Synthesis and structural characterization of the isomers of Rh 6(CO) 14L 2 clusters (L = NCME, Py, P(OPh) 3), X-ray crystal structure of trans-Rh 6(CO) 14{P(OPh 3)} 2

Abstract

The reaction of Rh 6(CO) 16 with two equivalents of Me 3 NO in the presence of a substituting ligand (L = NCME, Py, P(OPh) 3) affords a mixture of isomers of the general formula Rh 6(CO) 14L 2. The substituting ligands occupy two terminal sites in the structure of the parent cluster. For L = P(OPh) 3 three isomers ( I-III) were separated from the reaction mixture. The structure of the first isomer (I) has been established by X-ray analysis. This compound crystallizes in two polymorphic modifications, monoclinic and triclinic; both of which consist of identical molecules and differ only in the packing of the molecules in the crystals. It should be noted that both polymorphic forms contain in the unit cells the racemic mixture (RR and SS) of the Rh 6(CO) 14{P(OPh) 3} 2 molecules. This octahedral cluster may be considered as a derivative of the parent Rh 6(CO) 16 cluster with two terminal CO groups in trans positions at Rh(1) and Rh(2) atoms substituted by phosphite ligands. The structures of two other disubstituted clusters, (II) and (III) were established by 31P NMR spectroscopy. Phosphite ligands in these compounds occupy the terminal sites at the adjacent rhodium atoms of the Rh 6 octahedron but differ in their mutual orientation. Other disubstituted derivatives (L = NCME, Py) are labile compounds and exist in solution as inseparable mixtures of the isomers characterized by 1H and 13C NMR spectroscopy. A mechanism of interconversion of the isomers is proposed.