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

Abstract

The origins of regio- and stereoselectivity in the ring-opening metathesis polymerization of 3-substituted cis-cyclooctenes by monoaryloxide pyrrolide imido alkylidene (MAP) Mo- and W-based catalysts are determined at the M06-2X/SDD|6-311+G(2df,p)//M06-L/SDD|6-31G(d)|MIDI! level of density functional theory. Considering cis-cyclooctene (COE) and 3-methyl-cis-cyclooctene (3MCOE) as monomers and W(N-t-Bu)(CH-t-Bu)(OHMT)(Pyr) (OHMT = hexamethylterphenoxide, Pyr = pyrrolide) as a catalyst, all possible syn and anti combinations of alkylidene and cyclic olefin, relative to the imido ligand, are evaluated. The observed Z-selectivity for the ring-opening metathesis (ROM) of COE is due to the large size of the aryloxide ligand, which forces both the alkylidene and the incoming cyclic olefin to be syn relative to the imido ligand. As determined previously for Grubbs' second-generation catalyst (G2), breakdown of the metallacyclobutane intermediate is the rate-limiting step for cyclic olefins having ring sizes exceeding five carbon atoms. Contrary to the G2 case, however, the ring-opening of 3MCOE by MAP catalysts prefers a proximal (3-substituent closest to the metal center) over a distal (3-substituent furthest from the metal center) approach. In all calculated paths, we observe inversion of catalyst configuration after each catalytic cycle.

Regioselective Ring-Opening Metathesis Polymerization of 3-Substituted Cyclooctenes with Ether Side Chains.

“…Additionally, the coupling constants for olefinic protons were greater than 15 Hz for all polymers, consistent with the value for the trans double bond (Figure 2). 28 When the NMR measurement results are considered, there is definite evidence of a trans-HT regioregular sequence for all polymers. These results are fully consistent with the previously reported analyses of regio-and stereoselective ROMP, 23,24,26,27 which suggests that the polymers from alkoxy-substituted monomers also have remarkably high trans-HT regularity.…”

“…The regio- and stereoselectivity in the ROMP of functionalized monomers are strongly affected by the polarity of the systeme.g., solvent, functional groups at the monomer, and the temperature. ,, The regio- and stereoregularity of the polymerizations in both nonpolar (e.g., toluene, cyclohexane) and highly polar (e.g., THF) solvents tend to lead to a decrease in the regio- and stereoselectivity. In the applied polymerization condition, in which the monomer concentrations are the same, the introduction of a longer oligo­(ethylene glycol) chain into the monomer could lead to an increase in the polarity of the polymerization system; therefore, the regularity would likely be reduced.…”

“…Recently, Hillmyer et al reported a series of papers describing the synthesis of polymers with extremely high regio- and stereoregularities from the ROMP of 3-substituted cyclooctenes using Grubbs second- ( G2 ) and third-generation ( G3 ) catalysts, and the polymers with precisely placed side-chain branches on every eighth backbone carbon were also achieved via the ROMP-hydrogenation pathway. − Extensive research has been performed on the regio-/stereoselective ROMP of 3-substituted cycloalkenamerse.g., alkyl, phenyl, acetoxy, and a variety of polar functional groupsand details of the mechanism have gradually revealed that the high regio-/stereoregularity of the regioselective ROMP-produced polymer originated from the steric repulsion between the N -heterocyclic carbene ligand on the metathesis catalysts and the substituent on the allyl position of the monomer. , The energetically favorable distal- E monomer orientation leads to an intermediate with a substituent positioned γ to the ruthenium. The preferred reaction path provides polymers with a high degree of head-to-tail regioregularity .…”

“…23−27 Extensive research has been performed on the regio-/stereoselective ROMP of 3-substituted cycloalkenamerse.g., alkyl, phenyl, acetoxy, and a variety of polar functional groupsand details of the mechanism have gradually revealed that the high regio-/ stereoregularity of the regioselective ROMP-produced polymer originated from the steric repulsion between the N-heterocyclic carbene ligand on the metathesis catalysts and the substituent on the allyl position of the monomer. 28,29 The energetically favorable distal-E monomer orientation leads to an intermediate with a substituent positioned γ to the ruthenium. The preferred reaction path provides polymers with a high degree of head-to-tail regioregularity.…”

Aluminium Complexes Bearing Pyrrolide Ligand as Efficient Catalysts for Ring‐Opening Polymerization of ε‐Caprolactone

“…There is currently a renewed interest in the employment of organometallic complexes based on pyrrolide ligands as the initiators for the ROP of ε‐caprolactone . The flexibility of the pyrrolide ligands provides tunable steric and electronic features required for compensating coordinative unsaturation of metal atoms, and enhances catalytic activity of the complexes toward polymerization.…”