Coordination and derivatization of 3, 4, and 6-membered nitrogen heterocycles at a chiral tungsten(II) center

Reaction of Tp′W(CO)₂(PhCCPh)]OTf] (1b) (Tp′ = hydridotris(3,5-dimethylpyrazolyl)borate) with excess aziridine or 2-methylaziridine followed by protonation with produces chiral tungsten(II) amine complexes (3, 4; R = Me, Ph). An azetidine amido complex, Tp′W(CO)(PhCCMe)(H₂) (5) is synthesized by reaction of Tp′W(CO)₂(PhCCMe)]OTf] (1a) with excess azetidine. Oxidation of amido complex 5 with I₂ in the presence of a weak base provides the corresponding 1-azetine complex, (6). Addition of methylmagnesium bromide to complex 6 results in formation of predominantly one diastereomer (S_WR_C/R_WS_C) (96:4 dr) of the 2-methylazetidine complex, Tp′W(CO)(PhCCMe)(H₂) (7). Reaction of complex 5 with results in formation of a cationic azetidine complex, (8). Reaction of 1b with excess piperidine followed by oxidation affords 2,3,4,5-tetrahydropyridine complex 9b, . Formation of an enamido complex, Tp′W(CO)(PhCCPh)(H₂) (10), is observed upon addition of base to 9b. Subsequent addition of D⁺] to the enamido β-carbon results in the formation of the deuterated product, 9b-d₁, as determined by ²H NMR. Seven X-ray crystal structures have been determined, and these encompass complexes with 3, 4, and 6-membered heterocyclic ligands. Crystal structures are reported for two aziridine adducts (2, 4) two neutral amido complexes (5, 7), one cationic imine complex (6), and one cationic amine (8) complex derived from azetidine, and the imine complex formed from piperidine (9).