Synthesis and Structures of Ruthena-octahydrotetraborane Complexes

The reactivity of κ2-N,S-chelated ruthenium borate complexes, [Ru(PPh3)(κ2-N,S-(NC7H4S2)Ru{κ3-H,S,S′-H2B (NC7H4S2)2}] (1 a) and [Ru(PPh3)(κ2-N,S-(NC5H4S){κ3-H,S,S′-H2B(NC5H4S)2}] (1 b) with monoboranes have been explored. The prolonged room temperature reaction of [Ru(PPh3){κ2-N,S-(NC7H4S2)}{κ3-H,S,S′-H2B(NC7H4S2)2}], 1 a with an excess of [BH3 ⋅ THF] led to the formation of hydrogen-rich complex, arachno-[PPh3(κ2-B3H8)Ru{κ3-H,S,S′-H2B(NC7H4S2)2] (2). In a similar fashion, the isomeric ruthenatetraborane complexes of [Ru(PPh3)(κ2-N,S-(B3H8){κ3-H,S,S′-H2B(NC5H4S)2}], 4 and 5 were isolated from the room temperature reaction of 1 b with [BH3 ⋅ THF]. In complex 2, the borate ligand, [H2B(NC5H4S)2] and the PPh3 occupy the endo and exo sites of the butterfly-shaped RuB3 core, respectively. In contrast, the borate unit [H2B(NC5H4S)2] in 4 sits on the exo position of the butterfly core, while the phosphine ligand occupies the endo site. Multinuclear spectroscopic analyses were done to characterize all new complexes and the structures were further confirmed by single-crystal X-ray diffraction analysis. Density functional theory (DFT) calculations were performed to probe into the bonding modes of these complexes.