MOLYBDENUM(VI) BIS(AMIDATE) COMPLEXES FOR GROUP TRANSFER REACTIONS AND CATALYSIS

Abstract

Molybdenum complexes bearing bidentate amidate ligands have been synthesized and characterized using nuclear magnetic resonance spectroscopy (NMR), infrared spectroscopy (FTIR), and in most cases, single crystal X-ray diffraction (XRD). Three classes of bis(amidate) complexes are presented herein; dioxo, oxo/imido, and bis(imido) species. The tight bite-angle of the amidate ligand generates Mo complexes that exhibit distorted octahedral geometries. Density functional theory (DFT) calculations were employed to investigate the potential for isomerization and hemilability of the amidate ligand. A feature of the amidate complexes bearing imido groups, is a general trans-influence on the amidate ligand. This manifests as long Mo-O bonds for the amidate trans to the imido fragment in the case of the oxo/imido class. Hemilability is observed structurally with the [tBuNOtBu]2MoONtBu-THF complex 3.9. These complexes were utilized for various group transfer reactions. The dioxo class exhibits catalytic activity in oxygen atom transfer and epoxidation of various alkenes. The oxo/imido class demonstrates oxygen atom transfer capability, as well as catalytic epoxidation of cis-cyclooctene. The bis(imido) class enables some activity toward the cross metathesis of imines. Future directions of this work includes expansion of the amidate ligand set to alternative electron-withdrawing ligands, incorporation of sulfur to make thioamidate ligands, synthesis of new Mo-element multiple bonds via group transfer reactions, expansion of the reaction scope for epoxidation and imine metathesis, and the full investigation into deoxydehydration reactions of the Mo-oxo complexes.