Abstract
Early and late transition metal-carbon multiple bonds that have been widely used for many catalytic processes, organic transformations, and olefin metathesis reactions are described. Especially, the development of Schrock and Fischer type olefin metathesis catalysts aided by computational studies is discussed, focusing on work that aims at improving the reactivity, stability, and regioselectivity. The intriguing electronic feature and reactivity of a titanium alkylidyne, which leads to many unique transformations of organic molecules, are summarized. The development of Fischer type olefin metathesis catalysts to control the regioselectivity in cyclopolymerization of diynes with Ru-II-alkylidene catalysts employing quantum chemical studies is summarized.