CO2 reduction by lanthanide borohydride complexes and hydroboration reactivity

Although lanthanide borohydride precursors are useful building blocks to access a variety of molecular lanthanide complexes, the nucleophilic reactivity of the attached [BH4]– unit has not been thoroughly investigated. We herein report the reaction of [La(Cpttt)2(BH4)] (1, Cpttt = 1,2,4-tris(tert-butyl)cyclopentadienyl) towards CO2, leading to the formation of a formate complex, which exists as an equilibrium mixture between the dimeric and monomeric forms in aromatic solvents. DOSY 1H NMR experiments allowed a convenient analysis of the reaction mixture and provided an estimation of the hydrodynamic radii for both species. Hydroborane reagents (BH3, HBPin, H(9-BBN)) further react with the formate complex, leading to the formation of borylated methanol and the corresponding lanthanide boroxide complexes. Preliminary investigations were performed to investigate the viability of complex 1 as a pre-catalyst in the hydroboration of CO2.