Synthesis and Characterization of Chiral Platinum(II) Sulfonamides: (dppe)Pt(NN) and (dppe)Pt(NO) Complexes

Reaction of (dppe)Pt(CO(3)) with (1S,2S)-HN(R)CHPhCHPhNH(R) (R = SO(2)CF(3), 1a; SO(2)-4-(t)BuC(6)H(4), 1b) and (1S,2R)-HN(R)CHPhCHPhOH (R = SO(2)CF(3), 3a; SO(2)-4-(t)BuC(6)H(4), 3b) leads to well-behaved chiral (dppe)Pt[N(R)CHPhCHPhN(R)] (R = SO(2)CF(3), 2a; SO(2)-4-(t)BuC(6)H(4), 2b) and (dppe)Pt[N(R)CHPhCHPhO] (R = SO(2)CF(3), 4a; SO(2)-4-(t)BuC(6)H(4), 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 ( approximately 2.12 and 2.06 Å, respectively). Solid-state (X-ray) and solution ((1)H 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 > SO(2)Ar and NN > NO.