Singlet Spin State Drives V-Carbene To Catalyze Olefin Metathesis: A Computational Analysis

摘要

Olefin metathesis is a crucial reaction typically catalyzed by Mo and Ru metal-carbene complexes. Catalysts based on 3d metals have recently attracted much interest due to their abundance, low toxicity, and inexpensive cost. Recently prepared vanadium-carbene complexes with analogous ligands to those of the Schrock carbenes were shown to be efl'ective catalysts for norbornene's ring-opening metathesis polymerization (ROMP). In this work, we employ density functional theory (B3LYP) calculations to explore the reaction mechanism and the energetic performance of the VV(CHSiMe3)(NC6H5)[OC(CF3)(3)](-)(PMe3)(2) (D) complex in catalyzing the ROMP of norbornene. Calculations revealed that the reaction takes place in the singlet spin surface through the classical olefin metathesis mechanism. The electronic analysis indicates the absence of valence electrons in the metallic vanadium d0 center as a cause in favoring the singlet spin state. The deactivation pathways toward cyclopropanation and beta-hydride elimination were calculated, and they showed higher barriers than those for olefin metathesis. The replacement of the carbene substituent -SiMe3 by the substituent -CMe3 was also analyzed, showing no considerable difl'erences regarding previous catalysts. Our results suggest that the cross-metathesis reaction of styrene catalyzed by the D complex is viable since it presented a potential energy surface similar to that observed in the ROMP reaction of norbornene. The potential energy surfaces of the ROMP reaction catalyzed by D and a Schrock catalyst indicate that the classic molybdenum catalyst favors lower energy barriers compared to vanadium catalysts.