title: Effect of the nature of the metal atom on hydrogen bonding and proton transfer to [Cp*MH3(dppe)]: tungsten versus molybdenum.
abstract: The hydrogen-bonding and proton-transfer pathway to complex [Cp*W(dppe)H(3)] (Cp*=eta(5)-C(5)Me(5); dppe=Ph(2)PCH(2)CH(2)PPh(2)) was investigated experimentally by IR, NMR, UV/Vis spectroscopy in the presence of fluorinated alcohols, p-nitrophenol, and HBF(4), and by using DFT calculations for the [CpW(dhpe)H(3)] model (Cp=eta(5)-C(5)H(5); dhpe=H(2)PCH(2)CH(2)PH(2)) and for the real system. A study of the interaction with weak acids (CH(2)FCH(2)OH, CF(3)CH(2)OH, (CF(3))(2)CHOH) allowed the determination of the basicity factor, E(j)=1.73+/-0.01, making this compound the most basic hydride complex reported to date. A computational investigation revealed several minima for the [CpW(dhpe)H(3)] adducts with CF(3)CH(2)OH, (CF(3))(2)CHOH, and 2(CF(3))(2)CHOH and confirms that these interactions are stronger than those established by the Mo analogue. Their geometries and relative energies are closely related to those of the homologous Mo systems, with the most stable adducts corresponding to H bonding with M-H sites, however, the geometric and electronic parameters reveal that the metal center plays a greater role in the tungsten systems. Proton-transfer equilibria are observed with the weaker proton donors, the proton-transfer step for the system [Cp*W(dppe)H(3)]/HOCH(CF(3))(2) in toluene having DeltaH=(-3.9+/-0.3) kcal mol(-1) and DeltaS=(-17+/-2) cal mol(-1) K(-1). The thermodynamic stability of the proton-transfer product is greater for W than for Mo. Contrary to the Mo system, the protonation of the [Cp*W(dppe)H(3)] appears to involve a direct proton transfer to the metal center without a nonclassical intermediate, although assistance is provided by a hydride ligand in the transition state.
authors.affiliation: A. N. Nesmeyanov Institute of Organoelement Compounds, RAS, Vavilov Street 28, 119991 Moscow, Russia.
authors.forename: Natalia V
authors.initials: NV
authors.lastname: Belkova
authors.forename: Maria
authors.initials: M
authors.lastname: Besora
authors.forename: Miguel
authors.initials: M
authors.lastname: Baya
authors.forename: Pavel A
authors.initials: PA
authors.lastname: Dub
authors.forename: Lina M
authors.initials: LM
authors.lastname: Epstein
authors.forename: Agustí
authors.initials: A
authors.lastname: Lledós
authors.forename: Rinaldo
authors.initials: R
authors.lastname: Poli
authors.forename: Pavel O
authors.initials: PO
authors.lastname: Revin
authors.forename: Elena S
authors.initials: ES
authors.lastname: Shubina
mesh_terms: D006860:Hydrogen Bonding; D008958:Models, Molecular; D008982:Molybdenum / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D011522:Protons; D011789:Quantum Theory; D013816:Thermodynamics; D014414:Tungsten / Q000737:chemistry*
chemical_list: D009942:Organometallic Compounds; D011522:Protons; D008982:Molybdenum; D014414:Tungsten