Iron-SNS and -CNS Complexes: Selective Caryl-S Bond Cleavage and Amine-Borane Dehydrogenation Catalysis

The synthesis, structure, and reactivity of an electron-rich Fe-II thioether-imine-thiolate complex, [Fe-((SNS)-N-Me)(PMe3)(3)](OTf) (1-SNS), prepared by reaction of Fe(OTf)(2)(PMe3)(4) with the (SNS)-N-Me-S-H ligand in THF, are reported (OTf = CF3SO3). Substitution reactions of 1 with mono- and bidentate donor ligands afforded [Fe((SNS)-N-Me)L-(PMe3)(2)](OTf) (2,3-SNS; L = P(OMe)(3), CNxylyl) and [Fe((SNS)-N-Me)(dmpe)(PMe3)](OTf) [4-SNS; dmpe = 1,2-bis-(dimethylphosphino)ethane]. Heating 1-SNS in THF at 60 degrees C gave a new trivalent aryl-imine-thiolate complex, [Fe(CNS)-(PMe3)(3)](OTf) (1-CNS) via C-aryl-S bond cleavage. Reduction of 1-CNS with cobaltocene yielded divalent [Fe(CNS)-(PMe3)(3)] (2-CNS) which, upon dmpe addition, yields [Fe(CNS)(PMe 3 )(dmpe)] (3-CNS). Treatment of the previously reported cationic Fe amine-amido complex [Fe((SNSMe)-N-Me-S-H)((SNSMe)-N-Me)](+) with PMe3 gave Fe-II aryl-imine-thioether complex [Fe(CNSMe)(PMe3)(3)](+) (4-CNS') via selective activation of both C-aryl-S and benzylic C-H bonds. Assessment of complexes 3-CNS, 4-SNS, and 4-CNS' as precatalysts for amine-borane dehydrogenation catalysis in THF at 60 degrees C shows that 3-CNS forms a selective and robust bifunctional catalyst system.