Hypovalent radicals. 6. Electroreduction of diazodiphenylmethane - intermediacy of Ph2CN2-.cntdot. and Ph2C-.cntdot.

McDonald, Richard N.; Triebe, F.M.; R, January J; Borhani, K. J.; Hawley, M. Dale

doi:10.1021/ja00547a007

Cited by 20 publications

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“…The diminishing electric field (Figure a) will have a direct effect on the kinetics of electron hopping (vs spontaneous propagation), which was observed with increasing sample thickness between the working electrode and rheometer probe (Figure c). The mechanism of intermolecular dendrimer cross-linking is likely to be a complex mixture of carbene (C–H or N–H) insertion and azine cross-linking. , The mechanism of cross-linking allowed adhesion on both stainless steel (rheometer probe) and polypropylene/glass carbon substrate (Zensor chip electrode)cohesive failure coated a layer of adhesive on both substrates when separated (Figure b). Metallocenes other than ferrocene may improve the hole network properties in organic electrocuring.…”

Section: Discussionmentioning

confidence: 99%

“…The mechanism of intermolecular dendrimer cross-linking is likely to be a complex mixture of carbene (C−H or N−H) insertion and azine crosslinking. 69,70 The mechanism of cross-linking allowed adhesion on both stainless steel (rheometer probe) and polypropylene/ glass carbon substrate (Zensor chip electrode)cohesive failure coated a layer of adhesive on both substrates when separated (Figure 2b). Metallocenes other than ferrocene may improve the hole network properties in organic electrocuring.…”

Section: Macromoleculesmentioning

confidence: 99%

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Voltage-Activated Adhesion through Donor–Acceptor Dendrimers

et al. 2018

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Previous investigations on voltage-activated adhesives were restricted to aqueous solvents, where current directed crosslinking competed with water electrolysis.Replacing aqueous would expand applications of electrocuring technology and avoid excessive foaming, but many organic solvents have high ohmic resistances that prevent electrical conduction. These impediments were overcome through internal grafting of ferrocene (Fc) and diazirine (Dz) donor-acceptor pairs on fifth generation polyamidoamine (G5-PAMAM) dendrimers, forming G5-Fc-Dz cografted conjugates, where Fc internal additives provided an instantaneous conductive hole (+) network towards the redox conversion of diazirine to carbene insertion adhesion in non-toxic organic solvents of DMSO, DMF, and PEG400. Size exclusion chromatography and 1 H, 19 F NMR evaluated the formulations before and after electrocuring to quantitate grafting ratios and crosslinked dendrimers. Cyclic voltammetry confirmed the retained redox behavior of grafted Fc and Dz.Real-time electro-rheology established the dependence of crosslinking kinetics and adhesion strength on applied voltage. Liquid G5-Fc 15 -Dz 30 conjugates reached gelation within 2 min and with a storage modulus up to 3.4 ± 0.5 kPa. For the first time, a model system demonstrates the design components necessary towards organic, voltage-activated one-pot adhesives. This has broad implications for adhesives, cosmetics, implantable biomaterials, and flexible biosensors.

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Section: Discussionmentioning

confidence: 99%

Section: Macromoleculesmentioning

confidence: 99%

Voltage-Activated Adhesion through Donor–Acceptor Dendrimers

et al. 2018

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“…McDonald and Hawley reported that the electrochemical reduction of Ph 2 CN 2 in DMF afforded benzophenone azine through the carbene radical anion, Ph 2 C Ϫؒ , produced from electrogenerated Ph 2 CN 2 Ϫؒ by rapid loss of dinitrogen. 5 However, Bethell and his co-workers proposed that the azine was formed by the reaction of Ph 2 CN 2 Ϫؒ with Ph 2 CN 2 or Ph 2 CN 2 Ϫؒ on the basis of the data obtained by using their skilful cyclic voltammetric experiments, which ruled out the intervention of Ph 2 C Ϫؒ . 6 Based on the results of electrochemical reduction of various diazoalkanes, 7-9 they established that a unimolecular loss of dinitrogen from the diazoalkane radical anion giving the corresponding carbene radical anion occurred in the diazoalkanes having a carbonyl group at the position adjacent to the diazo group, such as azibenzil and diethyl diazomalonate.…”

Section: Introductionmentioning

confidence: 99%

Mechanistic studies of direct and sensitized photolysis of methyl (4-nitrophenyl)diazoacetate in the presence of an electron-donating amine: photochemical generation of the diazoalkane radical anion

Mizushima

Monden

Murata

et al. 2002

J. Chem. Soc., Perkin Trans. 2

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The direct and perylene-sensitized photolysis of methyl (4-nitrophenyl)diazoacetate (1) in the presence of an electron-donating amine was investigated by the characterization of reaction products and by the direct observation of reactive species using a laser flash photolysis technique. In the direct photolysis of 1 in the presence of N,N,NЈ,NЈtetramethyl-p-phenylenediamine (TMPD), electron transfer from TMPD occurs and the photoproducts are obtained through an intermediate other than the carbene 3, which we suppose to be the carbene radical anion 3 Ϫؒ . In the perylene-sensitized photolysis of 1 in the presence of an amine having a large electron-donating ability such as N,N-dimethylaniline and TMPD, the radical anion of 1 can be generated by perylene-mediated electron transfer from the amine to 1. The resulting 1 Ϫؒ appears to undergo extrusion of dinitrogen to give 3 Ϫؒ smoothly, the behavior of which is dependent on the amine employed as an additive. The product studies revealed that 3 Ϫؒ reacts readily with O 2 to give the ketoester 5 or abstracts hydrogen atoms to give the ester 7, which is not inconsistent with the theoretical prediction that 3 Ϫؒ has a σ radical character in its electronic structure.

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“…Diminishing electric field (Figure4.2a) will have a direct effect on the kinetics of electron hopping (vs. spontaneous propagation), which was observed with increasing sample thickness between the working electrode and rheometer probe (Figure4.3c). The mechanism of intermolecular dendrimer crosslinking is likely to be a complex mixture of carbene (C-H or N-H) insertion and azine crosslinking [69,70]. The mechanism of crosslinking allowed adhesion on both stainless steel (rheometer probe) and polypropylene/glass carbon substrate (Zensor® chip electrode)cohesive failure coated a layer of adhesive on both substrates when separated (Figure4.2b).…”

mentioning

confidence: 99%

Acceptor and donor one-pot voltage-activated adhesives

Tan¹

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Recent research has shown the voltage-activated adhesives are limited to waterbased solvents. Non-conductive environment and high solvent resistance from the organic solvents are the main causes that lead to difficulty in curing of adhesive by voltage activation. On the contrary, curing the adhesive in waterbased solvents like phosphate-buffered saline (PBS) results in no issue with voltage activation. However, water electrolysis occurs during voltage-curing.The generation of oxygen and hydrogen gases causes excessive foaming that compromises the structural properties of the adhesive. Thus, the advantages of replacing the water-based solvent with organic solvent are not limited to the adhesive application but can expand to other applications such as cosmetics and flexible implantable biosensors. Co-grafting the conductive additive ferrocene (Fc, donor) and the crosslinker diazirine (Dz, acceptor) onto the G5-PAMAM dendrimer in a biocompatible organic solvent (DMSO) can result in a donoracceptor dendrimer. Fc is oxidized to Fc+ (donor) and provides a conductive hole network, while Dz is reduced to Dz-(acceptor). Dz is oxidized to form carbenes, leading to intra/intermolecular crosslinking adhesion when voltage activation occurs. However, high donor-acceptor ratios co-grafted into one dendrimer leads to insolubility in organic solvents. Therefore, donor-acceptor blends overcome solubility limitations and provide faster throughput of structure-activity relationships with less synthetic investment. Despite these advantages, blend adhesives are constrained to intermolecular crosslinking adhesion upon voltage activation. In addition, the voltage activation concept of donor-acceptor pairs was not limited to ferrocene/diazirine designs. The concept was extended to donoracceptor pairs containing catechol and a Schiff base, which crosslinked upon voltage activation. However, catechol adhesives are susceptible to air oxidation, which leads to short shelf-stability. Thus, further work may explore catechol variants, such as vanillin, to resolve the problem of shelf-stability while retaining donor-acceptor electrocuring. This thesis demonstrates the first proof-of-concept voltage-activated adhesive in organic solvents with donor-acceptor functional groups that can be initiated at low voltages

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Hypovalent radicals. 6. Electroreduction of diazodiphenylmethane - intermediacy of Ph2CN2-.cntdot. and Ph2C-.cntdot.

Cited by 20 publications

References 0 publications

Voltage-Activated Adhesion through Donor–Acceptor Dendrimers

Voltage-Activated Adhesion through Donor–Acceptor Dendrimers

Mechanistic studies of direct and sensitized photolysis of methyl (4-nitrophenyl)diazoacetate in the presence of an electron-donating amine: photochemical generation of the diazoalkane radical anion

Acceptor and donor one-pot voltage-activated adhesives

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