Ruthenium and osmium metal carbene complexes for olefin metathesis polymerization

A compound of the formula ##STR35## wherein:

• M is Os or Ru;
• R and R.sup.1 are independently selected from hydrogen;
• C.sub.2 -C.sub.20 alkenyl, C.sub.2 -C.sub.20 alkynyl, C.sub.1 -C.sub.20 alkyl, aryl, C.sub.1 -C.sub.20 carboxylate, C.sub.1 -C.sub.20 alkoxy, C.sub.2 -C.sub.20 alkenyloxy, C.sub.2 -C.sub.20 alkynyloxy, aryloxy, C.sub.2 -C.sub.20 alkoxycarbonyl, C.sub.1 -C.sub.20 alkylthio, C.sub.1 -C.sub.20 alkylsulfonyl or C.sub.1 -C.sub.20 alkylsulfinyl;
• each optionally substituted with C.sub.1 -C.sub.5 alkyl, halogen, C.sub.1 -C.sub.5 alkoxy or with a phenyl group optionally substituted with halogen, C.sub.1 -C.sub.5 alkyl or C.sub.1 -C.sub.5 alkoxy;
• X and X.sup.1 are independently selected from any anionic ligand;
• L and L.sup.1 are independently selected from any neutral electron donor, and
• wherein any 2, or 3 of X, X.sup.1, L, and L.sup.1 are optionally bonded together to form a chelating multidentate ligand.