Reactions of a diborylstannylene with CO2 and N2O: diboration of carbon dioxide by a main group bis(boryl) complex

Abstract

The reactions of the boryl-substituted stannylene Sn{B(NDippCH)₂}₂ (1) with carbon dioxide have been investigated and shown to proceed via pathways involving insertion into the Sn–B bond(s). In the first instance this leads to formation of the (boryl)tin(II) borylcarboxylate complex Sn{B(NDippCH)₂}{O₂CB(NDippCH)₂} (2), which has been structurally characterized and shown to feature a κ² mode of coordination of the [(HCDippN)₂BCO₂]⁻ ligand at the metal centre. 2 undergoes B–O reductive elimination in hexane solution (in the absence of further CO₂) to give the boryl(borylcarboxylate)ester {(HCDippN)₂B}O₂C{B(NDippCH)₂} (3) i.e. the product of formal diboration of carbon dioxide. Alternatively, 2 can assimilate a second equivalent of CO₂ to give the homoleptic bis(borylcarboxylate) Sn{O₂CB(NDippCH)₂}₂ (4), which can be prepared via an alternative route from SnBr₂ and the potassium salt of [(HCDippN)₂BCO₂]⁻, and structurally characterized as its DMAP (N,N-dimethylaminopyridine) adduct. Structural and reactivity studies also point to the possibility for extrusion of CO from the [(HCDippN)₂BCO₂]⁻ fragment to generate the boryloxy system [(HCDippN)₂BO]⁻, a ligand which can be generated directly from 1via reaction with N₂O. The initially formed unsymmetrical species Sn{B(NDippCH)₂}{OB(NDippCH)₂} has been shown to be amenable to crystallographic study in the solid state, but to undergo ligand redistribution in solution to generate a mixture of 1 and the bis(boryloxy) complex Sn{OB(NDippCH)₂}₂.