CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

standard reduction potential (0.641 V) of [bmim][Br] also supported the possibility of CT
between Ga and the RTIL.
H H
H H
Br -
N + N
+ Ga
N +δ
Ga +δ
N Br -
C4 H 9 C4 H 9
H
H
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Scheme II.3.7
On continued stirring for 1-1.5 h, the mixture of [bmim][Br] and Ga (1.0 mmol)
eventually produced a gray solid. The thermal stability of the solid was studied using
differential scanning calorimetry (DSC). This showed a gradual mass loss starting at
~120 o C accompanied by a large endothermic thermal transition at ~162 o C producing Ga
metal (Fig. II.3.11). The residue after first heating was cooled and again heated; this time
it clearly indicated the presence of Ga metal. Sucessive experiments produced Ga metal in
pure form, leaving the carbine residue, which was confirmed by recording the 1 H NMR
spectrum of the organic residue left after the DSC experiment. This indicated the
generation of a N-heterocyclic carbene (NHC), suggesting it to be an organometallic
compound containing a NHC moiety. Its IR spectrum (thin film) displayed a strong –O-H
stretching band (3545 cm -1 ), while a 1 H NMR singlet at δ 7.21 (2H) (Fig. II.3.12) and 13 C
NMR (Fig. II.3.13) resonances at δ 121.7 and 123.3 (olefin) along with δ 175.9 (carbene)
revealed the presence of a N-heterocyclic carbene (NHC) moiety. The Raman spectrum
confirmed the Ga-C (697 cm -1 ) and Ga-O (330 and 662cm -1 ) bonds, while excluding any
Ga-Ga and Ga-O-Ga bonds. 89 The electron impact mass spectrum showed a [M + -57] ion
peak at m/z 264 (17 % ), a [M + -Br] ion peak at m/z 241 (11%), and a major fragmentation
peak at m/z 184 (18%) (GaBr(OH) 2 ) in the correct isotopic pattern. In addition, a major
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