TY - JOUR

T1 - Spectroscopic and Theoretical Study on Siloxy-Based Molybdenum and Tungsten Alkylidyne Catalysts for Alkyne Metathesis

AU - Haack, Alexander

AU - Hillenbrand, Julius

AU - Van Gastel, Maurice

AU - Fürstner, Alois

AU - Neese, Frank

N1 - Funding Information: Generous financial support by the MPG is gratefully acknowledged. We thank Dr. M. Leutzsch for help with NMR spectroscopy, and the analytical departments of our institute for excellent support. We further thank Dr. G. Bistoni for his great help with the LED and NOCV/ETS analysis.

PY - 2021/7/8

Y1 - 2021/7/8

N2 - A combined spectroscopic and theoretical study on triphenyl- and dimethyl-phenyl siloxy molybdenum and tungsten alkylidyne catalysts for alkyne metathesis is reported. Using NMR, X-ray, UV-vis, and resonance Raman spectroscopy and density functional theory calculations, the influence of different ligand systems and metal centers on the geometric and electronic structure and thermochemistry of different intermediates is investigated, that is, the starting alkylidyne and the derived metallacyclobutadiene (MCBD) and metallatetrahedrane (MTd). This includes a mechanistic and kinetic study on the formation and isomerization of MCBDs and MTds. Upon changing from monodentate to tripodal siloxy ligands, higher steric strain is imposed, which modulates the relative energies of the different intermediates. Additionally, intramolecular dispersion interactions between the bound substrate and the ligand can be operative. Tungsten as the central metal leads to stronger M-C σ-bonds, which overstabilize the reaction intermediates and preclude effective turnover. Furthermore, kinetic modeling strongly suggests that MTds are off-cycle intermediates based on the high barriers for direct formation but low barriers for isomerization from MCBDs. We infer from our findings that effective catalysis can only be achieved when factors that (over)stabilize intermediates, such as strong M-C bonds or large dispersion interactions, are prevented by appropriate catalyst design.

AB - A combined spectroscopic and theoretical study on triphenyl- and dimethyl-phenyl siloxy molybdenum and tungsten alkylidyne catalysts for alkyne metathesis is reported. Using NMR, X-ray, UV-vis, and resonance Raman spectroscopy and density functional theory calculations, the influence of different ligand systems and metal centers on the geometric and electronic structure and thermochemistry of different intermediates is investigated, that is, the starting alkylidyne and the derived metallacyclobutadiene (MCBD) and metallatetrahedrane (MTd). This includes a mechanistic and kinetic study on the formation and isomerization of MCBDs and MTds. Upon changing from monodentate to tripodal siloxy ligands, higher steric strain is imposed, which modulates the relative energies of the different intermediates. Additionally, intramolecular dispersion interactions between the bound substrate and the ligand can be operative. Tungsten as the central metal leads to stronger M-C σ-bonds, which overstabilize the reaction intermediates and preclude effective turnover. Furthermore, kinetic modeling strongly suggests that MTds are off-cycle intermediates based on the high barriers for direct formation but low barriers for isomerization from MCBDs. We infer from our findings that effective catalysis can only be achieved when factors that (over)stabilize intermediates, such as strong M-C bonds or large dispersion interactions, are prevented by appropriate catalyst design.

KW - catalysis

KW - dispersion interaction

KW - electronic structure

KW - ligands

KW - metathesis

UR - http://www.scopus.com/inward/record.url?scp=85111233647&partnerID=8YFLogxK

U2 - 10.1021/acscatal.1c01587

DO - 10.1021/acscatal.1c01587

M3 - Article

AN - SCOPUS:85111233647

VL - 11

SP - 9086

EP - 9101

JO - ACS catalysis

JF - ACS catalysis

SN - 2155-5435

IS - 15

ER -