10.1021/ja0641406.s001 Xiaolai Zheng Xiaolai Zheng Christopher W. Jones Christopher W. Jones Marcus Weck Marcus Weck Ring-Expanding Olefin Metathesis:  A Route to Highly Active Unsymmetrical Macrocyclic Oligomeric Co-Salen Catalysts for the Hydrolytic Kinetic Resolution of Epoxides American Chemical Society 2007 generation Grubbs catalyst metathesi HKR olefin macrocyclic oligomeric structures Co metal complexes bimetallic transition state salen Hydrolytic Kinetic Resolution species monomer concentrations results racemic terminal epoxides unsymmetrical pendent immobilization motif 2007-02-07 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Ring_Expanding_Olefin_Metathesis_A_Route_to_Highly_Active_Unsymmetrical_Macrocyclic_Oligomeric_Co_Salen_Catalysts_for_the_Hydrolytic_Kinetic_Resolution_of_Epoxides/3027745 In the presence of the third generation Grubbs catalyst, the ring-expanding olefin metathesis of a monocyclooct-4-en-1-yl functionalized salen ligand and the corresponding Co(II)(salen) complex at low monomer concentrations results in the exclusive formation of macrocyclic oligomeric structures with the salen moieties being attached in an unsymmetrical, flexible, pendent manner. The TOF-MALDI mass spectrometry reveals that the resulting macrocyclic oligomers consist predominantly of dimeric to tetrameric species, with detectable traces of higher homologues up to a decamer. Upon activation under aerobic and acidic conditions, these Co(salen) macrocycles exhibit extremely high reactivities and selectivities in the hydrolytic kinetic resolution (HKR) of a variety of racemic terminal epoxides under neat conditions with very low catalyst loadings. The excellent catalytic properties can be explained in terms of the new catalyst's appealing structural features, namely, the flexible oligomer backbone, the unsymmetrical pendent immobilization motif of the catalytic sites, and the high local concentration of Co(salen) species resulting from the macrocyclic framework. This ring-expanding olefin metathesis is suggested to be a simple way to prepare tethered metal complexes that are endowed with key features(i) a high local concentration of metal complexes and (ii) a flexible, single point of attachment to the supportthat facilitate rapid and efficient catalysis when a bimetallic transition state is required.