Bridging Bis(boryl) and Borylene Species Stabilized in the Coordination Sphere of Ruthenium Metals

Synthetic routes for the synthesis of doubly bridging bis(boryl) and triply bridging borylene species of ruthenium have been established. The room-temperature reaction of [Cp*RuCl2]2 with LiBH4·THF followed by the addition of [S2CPPh3] led to the formation of a diruthenium bridging bis(boryl) complex, [(Cp*Ru)2(μ-HBS(C═S)S-κ2B:κ2S)(μ-HBSCH2S-κ2B:κ2S)] (1) consisting of two unsymmetrical boryl ligands. In parallel to 1, this reaction also yielded a Cp*-based ruthenium dithioformate half-sandwich complex, [Cp*Ru(PPh3){η3-SC(H)S}] (2) depicting four-legged piano stool geometry. Interestingly, when the reaction of [Cp*RuCl2]2 was carried out with NaBH4, it led to the formation of a triruthenium cluster [(Cp*Ru)3(μ-H)5(μ3-BH)2] (3) having a triply bridging borylene moiety. Cluster 3 comprises two triply bridging {BH} units axially bound to both sides of the triangular Ru3 plane giving rise to a trigonal bipyramidal Ru3B2 core. Theoretical calculations were implemented on these bridging bis(boryl) and borylene species to understand their bonding scenarios.