A W/Cu Synthetic Model for the Mo/Cu Cofactor of Aerobic CODH Indicates That Biochemical CO Oxidation Requires a Frustrated Lewis Acid/Base Pair

Constructing
synthetic models of the Mo/Cu active site of aerobic
carbon monoxide dehydrogenase (CODH) has been a long-standing synthetic
challenge thought to be crucial for understanding how atmospheric
concentrations of CO and CO2 are regulated in the global
carbon cycle by chemolithoautotrophic bacteria and archaea. Here we
report a W/Cu complex that is among the closest synthetic mimics constructed
to date, enabled by a silyl protection/deprotection strategy that
provided access to a kinetically stabilized complex with mixed O2–/S2– ligation between (bdt)­(O)­WVI and CuI(NHC) (bdt = benzene dithiolate, NHC =
N-heterocyclic carbene) sites. Differences between the inorganic core’s
structural and electronic features outside the protein environment
relative to the native CODH cofactor point to a biochemical CO oxidation
mechanism that requires a strained active site geometry, with Lewis
acid/base frustration enforced by the protein secondary structure.
This new mechanistic insight has the potential to inform synthetic
design strategies for multimetallic energy storage catalysts.

构建需氧一氧化碳脱氢酶（aerobic carbon monoxide dehydrogenase, CODH）的钼/铜活性位点合成模型，长期以来都是一项极具挑战性的合成课题，该课题被认为对理解化能自养细菌与古菌如何调控全球碳循环中CO与CO₂的大气浓度至关重要。本文报道了一种迄今最为接近天然结构的合成模拟物——钨/铜配合物，其合成依托硅基保护/脱保护策略得以实现：该策略成功获得了(bdt)(O)Wᵛᴵ与Cuᴵ(NHC)位点间具有混合O²⁻/S²⁻配位的动力学稳定配合物（其中bdt为苯二硫醇盐（benzene dithiolate, bdt），NHC为氮杂环卡宾（N-heterocyclic carbene, NHC））。相较于天然CODH辅因子，该配合物在脱离蛋白质环境时，其无机核心的结构与电子特性存在差异，这提示一种依赖张力型活性位点几何构型的生化CO氧化机制：该机制的路易斯酸/碱受阻效应由蛋白质二级结构所强化。这一新的机制认知，有望为多金属储能催化剂的合成设计策略提供重要指导。