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-tBuC6H4, 1b) and
(1S,2R)-HN(R)CHPhCHPhOH (R = SO2CF3, 3a; SO2-4-tBuC6H4, 3b) leads to well-behaved chiral (dppe)Pt[N(R)CHPhCHPhN(R)] (R = SO2CF3, 2a; SO2-4-tBuC6H4, 2b) and (dppe)Pt[N(R)CHPhCHPhO] (R = SO2CF3,
4a; SO2-4-tBuC6H4, 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 (∼2.12 and
2.06 Å, respectively). Solid-state (X-ray) and solution (1H NMR) structural analysis indicates that the phenyl
groups α to the sulfonamide nitrogen adopt an axial conformation, as characteristic 3JPt-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.