Cooperative bimetallic reactivity of a heterodinuclear molybdenum–copper model of Mo–Cu CODH

Abstract

The synthesis of a heterodinucleating ligand LH2 (LH2 = (E)-3-(((2,7-di-tert-butyl-9,9-dimethyl-5-((pyridin-2-ylmethylene)amino)-9H-xanthen-4-yl)amino)methyl)benzene-1,2-diol) was undertaken toward a functional model of the bimetallic active site found in Mo-Cu carbon monoxide dehydrogenase (Mo-Cu CODH), and to understand the origins of heterobimetallic cooperativity exhibited by the enzyme. LH2 features a hard potentially dianionic catechol chelate for binding Mo(vi) and a soft iminopyridine chelate for binding Cu(i). Treatment of LH2 with either Cu(i) or M(vi) (M = Mo, W) sources leads to the anticipated site-selective incorporation of the respective metals. While both [CuI(LH2)]+ and [MVIO3(L)]2- complexes are stable in the solid state, [MVIO3(L)]2- complexes disproportionate in solution to give [MVIO2(L)2](NEt4)2 complexes, with [MVIO4]2- as the by-product. The incorporation of BOTH Mo(vi) and Cu(i) into L forms a highly reactive heterobimetallic complex [MoVIO3CuI(L)](NEt4)2, whose formation and reactivity was interrogated via1H NMR/UV-vis spectroscopy and DFT calculations. These studies reveal that the combination of the two metals triggers oxidation reactivity, in which a nucleophilic Mo(vi) trioxo attacks Cu(i)-bound imine. The major product of the reaction is a crystallographically characterized molybdenum(vi) complex [Mo(L')O2](NEt4) coordinated by a modified ligand L' that contains a new C-O bond in place of the imine functionality. This observed hydroxylation reactivity is consistent with the postulated first step of Mo-Cu CODH (nucleophilic attack of the Mo(vi)-oxo on the Cu(i)-bound electrophilic CO) and xanthine oxidoreductase (nucleophilic attack of Mo(vi)-oxo on the electrophilic xanthine carbon).

Kβ X‐Ray Emission Spectroscopic Study of a Second‐Row Transition Metal (Mo) and Its Application to Nitrogenase‐Related Model Complexes

“…The approach presented here may provide a means to more readily access electronic structural changes at the Mo in biological systems where molybdenum is involved either as a mononuclear active site (DMSO reductase, sulfite oxidase, etc) or as part of multinuclear metal centres, like Cu,Mo‐containing CO dehydrogenases …”

The Challenging in silico Description of Carbon Monoxide Oxidation as Catalyzed by Molybdenum-Copper CO Dehydrogenase

“…The relevance of MoCu-CODH as an inspiring system for future biomimetic and bioengineering applications is currently growing. This is due not only to the relevance of the reactions it catalyzes, but also to its resistance to atmospheric O 2 exposure—a rare feature in the case of enzymes expressing carbon monoxide dehydrogenase and hydrogenase activities (Choi et al, 2017; Gourlay et al, 2018; Groysman et al, 2018). Notably, the recent establishment of a functional heterologous expression system for the MoCu-CODH enzyme (Kaufmann et al, 2018) together with developments in the computational chemistry field will hopefully boost the positive feedback among biochemical, biomimetic and quantum chemical studies, opening new perspectives for a deeper understanding of this interesting metalloenzyme.…”

A bioinspired molybdenum–copper molecular catalyst for CO2 electroreduction

“…33 This metal cofactor has led to the synthesis of a number of biomimetic Mo-Cu complexes, but none of them had been reported to show catalytic activity for CO 2 reduction. [34][35][36][37][38] In this work, we have performed in-depth investigations of the CO 2 electroreduction catalytic activity of one of these complexes, 38 [(bdt)Mo VI (O)S 2 Cu I CN] 2À , 1, (bdt ¼ benzenedithiolate), in which Mo and Cu ions are connected by two m 2 -sulde ligands and the MPT ligand is mimicked by the bdt ligand chelating the Mo ion. While mimicking the structure of CODH2 active site, complex 1 reproduces the function of FDH, catalyzing CO 2 reduction with a high selectivity for formate production.…”