Stereoelectronic effects on the chelating properties of [2-(methylsulfinyl)ethyl]diphenylarsine and its phosphorus analogue.

Abstract

A pair of internally diastereomeric platinum(II) complex cations containing the orthometalated ( S)-(1-(dimethylamino)ethyl)naphthalene and the racemic form of the sulfinyl-substituted ligand Ph 2ECH 2CH 2S(O)Me ((E-S(O), where E = As, P) has been prepared via two routes originating from ( S)-(+)-bis( m-chloro)bis[1-[1-(dimethylamino)ethyl]-2-naphthalenyl- C, N]diplatinum(II). The crystal structure of the arsenic analogue (crystal data: triclinic. P1, a = 7.950(2) Å, b = 17.449(3) Å, c= 21.981(4) Å,α = 82.67(2)° β = 87.06(2)°,γ= 82.87(2)°, Z = 4 and R = 0.0409) shows the ligand being coordinated to platinum(II) in both diastereomers as a bidentate chelate exclusively via arsenic and sulfur donor atoms. Proton NMR studies also indicate the retention of this AsS coordination in solution. A similar bonding mode was observed for the analogous phosphine complex. The ES chelation appears to be governed by the electronic properties of platinum. In contrast to the previously documented palladium(II) analogues, the EO chelation is not observed in the present series of platinum(II) compounds although there will be less severe ligand-ligand interactions if the ES(O) ligands form six-membered chelate rings in these square-planar systems.