Generalizing metallocene mechanochemistry to ruthenocene mechanophores

Sha, Ye; Zhang, Yudi; Xu, Enhua; McAlister, C Wayne; Zhu, Tianyu; Craig, Stephen L.; Tang, Chuanbing

doi:10.1039/c9sc01347d

Cited by 67 publications

(50 citation statements)

References 54 publications

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“…Metallocenes play a pivotal role in the development of organometallic chemistry. The most studied members of the family are metallocenes of the transition metals, the reactivity and properties of which are remarkably diverse, leading to widespread applications in established areas such as olefin polymerization catalysis [1] and polymer chemistry, [2,3] whilst also accounting for new developments in small-molecule activation [4,5] and redox-active materials. [6,7] Metallocenes are also prominent in f-element chemistry owing to their distinct catalytic and stoichiometric reactivity, [8,9] and for their ability to provide platforms for the study of fundamental aspects of chemical bonding in lanthanide and actinide compounds.…”

Section: Isolation Of a Perfectly Linear Uranium(ii) Metallocenementioning

confidence: 99%

Isolation of a Perfectly Linear Uranium(II) Metallocene

et al. 2020

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Reduction of the uranium(III) metallocene [(η5‐C5iPr5)2UI] (1) with potassium graphite produces the “second‐generation” uranocene [(η5‐C5iPr5)2U] (2), which contains uranium in the formal divalent oxidation state. The geometry of 2 is that of a perfectly linear bis(cyclopentadienyl) sandwich complex, with the ground‐state valence electron configuration of uranium(II) revealed by electronic spectroscopy and density functional theory to be 5f3 6d1. Appreciable covalent contributions to the metal‐ligand bonds were determined from a computational study of 2, including participation from the uranium 5f and 6d orbitals. Whereas three unpaired electrons in 2 occupy orbitals with essentially pure 5f character, the fourth electron resides in an orbital defined by strong 7s‐6d mixing.

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Section: Isolation Of a Perfectly Linear Uranium(ii) Metallocenementioning

confidence: 99%

Isolation of a Perfectly Linear Uranium(II) Metallocene

et al. 2020

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“…Mechanistic studies have revealed that the use of F value accounts for variations in temperature, solvent, concentration, sonication amplitude, etc., but that the initial contour length (M n ) of the polymer does matter, with shorter polymers having higher F values (e.g., for a polybutadiene based gDCC polymer, F ¼ 0.92 for M n ¼ 59 kDa vs. F ¼ 0.69 for M n ¼ 92 kDa). 35 This quantication strategy has been applied to studies of the relationship between covalent bond strength and mechanical strength, 38,39 the mechanochemistry of metallocenes 40,41 the chain dynamics of cyclic polymers 42 under high strain rate elongational ows, and the subtle inuence of stereochemical effects on the mechanical reactivity of Diels-Alder adducts. 37…”

Section: Introductionmentioning

confidence: 99%

Oxidative regulation of the mechanical strength of a C–S bond

Lin

Craig

2020

Chem. Sci.

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“…In order to characterize the mechanochemical reactivity of the coumarin dimer, we targeted multi-mechanophore polymer P1 (Table 1), which uses a non-scissile gDCC mechanophore as an internal standard to characterize the relative strength of a scissile mechanophore co-repeating unit. [33][34][35] Briefly, a coumarin dimer macrocycle was synthesized via ring closing metathesis (RCM). The stereochemistry and regiochemistry of the coumarin dimer in the macrocycle (syn and head-to-tail, respectively) are enforced by the Z alkene tether, which restricts the arrangement of the two coumarin moieties for [2+2] photodimerization ( Figure 1b).…”

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Molecular Damage Detection in an Elastomer Nanocomposite with a Coumarin Dimer Mechanophore

Zhang

Lund

Gossweiler

et al. 2020

Macromol. Rapid Commun.

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resistance that result from dispersing stiffer particulates or fibers into the softer polymer matrix. [2,3] In high performance polymer composites, mechanical performance is often determined by how stress transfer from the matrix to the filler either prevents or facilitates the formation of voids, depending on the mechanism of toughening. [4,5] Stress overload can lead to the scission of covalent bonds or chain slippage and induce irreversible structural changes at the molecular, mesoscopic, and macroscopic levels, [6-8] ultimately leading to catastrophic material failure. Therefore, damage detection in polymer composites has long been an active area of study from both fundamental and applied perspectives. Currently, damage detection in composites is mostly achieved through techniques such as ultrasonics, computerized vibro-thermography, x-ray tomography and infrared thermography. [9] These techniques are non-destructive, and in some cases they have been applied in combination with methods for repairing the damage, such as resin injection and the use of reinforcing patches. [9] In addition, higher resolution techniques such as scanning electron microscopy and transmission electron microscopy have been used in post-mortem damage analysis in composites. [10,11] These methods have been quite successful, but they require that material damage has progressed to the point of nanoscale to mesoscale defects in order to be detected, and they do not directly probe the nature of the specific molecular events that are responsible for damage initiation and/or propagation. Polymer mechanochemistry offers exciting opportunities for stress-sensing and damage detection in polymer composites through incorporating mechanophores, which are molecular units that react in response to force. [12,13] By embedding different mechanophores, materials can be endowed with stress-responsive properties that include changes in modulus, [14,15] color, [16-19] and electronic properties. [20] Recent years have seen increased efforts to utilize mechanophores in bulk composites, [21-27] and mechanophores that provide irreversible optical responses to mechanical events are promising candidates to characterize the molecular stresses caused by wear or fatigue (Figure 1a). [12,28] But, to the best of our knowledge, mechanochromophores have Molecular force probes that generate optical responses to critical levels of mechanical stress (mechanochromophores) are increasingly attractive tools for identifying molecular sites that are most prone to failure. Here, a coumarin dimer mechanophore whose mechanical strength is comparable to that of the sulfur-sulfur bonds found in vulcanized rubbers is reported. It is further shown that the strain-induced scission of the coumarin dimer within the matrix of a particle-reinforced polybutadiene-based co-polymer can be detected and quantified by fluorescence spectroscopy, when cylinders of the nanocomposite are subjected to unconstrained uniaxial stress. The extent of the scission suggests that the coumarin dimers are mol...

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Generalizing metallocene mechanochemistry to ruthenocene mechanophores

Abstract: This work establishes ruthenocene as new metallocene-based mechanophores that exhibit an intriguing combination of force-free thermal stability and mechanical lability.

Cited by 67 publications

References 54 publications

Isolation of a Perfectly Linear Uranium(II) Metallocene

Isolation of a Perfectly Linear Uranium(II) Metallocene

Oxidative regulation of the mechanical strength of a C–S bond

Molecular Damage Detection in an Elastomer Nanocomposite with a Coumarin Dimer Mechanophore

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