Synthesis and characterization of chiral platinum(II) sulfonamides:: (dppe)Pt(NN) and (dppe)Pt(NO) complexes

Reaction of (dppe)Pt(CO3) with (1S,2S)-HN(R)CHPhCHPhNH(R) (R = SO2CF3, 1a; SO2-4-(BuC6H4)-Bu-t, 1b) and (1S,2R)-HN(R)CHPhCHPhOH (R = SO2CF3, 3a: SO2-4-(BuC6H4)-Bu-t, 3b) leads to well-behaved chiral (dppe)Pt[N(R)CHPhCHPhN(R)] (R = SO2CF3, 2a; SO2-4-(BuC6H4)-Bu-t, 2b) and (dppe)Pt[N(R)CHPhCHPhO] (R = SO2CF3, 4a; SO2-4-(BuC6H4)-Bu-t, 4b) complexes. X-ray structural analysis of 2a and 4b reveal that the Pt-N bond lengths are long with the triflamide bond lengths being slightly longer than the aryl sulfonamide bond lengths (similar to 2.12 and 2.06 Angstrom. respectively). Solid-state (X-ray) and solution (H-1 NMR) structural analysis indicates that the phenyl groups alpha to the sulfonamide nitrogen adopt an axial conformation, as characteristic (3)J(Pt-H) coupling constants are observed for equatorial, but not axially disposed hydrogens in the heterocycle. Relative binding affinities of 1a/b and 3a/b to the (dppe)Pt fragment were determined through pairwise ligand exchange reactions: Tf > SO2Ar and NN > NO.