The present invention provides unimolecular metal complexes having increased activity in the copolymerization of carbon dioxide and epoxides. Also provided are methods of using such metal complexes in the synthesis of polymers. According to one aspect, the present invention provides metal complexes comprising an activating species with catalytic activity tethered to a ligand that is coordinated to the active metal center of the complex.

A highly efficient, Z-selective ring-closing metathesis system for the formation of macrocycles using a stereoretentive, ruthenium-based catalyst supported by a dithiolate ligand is reported. This catalyst is demonstrated to be remarkably active as observed in initiation experiments showing complete catalyst initiation at −20° C. within 10 min. Using easily accessible diene starting materials bearing a Z-olefin moiety, macrocyclization reactions generated products with significantly higher Z-selectivity in appreciably shorter reaction times, in higher yield, and with much lower catalyst loadings than in previously reported systems. Macrocyclic lactones ranging in size from twelve-membered to seventeen-membered rings are synthesized in moderate to high yields (68-79% yield) with excellent Z-selectivity (95%-99% Z).

Disclosed herein are methods for preparing isotopically modified polyunsaturated lipids containing 1,4-diene systems involving selective isotopic modification of one or more bis-allylic positions of the polyunsaturated lipids in the presence of a transition metal catalyst.

A highly efficient, Z-selective ring-closing metathesis system for the formation of macrocycles using a stereoretentive, ruthenium-based catalyst supported by a dithiolate ligand is reported. This catalyst is demonstrated to be remarkably active as observed in initiation experiments showing complete catalyst initiation at −20° C. within 10 min. Using easily accessible diene starting materials bearing a Z-olefin moiety, macrocyclization reactions generated products with significantly higher Z-selectivity in appreciably shorter reaction times, in higher yield, and with much lower catalyst loadings than in previously reported systems. Macrocyclic lactones ranging in size from twelve-membered to seventeen-membered rings are synthesized in moderate to high yields (68-79% yield) with excellent Z-selectivity (95%-99% Z).

The present invention relates to a process for preparing nitrile rubbers having reduced molecular weight by metathesis of a first nitrile rubber in the presence of specific ruthenium complex catalysts that have particular N-heterocyclic carbene ligands.

Disclosed herein are methods for preparing isotopically modified polyunsaturated lipids containing 1,4-diene systems involving selective isotopic modification of one or more bis-allylic positions of the polyunsaturated lipids in the presence of a transition metal catalyst.

The invention relates to the use of ruthenium complexes, which are homogeneous catalysts and/or precatalysts of the olefin metathesis reaction, which lead to the production of alkenes containing an internal (non-terminal) double C═C bond. ##STR00001##

The present disclosure provides a catalyst system having a salan catalyst compound and borate or aluminate activators comprising cations having alkyl groups and methods for polymerizing olefins using such catalyst systems. In still another embodiment, the present disclosure provides a polymerization process comprising a) contacting one or more olefin monomers with a catalyst system comprising: i) an activator as described herein, ii) a catalyst compound as described herein, and iii) optional support.

A highly efficient, Z-selective ring-closing metathesis system for the formation of macrocycles using a stereoretentive, ruthenium-based catalyst supported by a dithiolate ligand is reported. This catalyst is demonstrated to be remarkably active as observed in initiation experiments showing complete catalyst initiation at 20 C. within 10 min. Using easily accessible diene starting materials bearing a Z-olefin moiety, macrocyclization reactions generated products with significantly higher Z-selectivity in appreciably shorter reaction times, in higher yield, and with much lower catalyst loadings than in previously reported systems. Macrocyclic lactones ranging in size from twelve-membered to seventeen-membered rings are synthesized in moderate to high yields (68-79% yield) with excellent Z-selectivity (95%-99% Z).

The present invention relates to a process for preparing nitrile rubbers having reduced molecular weight by metathesis of a first nitrile rubber in the presence of specific ruthenium complex catalysts that have particular N-heterocyclic carbene ligands.