Synthesis and characterization of a trianionic pincer supported Mo-alkylidene anion and alkyne insertion into a Mo(IV)-C_(pincer) bond to form metallocyclopropene(η~2-vinyl) complexes

摘要

This report describes two approaches to form complexes featuring Mo-C multiple bonds and a trianionic pincer ligand. Treating the trianionic pincer ligand precursor [~tBuOCO]H_3 (1) with MeLi provides the corresponding dilithio salt [~tBuOCHO]Li_2(THF)_3 (6) in situ, which further reacts with Mo(NAr) (CHCMe_2Ph)(OTf) _2(DME) to provide the terphenyl diphenolate complex [ ~tBuOCHO]Mo(NAr)CHCMe_2Ph (5). Complex 5 is characterized by ~1H, ~(13)C{~1H} NMR spectroscopy, combustion analysis, and single crystal X-ray diffraction. The solid state structure of 5 reveals a distorted trigonal pyramidal geometry for the Mo(VI) ion. Treating 5 with one equiv. of phosphorane in toluene converts the diphenolate ligand into a trianionic pincer ligand by deprotonation of the pincer C_(ipso)-H proton to give the alkylidene salt {[~tBuOCHO]Mo(NAr)(CHCMe _2Ph)}{Ph_3PCH_3} (7). Treating [ ~tBuOCO]MoNMe_2(NHMe_2)_2 (2), containing a d~2 Mo(IV) ion, with terminal alkynes (H-C≡CR, R = Ph, 3,5-F_2C_6H_3, 3,5-(CF_3) _2C_6H_3 and SiMe_3) produces in excellent yield the corresponding metallocyclopropylidene complexes 10-R (R H, F, CF_3) and 11 (R = SiMe_3). X-ray diffraction studies on single crystals of 10-H and 11 reveal three important features: 1) a highly distorted hexacoordinate Mo(VI) center, 2) a metallocyclopropene(η ~2-vinyl) fragment, and 3) a highly distorted CH group in the metallocyclopropene unit. A single point calculation and an NBO analysis performed on 10-H′ confirms the multiple bond between Mo1 and C28. The highest occupied Kohn-Sham molecular orbital (HOMO) represents a π-combination between d_(yz) of Mo1 and the p_y orbital of C28, and the corresponding π-combination of those orbitals constitutes the lowest unoccupied molecular orbital (LUMO).