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((IBuPr)-Bu-t-Pr-i ')((IBuPr)-Bu-t-Pr-i)][BArF], 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 sigma-BH complexes [Pt(HBR2)((IBuPr)-Bu-t-Pr-i ')((IBuPr)-Bu-t-Pr-i)][BArF], one of which has been isolated. From -15 to +10 degrees C, the sigma-BH species undergo a carbon-boron coupling process leading to the platinum hydride derivative [Pt(H)((IBuPr)-Bu-t-Pr-i-BR2)((IBuPr)-Bu-t-Pr-i)][BArF], 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)((IBuPr)-Bu-t-Pr-i)(2)][BArF], 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.

Automated summary

A reversible carbon-boron bond formation has been observed in the reaction between a coordinatively unsaturated Pt(ii) complex and tricoordinated boranes, leading to the formation of several intermediate complexes. Computational methods suggest that the kinetic formation of carbon-boron coupling products is under kinetic control, while the platinum boryl species resulting from competitive C-H bond coupling are thermodynamically more stable. These findings provide valuable insights into productive carbon-boron coupling reactions at transition metal centers.