title: Pyridyne radical cations produced by photodissociation of Mg*+ (multifluoro-pyridine) complexes: a combined experimental and theoretical study.
abstract: Gas phase complexes Mg*+ (2,6-difluoropyridine) (1) and Mg*+ (pentafluoropyridine) (2) have been subjected to photodissociation in the spectral range of approximately 230-440 nm. Except for the evaporative photofragment Mg*+ , the primary photoproduct for is C(5)H(3)N*(+), which is associated with the rupture of two C-F bonds by the photoexcited Mg*+ , forming very stable MgF(2). In contrast, the direct loss of MgF(+) is more favorable for due to fluorine substitution. Given enough energy, C(5)H(3)N*(+) can undergo decomposition to form C(4)H(2)*(+) and HCN. These results are very different from those for Mg*+ (2-fluoropyridine), highlighting the significance of the additional F at C6 of and . Density functional theory (DFT) calculations have been employed to examine the geometries and energetics of the complexes as well as relevant reaction mechanisms. All of the complexes feature the direct attachment of Mg*+ to the N atom. The key intermediate is found to be FMg(+) (C(5)H(x)F(4-x)N) (x = 3 or 0), which can lead to the formation of MgF(+) directly or MgF(2) through activation of another C-F bond adjacent to N, producing the pyridyne radical cations. However, hydrogen-transfer prior to the rupture of the second C-F bond followed by ring-opening of C(5)H(3)N*(+) may result in the formation of chain forms of C(5)H(3)N*(+). The influence of the fluorine substitution on the competition of the two routes have been demonstrated.
authors.affiliation: Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China.
authors.forename: Hai-Chuan
authors.initials: HC
authors.lastname: Liu
authors.forename: Xin-Hao
authors.initials: XH
authors.lastname: Zhang
authors.forename: Changsheng
authors.initials: C
authors.lastname: Wang
authors.forename: Yun-Dong
authors.initials: YD
authors.lastname: Wu
authors.forename: Shihe
authors.initials: S
authors.lastname: Yang
mesh_terms: D002412:Cations / Q000737:chemistry / Q000528:radiation effects; D020650:Combinatorial Chemistry Techniques; D005609:Free Radicals / Q000737:chemistry / Q000528:radiation effects; D008274:Magnesium / Q000737:chemistry* / Q000528:radiation effects; D008956:Models, Chemical; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry* / Q000528:radiation effects; D010777:Photochemistry; D011725:Pyridines / Q000737:chemistry* / Q000528:radiation effects; D011789:Quantum Theory; D013997:Time Factors; D014466:Ultraviolet Rays; D005466:Fluorocarbons
chemical_list: D002412:Cations; D005609:Free Radicals; D008274:Magnesium; D009942:Organometallic Compounds; D011725:Pyridines; C518916:2,6-difluoropyridine; C486857:pentafluoropyridine; D005466:Fluorocarbons