Design and Reactivity of Early-Late Bimetallics as Structural and Functional Models of Mo Cu CODH

This review focuses on the synthetic inorganic chemistry of structural and functional models of Mo-Cu CO dehydrogenase (CODH). Mo-Cu CODH is an aerobic enzyme that catalyzes CO oxidation. The active site of Mo-Cu CODH demonstrates a structural motif unprecedented in inorganic chemistry: dithiolene-ligated (MoO2S)-O-VI linked to a two-coordinate Cu(I) through a single bridging sulfido, {(MoO2)-O-VI(mu(2)-S)Cu-I}. There is significant interest in understanding how this unusual active site structure enables reactivity. Structural analogues of varying accuracy have been reported by several research groups and are discussed in this review. Most of the modeling chemistry indicates that the single sulfido-bridged Mo-VI-(mu(2)-S)-Cu-I structure is unstable when the metals are coordinatively unsaturated, generally collapsing into the stable Mo-VI-(mu(2)-S)(2)-Cu-I or Mo-VI-(mu(2)-S)(mu(2)-O)-Cu-I diamond cores outside of the protein environments. Whereas singly bridged {(MoO2)-O-VI(mu(2)-S)Cu-I} oxidizes CO and inserts CNR (isocyanide) efficiently, no biomimetic CODH-relevant reactivity was observed for the synthetic analogues containing the aforementioned diamond cores. An alternative synthetic approach pursuing a "bioinspired" functional model is also discussed. In this approach, two relevant metal sites (hypothesized to be primarily responsible for the reactivity) are combined into a heterobimetallic complex using appropriate heterodinucleating ligands. Syntheses, structures, and cooperative bimetallic reactivity of these heterobimetallic complexes will be discussed. [GRAPHICAL ABSTRACT]