Unexpected rhodium-templated reductive coupling of two acetylene groups : synthesis and X-ray structure of [{RhClI2(CO)}2(dppbute)] dppbute = Z-1,2,3,4-tetrakis(diphenylphosphano)but-2-ene

Bis(diphenylphosphano)acetylene is known to join metal centres through one, two, or three molecules. However, few examples of coupling reactions between coordinated ligands containing acetylene groups are reported. Synthesis and X-ray structure of the title compound are here described. It consists of two Rh(III) atoms bridged by a tetradentate phosphane ligand, Z-1,2,3,4-tetrakis(diphenylphosphano)but-2-ene, generated by reductive coupling of two acetylenic moieties of the dimeric complex (A). Two condensate metallacycles are so generated. A carbonyl molecule, a chlorine and two iodine atoms complete the coordination sphere at each octahedral rhodium centre. Proton source it is likely to be water traces in solvents. The species was synthesised the first time by serendipity and then it was obtained again in several condition.