Aliphatic carbon{single bond}carbon bond activation of ketones by rhodium(II) porphyrin radical

Article abstract of DOI:10.1016/j.jorganchem.2006.05.032

Aliphatic carbon{single bond}carbon bond activation of both enolizable and non-enolizable ketones occurred successfully with rhodium(II) porphyrin radical to give rhodium(III) porphyrin alkyls. Added Ph₃P promoted the yields of products.

Full text of DOI:10.1016/j.jorganchem.2006.05.032

Journal of Organometallic Chemistry 691 (2006) 3782–3787
www.elsevier.com/locate/jorganchem
Aliphatic carbonAcarbon bond activation of ketones
by rhodium(II) porphyrin radical
*
Lirong Zhang, Kin Shing Chan
Department of Chemistry, The Chinese University of Hong Kong, Shatin, Hong Kong, China
Received 4 March 2006; received in revised form 8 May 2006; accepted 16 May 2006
Available online 27 May 2006
Abstract
Aliphatic carbonAcarbon bond activation of both enolizable and non-enolizable ketones occurred successfully with rhodium(II)
porphyrin radical to give rhodium(III) porphyrin alkyls. Added Ph3P promoted the yields of products.
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Rhodium(II) porphyrin; Ketones; CarbonAcarbon bond activation
1. Introduction
and C(alkyl)AC(alkynl) [17] bonds have also been
observed. However, the intermolecular activation of the
CalkylACalkyl bond by a transition metal complex in solu-
tion has remained a challenge, most likely due to steric fac-
tors of the shielded carbonAcarbon bonds.
Our group has reported the activation of aliphatic car-
bonAcarbon bonds of nitroxide radicals by 5,10,15,20-
tetra(2,4,6-trimethylphenyl)porphyrinate rhodium(II) [Rh
(tmp)] [18]. We have extended our studies in the activation
of carbonAcarbon bond of less coordinating ketones.
While carbonAcarbon bond activations of carbonyls have
been reported, they are in the category of C(car-
bonyl)AC(alkyl) bonds [19,20]. Hence, in this paper, we
report the successful activation of aliphatic carbonAcarbon
bond alpha to carbonyl groups in ketones by Rh(tmp)
radical.
The activations of inert chemical bonds are of funda-
mental importance in basic chemical research and industrial
applications [1–3]. Activations of aliphatic carbonAcarbon
bond (CCA) are among the most challenging reactions. The
potential applications of new methods to carbonAcarbon
bond activation may provide more energy-efficient routes
in the breakdown of long chain hydrocarbons such as the
catalytic cracking of fuels [4], depolymerization of polymer
waste [5], and enzymatic degradation of hydrocarbons for
methane production [6].
Several reported examples of CCA by transition metal
require extra driving force to realize the activation, includ-
ing ring strain relief [7–9], aromatization [10,11], the pres-
ence of an activating functionality [12,13] or in chelation
assisted system [14], etc. The activation of unstrained ali-
phatic carbonAcarbon bonds is very challenging [15]. The
difficulty is in the more facile activation of sterically more
accessible carbonAhydrogen over carbonAcarbon bonds.
The intramolecular activations of C(aryl)AC(alkyl) [16]
2. Results and discussion
The metal centered radical RhII(tmp) [21] (2) was gener-
ated in about 80% yield by the photolytic cleavage of
Rh(tmp)CH3 (1) in benzene at 6–10 °C for ꢀ8 h (Eq. (1);
see Fig. 1):
*
Corresponding author. Tel.: +86 852 26096376; fax: +86 852
C6H6; hm; 6–10 ꢁC
RhðtmpÞCH3
!
RhðtmpÞ
ð1Þ
26035057.
8 h; N2
1
2
E-mail address: ksc@cuhk.edu.hk (K.S. Chan).
0022-328X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.05.032

L. Zhang, K.S. Chan / Journal of Organometallic Chemistry 691 (2006) 3782–3787
3783
bonyl)AC(methyl) bond (BDEC–C = 85 kcalmolꢂ1) [22] is
lower than that of C(carbonyl)Ahydrogen bond (BDEC–H
= 96 kcalmolꢂ1) [22], no C(carbonyl)AC(methyl) bond acti-
vation occurred, therefore, kinetically favored CHA was
more facile.
N
For the case of propiophenone (3b), the C(sp3)AC(sp3)
activation product Rh(tmp)CH3 (1), and CHA product
Rh(tmp)CH2CH2C(O)C6H5 (5) were observed at 130 °C.
N
Rh
N
N
At
a
lower reaction temperature of 100 °C, no
Rh(tmp)CH3 was formed, even the reaction time was
lengthened to 5 days (Table 1, entries 2–4). The CCA
was proposed to occur via hemolytic bimolecular substitu-
tion (SH2) mechanism (Eq. (3)) [23,24]. However no
Rh(tmp)CH2C(O)Ph was observed, it may due to the insta-
bility of radical A:
Rh(tmp)
Fig. 1. Structure of Rh(tmp).
2.1. Reactions of Rh(tmp) and enoliazble ketones under
solvent-free conditions
O
O
Rh(tmp)
+
+
Rh(tmp)CH3
ð3Þ
RhðtmpÞ þketone solvent-free; Ph P
!
products
ð2Þ
3
A
temp: time
2
When diethyl ketone (3c) was used, multiple activation
products were observed. C(sp3)AC(sp3) activation product,
Rh(tmp)CH3 (1), C(sp2)AC(sp3) activation product
Rh(tmp)C(O)CH2CH3 (6), and CHA product Rh(tmp)
CH2CH2C(O)CH2CH3 (7) were formed (Table 1, entry
5). The lower bond energy of a-C(carbonyl)AC(ethyl)
First, the ketones containing a-protons were examined
(Table 1). When Rh(tmp) was reacted with acetophenone
(3a) at 130 °C for 1 day under solvent-free conditions in
the presence of 1 equiv. of Ph3P, a mixture products were
observed, and a carbonAhydrogen bond activation prod-
uct Rh(tmp)CH2COPh (4) was tentatively identified (Table
1, entry 1). However this compound proved to be unstable
to be purified by chromatography even for a sample pre-
pared by independent synthesis from Rh(tmp) anion and
ClCH2COph. Although the bond energy of a-C(car-
bond (BDEC–C = 82 kcalmolꢂ1
) than a-C(methyl)AC-
(methyl) bond (BDEC–C = 86 kcalmolꢂ1) [22] is consistent
with the higher yield of 6 than 1. Furthermore, the steri-
cally more accessible carbonyl carbon may favor the for-
mation of 6.
Table 1
The reactions of Rh(tmp) (2) and enolizable ketones
Entry
1
Substrate
Temperature (°C)
Time (d)
1
Rh(tmp)R (Yield [%]),a R =
CCA
CHA
130
Complex mixture pf productsb
O
3a
2
3
4
130
100
100
1
2
5
CH3 1 (3)
CH2CH2COPh 5 (26)
CH2CH2COPh 5 (trace)
CH2CH2COPh 5 (11)
O
3b
5
100
2
CH3 1 (6)
COC2H5 6 (11)
CH2CH2COC2H5 7 (33)
O
3c
a
% Yield was based on 80% of Rh(tmp) generated through photolysis.
Rh(tmp)CH2COPh was tentatively identified.
b

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L. Zhang, K.S. Chan / Journal of Organometallic Chemistry 691 (2006) 3782–3787
The enolizable ketones in Table 1 exhibit minor CCA
product Rh(tmp)CH3 was obtained in 18%, with nearly
equal efficiency as that in solvent-free conditions. So, sub-
sequent studies were carried out in benzene solution.
Rh(tmp) (2) also successfully activated carbonAcarbon
bond of 2,2,4,4-tetramethyl-pentan-3-one (3d) in benzene
solution to produce Rh(tmp)CH3 (1) as the CCA product.
To improve the yield, the effect of added ligand was
examined. Rh(II) radicals typically react as metalloradicals
with a variety of ligands (L = r donor and p acceptor), e.g.
triphenylphosphine and pyridine, to form adducts, which
are more electron-rich and reactive [31]. Ligand (triphenyl-
phosphine and pyridine) effects were therefore investigated.
To our delight, the CCA product yield was increased to
31% when triphenylphosphine was used as the ligand
(Table 2, entry 2). Addition of pyridine ligand, however,
did not promote CCA. It has been known that pyridine
ligand induces the disproportionation of Rh(tmp) to yield
[pyRhIII(tmp)]+ and [pyRhI(tmp)]ꢂ, [32,33]; therefore,
and major CHA. Only in the case of 3b, an increase of reac-
tion temperature favored CCA slightly but was not very
efficient. The formation of carbonAhydrogen bond activa-
tion products suggested that Rh(tmp) might react with the
enol tautomers [25]. To prevent this competitive CHA,
non-enolizable carbonyls were then examined.
2.2. Reactions of Rh(tmp) and non-enolizable ketones
ligand
RhðtmpÞ þketone
!
RhðtmpÞR
ð4Þ
benzene 130 ꢁC; time
2
A series of non-enolizable ketones were examined. The
solvent-free conditions was first examined using 3f. In sol-
vent-free conditions, 3f (ꢀ680 equiv.) reacted with Rh(tmp)
at 130 °C in 1 day to give the CCA produt Rh(tmp)CH3 in
16%. When 5 equiv. of 3f was used and the reaction was
carried out in benzene solvent, C(sp3)AC(sp3) activation
Table 2
CCA results between Rh(tmp) and ketones
Entry
Ketonea
Ligand
Time (d)
1
Product (Yield [%]d)
O
1
2
3
3d
None
Ph3Pb
pyc
Rh(tmp)CH3 1 (20)
Rh(tmp)CH3 1 (31)
Rh(tmp)CH3 1 (22)
O
4
5
6
7
8
3e
3f
Ph3Pb
Ph3Pb
Ph3Pb
Ph3Pb
Ph3Pb
3
1
1
1
3
Rh(tmp)CH3 1(trace)
Rh(tmp)CH3 1 (18, 16e)
Rh(tmp)CH3 1 (24)
Rh(tmp)CH3 1 (14)
No reaction
O
Ph
O
Ph
3g [26]
Ph
O O
3h [27]
3i [28]
Ph
Ph
Ph
O O
Ph
9
3j [29]
Ph3Pb
Ph3Pb
1
1
Rh(tmp)CH3 1 (25)
Rh(tmp)CH3 1 (30)
O
O
10
3k [30]
O
O
Ph3Pb
3
Rh(tmp)Bn 10 (6)
Bn
Bn
11
3l [30]
O
a
5 equiv. of ketone added to Rh(tmp).
1 equiv. of Ph3P based on Rh(tmp).
2 equiv. of pyridine based on Rh(tmp).
% Yield was based on 80% of Rh(tmp) generated through photolysis.
Under solvent-free conditions.
b
c
d
e

L. Zhang, K.S. Chan / Journal of Organometallic Chemistry 691 (2006) 3782–3787
3785
pyridine is not good promoter. Hence, triphenylphosphine
was chosen as the promoter ligand for the CCA of Rh(tmp)
and ketones.
Though, the acyclic ketone 3d (BDE(a(c)-a(methyl)) =
84 kcalmolꢂ1) [22] underwent successful carbonAcarbon
bond activation with Rh(tmp) (Table 2, entry 2) to give
Rh(tmp)CH3 in 31%, the cyclic ketone 2,2,5,5-tetra-
methyl-cyclopentanone (3e; entry 4) almost did not react.
It suggests that a cyclic substrate may be less reactive than
an acyclic one.
but not from incomplete photolysis, the progress of the
reaction was also monitored by H NMR in a sealed tube
1
experiment. Mixture of solution of Rh(tmp), 1 equiv. of
Ph3P and 10 equiv. of 3d in C6D6 was placed in a NMR
tube, then sealed under vacuo and was heated at 130 °C
for 30 h. Initially, no signal due to Rh(tmp)CH3 was
observed. Then, characteristic peak of RhACH3 (doublet,
2JRh–H = 3.0 Hz, d: ꢂ5.25 ppm) appeared after heating.
Therefore, Rh(tmp)CH3 was a true product of CCA. Fur-
thermore, the formation of Rh(tmp)Bn further supported
that CCA had occurred.
2,2-Dimethyl-1-phenyl-propan-1-one (3f; entry 5) and 2-
methyl-1, 2-diphenyl-propen-1-one (3g; entry 6) were acti-
vated with Rh(tmp) to produce Rh(tmp)CH3 in 18% and
24% yield, respectively. Only a slight increase of activity
was observed by changing a methyl to phenyl substituent
adjacent to the site of bond cleavage. We rationalize that
if a co-product carbon-centered radical is formed [18],
slight stabilization is gained through resonance with the
phenyl ring to account for the high yield.
In the hope of stronger ketone binding to Rh(tmp) to
give higher yield of product, 1,3-dicarbonyl substrates were
examined. However 2,2-dimethyl-1,3-diphenyl-propane-
1,3-dione (3h; Table 2, entry 7) only gave Rh(tmp)CH3
(1) in 14% yield. No improvement was made over 3f. It
might be due to the increased steric hindrance of benzoyl
over methyl group in blocking the access of carbonAcar-
bon bond to the metal center of Rh(tmp). When 1,1-dib-
enzoylcyclopentane (3i; entry 8) was used as the
substrate, no CCA occurred even after heating at 130 °C
for 3 days. Rh(tmp) may not be reactive enough to open
the ring. Alternatively, the ring opening occurs but is
reversible and unfavorable due to the instability of the car-
bon centered radical formed. Facile reverse reaction gives
back the starting materials likely via homolytic bimolecular
substitution (Eq. (5)) [34]:
3. Summary
In conclusion, enolizable ketones underwent car-
bonAcarbon bond and carbon hydrogen bond activation
with Rh(tmp) with low selectivity to give Rh(tmp)CH3
and Rh(tmp) acyl. Non-enolizable ketones underwent
selective a-carbonyl CCA with Rh(tmp) to give
Rh(tmp)CH3 and Rh(tmp)Bn.
4. Experimental
All materials were obtained from commercial suppliers
and used without further purification unless otherwise
specified. Benzene was distilled from sodium. Benzene-d6
was vacuum distilled from sodium, degassed thrice by
freeze–thaw–pump cycle and store in a Teflon scrawhead
stoppered flask. Pyridine was distilled over KOH under
N2. Triphenylphosphine was recrystallized from EtOH.
Thin layer chromatography was performed on Merck
pre-coated silica gel 60 F254 plates. Silica gel (Merck, 70–
230 and 230–400 mesh) or neutral aluminum oxide
(Merck, activity I, 70–230 mesh) was used for column
chromatography.
Ph Ph
O O
O
O
1H NMR spectra were recorded on a Bruker DPX 300
Rh(tmp)
+
Ph
¨
ð5Þ
(300 MHz) spectrometer. Spectra were referenced inter-
nally to the residual proton resonance in CDCl3 (d
7.26 ppm), tetramethylsilane (TMS, d 0.00 ppm), tetraki-
strimethylsilysilane ((TMS)4Si, d 0.00 ppm) or with C6D6
(d 7.15 ppm) as the internal standard. Chemical shifts (d)
were reported as part per million (ppm) in d scale downfield
from TMS or (TMS)4Si.
(pmt)Rh
When 1,1,3,3-tetramethyl-indan-2-one (3j; entry 9)
reacted with Rh(tmp), 25% yield of Rh(tmp)CH3 (1) was
produced. However, 2,2-dimethyl-indan-1,3-dione (3k;
entry 10) was more high-yielding. We speculate that 3k
gives a more stable co-product radical, which is symmetri-
cal and more resonance-stabilized through conjugation
with the two cabonyls.
Even benzyl-methine carbonAcarbon bond activation
was observed in case of 2,2-dibenzyl-indan-1,3-dione (3l;
entry 11), to give Rh(tmp)Bn (10), though in a lower yield
of 6% after 130 °C for 3 days. Presumably, the lower yield
is due to the steric hindrance of an adjacent benzyl group.
4.1. Preparation of 5,10,15,20-tetramesitylporphyrinatorho-
dium(II) [Rh(tmp)] (2) [21]
To a Teflon screwheaded stoppered flask, Rh(tmp)CH3
[21] (1) (10.0 mg, 0.011 mmol) was charged and dissolved
in C6H6 (4.0 mL) to obtain a clear orange solution. The
reaction mixture was then degassed by the freeze–pump–
thaw method (3 cycles) and refilled with N2. The reaction
mixture was irradiated under a 400 W Hg-lamp at 6–
10 °C until all the starting material was consumed as indi-
cated by TLC (ꢀ8 h) to give Rh(tmp) (2).
2.3. Sealed tube experiment
The product yields of Rh(tmp) alkyls were low. To
ascertain that Rh(tmp)CH3 was formed from the CCA

3786
L. Zhang, K.S. Chan / Journal of Organometallic Chemistry 691 (2006) 3782–3787
4.2. Reaction of Rh(tmp) (2) and acetophenone (3a) under
solvent-free conditions
Diethyl ketone (1.0 mL, 9.46 mmol) which was degassed
by the freeze–pump–thaw method (3 cycles) was added
via a micro-syringe to Rh(tmp) (0.0088 mmol) and the
reaction mixture was stirred at 100 °C for 2 days under
N2 in the absence of light. The crude product was purified
by chromatography on silica gel using a solvent mixture
hexane:CH2Cl2 (10:1) to hexane:CH2Cl2 (3:1) as the gradi-
ent eluent. Red solids of Rh(tmp)CH3 (1) (0.5 mg,
0.0006 mmol, 6%), and Rh(tmp)COCH2CH3 (6) (0.9 mg,
0.0009 mmol, 11%) were obtained; Rf = 0.14 (hex-
Triphenylphosphine (0.1 mL, 0.01 mmol, 0.1 M in ben-
zene) was added to the benzene solution of Rh(tmp) at
r.t. The mixture was then stirred for 0.5 h, and subse-
quently the solvent was removed. Acetophenone (1.0 mL,
8.57 mmol) which was degassed by the freeze–pump–thaw
method (3 cycles), was added via a micro-syringe to
Rh(tmp) (0.0088 mmol) and the reaction mixture was stir-
red at 130 °C for 1 day under N2 in the absence of light. A
complex mixture of products were formed by TLC analy-
1
ane:CH2Cl2 = 5:1); H NMR (C6D6, 300 MHz) d ꢂ2.73
(q, 3H, J1 = 7.5 Hz, J2 = 7.2 Hz), ꢂ1.53 (t, 3H,
J = 7.2 Hz), 1.84 (s, 12H), 2.14 (s, 12H), 2.44 (s, 12H),
7.09 (s, 4H), 7.19 (s, 4H), 8.79 (s, 8H). HRMS (FAB):
Calcd. for (C59H57N4ORh)+: m/z 940.5123. Found: m/z
940.5130. IR (KBr, cmꢂ1) m(C@O) 1600. Another orange
solid of Rh(tmp)CH2CH2COCH2CH3 (7) (2.8 mg,
0.0029 mmol, 33%) was produced. Rf = 0.42 (hex-
1
sis. From the H NMR spectrum of the crude reaction
mixture, the methylene signal of the complex Rh(tmp)-
CH2COC6H5 (4) was observed as a doublet at ꢂ3.88 ppm
(J = 4.2 Hz). Other signals could not be assigned due to
overlapping peaks. The compound was unstable towards
chromatography for purification. HRMS (FAB) verified
the formation of Rh(tmp)CH2COC6H5. HRMS (FAB):
Calcd. for (C64H59N4ORh)+: m/z 1002.3738. Found: m/z
1002.3696.
1
ane:CH2Cl2 = 1:1); H NMR (CDCl3, 300 MHz) d ꢂ4.74
(td, 2H, J = 7.5 Hz, JRh–H = 3.0 Hz), ꢂ3.35 (t, 2H,
J = 9.0 Hz), ꢂ0.15 (t, 3H, J = 7.5 Hz), 0.40 (q, 2H,
J = 7.5 Hz), 2.04 (s, 24H), 2.61 (s, 12H), 8.50 (s, 8H).
HRMS (FAB): Calcd. for (C61H61N4ORh)+: m/z
968.3895. Found: m/z 968.3883. IR (KBr, cmꢂ1) m(C@O)
1600. Some unidentified products were observed.
4.3. Reaction of Rh(tmp) (2) and propiophenone (3b) under
solvent-free conditions
Triphenylphosphine (0.1 mL, 0.01 mmol, 0.1 M in ben-
zene) was added to the solution of Rh(tmp) at r.t. The mix-
ture was stirred for 0.5 h, then the solvent was removed.
Propiophenone (1.0 mL, 6.94 mmol) which was degassed
by the freeze–pump–thaw method (3 cycles) was added
via a micro-syringe to Rh(tmp) (0.0088 mmol) and the
reaction mixture was stirred at 130 °C for 1 day under N2
in the absence of light. The crude product was purified
by chromatography on silica gel using a solvent mixture
hexane:CH2Cl2 (10:1) to hexane:CH2Cl2 (1:1) as the gradi-
ent eluent. Red solids of Rh(tmp)CH3 (1) (0.2 mg,
0.0003 mmol, 3%) Rf = 0.57 (hexane:CH2Cl2 = 5:1); 1H
4.5. Reactions of [Rh(tmp)] (2) and ketones 3d–3k with
Ph3P added
Triphenylphosphine (0.1 mL, 0.01 mmol, 0.1 M in
C6H6, 1 equiv.) solution (2 lL, 0.02 mmol, 2 equiv.) was
added to the solution of [Rh(tmp)] (2) at r.t. Degassed
ketone solution (5 equiv.) in benzene was then added,
and the mixture was heated at 130 °C under N2 in the
absence of light. Pure products were obtained after purifi-
cation on silica gel column chromatography.
2
NMR (C6D6, 300 MHz) d ꢂ5.26 (d, 3H, JRhH = 2.7 Hz),
4.6. Reaction of Rh(tmp) (2) and 2,2-dibenzyl-indan-1,3-
dione (3l) with Ph3P added
1.72 (s, 12H), 2.25 (s, 12H), 2.43(s, 12H), 7.07 (s, 4H),
7.20 (s, 4H), 8.75 (s, 8H), and Rh(tmp)CH2CH2COC6H5
(5) (2.3 mg, 0.0023 mmol, 26%) were obtained. Rf = 0.45
(hexane:CH2Cl2 = 1:1); 1H NMR (CDCl3, 300 MHz) d
ꢂ4.63 (td, 2H, J1 = 9.6 Hz, JRh–H = 3.0 Hz), ꢂ2.85 (t,
2H, J = 9.6 Hz), 2.01 (s, 12H), 2.04 (s, 12H), 2.61 (s,
12H), 5.75 (d, 2H, J = 7.6 Hz), 6.75 (t, 2H, J = 7.9 Hz),
7.03 (t, 1H, J = 7.7 Hz), 7.21 (s, 8H), 8.63 (s, 8H). HRMS
(FAB): Calcd. for (C65H61N4ORh)+: m/z 1016.3895.
Found: m/z 1016.3924. IR (KBr, cmꢂ1) m(C@O) 1600.
Some unidentified products were observed.
Triphenylphosphine (0.1 mL, 0.01 mmol, 0.1 M in ben-
zene) was added to the solution of Rh(tmp) at r.t..
Degassed (3i) solution (5 equiv.) in benzene was then
added, and the mixture was heated at 130 °C for 3 days
under N2 in the absence of light. The crude product
was purified by chromatography on silica gel to give a
red solid of Rh(tmp)Bn (10) (0.5 mg, 0.0005 mmol, 6%).
Rf = 0.54 (hexane:CH2Cl2 = 5:1); 1H NMR (300 MHz,
C6D6) d ꢂ3.15 (d, 2H, J = 3.9 Hz), 1.79 (s, 12H), 1.93
(s, 12H), 2.45 (s, 12H), 3.66 (d, 2H, J = 7.2 Hz), 5.76 (t,
2H, J = 7.8 Hz), 6.22 (t, 1H, J = 7.8 Hz), 8.80 (s, 8H).
13C NMR (C6D6, 75 MHz) 14.29, 21.93, 22.45, 22.80,
120.00, 123.56, 125.44, 126.66, 127.80, 127.86, 130.82,
137.53, 138.58, 138.73, 139.57, 142.76. HRMS (FAB):
Calcd. for (C63H59N4Rh)+: m/z 974.3789. Found: m/z
974.3806.
4.4. Reaction of Rh(tmp) (2) and diethyl ketone (3c) under
solvent-free conditions
Triphenylphosphine (0.1 mL, 0.01 mmol, 0.1 M in ben-
zene) was added to the solution of Rh(tmp) at r.t. The mix-
ture was stirred for 0.5 h, then the solvent was removed.

L. Zhang, K.S. Chan / Journal of Organometallic Chemistry 691 (2006) 3782–3787
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Triphenylphosphine (0.01 mL, 0.001 mmol, 0.1 M in
C6D6, 1 equiv.) was added to the solution of [Rh(tmp)]
(2) in a NMR tube at r.t. Degassed ketone solution (10
equiv.) in C6D6 was then added, then the NMR tube was
Hame-sealed under vacuum. The initial 1H NMR spectrum
was taken. No Rh(tmp)CH3 was observed. After the mix-
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of light. Rh(tmp)CH3 signal was observed.
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Acknowledgment
We thank the Research Grants Council of Hong Kong
of the SAR of China for financial support (No. 400203).
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