CO2reductionvia aluminum complexes of ammonia boranes

Abstract

Reactions of amine-boranes NH₃BH₃, Me₂NHBH₃, or Me₃NBH₃ with AlX₃ (X = Cl, Br, I, C₆F₅) have been examined. The species AlBr₃·H₃BNMe₃2, Al(C₆F₅)₃·H₃BNMe₃3, Al(C₆F₅)₃·H₃BNHMe₂4 and Al(C₆F₅)₃·H₃BNH₃5 have been prepared and isolated. The analogous reaction of B(C₆F₅)₃ and H₃BNMe₃ results in C₆F₅-transfer and the formation of (C₆F₅)BH₂·NMe₃6. 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′-C₆66F₅55), R = Mes (1-C₆6F₅5)) were prepared, and 1′-C₆66F₅55 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.