The Effect of Pyridine-2-thiolate Ligands on the Reactivity of Tungsten Complexes toward Oxidation and Acetylene Insertion.

Riccardo Bondi,Miljan Z Ćorović,Ferdinand Belaj,Michael Buchsteiner,Carina Vidovič,Nadia C Mösch-Zanetti

doi:10.1021/acs.organomet.1c00472

Abstract

Intending to deepen our understanding of tungsten acetylene (C2H2) chemistry, with regard to the tungstoenzyme acetylene hydratase, here we explore the structure and reactivity of a series of tungsten acetylene complexes, stabilized with pyridine-2-thiolate ligands featuring tungsten in both +II and +IV oxidation states. By varying the substitution of the pyridine-2-thiolate moiety with respect to steric and electronic properties, we examined the details and limits of the previously reported intramolecular nucleophilic attack on acetylene followed by the formation of acetylene inserted complexes. Here, we demonstrate that only the combination of high steric demand and electron-withdrawing features prevents acetylene insertion. Nevertheless, although variable synthetic approaches are necessary for their synthesis, tungsten acetylene complexes can be stabilized predictably with a variety of pyridine-2-thiolate ligands.

Highlights

Tungsten is the metal of choice for several challenging enzymatic reactions.[1]
Similar behavior has previously been observed for tungsten complexes but only with substituted alkynes.[27−34] To sterically prevent the insertion from taking place, and to favor the attack from an external nucleophile, we introduced a methyl group in position 6 of the PyS ligand
Ligand design is based on PyS and 6MePyS which previously allowed the preparation of tungsten acetylene complexes of the types [W(CO)(C2H2)(SN)2] and [WO(C2H2)(SN)2], (SN= bidentate pyridine-2-thiolate moiety).[24,26]

Summary

Introduction

Tungsten is the metal of choice for several challenging enzymatic reactions.[1] Besides being in the active site of the metalloenzymes that catalyze redox reactions, it is essential for the function of acetylene hydratase (AH) This is a unique example of a tungstoenzyme catalyzing the nonredox hydration of acetylene to acetaldehyde.[1−5] This reaction is the first metabolic step of the mesophilic bacterium Pelobacter acetylenicus, which consumes acetylene as its only carbon and energy source.[2] The only other known enzyme that accepts acetylene as a substrate is nitrogenase, which reduces acetylene to ethylene.[6] The mechanism of the catalysis of AH remains elusive, as there are no reported crystal structures of the enzyme containing substrate or any inhibitor. Since one of the mechanistic ideas of AH suggests coordination of acetylene to the tungsten(IV) center,[7−12] we aim to synthesize and understand tungsten acetylene adducts with ligands similar to those in tungstoenzymes.[13,14]

Objectives

Results

Conclusion