用Lewis鹼打開CoIII,IV2(μ-O)2鑽石核心可以提高C-H鍵的裂解反應性

用Lewis鹼打開CoIII,IV2(μ-O)2鑽石核心可以提高C-H鍵的裂解反應性

作者：

小柯機器人

發布時間：2020/12/22 21:34:50

一個由美國蒙大拿大學Dong Wang帶領的合作小組發現，用Lewis鹼打開Co^III,IV₂(μ-O)₂的「鑽石核心」可以提高C-H鍵的裂解反應性。該研究於2020年12月16日發表於國際一流學術期刊《美國化學會志》上。

研究人員於近日報導了一種高價Co^III,IV₂(μ-O)₂的「鑽石核心」 (1)，其對sp³雜化的C-H鍵具有高反應活性。在該文中，團隊展示了1的C-H鍵裂解活性可以通過引入一個Lewis鹼X進一步提高，使其動力學反應速率更快，且C-H鍵裂解能力比1更強。研究人員認為，1首先與X通過快速平衡形成開環化合物X–Co^III–O–Co^IV–O (1-X)，並通過電子自旋共振譜和密度泛函計算表徵了1-X。1-X表現出與母化合物1不同的S = 1/2電子自旋信號。密度泛函計算表明1-X有一個自旋密度在Co^IV-O中強烈離域的開環結構。

更重要的是，與1相比，1-X在進行C-H鍵活化反應時有更小的活化勢壘和更大的熱力學驅動力。值得注意的是，1-X比同類的二鐵開環化合物的反應活性要高4個數量級。這些研究表明，鑽石核心的異構化有可能是一個釋放sMMO-Q的氧化能力以進攻甲烷高度惰性的C-H鍵的一種可行的催化策略。

據了解，高價二鐵(IV)中間體Q是可溶性甲烷單加氧酶（sMMO）催化循環中用以裂解甲烷強C-H鍵的關鍵氧化物。sMMO-Q在之前的報導中為一個bis-μ-oxo Fe^IV₂(μ-O)₂鑽石核心，但最近被認為可能含一個Fe---Fe鍵較遠的開環核心。

附：英文原文

Title: Opening the CoIII,IV2(μ-O)2 Diamond Core by Lewis Bases Leads to Enhanced C–H Bond Cleaving Reactivity

Author: Yan Li, Suhashini Handunneththige, Jin Xiong, Yisong Guo, Marat R. Talipov, Dong Wang

Issue&Volume: December 16, 2020

Abstract: The high-valent diiron(IV) intermediate Q is the key oxidant that cleaves strong C–H bonds of methane in the catalytic cycle of soluble methane monooxygenase (sMMO). sMMO-Q was previously reported as a bis-μ-oxo FeIV2(μ-O)2 diamond core but was recently described to have an open core with a long Fe···Fe distance. We recently reported a high-valent CoIII,IV2(μ-O)2 diamond core complex (1) that is highly reactive with sp3 C–H bonds. In this work, we demonstrated that the C–H bond cleaving reactivity of 1 can be further enhanced by introducing a Lewis base X, affording faster kinetic rate constants and the ability to cleave stronger C–H bonds compared to 1. We proposed that 1 first reacts with X in a fast equilibrium to form an open core species X–CoIII–O–CoIV–O (1-X). We were able to characterize 1-X using EPR spectroscopy and DFT calculations. 1-X exhibited an S = 1/2 EPR signal distinct from that of the parent complex 1. DFT calculations showed that 1-X has an open core with the spin density heavily delocalized in the CoIV–O unit. Moreover, 1-X has a more favorable thermodynamic driving force and a smaller activation barrier than 1 to carry out C–H bond activation reactions. Notably, 1-X is at least 4 orders of magnitude more reactive than its diiron open core analogues. Our findings indicate that the diamond core isomerization is likely a practical enzymatic strategy to unmask the strong oxidizing power of sMMO-Q necessary to attack the highly inert C–H bonds of methane.

DOI: 10.1021/jacs.0c07294

Source: https://pubs.acs.org/doi/10.1021/jacs.0c07294