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 [PtMe<sub>2</sub>(<b>1</b>)], in which the ligand <b>1</b> is the unsymmetrical 2,2′-bipyridine derivative ethyl 5′-[(ethoxycarbonyl)amino]-2,2′-bipyridine-5-carboxylate, undergoes oxidative addition to give chiral and racemic (<i>C</i>/<i>A</i>=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 (<i>C</i>/<i>A</i>). The complex [PtMe<sub>2</sub>(<b>1</b>)] reacted with bromoacetic acid to give [PtBrMe<sub>2</sub>(CH<sub>2</sub>CO<sub>2</sub>H)(<b>1</b>)], which exists as a mixture of three isomers, of which the <i>trans</i> 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 <b>1</b>. The platinum(IV) complexes [PtBrMe<sub>2</sub>(4-CH<sub>2</sub>C<sub>6</sub>H<sub>4</sub>(CH<sub>2</sub>)<sub><i>n</i></sub>CO<sub>2</sub>H)(<b>1</b>)], <i>n</i>=0 or 1, form a supramolecular polymer (<i>n</i>=0) or double-stranded polymer (<i>n</i>=1) through a combination of hydrogen bonding and π-stacking. Reaction of these organoplatinum(IV) complexes with AgPF<sub>6</sub> and the pyridine-derived ligand L=3,5-C<sub>5</sub>H<sub>3</sub>N(CO<sub>2</sub>H)<sub>2</sub> gave the corresponding cationic complexes [PtMe<sub>2</sub>(CH<sub>2</sub>C<sub>6</sub>H<sub>4</sub>(CH<sub>2</sub>)<sub><i>n</i></sub>CO<sub>2</sub>H)(<b>1</b>)L]<sup>+</sup>, as the hexafluorophosphate salts. Hydrolysis of the ion [PF<sub>6</sub>]<sup>−</sup> to form [PO<sub>2</sub>F<sub>2</sub>]<sup>−</sup> occurred during recrystallization, and the supramolecular structures were dominated by hydrogen bonding between carboxylic acid groups and the [PO<sub>2</sub>F<sub>2</sub>]<sup>−</sup> ions through units CO<sub>2</sub>H···OPF<sub>2</sub>O···HO<sub>2</sub>C. The self-assembly occurs selectively, and individual supramolecular polymer chains may contain <i>C−C−C-C</i>, <i>A−A−A−A</i>, or <i>C−A−C−A</i> groupings.