| Summary: | <p>The reactions of the boryl-substituted stannylene Sn{B(NDippCH)<small><sub>2</sub></small>}<small><sub>2</sub></small> (<strong>1</strong>) with carbon dioxide have been investigated and shown to proceed <em>via</em> pathways involving insertion into the Sn–B bond(s). In the first instance this leads to formation of the (boryl)tin(<small>II</small>) borylcarboxylate complex Sn{B(NDippCH)<small><sub>2</sub></small>}{O<small><sub>2</sub></small>CB(NDippCH)<small><sub>2</sub></small>} (<strong>2</strong>), which has been structurally characterized and shown to feature a κ<small><sup>2</sup></small> mode of coordination of the [(HCDippN)<small><sub>2</sub></small>BCO<small><sub>2</sub></small>]<small><sup>−</sup></small> ligand at the metal centre. <strong>2</strong> undergoes B–O reductive elimination in hexane solution (in the absence of further CO<small><sub>2</sub></small>) to give the boryl(borylcarboxylate)ester {(HCDippN)<small><sub>2</sub></small>B}O<small><sub>2</sub></small>C{B(NDippCH)<small><sub>2</sub></small>} (<strong>3</strong>) <em>i.e.</em> the product of formal diboration of carbon dioxide. Alternatively, <strong>2</strong> can assimilate a second equivalent of CO<small><sub>2</sub></small> to give the homoleptic bis(borylcarboxylate) Sn{O<small><sub>2</sub></small>CB(NDippCH)<small><sub>2</sub></small>}<small><sub>2</sub></small> (<strong>4</strong>), which can be prepared <em>via</em> an alternative route from SnBr<small><sub>2</sub></small> and the potassium salt of [(HCDippN)<small><sub>2</sub></small>BCO<small><sub>2</sub></small>]<small><sup>−</sup></small>, and structurally characterized as its DMAP (<em>N</em>,<em>N</em>-dimethylaminopyridine) adduct. Structural and reactivity studies also point to the possibility for extrusion of CO from the [(HCDippN)<small><sub>2</sub></small>BCO<small><sub>2</sub></small>]<small><sup>−</sup></small> fragment to generate the boryloxy system [(HCDippN)<small><sub>2</sub></small>BO]<small><sup>−</sup></small>, a ligand which can be generated directly from <strong>1</strong><em>via</em> reaction with N<small><sub>2</sub></small>O. The initially formed unsymmetrical species Sn{B(NDippCH)<small><sub>2</sub></small>}{OB(NDippCH)<small><sub>2</sub></small>} 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 <strong>1</strong> and the bis(boryloxy) complex Sn{OB(NDippCH)<small><sub>2</sub></small>}<small><sub>2</sub></small>.</p>
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