Ligand Variations in Neutral and Cationic Molybdenum Alkylidyne NHC Catalysts

Abstract

Several neutral and cationic molybdenum alkylidyne complexes bearing mono-, bi-, and tridentate N-heterocyclic carbenes (NHCs) have been prepared. The NHCs were varied in terms of their steric demand, basicity, and the nature of the chelating function. The introduction of a variety of different anionic ligands, such as triflates, halides, and alkoxides, was accomplished by replacing one, two, or three anionic ligands, allowing for substantial variations in the structure of the complexes. tert-Butyl, anisole, and mesityl groups were chosen as alkylidyne substituents. Cationic, tetracoordinate complexes were synthesized, boasting the structure proposed for the active species of molybdenum alkylidyne NHC complexes in alkyne metathesis reactions. The formation of unanticipated structures such as a bis-NHC complex (Mo19) and a complex bearing an alkoxide (Mo16) as a result of the demethylation of 1,2-dimethoxyethane (DME) was observed. The crystal structures of selected complexes are presented. Notably, this work focused exclusively on the syntheses and structures of the complexes; therefore, the reactivity of the complexes in alkyne metathesis reactions was not investigated.