Insertion of Palladium(0) and Nickel(0) Complexes into the α-Carbon-Bromine Bonds of 2-Bromo- or 2,6-Dibromophosphinines: A Versatile Route to α-Functionalised Phosphinines
作者:Hans Trauner、Pascal Le Floch、Jean-Michel Lefour、Louis Ricard、François Mathey
DOI:10.1055/s-1995-3982
日期:1995.6
The reaction of 2,4,6-tribromo-3-methylphosphinine with a source of [Pd(dppe)] [dppe = 1,2-bis(diphenylphosphino)ethane] leads exclusively to the C2-Pd(dppe)-Br insertion products whose geometry has been established by X-ray crystal structure analysis. The Pd-C2 bond has a normal length at 2.072(6) Å and the (dppe)Pd plane is orthogonal to the plane of the phosphinine ring, thus avoiding any steric hindrance from the methyl C3-substituent. AM1 semi-empirical calculations suggest that this selective palladium insertion into the C2-Br bond results from the initial formation of a Br-C2-P-Pd chelate which is calculated to be more stable than the Br-C6-P-Pd chelate by 1.3 kcal mol-1. Several new cross-coupling reactions at the C2 position of 2,6-dibromophosphinines have been devised using this selective palladium insertion as the catalytic step. They include the arylation by arylzinc derivatives, the synthesis of 2,2’-biphosphinines by reaction with 2-stannylphosphinines, and the thiolation by tin thiolates. Various 2,6-difunctional phosphinines with two different functionalities (PhC ≡ C-, 2-furyl, 2-pyrrolyl, BuS-, Ph2P-) have also been synthesized. Preliminary experiments indicate that [Ni(dppe)] is also able to activate the C2-Br bond of 2-bromophosphinines. Several 2,2’-biphosphinine chelates of Ni(0), Cr(0), Mo(0), and W(0) have been thus prepared.
2,4,6-三溴-3-甲基膦与[Pd(dppe)][dppe = 1,2-双(二苯基膦)乙烷]的反应只产生 C2-Pd(dppe)-Br 插入产物,其几何形状已通过 X 射线晶体结构分析确定。Pd-C2 键的正常长度为 2.072(6)埃,(dppe)Pd 平面与膦环平面正交,从而避免了来自 C3-甲基取代基的任何立体阻碍。AM1 半经验计算表明,这种选择性钯插入 C2-Br 键的结果是,最初形成的 Br-C2-P-Pd 螯合物比 Br-C6-P-Pd 螯合物稳定 1.3 kcal mol-1。利用这种选择性钯插入作为催化步骤,在 2,6-二溴膦的 C2 位设计出了几种新的交叉耦合反应。这些反应包括芳基锌衍生物的芳基化反应、与 2-烷基膦反应合成 2,2'-联膦,以及硫代锡酸盐的硫代反应。此外,还合成了具有两种不同官能度(PhC ≡ C-、2-呋喃基、2-吡咯基、BuS-、Ph2P-)的各种 2,6-双官能膦。初步实验表明,[Ni(dppe)] 还能激活 2-溴膦的 C2-Br 键。由此制备出了几种 Ni(0)、Cr(0)、Mo(0) 和 W(0) 的 2,2'-联膦螯合物。