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The lithium salt of p-phenylisobutyrophenone (LiPhIBP) exists in tetrahydrofuran (THF) as a mixture of monomer and tetramer contact ion pairs (CIP). The equilibrium constant, K 1,4 ) 5.0 × 10 8 M -3 , indicates that the lithium enolate is primarily tetrameric at higher concentrations, but the monomer is still present in significant amounts even at concentrations typical of synthesis reactions. Alkylation reactions of LiPhIBP with various alkylating agents were investigated in THF at 25°C at concentrations of 10 -3 to 10 -2 M by using UV-vis spectroscopy. The kinetics followed rate laws of 0.50 to 0.30 order in the formal lithium enolate concentration but is first order in the monomer concentration. These rate studies provide direct evidence that the reactive species is the monomer, even when tetramer dominates the equilibrium.Reactions involving lithium enolates represent a large class of modern organic synthesis reactions and are important methods for C-C bond formation. 2-8 It is now well-known that these species, as well as other organolithium compounds (alkyl-and aryllithiums, lithium amides, etc.), exist generally as aggregates in ethereal solution and in the solid state. 9-19 What has not been clear is the actual role of such enolate aggregates in reactions with electrophiles. A better understanding of this subject is important in view of the possible influence of enolate aggregation and mixed aggregates on reactivity and regio-and stereoselectivity. [20][21][22][23][24][25] Jackman et al. have studied the lithium salt of isobutyrophenone by NMR and reported that it exists in tetrahydrofuran (THF) solution exclusively as a tetramer. 10,26,27 They concluded that these aggregates are directly involved in the alkylation reaction on the basis of the analysis of the product distribution (C-and O-alkylation) 28 and later hypothesized that dimers could also be involved. 29 This and other indirect evidence, especially the observation that lithium enolates crystallize generally as dimers, tetramers, or hexamers, led Amstutz et al. to propose that a tetrameric cubic structure is a reaction intermediate. 30,31 Although these mechanisms have not been confirmed, they are widely accepted and have been used as working hypotheses in the analysis of the reactivity and selectivity of lithium enolates. 4,16,17,[32][33][34] We recently showed for the lithium enolate of p-phenylsulfonylisobutyrophenone that the dimer and a mixed aggregate with LiBr are much less reactive in an alkylation reaction than the monomer in THF. 35,36 In the accompanying paper we showed that the cesium enolate of 1-(4-biphenylyl)-2-methyl-(1) Carbon Acidity. 102.(2) Evans, D. A.; Nelson, J. V.; Taber, T. R.

The hole transporting layer (HTL) plays an important role in realizing efficient and stable perovskite solar cells (PSCs). In spite of intensive research efforts toward the development of HTL materials, low‐cost, dopant‐free hole transporting materials that lead to efficient and stable PSCs remain elusive. Herein, a simple polycyclic heteroaromatic hydrocarbon‐based small molecule, 2,5,9,12‐tetra(tert‐butyl)diacenaphtho[1,2‐b:1′,2′‐d]thiophenen, as an efficient HTL material in PSCs is presented. This molecule is easy to synthesize and inexpensive. It is hydrophobic and exhibits excellent film‐forming properties on perovskites. It has unusually high hole mobility and a desirable highest occupied molecular orbital energy level, making it an ideal HTL material. PSCs fabricated using both the n‐i‐p planar and mesoscopic architectures with this compound as the HTL show efficiencies as high as 15.59% and 18.17%, respectively, with minimal hysteresis and high long term stability under ambient conditions.

Reinvestigation of the cesium enolate (CsPhIBP) of 1-biphenylyl-2-methylpropanone (p-phenylisobutyrophenone, PhIBP) in tetrahydrofuran (THF) solution at 25.0 °C shows that its UV−visible spectrum changes with concentration with λmax moving to longer wavelengths in more dilute solution. Analysis of the spectral data over a wide concentration range by singular value determination (SVD) combined with the pK measurements indicates a mixture of monomer (M), dimer (D), and tetramer (T) with equilibrium constants of K 1,2 = D/M2 = 2.89 × 104 M-1 and K 1,4 = T/M4 = 7.78 × 1012 M-3. The pK of the monomer is 25.08. The data are also compared with the corresponding data obtained for the lithium ion pair system reported in the following paper. We find that the cesium ion pair is more highly aggregated and much more basic than the lithium ion pair. The average aggregation number of CsPhIBP at 10-3 M is 3.2, substantially greater than the value of 2.2 reported previously; the revision arises from our taking into account the concentration-dependent extinction coefficient and absorption band shape of CsPhIBP. The revised value also requires that a correction be applied to our previously reported kinetics of the reaction of CsPhIBP with methyl tosylate (MeOTs); the data indicate that the CsPhIBP ion pair monomer reacts, instead of the free enolate ion that we reported previously. Similarly, alkylation by p-tert-butylbenzyl chloride (BnCl) occurs dominantly via the monomer. More limited studies at −20 °C indicate greater aggregation at the lower temperature. Alkylation reactions with MeOTs and BnCl again occur predominantly with the monomer. The reaction products at room temperature are those of C-alkylation with BnCl and equal amounts of C- and O-alkylation with MeOTs.