Non-least-motion potential surfaces. Dimerization of methylenes and nitroso compounds
01 Mar 1970-Journal of the American Chemical Society (American Chemical Society)-Vol. 92, Iss: 6, pp 1460-1466
About: This article is published in Journal of the American Chemical Society.The article was published on 1970-03-01. It has received 107 citations till now. The article focuses on the topics: Nitroso Compounds.
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TL;DR: The chiral stationary phase for Aminoaryland Phosphinoaryland Aminoalkylcarbenes showed good chiral recognition ability for both the H2O/O2 and the H3O/H2O2 phases, and showed good recognition of Aminophosphonio and Aminosilyl Carbenes as well as Aminothioand Aminooxy carbenes.
Abstract: 2.2.1. Diaminoand Aminohydrazinocarbenes 3338 2.2.2. Aminothioand Aminooxycarbenes 3340 2.3. Phosphinoaryland Phosphinoalkylcarbenes 3341 2.4. Aminoaryland Aminoalkylcarbenes 3344 2.5. Aminophosphonio and Aminosilylcarbenes 3346 2.6. Aminophosphinocarbenes 3347 3. Reactivity 3348 3.1. Typical Carbene Behavior 3348 3.1.1. Coupling Reactions 3348 3.1.2. Cycloaddition Reactions 3352 3.1.3. Insertion Reactions 3355 3.1.4. Migration Reactions 3358 3.2. Basic/Nucleophilic Behavior 3359 3.2.1. Protonation of Carbenes 3359 3.2.2. Reactions with Group 14 Electrophiles 3360 3.2.3. Reactions with Group 13 Lewis Acids 3360 3.2.4. Reactions with Group 15 Electrophiles 3361 3.3. Electrophilic Behavior 3362 3.3.1. Reaction with 1,5-Diazabicyclo[4.3.0]non-5-ene (DBN) 3362
347 citations
TL;DR: This work shows how predictably ordered covalent or non-covalent structures can both be built using a single modular strategy, and forges a strong new link between polymer science and supramolecular chemistry.
Abstract: An emerging strategy for making ordered materials is modular construction, which connects preformed molecular subunits to neighbours through interactions of properly selected reactive sites. This strategy has yielded remarkable materials, including metal-organic frameworks joined by coordinative bonds, supramolecular networks linked by strong non-covalent interactions, and covalent organic frameworks in which atoms of carbon and other light elements are bonded covalently. However, the strategy has not yet produced covalently bonded organic materials in the form of large single crystals. Here we show that such materials can result from reversible self-addition polymerizations of suitably designed monomers. In particular, monomers with four tetrahedrally oriented nitroso groups polymerize to form diamondoid azodioxy networks that can be fully characterized by single-crystal X-ray diffraction. This work forges a strong new link between polymer science and supramolecular chemistry by showing how predictably ordered covalent or non-covalent structures can both be built using a single modular strategy.
305 citations
TL;DR: The possibility of alkali-metal-promoted dimerization is raised, and circumstantial evidence for this is presented.
Abstract: No example of a simple uncatalyzed dimerization of a diaminocarbene has been clearly established, so it is timely to ask what factors control the thermodynamics of this reaction, and what mechanisms are responsible for the observed dimerizations? In agreement with qualitative experimental observations, the dimerizations of simple five- and six-membered-ring diaminocarbenes are calculated to be 100 kJ mol(-1) less favorable than those of acyclic counterparts. This large difference is semiquantitatively accounted for by bond and torsional angle changes around the carbene centers. Carbenes such as (Et(2)N)(2)C are kinetically stable in THF at 25 degrees C in agreement with calculated energy barriers, but they rapidly dimerize in the presence of the corresponding formamidinium ion. This proton-catalyzed process is probably the most common mechanism for dimer formation, and involves formation of C-protonated dimers, which can be observed in suitable cases. The possibility of alkali-metal-promoted dimerization is raised, and circumstantial evidence for this is presented.
258 citations
TL;DR: In this paper, the synthesis, characterization and X-ray crystallographic structure determination are described for a stable thiazol-2-ylidene 2 and its corresponding dimer.
Abstract: The synthesis, characterization and X-ray crystallographic structure determination are described for a stable thiazol-2-ylidene 2. This thiazol-2-ylidene is the first example of a stable, crystalline carbene in which the singlet carbene center bears a sulfur substituent. The carbene 2 is the closest stable analog of the important thiamin (vitamin B1) carbene. Although the thiazol-2-ylidene 2 is sufficiently stable to isolate at room temperature in the absence of moisture and oxygen, it will dimerize to form a normal carbene–carbene dimer {2}2. With the isolation and structure determination of both 2 and {22}, this system is the first in which a stable carbene and its corresponding dimer have been isolated and characterized. Additionally reported is the “reduced” 2H-thiazoline 2 · H2 in which the former carbene center in 2 has been reduced to a methylene (CH2) group. Thiazol-2-ylidenes with smaller groups on nitrogen (e.g. mesityl or methyl) are too unstable to allow easy isolation. The dimer from 3,4,5-trimethylthiazol-2-ylidene possesses a very unusual geometry in which one of the former carbene centers is planar while the second is pyramidal.
190 citations
TL;DR: In this article, the authors discuss the properties and preparation methods of furoxan and benzofuroxans and compare them with trifurazan and furazan.
Abstract: Publisher Summary This chapter discusses the properties and preparation methods of furoxans and benzofuroxans. The history of its structure is briefly outlined. Many furoxan structures are determined by crystallographic methods, and as a result the dimensions of the heterocyclic ring are known in a wide variety of fused and substituted examples. Dynamic resonance effects (DNMR)—signal-broadening and coalescence phenomena at medium and fast exchange rates—are characteristic of furoxans fused to aromatic rings. The spectrum of benzotrifuroxan is analyzed and compared with that of the trifurazan. The methods of benzofuroxans preparation are: (1) dimerization of nitrile oxides, (2) dehydrogenataion of dioximes, (3) preparations from olefins and nitrogen oxides, (4) miscellaneous furoxan synthesis, and (5) benzofuroxans and other aromatic-ring-fused systems. The simple deoxygenation of furoxans to furazans is provided. Furoxans can be reduced in a variety of ways, depending upon the conditions used. It includes: (1) catalytic hydrogenation, (2) reduction with complex hydrides, (3) reduction with phosphorus compounds, (4) reduction with dissolving metals and metal ions, (5) electrochemical and other reducing methods. The chapter considers the principal substituent groups on the furoxan ring and the reactions they undergo.
149 citations