CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

Fig. II.3.8. 13 C NMR spectrum of 60g
Mechanistic studies: For the mechanistic insight of the activating role of [bmim][Br], the
nature of the organometallic species, responsible for allylation was probed. For this, the
course of the reaction between Ga (1 mmol) and allyl bromide (1 mmol) in [bmim][Br] (2
mL) was followed over a time period (up to 8 h), by 1 H NMR spectra. The intensity of the
NMR peak due to the CH 2 -Ga protons in the allyl-gallium species was quantified by
comparing with that of the CH 2 Br signal of allyl bromide. The 1 H NMR spectra of the
reaction mixtures obtained in [bmim][Br] showed a new doublet at δ 1.63 (J = 6.4 Hz)
with simultaneous reduction of the signal at δ 3.9. In addition, new olefinic multiplets at δ
4.59 at the expense of that at δ 4.78 also emerged, and these resonances together accounted
for two protons over the entire period of studies. The 1 H NMR doublets for the CH 2 -Ga
protons suggested 66a (CH 2 CH=CH 2 ) 2 GaBr (III) as the active allyl-Ga species, which was
confirmed by its isolation (distillation at 45 o C), followed by spectral ( 1 H and 13 C NMR),
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