雙吡啶三牙彎曲型同碳雙碳烯及鈀金屬錯化物之結構探討及其催化應用

Abstract

我們成功合成雙吡啶三牙基彎曲型同碳雙碳烯 (carbodicarbene)並且得到其單晶結構，目前來說是第一個相關結構之結果，其中心碳-碳-碳角度143°，相較於過去我們實驗室之異丙基結構來說，角度更來的大，更具備連烯烃 (Allene) 之性質，同時我們也利用其前驅物合成三牙基同碳雙碳烯配位之鈀金屬錯化物，並且藉由理論計算得知其電子分佈性質，也成功應用於Heck-Mizoroki和Suzuki-Miyaura交錯偶合反應，並且得到良好之效果。 另外我們也針對其鈀金屬錯化物9進行可見光光致化氧化還原醯胺生成反應，並利用合理的推斷其反應機制，經由UV-Visible光譜得知其吸收為499 nm，而於藍光及綠光下可得到目標產物，氮於紅光下則無反應。 另外也成功應用於一鍋化(One-pot)C/C、C/N鍵生成反應、可見光光致碳氫鍵活化反應，並且得到良好之效果，和過去相似之光催化反應需使用雙金屬之配合，而在此我們的鈀金屬催化劑具有雙功能 (Bifunctional) 性質之”Janus catalyst”，同時能夠進行單電子及雙電子催化反應之機制。

The simple synthetic development of acyclic pincer bis(pyridine)carbodicarbene is depicted herein. Presented is the first isolated structural pincer carbodicarbene with a C-C-C angle of 143°, larger than the monodentate framework. More importantly theoretical analysis revealed that this carbodicarbene embodies a more allene-like character. Pd complexes supported by this pincer ligand are active catalysts for Heck-Mizoroki and Suzuki-Miyaura coupling reactions. The combination of conventional transition metal-catalyzed coupling reactions and photoredox catalysis has emerged as a powerful approach to catalyze difficult cross-coupling reactions under mild conditions (e.g. alkyl-olefin C-C and C-O bond formations). In these reactions, two distinct organometallic catalysts are necessary for promoting the catalytic photoredox and coupling sequences. Herein, we report a unique Pd complex that mediates both photoredox catalysis for C-N bond formation upon visible-light irradiation and conventional Suzuki-Miyaura coupling in the absence of light. These two catalytic pathways can be merged to promote both conventional transition-metal-catalyzed coupling and photoredox catalysis to mediate C-H arylation under ambient conditions with a single component catalyst in an efficient one-pot process. We demonstrate the potential of applying visible light to turn on a different type of cross-coupling reaction (through the excited-state scheme) in addition to the inherent ground-state catalysis using a single metal complex.