Topic
Steric effects
About: Steric effects is a research topic. Over the lifetime, 16112 publications have been published within this topic receiving 319615 citations. The topic is also known as: steric hindrance.
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TL;DR: Three series of P-chiral diphosphines based on ferrocene and biferrocenyl skeletons, including novel ligands 1f and 3c, were employed in palladium-catalyzed allylic substitution reactions, defining the regioselectivity of nucleophile addition.
Abstract: Three series of P-chiral diphosphines based on ferrocene (1a−f, 2a−c) and biferrocenyl skeletons (3a−c), including novel ligands 1f and 3c, were employed in palladium-catalyzed allylic substitution reactions. Steric effects imposed by the phosphine residues were studied using C2-symmetrical donors 1 (1 = 1,1‘-bis(arylphenylphosphino)ferrocene with aryl groups a = 1-naphthyl, b = 2-naphthyl, c = 2-anisyl, d = 2-biphenylyl, e = 9-phenanthryl, and f = ferrocenyl), whereas para-methoxy- and/or para-trifluoromethyl substitution of the phenyl moieties in 1a enabled investigation of ligand electronic effects applying ferrocenyl diphosphines 2a−c. Ligands 3 (3 = 2,2‘-bis(arylphenylphosphino)-1,1‘-biferrocenyls with aryl substituents a,c = 1-naphthyl (diastereomers) and b = 2-biphenylyl) allowed for comparison of backbone structure effects (bite angle variation) in catalysis. Linear and cyclic allylic acetates served as substrates in typical test reactions; upon attack of soft carbon and nitrogen nucleophiles on (...
68 citations
TL;DR: In this article, the application of silica-supported BF3 as a mild acid catalyst to the C- and O-alkylation of various aryl alcohols is described.
Abstract: The application of silica-supported BF3 as a mild solid acid catalyst to the C- and O-alkylation of various aryl alcohols is described. In the case of O-alkylation, the reactivity of the ether product in both heterogeneous and homogeneous systems is compared, and it is shown that the former can be used to affect selective C-alkylation of ethers, while in the latter system, ether rearrangement to ring poly-alkylated phenols also occurs. Ether rearrangement is thought to require coordination of the ether to an available Lewis acid site, which, in the case of the heterogeneous system, is apparently impossible. The difference between the homogeneous and the supported BF3 may be attributed to steric restrictions and/or relatively weak Lewis acidity of the supported system. Effects of steric hindrance at the reaction centre are examined. Possible routes to ethers and ring-alkylated products are also discussed.
68 citations
TL;DR: A comparison between the FIAs of known "free" phosphenium ions with those that are currently unknown and other highly electrophilic cations suggests that some diaryl- and dialkylphosphenIUM ions may yet be accessible under the right conditions.
Abstract: The fluoride ion affinities (FIAs) of 33 phosphenium ions with a range of substituents were calculated using ab inito and DFT methods. The use of these FIA data as a measure of the Lewis acidities of phosphenium ions is described and the FIAs of the species studied here are compared to FIA data for more commonly encountered Lewis acids. Phosphenium ions are often stronger Lewis acids than neutral species, but in many cases are less Lewis acidic than highly electrophilic cations such as [Me(3)C](+) or [Me(3)Si](+). The impact of mesomeric, inductive and steric substituent effects on FIAs are discussed and related to the underlying electronic structures of different cation types. A comparison between the FIAs of known "free" phosphenium ions with those that are currently unknown and other highly electrophilic cations suggests that some diaryl- and dialkylphosphenium ions may yet be accessible under the right conditions.
68 citations
TL;DR: Porous polymer networks based on sterically encumbered triphenylphosphine motifs, mimicking the basic sites employed in frustrated Lewis pair (FLP) chemistry, were synthesized via Yamamoto polymerization and their interactions with the strong Lewis acid B(C6F5)3 probed.
Abstract: Porous polymer networks based on sterically encumbered triphenylphosphine motifs, mimicking the basic sites employed in frustrated Lewis pair (FLP) chemistry, were synthesized via Yamamoto polymerization and their interactions with the strong Lewis acid B(C6F5)3 probed. The combinations yield semi-immobilized FLPs, which are able to cleave dihydrogen heterolytically at ambient temperature and low hydrogen pressure.
68 citations
TL;DR: The syntheses of salts containing ligand-stabilized Ph3Sb( 2+) and Ph3Bi(2+) dications have been realized by in situ formation of Ph3Pn(OTf)2 (Pn=Sb or Bi) and subsequent reaction with OPPh3, dmap and bipy.
Abstract: The syntheses of salts containing ligand-stabilized Ph3Sb(2+) and Ph3Bi(2+) dications have been realized by in situ formation of Ph3Pn(OTf)2 (Pn=Sb or Bi) and subsequent reaction with OPPh3, dmap and bipy The solid-state structures demonstrate diversity imposed by the steric demands and nature of the ligands The synthetic method has the potential for broad application enabling widespread development of the coordination chemistry for Pn(V) acceptors
68 citations