Double N-H bond activation of N,N'-bis-substituted hydrazines with stable N-heterocyclic silylene

The reaction of N-heterocyclic silylene (NHSi) L [L = CH{(C[double bond, length as m-dash]CH(2))(CMe)(2,6-iPr(2)C(6)H(3)N)(2)}Si] with benzoylhydrazine, 1,2-dicarbethoxyhydrazine, 1,2-diacetylhydrazine and 1,2-bis(tert-butoxycarbonyl)hydrazine in 1 : 1 molar ratio resulted in compounds 1-4 with an almost quantitative yield and five coordinate silicon atoms. Compounds 1-4 were formed by double N-H bond activation by deliberate selection of N,N'-bis-substituted hydrazine compounds bearing the -C(O)NHNH- unit. Compounds 1-4 were characterized by NMR spectroscopy, EI-MS and elemental analysis. The molecular structures of compounds 1-3 were unambiguously established by single crystal X-ray structural analysis.     

Aza-Baylis-Hillman reactions of diisopropyl azodicarboxylate or diethyl azodicarboxylate with acrylates and acrylonitrile

It has been found that in the Baylis-Hillman reactions of DIAD or DEAD with acrylates or acrylonitrile, the Lewis base and solvent can significantly affect the reaction rate. Using DABCO as Lewis base in DMF or THF, the corresponding aza-Baylis-Hillman adducts 2 or 3 can be obtained in moderate to good yields.     

Oxidation of alcohols to carbonyl compounds with diisopropyl azodicarboxylate catalyzed by nitroxyl radicals

A nitroxyl-radical-catalyzed oxidation of alcohols using diisopropyl azodicarboxylate (DIAD) as the terminal oxidant is reported. A variety of primary and secondary alcohols including aliphatic, benzylic, and allylic alcohols are efficiently oxidized to their corresponding aldehydes and ketones without overoxidation to carboxylic acid. 1,2-Diols are oxidized to hydroxyl ketones or diketones depending on the amount of DIAD used.     

Radical reactions of a stable N-heterocyclic silylene: EPR study and DFT calculation

Reaction of the stable silylene, 1,3-di-tert-butyl-1,3,2-diazasilol-2-ylidene, with the free radical sources TEMPO, Hg[P(O)(OPri)2]2, (CO)3CpM-MCp(CO)3 (M = W, Mo), (CO)5Re-Re(CO)5, and toluene leads to radical adducts. The EPR spectra of these radicals indicate that the unpaired electron is delocalized over the silicon-containing five-membered ring.     

Versatile conversion of N-heterocyclic silylene to silyl metal compounds by insertion of divalent silicon into metal-carbon and metal-hydrogen bonds

The facile one-pot reaction of the stable N-heterocyclic silylene LSi: 1 (L=(ArN)C(=CH(2))CH=C(Me)(NAr), Ar=2,6-iPr(2)C(6)H(3)) with Me(2)Zn, Me(3)Al, H(3)Al-NMe(3), and MeLi has been investigated. The silicon(II) atom in 1 is capable of insertion into the corresponding M-C and Al-H bonds under very mild reaction conditions. Thus, Me(2)Zn furnishes the bis(silyl) zinc complex LSi(Me)ZnSi(Me)L 2 as the sole product, irrespective of the molar ratio of the starting materials applied. Moreover, the reactions of 1 with Me(3)Al, H(3)Al-NMe(3), and MeLi lead directly to the 1,1-addition products LSi(Me)(Al(thf)Me(2)) 3, LSi(H)(AlH(2)(NMe(3))) 4, and LSi(Me)Li(thf)(3) 5, respectively. All new compounds 2-5 were fully characterized by multinuclear NMR spectroscopy, mass spectrometry, elemental analyses, and single-crystal X-ray diffraction analyses.     

Formation of a donor-stabilized tetrasilacyclobutadiene dication by a Lewis acid assisted reaction of an N-heterocyclic chloro silylene

The first donor-stabilized tetrasilacyclobutadiene dication species has been synthesized and fully characterized. Its unexpected formation occurs by the Lewis acid assisted reaction of the N-heterocyclic chloro silylene [L(Si:)Cl] (L = PhC(NtBu)(2); amidinate) with Cp*ZrCl(3) (Cp* = pentamethylcyclopentadienyl) in the molar ratio of 3:2. Remarkably, the four-membered Si(4) core consists of two N-donor stabilized silylium subunits and two silylene-like moieties. The dicationic charge is somewhat delocalized on the Si(4) core, which is supported by DFT calculations.     

N-heterocyclic carbene catalyzed reaction of enals and 1,2-dicarbonyl compounds: stereoselective synthesis of spiro gamma-butyrolactones

[reaction: see text]. Nucleophilic heterocyclic carbene (NHC) catalyzed annulation of enals and cyclic 1,2-dicarbonyl compounds, opening a route to gamma-spirolactones, has been observed for the first time. The strategy works well with isatins, leading to spiroannulated oxindole derivatives. It is conceivable that the spiroannulation protocol reported herein will be applicable to the synthesis of important natural products that are endowed with a spiro gamma-butyrolactone motif, especially oxindoles and norsesquiterpenoids.     

Formation of stable cyclic dicoordinated phosphorus compounds by reaction of cyclophosphazanes with lewis acids

Thermal equilibrium between dicoordinated and tricoordinated phosphorus compounds (i.e. benzodiazaphosphole ?cyclotetraphosphazane) has been observed. The dicoordinated compounds have been stabilized by complexing with Lewis acid and isolated.     

First allylboration of organic compounds with the NN double bond. Synthesis of N-allylpyrazolidines and allyl-1,2-diphenylhydrazine

Triallylborane adds to the NN double bond of pyrazolines 1 and 2 at 0 °C giving after deboronation the corresponding N-allylpyrazolidines 4 and 5. Further transformations of allylpyrazolidine 4 including the cyclopropane ring opening were studied. Allylboration of azobenzene with triallylborane gives rise to 1-allyl-1,2-diphenylhydrazine.     

Halophilic reactions of a stable silylene with chloro and bromocarbons

A number of disilanes have been synthesized from a stable silylene, 1 (N,N'-di-tert-butyl-1,3-diaza-2-silacyclopent-4-en-2-ylidene), and a variety of halocarbons. It is proposed that disilane formation is a result of an initial halophilic interaction between the silylene and halocarbon. Formation of disilanes from 1 and CCl4, 2a, CHCl3, 2b, CH2Cl2, 2c, benzyl chloride, 2d, and bromobenzene, 5, are described here. An X-ray crystal structure of 2b was determined.     

N-heterocyclic carbene catalyzed cyanation reaction of carbonyl compounds with ethyl cyanoformate and acetyl cyanide

N-heterocyclic carbene (NHC) has been employed as an efficient catalyst for cyanation reaction of carbonyl compounds. Under catalysis of 1 mol % NHCs, various aldehydes and 2,2,2-trifluoroacetophenone coupled with ethyl cyanoformate in THF to provide cyanohydrins ethyl carbonates in excellent yields. While in the presence of 10 mol % catalyst, different types of aldehydes and 2,2,2-trifluoroacetophenone reacted with acetyl cyanide in dichloroethane to give acylated cyanohydrins in moderate to high yields.     

The diels-alder reaction of α-ethenylidene cyclanones: a stereoselective approach to spirocyclic compounds.

The BF₃:Et₂O catalysed Diele-Alder reaction of α-ethenylidene cyclanones constitutes a highly stereoselective route to spirocyclic dienones.     

Formation and thermal decomposition of silicon oxynitride compounds II

In studies on the reactions of silicon oxynitride, Si₂N₂O, with lithium oxide and of lithium metasilicate with lithium nitride, the formation of a previously unknown compound with stoichiometry Li₅SiNO₃ has been observed.

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Zusammenfassung Eine bisher unbekannte Verbindung der Zusammensetzung Li₅SiNO₃ wurde bei Reaktionen von Siliciumoxynitrid (Si₂N₂O) mit Lithiumoxid und von Lithiummetasilikat mit Lithiumnitrid erhalten.

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(Si₂N₂O) , Li₅SiNO₃.

     

Formation and thermal decomposition of silicon oxynitride compounds I

The existence of formerly unknown compounds of the type M ₃ ¹ SiNO₂, suggested in previous papers, has been confirmed in reactions of lithium and sodium oxides with silicon oxynitride, Si₂N₂O.     

Formation of disilanes in the reaction of stable silylenes with halocarbons

Reactions of stable silylenes 1 and 2 with a variety of halogenated organic compounds have been studied. Depending on the nature of the halocarbon, the products can be disilanes, LSiX-LSiR, or monosilanes, LSiXR, or a mixture of both types of products. Hexachloroethane reacts with the silylenes to give mainly the dichlorodisilane, LSiX-LSiX. The experimental results are rationalized in terms of several related free-radical chain mechanisms.     

The thermally stable silylene Si[(NCH2Bu)2C6H4-1,2]: reaction with pyridine and quinoline

Two equivalents of the thermally stable silylene Si[(NCH₂Bu^t)₂C₆H₄-1,2] (1) react with pyridine to yield the 1-aza-2,3-disilacyclobutane derivative (2), which is labile and slowly rearranges via a 1,3-H shift to the 2-pyridyldisilane (3). A similar reaction of 1 with quinoline gives 1-aza-2,3-disilacyclobutane derivative (4), which is stable. The X-ray structures of 2 and 3 are discussed.     

Theoretical insights into the reaction between vinylidenesilanediyl and double bond compounds (formaldehyde and methyleneimine): the formation of heterocyclic silylene and spiro-Si-heterocyclic compounds

Abstract

The reaction mechanism between vinylidenesilanediyl and doubly bonded compounds (formaldehyde and methyleneimine) has been systematically investigated employing the second-order Møller-Plesset perturbation theory (MP2) method in order to better understand the reactivity of vinylidenesilanediyl. Geometry optimizations and vibrational analyses have been performed for the stationary points on the potential energy surfaces of the system. Calculations show that the four-membered heterocyclic silylene intermediate and Si-heterocyclic conjugated diene compound could be produced through addition and rearrangement processes between vinylidenesilanediyl and double bond compound. The silylene intermediate can react with second formaldehyde (or methyleneimine) to form a spiro-Si-heterocyclic product. The present study is helpful to understand further characterization of the C₂H₂Si molecular system and to offer an alternative approach to the formation of heterocyclic silylene and spiro-Si-heterocyclic compounds.