Iron-Catalyzed/Mediated C-N Bond Formation: Competition between Substrate Amination and Ligand Amination.

Iron catalyzed carbon-nitrogen bond formation reactions of a wide variety of nucleophiles and aryl halides using well-defined iron-complexes featuring redox noninnocent 2-(arylazo)-1,10-phenanthroline (L) ligands are reported. Besides substrate centered C-N coupling, C-N bond formation reactions were also observed at the ortho- and para-positions of the phenyl ring of the coordinated azo-aromatic scaffolds affording new tetradentate ligands, 2-N-aryl-(2-arylazo)-1,10-phenanthroline (L), and tridentate ligands, 4 -N-aryl-(2-arylazo)-1,10-phenanthroline (L), respectively. Control experiments and mechanistic studies reveal that the complex [FeLCl] (1) undergoes in situ reduction during the catalytic reaction to produce the monoanionic complex [1], which then acts as the active catalyst.

Redox-Induced Interconversion and Ligand-Centered Hemilability in Ni Complexes of Redox-Noninnocent Azo-Aromatic Pincers.

A series of nickel(II) complexes, namely, [Ni(L)Cl] (1a-c), [Ni(L)](X) {([2a](X), [2b](X)) (X = ClO, I)}, [Ni(L)(OH)](ClO) ([3](ClO)) and [Ni{(L)}] (4a, 4b) featuring the redox-active tridentate azo-aromatic pincer ligand 2-(arylazo)-1,10-phenanthroline (L) were synthesized. The coordinated azo-aromatic ligand showed reversible hemilability depending on its formal oxidation state. On the one hand, in its native state, the unreduced ligand L shows bidentate coordination; the 1,10-phenanthroline moiety binds the central Ni(II) atom in a bidentate fashion, while the azo-chromophore remains pendent.

Deprotonation Induced Ligand Oxidation in a Ni(II) Complex of a Redox Noninnocent N(1)-(2-Aminophenyl)benzene-1,2-diamine and Its Use in Catalytic Alcohol Oxidation.

Two nickel(II)-complexes, [Ni(II)(H3L)2](ClO4)2 ([1](ClO4)2) and [Ni(II)(HL)2] (2), containing the redox-active tridentate ligand N(1)-(2-aminophenyl)benzene-1,2-diamine (H3L) have been synthesized. Complex [1](ClO4)2 is octahedral containing two neutral H3L ligands in a facial coordination mode, whereas complex 2 is a singlet diradical species with approximately planar configuration at the tetracoordinate metal atom with two pendant NH2 side arms from each of the coordinated ligands. Both complexes are found to be chemically interconvertible; complex [1](2+) gets converted to complex 2 when exposed to base and oxygen via simultaneous deprotonation and oxidation of the coordinated ligands.