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In the calculations,we mainly focused on the mechanisms involving three different reactions mediated by cyclopentadienyl organometallic complexes.For the CO-induced N-N bond cleavage of N2O mediated by molybdenum complexes,we proposed the new reaction mechanism with an overall free energy barrier of 23.6 kcal/mol,significantly lower than that of the reaction mechanism(42.2 kcal/mol)proposed by Sita et al.The calculations indicated that CO-induced N-N bond cleavage of N2O is competitive with oxygen atom transfer to carbon monoxide due to the comparable free energy barriers.In addition,we demonstrated that why the analogous tungsten complex can not give nitrosyl isocyanate complex via CO-induced N-N bond cleavage of N2O.For the C=O hydrosilylation of isocyanate and the C=S bond cleavage of isothiocyanate mediated by the neutral ruthenium silylene hydride complex,the difference in reactivity between isocyanate and isothiocyanate towards the ruthenium silylene hydride complex has been explained and discussed.The different bond strengths and π-accepting abilities of C=O and C=S,and the different degrees of affinity of O and S towards the Si center in the silylene ligand contribute to the different reactivities of the isocyanate and isothiocyanate substrates observed experimentally.For the reactions of a tungsten-germylyne complex with alcohols and arylaldehydes,the calculations show that a germylyne complex reacts with only one molecule of alcohol,while this complex reacts with two molecules of arylaldehydes.