title: Coordination complexes of niobium and tantalum pentahalides with a bulky NHC ligand.
abstract: The 1 : 1 molar reactions of niobium and tantalum pentahalides with the monodentate NHC ligand 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (Ipr), in toluene (or benzene) at ca. 80 °C, afforded the complexes NbX5(Ipr) (X = F, ; Br, ) and TaX5(Ipr) (X = F, ; Cl, ; Br, ), in generally good yields. Complexes represent uncommon cases of stable NHC adducts of metal halides with the metal in an oxidation state higher than +4, and also rare examples of Nb-NHC and Ta-NHC bonding systems. In particular, the X-ray molecular structure determined for provides the unprecedented crystallographic characterization of a tantalum compound with a monodentate NHC ligand. DFT results indicate that the metal-carbon bond in is a purely σ one. According to NMR studies ((1)H, (13)C, (93)Nb), the formation of , , , as well as the previously communicated NbCl5(Ipr), , proceeded with the intermediacy of [MX6](-) salts, presumably due to steric reasons. On the other hand, the intermediate formation of MF6(-) in the pathways to and was not observed, according to (19)F (and (93)Nb in the case of ) NMR. DFT calculations were carried out in order to shed light on structural and mechanistic aspects, and allowed to trace possible reaction routes.
authors.affiliation: Ca' Foscari University of Venezia, Dipartimento di Scienze Molecolari e Nanosistemi Dorsoduro 2137, I-30123 Venezia, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Bortoluzzi
authors.affiliation: University of Pisa, Dipartimento di Chimica e Chimica Industriale, Via Moruzzi 13, I-56124 Pisa, Italy. fabio.marchetti1974@unipi.it.
authors.forename: Eleonora
authors.initials: E
authors.lastname: Ferretti
authors.affiliation: University of Pisa, Dipartimento di Chimica e Chimica Industriale, Via Moruzzi 13, I-56124 Pisa, Italy. fabio.marchetti1974@unipi.it.
authors.forename: Fabio
authors.initials: F
authors.lastname: Marchetti
authors.affiliation: University of Pisa, Dipartimento di Chimica e Chimica Industriale, Via Moruzzi 13, I-56124 Pisa, Italy. fabio.marchetti1974@unipi.it.
authors.forename: Guido
authors.initials: G
authors.lastname: Pampaloni
authors.affiliation: University of Bologna, Dipartimento di Chimica Industriale "Toso Montanari", Viale Risorgimento 4, I-40136 Bologna, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Zacchini