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

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 [3-L-3,3,8-{Ph2P(CH2)(4)PPh-mu-GRAPHICS (1) with aliphatic amines in dichloromethane solution at 40 degrees 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): [3-L-3,3,8-{Ph2P(CH2)(4)PPh-mu-GRAPHICS (2: L= PPh3; 4: L= CH3CN). A bis(orthophenylene)cycloboronated complex [3-CH3CN-3,3,7,8-{Ph2P(CH2)(4)P-mu-GRAPHICS (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)(4)PPh2-3-H-3-Cl-closo-3,1,2-RuC2B9H11] (7) gives 3-CH3CN-3,3-Ph2P(CH2)(4)PPh2-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. (C) 2018 Elsevier B.V. All rights reserved.