Yanfeng Dang, Zhi‐Xiang Wang, Xiaotai Wang
Oct 9, 2012
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Organometallics
Abstract
Density functional theory (DFT) calculations (B3LYP, M06, and M06-L) have been performed to investigate the mechanism and origins of Z selectivity of the metathesis homodimerization of terminal olefins catalyzed by chelated ruthenium complexes. The chosen system is, without any simplification, the experimentally performed homocoupling reaction of 3-phenyl-1-propene with 1cat, a pivalate and N-heterocyclic carbene (NHC) chelated Ru precatalyst. The six-coordinate 1cat converts to a trigonal-bipyramidal intermediate (3) through initial dissociation and isomerization. The metathesis reaction of complex 3 with 3-phenyl-1-propene occurs in a side-bound mechanism and generates the trigonal-bipyramidal Ru–benzylidene complex 6. Complex 6 is the active catalyst for the subsequent side-bound metathesis with 3-phenyl-1-propene, which forms metallacyclobutanes that lead to the (Z)- and (E)-olefin homodimers. The transition states of cycloreversion leading to the (Z)- and (E)-olefins differ in energy by 2.2 kcal/mol,...