Blocking the C2 position of an imidazole-derived classical N-heterocyclic carbene (NHC) with an aryl group is an essential strategy to establish a route to mesoionic carbenes (MICs), which coordinate to the metal via the C4 (or C5) carbon atom. An efficient catalytic route to MIC precursors by direct arylation of an NHC is reported. Treatment of 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) with an aryl iodide (RC6H4I) in the presence of 0.5 mol % of [Pd2(dba)3] (dba = dibenzylideneacetone) precatalyst affords the C2-arylated imidazolium salts {IPr(C6H4R)}I (R = H, 4-Me, 2-Me, 4-OMe, 4-COOMe) in excellent (up to 92%) yields. Treatment of {IPr(C6H5)}I with CuI and KN(SiMe3)2 exclusively affords the MIC-copper complex [(IPrPh)CuI].
N-heterocyclic olefins (NHOs), IPrCH2 (1) and SIPrCH2 (2) (IPrCH2 = {N(2,6-iPr2C6H3)CH}2CCH2 and SIPrCH2 = {N(2,6-iPr2C6H3)CH2}2CCH2), react with HSiCl3 and afford IPrCH(SiHCl2) (3) and SIPrCH(SiHCl2) (4), respectively. Compounds 3 and 4 have been isolated in almost quantitative yield. Interestingly, treatment of the silylene IPr·SiCl2 with 1 also affords 3, where silylene insertion into a C–H bond is observed. Computational analysis shows a high energy barrier for silylene insertion, therefore a protonation–deprotonation mechanism is more likely.
A highly efficient palladium-catalyzed fourfold tandem-domino reaction consisting of two carbopalladation and two C-H-activation steps was developed for the synthesis of two types of tetrasubstituted alkenes 3 and 6 with intrinsic helical chirality starting from substrates 1 and 4, respectively. A sixfold tandem-domino reaction was also developed by including a Sonogashira reaction. 20 compounds with different substitution patterns were prepared with yields of up to 97 %. Structure elucidation by X-ray crystallography confirmed helical chirality of the two alkene moieties. Photophysical investigations of some of the compounds showed pronounced switching properties through light-controlled changes of their stereochemical configuration.
The
promising properties of surface-active ionic liquids (SAILs)
make these salts interesting candidates for the optimization of surfactant-enhanced
oil recovery (EOR) methods. The tests that should be performed at
the laboratory scale before a SAIL is proposed for EOR were carried
out with tributyl(tetradecyl)phosphonium chloride ([P4 4 4 14]Cl). The phase diagrams with water and n-dodecane
showed that the affinity of the surfactant for water is greater than
that for oil, even in the presence of a high salt content. The advantage
of the use of Winsor type I microemulsions in EOR is the low phase
trapping/adsorption. A formulation consisting of 4000 ppm [P4 4 4 14]Cl, 4 wt % NaCl, and 5000 ppm NaOH was able to reduce the interfacial
tension between water and Saharan crude oil from 19.2 to 0.1 mN·m–1. Core-flooding experiments were carried out at room
temperature and an injection rate of 2 mL/min, mimicking enhanced
oil recovery with brine solutions of SAIL, NaOH, and the optimized
formulation combining the two chemicals. The injection of the proposed
formulation, after flooding with brine, led to an additional recovery
of about 8% of the original oil in place.
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