Rapid intermolecular carbon-fluorine bond activation of pentafluoropyridine at nickel(0): Comparative reactivity of fluorinated arene and fluorinated pyridine derivatives
Rapid intermolecular carbon-fluorine bond activation of pentafluoropyridine at nickel(0): Comparative reactivity of fluorinated arene and fluorinated pyridine derivatives
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DOI：
10.1021/om9705160
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发表时间：
1997-10-28
期刊：
影响因子：
2.8
通讯作者：
Perutz, RN
中科院分区：
文献类型：
--
作者：
Cronin, L;Higgitt, CL;Perutz, RN
六氟苯与Ni(COD)(2) （COD = 1,5，-环二烯）在三乙基膦存在下或与Ni(PEt3)(4)在室温下反应，生成反式Ni(PEt3)(2)(C6F5)F(1)的速度非常慢。x射线晶体结构显示，分子配合物在镍处具有近似方平面配位，Ni-F距离为1.836(5)埃，Ni-C距离为1.878(7)埃。与五氟吡啶和2,3,5,6-四氟吡啶的类似反应进行得快得多。两种反应都产生类似于1的C-F活化产物，其中单个区域异构体占主导地位。反式ni (PEt3)(2)(C5HF3N)F(3)的晶体结构表明，三氟吡啶配体在2位被金属化。Ni-F和Ni-C的距离分别为1.856(2)和1.869(4)埃。在结构1和3中，芳基环的平面垂直于镍配位平面，这些结构提供了Ni（II）方形平面上镍-氟距离的第一值。Ni(COD)(2)与PEt3和3,5-二氯-2,4,6-三氟吡啶反应生成反式Ni(PEt3)(2)(C5ClF3N)Cl(4)，这是C-Cl与环上3位金属活化的产物。与2,3,4,5,6，-五氟苯乙烯的相应反应导致烯烃配位产物Ni(PEt3)(2)(eta(2)-CH2=CHC6F5)(6)的快速生成。6的晶体结构表现为典型的三角形Ni(0)几何形状，配位原子与镍几乎完全共面。Ni-C距离平均为1.960(6)埃；P-Ni-P角为115.0(1)度。与五氟苯和甲氧基五氟苯反应生成C-F活化产物非常缓慢，区域选择性很小。本文所报道的研究表明，通过选择合适的底物，在第一排过渡金属上，氟芳烃的分子间C-F活化可以快速而高产地进行。
Reaction of hexafluorobenzene with Ni(COD)(2) (COD = 1,5,-cyclooctadiene) in the presence of triethylphosphine or with Ni(PEt3)(4) at room temperature results in very slow formation of trans-Ni(PEt3)(2)(C6F5)F (1). The X-ray crystal structure reveals a molecular complex with approximately square-planar coordination at nickel, a Ni-F distance of 1.836(5) Angstrom and a Ni-C distance of 1.878(7) Angstrom. Analogous reactions with pentafluoropyridine and 2,3,5,6-tetrafluoropyridine proceed much faster. Both reactions yield C-F activation products analogous to 1 in which a single regioisomer is dominant. The crystal structure of trans-Ni(PEt3)(2)(C5HF3N)F (3) shows that the trifluoropyridyl ligand is metalated at the 2-position. The Ni-F and Ni-C distances are 1.856(2) and 1.869(4) Angstrom, respectively. In the structures of both 1 and 3, the plane of the aryl ring is perpendicular to the nickel coordination plane, These structures provide the first values of nickel-fluorine distances at square-planar Ni(II). The reaction of Ni(COD)(2) with PEt3 and 3,5-dichloro-2,4,6-trifluoropyridine yields exclusively trans-Ni(PEt3)(2)(C5ClF3N)Cl (4), the product of C-Cl activation with the metal at the 3-position of the ring. The corresponding reaction with 2,3,4,5,6,-pentafluorostyrene results in rapid formation of the alkene coordination product, Ni(PEt3)(2)(eta(2)-CH2=CHC6F5) (6). The crystal structure of 6 shows the typical trigonal Ni(0) geometry with the coordinated atoms almost perfectly coplanar with the nickel. The Ni-C distances average 1.960(6) Angstrom; the P-Ni-P angle is 115.0(1)degrees. Reaction with pentafluorobenzene and methoxypentafluorobenzene yield C-F activation products very slowly with little regioselectivity. The studies reported in this paper demonstrate that intermolecular C-F activation of a fluoroaromatic can take place rapidly and in good yield at a first row transition metal through the suitable choice of substrate.