Computational study of productive and non-productive cycles in fluoroalkene metathesis

Abstract

SummaryA detailed DFT study of the mechanism of metathesis of fluoroethene, 1-fluoroethene, 1,1-difluoroethene, cis- and trans-1,2-difluoroethene, tetrafluoroethene and chlorotrifluoroethene catalysed with the Hoveyda–Grubbs 2nd generation catalyst was performed. It revealed that a successful metathesis of hydrofluoroethenes is hampered by a high preference for a non-productive catalytic cycle proceeding through a ruthenacyclobutane intermediate bearing fluorines in positions 2 and 4. Moreover, the calculations showed that the cross-metathesis of perfluoro- or perhaloalkenes should be a feasible process and that the metathesis is not very sensitive to stereochemical issues.

Structural Assignment of Fluorocyclobutenes by 19F NMR Spectroscopy – Comparison of Calculated 19F NMR Shielding Constants with Experimental 19F NMR Shifts

“…Recently, the successful cross‐metathesis of polyfluoroalkenes with vinyl ethers has demonstrated the critical role of the other metathesis partner. This was in excellent agreement with our computational analysis, which indicated the key role of productive and nonproductive cycles in fluoroalkene metathesis …”

“…This was in excellent agreement with our computational analysis, which indicated the key role of productive and nonproductive cycles in fluoroalkene metathesis. [14] Surprisingly, no ring-opening metathesis (ROM) of fluorocycloalkenes has been reported, except for the ROM polymerization (ROMP) of fluorinated norbornenes (Scheme 1). [8a,15] Therefore, in connection with our recent activity in the field Scheme 1.…”

Highly Active Cross-Metathesis of Tetrafluoroethylene with a Seven-Membered N-Heterocyclic-Carbene–Ruthenium Catalyst

“…Scheme 6b plots the energy diagram with the Gibbs free energy correction from E′ to H, calculated at the M06L/aug-cc-pVDZ(PP) level of theory. 46−48 Consistent with the literature, 44,45 our computational study indicates a large energy difference between difluoromethylidene (F) and the alkylidene complex (H), which is reflected in the high energy of transition state TS2 (Scheme 6b, blue line). The existence of the diruthenium complex E′ located lower than F causes an even higher energy for TS2 relative to E′ (30.2 kcal mol −1 ), which is necessary for the catalysis turnover.…”

Non‐Symmetrical Tetrafluoroalkadienes Synthesized by ROCM of 3,3,4,4‐Tetrafluorocyclobutene

“…Quite recently, successful CM of tetrafluoroethylene and its analogues with enol ethers was described, where the significance of the metathesis partner structure and the choice of ruthenium catalyst was discussed (Scheme 1a) [15] . In agreement with this, a computational study disclosed that the key problem in CM of perfluorinated alkenes, i. e. formation of highly stable (difluoromethylene)ruthenium intermediate in the productive catalytic cycle, can be overcome by an appropriate choice of the second alkene [16] . Although ethyl vinyl ether is often used to quench ROMP, [17] there are several examples of ROCM between enol ethers and strained cycloalkenes [18] .…”

“…[15] In agreement with this, a computational study disclosed that the key problem in CM of perfluorinated alkenes, i. e. formation of highly stable (difluoromethylene)ruthenium intermediate in the productive catalytic cycle, can be overcome by an appropriate choice of the second alkene. [16] Although ethyl vinyl ether is often used to quench ROMP, [17] there are several examples of ROCM between enol ethers and strained cycloalkenes. [18] Surprisingly, examples of ROM of fluorinated substrates are extremely scarce, polymerization of fluorinated norbornene derivatives being the only known example.…”