The synthesis and characterization of a bidentate complex of 1,1′-(1,3-phenylene)bis(3-butylimidazolium) pincer proligand with molybdenum – A non-pincer binding mode

Abstract

The synthesis of the bidentate Mo complex tetrachlorido[6-(3′-butylimidazolium-1′-yl)-2-(3″-butylimidazol-1″-yl-2″-idene-κC2)phenyl-κC1]molybdenum(IV) 3 was carried out using the metalation followed by transmetalation methodology. The transmetalation process led to a bidentate complex after the reaction of DCM with HNMe2 formed an acidic ammonium ion that protonated the bidentate complex. Optimization of the synthetic methodology provided the tetrachlorido[6-(3′-butylimidazolium-1′-yl)-2-(3″-butylimidazol-1″-yl-2″-idene-κC2)phenyl-κC1]molybdenum(IV) complex in high yield. The crystal structure of the bidentate complex, 3, is reported herein. Attempts to avoid the acidic reaction conditions with different solvents or starting materials produced the bis-ligated Mo complex bis[2,6-bis(3′-butylimidazol-1′-yl-2′-idene-κC2)phenyl-κC1]molybdenum(IV) dichloride based on MS analysis. Electronic and coordinative unsaturation in the resulting bidentate complex, 3, open new possibilities for coordination of incoming substrates while also allowing access to the pincer-like motif via oxidative addition. Access to the interconversion of a NHC to/from imidazolium opens new avenues of non-innocent ligand pathways for proton shuttling in reactions such as nitrogen reduction to ammonia.