title: Mono- and bimetallic zwitterionic chromium(0) and tungsten(0) allenyls.
abstract: A series of stable chiral (racemic), formally neutral, zwitterionic mono- and bimetallic M(CO)5[C(OEt)═C═CR(NHC)] (M = Cr, W) σ-allenyls are ready available by the addition of N-heterocyclic carbenes (NHCs) to Cr(0) and W(0) alkynyl Fischer carbene complexes. Different classes of NHCs, (e.g., 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene, 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene, and their six- and seven-membered analogues and 1,3-bis(dimethyl)imidazol-2-ylidene) were employed as nucleophiles in these C-C bond-forming reactions yielding the novel complexes in essentially quantitative yields. A systematic experimental and computational study of the electronic properties of the Cr- and W-allenyls shows that their UV-vis spectra are directly influenced by the structure of the heterocyclic moiety derived from the NHC (ring size, substituents on the N atoms) and by the nature of the metal fragment (Cr/W). The electron-releasing nature of these complexes allows them to participate in electron-transfer reactions in the ground state, leading to a type of charged α,β-unsaturated Fischer carbenes that incorporate an NHC fragment in their structure.
authors.affiliation: †Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Complutense, 28040 Madrid, Spain.|∥Centro de Innovación en Química Avanzada, ORFEO-CINQA, Madrid, Spain.
authors.forename: Elena A
authors.initials: EA
authors.lastname: Giner
authors.affiliation: †Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Complutense, 28040 Madrid, Spain.|∥Centro de Innovación en Química Avanzada, ORFEO-CINQA, Madrid, Spain.
authors.forename: Alicia
authors.initials: A
authors.lastname: Santiago
authors.affiliation: †Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Complutense, 28040 Madrid, Spain.|∥Centro de Innovación en Química Avanzada, ORFEO-CINQA, Madrid, Spain.
authors.forename: Mar
authors.initials: M
authors.lastname: Gómez-Gallego
authors.affiliation: ‡Departamento de Química Orgánica, Facultad de Química, Universidad de Valencia, 46100-Valencia, Spain.|∥Centro de Innovación en Química Avanzada, ORFEO-CINQA, Madrid, Spain.
authors.forename: Carmen
authors.initials: C
authors.lastname: Ramírez de Arellano
authors.affiliation: §Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, U.K.
authors.forename: Rebecca C
authors.initials: RC
authors.lastname: Poulten
authors.affiliation: §Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, U.K.
authors.forename: Michael K
authors.initials: MK
authors.lastname: Whittlesey
authors.affiliation: †Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Complutense, 28040 Madrid, Spain.|∥Centro de Innovación en Química Avanzada, ORFEO-CINQA, Madrid, Spain.
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Sierra