Platinum(II) phosphoryl-substituted thiourea complexes with bis-phosphine ligands and some triphenylarsine and triphenylstibine analogues

Reactions between the phosphorylthiourea ligands (EtO)2PONHC(S)NHPh (L1), (EtO)2PONHC(S)NHCH(CH3)3) (L2) and (EtO)2PONHC(S)NHCH2CH3 (L3) and cis-[PtCl2(PPh3)2] gave complexes in which the ligands bind to the platinum(II) centre as dianionic ligands. For ligands L1 and L3, the ligand binds through the thiourea sulfur and the N-alkyl nitrogen atoms, giving the distal isomer. In contrast, the ligand L2, on account of the bulky t-butyl substituent on the ligand, coordinates via the sulfur and N-phosphoryl nitrogen atoms, giving the proximal isomer. The identities of the isomers were confirmed by single crystal X-ray analysis and 31P{1H} NMR spectroscopy. The latter showing that the appearance or absence of 3J(PP) couplings between the ligand and ancillary ligands provides indicative isomeric information. Further reactions between the ligand L1 and a series of bis-phosphine, triphenylarsine and triphenylstibine platinum(II) starting complexes gave the corresponding products also as the distal linkage isomer. Computational analysis reveals a possible chalcogen bond non-covalent interaction that may be responsible for the preference for the distal isomer.