CO2 reduction via aluminum complexes of ammonia boranes.

Reactions of amine-boranes NH3BH3, Me2NHBH3, or Me3NBH3 with AlX3 (X = Cl, Br, I, C6F5) have been examined. The species AlBr3·H3BNMe3 2, Al(C6F5)3·H3BNMe3 3, Al(C6F5)3·H3BNHMe2 4 and Al(C6F5)3·H3BNH3 5 have been prepared and isolated. The analogous reaction of B(C6F5)3 and H3BNMe3 results in C6F5-transfer and the formation of (C6F5)BH2·NMe3 6. While the adduct 6 was unreactive to CO2, species 3 reacts with CO2 to give the formate linked Al(C6F5)3(HCO2)H2BNMe38. The species R3PC(OAl(C6F5)3)2 (R = o-tol (1'-C6F5), R = Mes (1-C6F5)) were prepared, and 1'-C6F5 was shown to react with amine-boranes to effect the reduction of this bound-CO2 to formate and methoxide-derivatives, proceeding through intermediates including 8 and [(Me3NBH2)2(μ-H)][(HCO2)(Al(C6F5)3)2] 9. The salt [tBu3PH][(HCO2)(Al(C6F5)3)2] 10 was prepared independently.