Mononuclear and Dinuclear Molybdenum and Tungsten Complexes of p-tert-Butyltetrathiacalix[4]arene and p-tert-Butyltetrasulfonylcalix[4]arene: Facile Cleavage of the Calixarene Ligand Framework by Nickel

摘要

As part of our efforts to model species relevant to hydrodesulfur-ization (HDS) and hydrodenitrogenation (HDN), we are particularly interested in synthesizing heterodinuclear complexes that incorporate combinations of molybdenum and tungsten with promoter metals such as cobalt and nickel. Calixarenes are a class of multidentate macro-cyclic phenols that offer considerable potential for achieving this objective, especially if the linker between the phenolic groups also contains donor atoms. For this reason, we have focused our attention on the applications of calixarenes that feature S and [SO_2] linkers, specifically p-tert-butyltetrathiacalix[4]arene, S_4Calix~(Bu~1)(OH)_4], and p-tert-butyltetrasulfonylcalix[4]arene, [(SO_2)_4Calix~(Bu~1)(OH)_4]. An investigation of these calixarenes is also pertinent since we have recently demonstrated that the methylene linker of p-tert-butylcalix[4]arene, [Calix~(Bu~1) (OH)_4], can serve as a binding functionality in molybdenum and tungsten chemistry. Here we report that the nature of the linker has a profound effect on the chemistry of the system and influences the ability of the calixarene to coordinate a second metal center.