title: Dynamic ligand reactivity in a rhodium pincer complex.
abstract: Ligand cooperativity provides (transition) metal complexes with new reactivities in substrate activation and catalytic reactions, but usually the ligand acts as an internal (Brønsted) base, while the metal acts as a (Lewis) acid. We describe the synthesis and stepwise activation of a new phosphane-pyridine-amide ligand PNN(H2) in combination with Rh(I) . The ligand is susceptible to stepwise proton and hydride loss from the nitrogen arm (imine formation) and deprotonation at the pyridylphosphine arm (dearomatization), giving rise to amine complex 1, amido species 2, imine complex 3 and dearomatized compound 4. Complex 4 bears a dual-mode cooperative PNN' ligand containing both a (nucleophilic) basic methine fragment and a reactive (electrophilic) imine moiety. The basic ligand arm enables substrate deprotonation while the imine ligand arm enables reversible "storage" of the activated (nucleophilic) form of a sulfonamide substrate at the ligand. In combination with metal-based reactivity, this allows for the mono-alkylation of o-toluenesulfonamide with iodomethane. Compounds 1, 3 and 4 are structurally characterized. We also report the first structurally characterized example of an aminal in the coordination sphere of rhodium, complex 5, [Rh(CO)(PNN'')], formed by sequential NH activation of sulfonamide by the dearomatized ligand PNN' and follow-up nucleophilic attack of anionic sulfonamide onto the imine fragment.
authors.affiliation: Homogeneous, Bio-inspired & Supramolecular Catalysis van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904 (The Netherlands).
authors.forename: Zhou
authors.initials: Z
authors.lastname: Tang
authors.affiliation: Stratingh' Institute, University of Groningen, Nijenborgh 8, Groningen (The Netherlands).
authors.forename: Edwin
authors.initials: E
authors.lastname: Otten
authors.affiliation: Homogeneous, Bio-inspired & Supramolecular Catalysis van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904 (The Netherlands).
authors.forename: Joost N H
authors.initials: JN
authors.lastname: Reek
authors.affiliation: Homogeneous, Bio-inspired & Supramolecular Catalysis van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904 (The Netherlands). j.i.vandervlugt@uva.nl.
authors.forename: Jarl Ivar
authors.initials: JI
authors.lastname: van der Vlugt
authors.affiliation: Homogeneous, Bio-inspired & Supramolecular Catalysis van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904 (The Netherlands). b.debruin@uva.nl.
authors.forename: Bas
authors.initials: B
authors.lastname: de Bruin
keywords: amine activation; cooperative reactivity; pincer; reactive ligand; rhodium; sulfonamide