The Resurgence of the Highly Ylidic N‐Heterocyclic Olefins as a New Class of Organocatalysts

In recent decades, N‐heterocyclic carbenes have become established as a prevalent family of organocatalysts. N‐Heterocyclic olefins, the alkylidene derivatives of N‐heterocyclic carbenes, have recently also emerged as efficient promoters for CO2 fixation and polymerization reactions. Their extraordinarily strong Lewis/Brønsted basicity suggests great potential as a new class of organocatalysts for a broad range of reactions in synthetic chemistry.One carbon better: N‐Heterocyclic olefins, the alkylidene derivatives of the prevalent N‐heterocyclic carbenes, have recently emerged as efficient promoters for CO2 fixation and polymerization reactions. Their extraordinarily strong Lewis/Brønsted basicity suggests great potential as a new class of organocatalysts for a broad range of reactions in synthetic chemistry.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137526/1/chem201503575_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137526/2/chem201503575.pd

Structure and reactivity studies of simple phospholes

Newer techniques of phosphole synthesis, particularly those which lead to simple phospholes substituted with active functional groups, are briefly surveyed. A detailed account of chemical, physico-chemical, spectroscopic and theoretical studies related to the phosphole aromaticity problem is given and the present conflicting position is discussed

Radical Reactivity of Frustrated Lewis Pairs with Diaryl Esters

Advances in the chemistry of metal-free systems known as frustrated Lewis pairs (FLPs) has exposed new reactivity of the p-block elements, particularly in small-molecule activation and catalysis. Typically, the mode of activation by FLPs has been predicated on a heterolytic two-electron process, although recently, select FLPs have been shown to participate in single-electron processes. Here, we report the reaction of diaryl substituted esters with FLPs. This results in divergent pathways, one whereby the diaryl moiety is stabilized by the Lewis basic phosphine, and the alternative pathway, wherein a single-electron transfer process occurs, generating the [Mes_{3}P]+⋅/[C(H)Ar_{2}]⋅ radical ion pair. The latter species undergoes a homocoupling reaction to yield tetraphenylethane derivatives. In the presence of olefins, this reactivity can be harnessed through an sp^{2}-sp^{3} C–C heterocoupling reaction to generate α,β-substituted olefins. Notably, this work showcases an FLP approach to metal-free radical C–H bond activation with subsequent C–C bond formation, which also displays complementary reactivity to other approaches

A study of the interactions between ylidic phosphorus species and s-blockmetals

This thesis details the synthesis and characterisation of alkaline earth metal complexes of phosphonium ylides and iminophosphoranes, together with some related phosphine oxide species. This thesis also contains the synthesis and structural characterisation of a number of novel phosphonium ylides and iminophosphoranes. Chapter 1 provides an introduction to the field of phosphonium ylides and related compounds, describing their preparation and subsequent reactivity. Chapter 2 contains an explanation of the experimental techniques and analytical tools used, whilst Chapter 3 details the syntheses and analyses for all of the complexes discussed in the thesis. Chapter 4 discusses novel alkaline earth metal phosphonium ylide complexes. The chapter contains the first structurally characterised neutral phosphonium ylide complexes of calcium, strontium and barium with the general formula (Ph(_3)PCH(_2))(_2) M[N(SiMe(_3))(_2)](_2), where M = Ca, Sr and Ba. The analogous iminophosphorane and phosphine oxide complexes are discussed in detail in chapter 5. Complexes of the general formula (Ph(_3)PNH)(_2) M[0C(_6)H2(Me)(^1)Bu(_2)](_2),(Ph(_3)P0)(_2) M[0C(_6)H(_2)(Me)’Bu(_2)](_2) and (Ph(_3)PO)(_2) M[N(SiMe(_3))(_2)](_2), are described where M =Ca, Sr and Ba. Chapter 6 details the synthesis of novel litbiated iminophosphoranes and related compounds as well as the synthesis of a novel dianion [Ph(_2)(PhCH')PN"] for use in synthetic organic chemistry. The final Chapter (7) details the synthesis and structural characterisation of a number of novel phosphonium ylides Ph(_2)R'PCHR" and iminophosphoranes Ph(_2)R’’’PNH and their corresponding salts e.g Ph(_2)R'PTH(_2)R"X and Ph(_2)R 'P+NH(_2)X

Synthetic approaches to new heterocycles containing two phosphorus atoms

Reactions involving nucleophilic attack of tertiary phosphines and related compounds upon acetylenic systems have been reviewed and the literature has been covered to the end of 1970. In an extension of some of the work outlined in the above review, the bisphosphines 1,2- bis (diphenylphosphino)ethane, bis(diphenylphosphino) methane, o'is 1,2-bis (diphenylphosphino)- ethylene and trans 1,2-bis(diphenylphosphino)- ethylene and the biphosphine derivative tetraphenyibiphosphine were treated with the powerful electrophile dimethyl acetylenedicarboxylate in attempts to synthesize new cyclic phosphonium ylides containing two phosphorus atoms. On reaction with the acetylenic ester, the first three of these bisphosphosphines produced in high yield, cyclic phosphonium ylides character ized as dimethyl 1,1,4,4-tetraphenyl-l,4- diphosphacyclohexa-1,3-diene-2,3-dicarboxylate, dimethyl 1,1,3,3-tetraphenyl-5^-l,3-diphosph(V)ole 4,5-dicarboxylate and dimethyl 1,1,4,4-tetraphenyl 1,4-diphosphorin-2,3-dicarboxylate respectively. The adducts were found to be extremely sensitive to water and they were characterized largely by extensive spectroscopic (mainly NMR) investigations although certain cheinical reactions assisted in the structure determinations« Dimethyl 1,1,4,4- tetraphenyl-1,4-diphosphorin-2,3-dicarboxylate showed some evidence of aromatic character. The fourth of the bisphosphines, trans 1,2- bis(diphenyiphosphino)ethylene, was found to react with dimethyl acetylenedicarboxylate to give a 1:1 adduct. NMR evidence suggests that this adduct has a zwitterionic rather than an ylidic structure while protonation experiments, hydrolyses and deuterolyses are consistent with an ylidic structure. The sum of the evidence suggested that the adduct in solution is an equilibrium of two or more isomers in which a zwitterionic form is the major component while an ylidic form is the most reactive component of the mixture. Hydrolysis of the adduct led to an unusual reaction in which one of the diphenyiphosphino groups was eliminated to give a product identical to the 1:1:1 adduct formed from diphenylvinyIphosphine, dimethyl acetylenedicarboxylate and water. A mechanism has been postulated for this reaction and deuterium labelling studies gave some support to this mechanism. Tetraphenylbiphosphine gave a derivative of the o'ls 1,2-bis (diphenylphosphino) ethylene system on reaction with the acetylenic ester

Twisted Push-Pull Alkenes Bearing Geminal Cyclicdiamino and Difluoroaryl Substituents

The systematic combination of N-heterocyclic olefins (NHOs) with fluoroarenes resulted in twisted push-pull alkenes. These alkenes carry electron-donating cyclicdiamino substituents and two electron-withdrawing fluoroaryl substituents in the geminal positions. The synthetic method can be extended to a variety of substituted push-pull alkenes by varying the NHO as well as the fluoroarenes. Solid-state molecular structures of these molecules reveal a notable elongation of the central C-C bond and a twisted geometry in the alkene motif. Absorption properties were investigated with UV-vis spectroscopy. The redox properties of the twisted push-pull alkenes were probed with electrochemistry as well as UV-vis/NIR and EPR spectroelectrochemistry, while the electronic structures were computationally evaluated and validated.Fil: Kundu, Abhinanda. International Centre Of Theoretical Science. Tata Institute Of Fundamental Research; EspañaFil: Chandra, Shubhadeep. Universitat Stuttgart; AlemaniaFil: Mandal, Debdeep. International Centre Of Theoretical Science. Tata Institute Of Fundamental Research; EspañaFil: Neuman, Nicolás Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Mahata, Alok. International Centre Of Theoretical Science. Tata Institute Of Fundamental Research; EspañaFil: Anga, Srinivas. International Centre Of Theoretical Science. Tata Institute Of Fundamental Research; EspañaFil: Rawat, Hemant. International Centre Of Theoretical Science. Tata Institute Of Fundamental Research; EspañaFil: Pal, Sudip. International Centre Of Theoretical Science. Tata Institute Of Fundamental Research; EspañaFil: Schulzke, Carola. ERNST MORITZ ARNDT UNIVERSITÄT GREIFSWALD (UG);Fil: Sarkar, Biprajit. Universität Stuttgart; AlemaniaFil: Chandrasekhar, Vadapalli. Indian Institute Of Technology Kanpur; IndiaFil: Jana, Anukul. Tata Institute Of Fundamental Research, Hyderabad; Indi

Developing Novel Synthetic Methodologies Using Hypervalent Iodine(III) Reagents and Diazonium- or Iodonium Ylides

Hypervalent iodine compounds have been established as useful reagents in synthetic chemistry due to their ease of handling and wide range of chemical reactivity under mild reaction conditions. Reported within are studies into the development of new methods for the gem-difunctionalization reactions using hypervalent iodine(III) compounds. Classic or modern hypervalent iodine reagents such as PhICl2, TolIF2, PhI(OAc)2, and 1-(tert-butylperoxy)-1,2-benziodoxol-3(1H)-one were reacted with either a diazonium ylide or an iodonium ylide to facilitate gem-dichlorination, gem-difluorination, halogenative semi-pinacol, or cyclopropanation reactions. Oftentimes, catalytic amounts of additives served to activate the iodane and provide increased yields, faster reaction times, and higher chemoselectivity

Self-consistent acidity scales of neutral and cationic brønsted acids in acetonitrile and tetrahydrofuran

http://www.ester.ee/record=b1755458*es