Hydroboration and Deoxygenation of CO Mediated by a Gallium(I) Cation.

Hydroboration of CO to formoxy borane occurs under ambient conditions in acetonitrile using pinacolborane HBpin in the presence of gallium(I) cation [(MeTACD)Ga][BAr] (; MeTACD = ,',″,'''-tetramethyl-1,4,7,10-tetraazacyclododecane; Ar = CH-3,5-Me). Slow turnover was accompanied by side reactions including ligand scrambling of HBpin to give BH(CHCN) and crystalline Bpin. When was reacted with CO alone, the formation of the gallium(III) carbonato complex [(MeTACD)Ga(κ-OCO)][BAr] () along with CO was observed. This complex was assumed to form via the unstable oxido cation [(MeTACD)Ga=O] (). Reaction of with NO in the presence of BPh confirmed the formation of the oxido cation, which was spectroscopically characterized as a triphenylborane adduct [(MeTACD)Ga=O(BPh)][BAr] (). CO was also detected when CO was reacted with in the presence of HBpin, suggesting that compound may also be formed in initial stages of catalysis. Compound reacts with HBpin to give formoxy borane, borane redistribution products, and an unidentified MeTACD-containing species , which was also observed in "catalytic" runs starting from , HBpin, and CO. Hydroboration of CO using HBpin with slow turnover and competitive ligand scrambling was also observed in the presence of gallium(III) hydride dication [(MeTACD)GaH][BAr] (), which is unreactive toward CO in the absence of HBpin.