title: Ruthenium dihydrogen complexes with wide bite angle diphosphines.
abstract: The wide bite angle diphosphines homoxantphos (10,11-dihydro-4,5,-bis(diphenylphosphino)dibenzo[b,f]oxepine), sixantphos (4,6-bis(diphenylphosphino)-10,10-dimethylphenoxasilin), and thixantphos (2,8-dimethyl-4,6-bis(diphenylphosphino)phenoxathiin) were used to prepare cis[MH(2)(diphosphine)(2)] complexes (1a-f) by reaction of [Ru(cod)(cot)] (cod = cyclo-octa-1,5-diene, cot = cyclo-octa-1,3,5-triene) with 2 equiv of the diphosphine under dihydrogen pressure. The electronic properties of the thixantphos ligand were varied. Complexes 1a-f can be protonated with HBF(4) or CF(3)COOH to yield hydrido(dihydrogen) complexes cis[MH(H(2))(diphosphine)(2)](+) (2a-f), which were characterized by VT (variable temperature) NMR and T(1) measurements. These complexes show fast hydrogen atom exchange between the eta(2)-H(2) and the terminal hydride at all temperatures studied. They are thermally unstable toward dihydrogen loss yielding the cationic monohydride complexes cis[MH(diphosphine)(2)](+) (3a-f). Coordination of the eta(2)-H(2) is dominated by sigma --> d donation, and hence, the H-H distance is hardly influenced by the electronic properties of the ligands.
authors.affiliation: Institute of Molecular Chemistry, University of Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands.
authors.forename: Karina
authors.initials: K
authors.lastname: Almeida Leñero
authors.forename: Mirko
authors.initials: M
authors.lastname: Kranenburg
authors.forename: Yannick
authors.initials: Y
authors.lastname: Guari
authors.forename: Paul C J
authors.initials: PC
authors.lastname: Kamer
authors.forename: Piet W N M
authors.initials: PW
authors.lastname: van Leeuwen
authors.forename: Sylviane
authors.initials: S
authors.lastname: Sabo-Etienne
authors.forename: Bruno
authors.initials: B
authors.lastname: Chaudret