Ferra- and Ruthenatricarbollides CpFeC₃B₈H₁₁ and Cp*RuC₃B₈H₁₁

The room-temperature photochemical reaction of the tricarbollide anion [nido-7,8,9-C3B8H11]- (1a) with [CpFe(C6H6)]+ proceeds without cluster rearrangement to form the 12-vertex closo-ferratricarbollide 1-Cp-1,2,3,4-FeC3B8H11 (2a, the metal atom is assigned number 1). 2a rearranges to the isomeric complex 1-Cp-1,2,3,5-FeC3B8H11 (2b) at 110 °C and further to 1-Cp-1,2,4,10-FeC3B8H11 (2c) at 165 °C. The reaction of 1a with [Cp*RuCl]4 is accompanied by polyhedral rearrangement giving 1-Cp*-1,2,3,5-RuC3B8H11 (3b). Its further isomerization occurs slowly at room temperature and rapidly at 65 °C to give complex 1-Cp*-1,2,4,10-RuC3B8H11 (3c). Similar reactions of [nido-7,8,10-C3B8H11]- (1b) with [CpFe(C6H6)]+ and [Cp*RuCl]4 afford 2b and 3b, respectively. A diamond-square-diamond mechanism for the 2a → 2b → 2c rearrangement sequence is proposed. The relative stability of isomers 2a−c was estimated by DFT calculations. The constitution of the compounds prepared was determined by multinuclear NMR spectroscopy and mass spectrometry. The structures of 2a, 2b, and 3c were established by X-ray diffraction.