Reversible carbon–boron bond formation at platinum centers through σ-BH complexes

A reversible carbon–boron bond formation has been observed in the reaction of the coordinatively unsaturated, cyclometalated, Pt(ii) complex Pt(I^tBuⁱPr′)(I^tBuⁱPr)]BAr^F], 1, with tricoordinated boranes HBR₂. X-ray diffraction studies provided structural snapshots of the sequence of reactions involved in the process. At low temperature, we observed the initial formation of the unprecedented σ-BH complexes Pt(HBR₂)(I^tBuⁱPr′)(I^tBuⁱPr)]BAr^F], one of which has been isolated. From −15 to +10 °C, the σ-BH species undergo a carbon–boron coupling process leading to the platinum hydride derivative Pt(H)(I^tBuⁱPr–BR₂)(I^tBuⁱPr)]BAr^F], 4. Surprisingly, these compounds are thermally unstable undergoing carbon–boron bond cleavage at room temperature that results in the 14-electron Pt(ii) boryl species Pt(BR₂)(I^tBuⁱPr)₂]BAr^F], 2. This unusual reaction process has been corroborated by computational methods, which indicate that the carbon–boron coupling products 4 are formed under kinetic control whereas the platinum boryl species 2, arising from competitive C–H bond coupling, are thermodynamically more stable. These findings provide valuable information about the factors governing productive carbon–boron coupling reactions at transition metal centers.

A reversible carbon–boron bond formation has been observed in the reaction of the coordinatively unsaturated, cyclometalated, Pt(ii) complex Pt(I^tBuⁱPr′)(I^tBuⁱPr)]BAr^F], 1, with tricoordinated boranes HBR₂.