title: Activation of organonitriles toward beta-electrophilic attack. Synthesis and characterization of methyleneamide (azavinylidene) complexes of rhenium.
abstract: Treatment of the nitrile complexes cis-[ReCl(NCR)(dppe)(2)] (R = aryl; dppe = Ph(2)PCH(2)CH(2)PPh(2)) with [Et(2)OH][BF(4)] or SiMe(3)CF(3)SO(3) in CH(2)Cl(2) led to the formation of the methyleneamide (alkylideneamide or azavinylidene) compounds cis-[ReCl[NC(E)C(6)H(4)X-4](dppe)(2)]Y [E = H; X = OMe (1b), Me (1c), H (1d), F (1e), or Cl (1f), Y = BF(4); E = SiMe(3), X = Me (1c'), Y = CF(3)SO(3)] and trans-[ReCl[NC(H)C(6)H(4)X-4](dppe)(2)][BF(4)] [X = NEt(2) (2a), OMe (2b), H (2d), F (2e), or Cl (2f)]. They were characterized by multinuclear NMR spectrometry and X-ray crystallography (2e) which shows that the methyleneamide ligand exhibits linear (three-electron donor) geometry and behaves as a strong pi-electron acceptor. The complex (31)P[(1)H] and (1)H [NC(H)C(6)H(4)X-4] NMR patterns for the cis isomers were analyzed as ABCD and ABCDX (X part) spin systems, respectively. Complexes 1 and 2 undergo deprotonation by base to form the trans isomers of the corresponding nitrile complexes, trans-[ReCl(NCC(6)H(4)X-4)(dppe)(2)] [X = NEt(2) (3a), OMe (3b), H (3d), F (3e), or Cl (3f)] whose spectroscopic data are also presented and which on protonation give the corresponding trans isomers of the methyleneamide complexes (2). Reactions of cis-[ReCl(NCR)(dppe)(2)] with [Et(3)O][PF(6)] resulted in their oxidation and isomerization to afford trans-[ReCl(NCC(6)H(4)X-4)(dppe)(2)][PF(6)] [X = Me (4c), H (4d), or Cl (4f)].
authors.affiliation: Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisbon, Portugal.
authors.forename: M Fátima C
authors.initials: MF
authors.lastname: Guedes da Silva
authors.forename: João J R
authors.initials: JJ
authors.lastname: Fraústo da Silva
authors.forename: Armando J L
authors.initials: AJ
authors.lastname: Pombeiro