BH3 Activation by Phosphorus-Stabilized Geminal Dianions: Synthesis of Ambiphilic Organoborane, DFT Studies, and Catalytic CO2 Reduction into Methanol Derivatives

The reaction of the geminal dianion (SCS)2– 1 with 2 equiv of BH3·SMe2 leads to the isolation and full characterization of the new organoborane [(SCS)­BH2]­[Li­(THF)2] 2, in which the CB bond possesses ambiphilic, multiple character. Treatment of 2 with another 1 equiv of BH3·SMe2 allows the isolation of the rare cyclic diborane species [(SCS)­B2H5]­[Li­(OEt2)] 4. The electronic structures of both compounds were investigated by means of DFT calculations. Compound 4 is an efficient catalyst for the reduction of CO2 to methanol derivatives by BH3·SMe2. A TON of ca. 2800 (TOF = 127 h–1) was achieved using 0.1 mol % of 4 in THF.