title: Variable coordination of amine functionalised N-heterocyclic carbene ligands to Ru, Rh and Ir: C-H and N-H activation and catalytic transfer hydrogenation.
abstract: Chelating amine and amido complexes of late transition metals are highly valuable bifunctional catalysts in organic synthesis, but complexes of bidentate amine-NHC and amido-NHC ligands are scarce. Hence, we report the reactions of a secondary-amine functionalised imidazolium salt 2a and a primary-amine functionalised imidazolium salt 2b with [(p-cymene)RuCl(2)](2) and [Cp*MCl(2)](2) (M = Rh, Ir). Treating 2a with [Cp*MCl(2)](2) and NaOAc gave the cyclometallated compounds Cp*M(C,C)I (M = Rh, 3; M = Ir, 4), resulting from aromatic C-H activation. In contrast, treating 2b with [(p-cymene)RuCl(2)](2), Ag(2)O and KI gave the amine-NHC complex [(p-cymene)Ru(C,NH(2))I]I (5). The reaction of 2b with [Cp*MCl(2)](2) (M = Rh, Ir), NaO(t)Bu and KI gave the amine-NHC complex [Cp*Rh(NH(2))I]I (6) or the amido-NHC complex Cp*Ir(C,NH)I (7); both protonation states of the Ir complex could be accessed: treating 7 with trifluoroacetic acid gave the amine-NHC complex [Cp*Ir(C,NH(2))I][CF(3)CO(2)] (8). These are the first primary amine- or amido-NHC complexes of Rh and Ir. Solid-state structures of the complexes 3-8 have been determined by single crystal X-ray diffraction. Complexes 5, 6 and 7 are pre-catalysts for the catalytic transfer hydrogenation of acetophenone to 1-phenylethanol, with ruthenium complex 5 demonstrating especially high reactivity.
authors.affiliation: Department of Chemistry, University of Leicester, UK. wbc2@le.ac.uk
authors.forename: Warren B
authors.initials: WB
authors.lastname: Cross
authors.forename: Christopher G
authors.initials: CG
authors.lastname: Daly
authors.forename: Youcef
authors.initials: Y
authors.lastname: Boutadla
authors.forename: Kuldip
authors.initials: K
authors.lastname: Singh
mesh_terms: D000577:Amides / Q000737:chemistry; D000588:Amines / Q000737:chemistry*; D002384:Catalysis; D002614:Chelating Agents / Q000138:chemical synthesis* / Q000737:chemistry; D018360:Crystallography, X-Ray; D006571:Heterocyclic Compounds / Q000737:chemistry*; D006865:Hydrogenation; D007495:Iridium / Q000737:chemistry; D008024:Ligands; D008697:Methane / Q000031:analogs & derivatives* / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D012211:Rhenium / Q000737:chemistry; D012428:Ruthenium / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: D000577:Amides; D000588:Amines; D002614:Chelating Agents; D006571:Heterocyclic Compounds; D008024:Ligands; D009942:Organometallic Compounds; C030011:carbene; D007495:Iridium; D012211:Rhenium; D012428:Ruthenium; D008697:Methane