Reduction of Benzonitriles via Osmium-Azavinylidene Intermediates Bearing Nucleophilic and Electrophilic Centers.

Author(s) Babón, J.C.; Esteruelas, M.A.; Fernández, I.; López, A.M.; Oñate, E.
Journal Inorg Chem
Date Published 2019 Jul 01
Abstract

The reduction of the N≡C bond of benzonitriles promoted by OsH(PPr) (1) has been studied. Complex 1 releases a H molecule and coordinates 2,6-dimethylbenzonitrile to afford the tetrahydride OsH{κ- N-(N≡CCHMe)}(PPr) (2), which is thermally stable toward the insertion of the nitrile into one of the Os-H bonds. In contrast to 2,6-dimethylbenzonitrile, benzonitrile and 2-methylbenzonitrile undergo insertion, via Os(η-N≡CR) intermediates, to give the azavinylidene derivatives OsH(═N═CCHR)(PPr) [R = H (3) or Me (4)]. The analysis by means of computational tools (EDA-NOCV) of the bonding situation in these compounds suggests that the donor-acceptor nature of the osmium azavinylidene bond dominates over the mixed electron-sharing/donor-acceptor and pure electron-sharing bonding modes. The N atom is strongly nucleophilic, whereas one of the hydrides is electrophilic. In spite of the different nature of these centers, the migration of the latter to the N atom is kinetically prevented. However, the use of water as a proton shuttle allows hydride migration, as a consequence of a significant decrease in the activation barrier. The resulting phenylaldimine intermediates evolve by means of orthometalation to give OsH{κ- N, C-(NH═CHCHR)}(PPr) [R = H (5) or Me (6)]. The presence of electrophilic and nucleophilic centers in 3 confers upon it the ability to activate σ-bonds, including H and pinacolborane (HBpin). The reaction with the latter gives OsH{κ- N, C-[N(Bpin)═CHCH]}(PPr) (7).

DOI 10.1021/acs.inorgchem.9b01013
ISSN 1520-510X
Citation Babón JC, Esteruelas MA, Fernández I, López AM, Oñate E. Reduction of Benzonitriles via Osmium-Azavinylidene Intermediates Bearing Nucleophilic and Electrophilic Centers. Inorg Chem. 2019;58(13):8673-8684.

Related Applications, Forms & Industries