Polymer mechanochemistry-enabled pericyclic reactions

Izak‐Nau, Emilia; Campagna, Davide; Baumann, Christoph; Göstl, Robert

doi:10.1039/c9py01937e

Cited by 89 publications

(85 citation statements)

References 233 publications

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“…Over the last decade or so, coupled mechanical forces have been used to drive a range of targeted covalent responses in isolated polymers and in bulk polymeric materials (covalent polymer mechanochemistry). 1,2 Mechanochemical strategies continue to evolve, including in very recent years their use in biasing and probing reaction pathways, 3,4 the release of small molecules and protons, 5,6 stress reporting, [7][8][9][10][11] stress strengthening, 12,13 degradable polymers, 14,15 and fundamental studies of polymer behavior under load. 16 In organic reactions, mechanochemical coupling has been investigated in simple bond dissociation reactions [17][18][19] and in a wide variety of reaction classes with respect to regiochemistry, [20][21][22][23][24] orbital symmetry, 20,[25][26][27] stereochemistry, 28,29 supramolecular architecture, [30][31][32] dynamic effects, 33,34 and the alignment and/or loading of scissile bonds with applied tension.…”

Section: Introductionmentioning

confidence: 99%

Force-Modulated Reductive Elimination from Platinum(II) Diaryl Complexes

Yu¹,

Wang²,

Wang³

et al. 2020

Preprint

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<div>Coupled mechanical forces are known to drive a range of covalent chemical reactions, but the interplay of mechanical force applied to a spectator ligand and transition metal reactivity is relatively unexplored. Here we report the effect of mechanical force on the rate of C(sp2)-C(sp2) reductive elimination from platinum(II) diaryl complexes containing macrocyclic bis(phosphine) force probe ligands. Compressive forces decreased the rate of reductive elimination whereas extension forces increased the rate of reductive elimination relative to the strain-free MeOBiphep complex with a 3.4-fold change in rate over a ~290 pN range of restoring forces. The natural bite angle of the free ligand changes with force, but 31P NMR analysis strongly suggests no significant force-induced perturbation of the ground state geometry of the (P–P)PtAr2 complexes. Rather, the force/rate behavior observed across this range of forces (from ca. 65 pN in compression to >200 pN in extension) for reductive elimination is attributed to the coupling of force to the elongation of the O…O distance in the transition state for reductive elimination. The results suggest opportunities to experimentally map geometry changes associated with reactions in transition metal complexes and potential strat-egies for force-modulated catalysis. </div>

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Section: Introductionmentioning

confidence: 99%

Force-Modulated Reductive Elimination from Platinum(II) Diaryl Complexes

Yu¹,

Wang²,

Wang³

et al. 2020

Preprint

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“…We therefore sought a system in which mechanical force could trigger a delayed degradation, allowing polymer topology and mechanical properties to be retained so that many such initiating events could be induced. In particular, mechanophores 18 have been used in recent years to create a wide range of stress-coupled responses in polymer materials [18][19][20][21] , including the extensive remodeling of polymers under processing conditions that might be suitable for inducing a large extent of degradation 19,[22][23][24][25][26] .…”

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confidence: 99%

Enhanced polymer mechanical degradation through mechanochemically unveiled lactonization

et al. 2020

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The mechanical degradation of polymers is typically limited to a single chain scission per triggering chain stretching event, and the loss of stress transfer that results from the scission limits the extent of degradation that can be achieved. Here, we report that the mechanically triggered ring-opening of a [4.2.0]bicyclooctene (BCOE) mechanophore sets up a delayed, force-free cascade lactonization that results in chain scission. Delayed chain scission allows many eventual scission events to be initiated within a single polymer chain. Ultrasonication of a 120 kDa BCOE copolymer mechanically remodels the polymer backbone, and subsequent lactonization slowly (~days) degrades the molecular weight to 4.4 kDa, > 10× smaller than control polymers in which lactonization is blocked. The force-coupled kinetics of ring-opening are probed by single molecule force spectroscopy, and mechanical degradation in the bulk is demonstrated. Delayed scission offers a strategy to enhanced mechanical degradation and programmed obsolescence in structural polymeric materials.

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“…During recent years, the field of polymer mechanochemistry [1–6] has matured to a point where a plethora of useful applications are available. Examples include the optical sensing of stress and strain using mechanochromic materials, [7–17] the self‐healing of polymers, [18–20] and the force‐induced activation of latent catalysts [21–23] .…”

Section: Methodsmentioning

confidence: 99%

The Mechanism of Flex‐Activation in Mechanophores Revealed By Quantum Chemistry

et al. 2020

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Flex‐activated mechanophores can be used for small‐molecule release in polymers under tension by rupture of covalent bonds that are orthogonal to the polymer main chain. Using static and dynamic quantum chemical methods, we here juxtapose three different mechanical deformation modes in flex‐activated mechanophores (end‐to‐end stretching, direct pulling of the scissile bonds, bond angle bendings) with the aim of proposing ways to optimize the efficiency of flex‐activation in experiments. It is found that end‐to‐end stretching, which is a traditional approach to activate mechanophores in polymers, does not trigger flex‐activation, whereas direct pulling of the scissile bonds or displacement of adjacent bond angles are efficient methods to achieve this goal. Based on the structural, energetic and electronic effects responsible for these observations, we propose ways of weakening the scissile bonds experimentally to increase the efficiency of flex‐activation.

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Polymer mechanochemistry-enabled pericyclic reactions

Abstract: Polymer mechanochemical pericyclic reactions are reviewed with regard to their structural features and substitution prerequisites to the polymer framework.

Cited by 89 publications

References 233 publications

Force-Modulated Reductive Elimination from Platinum(II) Diaryl Complexes

Force-Modulated Reductive Elimination from Platinum(II) Diaryl Complexes

Enhanced polymer mechanical degradation through mechanochemically unveiled lactonization

The Mechanism of Flex‐Activation in Mechanophores Revealed By Quantum Chemistry

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