Abstract
Hydrogen is a widely used reductive reagent in organic synthesis. The direct reactions between dihydrogen and other organic compounds are very difficult, due to the high stability of hydrogen molecules. To solve this problem, some strategies for dihydrogen activation have been developed. In this review, we are going to introduce the dihydrogen activation using metals and alloys, metal complexes, divalent main group compounds and frustrated Lewis pairs by introducing the mechanisms, advantages and limitations.