Synthesis, characterisation and coordination chemistry of novel chiral N,N-dialkyl-N-menthyloxycarbonylthioureas. Crystal and molecular structures ofN,N-diethyl-N-(-)-(3R)-menthyloxycarbonylthiourea and cis-(S,S)-[Pt(L)Cl(DMSO)] [where HL = N-(+)-(3R)-menthyloxycarbonyl-N'-morpholinothiourea or N-benzoyl-N',N'-diethylthiourea]

The novel ligands N,N-diethyl-N'-(-)-(3R)-menthyloxycarbonylthiourea (HL3), N,N-diethyl-N'-(+)-(3R)-menthyloxycarbonylthiourea (HL4), N-(-)-(3R)-menth yloxycarbonyl-N'-morpholinothiourea (HL5) and N-(+)-(3R)-menthyloxycarbonyl -N'-morpholinothiourea (HL6) have been prepared and characterised. The mole cular structure of HL3 has been confirmed by X-ray crystallography. The rea ction of these N,N-disubstituted-N'-menthyloxycarbonylthiourea ligands with cis-[PtCl2(DMSO)(2)] in the presence of sodium acetate yields geometric is omers of the resultant [Pt(L)Cl(DMSO)] complexes, that is the DMSO is sulfu r bonded to the platinum in either a cis-(S,S) or trans-(S,S) arrangement w ith respect to the sulfur donor atom of the chelated ligand. This is in con trast to the complexation reaction of cis-[PtCl2(DMSO)(2)] with N-benzoyl-N ',N'-diethylthiourea (HL1) or N-benzoyl-N'-morpholinothiourea (HL2) which y ields only one [Pt(L)Cl(DMSO)] complex in which the DMSO is in a cis-(S,S) arrangement with respect to the sulfur donor atom of the chelated ligand. T he molecular structures of cis-(S,S)-[Pt(L)Cl(DMSO)], where L=(L-1)(-) or ( L-6)(-), have been determined by X-ray crystallography. The difference in t he coordination chemistry of the acylthiourea and alkoxycarbonylthiourea li gands has been examined further by treating the [Pt(L)Cl(DMSO)] complexes w ith PPh3 to give the corresponding mono- and bis-(phosphine) complexes, [Pt (L)Cl(PPh3)] and [Pt(L)(PPh3)(2)](+). The P-31 NMR studies of these complex es reveal that the alkoxycarbonylthiourea ligands bind less strongly than t he acylthiourea ligands, which is consistent with the crystallographic stud ies. The weaker binding properties of the alkoxycarbonylthiourea ligands mi ght be a possible explanation for the observed geometric isomerisation of t he complexes and that the mechanism could involve a chelate ring opening st ep.