Concentration dependent switch from addition to substitution in the reaction between salicylaldoxime and a nitrile platinum(IV) complex

The nitrile complex [Ph3PCH2Ph][PtCl5(EtCN)] reacts with one equivalent of salicylaldoxime, HONCH(C6H4OH-o), in CH2Cl2 to afford mainly the addition product [Ph3PCH2Ph][PtCl5{NHC(Et)ONCH(C6H4OH-o)}] (1). In a diluted solution, i.e. if the same amount of the reagents is dissolved in 50-fold volume of dichloromethane, the four platinum-containing species, i.e.1, [Ph3PCH2Ph][PtCl4{C6H4(O)C(H)NOH}] (2) [Ph3PCH2Ph][PtCl5(NH3)] (3), and [Ph3PCH2Ph]2[PtCl6] (4), are formed and the substitution compound 2 is the major product at low concentrations. Addition of EtCN to the less concentrated solution suppresses the formation of the substitution product 2 and moves the reaction back towards formation of the addition product 1. The complex 1 is unstable in non-dried solutions and decomposes to give 2 along with 3, 4 and EtCO2H. Compounds 1, 2 and 4·1/2H2O were characterized by elemental analyses, FAB mass-spectrometry, IR and 1H, 13C{1H}, 31P{1H} and 195Pt NMR spectroscopies. X-ray structure determinations have been performed for 2 and 4·1/2H2O.