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´
A. DeHope, B. Donnadieu, G. Frenking and G. Bertrand, J. Am.
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Scheme 4 Synthesis of dicarbonyl Rh complexes 8a–c and 9a–c.
which afforded the Rh dicarbonyl species 8a–c and 9a–c in
75–98% yields, respectively. Although there is some limitation
of the method for evaluating ligand donor properties,4j,14 the
average CO vibration frequency of the Rh carbonyl complexes
(d) R. Lalrempuia, N. D. McDaniel, H. Muller-Bunz,
¨
S. Bernhard and M. Albrecht, Angew. Chem., Int. Ed., 2010,
49, 9765; (e) G. Guisado-Barrios, J. Bouffard, B. Donnadieu and
G. Bertrand, Angew. Chem., Int. Ed., 2010, 49, 4759;
(f) K. J. Kilpin, U. S. D. Paul, A.-L. Lee and J. D. Crowley,
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(h) R. Saravanakumar, V. Ramkumarand and S. Sankararaman,
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(j) A. Poulain, D. Canseco-Gonzalez, R. Hynes-Roche,
8a–c (nav = 2026–2028 cmÀ1) and 9a–c (nav = 2021–2022 cmÀ1
)
suggests that the corresponding thiazol-4-ylidenes are probably
stronger than the corresponding oxazol-4-ylidenes (Scheme 4).
In conclusion, we have established a facile and modular
method for the preparation of a series of new 2,3,5-triaryl-
substituted oxazolium and thiazolium salts. The oxazolium
and thiazolium salts can act as precursors for the synthesis of
novel oxazol-4-ylidene and thiazol-4-ylidene rhodium com-
plexes, which are robust and thermally stable. Future work
will be aimed at investigating the applications of these novel
aNHC ligands in transition-metal catalyzed reaction.
H. Muller-Bunz, O. Schuster, H. Stoeckli-Evans, A. Neels and
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M. Albrecht, Organometallics, 2011, 30, 1021; (k) J. Bouffard,
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Financial support from Shanghai Pujiang Talent Program
(11PJ1402500), the Fundamental Research Funds for the
Central Universities (WK1114014), the Shanghai Municipal
Committee of Science and Technology (08dj1400100-2),
National Basic Research Program of China (973)-2010CB833302,
and the National Natural Science Foundation of China (21171056,
21072206, 20472096, 20872162, 20672127, 20821002 and 20732008)
is greatly acknowledged.
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c
This journal is The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 9625–9627 9627