The invention is directed to the cross-metathesis and ring-closing metathesis reactions between geminal disubstituted olefins and terminal olefins, wherein the reaction employs a Ruthenium or Osmium metal carbene complex. Specifically, the invention relates to the synthesis of null-functionalized or unfunctionalized olefins via intermolecular cross-metathesis and intramolecular ring-closing metathesis using a ruthenium alkylidene complex. The catalysts preferably used in the invention are of the general formula 1 wherein: M is ruthenium or osmium; X and X1 are each independently an anionic ligand; L is a neutral electron donor ligand; and, R, R1R6, R7, R8, and R9 are each independently hydrogen or a substituent selected from the group consisting of C1-C20 alkyl, C2-C20 alkenyl, C2-C20 alkynyl, aryl, C1-C20 carboxylate, C1-C20 alkoxy, C2-C20 alkenyloxy, C2-C20 alkynyloxy, aryloxy, C2-C20 alkoxycarbonyl, C1-C20 alkylthio, C1-C20 alkylsulfonyl and C1-C20 alkylsulfinyl.