Five and six CO-ordinate σ-aryl derivatives of Ru(II) and Os(II) and the equilibrium RuRX(CO)2 (PPh3)2⇄ Ru[C(O)R]X(CO) (PPh3)2

Abstract Reaction of MHCl(CO) (PPh 3 ) 3 (M = Ru or Os) with HgR 2 (R = p -tolyl) yields red five co-ordinate, MRCl(CO) (PPH 3 ) 2 (square pyramidal R apical) and Hg; uptake of CO gives colourless MRCl(CO) 2 (PPh 3 ) 2 and in CH 2 Cl 2 the ruthenium dicarbonyl complex is in equilibrium with the acyl derivative Ru[C(O)R]Cl(CO) (PPh 3 ) 2 , for which evidence suggests a possible di-hapto -acyl ligand.