Transformation of [PPh4][Fe5RhC(CO)16] under hydroformylation conditions: synthesis and crystal structure of [PPh4][Fe3Rh3C(CO)15]

Abstract

The cluster [PPh₄][Fe₅RhC(CO)₁₆](1), used as the catalyst precursor for the hydroformylation of 1-pentene (60 atm of a 1 : 1 mixture of CO + H₂, 100 °C), evolves to a mixture of [Fe₄Rh₂C(CO)₁₆](2) and [PPh₄][Fe₄RhC(CO)₁₄](3). When hydroformylation is performed with (3) as the catalyst precursor, the new cluster [PPh₄][Fe₃Rh₃C(CO)₁₅](4) is formed. The structure of (4) has been determined by a single-crystal X-ray diffraction study and was found to consist of an octahedral cluster anion with the three rhodium and the three iron atoms in fac positions. The encapsulated carbido-carbon atom is octahedrally co-ordinated to the six metal atoms. The transformations (1)→(2)+(3) and (3)→(4) are nearly quantitative with regard to the rhodium metal and are also observed under CO pressure at 100 °C without adding 1-pentene or hydrogen. Complexes (2) and (4) are catalyst precursors for the hydroformylation of 1-pentene and are the only spectroscopically detectable compounds after catalysis, (4) being recovered in 70–80% yield after catalysis.