Quest for Active Species in Al/B-Catalyzed CO Hydrosilylation.

We demonstrate the catalytic role of aluminum and boron centers in aluminum borohydride [(2-MeCHCH)(CH)Al(μ-H)B(CH)] () during carbon dioxide (CO) hydrosilylation. Preliminary investigations into CO reduction using [(2-MeNCHCH)(H)Al(μ-H)] () and [PhC][B(3,5-CHCl)] () in the presence of EtSiH and PhSiH resulted in CH(OSiR) and CHOSiR, which serve as formaldehyde and methanol surrogates, respectively. In pursuit of identifying the active catalytic species, three compounds, B(3,5-CHCl) (), [(2-MeNCHCH)(3,5-CHCl)Al(μ-H)B(3,5-CHCl)] (), and [(2-MeNCHCH)Al(THF)][B(3,5-CHCl)] (), were isolated. Among compounds -, the highest catalytic conversion was achieved by . Further, and were prepared in a straightforward method by treating with and BPh, respectively. was found to be in equilibrium with and BPh, thus making the catalytic process of more efficient than that of . Computational investigations inferred that CO reduction occurs across the Al-H bond, while Si-H activation occurs through a concerted mechanism involving an generated aluminum formate species and BPh.