Thiolate-Bridged Nickel–Iron and Nickel–Ruthenium Complexes Relevant to the CO-Inhibited State of [NiFe]-Hydrogenase
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By employing S(CH2CH2S–)2 (tpdt) and O(CH2CH2S–)2 (opdt) as bridging ligands, two nickel–iron and two nickel–ruthenium heterodimetallic complexes, [Cp*M(μ-1κ3SSS′:2κ2SS-tpdt)Ni(dppe)][PF6] (1, M = Fe; 3, M = Ru) and [Cp*M(μ-1κ3SSO:2κ2SS-opdt)Ni(dppe)][PF6] (2, M = Fe; 4, M = Ru) (Cp* = η5-C5Me5; dppe = Ph2P(CH2)2PPh2), were obtained by a one-pot synthetic method and were identified by spectroscopy and X-ray crystallography. At 1 atm of CO, the pendant oxygen atom dissociated from the iron or ruthenium center and rapidly transferred to the nickel center when a CO molecule attacked the iron or ruthenium center in 2 and 4. However, there was no similar reaction occurring in 1 and 3 with the pendant sulfur atom. We confirmed the solid-state structure of the CO complex [Cp*Fe(t-CO)(μ-1κ2SS:2κ3SSO-opdt)Ni(dppe)][PF6] (5), which represents a possible configuration in the CO-inhibited state of [NiFe]-hydrogenase and exhibits no catalytic activity in electrochemical proton reduction.
本研究以S(CH₂CH₂S⁻)₂（tpdt）与O(CH₂CH₂S⁻)₂（opdt）作为桥联配体，通过一锅法合成了两种镍-铁异双核配合物与两种镍-钌异双核配合物，即[Cp*M(μ-1κ³SSS′:2κ²SS-tpdt)Ni(dppe)][PF₆]（1，M = Fe；3，M = Ru）与[Cp*M(μ-1κ³SSO:2κ²SS-opdt)Ni(dppe)][PF₆]（2，M = Fe；4，M = Ru），其中Cp* = η⁵-C₅Me₅，dppe = Ph₂P(CH₂)₂PPh₂。所有配合物均通过光谱学方法与X射线晶体衍射技术完成了结构鉴定。在1标准大气压的一氧化碳（CO）氛围中，当CO分子进攻配合物2与4中的铁或钌中心时，其配体上的悬挂氧原子会从铁/钌中心解离，并快速转移至镍中心。而对于配合物1与3，其配体上的悬挂硫原子则未发生类似反应。我们成功表征了CO加合产物[Cp*Fe(t-CO)(μ-1κ²SS:2κ³SSO-opdt)Ni(dppe)][PF₆]（5）的固态结构；该产物模拟了[NiFe]-氢化酶（[NiFe]-hydrogenase）被CO抑制时的可能构型，且在电化学质子还原反应中未表现出催化活性。
