Scope and mechanism of carbonyl carbon and α-carbon bond cleavage of ketones by Iridium(III) porphyrin complexes

Article abstract of DOI:10.1021/om200026y

Chemoselective carbonyl carbon and α-carbon bond activation (CCA) of ketones (RCOR) was successfully achieved with various iridium(III) tetrakis-4-tolylporphyrinato complexes Ir(ttp)X (X = (BF₄)(CO), Cl(CO), and Me) to give the corresponding Ir(ttp)COR (R = Ar, Me, or Et) and Ir(ttp)R (R = Me or Et) complexes. Ir(ttp)(BF₄)(CO) exhibited the highest reactivity toward CCA, as it possesses a higher Lewis acidity in catalyzing the aldol condensation of ketones to give water, which hydrolyzes the kinetic products, C-H bond activation (CHA) complexes, into the proposed Ir(ttp)OH for a subsequent CCA process. The CCA step is nonregioselective in giving both Ir(ttp)R and Ir(ttp)COR. However, Ir(ttp)R was kinetically less stable toward hydrolysis to give Ir(ttp)OH. Thus, only Ir(ttp)COR was observed as the sole CCA product.

Full text of DOI:10.1021/om200026y

ARTICLE
pubs.acs.org/Organometallics
Scope and Mechanism of Carbonyl Carbon and r-Carbon Bond
Cleavage of Ketones by Iridium(III) Porphyrin Complexes
Bao Zhu Li, Hong Sang Fung, Xu Song, and Kin Shing Chan*
Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, People’s Republic of China
S Supporting Information
b
ABSTRACT: Chemoselective carbonyl carbon and R-carbon bond
activation (CCA) of ketones (RCOR0) was successfully achieved with
various iridium(III) tetrakis-4-tolylporphyrinato complexes Ir(ttp)X
(X = (BF4)(CO), Cl(CO), and Me) to give the corresponding Ir(ttp)COR (R = Ar, Me, or Et) and Ir(ttp)R0 (R0 = Me or Et)
complexes. Ir(ttp)(BF4)(CO) exhibited the highest reactivity toward CCA, as it possesses a higher Lewis acidity in catalyzing the
aldol condensation of ketones to give water, which hydrolyzes the kinetic products, C-H bond activation (CHA) complexes, into
the proposed Ir(ttp)OH for a subsequent CCA process. The CCA step is nonregioselective in giving both Ir(ttp)R0 and
Ir(ttp)COR. However, Ir(ttp)R0 was kinetically less stable toward hydrolysis to give Ir(ttp)OH. Thus, only Ir(ttp)COR was
observed as the sole CCA product.
’ INTRODUCTION
more reactive.5 Mechanistic studies revealed that Rh(ttp)OH was
the intermediate in cleaving the C(dO)-C(R) bonds.
Carbon-carbon bond activation (CCA) of carbonyl com-
pounds at the C(dO)-C(R) bond with low-valent transition
metal complexes has been applied in organic synthesis by
utilizing ring-strained1 and chelation-assisted systems.2 These
applications have furnished valuable organic intermediates, and
mechanistic studies suggested that oxidative addition (OA) is the
commonly accepted mechanism.1,2
For high-valent Rh(III) and Ir(III) complexes, OA is challeng-
ing due to the much less accessible M(V) intermediate.3 OA is
even more difficult for group 9 metalloporphyrins, as it involves
the sterically demanding intermediate with three substituents
located in a cis-manner to the porphyrin plane.
We have thus undertaken systematic studies of the CCA of
various ketones (RCOR0) with iridium porphyrin complexes
bearing different counteranions to define the scopes and the
reactivties. Furthermore, mechanistic studies revealed that the
CCAstep is chemo- but not regioselective, givingboth Ir(ttp)COR
and Ir(ttp)R0. The formation of Ir(ttp)COR as the only or major
product is due to its higher stability toward hydrolysis than
Ir(ttp)R0. We have thus proposed that Ir(ttp)OH is the more
likely intermediate for CCA. We now report our findings.
’ RESULTS AND DISCUSSION
Recently, we have communicated that high-valent iridium(III)
tetrakis-4-tolylporphyrinato carbonyl chloride (Ir(ttp)Cl(CO))
cleaved the carbonyl carbon and R-carbon bond of acetophenones
(ArCOMe) to give the corresponding iridium porphyrin acyl
complexes (Ir(ttp)COAr) (eq 1).4 Mechanistic studies suggested
that Ir(ttp)Cl(CO) reacted with acetophenonesto givethe R- and
aromatic carbon-hydrogen bond activation (CHA) products as
the kinetic products. Then the CHA products further underwent
hydrolysis with water, formed from the iridium porphyrin-cata-
lyzed aldol condensation of ketones, to give the proposed inter-
mediates of Ir(ttp)OH and/or Ir(ttp)H. Finally, Ir(ttp)OH and/
or Ir(ttp)H likely underwent σ-bond metathesis in the CCA
process (Scheme 1). An intriguing reaction feature is the sole
formation of Ir(ttp)COAr as the only CCA product, suggesting
the apparent and surprisingly highly regioselective bond cleavage.
Ir(ttp) X-Anion Effect on CCA. Initially, the chemoselective
C(dO)-C(R) bond activation of ketone was studied by heating
Ir(ttp)X (X = (BF4)(CO), 1b, Cl(CO), 1a, Me, 1c) in aceto-
phenone 2b at 200 °C, respectively (Table 1 and eq 2). The
most Lewis acidic, Ir(ttp)(BF4)(CO) 1b, reacted with acetophe-
none 2b to give the sole CCA product of Ir(ttp)COPh 3b in 58%
yield together with the aromatic carbon-hydrogen bond activa-
tion (ArCHA) products of Ir(ttp)(para- and meta-COMe-
C6H4) 4b,c in trace amount (<5%) in the shortest reaction time
of 2 days (Table 1, entry 1). Similarly, the more electron-rich
Ir(ttp)Cl(CO) 1a and Ir(ttp)Me 1c cleaved the C(dO)-C(R)
bond of acetophenone 2b to give Ir(ttp)COPh 3b in 71% and
80% yields in longer reaction times of 20 days4 and 26 days,
respectively (Table 1, entries 2 and 3).
To identify the reaction intermediates, the reaction of acet-
ophenone 2b with Ir(ttp)(BF4)(CO) 1b was then conducted in a
shorter time. In 4 h, Ir(ttp)(BF4)(CO) 1b reacted with acet-
ophenone 2b to give a mixture of CHA products of 4a-c in <5%
(4a), 13% (4b), and 26% (4c) yields, in addition to a 13% yield of
oC
IrðttpÞClðCOÞ þ ArCOMe N , 200f IrðttpÞCOAr
2
2a-d
12 - 20 d
3a-d 71 - 79%
1a
ð1Þ
Ar ¼ p-F-C6H4, Ph, p-Me-C6H4, p-OMe-C6H4
Recently, we have reported the CCA of various unstrained
ketones, with Rh(ttp)Me with the bulkier isopropyl ketones being
Received: January 12, 2011
Published: March 09, 2011
r
2011 American Chemical Society
1984
dx.doi.org/10.1021/om200026y Organometallics 2011, 30, 1984–1990
|

Organometallics
ARTICLE
Scheme 1. Previous Proposed Pathway for the CCA of
Acetophenone with Ir(ttp)X (X = OH, H) via σ-Bond
Metathesis4
Table 2. para-Substituent Effect on the CCA of Acetophe-
nones by Ir(ttp)X
Table 1. CCA of Acetophenone by Ir(ttp)X
oC
IrðttpÞX þ PhCOMe N , 200f IrðttpÞCOPh
ð2Þ
2
time
2b
1a-c
3b
entry
X
time/d
yield 3b/%
1a
2b
3
(BF4)(CO), 1b
Cl(CO), 1a
Me, 1c
2
20
26
58
71
80
a 4b and 4c were observed by TLC analysis in trace amount (<5%). b 4b
and 4c were isolated in 4% and 8% yield, respectively. See ref 4 for
details.
Ir(ttp)COPh 3b. Ir(ttp)Me 1c, resulting from nonregioselective
CCA, was also observed in trace amount (<5%) (eq 3). No
Ir(ttp)Ph or Ir(ttp)COMe was observed from the C(dO)-
C(Ph) cleavage probably due to the stronger C(dO)-C(Ph)
bond (∼94.7 kcal mol-1)6 over the C(dO)-C(Me) bond (85.0
kcal mol-1)6 and the sterically more hindered phenyl group. This
result suggests that the R-carbon-hydrogen bond activation (R-
CHA) product (Ir(ttp)CH2COPh, 4a), ArCHA products
(Ir(ttp)(para- and meta-COMe-C6H4), 4b,c), and Ir(ttp)Me
1c are possible intermediates to afford Ir(ttp)COPh 3b.
a See ref 4 for details.
to cleave the C(dO)-C(R) bond of ketones, the same as in the
rhodium porphyrin complex.5 Further evidence for the inter-
mediacy of Ir(ttp)OH is discussed in the reaction between
Ir(ttp)(BF4)(CO) 1b and acetone 2e (eq 12).
Therefore, Ir(ttp)CH2COPh 4a, Ir(ttp)Ph 4b0 (as an ArCHA
complex analogue), and Ir(ttp)Me 1c were independently
heated in acetophenone 2b at 200 °C. Ir(ttp)Ph 4b0 reacted
poorly to give Ir(ttp)COPh 3b in <5% yield with 88% recovery
yield even upon prolonged heating for 28 days (eq 4).4 Trans-
formations of Ir(ttp)CH2COPh 4a to ArCHA complexes 4b,c
and Ir(ttp)Me 1c to the R-CHA complex 4a as the major
products were observed in a shorter reaction time of 15 and
5 days (eqs 54 and 6), respectively. These results suggest none of
Ir(ttp)CH2COPh 4a, Ir(ttp)(para- and meta-COMe-C6H4) 4b,
c, and Ir(ttp)Me 1c directly reacted with acetophenone 2b to
give Ir(ttp)COPh 3b, as these reaction are much too slow
compared to that of Ir(ttp)(BF4)(CO) (eq 2). It is believed that
Ir(ttp)CH2COPh 4a, Ir(ttp)(para- and meta-COMe-C6H4) 4b,
c, and Ir(ttp)Me 1c are first hydrolyzed by water, generated from
the aldol condensation,4 to give Ir(ttp)OH for the CCA process.
Indeed, Ir(ttp)CH2COPh 4a was hydrolyzed by water (100
equiv) in a less polar solvent of benzene-d6 to give acetophenone
2b in 20% yield in 3 days (eq 7). The reaction stoichiometry
suggests that the iridium porphyrin coproduct would be Ir-
(ttp)OH.4 Thus, Ir(ttp)OH is proposed to be the intermediate
200 oC
IrðttpÞCH2COPh þ H2O
f IrðttpÞH þ PhCOMe
2b 20%
20%
3 d, C6D6
100 equiv
4a
ð7Þ
Ir(ttp) X-Effect on Aldol Condensation. To verify the
importance of water formation, the rate of the aldol condensation
catalyzed by Ir(ttp)X (X = (BF4)(CO), 1b, Cl(CO), 1a, Me, 1c)
was examined. The most Lewis acidic, Ir(ttp)(BF4)(CO) 1b,
gave higher yields of the aldol condensation products (5a and
5b) in the shortest reaction time than Ir(ttp)Cl(CO) 1a4 and
Ir(ttp)Me 1c (eq 8).7 These results rationalize the higher
reactivity of Ir(ttp)(BF4)(CO) 1b toward ketone CCA in two
ways: (1) It serves as a more efficient aldol condensation catalyst
for the generation of water; and (2) HBF4 (pKa ca. 0.1 in MeCN,
bp 130 °C (dec)),8,9 formed from R-CHA, also catalyzes the
aldol condensation more rapidly than HCl (pKa ca. 8.6 in MeCN,
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Organometallics
ARTICLE
bp -85 °C).8,10 The water formed from the aldol condensation
facilitates the hydrolytic generation of Ir(ttp)OH for CCA.
Table 3. CCA of Aliphatic Ketones with Ir(ttp)(BF4)(CO)
yield/%
entry
1
RCOR0
product (yield)
total
33
MeCOEt 2f
Ir(ttp)Me 1c (5); Ir(ttp)COMe 3e (23);
Ir(ttp)Et 3f (<5); Ir(ttp)COEt 3g (5)
Acetophenones: para-Substituent Effect. para-Substituted
acetophenones 2a,c,d successfully reacted with Ir(ttp)X to give
Ir(ttp)CO(p-FG-C6H4) 3a,c,d in 54-92% yields at 200 °C
(Table 2, eq 9). para-Substituted acetophenones 2a,c,d underwent
CCA with the most reactive iridium porphyrin, Ir(ttp)(BF4)(CO)
1b, at the same rate as acetophenone 2b. para-Substituted acet-
ophenones 2a,c,d, however, reacted faster with the less reactive
Ir(ttp)Cl(CO) 1a4 and Ir(ttp)Me 1c than acetophenone 2b likely
due to the reduction or elimination of Ar-CHA by steric hindrance
(Table 1 vs Table 2). The largest difference in reactivity order for
para-substituted acetophenones was observed with Ir(ttp)Me 1c,
and the order is 2a > 2c ∼ 2d, in the order of electron deficiency of
ketones. We rationalize that the trend is due to the more facile aldol
condensation of more acidic ketones (pKa in DMSO: 2a (24.45);
2b (24.70); 2c (25.19); 2d (25.70)).11
Aliphatic Ketone CCA. To extend the substrate scope of the
CCA reaction with Ir(ttp)X, the prototypical aliphatic ketone,
acetone 2e, was examined first. Initially, Ir(ttp)(BF4)(CO) 1b
was heated in acetone 2e at 120 °C for 9 h. No CCA occurred,
but only the R-CHA product of Ir(ttp)CH2COMe 4d in 10%
yield was isolated with 72% yield of Ir(ttp)(BF4)(CO) 1b
remaining unreacted (eq 10). When the reaction mixture of
Ir(ttp)(BF4)(CO) 1b and acetone 2e was heated at a higher
temperature of 200 °C for 1 day, CCA was successfully achieved
though nonregioselectively to give Ir(ttp)COMe 3e in 19% yield
and Ir(ttp)Me 1c in 40% yield (eq 11). Upon further heating,
Ir(ttp)Me 1c was slowly converted to Ir(ttp)COMe 3e (eq 11).
On the other hand, MeCOOH in 836% yield (cf. Ir) was quantified
from the reaction between acetone 2e andIr(ttp)(BF4)(CO) 1b at
200 °C for 1 day (eq 12). Although HBF4, cogenerated from the R-
CHA process, alone also assisted the formation of MeCOOH in
164% yield (cf. HBF4) from acetone 2e (eq 12), the significant
yield enhancement with Ir(ttp)(BF4)(CO) 1b still suggests that
the chemo- but not regioselective C(dO)-C(R) bond cleavage is
via Ir(ttp)OH (Scheme 2).12 The catalytic generation of Me-
COOH is likely due to hydrolysis of Ir(ttp)COMe.13 Thus, a
catalytic CCA of acetone 2e to acetic acid was achieved.
2
3
MeCOiPr 2g Ir(ttp)Me 1c (43); Ir(ttp)COMe 3e (9)
52
30a
EtCOEt 2h Ir(ttp)Et 3f (19); Ir(ttp)COEt 3g (11)
a 1c and 3e were observed in trace amounts (<5%). We proposed that 1c
was formed from the reduction of CO with Ir(ttp)H, and 3e was
generated from the CO insertion into 1c. See ref 15 for details.
in acetone 2e, and hence only trace amounts of CCA products
Ir(ttp)Me 1c and Ir(ttp)COMe 3e were isolated, with most of
the Ir(ttp)Cl(CO) 1a unreacted upon prolonged heating at
200 °C for 10 days (eq 13). Besides, the lower acidity of acetone
2e (pKa in DMSO: 2b (24.70);11a 2e (26.5)14) may account for
the lower reactivity. Unlike acetophenone, acetone 2e did not
react well with Ir(ttp)Me 1c at 200 °C for 5 days (eq 14).
Therefore, only the more Lewis acidic Ir(ttp)(BF4)(CO) 1b can
activate the C(dO)-C(R) of acetone efficiently.
With the successful reaction with acetone 2e, various aliphatic
ketones 2f-h were then reacted with Ir(ttp)(BF4)(CO) 1b at
200 °C (Table 3, eq 15). Generally, the CCA was chemoselective
but not regionselective at the C(dO)-C(R) bond to give both
Ir(ttp)COR and Ir(ttp)R0. The regioselectivity of CCA of
ketones was dependent on the steric hindrance of the alkyl
groups as well as the bond dissociation energy (BDE) of
C(dO)-C(R) bonds (Table 3, entries 1 and 2).
Four CCA products were obtained from methyl ethyl ketone
2f as a result of nonregioselective CCA (Table 3, entry 1). The
C(dO)-C(Et) bond was dominantly cleaved to give 23% yield
of Ir(ttp)COMe 3e and a trace amount of Ir(ttp)Et 3f (<5%),
while It(ttp)COEt 3g and Ir(ttp)Me 1c were both obtained in
5% yield from the C(dO)-C(Me) bond cleavage. The prefer-
ential cleavage of the C(dO)-C(Et) bond (83.0 kcal mol-1 6
)
over the C(dO)-C(Me) bond (84.3 kcal mol-1)6 is likely due
to the weaker bond strength. However, steric effects play a
significant role when the ketone possesses an isopropyl group.
The C(dO)-C(Me) bond of methyl isopropyl ketone 2g was
cleaved mainly to give a 43% yield of Ir(ttp)Me 1c. The
C(dO)-C(iPr) bond cleavage also occurred but only gave a
low yield of Ir(ttp)COMe 3e of 9% (Table 3, entry 2). We reason
that the isopropyl group is sterically large enough to inhibit cleavage
of the weaker C(dO)-C(iPr) bond (81.3 kcal mol-1).6 For the
symmetric diethyl ketones 2h, chemoselective CCA occurred at the
C(dO)-C(Et) bond to give Ir(ttp)COEt 3g in 11% yield and
Ir(ttp)Et 3f in 19% yield, respectively (Table 3, entry 3).
The less reactive iridium porphyrin complexes were then
examined. Unfortunately, Ir(ttp)Cl(CO) 1a dissolved poorly
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ARTICLE
Scheme 2. Modified Proposed Mechanism4 for the CCA of Ketones by Ir(ttp)X
Stability of Ir(ttp)COMe and Ir(ttp)Me. It is puzzling that the
C(dO)-C(R) bond activation of ketone is nonregioselective,
but Ir(ttp)COR is generally the final observed product. It is
conceivable that Ir(ttp)R0 can further convert to Ir(ttp)COR
upon prolonged heating (Table 1, entry 3, and eq 11). Therefore,
the thermal and hydrolytic stabilities of Ir(ttp)Me 1c and
Ir(ttp)COMe 3e in acetone 2e were studied. Both Ir(ttp)Me
1c and Ir(ttp)COMe 3e were thermally and hydrolytically stable
in acetone 2e0 at 200 °C in the presence of water (100 equiv)
(eqs 16 and 17). Upon the addition of HBF4 (1.0 equiv, 35%
solution), Ir(ttp)CD3 1c0 reacted with acetone 2e at 200 °C in
1 day to give both Ir(ttp)Me 1c and Ir(ttp)COMe 3e in 24% and
10% yield (eq 18), respectively. On the other hand, Ir-
(ttp)COMe 3e was found to be stable under the same reaction
conditions, and only a 7% yield of Ir(ttp)Me 1c was isolated with
the recovery of Ir(ttp)COMe 3e in 91% yield (eq 19).16 There-
fore, Ir(ttp)Me 1c undergoes more facile acid-catalyzed hydro-
lysis than Ir(ttp)COMe 3e, likely to generate an unstable
Ir(ttp)OH.
(Ir(ttp)X, X=(BF4)(CO), 1b, Cl(CO), 1a, Me, 1c) (Scheme 2).
First, Ir(ttp)X catalyzes the aldol condensation of ketone to give
water (eq 8). Concurrently, Ir(ttp)X reacts in a stoichiometric
manner with ketones to give the R-CHA complexes as the kinetic
products. Then the R-CHA complexes are hydrolyzed by water
(catalyzed by acid as well) to give Ir(ttp)OH (eq 7), which cleaves
the C(dO)-C(R) bond of ketone in a nonregioselective manner
to give both Ir(ttp)COR and Ir(ttp)R0 (eqs 3, 11, and 15). Since
Ir(ttp)R0 is hydrolytically less stable than Ir(ttp)COR, Ir(ttp)R0 is
hydrolyzed to Ir(ttp)OH, which yields Ir(ttp)COR as product
(Table 1, entry 3, and eq 11). This mechanism accounts for the sole
formation of Ir(ttp)COAr from the CCA of acetophenones, as
Ir(ttp)Me hydrolyzes much more rapidly than Ir(ttp)COAr.
In conclusion, we have systematically studied the CCA of
ketones with high-valent iridium(III) porphyrin complexes. We
discovered that Ir(ttp)(BF4)(CO) 1b exhibited a higher reactiv-
ity toward the CCA of ketones, which is likely due to its higher
Lewis acidity, and the coformation of strong Brønsted acid HBF4
to catalyze the aldol condensation of ketones. Ir(ttp)OH was
proposed as the intermediate to cleave the C(dO)-C(R) bonds
of ketones to give the corresponding iridium porphyrin acyl and
alkyl complexes nonregioselectively. The final isolation of iri-
dium porphyrin acyls in the reaction with acetophenones is due
to its hydrolytic stability. For the unsymmetric aliphatic ketones,
the selectivity was dependent on the bond dissociation energy as
well as the steric hindrance of the alkyl group.
’ EXPERIMENTAL SECTION
Unless otherwise noted, all chemicals were obtained from commercial
suppliers and used without further purification. Hexane for chromatog-
raphy was distilled from anhydrous calcium chloride. Thin-layer chro-
matography analysis for the reaction was performed on precoated silica
gel 60 F254 plates. All preparation reactions were carried out in a Teflon
screw-head stoppered tube under N2. For purification of iridium
porphyrin complexes, fresh column chromatography was used and
carried out in air using alumina (90 active neutral, 70-230 mesh).
Ir(ttp)(BF4)(CO)17 1a, Ir(ttp)Cl(CO)18 1b, Ir(ttp)Me18 1c, and Ir-
19
(ttp)CD3 1c0 were prepared according to the literature.
1H NMR spectra were recorded on a Bruker AV400 (400 MHz).
Chemical shifts were reported with reference to the residual solvent
protons in CDCl3 (δ 7.26 ppm) or C6D6 (δ 7.15 ppm) as the internal
standards. Chemical shifts (δ) were reported in parts per million (ppm)
in δ scale downfield from TMS. Coupling constants (J) are reported in
hertz (Hz). 13C NMR spectra were recorded on a Bruker AV400 (100
MHz) spectrometer and referenced to CDCl3 (δ 77.10 ppm). High-
resolution mass spectra (HRMS) were performed on a Thermofinnign
MAT 95 XL in FAB (using 3-nitrobenzyl alcohol (NBA) matrix and
Mechanistic Studies. Based on the above experimental
results and the mechanism reported in the ketone CCA with
Rh(ttp)Me, we propose a more complete mechanism for the
CCA of ketones with iridium(III) porphyrin complexes
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Organometallics
ARTICLE
CH2Cl2 as the solvent) and ESI model (MeOH/CH2Cl2, 1:1, as the
solvent).
mixture was heated at 200 °C for 2 days, and the crude product was
purified by column chromatography on alumina eluting with hexane/
CH2Cl2 (3:1). A purple solid of Ir(ttp)CO(4-F-C6H4)4,17 3a (6.9 mg,
0.0070 mmol, 54%) was isolated. Rf = 0.28 (hexane/CH2Cl2, 1:1). 1H
NMR (C6D6, 400 MHz): δ 2.41 (s, 12 H), 2.73 (dd, 2 H, 4JH-F = 5.4 Hz,
J = 8.6 Hz), 5.50 (dd, 2 H, 3JH-F = 8.8 Hz, J = 8.8 Hz), 7.28 (d, 4 H, J =
8.0 Hz), 7.34 (d, 4 H, J = 7.6 Hz),7.98 (dd, 4 H, J = 1.6, 7.6 Hz), 8.14 (dd,
4 H, J = 1.6, 8.4 Hz), 8.85 (s, 8 H).
Reaction between Ir(ttp)(BF4)(CO) 1b and 4-Methylaceto-
phenone 2c. 4-Methylacetophenone 2c (0.8 mL, 500 equiv) was
added to Ir(ttp)(BF4)(CO) 1b (12.5 mg, 0.013 mmol). Then the
mixture was heated at 200 °C for 2 days, and the crude product was
purified by column chromatography on alumina eluting with hexane/
CH2Cl2 (3:1). A purple solid of Ir(ttp)CO(4-Me-C6H4)4,17 3b (9.6 mg,
0.0098 mmol, 75%) was isolated. Rf = 0.28 (hexane/CH2Cl2, 1:1). 1H
NMR (C6D6, 400 MHz): δ 1.65 (s, 3 H), 2.42 (s, 12 H), 2.83 (d, 2 H, J =
8.0 Hz), 5.67 (d, 2 H, J = 8.0 Hz), 7.28 (d, 4 H, J = 7.6 Hz), 7.35 (d, 4 H,
J = 7.6 Hz), 7.96 (dd, 4 H, J = 1.6, 7.6 Hz), 8.17 (dd, 4 H, J = 1.6, 7.6 Hz),
8.86 (s, 8 H).
Reaction between Ir(ttp)(BF4)(CO) 1b and 4-Methoxyla-
cetophenone 2d. 4-Methoxylacetophenone 2d (0.8 mL, 500 equiv)
was added to Ir(ttp)(BF4)(CO) 1b (12.4 mg, 0.013 mmol). Then the
mixture was heated at 200 °C for 2 days, and the crude product was
purified by column chromatography on alumina eluting with hexane/
CH2Cl2 (3:1). A purple solid of Ir(ttp)CO(4-OMe-C6H4)4,17 3b (10.4
mg, 0.0104 mmol, 80%) was isolated. Rf = 0.11 (hexane/CH2Cl2, 1:1).
1H NMR (C6D6, 400 MHz): δ 2.42 (s, 12 H), 2.90 (d, 2 H, J = 6.8 Hz),
2.92 (s, 3H), 5.45 (d, 2H, J = 8.8 Hz), 7.27 (d, 4 H, J = 8.1 Hz), 7.35 (d, 4
H, J = 7.6 Hz), 8.01 (d, 4 H, J = 7.6 Hz), 8.17 (d, 4 H, J = 7.6 Hz), 8.87 (s,
8 H).
Reaction between Ir(ttp)Me 1c and 4-Fluoroacetophe-
none 2a. 4-Fluoroacetophenone 2a (0.9 mL, 500 equiv) was added
to Ir(ttp)Me 1c (13.1 mg, 0.015 mmol). Then the mixture was heated at
200 °C for 6 days, and the crude product was purified by column
chromatography on alumina eluting with hexane/CH2Cl2 (3:1). A
purple solid of Ir(ttp)CO(4-F-C6H4)4,17 3a (13.6 mg, 0.0138 mmol,
92%) was isolated.
Reactions of Ir(ttp)X 1b,c with Acetophenones. General
Procedure. The reaction of Ir(ttp)(BF4)(CO) 1b with acetophenone
2b for 2 days is described as a typical example. Acetophenone 2b
(0.8 mL, 500 equiv) was added to Ir(ttp)(BF4)(CO) (12.5 mg, 0.013
mmol), and the mixture was degassed by the freeze-pump-thaw
method (3 cycles). Then the mixture was heated at 200 °C for 2 days.
The crude product was purified by column chromatography on alumina
eluting with hexane/CH2Cl2 (3:1). A purple solid of Ir(ttp)COPh4,17 3b
(7.3 mg, 0.0075 mmol, 58%) was isolated. Rf = 0.28 (hexane/CH2Cl2,
1:1). 1H NMR (C6D6, 400 MHz): δ 2.42 (s, 12 H), 2.90 (d, 2 H, J = 7.2
Hz), 5.87 (t, 2 H, J = 7.6 Hz), 6.21 (t, 1 H, J = 7.2 Hz), 7.27 (d, 4 H, J = 7.6
Hz), 7.34 (d, 4 H, J = 7.2 Hz), 7.99 (d, 4 H, J = 7.6 Hz), 8.16 (d, 4 H, J =
7.6 Hz), 8.86 (s, 8 H). Then the solvent was changed to hexane/CH2Cl2
(1:2), and a purple solid mixture of Ir(ttp)(para-COMe-C6H4)4 4b and
Ir(ttp)(meta-COMe-C6H4)4 4c was isolated in trace amount (<5%).
1
Ir(ttp)(para-COMe-C6H4) 4b: Rf = 0.14 (hexane/CH2Cl2, 1:2). H
NMR (C6D6, 400 MHz): δ 0.95 (s, 3 H), 1.00 (d, 2 H, J = 8.8 Hz), 2.39
(s, 12 H), 5.24 (d, 2 H, J = 8.4 Hz), 7.20 (d, 4 H, J = 8.0 Hz), 7.34 (d, 4 H,
J = 7.6 Hz), 7.93 (dd, 4 H, J = 1.6, 7.8 Hz), 8.12 (dd, 4 H, J = 1.2, 6.6 Hz),
8.82 (s, 8 H). Ir(ttp)(meta-COMe-C6H4) 4c: Rf = 0.23 (hexane/
1
CH2Cl2, 1:2). H NMR (C6D6, 400 MHz): δ 1.12 (s, 3 H), 1.19 (d,
1 H, J = 8.0 Hz), 1.69 (s, 1 H), 2.39 (s, 12 H), 4.73 (t, 1 H, J = 8.0 Hz),
5.53 (d, 1 H, J = 7.6 Hz), 7.23 (d, 4 H, J = 7.6 Hz), 7.34 (d, 4 H, J =
7.6 Hz), 8.09 (d, 4 H, J = 7.6 Hz), 8.14 (d, 4 H, J = 7.6 Hz), 8.82 (s, 8 H).
Reaction between Ir(ttp)(BF4)(CO) 1b and Acetophenone
2b for 4 Hours. Acetophenone 2b (0.9 mL, 500 equiv) was added to
Ir(ttp)(BF4)(CO) 1b (14.9 mg, 0.015 mmol). Then the mixture was
heated at 200 °C for 4 h, and the crude product was purified by column
chromatography on alumina eluting with hexane/CH2Cl2 (3:1). A
purple solid mixture of Ir(ttp)COPh4,17 3b (1.9 mg, 0.0020 mmol,
13%) and Ir(ttp)Me (<5%) was isolated. Then the solvent was changed
to hexane/CH2Cl2 (1:2), and a purple solid mixture of Ir(ttp)-
CH2COPh4 4a (<5%), Ir(ttp)(para-COMe-C6H4)4 4b (2.0 mg,
0.0020 mmol, 13%), and Ir(ttp)(meta-COMe-C6H4)4 4c (4.0 mg,
0.0040 mmol, 26%) was isolated. On the other hand, the aldol
condensation products PhCOCHdCMePh 5a and 1,3,5-triphenylben-
zene 5b were both observed in 1000% yields (cf. Ir), respectively,
according to the 1H NMR with Si(SiMe3)4 used as the internal standard.
Reaction between Ir(ttp)Me 1c and Acetophenone 2b for
26 Days. Acetophenone 2b (0.8 mL, 500 equiv) was added to
Ir(ttp)Me 1c (12.7 mg, 0.014 mmol). Then the mixture was heated at
200 °C for 26 days, and the crude product was purified by column
chromatography on alumina eluting with hexane/CH2Cl2 (3:1). A
purple solid of Ir(ttp)COPh4,17 3b (10.8 mg, 0.0112 mmol, 80%) was
isolated.
Reaction between Ir(ttp)Me 1c and Acetophenone 2b for
5 Days. Acetophenone 2b (1.1 mL, 500 equiv) was added to Ir(ttp)Me
1c (15.9 mg, 0.018 mmol). Then the mixture was heated at 200 °C for
5 days, and the crude product was purified by column chromatography on
alumina eluting with hexane/CH2Cl2 (3:1). A purple solid of Ir(ttp)Me
(11.7 mg, 0.0134 mmol, 74%) was recovered together with Ir(ttp)COPh
3b (<5%). Then the solvent was changed to hexane/CH2Cl2 (1:2), and a
purple solid of Ir(ttp)CH2COPh4 4a (1.9 mg, 0.0019 mmol, 11%) was
isolated. Rf = 0.18 (hexane/CH2Cl2, 1:2). 1H NMR (C6D6, 400 MHz): δ
-3.53 (s, 2 H), 2.42 (s, 12 H), 5.13 (d, 2 H, J = 7.6 Hz), 6.48 (t, 2 H, J =
7.8 Hz), 6.81 (t, 1 H, J = 7.2 Hz), 7.30 (dd, 8 H, J = 8.0, 8.0 Hz), 8.04 (d,
4 H, J = 7.6 Hz), 8.14 (d, 4 H, J = 7.6 Hz), 8.75 (s, 8 H). No aldol
condensation products of PhCOCHdCMePh 5a and 1,3,5-triphenylben-
zene 5b were observed by both 1H NMR and GC-MS analysis.
Reaction between Ir(ttp)Me 1c and 4-Methylacetophe-
none 2c. 4-Methylacetophenone 2c (0.9 mL, 500 equiv) was added to
Ir(ttp)Me 1c (11.5 mg, 0.013 mmol). Then the mixture was heated at
200 °C for 21 days, and the crude product was purified by column
chromatography on alumina eluting with hexane/CH2Cl2 (3:1). A
purple solid of Ir(ttp)CO(4-Me-C6H4)4,17 3a (7.4 mg, 0.0075 mmol,
58%) was isolated.
Reaction between Ir(ttp)Me 1c and 4-Methoxylacetophe-
none 2d. 4-Methoxylacetophenone 2d (0.9 mL, 500 equiv) was added
to Ir(ttp)Me 1c (12.6 mg, 0.014 mmol). Then the mixture was heated at
200 °C for 24 days, and the crude product was purified by column
chromatography on alumina eluting with hexane/CH2Cl2 (3:1). A
purple solid of Ir(ttp)CO(4-OMe-C6H4)4,17 3a (11.4 mg, 0.0114 mmol,
82%) was isolated.
Reaction between Ir(ttp)(BF4)(CO) 1b and Acetone 2e for
9 Hours at 120 °C. Acetone 2e (0.7 mL, 500 equiv) was added to
Ir(ttp)(BF4)(CO) 1b (18.1 mg, 0.018 mmol). Then the mixture was
heated at 120 °C for 9 h, and the crude product was purified by column
chromatography on alumina eluting with hexane/CH2Cl2 (1:2). A
purple solid of Ir(ttp)CH2COMe 4d (1.8 mg, 0.0018 mmol, 10%)
1
was isolated. Rf = 0.23 (hexane/CH2Cl2, 1:2). H NMR (C6D6, 400
MHz): δ -4.03 (s, 2 H), -1.54 (s, 3 H), 2.41 (s, 12 H), 7.25 (d, 4 H, J =
7.6 Hz), 7.36 (d, 4 H, J = 7.6 Hz), 8.10 (dd, 4 H, J = 1.5, 7.6 Hz), 8.19 (dd,
4 H, J = 1.5, 7.6 Hz), 8.78 (s, 8 H). 13C NMR (CDCl3, 100 MHz): δ -
13.0, 21.6, 25.4, 124.0, 127.5, 127.7, 131.6, 133.3, 134.2, 137.4, 138.6,
143.2, 207.2. HRMS (FAB): calcd for (C51H41N4O1Ir1)þ m/z
918.2904; found m/z 918.2899.
Reaction between Ir(ttp)(BF4)(CO) 1b and 4-Fluoroaceto-
phenone 2a. 4-Fluoroacetophenone 2a (0.8 mL, 500 equiv) was
added to Ir(ttp)(BF4)(CO) 1b (12.6 mg, 0.013 mmol). Then the
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Reaction between Ir(ttp)(BF4)(CO) 1b and Acetone 2e for
1 Day at 200 °C. Acetone 2e (0.7 mL, 500 equiv) was added to
Ir(ttp)(BF4)(CO) 1b (18.4 mg, 0.019 mmol). Then the mixture was
heated at 200 °C for 1 day, and the crude product was purified by column
chromatography on alumina eluting with hexane/CH2Cl2 (5:1). A
purple solid of Ir(ttp)COMe 3e (3.3 mg, 0.0037 mmol, 19%) was
isolated. Rf = 0.35 (hexane/CH2Cl2, 1:2). 1H NMR (C6D6, 400 MHz):
δ -2.65 (s, 3 H), 2.41 (s, 12 H), 7.22 (d, 4 H, J = 7.7 Hz), 7.34 (d, 4 H,
J = 7.1 Hz), 7.99 (dd, 4 H, J = 1.7, 7.7 Hz), 8.16 (dd, 4 H, J = 1.7, 7.6 Hz),
8.88 (s, 8 H). 13C NMR (CDCl3, 100 MHz): δ 21.6, 28.9, 123.9, 127.5,
127.6, 131.4, 133.6, 134.0, 137.4, 138.8, 142.9, 164.3. HRMS (ESIMS):
calcd for [C50H39N4OIrþH]þ m/z 905.2826; found m/z 905.2785.
Then the solvent was changed to hexane/CH2Cl2 (3:1), and a purple
solid of Ir(ttp)Me (6.6 mg, 0.0075 mmol, 40%) was isolated. In addition,
CH3COOK was observed in 1.67% yield based on acetone (836% yield
based on Ir(ttp)(BF4)(CO)) according to the 1H NMR spectrum with
tBuOH (10 μL) used as the internal standard when KOH (ex) was
added to the reaction mixture.
Reaction between Ir(ttp)(BF4)(CO) 1b and Acetone 2e for
2 Days at 200 °C. Acetone 2e (0.8 mL, 500 equiv) was added to
Ir(ttp)(BF4)(CO) 1b (22.4 mg, 0.023 mmol). Then the mixture was
heated at 200 °C for 2 days, and the crude product was purified by
column chromatography on alumina eluting with hexane/CH2Cl2 (5:1).
A purple solid of Ir(ttp)COMe 3e (4.9 mg, 0.0054 mmol, 24%) was
isolated. Then the solvent was changed to hexane/CH2Cl2 (3:1), and a
purple solid of Ir(ttp)Me 1c (3.8 mg, 0.0043 mmol, 19%) was isolated.
Reaction between Ir(ttp)Cl(CO) 1a and Acetone 2e. Acet-
one 2e (0.9 mL, 500 equiv) was added to Ir(ttp)Cl(CO) 1a (23.1 mg,
0.025 mmol). Then the mixture was heated at 200 °C for 10 days, and
the crude product was purified by column chromatography on alumina
eluting with hexane/CH2Cl2 (5:1). A purple solid mixture of Ir-
(ttp)COMe 3e and Ir(ttp)Me 1c was isolated in trace amount (<5%).
Ir(ttp)Cl(CO) 1a (∼92%) remained according to the 1H NMR
spectrum of the crude reaction mixture.
CH2Cl2 (3:1). A purple solid of Ir(ttp)COMe 3e (1.6 mg, 0.0018 mmol,
9%) was isolated. Then the solvent was changed to hexane/CH2Cl2
(2:1), and a purple solid of Ir(ttp)Me 1c (7.6 mg, 0.0087 mmol, 43%)
was isolated.
Reaction between Ir(ttp)(BF4)(CO) 1b and Diethyl Ketone
2h. Diethyl ketone 2h (0.7 mL, 500 equiv) was added to Ir(ttp)(BF4)-
(CO) 1b (13.0 mg, 0.013 mmol). Then the mixture was heated at
200 °C for 4 days, and the crude product was purified by column
chromatography on alumina eluting with hexane/CH2Cl2 (5:1). A
purple solid mixture of Ir(ttp)COMe 3e (<5%), Ir(ttp)COEt17 3g
(1.3 mg, 0.0014 mmol, 11%), Ir(ttp)Me 1c (<5%), and Ir(ttp)Et18 3f
(2.2 mg, 0.0025 mmol, 19%) was isolated.
Reaction between Ir(ttp)Me 1c and Acetone-d6 2e0 with
100 Equivalents of Water. Acetone-d6 2e0 (0.5 mL, 1000 equiv) and
H2O (9 μL, 100 equiv) were added to Ir(ttp)Me 1c (4.5 mg, 0.0052
mmol) in a NMR tube with a Rotaflo stopper, and the mixture was
degassed by the freeze-pump-thaw method (3 cycles). Then the
NMR tube was flamed-sealed under vacuum. The mixture was heated at
200 °C and was monitored with 1H NMR spectroscopy. After 11 days,
Ir(ttp)Me remained in quantitative yield, and no Ir(ttp)COMe was
observed.
Reaction between Ir(ttp)COMe 3e and Acetone-d6 2e0
with 100 Equivalents of Water. Acetone-d6 2e0 (0.5 mL, 1000
equiv) and H2O (11 μL, 100 equiv) were added to Ir(ttp)COMe 3e (5.2
mg, 0.0058 mmol) in a NMR tube with a Rotaflo stopper, and the
mixture was degassed by the freeze-pump-thaw method (3 cycles).
Then the NMR tube was flamed-sealed under vacuum. The mixture was
heated at 200 °C and was monitored with 1H NMR spectroscopy. After
12 days, Ir(ttp)COMe remained in quantitative yield, and no Ir(ttp)Me
was observed.
Reaction between Ir(ttp)CD3 1c0 and Acetone 2e with
HBF4. Acetone 2e (0.9 mL, 500 equiv) and HBF4 (4.8 μL, 1.0 equiv,
35%) were added to Ir(ttp)CD3 1c0 (20.8 mg, 0.024 mmol). Then the
mixture was heated at 200 °C for 1 day, and the crude product was
purified by column chromatography on alumina eluting with hexane/
CH2Cl2 (5:1). A purple solid mixture of Ir(ttp)COMe 3e (2.1 mg,
0.0023 mmol, 10%) was isolated. Then the solvent was changed to
hexane/CH2Cl2 (3:1), and a purple solid mixture of Ir(ttp)Me 1c (5.0
mg, 0.0057 mmol, 24%) and Ir(ttp)CD3 1c0 (2.5 mg, 0.0028 mmol,
12%) was isolated. In addition, CH3COOK was observed in 2.05% yield
based on acetone (1023% yield based on Ir(ttp)CD3) according to the
1H NMR spectrum with tBuOH (10 μL) used as the internal standard
when KOH (ex) was added to the reaction mixture.
Reaction between Ir(ttp)COMe 3e and Acetone 2e with
HBF4. Acetone 2e (0.8 mL, 500 equiv) and HBF4 (4.2 μL, 1.0 equiv,
35%) were added to Ir(ttp)COMe 3e (18.7 mg, 0.021 mmol). Then the
mixture was heated at 200 °C for 1 day, and the crude product was
purified by column chromatography on alumina eluting with hexane/
CH2Cl2 (3:1). A purple solid mixture of Ir(ttp)COMe 3e (17.3 mg,
0.0191 mmol, 91%) and Ir(ttp)Me 1c (1.3 mg, 0.0015 mmol, 7%) was
isolated.
Reaction between Ir(ttp)Me 1c and Acetone 2e. Acetone 2e
(0.9 mL, 500 equiv) was added to Ir(ttp)Me 1c (22.1 mg, 0.025 mmol).
Then the mixture was heated at 200 °C for 5 days, and the crude product
was purified by column chromatography on alumina eluting with
hexane/CH2Cl2 (3:1). A purple solid of Ir(ttp)Me 1c (19.7 mg,
0.0225 mmol, 90%) was recovered. No CH3COOK was observed when
KOH (ex) was added according to the 1H NMR spectrum.
Reaction between Ir(ttp)(BF4)(CO) 1b and Methyl Ethyl
Ketone 2f. Methyl ethyl ketone 2f (1.0 mL, 500 equiv) was added to
Ir(ttp)(BF4)(CO) 1b (21.1 mg, 0.022 mmol). Then the mixture was
heated at 200 °C for 4 days, and the crude product was purified by
column chromatography on alumina eluting with hexane/CH2Cl2 (5:1).
A purple solid mixture of Ir(ttp)COEt17 3g (1.0 mg, 0.0011 mmol, 5%)
was isolated. Rf = 0.66 (hexane/CH2Cl2, 1:2). 1H NMR (CDCl3, 300
MHz): δ -3.20 (q, 2 H, J = 7.2 Hz), -1.71 (t, 3 H, J = 7.2 Hz), 2.69 (s,
12 H), 7.52 (d, 8 H, J = 8.1 Hz), 8.02 (d, 8 H, J = 7.8 Hz), 8.67 (s, 8 H).
Then the solvent was changed to hexane/CH2Cl2 (3:1), and a purple
solid mixture of Ir(ttp)COMe 3e (4.5 mg, 0.0050 mmol, 23%) was
isolated. When the solvent was changed to hexane/CH2Cl2 (1:1), a
purple solid mixture of Ir(ttp)Me 1c (1.0 mg, 0.0011 mmol, 5%) and
Ir(ttp)Et18 3f (<5%) was isolated. Rf = 0.25 (hexane/CH2Cl2, 2:1). 1H
NMR (C6D6, 400 MHz): δ -5.20 (q, 2 H, J = 7.2 Hz), -4.27 (t, 3 H, J =
7.2 Hz), 2.41 (s, 12 H), 7.22 (d, 4 H, J = 7.6 Hz), 7.35 (d, 4 H, J = 7.6 Hz),
7.99 (dd, 4 H, J = 2.0, 7.6 Hz), 8.19 (dd, 4 H, J = 1.6, 7.8 Hz), 8.76 (s, 8
H).
Reaction of Acetone 2e with HBF4. Acetone 2e (0.8 mL, 500
equiv) and HBF4 (4.6 μL, 1.0 equiv, 35%) were heated at 200 °C for
1 day. CH3COOK was observed in 0.33% yield based on acetone (164%
yield based on HBF4) according to the 1H NMR spectrum with tBuOH
(10 μL) used as the internal standard when KOH (ex) was added to the
reaction mixture.
Reaction between Ir(ttp)(BF4)(CO) 1b and Methyl Isopro-
pyl Ketone 2g. Methyl isopropyl ketone 2g (0.8 mL, 500 equiv) was
added to Ir(ttp)(BF4)(CO) 1b (19.8 mg, 0.020 mmol). Then the
mixture was heated at 200 °C for 4 days, and the crude product was
purified by column chromatography on alumina eluting with hexane/
’ ASSOCIATED CONTENT
Supporting Information. 1H and 13C NMR spectra. This
S
b
material is available free of charge via the Internet at http://
pubs.acs.org.
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Organometallics
ARTICLE
’ AUTHOR INFORMATION
(16) For the reaction between Ir(ttp)COMe and acetone-d6, H-D
exchange occurred in the pyrrolic and COCH3 protons in the acidic
medium. So the hydrolysis rate of Ir(ttp)COMe cannot be determined.
It is expected to be the same case in the reaction between Ir(ttp)COCD3
and acetone.
Corresponding Author
*E-mail: ksc@cuhk.edu.hk.
(17) Song, X.; Chan, K. S. Organometallics 2007, 26, 965–970.
(18) Yeung, S. K.; Chan, K. S. Organometallics 2005, 24, 6426–6430.
(19) Cheung, C. W.; Fung, H. S.; Lee, S. Y.; Qian, Y. Y.; Chan, Y. W.;
Chan, K. S. Organometallics 2010, 29, 1343–1354.
’ ACKNOWLEDGMENT
We are grateful to the Research Grants Council of Hong Kong
SAR of China for financial support (No. 400308).
’ REFERENCES
(1) For the reported examples of carbon-carbon bond activation in
a ring-strained system by rhodium(I), see: (a) Murakami, M.; Tsuruta,
T.; Ito, Y. Angew. Chem., Int. Ed. 2000, 39, 2484–2486. (b) Matsuda, T.;
Makino, M.; Murakami, M. Org. Lett. 2004, 6, 1257–1259. (c) Matsuda,
T.; Makino, M.; Murakami, M. Bull. Chem. Soc. Jpn. 2005, 78, 1528–
1533.
(2) For reported examples of carbon-carbon bond activation by
rhodium(I) in a chelation-assitance system, see: (a) Jun, C.-H.; Lee, H. J.
Am. Chem. Soc. 1999, 121, 880–881. (b) Jun, C.-H.; Moon, C. W.; Lee,
D.-Y. Chem.—Eur. J. 2002, 8, 2422–2428. (c) Anh, J.-A.; Chang, D.-H.;
Park, Y. J.; Yon, Y. R.; Loupy, A.; Jun, C.-H. Adv. Synth. Catal. 2006,
348, 55–58. (d) Dreis, A. M.; Douglas, C. J. J. Am. Chem. Soc. 2009,
131, 412–413.
(3) For oxidative addition (OA) of the carbon-hydrogen bond, see:
(a) Gꢀomez, M.; Robinson, D. J.; Maitlis, P. M. J. Chem. Soc., Chem.
Commun. 1983, 825–826. For OA of the silicon-hydrogen bond, see:
(b) Klei, S. R.; Tilley, T. D.; Bergman, R. G. J. Am. Chem. Soc. 2000,
122, 1816–1817.
(4) Li, B. Z.; Song, X.; Fung, H. S.; Chan, K. S. Organometallics 2010,
29, 2001–2003. Ir(ttp)OH is proposed to react with water to give the
observed Ir(ttp)H.
(5) Fung, H. S.; Li, B. Z.; Chan, K. S. Organometallics 2010,
29, 4421–4423.
(6) Luo, Y.-R. Handbook of Bond Dissociation Energies in Organic
Compounds; CRC Press: Boca Raton; FL, 2003.
(7) (a) For the Lewis acid-catalyzed aldol condensation of ketones
via Rh(oep)CH2COR (oep = octaethylporphyrinato) intermediate
from a reactive Rh(oep)ClO4, see: Aoyama, Y.; Tanaka, Y.; Yoshida,
T.; Toi, H.; Ogoshi, H. J. Organomet. Chem. 1987, 329, 251–266.(b) For
the aldol condensation of acetophenone with Ir(ttp)Cl(CO), see ref 4
for details. (c) Lyle, R. E.; DeWitt, E. J.; Nichols, N. M.; Cleland, W. J.
Am. Chem. Soc. 1953, 75, 5959–5961.
(8) (a) Hu, X.; Cossairt, B. M.; Brunschwig, B. S.; Lewis, N. S.; Peter,
J. C. Chem. Commun. 2005, 4723–4725.(b) Kosuke, I. Acid-Base
Dissociation Constants in Dipolar Aprotic Solvents; Blackwell Scientific
Publications: Oxford, 1990.
(9) http://www.nanotech.wisc.edu./CNT_LABS/MSDS/Acids/
MSDS%20Fluoroboric%20Acid.htm. Accessed on September 15, 2010.
(10) Lide, D. R., Ed. CRC Handbook of Chemistry and Physics,
84th ed.; CRC Press: Boca Raton, FL, 2003.
(11) (a) For pKa of acetophenones: Bordwell, F. G.; Cornforth, F. J.
J. Org. Chem. 1978, 43, 1763–1768. (b) For rate of aldol condensation of
acetophenones: Kumar, A.; Dixit, M.; Singh, S. P.; Raghunandan, R.;
Maulik, P. R.; Goel, A. Tetrahedron Lett. 2009, 50, 4335–4339.
(12) MeOH, another CCA organic coproduct, was not detected by
GC/MS probably due to its low boiling point (64.7 °C) and possible
dehydrogenation to give formaldehyde (bp = -21 °C). For the reported
dehydrogenation of alcohol with metalloporphyrins: see refs 5 and 19 for
details.
(13) We do not understand in detail, but the closest example is the
Cativa process, which involves the indirect hydrolysis of [Ir]ICOMe
([Ir] = Ir(CO)2I2-) to give MeCO2H, HI, and [Ir] at 150-200 °C and
30-60 bar under acidic conditions.
(14) Bordwell, F. G. Acc. Chem. Res. 1988, 21, 456–463.
(15) Cheung, C. W.; Chan, K. S. Organometallics 2008, 27, 3043–
3055.
1990
dx.doi.org/10.1021/om200026y |Organometallics 2011, 30, 1984–1990