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() complex [Pt(I t Bu i Pr')(I t Bu i Pr)][BAr F ], 1, with tricoordinated boranes HBR. 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(HBR)(I t Bu i Pr')(I t Bu i Pr)][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 t Bu i Pr-BR)(I t Bu i Pr)][BAr F ], 4. Surprisingly, these compounds are thermally unstable undergoing carbon-boron bond cleavage at room temperature that results in the 14-electron Pt() boryl species [Pt(BR)(I t Bu i Pr)][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() complex [Pt(I t Bu i Pr')(I t Bu i Pr)][BAr F ], 1, with tricoordinated boranes HBR.