Transformations of nitrile, amido, and imine ligands in Tp′ tungsten complexes

Transformations of nitrogen-donor ligands bound to two similar tungsten moieties, [Tp′W(CO)2]+ and [Tp′W(CO)(PhC≡CMe)]+, have been investigated. A variety of methods for formation of imido complexes in the [Tp′W(CO)2]+ coordination sphere are discussed including net hydride abstraction from an N-protio amido complex and electrophilic addition to a nitrido complex. The variable electron-donating ability of the alkyne ligand in the [Tp′W(CO)(PhC≡CMe)]+ coordination sphere is reflected in the isolation of intermediates in the stepwise reduction of acetonitrile and stepwise oxidation of benzylamine. Diasteroselective addition to imine ligands has been investigated. A cationic tungsten(IV) acetonitrile complex, [Tp′W(O)(CO)(NCMe)]+, containing a σ- bound nitrile ligand, has been synthesized. Formation of the neutral tungsten(IV) η2- acetonitrile complex, Tp′W(O)(I)(NCMe), has been confirmed based on 1H, and 13C NMR spectroscopy and reactivity patterns. The η2-nitrile ligand may be replaced with CD3CN or phenylacetylene. Column chromatography of Tp′W(O)(I)(NCMe) has produced an acylimido complex, Tp′W(O)(I)(NC(O)Me), in addition to a product of dimerization, Tp′(O)(I)WNC(Me)C(Me)NW(I)(O)Tp′. Methylation of the η2-nitrile has been accomplished utilizing MeOTf to form an iminoacyl complex, [Tp′W(O)(I)(MeNCMe)][OTf]. Cyclic amido and imine complexes of tungsten(II) have been synthesized utilizing pyrrolidine as substrate. Oxidation of a pyrrolidine amido complex forms a 1-pyrroline complex. Diastereoselective nucleophilic addition to the imine carbon has been accomplished using MeMgBr and Li[DBEt3] to form a 2-methylpyrrolidine complex (SWRC/RWSC) (>95:5 dr) and an α-deuterated pyrrolidine amido complex (high dr) respectively. The second diastereomer (SWSC/RWRC) of the 2-methylpyrrolidine amido complex has been synthesized by hydride addition to a 2-methyl-1-pyrroline complex. Three, four, and six-membered nitrogen heterocycle-ligated tungsten complexes have been synthesized and characterized in the [Tp′W(CO)(PhC≡CR)]+ (R = Me, Ph) coordination sphere. Successful synthesis of aziridine complexes has been achieved at low temperature. A series of azetidine complexes have been synthesized and structurally characterized. Addition of a MeMgBr to a chiral cationic 1-azetine complex results predominantly in formation of one diastereomer (SWRC/RWSC) of the resulting 2-methylazetidine complex (96:4 dr). Synthesis and X-ray characterization of a 2,3,4,5-tetrahydropyridine complex has been achieved. Subsequent addition of base results in formation of an enamido complex. Addition of [D+] to the enamido β-carbon results in little diastereoselectivity in the formation of the deuterated product