Direct reaction of photogenerated diarylcarbenes at square-planar rhodium(I)

Article abstract of DOI:10.1039/b407735k

A series of carbene complexes RhCl(CR′₂)(PR ₃)₂ (R = Ph, Toi, Me, R′ = Ph and Tol) have been synthesised through direct reaction of photochemically generated free diarylcarbene with RhCl(CO)(PR₃)₂. This route to carbene complexes demonstrates the reactivity of simple diarylcarbenes towards transition metal complexes. The reactivity of some of these complexes towards H₂, C₂H₄ and Et₃SiH has been investigated.

Full text of DOI:10.1039/b407735k

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F U L L P A P E R
Direct reaction of photogenerated diarylcarbenes at square-planar
rhodium(I)
Simon B. Duckett, Maria-Dolores Gálvez-López, Robin N. Perutz* and Danièle Schott
Department of Chemistry, University of York, York, UK YO10 5DD. E-mail: rnp1@york.ac.uk
Received 21st May 2004, Accepted 2nd July 2004
First published as an Advance Article on the web 28th July 2004
A series of carbene complexes RhCl(CR′2)(PR3)2 (R = Ph, Tol, Me, R′ = Ph and Tol) have been synthesised through
direct reaction of photochemically generated free diarylcarbene with RhCl(CO)(PR3)2. This route to carbene complexes
demonstrates the reactivity of simple diarylcarbenes towards transition metal complexes. The reactivity of some of these
complexes towards H2, C2H4 and Et3SiH has been investigated.
stable carbenes (e.g. N-heterocyclic carbenes)11,12 react with transi-
tion metal centres to form carbene complexes, it is not clear whether
simple diarylcarbenes will do the same.
Introduction
Interest in the use of carbenes as ligands in organometallic chemistry
has developed due to their high reactivity and their applications in
organic synthesis and catalysis.1 Diazoalkanes of general formula
R2CN2 undergo loss of N2 upon photolysis and generate extremely
reactive free carbenes. Photodissociation of dinitrogen may be
achieved either by irradiation into the near UV absorption band
or the visible (n–*) absorption band.2 Flash photolysis studies
have allowed measurement of the rate constants for reaction of free
carbenes with hydrocarbons in solution and have shown that steric
and electronic factors can have an enormous effect on the carbene
reactivity.3–6 In the case of dialkyl carbenes, reaction with solvent is
so rapid that there is little chance for reaction with solutes. Diphe-
nylcarbene decays in pure cyclohexane by pseudo first order kinet-
ics (kobs = 5.7 × 105 s−1) at 300 K to form the diphenylmethyl radical
by hydrogen abstraction from the solvent. It reacts with dissolved
substrates such as alkenes, chloroform and tetrachloromethane in
cyclohexane with second order rate constants of 105 to 107 dm3
mol−1 s−1. Reaction of Ph2C with other solvents containing aliphatic
C–H bonds (e.g. toluene, THF) also yields the diphenyl methyl
radical with similar, or greater, rate constants than for cyclohexane.
Simple diarylcarbenes react competitively with their parent diazo
compounds to yield the azine product R2CNNCR2. In CH3CN as
solvent, this is the principal pathway for decay of Ph2C.7 The elec-
tronic state of the carbene is of great importance in understanding
its reactivity. The reaction with diphenyldiazomethane takes place
both from the initially formed singlet state and the triplet ground
state (Scheme 1). The reaction of the triplet state is made possible
by mixing of the spin states, albeit ca. 700 times more slowly than
the singlet state.8 Triplet dimesityl carbene has a longer lifetime than
diphenylcarbene (ca. 200 s in cyclopentane at room temperature).
Since the energy gap between the triplet and singlet state is large,
this carbene does not react with dimesityldiazomethane, but the
carbene dimerises to form tetramesitylethene.
Recently, Werner and co-workers have shown that rhodium(I)
phosphine carbene complexes are accessible via indirect synthesis.
Treatment of RhCl(C2H4)(SbiPr3)2 with diphenyldiazomethane
Ph2CN2 gave RhCl(CPh2)(SbiPr3)2. Displacement of the stibine
ligand by a phosphine leads to RhCl(CPh2)(PR3)2 (R3 = Ph3, iPr3,
iPr2Ph, iPrPh2 Ph2Me).13–15 This work established a route to rhodium
carbene complexes lacking stabilisation through hetero-atoms.
Our strategy is to generate diarylcarbenes photochemically from
diaryldiazomethane and react the resulting carbene with a transition
metal substrate. If this methodology is to succeed, several condi-
tions need to be fulfilled. First, the transition metal substrate must
not react with diaryldiazomethane directly. Second, the absorption
spectrum of the diaryldiazomethane must not overlap with that
of the complex. Thirdly, the diarylcarbene must not react with
the solvent more rapidly than with the substrate. In view of these
requirements and the established work by Scaiano and Werner, we
began our study with the reaction of photochemically generated
free diphenylcarbene with the rhodium complex RhCl(CO)(PR3)2
(R = Ph, Tol) in benzene.
Results
UV spectra, recorded in C6H6, of the yellow RhCl(CO)(PPh3)2 and
the deep purple Ph2CN2 and Tol2CN2 are shown in Fig. 1. A strong
absorption band is seen at 298 and 364 nm for RhCl(CO)(PPh3)2
and weaker broad bands at 516 nm and 535 nm for the n–* bands
of Ph2CN2 and Tol2CN2, respectively. The wavelength gap between
the absorption bands for the rhodium complex and the diaryl di-
azomethane allows the use of irradiation that targets the diaryldia-
zoalkane selectively. Photochemistry of RhCl(CO)(PR3)2 (R = Ph,
Me, Tol) has been established with an excitation wavelength of 355
nm, but the complexes do not absorb in the region where we irradi-
ate.16–18 As controls, we established that, neither of the two diazoal-
kanes exhibited any thermal reaction with the rhodium complex at
room temperature.
A mixture of Ph2CN2 and RhCl(CO)(PPh3)2 in a C6D6 solution
in an NMR tube equipped with a Young’s tap was irradiated with a
mercury arc equipped with a  > 455 nm filter. The reaction was fol-
lowed by 1H and 31P NMR spectroscopy and by IR spectroscopy. On
photolysis, the deep purple colour of the diaryldiazoalkane gradu-
ally disappeared giving way to a yellow solution. The CO-stretch-
ing band of the rhodium complex also disappeared, but no new
carbonyl species was observed. The 31P NMR spectrum showed that
the doublet due to RhCl(CO)(PPh3)2 at  30.4 (JRhP = 128 Hz) was
replaced by a new doublet at  19.8 (JRhP = 182 Hz). These results
are consistent with formation of Werner’s RhCl(CPh2)(PPh3)2.15
Initial experiments established that a 10-fold excess of diaryldiazo-
methane is required in order to achieve a good yield of the product.
The azine, Ph2CN2CPh2, is also formed by attack of the free carbene
Scheme 1 Reactivity of diphenylcarbene towards diphenyldiazo-
methane.
Exhaustive studies have been completed on the rates of reaction
of carbenes generated photochemically with organic substrates, but
none encompassed the reactivity of such free carbenes towards tran-
sition metal complexes to yield carbene complexes.3–5,9,10 Although
2 7 4 6
D a l t o n T r a n s . , 2 0 0 4 , 2 7 4 6 – 2 7 4 9
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

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Table 1 NMR data recorded in C6D5Cl
Compounds
1H (, mult, J/Hz)
31P{1H} (, mult, J/Hz)
13C{1H} (, mult, J/Hz)
Other nuclei
a,c
RhCl(CO)(PPh3)2
7.87, m, PPh3; 6.96, m, PPh3
7.60, m, PTol3; 7.18, m, PTol3
1.38, br, PMe3
7.80, m, PPh3; 7.06, m, RhCPh2
7.96, m, PPh3
7.97, m, PTol3
7.88, m, PTol3; 6.97, m, PTol3
1.03, br, PMe3
30.4, d, JPRh 128.0
28.0, d, JPRh 126.0
−8.6, d, JPRh 114.4
19.8, d, JPRh 181.7
20.7, d, JPRh 182.2
17.1, d, JPRh 179.8
18.6, d, JPRh 181.0
−28.4, d, JPRh 160.5
−27.3, d, JPRh 161.1
53.2, d, JPRh 196.6
51.5, d, JPRh 195.8
6.04, d, JPRh186.8
36.7, d, JPRh129.9
40.7, d, JPRh128.4
a,c
RhCl(CO)(PTol3)2
RhCl(CO)(PMe3)2
b
a,c
RhCl(CPh2)(PPh3)2
363.0 (br)
a,c
b
RhCl(CTol2)(PPh3)2
RhCl(CPh2)(PTol3)2
RhCl(CTol2)(PTol3)2
RhCl(CPh2)(PMe3)2
RhCl(CTol2)(PMe3)2
b
b
311.4, d, JCRh 44.2
313.3, d, JCRh 57.1
b
1.08, br, PMe3
6.91, m, PPh3
7.96, m, PTol3
a,c
[RhCl(PPh3)2]2
b
[RhCl(PTol3)2]2
b
[RhCl(PMe3)2]2
b
RhCl(C2H4)(PPh3)2
8.00, m, PPh3
−14.6, dt, JHRh 22.7, JHP 28.6
8.04, m, PTol3;
b
RhCl(H)(SiEt3)(PPh3)2
29Si, 69.45, d, JSiRh 37.74 Hz
0.62, q, JHH 8.4, CH2CH3
1.12, t, JHH 8.43 Hz, CH2CH3
−16.4, dt, JHRh 27.9, JHP 36.0
−19.3, dt, JHRh 21.5, JHP 17.5
b
RhCl(H)(SiEt3)(PMe3)2
−1.59, d, JPRh116.2
37.0, d, JPRh(III) 118.3
54.1, d, JPRh(I) 194.1
a,c
(PPh3)2(H)2RhCl2Rh(PPh3)2
Ph2CN2CPh2
7.68, d, br, JHH 7.0
7.31, d, br, JHH 6.4
7.86, d, br, JHH 7.3
7.31, d, br, JHH 6.9
2.10, br, PhMe
Tol2CN2CTol2
a 295 K. b 255 K. c C6D6.
In both cases, the azine R2CN2CR2 (where R = Ph, Tol) was produced
in significant quantities and detected by 1H NMR spectroscopy.
Although RhCl(CR′2)(PPh3)2 was produced for both R′ = Ph
and Tol at room temperature by photolysis of RhCl(CO)(PPh3)2
and R′2CN2 in C6D6, no carbene product was formed when the
same reactions were attempted with RhCl(CO)(PR3)2 (R = Tol
and Me). In both cases an unassigned product was formed with a
broad singlet resonance at  28 in the 31P{1H} NMR spectrum. The
free carbene can also attack at C–H bonds within alkyl phosphine
ligands. In order to improve the selectivity of these reactions, we
needed to conduct the reactions at low temperature. Since C6H6
freezes at 280 K, and toluene or THF are not suitable solvents
for these reactions (see Introduction), C6D5Cl was chosen as a
replacement solvent. The strong C–D bonds should not be attacked
by the carbene. Chlorobenzene freezes at 228 K and the rhodium
complexes have higher solubility than in benzene. Experiments
with RhCl(CO)(PPh3)2 and Ph2CN2 demonstrated the validity
of the method.† Laser photolysis of Ph2CN2 (or Tol2CN2) with
RhCl(CO)(PTol3)2 in C6D5Cl solution in a bath maintained between
243 K and 273 K generated RhCl(CR′2)(PTol3)2 (R′ = Ph or Tol)
quantitatively. The products were characterised by 31P{1H}, 1H and
13C spectroscopy (see Table 1). The same method was applied to
the generation of RhCl(CR′2)(PMe3)2 (R′ = Ph or Tol). A C6D5Cl
solution of RhCl(CO)(PMe3)2 was photolysed at low temperature
(233 to 263 K) in the presence of Ph2CN2 or Tol2CN2 yielding two
novel compounds, RhCl(CPh2)(PMe3)2 and RhCl(CTol2)(PMe3)2,
respectively. The formation of RhCl(CPh2)(PMe3)2 was indicated
by a doublet at  −28.4 (JPRh = 161 Hz) in the 31P{1H} NMR spec-
trum and a 13C carbene resonance at  311.4 (JCRh = 44 Hz) at 255 K.
RhCl(CTol2)(PMe3)2 exhibits a doublet at  −27.3 (JPRh = 161 Hz)
in the 31P{1H} spectrum and a doublet for the 13C carbene nucleus
at  313.3 (JCRh = 57 Hz) (Fig. 2). The formation of the carbene
complexes is summarised in Scheme 2.
Fig. 1 UV spectrum for RhCl(CO)(PPh3)2 ──, Ph2CN2 −−−, and Tol2CN2
−·− in C6H6.
on the diazomethane in solution.8 The experiments showed that it
is possible to produce RhCl(CPh2)(PPh3)2 photochemically, but
it is difficult to achieve complete conversion. Moreover at this
photolysis wavelength, [RhCl(PPh3)2]2 is formed as a secondary
product.Attempts to improve the product distribution by employing
longer wavelength filters with the mercury arc were unsuccessful.
As an alternative method of improving the efficiency of
photolysis, we replaced the mercury arc by a laser source. A C6D6
solution of RhCl(CO)(PPh3)2 and Ph2CN2 was irradiated with
an Ar+ laser at 514.5 nm at a power of 260 mW. After 3 h, the
RhCl(CO)(PPh3)2 is fully converted to RhCl(CPh2)(PPh3)2 which is
the only product detected by 31P NMR spectroscopy (Table 1). The
use of the laser was therefore shown to be of crucial importance in
obtaining efficient and selective conversion to product.
When the RhCl(CR′2)(PMe3)2 complexes (R′ = Ph or Tol) were
left at room temperature under vacuum, decomposition led to the
formation of the known dimeric species [RhCl(PMe3)2]2 (Table 1)
in a similar way to formation of [RhCl(PR3)2]2 (R = Ph or Tol).19
Wilkinson’s dimer [RhCl(PPh3)2]2 was also tested for reactiv-
ity towards a 10-fold excess of Ph2CN2 upon photolysis at room
1
A H–13C HMQC NMR experiment optimised for long range
couplings (295 K, C6D6) showed a correlation between a 1H signal
centred at  7.06 and an unresolved 13C resonance at  363.0. Werner
and co-workers reported a value of  342.0 for the chemical shift of
the 13C carbene for RhCl(CPh2)(PPh3)2 in CD2Cl2.15 We therefore
removed the C6D6 in vacuo, redissolved the solid in CD2Cl2 and
obtained a broad signal at  342 for the 13C carbene resonance in the
1
corresponding H–13C correlation spectrum. The carbene complex
† Neither toluene nor acetonitrile were effective solvents for the production
of carbene complexes.
RhCl(CTol2)(PPh3)2 was synthesised following the same procedure.
D a l t o n T r a n s . , 2 0 0 4 , 2 7 4 6 – 2 7 4 9
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Fig. 2 1H–13C long range HMQC spectrum showing correlation between
the 13C carbene nucleus and the ortho-phenyl protons of the carbene ligands
in RhCl(CTol2)(PMe3)2.
Scheme 3 Pathway for formation of RhCl(CPh2)(PR3)2 and subsequent
reactions.
Scheme 2 Photochemical formation of carbene complexes.
temperature in C6D5Cl. Under the same room temperature reaction
conditions as for RhCl(CO)(PPh3)2, the RhCl(CPh2)(PPh3)2
carbene complex was formed quantitatively. Following this suc-
cess, RhCl(C2H4)(PPh3)2 was also tested for reactivity towards free
diphenylcarbene. After 2 h of irradiation, free ethene was observed
in the 1H NMR spectrum and the initial rhodium complex was com-
pletely converted to RhCl(CPh2)(PPh3)2.
Discussion
Tremendous effort has been made to understand the reactivity of
photochemically generated free carbenes in solution, but it seems
that no study of their reactivity toward transition metal centres has
been attempted. In contrast, the reactivity of stable carbenes is well
documented.24–29 We chose to study the reactivity of square planar
Rh(I) complexes of the type RhCl(L)(PR3)2 (L = CO, C2H4) towards
carbenes anticipating initial formation of a 5-coordinate species. In
reality, CO and ethene were lost during these reactions giving us
a direct route to a group of complexes RhCl(CR′2)(PR3)2 (R = Ph,
Tol, Me; R′ = Ph, Tol) that had been made previously through a
multi-step method.15
The use of laser irradiation allowed us to target the diaryldiazo-
methane selectively with no excitation of the rhodium complexes.
In the next step, the photochemically generated free carbene attacks
the 16-electron metal centre and the ligand L dissociates. Laser
photolysis was required in order to prevent formation of unwanted
rhodium products, especially [Rh(PPh3)2Cl]2, and achieve high
yields. The first set of experiments involving RhCl(CO)(PPh3)2 and
R2CN2 (R = Ph or Tol) in benzene solution at room temperature was
successful, but when the phosphine ligand was switched from PPh3
to PTol3 very little carbene complex RhCl(CR′2)(PTol3)2 (R′ = Ph
or Tol) was formed. With PMe3 in place of PPh3, no carbene com-
plex was observed at all. In view of Scaiano’s5 demonstration that
diphenylcarbene abstracts hydrogen from aliphatic carbon, we
surmise that the carbene abstracts hydrogen from the PTol3 or PMe3
ligand at room temperature. Hydrogen abstraction from the ligand
can be avoided through the use of chlorobenzene as a low tempera-
ture solvent. Under our reaction conditions, the required carbene
complex is the only rhodium-containing product.
The demonstration that free diarylcarbenes react selectively to
form metal carbene complexes is especially remarkable given their
propensity for hydrogen abstraction or reaction with the diazoalkane
precursor. Our initial concentrations of Ph2CN2 and RhCl(CO)(PR3)2
were 0.2 and 0.014 mol dm−3, respectively. We deduce that the rate
constant for reaction of Ph2C with RhCl(CO)(PPh3)2 in C6D6 must
be ca. 107 dm3 mol−1 s−1 or greater (see Scheme 1). In the case of
PTol3 or PMe3 ligands, the rate of hydrogen abstraction exceeds
the rate of carbene formation at room temperature but not at low
temperature. Considering the rate constant for intersystem crossing
of Ph2C and the millimolar concentration of rhodium, we can be
certain that reaction with the rhodium complex involves the triplet
state of Ph2C.
The reactivity of the carbene complexes towards H2, C2H4 and
HSiEt3 was investigated at room temperature. Upon addition
of H2, RhCl(CPh2)(PPh3)2 converts to the known dimer species
H2(PPh3)2Rh(III)(-Cl)2Rh(I)(PPh3)2 (Table 1).20 Addition of
1
atmosphere of C2H4 above a solution of RhCl(CPh2)(PPh3)2 in
an NMR tube yields RhCl(C2H4)(PPh3)2.21,22 Upon addition of
HSiEt3 to a C6D5Cl solution of RhCl(CPh2)(PPh3)2, the complex
RhCl(H)(SiEt3)(PPh3)2 was formed. This complex was charac-
terised at 255 K, where a doublet resonance was observed in the
31P{1H} NMR spectrum at  40.7 (d, JPRh = 128.4 Hz). A hydride
resonance at  −14.6 (dt, JHRh = 22.7 Hz and JPH 28.6 Hz) and 29Si
resonance centred at  69.45 (d, JSiRh = 37.7 Hz) provided further
evidence for this complex. Analogous complexes have been re-
ported by Osakada and coworkers, who studied a series of RhX(H)-
(SiR1 R2 n)(PPh3)2 complexes (X = Cl, I, R1 = OSiMe3, OEt,
n
3 −
R2 = Me).23 During these reactions, formation of the Wilkinson’s
dimer [RhCl(PR3)2]2 is also observed in the early stages of reaction,
but the dimer reacts with the substrates itself, and is no longer pres-
ent when the reaction is complete. Formation of RhCl(C2H4)(PPh3)2
and RhCl(H)(SiEt3)(PPh3)2 is consistent with loss of the carbene li-
gand from RhCl(CPh2)(PPh3)2 to form the 14-electron intermediate
RhCl(PPh3)2 followed by coordination of C2H4 or oxidative addition
of HSiEt3. The 14-electron species RhCl(PR3)2 has been shown to
be in equilibrium with the dimer [RhCl(PR3)2]2.21,22 Thermal con-
version of RhCl(C2H4)(PPh3)2 and RhCl(H)(SiEt3)(PPh3)2 to the
starting material RhCl(CO)(PPh3)2 occurred upon addition of CO
(Scheme 3). The reaction of RhCl(CPh2)(PTol3)2 with H2, C2H4
and Et3SiH followed the same pathways (Scheme 3, NMR data in
Table 1).The reaction of RhCl(CPh2)(PMe3)2 with Et3SiH proceeded
like that for the PPh3 complex, yielding RhCl(H)(SiEt3)(PMe3)2 as
final product (Table 1).
A series of EI GC-MS experiments were run in order to
identify the organic material produced during the reactions of
RhCl(CPh2)(PPh3)2. In the case of HSiEt3, the mass spectrum
shows the formation of Ph2CHSiEt3 (m/z = 282 (50), 253 (14), 183
(30), 115 (100), 87(95) 59(35)) alongside unidentified compounds
of greater molecular mass. In the case of C2H4, the dominant prod-
uct proved to be 1,1-diphenylpropene in agreement with Werner’s
observations.13–15 In addition, NMR resonances due to the azines
(Ar2CN2CAr2) increased in intensity during these reactions.
Theseresults demonstratethatthereactivityoffreediarylcarbenes
towards transition metal centres in solution is sufficient to compete
with other pathways. It should now be possible to extend the prin-
2 7 4 8
D a l t o n T r a n s . , 2 0 0 4 , 2 7 4 6 – 2 7 4 9

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ciples to other metals and other geometries and to measure quantita-
tive kinetics by time-resolved spectroscopy. As a synthetic method,
however, free carbenes will probably be useful only when alterna-
tive methods are unavailable.
at 514.5 nm (Spectra Physics, 260 mW) that was focussed with a
microscope lens and then converted to a vertical stripe of dimen-
sions ca. 2 × 60 mm with a semi-convex cylindrical lens.
Acknowledgements
Conclusion
We thank EPSRC, Thermo Ltd and Fundación Seneca for funding,
and Dr J. N. Moore for access to the laser.
We have shown that it is possible to access a series of rhodium car-
bene complexes of general formula RhCl(CR′2)(PR3)2 (R = Ph, Tol,
Me; R′ = Ph, Tol) via direct attack of a photochemically generated
carbene ligand at a 16-electron rhodium centre. This route offers
a new pathway for the formation of rhodium carbene complexes
from RhCl(CO)(PR3)2, RhCl(C2H4)(PPh3)2 or [RhCl(PPh3)2]2. The
use of C6D5Cl as a low-temperature solvent increased the scope of
the method. The free diarylcarbenes have been shown to react with
the rhodium complexes faster than with the diaryldiazomethane
precursors.
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The diaryldiazomethanes were synthesised from their respec-
tive hydrazones and HgO with a modified literature procedure.34
Diarylbenzophenone hydrazone (4 mmol) and HgO (4.5 mmol) in
petroleum ether (10 mL) (bp 40–60 °C) were placed in a round bot-
tom flask wrapped in aluminium foil equipped with a condenser.
The solution was warmed to 50 °C and left for another 2 h at
50 °C. The colour of the solution changed rapidly from yellow to
deep purple. The solution was cooled and filtered yielding a deep
purple filtrate that was dried in vacuo. The product was obtained
as a purple oil for diphenyldiazomethane, whereas a purple solid
was obtained for the ditolyldiazomethane. Diphenyldiazomethane
was purified by sublimation at room temperature, if necessary.
Ditolyldiazomethane was purified by recrystallisation in the
minimum amount of pentane at −20 °C. The compounds were
protected from light at all stages and stored in the glove-box under
N2 to avoid decomposition. Diphenyldiazomethane was stored
at −30 °C.
Spectroscopic and photochemical methods
NMR spectra were recorded on Bruker DRX400 and DSX400
1
spectrometers. H spectra were referenced to C6D5H at  7.16, or
the para proton of C6D4HCl at  7.16. 13C spectra were referenced
to C6D6 at  128 and 31P spectra relative to external H3PO4. 29Si
NMR were referenced to TMS. [2H5]-chlorobenzene was purchased
from Goss.
26 F. J. Lalor and S. A. O’Neill, J. Organomet. Chem., 2003, 684, 249.
27 H. Rudler, C. Alvarez, B. Denise, A. Parlier and J. Vaissermann, J.
Organomet. Chem., 2003, 684, 105.
28 C. D. Abernethy, R. J. Baker, M. L. Cole, A. J. Davies and C. Jones,
Transition Met. Chem., 2003, 28, 296.
UV/vis spectra were recorded on a Perkin-Elmer Lambda 7
spectrometer in cuvettes fitted with Young’s taps.
29 W. J. Marshall and V. V. Grushin, Organometallics, 2003, 22, 1591.
30 D. Evans, J. A. Osborn and G. Wilkinson, Inorg. Synth., 1990, 28, 79.
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ganometallics, 1993, 12, 1720.
32 G. Giordano and R. H. Crabtree, Inorg. Synth., 1990, 28, 88.
33 B. P. Giri, G. Prasard and K. N. Mehrotra, Can. J. Chem., 1979, 57,
1158.
Samples were photolysed in an NMR tube equipped with a
concentric Young’s tap. Typical quantities of rhodium complex and
diaryldiazomethane in an NMR tube were 2 and 12 mg, respec-
tively. Conventional photolysis was carried out either with a xenon
arc or mercury arc fitted with a water filter and a cut-off filter ( >
455 nm, Schott). Laser photolysis was performed with an Ar+ laser
34 L. I. Smith and K. L. Howard, Org. Synth., 1955, 3, 351.
D a l t o n T r a n s . , 2 0 0 4 , 2 7 4 6 – 2 7 4 9
2 7 4 9