catalysts reported before were unsuccessful in this enantioselective radical C−N bond formation. The surprising preference for rhodium over iridium is attributed to much faster ligand‐exchange kinetics of the rhodium complexes involved in the catalytic cycle, which is crucial to keep pace with the highly reactive and thus short‐lived nitrogen‐centered radical intermediate.
双环
金属化
铑(III)络合物可催化可见光活化的2酰基
咪唑对映体选择性α-胺化反应,产率高达99%,ee高达98%。
铑催化剂被赋予了双重功能,即手性
路易斯酸,同时又是通过中间
氨基自由基进行自由基链反应的光活化智能
引发剂。值得注意的是,以前报道的相关
铱基光氧化还原催化剂在这种对映选择性自由基CN键形成中没有成功。
铑优于
铱的出人意料的偏好归因于参与催化循环的
铑配合物的
配体交换动力学快得多,这对于跟上高反应性且因此寿命短的以氮为中心的自由基中间体至关重要。