214
J. Wang et al. / Journal of Organometallic Chemistry 696 (2011) 211e215
OC
R1
Then, the resulting mixture was cooled to room temperature,
H
[IrIII]
filtered through a short silica gel plug eluted with ethyl acetate. The
volatiles were removed in vacuo and the residue was purified by
column chromatography (silica gel, hexane/diethyl ether ¼ 100:1)
or by silica gel pre-coated plate (eluent: hexane/diethyl
ether ¼ 80:1) to give 3a (31 mg, 62%) as a colorless liquid. 3a
(mixture of E/Z isomer) was obtained as colorless liquid (31 mg,
R2
H
R2
R1
D
R2
+
CO
OC
R1
[IrI]
[IrIII]
62%) [15]. 1H NMR (300Hz, CDCl3):
d 7.44e7.46 (m, 0.19H),
H
A
C
7.27e7.29 (d, 1.03H, J ¼ 3.5Hz), 7.12e7.16 (m, 0.45H), 6.81e6.85 (dd,
2.44H, J ¼ 3.5Hz, 11.5Hz), 6.28e6.34 (d, 1H, J ¼ 26.5Hz), 6.04e6.11
(m, 0.94H), 5.61(m, 0.11H), 3.81e3.89 (m, 3H), 2.65e2.67(m,
0.04H), 2.15e2.19 (q, 1.98H, J ¼ 7Hz, 11.5Hz), 1.44 (m, 2H), 1.28 (br,
O
O
R1
H
R1
[IrIII
] H
B
10H), 0.85e0.91(t, 3H, J ¼ 11Hz). 13C NMR (75Hz, CDCl3):
d158.5,
130.8, 129.1,129.0, 126.9, 113.9, 55.3, 33.0, 31.9, 29.5, 29.5, 29.3, 29.2,
22.7, 14.1.
Scheme 2. Tentative mechanism for the iridium-catalyzed aldehyde-alkyne addition.
on the aromatic ring gave much higher yields than those without
them. Furthermore, an excellent E/Z geometrical selectivity (11/1)
was obtained with the nitro derivative. The attachment of a chloro
group lowered the product yield significantly (Table 2, entry 10). No
desired product was observed with 2,6-dichlorobenzaldehye,
possibly due to both steric effect and chloro’s coordination effect
(Table 2, entry 11). Interestingly, unlike the ruthenium catalytic
system, aliphatic aldehydes of both conjugated and non-conjugated
reacted with terminal alkynes efficiently to give the olefination
product in good yields (Table 2, entries 12e15). However, internal
alkynes failed to participate in the decarbonylative addition reaction.
A tentative mechanism of the decarbonylative addition reaction
is illustrated in Scheme 2. An active [IrI] A, generated in situ,
undergoes oxidative addition of the CeH bond with aldehydes to
generate an [IrIII] intermediate B, similar to the proposed catalytic
cycle by Tsuji for the decarbonylation reactions [14]. Decarbon-
ylation of B generated the intermediate C. Then addition of the IreH
bond of C across the alkyne bond resulted in the vinyl iridium
species D, which underwent reductive elimination to generate the
decarbonylative coupling product and regenerated the active
catalyst A. It is also possible that the reaction proceeds by an
alternative mechanism analogous to the one reported by Verela and
co-workers [13c]. As in our former report,[12] the chloride ion may
serve as a weak coordinating ligands to facilitate these steps.
However, the role of copper chloride in the process is still unclear,
and is under further investigation.
Acknowledgments
We are grateful to the Canada Research Chair (Tier I) Foundation
(to CJL), CFI, FQRNT and NSERC for partial support of our research.
JW thanks SINOPEC for providing a fellowship to visit McGill
University.
Appendix A. Supplementary data
Supplementary data associated with this article can be found in
References
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An oven-dried reaction vessel was charged with H2IrCl6 hydrate
(16.1 mg, 0.04 mmol), CuCl2 (26.8 mg, 1 equiv.), toluene (0.8 mL), n-
Bu3P (20
temperature under argon (1 atm). p-Anisaldehyde (24
0.2 mmol), 1-decyne (144 L, 0.8 mmol), and toluene (0.7 mL) were
mL, 0.08 mmol). The mixture was stirred for 36h at room
mL,
m
added to the above vessel under argon. The reaction vessel was
(c) Verela et al. reported an alternative ruthenium catalyzed formation of
cyclic alkene from aldehyde and alkyne via the cleavage of ChC bond, see
sealed and the resulting solution was stirred at 135 ꢀC for 48 h.