Rotational Isomers of Mo(VI) Alkylidene Complexes and Cis/Trans PolymerStructure: Investigations in Ring-Opening Metathesis Polymerization

摘要

In the last few years well-defined metathesis catalysts of the general typeM(NR)(CHR)(OR')2 (M=Mo or W) have proven useful in a variety of olefin metathesis studies, in part because the activity of catalysts can be varied systematically by altering the electron-withdrawing ability of the alkoxides. Complexes containing t-butoxides (OCMe3 and OCMe(Cf3)2 in particular), an arylimido ligand (often NAr, where Ar= 2,6-i-Pr2C6H3), and molybdenum have been the most versatile. In the area of ring-opening metathesis polymerization (ROMP)molybdenum complexes have been employed most often to prepare polymers from a variety of norbornenes and norbornadienes. Molybdenum complexes appear to tolerate a wide range of functionalities, are stable and active in a variety of solvents,and have been shown to produce polymers that are virtually all trans and highly tactic or all cis with a tactic bias of approx. 75%. Alkylidene rotational isomers or rotamers (eq 1) are found for many high-oxidation state alkylidene complexes.