Self-Assembly of Chiral Organoplatinum(IV) Complexes with Both Carboxylic Acid and Amide Groups

The synthesis and self-assembly of organoplatinum(IV) complexes containing both a carboxylic acid and an amide group is described. The complex [PtMe2(1)], in which the ligand 1 is the unsymmetrical 2,2′-bipyridine derivative ethyl 5′-[(ethoxycarbonyl)amino]-2,2′-bipyridine-5-carboxylate, undergoes oxidative addition to give chiral and racemic (C/A=clockwise/anticlockwise) organoplatinum(IV) complexes. The most predictable form of self-assembly was through π-stacking, which always connected pairs of molecules of opposite chirality (C/A). The complex [PtMe2(1)] reacted with bromoacetic acid to give [PtBrMe2(CH2CO2H)(1)], which exists as a mixture of three isomers, of which the trans isomer forms a supramolecular network material through a combination of intermolecular NH···OC, OH···O, OH···Br, and CH···Br hydrogen bonding, with support through π-stacking between bipyridyl groups 1. The platinum(IV) complexes [PtBrMe2(4-CH2C6H4(CH2)nCO2H)(1)], n=0 or 1, form a supramolecular polymer (n=0) or double-stranded polymer (n=1) through a combination of hydrogen bonding and π-stacking. Reaction of these organoplatinum(IV) complexes with AgPF6 and the pyridine-derived ligand L=3,5-C5H3N(CO2H)2 gave the corresponding cationic complexes [PtMe2(CH2C6H4(CH2)nCO2H)(1)L]+, as the hexafluorophosphate salts. Hydrolysis of the ion [PF6] to form [PO2F2] occurred during recrystallization, and the supramolecular structures were dominated by hydrogen bonding between carboxylic acid groups and the [PO2F2] ions through units CO2H···OPF2O···HO2C. The self-assembly occurs selectively, and individual supramolecular polymer chains may contain C−C−C-C, A−A−A−A, or C−A−C−A groupings.