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Tungsten(VI) Carbyne/Bis(carbene) Tautomerization Enabled by N‐Donor SBA15 Surface Ligands: A Solid‐State NMR and DFT Study
Author(s) -
BendjeriouSedjerari Anissa,
SofackKreutzer Julien,
Minenkov Yury,
AbouHamad Edy,
Hamzaoui Bilel,
Werghi Baraa,
Anjum Dalaver H.,
Cavallo Luigi,
Huang KuoWei,
Basset JeanMarie
Publication year - 2016
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201605934
Subject(s) - chemistry , tautomer , carbene , carbyne , geminal , catalysis , nuclear magnetic resonance spectroscopy , medicinal chemistry , metathesis , triflic acid , stereochemistry , crystallography , organic chemistry , polymer , polymerization
Designing supported well‐defined bis(carbene) complexes remains a key challenge in heterogeneous catalysis. The reaction of W(≡C t Bu)(CH 2 t Bu) 3 with amine‐modified mesoporous SBA15 silica, which has vicinal silanol/silylamine pairs [(≡SiOH)(≡SiNH 2 )], leads to [(≡SiNH 2 −)(≡SiO−)W(≡CH t Bu)(CH 2 t Bu) 2 ] and [(≡SiNH 2 −)(≡SiO−)W(=CH t Bu) 2 (CH 2 t Bu). Variable temperature, 1 H– 1 H 2D double‐quantum, 1 H– 13 C HETCOR, and HETCOR with spin diffusion solid‐state NMR spectroscopy demonstrate tautomerization between the alkyl alkylidyne and the bis(alkylidene) on the SBA15 surface. Such equilibrium is possible through the coordination of W to the surface [(≡Si−OH)(≡Si−NH 2 )] groups, which act as a [N,O] pincer ligand. DFT calculations provide a rationalization for the surface–complex tautomerization and support the experimental results. This direct observation of such a process shows the strong similarity between molecular mechanisms in homogeneous and heterogeneous catalysis. In propane metathesis (at 150 °C), the tungsten bis(carbene) tautomer is favorable, with a turnover number (TON) of 262. It is the highest TON among all the tungsten alkyl‐supported catalysts.