Ring opening of monocyclic dimethyl cyclopropene via metathesis by tungsten catalyst– A computational study

Abstract

Metathesis reaction of 3,3-disubstituted cyclopropene mediated by the model catalyst tungsten alkylidene W(NH)(CH 2)(OCH 3) 2 has been studied at the B3LYP/LANL2DZ level of theory. The stationary points on the potential energy surface for ring opening metathesis were calculated considering all stereochemically distinct approaches of the 3,3-disubstituted cyclopropene to the model tungsten catalyst. The ring opening of cyclopropene moiety proceeds in two steps i.e., cycloaddition and ring opening. Each step involves a twisted trigonal bipyramidal transition structure. The syn orientation of cyclopropene to the NH group of the tungsten alkylidene is more favourable for product formation. Cyclopropene addition to tungsten alkylidene takes place preferentially on the CNO face; which is favoured by 10.89 kcal/mol over the COO face. The energy barriers for the syn cycloaddition and syn ring opening steps are 8.47 and 10.94 kcal/mol, respectively. The ring opening step is the rate determining step for the reaction of cyclopropene with tungsten catalyst, in contrast with the case of the molybdenum catalyst.

Factors Controlling Selectivity in the Ring-Opening Metathesis Polymerization of 3-Substituted Cyclooctenes by Monoaryloxide Pyrrolide Imido Alkylidene (MAP) Catalysts

“…Previous gas-phase computational calculations in the ROM of cyclopropene , showed that the RLS is the [2+2] cycloaddition, which contrasts with our results for the ROM of COE, where the breakdown of the MCB ( TS2 ) is the RLS. To validate our results, the potential energy surface for the ROMs of cyclopentene and cycloheptene were calculated in the gas phase at the composite M06-2X level and compared to those with COE (Table ).…”

“…From Figure and Table , one can see that in every instance the rate-limiting step (RLS) is the retro-[2+2] of the MCB intermediate. Although this is consistent with previous reports on the ROM of COE with G2, it is contrary to other reports combining Mo- and W-based catalysts with smaller, cyclic olefins. , The product, calculated for the lowest energy path ( II- syn - syn ), is 1.1 kcal/mol lower in enthalpy than separated reactants and 8.1 kcal/mol higher in free energy. Of course, this reaction occurs spontaneously at room temperaturethe predicted endergonicity is associated with (i) using only a single-chain conformation in the product (which underestimates its entropy substantially), (ii) leaving an open site on the metal, and (iii) a possible smaller driving force for initiation than for propagation.…”

“…The stereogenic nature of the metal center of the MAP catalysts (Figure c) leads to the availability of two side approaches, one that is trans to the pyrrolide ligand and the other that is trans to the aryloxide ligand. The better σ-donor ability of the pyrrolide ligand should cause the olefin to approach the side trans to this ligand (CNO face) in the absence of other influences. ,, Therefore, we restrict our consideration here to the pyrrolide trans approach. Although it has been reported that the syn -alkylidene, relative to the imido group, is more stable than the anti -alkylidene, both of these geometries are fully examined here .…”

“…Considering conformational issues in the metathesis intermediates, previous reports have indicated that SP MCB intermediates are more stable than the corresponding TBP isomer. ,,,, However, only the TBP MCB intermediate undergoes retro[2+2] to generate the product. In our calculated structures, the [2+2] cycloaddition ( TS1 ) leads to the formation of the MCB intermediate with a TBP geometry.…”

The chemistry of the carbon-transition metal double and triple bond: Annual survey covering the year 2014

“…Tungsten catalysts of general structure 40 were highly effective in promoting Z-selective and stereoregular polymerization of norbornadiene diester derivative 39 [242]. Severally computationally-based studies of olefin metathesis were reported in 2014, including publications that focus on the following topics: (1) the feasibility of iron olefin metathesis catalysts (the pathway involving the iron analog of catalyst 2 is slightly less endothermic than ruthenium catalyst 2) [275,276]; (2) a comparison of various computational techniques (comparison of time and accuracy) for the complete ruthenium-catalyzed olefin metathesis pathway [277]; (3) orbital symmetry in the [2+2] cycloaddition step of olefin metathesis [278]; (4) the electronic effect of various alkylidene groups on the carbon-metal double bond strength (=CH 2 vs =CHF vs =CF 2 ), plus a comparison of Group 8 metals and similar studies on ruthenium metallacyclobutanes using coupled cluster theory [279]; (5) the cross metathesis of propene and styrene focused on the energies and interconversions of metallacyclobutane intermediates [280]; (6) 1-octene self metathesis [281,282]; (7) the ring opening of 3,3-dimethylcyclopropane using W(NH)(CH 2 )(OMe) 2 [283]; (8) olefin metathesis focusing on cis/trans olefin substrate coordination issues [284]; (9) microwave assisted RCM…”