Paramagnetic (1,3-Diborolyl)ruthenium Triple-Decker Complexes and Transformation into Diamagnetic Complexes Having Bridging 1,3-Diborafulvene Ligands

The paramagnetic triple-decker complexes [(Cp*Ru)(2){mu-(CMe)(3)(BCl)(BMe)}] (3b) and [(Cp*Ru)(2){mu-(CMe)(3)(BCl)(2)}] (3c) are formed by refluxing a mixture of [Cp*RuCl](4) and pentamethy1-2,3-dihydro-1,3-diborole in thf. In CH2Cl2 under air complex 3b slowly looses a hydrogen atom with formation of the diamagnetic triple-decker [(Cp*Ru)(2){mu-eta(5):eta(6)-(CMe)(3)-(BCl)(BCH2)}] (413) with the unsymmetrical dihydrodiborafulvene derivative in a bridging position. The analogous complex [(Cp*Ru)(2){mu-eta(5):eta(6)-(CMe)(3)(BMe)-(BCH2)]} (4a) is obtained by interaction of HCl with the triple-decker [(CP*Ru)(2)-{mu-(CMe)(3)(BMe)(2)}] (3a). According to calculations, complexes 4a and 4b have an almost non-distorted triple-decker arrangement with a strong bending of the B=CH2 group toward one of the Ru atoms. For the formation of 3b and 3c the chloro-containing sandwich complexes [Cp*Ru{eta(5)-(CMe)(3)-(BCl)(BR1)}] (2b,c R-1 = Me, Cl) are proposed as intermediates. The constitutions of the complexes are derived from NMR, MS and DFT data, and the molecular structure of 3b is confirmed by an X-ray diffraction analysis.