Molybdenum(IV)-d² Reactivity in a Quasiplanar Oxo-Environment Modeled by Calix[4]arene: The Reductive Cleavage of NN Double Bond and the Formation of 1-Metallacyclopropene from the Corresponding Alkyne Complexes

Abstract

[p-But-calix[4]-(O)4-MoIV], generated in situ from [MoCl4·THF2] and the alkali salts of p-But-calix[4]arene, displays the reactivity expected for a d2-carbenoid metal. The reaction carried out in the presence of azobenzene led to the cleavage of the NN bond and the formation of a dimeric MoVI-phenylimido derivative, [{μ-p-But-calix[4]-(O)4}2{MoVI⋮NPh}2], while the reaction with acetylenes led to 2-metallacyclopropene complexes [{p-But-calix[4]-(O)4-Mo}(η2-C2R2)], which converted to 1-metallacyclopropenes, the precursor of alkylidene and alkylidyne functionalities, in the reaction with a hydride source.