title: An octanuclear molybdenum(VI) complex containing coordinatively bound 4,4'-di-tert-butyl-2,2'-bipyridine, [Mo8O22(OH)4(di-tBu-bipy)4]: synthesis, structure, and catalytic epoxidation of bio-derived olefins.
abstract: The reaction of [MoO(2)Cl(2)(di-tBu-bipy)] (1) (di-tBu-bipy = 4,4'-di-tert-butyl-2,2'-bipyridine) with water at 100-120 °C in a Teflon-lined stainless steel autoclave, in an open reflux system, or in a microwave synthesis system gave the octanuclear complex [Mo(8)O(22)(OH)(4)(di-tBu-bipy)(4)] (2) as a microcrystalline powder in good yields. Single crystals of 2 suitable for X-ray diffraction were obtained by the reaction of MoO(3) and di-tBu-bipy in water at 160 °C for 3 days. The molecular structure of 2 comprises a purely inorganic core, Mo(4)O(8)(μ(3)-OH)(2)(μ(2)-O)(2), attached to two peripheral oxo-bridged binuclear units, Mo(2)O(4)(μ(2)-O)(2)(OH)(di-tBu-bipy)(2). The inorganic core is composed of a unique assembly of four {MoO(5)} distorted square pyramids connected to each other via edge-sharing. Overall, the octanuclear complex adopts a highly distorted form strongly resembling an "S"-shaped molecular unit. Complex 2 was applied in the catalytic epoxidation of the biorenewable olefins DL-limonene (Lim) and methyl oleate (Ole), using tert-butylhydroperoxide (TBHP) as an oxygen donor, under mild reaction conditions (55 °C, air). The reactions of Lim and Ole gave the respective epoxide monomers in fairly high selectivities at high conversions (89% 1,2-epoxy-p-menth-8-ene selectivity at 96% Lim conversion; 99% methyl 9,10-epoxystearate selectivity at 94% Ole conversion, reached within 24 h reaction). Iodometric titrations revealed no measurable "non-productive" decomposition of TBHP.
authors.affiliation: Department of Chemistry, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal.
authors.forename: Tatiana R
authors.initials: TR
authors.lastname: Amarante
authors.forename: Patrícia
authors.initials: P
authors.lastname: Neves
authors.forename: Cátia
authors.initials: C
authors.lastname: Tomé
authors.forename: Marta
authors.initials: M
authors.lastname: Abrantes
authors.forename: Anabela A
authors.initials: AA
authors.lastname: Valente
authors.forename: Filipe A Almeida
authors.initials: FA
authors.lastname: Paz
authors.forename: Martyn
authors.initials: M
authors.lastname: Pillinger
authors.forename: Isabel S
authors.initials: IS
authors.lastname: Gonçalves
mesh_terms: D015082:2,2'-Dipyridyl / Q000737:chemistry*; D002384:Catalysis; D018360:Crystallography, X-Ray; D004852:Epoxy Compounds / Q000737:chemistry; D007700:Kinetics; D008958:Models, Molecular; D008982:Molybdenum / Q000737:chemistry*
chemical_list: D004852:Epoxy Compounds; D015082:2,2'-Dipyridyl; D008982:Molybdenum