The formation of cis- and trans-[Ru(CN)2(CNtBu)4] by reductive cleavage of isocyanide ligands; isomer separation by supramolecular interactions with various solvents

Abstract

The octahedral complexes cis- and trans-[Ru(CN)₂(CN^tBu)₄] are prepared in quantitative yields from the reaction of Ru₃(CO)₁₂ with an excess of the isocyanide and under CO pressure. During the reaction, part of the isocyanide ligands are reductively cleaved to yield the cyanide ligands, isobutene and hydrogen. The latter were unequivocally detected by GC and GC-MS measurements. The complexes are observed in a 1 ∶ 1 mixture of the two isomers. These isomeric coordination compounds may be separated by recrystallization from various solvents. The crystal structures are built up by supramolecular arrangements in which the cyanide ligands act as hydrogen bond acceptors. Therefore the properties of the solvents to act as hydrogen bond donors or acceptors together with the different steric requirements of cyanide ligands arranged in a cis or trans configuration lead to the crystallization of either the cis- or trans-isomer or crystalline material containing both isomers, respectively. The use of dichloromethane leads to the precipitaion of crystals with a 1 ∶ 1 mixture of both isomeric complexes. With dry chloroform as the solvent, the trans-isomer crystallizes within days, whereas the cis-isomer precipitates after months. Using neat chloroform leads to the formation of crystals of the cis-isomer only. The use of acetone yields crystals with only the trans-isomer present for the dry as well as for the neat solvent.