)2(Me)I, which converts
to the trans isomer on prolonged reaction or in the presence of neutral alumina. The X-ray
structure of the trans isomer has been determined. The related chloro complexes Cp*Re-
(CO)2(Me)Cl and Cp*Re(CO)2(p-tolyl)Cl are formed in the photolyses of compounds 3 and 1
(below) in CCl4. Photolysis of Cp*Re(CO)2(Me)R (R ) p-tolyl (1), Ph (2), Me (3)) in the presence
of CO has been carried out in hydrocarbons, CCl4, and benzene-d6. In hydrocarbons, 1 and
2 produce Cp*Re(CO)3, CH4, and either toluene or benzene, respectively; 3 produces Cp*Re-
(CO)3 and CH4. In benzene-d6 1 gave CH3D and toluene-4-d, and 3 gave mainly CH3D. These
results are consistent with a general scheme involving successive homolysis of the metal-
methyl and metal-aryl bonds to give methyl and aryl radicals that abstract H or D from
the solvent and carbonylation of the rhenium dicarbonyl fragment. Products known or
expected to arise from further photolysis of Cp*Re(CO)3 in benzene-d6, such as Cp*2Re2(CO)3,
Cp*2Re2(CO)5, and Cp*Re(CO)2(η2-C6D6), were also found. Photolysis of 1 in CCl4 in the
presence or absence of CO gave CH3Cl and Cp*Re(CO)2(p-tolyl)Cl, but no p-chlorotoluene,
indicating the preferential homolysis of the Re-Me bond and the rapid scavenging of the
subsequent radicals by the chlorinated solvent. Photolysis of the dimethyl complex 3 gave
CH3Cl and some evidence of a small amount of Cp*Re(CO)2(Me)Cl, but the major rhenium
product was Cp*Re(CO)2Cl2, consistent with the more facile homolysis of both Re-Me bonds
in 3. Production of small amounts of CH2D2 (in benzene-d6) and CH4 and CH2Cl2 (in CCl4)
are discussed in terms of a competing pathway. Notably, in none of these photolyses were
there observed other than trace amounts of products such as p-xylene, which would be
expected to be major products if reductive elimination were to occur.
In tr od u ction
nophosphine or phosphite) in chlorobenzene furnished
the phenyl chloro complexes Cp*Re(CO)(L)(Ph)Cl.3 In
this paper we report two further developments of this
chemistry.
As part of a continuing investigation of the syntheses,
structures, and reactions of (pentamethylcyclopentadi-
enyl)rhenium half-sandwich complexes, we have re-
cently turned our attention to the synthesis of examples
with rhenium-alkyl or rhenium-aryl bonds. The step-
wise substitution of the rhenium-iodide bonds in
Cp*Re(CO)2I2 afforded the aryl iodo and aryl methyl
complexes Cp*Re(CO)2(Ar)I and Cp*Re(CO)2(Ar)Me.1
Alkylation of the dichloro complex Cp*Re(CO)2Cl2 by
using an organocopper reagent provided the dialkyl
complexes Cp*Re(CO)2R2 (R ) Me, Et).2 Photolysis of
the dinitrogen complexes Cp*Re(CO)(L)(N2) (L ) orga-
First, we show that changing the halogen in Cp*Re-
(CO)2X2 from Cl to I allows the reaction with methyl-
copper to proceed only with monosubstitution, affording
Cp*Re(CO)2(Me)I. This is initially obtained as the cis
isomer, which converts to the trans isomer on prolonged
reaction or in the presence of neutral alumina. The
X-ray structure of the trans isomer has been deter-
mined.
Second, we have investigated the results of photolyz-
ing the aryl methyl and dimethyl complexes Cp*Re-
(CO)2(Me)R (R ) Ph, p-tolyl, Me) in solution in the
presence of CO. The objective here was to extend the
previous work of Hill4 on the photochemistry of cis-
† Simon Fraser University.
‡ Universidad Catolica de Valparaiso.
§ Universidad de Chile.
(1) Klahn, A. H.; Toro, A.; Arenas, M.; Manriquez, V.; Wittke, O. J .
Organomet. Chem. 1997, 532, 39.
(2) Klahn, A. H.; Manzur, C.; Toro, A.; Moore, M. J . Organomet.
Chem. 1996, 516, 51.
(3) Leiva, C.; Sutton, D. Organometallics 1998, 17, 4568.
(4) Hill, R. H.; Palmer, B. J . Organometallics 1989, 8, 1651.
10.1021/om980688c CCC: $18.00 © 1999 American Chemical Society
Publication on Web 12/31/1998

340 Organometallics, Vol. 18, No. 3, 1999
Leiva et al.
Cp*Re(CO)2Me2 in order to try to determine the primary
photoreaction and the fate of the alkyl and aryl ligands
in this process and to compare the results with those
previously obtained by Goldberg and Bergman5 using
the cyclopentadienyl analogue CpRe(CO)2Me2. The prod-
ucts formed in hydrocarbon solvents under the condi-
tions of our experiments are consistent with a general
scheme involving metal-carbon bond homolysis to give
aryl and methyl radicals that abstract H from the
hydrocarbon solvent. The products from photolyses in
CCl4 indicate significant differences in the chemistry in
this solvent, and the methyl chloro and aryl chloro
complexes Cp*Re(CO)2(Me)Cl and Cp*Re(CO)2(p-tolyl)-
Cl have been characterized in these reactions. Notably,
products that would be anticipated if reductive elimina-
tion were to occur were generally not observed for
photolyses in either solvent.
F igu r e 1. X-ray structure of trans-Cp*Re(CO)2(Me)I.
Ta ble 1. Selected Bon d Len gth s a n d In ter bon d
An gles for Cp *Re(CO)2(Me)I
Resu lts
(a) Bond Lengths (Å)
Re(l)-I(l)
Re(l)-C(2)
Re(l)-C(7)
C(l)-C(2)
C(2)-C(3)
C(3)-C(4)
2.800(1)
2.309(6)
1.939(6)
1.412(8)
1.419(8)
1.488(8)
Re(l)-C(l)
Re(l)-C(3)
Re(l)-C(8)
C(l)-C(5)
C(2)-C(6)
C(1)-C(7)
2.326(9)
2.298(6)
2.267(9)
1.504(13)
1.509(8)
1.127(7)
1. Syn t h esis a n d Ch a r a ct er iza t ion of cis- a n d
tr a n s-Cp *Re(CO)2(Me)I. The reaction of Cp*Re(CO)2I2
with methylcopper in THF led to the loss of IR absorp-
tion bands for the diiodide complex and the formation
of new absorptions at 2004 and 1939 cm-1 due to the
initial formation of cis-Cp*Re(CO)2(Me)I. Upon comple-
tion of the reaction, column chromatography on silica
gel allowed isolation of first the trans isomer and then
the cis isomer. It was observed that increasing the
reaction time before the workup increased the propor-
tion of the trans isomer which was eventually recovered
and that chromatography of the pure cis isomer on
neutral alumina also led to isomerization, indicating
that cis-trans isomerization occurs in solution and is
promoted by contact with alumina.
The assignment of the geometry of the two isomers
is based upon the observed relative intensity patterns
for the two ν(CO) absorption bands in each case. For
the trans isomer, the lower wavenumber band is the
more intense, and this is consistent with similar relative
intensities previously observed for related trans isomers
of the type Cp*Re(CO)2X2 or Cp*Re(CO)2XY. Examples
are trans-Cp*Re(CO)2(Ph)I,1 trans-Cp*Re(CO)2R2 (R )
Me, Et),2 trans-Cp*Re(CO)2I2,6 trans-Cp*Re(CO)2{PO-
(OMe)2}I,7 and trans-Cp*Re(CO)2(Et)Br.8 This assign-
ment is further supported by the determination of the
X-ray crystal structure and the observation of a single
13C resonance for the chemically equivalent carbonyl
ligands. Correspondingly, the cis isomer exhibits spec-
troscopic properties consistent with a cis geometry, such
as a higher intensity for the higher wavenumber of the
two ν(CO) absorptions and two carbonyl carbon reso-
nances. Finally, the ν(CO) absorptions of this isomer
occur at lower wavenumbers compared with that of the
trans isomer, as has commonly been seen in similar
cases.2,6
(b) Interbond Angles (deg)
I(l)-Re(l)-C(7)
C(7)-Re(l)-C(8)
C(2)-C(l)-C(5)
C(l)-C(2)-C(3)
C(3)-C(2)-C(6)
C(2)-C(3)-C(3A)
Re(l)-C(7)-O(1)
79.5(2)
74.5(2)
I(l)-Re(l)-C(8)
136.5(3)
104.8(4)
109.6(9)
126.7(6)
127.4(6)
125.2(4)
C(7)-Re(l)-C(7A)
C(2)-C(l)-C(2A)
C(l)-C(2)-C(6)
C(2)-C(3)-C(4)
C(4)-C(3)-C(3A)
125.0(4)
108.3(6)
124.7(6)
107.0(4)
176.1(6)
addition to the list of structure determinations of related
cyclopentadienylrhenium alkyl or aryl complexes. These
include trans-Cp*Re(CO)2(Ph)I,1 trans-Cp*Re(CO)2Et2,2
trans-CpRe(CO)2(CH2Ph)H,9 and trans-CpRe(CO)2-
(COMe)Me.5 Selected bond lengths and angles are
presented in Table 1. The Re-C(Me) bond (2.267(9) Å)
is, as expected, longer than the Re-C(Ph) bond (2.191(6)
Å) in the corresponding phenyl complex trans-Cp*Re-
(CO)2(Ph)I.1 It compares well with corresponding rhe-
nium-alkyl bonds in trans-CpRe(CO)2(COMe)Me5
(2.245(4) Å), trans-CpRe(CO)2(CH2Ph)H9 (2.29(1) Å),
and trans-Cp*Re(CO)2Et22 (2.262(10) Å). The interbond
angle subtended by the two CO groups at Re (105°) is
also close to the angle in similar trans complexes.1,2,5-7,9
2. P h otolysis of Cp *Re(CO)2(Me)R (R ) P h , p-
Tolyl, Me) u n d er CO. a . Ch a r a cter iza tion of th e
P r od u cts. The photolysis (λ g 275 nm) of degassed
cyclohexane solutions of trans-Cp*Re(CO)2Me(p-tolyl)
(1) in a Pyrex vessel at room temperature under 1 atm
of CO for 20 min led to the decrease of ν(CO) IR bands
for the starting complex at 2002 and 1927 cm-1 and the
production of Cp*Re(CO)3 (ν(CO) 2012 and 1921 cm-1).
1
The H NMR spectrum of the sample after irradiation
showed, in the aromatic region, the presence of some
starting material and a new set of resonances assigned
to free toluene. The organometallic and organic compo-
nents from the photolysis of 1 in cyclohexane were
separated by vacuum transfer and were analyzed inde-
pendently.
The X-ray structure of trans-Cp*Re(CO)2(Me)I (Figure
1) confirms the geometry of the isomer and is an
(5) (a) Goldberg, K. I.; Bergman, R. G. Organometallics 1987, 6, 430.
(b) Goldberg, K. I.; Bergman, R. G. J . Am. Chem. Soc. 1989, 111, 1285.
(6) Einstein, F. W. B.; Klahn, A. H.; Sutton, D.; Tyers, K. G.
Organometallics 1986, 5, 53.
(7) Klahn, A. H.; Leiva, C.; Mossert, K.; Sutton, D. J . Organomet.
Chem. 1994, 469, 69.
The GC spectrum of the organic fraction showed a
peak with a retention time (RT) of 2.11 min, and the
(8) Nunn, C. M.; Cowley, A. H.; Lee, S. W.; Richmond, M. G. Inorg.
Chem. 1990, 29, 2105.
(9) Fischer, E. O.; Frank, A. Chem. Ber. 1978, 111, 3740.

Rhenium Methyl Complexes
Organometallics, Vol. 18, No. 3, 1999 341
corresponding GC/MS spectrum gave peaks at m/z 92
(M+, 37) and 91 (M+ - H, 100). A toluene sample in
cyclohexane showed a similar RT and fragmentation
pattern. No evidence of 1,4-dimethylbenzene (p-xylene)
b. Isotop ic La belin g Stu d ies. Isotopic labeling
experiments were done in order to elucidate the hydro-
gen source in the production of toluene, benzene, and
methane in the photolysis of 1-3. First, the photolysis
of trans-Cp*Re(CO)2(Me)(p-tolyl) (1) in degassed benzene-
d6 in a sealed NMR tube under CO (1 atm) was
1
was observed. The H NMR spectrum of the organome-
tallic component in benzene-d6 showed a resonance at
δ 1.72 assigned to Cp*Re(CO)3 and resonances due to
residual starting material. The IR spectrum in hexane
showed ν(CO) bands corresponding to the starting
material and the tricarbonyl complex.10
1
monitored by H NMR spectroscopy. After ∼20 min of
irradiation there was a decrease in intensity of the
resonances for the starting material and production of
resonances due to toluene-4-d and Cp*Re(CO)3.
After ∼45 min photolysis, the 1H NMR spectrum
showed the complete disappearance of the starting
material, a decrease in intensity of the resonance due
to Cp*Re(CO)3, and new resonances in the Cp* region
assigned to Cp*2Re2(CO)5 and Cp*2Re2(CO)3 by com-
parison of the 1H NMR and IR spectra with those
reported previously.12 A resonance at δ 1.59 was ten-
tatively assigned to Cp*Re(CO)2(η2-C6D6), by compari-
son with the 1H NMR and IR spectra of the known
compound Cp*Re(CO)2(η2-C6H6).12a Subsequent GC/MS
analysis of the organic fraction showed a major product
with RT 3.19 min which gave peaks at m/z 93 (M+, 64)
and 92 (M+ - H, 100), identified as C6H4DCH3. There
was also a peak at m/z 97 (M+, 23), which was identified
as C6D5CH3. The pattern for C6H4DCH3 was similar to
that observed for a synthesized sample of toluene-4-d
(see below). There was also a trace amount of a material
giving a peak with RT 5.95 having m/z 106 (M+, 50) and
91 (M+ - CH3, 100), identified as 1,4-dimethylbenzene
(p-xylene).
The photolysis was repeated under the same condi-
tions, but this time the gas-phase product was analyzed
by GC/MS. This showed a peak with a RT of 2.71 min
with m/z 16 (M+, 100), 15 (M+ - H, 80), 14 (M+ - 2H,
25) as the sole product. Methane and CO samples were
analyzed independently (the latter to check the possible
presence of CH4 in the CO used; none was found), to
provide data on the retention time and the fragmenta-
tion pattern of the parent ion under our experimental
conditions. The CH4 showed a RT of 2.71 min with m/z
16 (M+, 100), 15 (M+ - H, 76), 14 (M+ - 2H, 28). The
gas-phase product was therefore identified as methane.
No evidence of ethane or acetone was observed.
Photolysis for 20 min of a degassed pentane solution
of trans-Cp*Re(CO)2(Me)Ph (2) in a Pyrex vessel at room
temperature under 1 atm of CO also led to loss of ν(CO)
IR bands at 2002 and 1927 cm-1 for the starting
material and the formation of Cp*Re(CO)3. The orga-
nometallic and organic components were separated and
analyzed as above. The GC spectrum of the organic
phase showed a peak with a RT of 1.32 min, and the
GC/MS showed peaks at m/z 78 (M+, 100) and 77 (M+
- H, 30). A benzene sample in pentane showed a similar
RT and fragmentation pattern. The organometallic
component showed the presence of complex 2 and
Cp*Re(CO)3. Photolysis of 2 was then carried out in
cyclohexane at room temperature for 20 min. Methane
was the only product observed in the GC/MS of the
The same experiment was carried out for trans-
Cp*Re(CO)2(Me)Ph (2) and trans-Cp*Re(CO)2Me2 (3)
1
under conditions similar to those above. The H NMR
spectra in benzene-d6 after 25 min of photolysis again
showed the formation of Cp*Re(CO)3, Cp*2Re2(CO)5,
Cp*2Re2(CO)3, and Cp*Re(CO)2(η2-C6D6), as observed
above in the reaction of 1 in benzene-d6. The GC/MS of
the organic fraction after photolysis of 2 showed a peak
with RT 3.23 min having m/z 97 (M+, 100), which was
identified as C6D5CH3 (Figure 2), and a small unas-
signed peak having RT 6.54 min with m/z 107.
1
headspace gas. A new H NMR resonance observed at
δ 7.20 was assigned as free benzene. No evidence of
1
toluene was observed in either the H NMR spectrum
These experiments were repeated under the same
conditions in a Pyrex vessel, and this time the gas phase
and the organic material were analyzed by GC and GC/
MS. After 1 was irradiated in benzene-d6 under CO (1
atm) for 20 min, the GC/MS of the gas phase showed a
peak with RT 2.72 min having m/z 17 (relative intensity
53), 16 (100), and 15 (40). From a comparison with the
spectra of the pure compounds, this spectrum was
deduced to be that of a mixture of 68% CH4 and 32%
CH3D. The highest m/z value of 17 corresponds to M+
of CH3D. However, the peak at m/z 16 in the sample is
the most intense. The GC and GC/MS of the organic
fraction showed the presence of C6H4DCH3 as the major
product and a trace of C6D5CH3. A sample of toluene-
4-d for comparison showed a peak in the GC/MS with a
RT of 3.45 min having m/z 93 (M+, 65), 92 (M+ - H,
100), and 91 (M+ - 2H or M+ - D, 25). Thus, this
showed the same fragments as observed for toluene but
a parent peak of 1 mass unit greater, as expected.
Following the photolysis of trans-Cp*Re(CO)2Me2 (3)
in benzene-d6 under 1 atm of CO the GC/MS of the gas
or GC/MS.
Photolysis of trans-Cp*Re(CO)2Me2 (3) under 1 atm
of CO in cyclohexane at room temperature for 20 min
gave Cp*Re(CO)3 and methane as the only products. No
evidence of the formation of ethane, acetone, or 2,3-
butanedione was obtained.
To test for the possible photodissociation of CO from
the aryl methyl or dimethyl complexes, an n-hexane
solution of trans-Cp*Re(CO)2MeR (R ) Ph (2), Me (3))
in a Pyrex vessel was photolyzed for 25 min at room
temperature in the presence of a large excess of PPh3.
Gas chromatographic analysis of the product mixture
indicated the production of methane in both cases, and
for 2 the GC/MS of the organic sample showed the
production of benzene. The IR spectrum of the organo-
metallic material only showed new ν(CO) frequencies
at 1913 and 1865 cm-1, identified as those of Cp*Re-
(CO)2PPh3.11 There was no indication of the formation
of Cp*Re(CO)(PPh3)(Ph)Me or Cp*Re(CO)(PPh3)Me2.
(10) Patton, A. T.; Strouse, C. E.; Knobler, C. B.; Gladysz, J . A. J .
Am. Chem. Soc. 1983, 105, 5810.
(11) Angelici, R. J .; Facchin, G.; Singh, M. M. Synth. React. Inorg.
Met.-Org. Chem. 1990, 20, 275.
(12) (a) van der Heijden, H.; Orpen, A. G.; Pasman, P. J . Chem. Soc.,
Chem. Commun. 1985, 1576. (b) Hoyano, J . K.; Graham, W. A. G. J .
Chem. Soc., Chem. Commun. 1982, 27.

342 Organometallics, Vol. 18, No. 3, 1999
Leiva et al.
F igu r e 2. GC/MS results for the organic fraction following
the photolysis of 2 in benzene-d6: (a) GC trace; (b) GC/MS
for peak with RT ) 3.23 min, indicating C6D5CH3.
F igu r e 3. IR spectra before and after photolysis of 1 in
CCl4: (solid line) spectrum of 1; (dotted line) spectrum after
photolysis for 10 min.
phase showed a product with a RT of 2.05 min having
m/z 18 (relative intensity 66), 17 (32) 16 (100), 15 (39),
and 14 (35). This was deduced to be a mixture of CH4,
CH3D, and CH2D2. The highest m/z value of 18 corre-
sponds to M+ for CH2D2. However, the peak at m/z 16
is the most intense. Methane-d2 was synthesized for a
comparison, and the mass spectrum showed that M+ at
m/z 18 is the most intense peak, there is a less intense
peak at m/z 17 for M+ - H, and the m/z 16 peak is weak
(indicating preferential loss of H over D). The relative
ratios of the different constituents in the gas mixture
were calculated to be CH4:CH3D:CH2D2 ) 73:8:32. The
mechanism proposed for their formation will be dis-
cussed below.
and 1962 cm-1 (Figure 3).13,14 The IR and 1H NMR
spectra of the product after chromatography were in
agreement with those observed for the crude material.
The EIMS gave a weak parent peak at m/z 504, a
fragment at m/z 476, and a base peak at m/z 446. The
isotopic pattern was consistent with the presence of one
chlorine atom. All the spectroscopic data indicated that
the product was Cp*Re(CO)2(p-tolyl)Cl, which was
synthesized by a similar procedure in the absence of CO
for comparison (see Experimental Section).
The GC/MS of the headspace gas (Figure 4) showed
a peak at RT 8.12 min having m/z 50 (M+, 100) (Figure
4c) and a peak at RT 12.65 min having m/z 117 (M+
-
c. P h otolysis of tr a n s-Cp *Re(CO)2(Me)R (R )
p-Tolyl (1), Me (3)) in CCl4. When the photolysis of
trans-Cp*Re(CO)2(Me)(p-tolyl) (1) under CO at room
temperature for 20 min was carried out in CCl4, 1
disappeared and the products observed were Cp*Re-
Cl, 100). These were identified as CH3Cl and CCl4
solvent, respectively, by a comparison with the retention
times and fragmentation patterns observed for authen-
tic samples. The spectrum also revealed traces of CH4
present in the sample (RT 2.73 min with m/z 16 (M+,
100)) (Figure 4b), the formation of which will be
discussed below. The photolysis was repeated in the
absence of CO, and the same products (CH3Cl, CH4
(trace), and Cp*Re(CO)2(p-tolyl)Cl) were observed in the
GC/MS and IR spectra. The sample was photolyzed an
additional 30 min, and no evidence of decomposition or
any new products was observed.
1
(CO)2(p-tolyl)Cl and CH3Cl. The H NMR spectrum of
1 before irradiation showed resonances at δ 0.76 (3H),
1.75 (15H), and 2.39 (3H) assigned to Re-Me, Cp*, and
the tolyl ligand, respectively, and tolyl ring proton
resonances at δ 6.87 (2H) and 7.52 (2H). The spectrum
after irradiation showed new resonances at δ 1.78 (15H)
and 2.37 (3H), 6.93 (d, 2H), and 7.51 (d, 2H) assigned
respectively to the Cp* and tolyl ligands in the product.
The IR spectrum showed two new bands at ν(CO) 2039
Photolysis of trans-Cp*Re(CO)2Me2 (3) in CCl4 under
CO at room temperature for 10 min led to the loss of
ν(CO) IR absorption bands from the starting material
(1993 and 1915 cm-1) and the formation of four new
bands in the carbonyl region at 2064, 2031, 1997, and
1958 cm-1 (Figure 5). The more intense bands at 2064
and 1997 cm-1 were assigned to trans-Cp*Re(CO)2Cl2.14
The two weaker bands at 2031 and 1958 cm-1 were
(13) The IR spectrum in CCl4 also shows absorptions at 2064 and
1998 cm-1 assigned to the presence of a small amount of trans-Cp*Re-
(CO)2Cl2.14
(14) Klahn-Oliva, A. H.; Ph.D. Thesis, Simon Fraser University,
1986;
p 143. Characterizing data are as follows. trans-Cp*Re-
(CO)2Cl2: IR (CH2Cl2) νCO 2059, 1986 cm-1 1H NMR (CDCl3) δ 1.89.
;
cis-Cp*Re(CO)2Cl2: IR (CH2Cl2) νCO 2037, 1959 cm-1; 1H NMR (CDCl3)
δ 1.98.

Rhenium Methyl Complexes
Organometallics, Vol. 18, No. 3, 1999 343
F igu r e 5. IR spectra before and after photolysis of 3 in
CCl4 (solid line) spectrum of 3; (dotted line) spectrum after
photolysis for 10 min.
at δ 1.88 assigned14 to trans-Cp*Re(CO)2Cl2 (the major
product) and resonances assigned to Cp*Re(CO)2(Me)-
Cl at δ 0.74 (3H) and 1.80 (15H). The IR, NMR, and
mass spectra of a similar product isolated from the
irradiation of 3 in CCl4 under N2 confirmed the assign-
ment (see Experimental Section).
Discu ssion
F igu r e 4. CG/MS results for the volatile products from
the reaction of 1 in CCl4: (a) GC trace; (b) CG/MS for peak
with RT ) 2.73 min, indicating CH4; (c) CG/MS for peak
with RT ) 8.12 min, indicating CH3Cl.
In previous work, Hill and Palmer studied the pho-
tochemistry of cis-Cp*Re(CO)2Me2 in methylcyclohexene
and found that room-temperature photolysis led to the
production of trans-Cp*Re(CO)2Me2 and Cp*Re(CO)3.4
At low temperatures, however, the cis-trans isomer-
ization was the only detectable reaction. This isomer-
ization was determined to proceed by photochemical CO
loss to give the unsaturated complex Cp*Re(CO)Me2
followed by recombination with CO. The production of
the tricarbonyl species at ambient temperature was
presumed to arise from a reaction of the photogenerated
unsaturated species with starting complex. This pre-
liminary study was primarily focused on the cis-trans
isomerization, and other products associated with the
formation of Cp*Re(CO)3 were not investigated. It was,
however, recognized that the low-temperature experi-
ments conducted in a glass may not be representative
of reactions at room temperature in solution. This is
because bond homolysis may be rapidly followed by
recombination in the low-temperature glass, so that no
net reaction is observed,15 whereas homolytic cleavage
of the metal-methyl bonds could be an important
process under the latter conditions. In this study, by
carrying out the ambient-temperature photolysis of the
trans isomer (3) mainly under CO, we have sought to
capture the primary rhenium photoproduct, identify the
tentatively assigned to Cp*Re(CO)2(Me)Cl. The GC/MS
of the gas phase showed a peak (RT 7.66 min) with m/z
50 (M+, 100), which was identified as CH3Cl. This was
the major product. The spectrum also showed evidence
of the formation of CH4 (RT 2.64 min, m/z 16 (M+, 100))
and CH2Cl2 (RT 9.94 min, m/z 84 (M+, 100)) as minor
products.
1
The photolysis was repeated and was followed by H
NMR spectroscopy in CCl4. The spectrum after 5 min
of photolysis showed resonances at δ 1.93 (s, 15H, Cp*)
and at δ 0.82 (s, 3H, Me), which were tentatively
assigned to Cp*Re(CO)2(Me)Cl. The spectrum also
showed a broad resonance at δ 5.15, which was identi-
fied as CH2Cl2; no evidence of Cp*Re(CO)3 was observed.
1
The H NMR spectrum taken after 22 min of photolysis
showed a Cp* signal corresponding to trans-Cp*Re-
(CO)2Cl2 at δ 2.00 and a weak Cp* signal at δ 2.21,
indicating traces of the cis isomer. The reaction was
repeated to try to isolate the rhenium products. The IR
spectrum after 10 min of photolysis showed the carbonyl
bands associated with the unreacted starting material
3 and trans-Cp*Re(CO)2Cl2 and a small amount of the
tentatively assigned Cp*Re(CO)2(Me)Cl. A yellow-
orange solid obtained following chromatography showed
(15) Van Leeuwen, P. W. N. M.; van der Heijden, H.; Roobeek, C.
F.; Frijns, J . H. G. J . Organomet. Chem. 1981, 209, 169.
1
a H NMR spectrum (in CDCl3) with a strong resonance

344 Organometallics, Vol. 18, No. 3, 1999
Leiva et al.
Sch em e 1
Sch em e 2
fate of the methyl groups, and so determine the details
of the photoreaction under these conditions. Further-
more, we have sought to compare the results for the
dimethyl compound with two examples of similar aryl
methyl complexes. What then emerges is that under
these conditions CO loss is unimportant, whereas rhe-
nium-methyl and rhenium-aryl bond homolyses con-
stitute the dominant photoreactions.
carbon bond homolysis may not be observable in a low-
temperature glass due to rapid back-reaction but may
be overwhelmingly faster than CO dissociation in solu-
tion at ambient temperature.
No evidence of the reductive-elimination products
p-xylene and toluene was observed in the photolysis of
1 or 2 in cyclohexane, but when the photolysis of 1 was
carried out in benzene-d6, traces of p-xylene were
detected. One explanation for this is a degree of recom-
bination of CH3• with CH3C6H5• in the benzene solvent
cage. Nevertheless, carbon-carbon bond formation by
reductive elimination from the photoexcited rhenium
aryl methyl complexes does not appear to be an impor-
tant pathway.
Further evidence for homolytic cleavage of the metal-
methyl bond in these aryl methyl complexes is the
formation of CH3Cl in the photolysis of 1 in CCl4 under
CO. However, it is significant that we did not also
observe the correspondingly trapped aryl radical as
CH3C6H4Cl. Furthermore, the products differed in
several ways from those observed for photolyses in
hydrocarbon solvents (Scheme 1). No Cp*Re(CO)3 was
detected, but instead the formation of the aryl chloro
complex Cp*Re(CO)2(p-tolyl)Cl was indicated. These
results suggest that homolysis of the Re-methyl bond
is much faster than that of the Re-aryl bond (in accord
with the expectation that the Re-methyl bond is
weaker) and that the radicals so formed (CH3 and
Cp*Re(CO)2(p-tolyl)) rapidly abstract Cl from CCl4. The
solvent dependence of the product distribution in each
case reflects the relative ease of Cl abstraction from the
chlorinated solvent compared with H from the hydro-
carbon solvent. Noticeably, in CCl4 the same products
were obtained in the presence or absence of added CO
and did not include Cp*Re(CO)3, indicating also that
the rate of successive homolysis of the Re-CH3 and Re-
aryl bonds necessary to furnish the Cp*Re(CO)2 frag-
ment required for CO uptake to give Cp*Re(CO)3 is
Photolysis of trans-Cp*Re(CO)2(Me)(p-tolyl) (1) under
CO in cyclohexane produced Cp*Re(CO)3, toluene, and
methane. Similarly, photolysis of the phenyl methyl
complex 2 in pentane gave the tricarbonyl species,
benzene, and methane (Scheme 1). A mechanism con-
sistent with these products is successive homolytic
cleavage of the rhenium-methyl and rhenium-aryl
bonds to give methyl and aryl radicals followed by
hydrogen abstraction from the solvent. In agreement
with this hypothesis, photolysis of 1 under CO in
benzene-d6 provided the monodeuterated products tolu-
ene-4-d and methane-d (Scheme 1). In addition, how-
ever, a small amount of toluene-d5 was observed. We
consider that this most likely arises from a radical
aromatic substitution involving the CH3 radical with the
solvent C6D6, as has been proposed by others.16 Another
possible explanation for this product could be oxidative
addition of C6D6 to a methylrhenium intermediate
followed by reductive elimination of C6D5CH3. This does
not seem likely, for several reasons. It would involve a
rhenium(IV) or -(V) oxidation level and require loss of
a CO ligand in order to provide a vacant site for the
activation of the solvent. However, when 1 was photo-
lyzed in the presence of a large excess of PPh3, we did
not observe any evidence for the formation of the
(triphenylphosphine)rhenium complex Cp*Re(CO)(PPh3)-
(Me)Ph, suggesting that overall photochemical loss of
CO from 1 does not readily occur. This is not necessarily
in conflict with the previous evidence for CO dissociation
in the case of cis- and trans-Cp*Re(CO)2Me2 in low-
temperature glasses,4 since as mentioned above metal-
(16) Rausch, M. D.; Boon, W. H.; Mintz, E. A. J . Organomet. Chem.
1978, 160, 81.

Rhenium Methyl Complexes
Sch em e 3
Organometallics, Vol. 18, No. 3, 1999 345
above to leave the Cp*Re(CO)2 or Cp*Re(CO)2Cl frag-
ments that are also scavenged by the solvent. The
positions and intensity ratios of the ν(CO) absorption
bands and the positions of the Me and Cp* resonances
of trans-Cp*Re(CO)2(Me)Cl are similar to those observed
for trans-Cp*Re(CO)2(Me)I, whose structure has been
determined in this work, and thus support the assign-
ment of trans stereochemistry.
The formation of also some methane and dichlo-
romethane from the photolysis of 3 in CCl4 can be
accounted for in much the same way as the formation
of CH4 and CH2D2 in the reaction with benzene-d6, as
discussed above and shown in Scheme 3. The production
of Cp*Re(CO)2(η2-C6D6), Cp*2Re2(CO)5, and Cp*2Re2-
(CO)3 complexes from the photolysis of 1-3 in benzene-
d6 is not unexpected, since these are known photoprod-
ucts of the photolysis of Cp*Re(CO)3.12
While in the photolyses reported here the overwhelm-
ing evidence is for homolysis of the rhenium-methyl
and -aryl bonds, in previous studies of the photochem-
istry of metal-methyl and metal-aryl complexes, evi-
dence supporting either bond homolysis or reductive
elimination has been obtained, depending on the par-
ticular case.18 The photolysis of diphenylbis(cyclopen-
tadienyl)titanium16,19 and -zirconium20 complexes yielded
benzene and biphenyl, and it was shown that the
biphenyl arises both from reductive elimination and
(along with benzene) by homolysis followed by attack
of a radical-like species on the solvent.16
Metal-methyl bond homolysis has been observed in
the photolysis of CpCo(PPh3)Me2 or [Me2Co(bpy)2]ClO4
in toluene or benzene, where methane was a major
product.21 Similar results have been reported for the
photolysis of Cp2TiMe2 and Cp2ZrMe2, where again
methane was a major product.15,22 In each of these cases,
the source of abstracted hydrogen was identified to be
the solvent. However, there is also the possibility of
a cyclopentadienyl ligand providing the hydrogen
source.16,20 On the other hand, photochemical reductive
elimination of methyl groups to give ethane has also
been observed in a few specific cases.21,23
prohibitively slow compared with the abstraction of Cl
by the primary photoproducts indicated above.
Turning now to the simpler dimethyl complex, the
photolysis of trans-Cp*Re(CO)2Me2 (3) under CO in
cyclohexane formed CH4 and Cp*Re(CO)3 as the only
products (Scheme 2). Again, no evidence of reductive-
elimination products such as ethane and acetone was
observed. These products are consistent with the pri-
mary photoprocess being successive homolysis of the
•
Re-methyl bonds to give Cp*Re(CO)2 and CH3 that
abstracts hydrogen from the solvent. However, further
investigation on the photolysis of 3 carried out in
benzene-d6 showed that methane, methane-d, methane-
d2, and Cp*Re(CO)3 were all formed. The methane-d
must result from deuterium abstraction from the solvent
by CH3, in agreement with the postulated mechanism.
The formation of undeuterated methane may result
from a methyl group abstracting hydrogen from the
other methyl group that remains coordinated to the
metal center. The concurrent formation of CH2D2 is
consistent with such a mechanism, where it may be
envisaged that in the presence of CO the rhenium
methylene intermediate Cp*Re(CO)2CH2 reacts further
with the deuterated solvent or dissociates a transient
methylene which does so (Scheme 3).
Another possible explanation for the formation of
methane is an intramolecular R-hydrogen transfer,
which would also form the same rhenium methylene
intermediate. This mechanism has been proposed to
occur for manganese, cobalt, and tungsten alkyl com-
plexes.17 Our results, however, suggest that the domi-
nant photoprocess in the case of 3 is homolytic cleavage
of the methyl-rhenium bonds.
The photolysis of 3 under CO in CCl4 produced CH3-
Cl, as expected if Re-CH3 homolysis occurs. A product
with IR ν(CO) bands, mass spectrum, and 1H NMR
resonances consistent with the formulation trans-Cp*Re-
(CO)2(Me)Cl was formed in moderate yield, but the
major rhenium product was trans-Cp*Re(CO)2Cl2
(Scheme 2). Notably, no Cp*Re(CO)3 was formed from
photolysis in this solvent. These results suggest that the
initial rhenium photolysis product Cp*Re(CO)2Me is
rapidly scavenged by the chlorinated solvent to give
Cp*Re(CO)2(Me)Cl. The Cp*Re(CO)2Cl2 formed could
arise from loss of the second methyl from either of the
While the only previous photochemical study of
Cp*Re(CO)2Me2 has been that of Hill and Palmer
mentioned above,4 the cyclopentadienyl analogue CpRe-
(CO)2Me2 was studied by Goldberg and Bergman under
photochemical and thermal conditions.5 They found that
irradiation of CpRe(CO)2Me2 under 20 atm of CO gave
a clean conversion to 2,3-butanedione, CpRe(CO)3, and
a trace of acetone but no evidence of ethane or methane
was observed. They proposed that homolysis of rhe-
nium-methyl bonds occurs in this reaction and that the
methyl radicals undergo carbonylation followed by
combination of the acetyl radicals to yield the 2,3-
butanedione. Upon photolysis of CpRe(CO)2Me2 in CCl4,
(18) For reviews of organometallic photochemistry see: (a) Pourreau,
D. B.; Geoffroy, G. L. Adv. Organomet. Chem. 1985, 24, 249. (b)
Geoffroy, G. L.; Wrighton, M. S. Organometallic Photochemistry;
Academic Press: New York, 1979.
(19) Peng, W.; Brubaker, C. H., J r. Inorg. Chim. Acta 1978, 26, 231.
(20) Tung, H.-S.; Brubaker, C. H., J r. Inorg. Chim. Acta 1981, 52,
197.
(21) (a) Becalska, A.; Hill, R. H. J . Am. Chem. Soc. 1989, 111, 4346.
(b) Fukuzumi, S.; Ishikawa, K.; Tanaka, T. Organometallics 1987, 6,
358.
(22) Samuel, E. J . Organomet. Chem. 1980, 198, C65 and references
therein.
(17) (a) Kochi, J . K. Organometallic Mechanisms and Catalysis;
Academic Press: New York, 1978; Part I, Chapter 7, p 285. (b) Cross,
R. J . In The Chemistry of the Metal-Carbon Bond; Hartley, F. R., Patai,
S., Eds.; Wiley: New York, 1985; Vol. 2, p 599.
(23) Hill, R. H.; Puddephatt, R. J . Organometallics 1983, 2, 1472.

346 Organometallics, Vol. 18, No. 3, 1999
Leiva et al.
warmed to room temperature and stirred for an additional 40
min. At this point the IR spectrum in THF showed the
complete disappearance of the diiodo complex and strong
absorption bands at 2004 and 1939 cm-1. The reaction mixture
was then concentrated under vacuum to about one-third of its
initial volume and 2 drops of water were added to destroy the
excess MeCu. Filtration through Celite and evaporation of the
solvent to dryness yielded an orange solid. In column chro-
matography on silica gel 60 (prepared in hexane), a mixture
of hexane/CH2Cl2 (4:1) moved an orange-yellow band of trans-
Cp*Re(CO)2(Me)I, from which a yellow solid was obtained.
Further elution with hexane/CH2Cl2 (1:1) moved a red band
of the cis isomer.
acetyl chloride, CH3Cl, and CpRe(CO)3, and a trace of
acetone were obtained. When the reaction was carried
out with a better radical trap (CBrCl3), the only products
observed were CH3Br and CpRe(CO)2(Me)Br.5 In our
experiments, we did not observe any CO incorporation
into the organic products at 1 atm of CO, but we did
not carry out photolyses with higher CO pressures.
Con clu sion
The complexes cis- and trans-Cp*Re(CO)2(Me)I have
been synthesized, and the crystal structure of the trans
isomer has been determined. The photochemistry of
trans-Cp*Re(CO)2Me2 in solution at room temperature
is found to differ from that previously reported in a glass
at low temperature and involves homolysis of the
rhenium-methyl bonds. The methyl radicals then react
with the hydrocarbon or chlorinated solvent to give CH4
or CH3Cl. The corresponding methyl phenyl or methyl
p-tolyl complexes are found to undergo homolysis of the
Re-methyl bond faster than that of the Re-aryl bond
so that photolysis in CCl4 results in the ability to
observe the aryl chloro complexes Cp*Re(CO)2(Ph)Cl
and Cp*Re(CO)2(p-tolyl)Cl.
Data for trans-Cp*Re(CO)2(Me)I are as follows. Mp: decom-
posed over 185 °C. IR (CH2Cl2): νCO 2010 (s), 1937 (vs) cm-1
.
IR (hexane): νCO 2018 (s), 1954 (vs) cm-1 1H NMR (CDCl3):
.
δ 0.79 (s, 3H, Me) and 1.97 (s, 15H, Cp*). 13C{1H} NMR
(CDCl3): δ -26.90 (Me), 10.40 (C5Me5), 99.80 (C5Me5), and
193.98 (CO). EIMS (m/z): 520 (M+), 505 (M+ - Me), 492 (M+
- CO). Anal. Found: C, 30.02; H, 3.35. Calcd for C13H18O2-
IRe: C, 30.00; H, 3.46.
Data for cis-Cp*Re(CO)2(Me)I are as follows. Red crystals.
Mp: decomposed over 185 °C. IR (CH2Cl2): νCO 2041 (vs), 1966
(s) cm-1. 1H NMR (CDCl3): δ 1.19 (s, 3H, Me) and 2.00 (s, 15H,
Cp*). 13C{1H} NMR (CDCl3): δ -18.20 (Me), 10.19 (C5Me5),
101.24 (C5Me5), and 204.06 and 207.96 (CO). EIMS (m/z): 520
(M+), 505 (M+ - Me), 492 (M+ - CO). Anal. Found: C, 30.04;
H, 3.34. Calcd for C13H18O2IRe: C, 30.00; H, 3.46.
Exp er im en ta l Section
Cr ysta l Str u ctu r e Deter m in a tion . Dark orange crystals
of trans-Cp*Re(CO)2(Me)I suitable for X-ray crystallography
were obtained from CH2Cl2/hexane (1:1) at -20 °C. A dark
orange polyhedral-shaped crystal of dimensions ca. 0.16 × 0.14
× 0.08 mm was mounted on a glass fiber and used for
crystallographic measurements. The intensity data were col-
lected at 298 K on a Siemens R3/V diffractometer using
graphite-monochromated Mo KR radiation in the 2θ/θ scan
mode with 2 standard reflections monitored every 100 reflec-
tions. A total of 1419 unique reflections were collected, of which
1215 were considered as observed with I > 2σ(I). Lattice
parameters and their esds were derived from the setting angles
of 25 reflections with 5° e 2θ e 40°. The structure was solved
by direct phase determination. The positional and anisotropic
thermal parameters for all non-hydrogen atoms were refined
by full-matrix least-squares cycles. The hydrogen atom posi-
tions were calculated geometrically and were allowed to ride
on their parent carbon atoms with fixed isotropic U values.
The programs used to solve and refine the structure were
SHELXS-97 and SHELXL-97, respectively. Final agreement
factors were R ) 0.035, Rw ) 0.061, and S ) 0.978, on the
basis of all data. Final (∆/σ)max ) 0.001, ∆Fmax ) 0.74, and ∆Fmin
) -0.97 e Å-3 on the final difference Fourier map. The atomic
scattering factors were taken from the SHELXL-97 program.
Selected interatomic distances and bond angles are included
in Table 1. All other data are provided as Supporting Informa-
tion.
Ga s Ch r om a togr a p h y a n d GC/MS Con tr ol. Authentic
samples of benzene, toluene, o-, m-, and p-xylene (dimethyl-
benzene), acetone, chlorobenzene, p-chlorotoluene, and biacetyl
in solution were examined by GC and GC/MS to establish
retention times and mass spectral patterns. These runs were
repeated for the different solvents used in the photolysis
experiments. Similarly, gas analysis was carried out for CO,
N2, CH4, CH3Cl, CH2Cl2, CCl4, benzene-d6, cyclohexane, and
hexane.
Room -Tem p er a tu r e P h otolysis. All the experiments
were conducted in a similar manner. Therefore, a typical
procedure will be described. A solution of trans-Cp*Re(CO)2Me-
(p-tolyl) (1) (20 mg, 0.041 mmol) in cyclohexane (5 mL) was
transferred to a Pyrex Carius tube (fitted with a Teflon valve)
and subjected to three freeze-pump-thaw cycles. The vessel
was then filled with CO (1 atm) and sealed. The solution was
Gen er a l Meth od s. All manipulations were performed
under nitrogen by using standard Schlenk or vacuum line
techniques unless stated otherwise. The complexes trans-
Cp*Re(CO)2MeR (R ) p-tolyl, Ph, Me) were prepared by the
published procedures.1,2 All solvents were freshly distilled
under nitrogen. Pentane, cyclohexane, and hexane were
distilled from sodium wire, diethyl ether was distilled from
sodium and benzophenone, and CCl4 was dried over P4O10 and
distilled from 4A sieves. All reagents were obtained from
Aldrich except where mentioned. The CO was purchased from
Linde, D2 was purchased from Matheson, and D2O (99.9%) was
purchased from Isotec Inc. IR spectra were recorded on a
Bomem Michelson-120 spectrophotometer. The samples were
1
run in solution in a CaF2 cell. H NMR spectra were recorded
on a Bruker WM-400 instrument operating at 400.13 MHz.
1
The H NMR spectra in nondeuterated solvents were carried
out using a standard suppression program from the Bruker
pulse program library. Gas chromatographic analyses were
performed by using a Hewlett-Packard 5880A instrument
equipped with a flame ionization detector and a fused-silica
DB-1 coated column (15 m × 0.25 mm i.d.; 0.25 mm film). Mass
spectra and CG/mass spectra were obtained on Hewlett-
Packard 5985B or G1800A GC/MS instruments equipped with
a DB-1 fused-silica column (30 m × 0.25 mm i.d.; 0.25 mm
film) or a GSQ column (30 m × 0.53 mm i.d.) (J & W Scientific)
with a 100 µL sampling loop at variable pressure, operating
at 70 eV for electron impact (EI). Because of different
instrumental conditions (e.g., column length) quoted retention
times for GC and/or GC/MS runs on different samples are not
necessarily comparable, except where indicated. The masses
are reported for 35Cl and 187Re isotopes where present.
Photochemical reactions were carried out under CO (1 atm)
at room temperature with a water-jacketed 200 W Hanovia
medium-pressure mercury lamp as the UV source. The ir-
radiation was conducted in a Pyrex tube, which was placed
adjacent to the lamp, or in sealed 5 mm NMR tubes.
P r ep a r a tion of cis- a n d tr a n s-Cp *Re(CO)2(Me)I. To a
suspension of yellow MeCu in 10 mL of THF (prepared from
200 mg (0.9 mmol) of CuBr‚SMe2 (Aldrich) and 1.2 mL (1.9
mmol) of MeLi (Aldrich, 1.4 M in diethyl ether) at -23 °C)
was added 150 mg (0.24 mmol) of solid Cp*Re(CO)2I2. The
resulting mixture was stirred at -23 °C for 40 min and then

Rhenium Methyl Complexes
Organometallics, Vol. 18, No. 3, 1999 347
irradiated for approximately 20 min in a water bath at room
temperature. After photolysis the crude sample was analyzed
by IR and 1H NMR spectroscopy, gas chromatography (GC),
and GC/MS.
ether mixture (5:1). A yellow band was collected, and the
solvent was removed under vacuum to give a yellow-orange
1
powder. IR (hexane): νCO 2041, 1966 cm-1. H NMR (CDCl3):
δ 1.70 (s, 15H, Cp*), 2.28 (s, 3H, Me), 6.92 (d, 2H, C6H4Me,
J H-H ) 8.0 Hz), 7.50 (d, 2H, C6H4Me, J H-H ) 8.0 Hz). EIMS
(m/z): 504 (M+), 476 (M+ - CO), 446 (M+ - 2CO - 2H).
Syn th esis of Tolu en e-4-d. A solution of p-tolylmagnesium
bromide was prepared by standard methods.24 A 2 mL sample
was transferred under N2 into a Schlenk tube in a cold water
bath, and D2O was slowly added dropwise until no further
reaction was observed. The product was extracted with hexane
(2 × 2 mL). The GC showed a peak with RT 4.44 min. The
GC/MS showed a peak with RT 3.45 having m/z 93 (M+, 65),
92 (M+ - H, 100), and 91 (M+ - 2H or M+ - D, 25). A toluene
sample was run under the same experimental conditions to
aid in the identification. The GC showed a peak with RT 4.47
min. The GC/MS showed a peak with RT 3.45 having m/z 92
(M+, 55) and 91 (M+ - H, 100).
Syn th esis of Meth a n e-d. Methylmagnesium bromide was
prepared by a standard method.24 A 6 mL sample was
transferred under N2 into a Schlenk tube in a cold water bath
and subjected to three freeze-pump-thaw cycles, and D2O
(99.9%) was slowly added by syringe until no further reaction
was observed. The mass spectrum was run by taking a
headspace sample in a gas syringe and injecting the sample
into the GC/MS. The GC/MS showed a peak with RT 1.37
having m/z 17 (M+, 100), 16 (M+ - H, 61) and 15 (M+ - 2H or
M+ - D, 22).25
Ch a r a cter iza tion of Cp *Re(CO)2(Me)Cl. A solution of
Cp*Re(CO)2Me2 (3; 20 mg, 0.05 mmol) in 3 mL of freshly
distilled CCl4 was degassed by two freeze-pump-thaw cycles
and then irradiated for 10 min at room temperature. During
the photolysis a slow flux of N2 was maintained. The IR
spectrum after the photolysis exhibited carbonyl bands as-
sociated with the starting material 3, Cp*Re(CO)2Cl2, and
Cp*Re(CO)2(Me)Cl. The solvent was removed, and the residual
solid was dissolved in ca. 2 mL of hexane and the solution
transferred to an air-free neutral alumina column prepared
in hexane. The starting material 3 was eluted with hexane,
and a yellow band was eluted with a hexane/diethyl ether
mixture (5:1). The solvent was removed under vacuum, and a
yellow-orange powder was obtained. The IR spectrum of the
yellow-orange product in hexane showed two different species.
One species was identified as trans-Cp*Re(CO)2Cl2 as the
major product. IR (hexane): νCO 2066, 2000 cm-1 1H NMR
.
(CDCl3): δ 1.88 (s, Cp*). EIMS (12 eV; m/z): 448 (M+), 420
(M+ - CO), 392 (M+ - 2CO). The minor species present was
identified as Cp*Re(CO)2(Me)Cl. IR (hexane): νCO 2033, 1960
cm-1. 1H NMR (CDCl3): δ 0.74 (s, 3H, Me), 1.80 (s, 15H, Cp*).
EIMS (12 eV; m/z): 428 (M+), 400 (M+ - CO), 372 (M+ - 2CO).
Syn th esis of Meth a n e-d 2.26 Raney nickel was prepared by
a standard method27 and was washed several times with D2O
to remove any ethanol present. A D2O solution of 1,3-dithiane
was added to the Raney nickel under N2 at room temperature.
The mixture was subjected to three cycles of freeze-pump-
thaw and was slowly warmed to room temperature. D2 gas
was bubbled into the closed system for 3 min. The mass
spectrum was run by taking a headspace sample in a gas
syringe and injecting into the GC/MS. The GC/MS showed a
peak with a RT 1.40 with m/z 18 (M+, 100), 17 (M+ - H, 28)
and 16 (M+ - 2H or M+ - D, 3).25
Ch a r a cter iza tion of Cp *Re(CO)2(p-tolyl)Cl. A solution
of Cp*Re(CO)2Me(p-tolyl) (1; 25 mg, 0.05 mmol) in 3 mL of
freshly distilled CCl4 was degassed twice by freeze-pump-
thaw and then irradiated for 15 min at room temperature.
During the photolysis, a slow flux of N2 was maintained. The
IR spectrum after the photolysis indicated the disappearance
of the methyl tolyl complex 1. The solvent was removed, and
the residue was dissolved in ca. 2 mL of hexane and the
solution transferred to an air-free neutral alumina column
prepared in hexane. The complex was eluted with a hexane/
Ack n ow led gm en t. A.H.K. acknowledges the finan-
cial support of the DGIP of the Universidad Catolica
de Valparaiso and the FONDECYT-Chile through op-
erating grants 125.782/97 and 708/92, respectively. This
work was also supported by the Natural Sciences and
Engineering Research Council of Canada through a
research grant to D.S. We are pleased to acknowledge
the assistance of colleagues at Simon Fraser Univer-
sity: Profs. R. H. Hill and A. Bennet for helpful
discussions and Dr. A. Becalski and Prof. T. N. Bell for
recording the mass spectra of gaseous samples.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal-
lographic data and collection conditions, coordinates and
displacement coefficients for the non-hydrogen atoms, all bond
lengths and interbond angles, anisotropic displacement coef-
ficients, and H-atom coordinates and isotropic displacement
coefficients for Cp*Re(CO)2(Me)I (7 pages). This material is
contained in many libraries on microfiche, immediately follows
this article in the microfilm version of the journal, can be
ordered from the ACS, and can be downloaded from the
Internet; see any current masthead page for ordering informa-
tion and Internet access instructions.
(24) Furniss, B. S.; Hannaford, A. J .; Smith, P. W. G.; Tatchell, A.
R. Practical Organic Chemistry, 5th ed.; Longman Scientific & Techni-
cal: New York, 1989; p 531.
(25) For a discussion of the mass spectra of deuterium-substituted
methanes see: (a) Evans, M. W.; Bauer, N.; Beach, J . Y. J . Chem. Phys.
1946, 14, 701. (b) Stevenson, D. P.; Wagner, C. D. J . Chem. Phys. 1951,
19, 11.
(26) Larock, R. C. Comprehensive Organic Transformations; VCH:
New York, 1989; p 29.
(27) Reference 24, p 450.
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