title: C--N bond formation on addition of aryl carbanions to the electrophilic nitrido ligand in TpOs(N)Cl(2).
abstract: The osmium(VI) nitrido complex TpOs(N)Cl(2) (1) has been prepared from K[Os(N)O(3)] and KTp in aqueous ethanolic HCl. It reacts rapidly with PhMgCl and related reagents with transfer of a phenyl group to the nitrido ligand. This forms Os(IV) metalla-analido complexes, which are readily protonated to give the analido complex TpOs(NHPh)Cl(2) (4). The nitrido-phenyl derivatives TpOs(N)PhCl and TpOs(N)Ph(2) react more slowly with PhMgCl and are not competent intermediates for the reaction of 1 with PhMgCl. Reactions of 1 with alkyl- and arylboranes similarly result in transfer of one organic group to nitrogen, leading to isolable borylamido complexes such as TpOs[N(Ph)(BPh(2))]Cl(2) (11). This is an unprecedented insertion of a nitrido ligand into a boron--carbon bond. Hydrolysis of 11 gives 4. Mechanistic studies suggest that both the Grignard and borane reactions proceed by initial weak coordination of Mg or B to the nitrido ligand, followed by migration of the carbanion to nitrogen. The hydrocarbyl group does not go to osmium and then move to nitrogen--there is no change in the atoms bound to the osmium during the reactions. It is suggested that there may be a general preference for nucleophiles to add directly to the metal--ligand multiple bond rather than binding to the metal first and migrating. Ab initio calculations show that the unusual reactivity of 1 results from its accessible LUMO and LUMO + 1, which are the Os = N pi* orbitals. The bonding in 1 and its reactivity with organoboranes are reminiscent of CO.
authors.affiliation: Department of Chemistry, Campus Box 351700, University of Washington, Seattle, Washington 98195-1700, USA.
authors.forename: T J
authors.initials: TJ
authors.lastname: Crevier
authors.forename: B K
authors.initials: BK
authors.lastname: Bennett
authors.forename: J D
authors.initials: JD
authors.lastname: Soper
authors.forename: J A
authors.initials: JA
authors.lastname: Bowman
authors.forename: A
authors.initials: A
authors.lastname: Dehestani
authors.forename: D A
authors.initials: DA
authors.lastname: Hrovat
authors.forename: S
authors.initials: S
authors.lastname: Lovell
authors.forename: W
authors.initials: W
authors.lastname: Kaminsky
authors.forename: J M
authors.initials: JM
authors.lastname: Mayer