Thermal Properties

Regitz, Manfred

doi:10.1016/b978-0-12-585840-3.50006-4

Cited by 104 publications

(152 citation statements)

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“…Die thermische oder photochemische Abspaltung von molekularem Stickstoff aus Diazoverbindungen vermittelt einen Einstieg in die CarbenChemie, [1] und die Übergangsmetall-katalysierte Zersetzung führt in der Regel über kurzlebige Metall-Carben-Komplexe zu einer breiten Palette carbenoider Reaktionen mit oft beachtlicher Chemo-, Regio-und Stereoselektivität (z. B. Cyclopropanierung von Olefinen; C,H-, O,H-und N,H-Insertion; Bildung von Yliden und formalen Carbendimeren).…”

Section: Introductionunclassified

Neues zur Synthese von Diazoverbindungen

Maas

2009

Angewandte Chemie

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Aufgrund der vielseitigen und nützlichen Folgechemie von Diazoverbindungen (R1R2CN2) ist das Interesse an dieser Substanzklasse seit Jahren ungebrochen. Dabei wird auch das bereits vorhandene Methodenrepertoire zur Herstellung von Diazoverbindungen immer wieder um neue Verfahren oder um neuartige Varianten etablierter Synthesewege ergänzt. Nicht selten tragen die neuen Synthesevorschläge der Labilität und beachtlichen chemischen Reaktivität bestimmter Typen von Diazoverbindungen Rechnung, aber auch dem Aspekt umweltfreundlicherer Methodik wurde Beachtung geschenkt.

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Section: Introductionunclassified

Neues zur Synthese von Diazoverbindungen

Maas

2009

Angewandte Chemie

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“…They are, for example, formed in appreciable amounts by the carbon protonation of diazo compounds only in super acids at low temperatures. 13 Carbon protonation of 2-(diazoacetyl)benzoic acid is therefore an endoergic process, and the rate acceleration effected in going from the high acidity to the low acidity regions of the rate profile of Figure 2 should strengthen the isotope effect if the acceleration is caused by electrostatic transition state stabilization. Since the isotope effect becomes weaker rather than stronger, this explanation cannot be correct and must consequently be discarded.…”

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Kinetics and mechanism of the base–catalyzed cleavage of 2-diazo-1,3-indanedione and the acid–catalyzed decomposition of its hydrolysis product, 2-(diazoacetyl)benzoic acid

Chiang¹,

Kresge²,

Zhu³

2001

Arkivoc

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A mechanism is proposed involving hydroxide ion addition to one of the substrate carbonyl groups, and hydroxide-ion induced ionization of the O-H bond of this adduct in the more concentrated solutions, followed by C-C bond cleavage.Rates of acid-catalyzed transformation of the product of this cleavage, 2-(diazoacetyl)benzoic acid, to 1,4-isochromandione were measured in aqueous (H2O and D2O) perchloric acid solutions over the concentration range [LClO4] = 0.0001-0.1 M and in formic acid and acetic acid buffers. The isotope effects that these data provide suggest that the reaction occurs by rate-determining proton transfer from hydronium ion to the substrate diazo carbon in the more acidic region of the range examined, but that in the less acidic region the reaction mechanism switches to intramolecular general acid catalysis by the substrate's carboxylic acid group.

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“…20 It is well-known that these metals are good catalysts for decomposing diazo groups. 18,21 Thus, one might expect that decomposition of the diazo functional groups may occur. However, the crosscoupling reaction proceeded with the diazo group intact, and the student was able to isolate the desired ethynylated diphenyldiazomethane (2) in a fairly good yield.…”

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“…The synthetic pathway to prepare sterically congested diphenyldiazomethane is summarized in Scheme 3. 18,19 Many steps are required to reach to the desired diazo compound, which suggests that it is impossible to prepare sterically congested poly-(diazomethane)s by extending the method.…”

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From Persistent Triplet Carbenes to Persistent High-Spin Polycarbenes

Itoh¹,

Hirai²,

Tomioka³

2007

Bulletin of the Chemical Society of Japan

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Triplet carbenes are regarded as one of the most effective spin sources for organic ferromagnetic materials since the magnitude of the exchange coupling between the neighboring centers is large. However, those systems have two disadvantages that prevent their use as practical magnetic materials. First, a triplet carbene unit is highly unstable and lacks the stability for practical applications under ambient conditions. Second, diazo groups, which are precursors for triplet carbenes, are generally labile and, hence, cannot be used as building blocks to prepare a more complicated poly(diazo) compound. After great efforts to stabilize the triplet carbenes, we have succeeded in preparing fairly stable triplet carbenes that survive for days. We found that a diazo precursor for a persistent triplet carbene was also persistent and, hence, can be further modified into a more complicated diazo compound that can generate persistent high-spin polycarbenes. In this account, we would like to summarize our efforts along this line. We employed the following three approaches to prepare poly(diazo) compounds; (1) synthesis of dendritic molecules having peripheral diazo groups starting from diazo compounds, (2) preparation of a poly(phenylacetylene) with a diazo unit using Rh-complex-catalyzed polymerization of diazo compounds with p-ethynyl substituents, and (3) preparation of a polymer chain as a result of complexation of the pyridine ligand on diazo compounds with coordinatively unsaturated metal ions. We also characterized the magnetic properties of photoproducts obtained by photolysis of those poly(diazo) compounds. Although spin-states observed for those photoproducts were not so high, the results suggest that our approach using persistent triplet carbenes will eventually lead us to a persistent high-spin polycarbenes by taking advantage of the stability of our diazo compounds.An increasing amount of interest is being paid to molecular magnetism, in which spins of unpaired electrons in -orbitals of light atoms such as carbon, nitrogen, and oxygen are mainly responsible for the magnetic properties. Many attempts have been made to prepare organic ferromagnetic materials. 1,2There are two major structural determinants for constructing high-spin organic molecules. The first one is based on a valence bond model, which assumes that electrons are perfectly correlated. Thus, the ground state of any molecule is determined by which set of possible distribution of -and -electron spins allows the formation of the maximum number of bonds. 4 This can be simply expressed by Eq. 1, known as Ovchinnikov equation, 3 where the atoms can be divided into two sets, traditionally called starred and unstarred and n Ã and n are the numbers of the starred and unstarred atoms. If the numbers of starred and unstarred atoms are equal, the number of -and -spin electrons will also be the same, and the ground state will be a singlet. However, if there are more starred atoms than unstarred atoms, the number of -spin electrons will exceed the number of -spi...

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Thermal Properties

Cited by 104 publications

References 59 publications

Neues zur Synthese von Diazoverbindungen

Neues zur Synthese von Diazoverbindungen

Kinetics and mechanism of the base–catalyzed cleavage of 2-diazo-1,3-indanedione and the acid–catalyzed decomposition of its hydrolysis product, 2-(diazoacetyl)benzoic acid

From Persistent Triplet Carbenes to Persistent High-Spin Polycarbenes

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