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

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 kappa(2) mode of coordination of the [(HCDippN)(2)BCO2](-) 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)(2)B}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(NDippal)(2)}(2) (4), which can be prepared via an alternative route from SnBr2 and the potassium salt of [(HCDippN)(2)BCO2]-, 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)(2)BCO2](-) fragment to generate the boryloxy system [(HCDippN)(2)BO](-), a ligand which can be generated directly from 1 via 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).

Automated summary

The reaction of boryl-substituted stannylene with carbon dioxide proceeds via pathways involving insertion into the Sn-B bonds. Several different products can be derived from this reaction, including boryl(borylcarboxylate)ester and bis(borylcarboxylate) stannylene complexes. The possibility of extrusion of CO from the reaction products to generate boryloxy systems has also been observed.