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

Abstract

Reaction of [Tp′W(CO) 2(PhC CPh)][OTf] ( 1b) (Tp′ = hydridotris(3,5-dimethylpyrazolyl)borate) with excess aziridine or 2-methylaziridine followed by protonation with [ H(OEt 2 ) 2 ] [ BAr 4 ′ ] produces chiral tungsten(II) amine complexes [ Tp ′ W(CO) ( PhC CPh ) ( ▪HR ) ] [ BAr 4 ′ ] ( 3, 4; R = Me, Ph). An azetidine amido complex, Tp′W(CO)(PhC CMe)( ▪H 2) ( 5) is synthesized by reaction of [Tp′W(CO) 2(PhC CMe)][OTf] ( 1a) with excess azetidine. Oxidation of amido complex 5 with I 2 in the presence of a weak base provides the corresponding 1-azetine complex, [ Tp ′ W(CO)(PhC CMe ) ( ▪ H 2 ) ] [ BAr 4 ′ ] ( 6). Addition of methylmagnesium bromide to complex 6 results in formation of predominantly one diastereomer ( S W R C/ R W S C) (96:4 dr) of the 2-methylazetidine complex, Tp′W(CO)(PhC CMe)( ▪H 2) ( 7). Reaction of complex 5 with [ H ( OEt 2 ) 2 ] [ BAr 4 ′ ] results in formation of a cationic azetidine complex, [ Tp ′ W(CO)(PhC CMe ) ( ▪ H 2 ) ] [ BAr 4 ′ ] ( 8). Reaction of 1b with excess piperidine followed by oxidation affords 2,3,4,5-tetrahydropyridine complex 9b, [ Tp ′ W(CO)(PhC CPh ) ( ▪ H 2 ) ] [ BAr 4 ′ ] . Formation of an enamido complex, Tp′W(CO)(PhC CPh)( ▪H 2) ( 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– d 1, 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).