title: An Entry to Mixed NHC-Fischer Carbene Complexes and Zwitterionic Group 6 Metal Alkenyls.
abstract: The addition of NHCs to α,β-unsaturated Cr(0) and W(0) (Fischer) carbene complexes is strongly dependent on the electrophilicity of the carbene carbon. Electrophilic alkoxy-carbene complexes quantitatively react with NHCs to yield stable zwitterionic (racemic) Cr(0) - and W(0) -alkenyls with total regio- and E-stereoselectivity. Less electrophilic aminocarbenes react with NHCs to promote the displacement of a CO ligand and yield "mixed" NHC/Fischer biscarbenes in a process that is unprecedented in group 6 metal-carbene chemistry. In fact, the compounds prepared, are some of the scarce examples of Fischer bisylidenes reported in the literature. The electrochemistry of the zwitterionic Cr(0) - and W(0) -alkenylcomplexes made, show that these compounds have a strong reductor character, which is demonstrated in their reactions towards [Ph3 C][PF6 ]. The oxidation processes lead to new types of cationic Fischer mono- and biscarbene complexes having a charged NHC fragment in their structures, in a new example of the use of electron-transfer reactions as a method to prepare novel group 6 (Fischer) carbene complexes.
authors.affiliation: Departamento de Química Orgánica I, Facultad de Ciencias Químicas, Universidad Complutense, 28040, Madrid, Spain. sierraor@quim.ucm.es.|Centro de Innovación en Química Avanzada (ORFEO-CINQA). sierraor@quim.ucm.es.
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Sierra
authors.affiliation: Departamento de Química Orgánica I, Facultad de Ciencias Químicas, Universidad Complutense, 28040, Madrid, Spain.|Centro de Innovación en Química Avanzada (ORFEO-CINQA).
authors.forename: Alba D
authors.initials: AD
authors.lastname: Merinero
authors.affiliation: Departamento de Química Orgánica I, Facultad de Ciencias Químicas, Universidad Complutense, 28040, Madrid, Spain.|Centro de Innovación en Química Avanzada (ORFEO-CINQA).
authors.forename: Elena A
authors.initials: EA
authors.lastname: Giner
authors.affiliation: Departamento de Química Orgánica I, Facultad de Ciencias Químicas, Universidad Complutense, 28040, Madrid, Spain. margg@quim.ucm.es.|Centro de Innovación en Química Avanzada (ORFEO-CINQA). margg@quim.ucm.es.
authors.forename: Mar
authors.initials: M
authors.lastname: Gómez-Gallego
authors.affiliation: Departamento de Química Orgánica, Universidad de Valencia, 46100, Valencia, Spain.|Centro de Innovación en Química Avanzada (ORFEO-CINQA).
authors.forename: Carmen
authors.initials: C
authors.lastname: Ramírez de Arellano
keywords: N-heterocyclic carbenes; bisylidenes; carbenes; radical cations; zwitterions