title: Transient palladadiphosphanylcarbenes: singlet carbenes with an "inverse" electronic configuration (p(pi)2 instead of sigma2) and unusual transannular metal-carbene interactions (piC-->Pd donation and sigmaPd-->C back-donation).
abstract: Upon treatment with [PdCl(allyl)]2, asymmetrically substituted alpha,alpha'-diphosphanyl diazo compounds eliminate dinitrogen to afford C-chlorodiphosphanylmethanide complexes in high yields. In the presence of a chloride-abstracting agent, such as sodium tetraphenylborate, the C-chlorodiphosphanylmethanide complexes react with pyridine and trimethylphosphine, readily affording the corresponding nitrogen and phosphorus ylides. The postulated intermediate in this process, namely palladadiphosphanylcarbenes, could not be spectroscopically characterized, but their transient formation was chemically supported further by a Lewis base exchange reaction between pyridine and 4-dimethylaminopyridine. This hypothesis has also been substantiated by computing the corresponding dissociation energy using two model systems featuring methyl groups at the phosphorus. Of particular interest, density functional theory calculations reveal that these palladadiphosphanylcarbenes have a singlet ground state with an "inverse" ppi2 electronic configuration and a distorted geometry associated with unusual transannular metal-carbene interactions (piC-->Pd donation and sigmaPd-->C back-donation).
authors.affiliation: Laboratoire Hétérochimie Fondamentale et Appliquée du CNRS (UMR 5069), Université Paul Sabatier, 118, route de Narbonne, F-31062 Toulouse Cedex 9, France.
authors.forename: Joan
authors.initials: J
authors.lastname: Vignolle
authors.forename: Heinz
authors.initials: H
authors.lastname: Gornitzka
authors.forename: Laurent
authors.initials: L
authors.lastname: Maron
authors.forename: Wolfgang W
authors.initials: WW
authors.lastname: Schoeller
authors.forename: Didier
authors.initials: D
authors.lastname: Bourissou
authors.forename: Guy
authors.initials: G
authors.lastname: Bertrand
mesh_terms: D004583:Electrons; D006838:Hydrocarbons / Q000138:chemical synthesis / Q000737:chemistry; D008697:Methane / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*
chemical_list: D006838:Hydrocarbons; D009942:Organometallic Compounds; C030011:carbene; D010165:Palladium; D008697:Methane