title: One- and two-electron reactivity of a tantalum(V) complex with a redox-active tris(amido) ligand.
abstract: A new redox-active, tris(amido) ligand platform, bis(2-isopropylamino-4-methoxyphenylamine [NNN(cat)](3-), has been prepared and used in the preparation of tantalum(V) complexes. The ligand was prepared in its protonated form by a three-step procedure from commercially available 4-methoxy-2-nitroaniline and 1-iodo-4-methoxy-2-nitrobenzene. Direct reaction of [NNN(cat)]H(3) with TaCl(2)Me(3) afforded five-coordinate [NNN(cat)]TaCl(2) (1), which accepted the strong sigma-donor ligand (t)BuNC to form the six-coordinate adduct [NNN(cat)]TaCl(2)(CN(t)Bu) (2). Complex 1 is formally a d(0), Ta(V) complex; however, one- and two-electron reactivity is enabled at the metal center by the redox-activity of the ligand platform. Complex 1 was oxidized by one electron to afford the radical species [NNN(sq*)]TaCl(3) (3), which was characterized by solution EPR spectroscopy. Cyclic voltammetry studies of complex 3 showed clean one-electron oxidation and reduction processes at 0.148 and -0.324 V vs [Cp(2)Fe](+/0), indicating the accessibility of three oxidation states, [NNN(cat)](3-), [NNN(sq*)](2-), and [NNN(q)](-), for the metallated ligand. Complex 1 also can undergo two-electron reactions, as evidenced by the reaction with nitrene transfer reagents to form tantalum imido species. Thus 1 reacted with organic azides, RN(3) (R = Ph, p-C(6)H(4)Me, p-C(6)H(4)(t)Bu), to form [NNN(q)]TaCl(2)(NR) (4). Similarly, the tantalum diphenylmethylidenehydrazido complex, [NNN(q)]TaCl(2)(NNCPh(2)) (5), was formed by reaction of 1 with the diazoalkane, N(2)CPh(2).
authors.affiliation: Department of Chemistry, University of California, Irvine, California 92697, USA.
authors.forename: Andy I
authors.initials: AI
authors.lastname: Nguyen
authors.forename: Karen J
authors.initials: KJ
authors.lastname: Blackmore
authors.forename: Shawn M
authors.initials: SM
authors.lastname: Carter
authors.forename: Ryan A
authors.initials: RA
authors.lastname: Zarkesh
authors.forename: Alan F
authors.initials: AF
authors.lastname: Heyduk
mesh_terms: D000588:Amines / Q000737:chemistry*; D004583:Electrons; D008024:Ligands; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D010084:Oxidation-Reduction; D013635:Tantalum / Q000737:chemistry*
chemical_list: D000588:Amines; D008024:Ligands; D009942:Organometallic Compounds; D013635:Tantalum