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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70 citations
TL;DR: The effects of aryl ring ortho-, meta-, and para-substitution on site selectivity and enantioselectivity were investigated in reactions and it was demonstrated that the electronic and steric effects of various substituents on selectivities obtained in these reactions can be described by NBO charges, the IR carbonyl stretching frequency, and Sterimol values of various substituted benzoic acids.
Abstract: The effects of aryl ring ortho-, meta-, and para-substitution on site selectivity and enantioselectivity were investigated in the following reactions: (1) enantioselective Pd-catalyzed redox-relay Heck reaction of arylboronic acids, (2) Pd-catalyzed β-aryl elimination of triarylmethanols, and (3) benzoylformate decarboxylase-catalyzed enantioselective benzoin condensation of benzaldehydes. Through these studies, it is demonstrated that the electronic and steric effects of various substituents on selectivities obtained in these reactions can be described by NBO charges, the IR carbonyl stretching frequency, and Sterimol values of various substituted benzoic acids. An extended compilation of NBO charges and IR carbonyl stretching frequencies of various substituted benzoic acids was used as an alternative to Hammett values. These parameters provide a correlative tool that allows for the analysis of a much greater range of substituent effects because they can also account for proximal and remote steric effects.
70 citations
TL;DR: In this paper, the authors presented a semiquantitative approach to predict possible reactions of cationic electrophiles (carbenium ions, metal π-complexes, diazonium ions) with neutral nucleophiles (alkenes, alkynes, arenes, hydrides, organometallics and n-nucleophiles).
70 citations
TL;DR: The surprising conclusion that phosphines with relatively small Tolman steric parameters not only give highly reactive FLPs but are often seen to have the highest selectivity for the desired product is found.
Abstract: We report intermolecular transition metal frustrated Lewis pairs (FLPs) based on zirconocene aryloxide and phosphine moieties that exhibit a broad range of small molecule activation chemistry that has previously been the preserve of only intramolecular pairs. Reactions with D2, CO2, THF, and PhCCH are reported. By contrast with previous intramolecular examples, these systems allow facile access to a variety of steric and electronic characteristics at the Lewis acidic and Lewis basic components, with the three-step syntheses of 10 new intermolecular transition metal FLPs being reported. Systematic variation to the phosphine Lewis base is used to unravel steric considerations, with the surprising conclusion that phosphines with relatively small Tolman steric parameters not only give highly reactive FLPs but are often seen to have the highest selectivity for the desired product. DOSY NMR spectroscopic studies on these systems reveal for the first time the nature of the Lewis acid/Lewis base interactions in transition metal FLPs of this type.
70 citations
TL;DR: A series of pyridine-amine nickel complexes with various substituents were synthesized and used to evaluate substituent effects of catalyst precursors on the reactivity of ethylene polymerization as discussed by the authors.
Abstract: A series of pyridine-amine nickel complexes with various substituents were synthesized and used to evaluate substituent effects of catalyst precursors on the reactivity of ethylene polymerization. Substituent effects, including the steric effect of the pyridine moiety, steric effect of the bridge carbon, and steric and electronic effects of the amine moiety, were investigated systematically. Introduction of bulky aryls onto the pyridine moiety on amine pyridine nickel leads to a significant decrease in the activity and molecular weight of polyethylene, whereas an increase in bulk of substituents on the bridge carbon causes an increase in the polymerization activity and molecular weight of polyethylene. For the amine moiety, increasing the steric hindrance results in decreasing activity and affords a higher molecular weight polyethylene with a narrower polydispersity, and introduction of an electron-donating group on the amine moiety leads to formation of a high molecular weight polyethylene with enhanced ...
70 citations