title: Hydrogen activation by an aromatic triphosphabenzene.
abstract: Aromatic hydrogenation is a challenging transformation typically requiring alkali or transition metal reagents and/or harsh conditions to facilitate the process. In sharp contrast, the aromatic heterocycle 2,4,6-tri-tert-butyl-1,3,5-triphosphabenzene is shown to be reduced under 4 atm of H2 to give [3.1.0]bicylo reduction products, with the structure of the major isomer being confirmed by X-ray crystallography. NMR studies show this reaction proceeds via a reversible 1,4-H2 addition to generate an intermediate species, which undergoes an irreversible suprafacial hydride shift concurrent with P-P bond formation to give the isolated products. Further, para-hydrogen experiments confirmed the addition of H2 to triphosphabenzene is a bimolecular process. Density functional theory (DFT) calculations show that facile distortion of the planar triphosphabenzene toward a boat-conformation provides a suprafacial combination of vacant acceptor and donor orbitals that permits this direct and uncatalyzed reduction of the aromatic molecule.
authors.affiliation: Department of Chemistry, University of Toronto , 80 St. George Street, Toronto, Ontario, Canada M5S 3H6.
authors.forename: Lauren E
authors.initials: LE
authors.lastname: Longobardi
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Russell
authors.forename: Michael
authors.initials: M
authors.lastname: Green
authors.forename: Nell S
authors.initials: NS
authors.lastname: Townsend
authors.forename: Kun
authors.initials: K
authors.lastname: Wang
authors.forename: Arthur J
authors.initials: AJ
authors.lastname: Holmes
authors.forename: Simon B
authors.initials: SB
authors.lastname: Duckett
authors.forename: John E
authors.initials: JE
authors.lastname: McGrady
authors.forename: Douglas W
authors.initials: DW
authors.lastname: Stephan
mesh_terms: D001643:Bridged Bicyclo Compounds / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006859:Hydrogen / Q000737:chemistry*; D006865:Hydrogenation; D007536:Isomerism; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009943:Organophosphorus Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction
chemical_list: C523339:2,4,6-tri-tert-butyl-1,3,5-triphosphabenzene; D001643:Bridged Bicyclo Compounds; D009943:Organophosphorus Compounds; D006859:Hydrogen