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

Abstract

The nitrile complex [Ph 3PCH 2Ph][PtCl 5(EtCN)] reacts with one equivalent of salicylaldoxime, HONCH(C 6H 4OH- o), in CH 2Cl 2 to afford mainly the addition product [Ph 3PCH 2Ph][PtCl 5{NHC(Et)ONCH(C 6H 4OH- 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, [Ph 3PCH 2Ph][PtCl 4{C 6H 4(O)C(H)NOH}] ( 2) [Ph 3PCH 2Ph][PtCl 5(NH 3)] ( 3), and [Ph 3PCH 2Ph] 2[PtCl 6] ( 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 EtCO 2H. Compounds 1, 2 and 4·1/2H 2O 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 4·1/2H 2O.