Activation and functionalisation of carbon dioxide by bis-tris(pyrazolyl)borate-supported divalent samarium and trivalent lanthanide silylamide complexes†

Synthesis and reactivity with carbon dioxide (CO₂) of divalent samarium in the bis-tris(pyrazolyl)borate ligand environment has been reported. In addition, CO₂ activation and functionalisation by lanthanide silylamides in the bis-tris(pyrazolyl)borate ligand environment was demonstrated. Reduction of the Sm(III) precursor [Sm(Tp)₂(OTf)] (Tp = hydrotris(1-pyrazolyl)borate; OTf = triflate) with KC₈ yielded the insoluble Sm(II) multi-metallic coordination polymer [{Sm(Tp)₂}_n] 1-Sm. Addition of 1,2-dimethoxyethane (DME) to 1-Sm enabled isolation of the monomeric complex [Sm(Tp)₂(DME)] 1-Sm(DME). Complex 1-Sm(DME) reduced CO₂ to yield the oxalate-bridged dimeric Sm(III) complex [{Sm(Tp)₂}₂(μ-η²:η²-O₂CCO₂)] 2-Sm. The reactions of heteroleptic Ln(III) silylamide complexes [Ln(Tp)₂(N′′)] (Ln = Y, Sm; N′′ = N(SiMe₃)₂) with CO₂ yielded monomeric Ln(III) silyloxides [Ln(Tp)₂(OSiMe₃)] 3-Ln and trimethylsilyl isocyanate (OCNSiMe₃). Complexes 3-Ln are the first crystallographically characterised examples of Ln(III)–OSiMe₃ bonds accessed via CO₂ activation and functionalisation. Full characterisation data are presented for all complexes, including solid-state molecular structure determination by single-crystal X-ray diffraction.