A Hemilabile Diphosphine Pyridine Pincer Ligand: σ- and π-Binding in Molybdenum Coordination Complexes

A series of molybdenum compounds supported by a hemilabile pyridine diphosphine pincer ligand have been synthesized. The ligand demonstrates variable binding modes, adapting to the electronic and geometric requirements of the metal center. In Mo⁰ and Mo^(II) polycarbonyl complexes, coordination through the σ-donating pyridine nitrogen lone pair is observed. Upon oxidative group transfer with anionic azide, a Mo^(IV) nitride compound is formed, accompanied by a change in the ancillary ligand binding mode to the pyridine π-system. The σ-coordination was restored by subsequent functionalization of the nitride moiety with either silyl electrophiles or protons. Protonation results in redox disproportionation with concomitant nitride functionalization. Characterization by single crystal X-ray diffraction, nuclear magnetic resonance, and infrared spectroscopy is discussed