Molybdenum(IV)-d(2) reactivity in a quasiplanar oxo-environment modeled bycalix[4]arene: The reductive cleavage of N=N double bond and the formationof 1-metallacyclopropene from the corresponding alkyne complexes

[p-Bu-t-calix[4]-(O)(4)-Mo-IV], generated in situ from [MoCl4. THF2] and th e alkali salts of p-Bu-t-calix-[4]arene, displays the reactivity expected f or a d(2)-carbenoid metal. The reaction carried out in the presence of azob enzene led to the cleavage of the N=N bond and the formation of a dimeric M o-VI-phenylimido derivative, [{mu -p-Bu-t-calix[4]-(O)(4)}(2){Mo(VI)equival ent to NPh}(2)], while the reaction with acetylenes led to 2-metallacyclopr opene complexes [{p-Bu-t-calix[4]-(O)(4)-Mo}(eta (2)-C2R2)], which converte d to 1-metallacyclopropenes, the precursor of alkylidene and alkylidyne fun ctionalities, in the reaction with a hydride source.