Synthesis and Evaluation of Molybdenum and Tungsten Monoaryloxide Halide Alkylidene Complexes for Z-Selective Cross-Metathesis of Cyclooctene and Z-1,2-Dichloroethylene
Author(s)Hoveyda, Amir; Lam, Jonathan K; Zhu, Congqing; Bukhryakov, Konstantin; Mueller, Peter; Schrock, Richard Royce; ... Show more Show less
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Molybdenum complexes with the general formula Mo(NR)(CHR′)(OR″)(Cl)(MeCN) (R = t-Bu or 1-adamantyl; OR″ = a 2,6-terphenoxide) recently have been found to be highly active catalysts for cross-metathesis reactions between Z-internal olefins and Z-1,2-dichloroethylene or Z-(CF₃)CH═CH(CF₃). In this paper we report methods of synthesizing new potential catalysts with the general formula M(NR)(CHR′)(OR″)(Cl)(L) in which M = Mo or W, NR = N-2,6-diisopropylphenyl or NC6F5, and L is a phosphine, a pyridine, or a nitrile. We also test and compare all catalysts in the cross-metathesis of Z-1,2-dichloroethylene and cyclooctene. Our investigations indicate that tungsten complexes are inactive in the test reaction either because the donor is bound too strongly or because acetonitrile inserts into a W═C bond. The acetonitrile or pivalonitrile Mo(NR)(CHR′)(OR″)(Cl)(L) complexes are found to be especially reactive because the 14e Mo(NR)(CHR′)(OR″)Cl core is accessible through dissociation of the nitrile to a significant extent. Pivalonitrile can be removed (>95%) from Mo(NAr)(CHCMe₂Ph)(OHMT)(Cl)(t-BuCN) (Ar = 2,6-diisopropylphenyl; OHMT = 2,6-dimesitylphenoxide) to give 14e Mo(NAr)(CHCMe₂Ph)(OHMT)Cl in solution as a mixture of syn and anti (60:40 at 0.015 M) nitrile-free isomers, but these 14e complexes have not yet been isolated in pure form. The syn isomer of Mo(NAr)(CHCMe₂Ph)(OHMT)Cl binds pivalonitrile most strongly. Other Mo(NR)(CHR′)(OR″)(Cl)(L) complexes can be activated through addition of B(C₆F₅)₃. High stereoselectivities (>98% Z,Z) of ClCH═CH(CH₂)₆CH═CHCl are not restricted to tert-butylimido or adamantylimido complexes; 96.2% Z selectivity is observed with boron-activated Mo(NC₆F₅)(CHR′)(OHIPT)(Cl)(PPhMe₂). So far no Mo═CHCl complexes, which are required intermediates in the test reaction, have been observed in NMR studies at room temperature.
DepartmentMassachusetts Institute of Technology. Department of Chemistry
Journal of the American Chemical Society
American Chemical Society (ACS)
Lam, Jonathan K. et al. “Synthesis and Evaluation of Molybdenum and Tungsten Monoaryloxide Halide Alkylidene Complexes for Z-Selective Cross-Metathesis of Cyclooctene and Z-1,2-Dichloroethylene.” Journal of the American Chemical Society 138, 48 (November 2016): 15774–15783 © 2016 American Chemical Society