Search results for "ALK"

The oligomerisation of phenylacetylenes with rhodium(I) and P ligands as the catalytic system

1991

Abstract The dependence of the oligomerisation of phenylacetylene to cyclotrimers and dimers upon a Rh(I) complex with different P ligands as the catalytic system has been studied. The influence of substituents in the phenyl ring of the substrate has been examined as well. A selective cyclotrimerisation of phenylacetylenes is achieved with [1,5-C6H10RhCl]2 as the catalyst. A decrease of the selectivity appears with very bulky o-substituents or a substitution in the 2,6-position of phenylacetylene. [P]-control maps indicate a mono-association of the ligand accompanied by a reduced activity of the system. The second association of a P ligand results in an inhibition of the cyclotrimerisation …

Cooperative Binding of Divalent Diamides by N-Alkyl Ammonium Resorcinarene Chlorides

2015

N-Alkyl ammonium resorcinarene chlorides, stabilized by an intricate array of hydrogen bonds leading to a cavitand-like structure, bind amides. The molecular recognition occurs through intermolecular hydrogen bonds between the carbonyl oxygen and the amide hydrogen of the guests and the cation-anion circular hydrogen-bonded seam of the hosts, as well as through CH⋅⋅⋅π interactions. The N-alkyl ammonium resorcinarene chlorides cooperatively bind a series of di-acetamides of varying spacer lengths ranging from three to seven carbons. Titration data fit either a 1:1 or 2:1 binding isotherm depending on the spacer lengths. Considering all the guests possess similar binding motifs, the first bin…

Aluminum complexes of sterically hindered tetradentate Schiff bases: Synthesis, structure, and reactivity toward ɛ-caprolactone

1997

Abstract The sterically hindered Schiff bases tbmSalenH2 [tbmSalen = N,N′-1,2-ethylenebis(3-tert-butyl-5-methylsalicylideneimine)] and tbmSalcenH2 [tbmSalcen = N,N′-trans-1,2-cyclohexanediyl-bis(3-tert-butyl-5-methylsalicylideneimine)] afforded a series of aluminum complexes of the general formulae [Al(tbmSalen)X] and [Al(tbmSalcen)X] (X = Cl, Me, Et). The molecular structure of [Al(tbmSalcen)Cl] was determined by single-crystal X-ray structural analysis which revealed a five-coordinate aluminum center with a distorted square pyramidal geometry. The alkyl complexes were found to oligomerize ɛ-caprolactone.

Phosphido- and Amidozirconocene Cation-Based Frustrated Lewis Pair Chemistry

2015

Methyl abstraction from neutral [Cp2ZrMe(ERR')] complexes 1 (E = N, P; R, R' = alkyl, aryl) with either B(C6F5)3 or [Ph3C][B(C6F5)4] results in the formation of [Cp2Zr(ERR')][X] complexes 2 (X(-) = MeB(C6F5)3(-), B(C6F5)4(-)). The X-ray structure of amido complexes [Cp2Zr(NPh2)][MeB(C6F5)3] (2d) and [Cp2Zr(N(t)BuAr)][B(C6F5)4] (2e', Ar = 3,5-C6H3(CH3)2) is reported, showing a sterically dependent Zr/N-π interaction. Complexes 2 catalyze the hydrogenation of electron-rich olefins and alkynes under mild conditions (room temperature, 1.5 bar H2). Complex 2e binds CO2, giving [Cp2Zr(CO2)(N(t)BuAr)]2[MeB(C6F5)3]2 (3e). Amido complex 2d reacts with benzaldehyde yielding [Cp2Zr(OCH2Ph)((OC)PhNPh2)…

Synthesis of nonracemic α-trifluoromethyl α-amino acids from sulfinimines of trifluoropyruvate

2001

We describe a novel and useful method for the synthesis of nonracemic α-trifluoromethyl α-amino acids (α-Tfm-AAs). Key building blocks are the sulfinimines (S)-1a and (S)-1b, prepared by Staudinger reaction from trifluoropyruvate esters and the chiral N-sulfinyl iminophosphorane (S)-8, which were treated with benzyl, allyl, and alkylmagnesium halides. The resulting diastereomeric N-sulfinyl α-Tfm α-amino esters, 12 and 13, were produced with moderate to good stereoselectivity and yields. When alkyl Grignard reagents were used, stereocontrol became progressively higher with increasing steric bulk, while reversed, though poor, stereocontrol was achieved with benzyl/allyl Grignard reagents. An…

Synthesis of N-methyl alkylaminomethane-1,1-diphosphonic acids and evaluation of their complex-formation abilities towards copper(II)

2015

Abstract A series of N -methyl alkylaminomethane-1,1-diphosphonic acids ( 3a – g ) with a common tertiary nitrogen atom (CH 3 –N–R) bearing linear or branched alkyl, cycloheptyl or phenylalkyl R substituents was synthesized in the reaction of diethylphosphonate with triethyl orthoformate and secondary amine followed by hydrolysis, and by the Eschweiler–Clarke methylation of the alkylaminomethane-1,1-diphosphonic acids with formic acid and formaldehyde. Complex-formation abilities of 3a – g towards copper(II) in solution were studied by means of pH-potentiometry, ESI-MS spectrometry, UV–Vis and EPR methods. Evaluation of stability constants for the Cu(II) complexes of 3a – g has revealed the…

A clickable NHC–Au(i)-complex for the preparation of stimulus-responsive metallopeptide amphiphiles

2018

We report the synthesis of an alkyne functionalised NHC-Au(i)-complex which is conjugated with amphiphilic oligopeptides using a copper(i) catalysed cycloaddition. The resulting Au(i)-metalloamphiphiles are shown to self-assemble into charge-regulated stimulus-responsive supramolecular polymers in water via a weakly cooperative polymerisation mechanism.

Erratum to “3D-Structure and function of strictosidine synthase – The key enzyme of monoterpenoid indole alkaloid biosynthesis” [Plant Physiol. Bioch…

2008

Highly enantioselective zinc/binol-catalyzed alkynylation of N-sulfonyl aldimines.

2008

Triarylamines connected via phenylenevinylene segments

2003

Abstract The influences of the conjugation length and of side chains with various electronic character on the electro-optical properties of oligo(phenylenevinylene)s end-capped with diphenylamino groups are investigated. Horner-Olefinations were used for the synthesis of chromophores with 3–7 rings in the conjugated system, additionally, Pd-catalysed amination of bromo-OPVs is a useful route to introduce the end groups. Compared with the “electronically neutral” alkyl side chains, electron donating ethers and, more pronounced, electron withdrawing sulfonyl side chains shift the absorption and emission spectra to longer wavelengths. The elongation of the π-system from 3 to 5 and 7 rings has …