Synthesis of novel closo-carborane complexes of ruthenium (II) with triphenylphosphine or acetonitrile ligands via reduction of paramagnetic Ru(III) derivatives

Abstract

A novel method for synthesis of diamagnetic Ru(II) carborane clusters based on reduction of corresponding Ru(III) species by amines was developed. The interaction of paramagnetic 17-electron complex ▪ (1) with aliphatic amines in dichloromethane solution at 40 °C proceeds with the abstraction of chlorine atom from the ruthenium center and results in formation of corresponding 16-electron species. The latter can be stabilized by 2-electron ligands such as triphenylphosphine or acetonitrile through the formation of novel stable complexes of ruthenium (II): ▪ (2: L = PPh3; 4: L = CH3CN). A bis(ortho-phenylene)cycloboronated complex ▪ (6) may be obtained in a similar way from corresponding precursor. The related reaction conducted with diamagnetic closo-carborane cluster of ruthenium (IV) 3,3-Ph2P(CH2)4PPh2-3-H-3-Cl-closo-3,1,2-RuC2B9H11] (7) gives 3-CH3CN-3,3-Ph2P(CH2)4PPh2-closo-3,1,2-RuC2B9H11] (8). The obtained complexes were characterized by means of NMR and IR spectroscopy and mass spectrometry. A single-crystal X-ray diffraction study confirmed closo-structure of the obtained complexes and the presence of acetonitrile molecule as a ligand. The performed electrochemical investigation of the obtained ruthenacarboranes testified its ability to undergo reversible oxidation to Ru(III) species. The comparison of the properties of the obtained complex 2 with its analogue with shorter alkyl fragment in diphosphine moiety shows that the slight difference in the structure leads to the decrease of stability.