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183 W NMR Spectroscopy Guides the Search for Tungsten Alkylidyne Catalysts for Alkyne Metathesis
Author(s) -
Hillenbrand Julius,
Leutzsch Markus,
Gordon Christopher P.,
Copéret Christophe,
Fürstner Alois
Publication year - 2020
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.202009975
Subject(s) - chemistry , heteronuclear molecule , metathesis , cycloaddition , catalysis , nuclear magnetic resonance spectroscopy , ligand (biochemistry) , carbene , alkoxide , lewis acids and bases , alkyne , denticity , medicinal chemistry , stereochemistry , crystallography , organic chemistry , crystal structure , receptor , biochemistry , polymerization , polymer
Triarylsilanolates are privileged ancillary ligands for molybdenum alkylidyne catalysts for alkyne metathesis but lead to disappointing results and poor stability in the tungsten series. 1 H, 183 W heteronuclear multiple bond correlation spectroscopy, exploiting a favorable 5 J ‐coupling between the 183 W center and the peripheral protons on the alkylidyne cap, revealed that these ligands upregulate the Lewis acidity to an extent that the tungstenacyclobutadiene formed in the initial [2+2] cycloaddition step is over‐stabilized and the catalytic turnover brought to a halt. Guided by the 183 W NMR shifts as a proxy for the Lewis acidity of the central atom and by an accompanying chemical shift tensor analysis of the alkylidyne unit, the ligand design was revisited and a more strongly π‐donating all‐alkoxide ligand prepared. The new expanded chelate complex has a tempered Lewis acidity and outperforms the classical Schrock catalyst, carrying monodentate tert ‐butoxy ligands, in terms of rate and functional‐group compatibility.