CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

the imidazolium salts to Pt(o) has been shown to be exothermic. 94 Since their description
by Wanzlic 95a-c and Arduengo, 95d-f stable NHCs have been a significant area of study and
several crystalline and well-characterized NHC complexes with main group and especially
transition metals have been synthesized. 96 The NHCs can stabilize thermally labile or low
oxidation state metal fragments, and the complexes can be used for various organic
transformation. The use of NHCs as good σ-donor molecules to stabilize trivalent group 13
compounds is well established. 96a,97 Over the past few years there has been a rapidly
increasing interest in the chemistry of metastable gallium complexes. The propensity of
alkyl gallium reagents to interact with Lewis bases has become a cornerstone in
organometallic chemistry. To this end, a large number of NHC-complexes with metal (Al,
In, and Ga) hydrides and halides have since been synthesized. 95e,98 However, formation of
Ga-NHC directly from the metal is novel and opens various new possibilities in organic
synthesis as well as material developments. Sterically non-hindered NHCs are often
sensitive to air and moisture, making their isolation and use difficult. 95d,99 However, in this
case its formation was achieved in a hygroscopic RTIL, also required O 2 .
Earlier, the Pd-carbene complexes have been shown to be efficient catalysts for the
Heck and related CC bond forming reactions. 69e It was also found that the Ga-carbene
complex IV acts as a catalyst in the formation of III. A catalytic amout of IV was added to
the mixture of Ga metal and [bmim][Br] prior to the addition of allyl bromide, and it was
observed that the formation of III was catalysed and subsequently the reaction (Scheme
II.3.9) was also faster. The exact mechanism of the catalysis is at present, far from clear. It
may in fact turn out to follow a much more complex pathway. The Ga-NHC complex
might be the precursor, which would generate a zero-valent Ga-NHC species as the likely
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