Five-coordinate dicarbonyl complexes of rhodium(I): [RhX(CO)2(PPh3)2] (X = Cl, Br, I)

The complexes trans-[RhX(CO)PPh 3 ) 2 ] (1, X = Cl, Br, I) react with CO to form [RhX(CO) 2 (PPh 3 ) 2 ] (2), and not to form cis-[RhX(CO)(PPh 3 ) 2 ]. Complexes 2 contain equivalent axial carbonyl ligands. It is proposed that a series of dicarbonyl complexes, including 2, is formed during decarbonylation reactions catalyzed by 1.