Alkyl carbon - nitrogen reductive elimination from Platinum(IV) - Sulfonamide complexes

Platinum(IV) complexes containing monodentate sulfonamide ligands, fac-(dppbz)PtMe3(NHSO2R) (dppbz = o-bis(diphenylphosphino)benzene; R = p-C6H4(CH2)(3)CH3 (1a), p-C6H4CH3 (1b), CH3 (1c)), have been synthesized and characterized, and their thermal reactivity has been explored. Compounds 1a-c undergo competitive C-N and C-C reductive elimination upon thermolysis to form N-methylsulfonamides and ethane, respectively. Selectivity for either C-N or C-C bond formation can be achieved by altering the reaction conditions. Good yields of the C-N-coupled products were observed when the thermolyses of 1a-c were conducted in benzene-d(6). In contrast, exclusive C-C reductive elimination occurred upon themolysis of 1a,b in nitrobenzene-d(5). When the thermolyses of 1a were performed in the presence of sulfonamide anion NHSO2R- in benzene-d(6), ethane elimination was completely inhibited and C-N reductive elimination products were formed in high yield. Mechanistic studies support a two-step reaction pathway involving initial dissociation of NHSO2R- from the platinum center, followed by nucleophilic attack of this anion on a methyl group of the resulting five-coordinate platinum(IV) cation to form MeNHSO2R and (dppbz)PtMe2. C-C reductive elimination to form ethane occurs directly from the five-coordinate Pt(IV) cation.