Zwitterionic tetramethylenes as the common intermediates in the cycloaddition and polymerization reactions of N-vinylcarbazole with electrophilic tetrasubstituted ethylenes:  a new explanation for charge-transfer initiation

Gotoh, Tetsuya; Padías, Anne Buyle; Hall, H. K.

doi:10.1021/ja00276a037

Cited by 63 publications

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“…V(CO) 6 , was prepared by oxidizing NEt 4 [V(CO) 6 ] with phosphoric acid and purified by vacuum sublimation (25°C, 0.1 Torr; 1 Torr ≈ 133 Pa) [26]. MeTCEC was synthesized following a literature route [12], except that purification was carried out by repeated sublimations. Elemental analyses were performed by Chemisar Laboratories Inc. (Guelph, Ontario, Canada)…”

Section: Methodsmentioning

confidence: 99%

“…Herein, we report a new organicbased magnet prepared from the reaction of V(CO) 6 and MeTCEC with T c close to room temperature. MeTCEC underwent a reversible one-electron reduction at -0.05 V (vs. saturated calomel electrode (SCE) in MeCN), [12] that is ca. 0.3 V harder to reduce than TCNE, but easier to reduce than tetracyanopyrazine (-0.31 V), [13] and a reaction with V(CO) 6 was expected.…”

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confidence: 99%

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A Methyl Tricyanoethylenecarboxylate‐Based Room‐Temperature Magnet

2007

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Since the discovery of the first organic-based magnet, [Fe(C 5 Me 5 ) 2 ][TCNE] (TCNE = tetracyanoethylene), [1] efforts worldwide have focused on the discovery and characterization of new magnetic materials with enhanced and controllable magnetic properties.[2]The organic-based magnet of V[TCNE] x ·zCH 2 Cl 2 (x ≈ 2; z ≈ 0.5) composition with an ordering temperature T c of about 400 K can be synthesized via the reaction of V(C 6 H 6 ) 2 [3a] or V(CO) [5]With the goal of finding new organic-based magnets the reaction of V(CO) 6 with numerous polynitrile electron acceptors led to the discovery of several new V-based magnets with T c below room temperature. These include a,a′-dicyanoperfluorostilbene, (T c = 205 K), [6] tetracyanopyrazine (T c = 200 K), [7] and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ; T c = 52 K). (CO) 6 ] 1/2 ·zS (4>x > 3.5; S = CH 2 Cl 2 , PhCF 3 ) composition that orders above room temperature at 50°C (323 K). [9] A mild electronic acceptor methyl tricyanoethylenecarboxylate (MeTCEC; Scheme 1) has recently been used to synthesize isostructural decamethylmetallocene electron-transfer salt magnets of [MCp* 2 ][MeTCEC] (M = Cr, Mn, Fe) composition from which only Mn salt orders ferromagnetically below 7 K.[10] This is a little attenuated with respect to that observed for [MCp* 2 ][TCNE] (T c = 8.8 K).[11] Nonetheless, we targeted V[MeTCEC] 2 as a new organic-based magnet to identify the advantages and disadvantages of the reduced symmetry of the electron acceptor as well as the role of the ester carbonyl oxygen (C = O) in formation of additional superexchange pathways. Herein, we report a new organicbased magnet prepared from the reaction of V(CO) 6 and MeTCEC with T c close to room temperature. MeTCEC underwent a reversible one-electron reduction at -0.05 V (vs. saturated calomel electrode (SCE) in MeCN), [12] that is ca. 0.3 V harder to reduce than TCNE, but easier to reduce than tetracyanopyrazine (-0.31 V), [13] and a reaction with V(CO) 6 was expected. Reaction of MeTCEC with V(CO) 6 in CH 2 Cl 2 rapidly occurred and the system turned dark blue with CO evolution, and a dark precipitate formed suggesting the formation of an organometallic polymer similar to V

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Section: Methodsmentioning

confidence: 99%

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confidence: 99%

A Methyl Tricyanoethylenecarboxylate‐Based Room‐Temperature Magnet

2007

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“…± Completely different results were obtained in the reaction of N-vinyl-9H-carbazole with dimethyl (dicyanomethylidene)malonate (Scheme 3) [10]. Here, a cyclobutane was formed as the kinetically favored product.…”

Section: Scheme 1 Tetramethylene Intermediates Initiating Spontaneoumentioning

confidence: 95%

The Relationship of Cycloaddition Reactions to Spontaneous Vinyl Polymerizations

Hall

Padías

2005

Helvetica Chimica Acta

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To Professor Rolf Huisgen with grateful appreciation for his contributions to organic polymer chemistry! The zwitterionic ± biradical tetramethylene proposed by Huisgen as the key intermediate in stepwise [2 2] cycloaddition reactions has been shown to be the crucial intermediate in spontaneous vinyl polymerizations as well. Predominantly biradical tetramethylenes initiate free-radical copolymerizations, while predominantly zwitterionic tetramethylenes initiate cationic or anionic homopolymerizations. Stepwise cycloaddition is viewed as a spontaneous polymerization lacking a propagation step. These tendencies could be correlated in the form of an organic chemists Periodic Table, which has recently been put on a quantitative basis.Huisgen also showed experimentally that [4 2] Woodward ± Hoffman-allowed cycloadditions are completely concerted. Spontaneous copolymerizations accompanying these cycloadditions, therefore, were ascribed to the s-trans diene form. This concept was given support by kinetics studies, as well as by exclusive cycloaddition from s-cis cyclopentadiene, and exclusive copolymerization from s-trans verbenene.Introduction. ± The great poet builds larger than he knows. This familiar saying also applies to great scientists. When Rolf Huisgen was studying the role of the tetramethylene intermediate in [2 2] cycloaddition reactions, surely the idea that this intermediate might play an important role in polymer chemistry never crossed his mind. Yet this has proven to be the case.During the 1960s and 1970s, polymer chemists encountered various unexpected and perplexing observations in vinyl polymerizations. A tendency of the monomer units to alternate in the copolymer chain was observed. This was the case when electron-rich monomers, such as styrene or vinyl ethers, were copolymerized with electron-poor monomers, such as methyl acrylate or acrylonitrile. As the donor and acceptor character of the co-monomers increased, the alternation tendency grew stronger and stronger. Eventually, a new phenomenon set in, namely spontaneous polymerization. At first, spontaneous copolymerization occurred by a radical mechanism to form strictly alternating copolymers. With still stronger donor-substituted monomers, homopolymers of the donor monomer were found, which could only be formed by a spontaneous cationic homopolymerization.Attempts by polymer chemists to understand these phenomena centered on the visible charge-transfer (CT) complexes formed by the two monomers. It was attractive to suppose that free-radical homopolymerization of this CT complex would lead to the observed strictly alternating copolymers. But how this explained the cationic homopolymers or the CT complex initiated polymerizations, was not made clear.

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“…Owing to the measuring arrangement, reduction potentials < -2.2 V could not be determined. Hall et al [19] have investigated the reduction of the reactive dienophiles cyclovoltammetrically. With exception of TCNE and of the dimethyl esters of the 1,2-dicyanofumaric and 1,2-dicyanomaleic acids, the reductions were irreversible.…”

Section: A/6bmentioning

confidence: 99%

[4 + 2]‐Cycloadditions with 1,4‐Bis(N,N‐dimethylamino)‐1,3‐dienes: Stereochemical Studies and Observation of Radical Ions

Sustmann¹,

Lücking²,

Kopp³

et al. 1989

Angew. Chem. Int. Ed. Engl.

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For a long time, and particularly following the presentation of the Woodward-Hoffmann rules, it was assumed that there is one universally valid mechanism for [4 + 21-cycloadditions. Recent investigations, however, indicate that the mechanism is dependent on the pattern of substitution of the diene and the dienophile.[" Thus, some cycloadditions proceed via diradicals,". ' 1 while others are reported to proceed via polar intermediate~. [~] Even an electron transfer with formation of radical ions has been proposed as primary step.I4' The observation of charge-transfer (CT) complexes and the analysis of their significance in Diels-Alder reactions have stimulated further discussion on the degree of charge transfer during these cycl~additions.~~ Herein we report on cycloadditions of the stereoisomeric dienes 1 and 2 and of the bicyclic diene 3 with dienophiles of different acceptor strength. A combination of stereochemical studies with electrochemical measurements and ESR investigations should provide information on the significance of electron transfer in the reactions. For 1, this result can be explained in terms of a thermal isomerization of 1 to 2 prior to the cycloaddition and a rapid reaction of 2, whereas for 2, product formation can be rationalized in terms of concerted cycloaddition. This explanation is consistent with the observation that Z-I-substituted dienes react considerably slower than the Eisomer.['ol It has been shown independently that 1 isomerizes quantitatively to 2 within 5d at 35 "C. If the cycloaddition of 1 and fumaric dinitrile is carried out at 50 "C using the 16-fold higher concentration described in the l i t e r a t~r e ,~~] the isomerization is suppressed and up to 96% of 5 is formed. [''] In each case it was demonstrated by mixing that 1.5 YO of the other isomer could have been detected by 'H-NMR spectroscopy. The stereoselectivity of the reactions is accordingly 2 98.5 %.Maleic dinitrile reacts with 2 in benzene (c = 0.2 M for both components, T = 35 "C) within 23 d to give a mixture of 6 a and 6 b (96%, ratio 86:14, determined by 'H-NMR spectroscopy). A CT complex is formed initially and absorbs at i,,,, = 486 nm. The products could not be separated without decomposition and were characterized spectroscopical-IY.['~] In the reaction of maleic dinitrile with I the same product was formed as in the reaction with 2. Isomerization of 1 could not be suppressed upon reaction with the less reactive maleic dinitrile. 6a/6bThe reactions of the respective 1,2-dicyano-substituted dimethyl esters of fumaric acid and maleic acid with 1 and 2 were carried out (0.2 M solution of the components in methylene chloride) at -50 "C, since a higher temperature led to unidentifiable products. The reaction was complete within 5 min-the minimum time required for the recording of a 'H-NMR spectrum after mixing the compounds-and a single adduct was always isolated (97 %) with all four combinations of the reaction partners. At -95°C formation of a bluish-green CT complex (A,,, = 540 nm) is briefly observed. ...

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Zwitterionic tetramethylenes as the common intermediates in the cycloaddition and polymerization reactions of N-vinylcarbazole with electrophilic tetrasubstituted ethylenes: a new explanation for charge-transfer initiation

Cited by 63 publications

References 0 publications

A Methyl Tricyanoethylenecarboxylate‐Based Room‐Temperature Magnet

A Methyl Tricyanoethylenecarboxylate‐Based Room‐Temperature Magnet

The Relationship of Cycloaddition Reactions to Spontaneous Vinyl Polymerizations

[4 + 2]‐Cycloadditions with 1,4‐Bis(N,N‐dimethylamino)‐1,3‐dienes: Stereochemical Studies and Observation of Radical Ions

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