This invention relates to a metathesis catalyst comprising a Group 8 metal complex represented by the formula: wherein: M is a Group 8 metal; each X is independently an anionic ligand; R1 and R2 are independently selected from the group consisting of hydrogen, a C1 to C30 hydrocarbyl, and a C1 to C30 substituted hydrocarbyl; R3 and R4 are independently selected from the group consisting of hydrogen, C1 to C12 hydrocarbyl groups, substituted C1 to C12 hydrocarbyl groups, and halides; and L is a neutral donor ligand. This invention also relates to processes for performing a metathesis reaction, in particular ring opening cross metathesis reactions and ring opening metathesis polymerization reactions, using the Group 8 metal complexes.