Oxidative addition of acid chlorides to cationic rhodium(I) complexes of chelating diphosphines

The reaction of benzoyl chloride with [Rh(dppp)2]Cl at 190°C and with [Rh(dppp)Cl]1 or 2 at 25°C where dppp  1,3-bis(diphenylphosphino)propane has been examined. In both cases the five coordinate compound RhCl2(COPh)-(dppp) was rapidly formed and isolated in high yield. This compound does not undergo phenyl migration to RhCl2(CO)(Ph)(dppp) even upon warming to 190°C in benzoyl chloride solution and no decarbonylation products are observed. This is in marked contrast to the reaction of RhCl(PPh3)3 with benzoyl chloride where the migrated product RhCl2(CO)(Ph)(PPh3)2 is formed with the eventual reductive elimination of chlorobenzene. The single crystal X-ray analysis of RhCl2(COPh)(dppp) has been carried out (R  0.036). The compound is square pyramidal with the COPh group in the apical position. The Rh—C bond distance of 1.992(3) Å is short for a RhIII—Cσ bond and indicates dπ → π★ back bonding.