The discovery of dihydrogen complexes, LnM(H-2), pointed to direct transfer of hydrogen from coordinated H-2 ligands to substrates as an operable pathway in catalysis both in homogeneous and heterogeneous systems. Sigma complexes, LnM(eta(2)-H-X) (X = H, Si, C, etc), are indeed relevant in hydrogenation as well as silane alcoholysis and methane conversion.