Platinum complexes of P,N- and P,N,P-ligands and their application in the hydroformylation of styrene

Neutral complexes of the formula PtCl2(L) (where L = ortho-diphenylphosphino-N-(2-hydroxyethyl)-N-methylaniline (1), ortho-diphenylphosphino-N-2-(diphenylphoshinoxy)-ethyl)-N-methylaniline (2) and N,N-bis(2-(diphenylphoshinoxy)ethyl)aniline (3)) were prepared. Various binding modes, such as P,N- and P,P-bidentate and monodentate coordinations were observed with these hemilabile ligands in the parent complexes and in the triphenylphosphine-added systems. 31P NMR studies on the ‘in situ’ systems revealed the hemilabile character of the ligands. The platinum complexes proved to be precursors to catalysts of low activity for the hydroformylation of styrene in platinum-ligand (1, 2 or 3)-tin(II) chloride system. High chemoselectivities (up to 82%) were obtained, while the two aldehyde regioisomers were formed in almost equimolar ratio with the slight preference of the branched aldehyde, 2-phenylpropanal. Remarkable increase in regioselectivity was observed in the presence of para-toluenesulfonic acid additive using platinum-ligand (1) systems.