title: Synthesis, structure, and electrochemical properties of sterically protected molybdenum trihydride redox pairs: a paramagnetic "stretched" dihydrogen complex?
abstract: Complexes [MoCp(#)(PMe(3))(2)H(3)] (Cp(#)=1,2,4-C(5)H(2)tBu(3), 2 a; C(5)HiPr(4), 2 b) have been synthesized from the corresponding compounds [MoCp(#)Cl(4)] (1 a, 1 b) and fully characterized, including by X-ray crystallography and by a neutron diffraction study for 2 a. Protonation of 2 a led to complex [Mo(1,2,4-C(5)H(2)tBu(3))(PMe(3))(2)H(4)](+) (3 a) in THF and to [Mo(1,2,4-C(5)H(2)tBu(3))(PMe(3))(2)(MeCN)H(2)](+) (4 a) in MeCN. Complex 4 b analogously derives from protonation of 2 b in MeCN, whereas the tetrahydride complex 3 b is unstable. One-electron oxidation of 2 a and 2 b by [FeCp(2)]PF(6) produces the EPR-active 17-electron complexes 2 a(+) and 2 b(+). The former is thermally more stable than the latter and could be crystallographically characterized as the PF(6) (-) salt by X-ray diffraction, providing evidence for the presence of a stretched dihydrogen ligand (H...H=1.36(6) angstroms). Controlled thermal decomposition of 2 a(+) yielded the product of H(2) elimination, the 15-electron monohydride complex [Mo(1,2,4-C(5)H(2)tBu(3))(PMe(3))(2)H]PF(6) (5 a), which was characterized by X-ray crystallography and by EPR spectroscopy at liquid He temperature. The compound establishes an equilibrium with the solvent adduct in THF. An electrochemical study by cyclic voltammetry provides further evidence for a rapid H(2) elimination process from the 17-electron complexes. In contrast to the previously investigated [MoCp*(dppe)H(3)](+) system (dppe=1,2-bis(diphenylphosphino)ethane; Cp*=pentamethylcyclopentadienyl), the decomposition of 2 a(+) by H(2) substitution with a solvent molecule appears to follow a dissociative pathway in MeCN.
authors.affiliation: Laboratoire de Chimie de Coordination, UPR CNRS 8241 liée par convention à l'Université Paul Sabatier et à l'Institut National Polytechnique de Toulouse, 205 Route de Narbonne, 31077 Toulouse Cedex, France.
authors.forename: Miguel
authors.initials: M
authors.lastname: Baya
authors.forename: Jennifer
authors.initials: J
authors.lastname: Houghton
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Daran
authors.forename: Rinaldo
authors.initials: R
authors.lastname: Poli
authors.forename: Louise
authors.initials: L
authors.lastname: Male
authors.forename: Alberto
authors.initials: A
authors.lastname: Albinati
authors.forename: Matthias
authors.initials: M
authors.lastname: Gutman
mesh_terms: D018360:Crystallography, X-Ray; D003517:Cyclopentanes / Q000138:chemical synthesis* / Q000737:chemistry; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D009682:Magnetic Resonance Spectroscopy; D008982:Molybdenum / Q000737:chemistry*; D033363:Neutron Diffraction; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D010084:Oxidation-Reduction; D011199:Potentiometry
chemical_list: D003517:Cyclopentanes; D009942:Organometallic Compounds; D008982:Molybdenum