A mechanistic investigation of carbon–hydrogen bond stannylation: synthesis and characterization of nickel catalysts
作者:Samuel A. Johnson、Meghan E. Doster、Jacob Matthews、Manar Shoshani、Michelle Thibodeau、Amanda Labadie、Jillian A. Hatnean
DOI:10.1039/c2dt30310h
日期:——
The complex (iPr3P)Ni(η2-Bu3SnCHCH2)2 (1a) was characterized by NMR spectroscopy and was identified as the active species for catalytic CâH bond stannylation of partially fluorinated aromatics, for example in the reaction between pentafluorobenzene and Bu3SnCHCH2, which generates C6F5SnBu3 and ethylene. The crystalline complex (iPr3P)Ni(η2-Ph3SnCHCH2)2 (1b) provides a more easily handled analogue, and is also capable of catalytic stannylation with added Ph3SnCHCH2 and C6F5H. Mechanistic studies on 1b show that the catalytically active species remains mononuclear. The rate of catalytic stannylation is proportional to [C6F5H] and inversely proportional to [Ph3SnCHCH2]. This is consistent with a mechanism where reversible Ph3SnCHCH2 dissociation provides (iPr3P)Ni(η2-Ph3SnCHCH2), followed by a rate-determining reaction with C6F5H to generate the stannylation products. Kinetic competition reactions between the fluorinated aromatics pentafluorobenzene, 1,2,4,5-tetrafluorobenzene, 1,2,3,5-tetrafluorobenzene, 1,2,4-trifluorobenzene, 1,3,5-trifluorobenzene and 1,3-difluorobenzene all suggest significant Niâaryl bond formation in the rate-determining step under catalytic conditions. Labelling studies are consistent with an insertion of the hydrogen of the arene into the vinyl group, followed by β-elimination or β-abstraction of the SnPh3 moiety.
络合物 (iPr3P)Ni(δ-2-Bu3SnCHCH2)2 (1a) 通过核磁共振光谱进行表征,并被确定为部分氟化芳烃催化 CâH 键烷基化的活性物质,例如在五氟苯和 Bu3SnCHCH2 的反应中,可生成 C6F5SnBu3 和乙烯。结晶络合物 (iPr3P)Ni(δ-2-Ph3SnCHCH2)2 (1b) 提供了一种更易于处理的类似物,也能在添加 Ph3SnCHCH2 和 C6F5H 的情况下催化链烷化反应。对 1b 的机理研究表明,催化活性物质仍然是单核的。催化链烷酰化的速率与[C6F5H]成正比,与[Ph3SnCHCH2]成反比。这与 Ph3SnCHCH2 可逆解离提供 (iPr3P)Ni(δ-2-Ph3SnCHCH2),然后与 C6F5H 发生决定速率的反应生成链烷酰化产物的机理是一致的。五氟苯、1,2,4,5-四氟苯、1,2,3,5-四氟苯、1,2,4-三氟苯、1,3,5-三氟苯和 1,3-二氟苯等氟化芳烃之间的动力学竞争反应均表明,在催化条件下,决定速率的步骤中形成了大量的镍芳基键。标记研究表明,炔烃的氢插入乙烯基,然后δ-消除或δ-萃取 SnPh3 分子。