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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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Book ChapterDOI
TL;DR: A survey of the electronic and steric characteristics of anionic (RPCP, RPOCOP, RPNCNP) and neutral (RPNP, RPNP and RPNNNP) phosphine terdentate ligands is presented in this paper, where pincer arm conformations are categorized in terms of C2 twist, Cs "gull wing", and asymmetric bending.
Abstract: A survey of the electronic and steric characteristics of anionic (RPCP, RPOCOP, RPNCNP) and neutral (RPNP, RPONOP, RPNNNP) phosphine terdentate ligands is presented. A review of the scope of syntheses, particularly in regard to the variation of phosphine PR2 substituents, is followed by a general discussion of pincer steric variation, terdentate ligand conformations, and coordination geometries. Buried volume parameters, %Vbur, provide a measure of overall steric influence, while the concepts of cis and trans ligand void space and PR2 steric influence are used to more completely define asymmetric steric influence. Pincer arm conformations are categorized in terms of C2 twist, Cs “gull wing,” and asymmetric bending, which accommodate a range of non-meridional P–M–P bending geometries. For 5-coordinate metal complexes, geometries can vary between two square pyramidal and two trigonal bipyramidal geometrical extremes and are distinguished using subtending angle parameters α, β, and γ. A key feature to note is that pincer ligands often assume non-meridional geometries with P–M–P angles as small as 107°. DFT studies on P–Ir–P bending energetics for (RPCP)Ir(L) (L = CO, NH3) with a wide range of R substituents show that destabilization from bending is primarily steric in origin and is particularly significant (+12 to 30 kcal mol−1) for tBuPCP systems. Pincer electronic effects are surveyed using comparative IR, electrochemical, and binding affinity data. While R electronic effects are significant, particularly for our R = CF3 systems, DFT calculations of ΔG diss(Ir–CO) for (RPCP)Ir(CO)2 systems show that reduced Ir–CO binding correlates mostly with steric destabilization in non-meridional tBu-substituted pincer systems.

77 citations

Journal ArticleDOI
TL;DR: The domain-based local pair natural orbital coupled-cluster (DLPNO-CCSD(T) method is used in conjunction with the recently introduced local energy decomposition (LED) analysis to obtain state-of-the-art dissociation energies and a clear-cut definition of the London dispersion component of the interaction.
Abstract: The interaction of Lewis acids and bases in both classical Lewis adducts and frustrated Lewis pairs (FLPs) is investigated to elucidate the role that London dispersion plays in different situations. The analysis comprises 14 different adducts between tris(pentafluorophenyl)borane and a series of phosphines, carbenes, and amines with various substituents, differing in both steric and electronic properties. The domain-based local pair natural orbital coupled-cluster (DLPNO-CCSD(T)) method is used in conjunction with the recently introduced local energy decomposition (LED) analysis to obtain state-of-the-art dissociation energies and, at the same time, a clear-cut definition of the London dispersion component of the interaction, with the ultimate goal of aiding in the development of designing principles for acid/base pairs with well-defined bonding features and reactivity. In agreement with previous DFT investigations, it is found that the London dispersion dominates the interaction energy in FLPs, and is also remarkably strong in Lewis adducts. In these latter systems, its magnitude can be easily modulated by modifying the polarizability of the substituents on the basic center, which is consistent with the recently introduced concept of dispersion energy donors. By counteracting the destabilizing energy contribution associated with the deformation of the monomers, the London dispersion drives the stability of many Lewis adducts.

77 citations

Journal ArticleDOI
TL;DR: A series of co-crystallizations between four biimidazole-based compounds (1,1′-bis(pyridin-4-ylmethyl)-2,2′-biimidrazole A1, 1, 1′)-bis(polycyclic polycyclic di-acids)-2.2.
Abstract: A series of co-crystallizations between four biimidazole based compounds (1,1′-bis(pyridin-4-ylmethyl)-2,2′-biimidazole A1, 1,1′-bis(pyridin-3-ylmethyl)-2,2′-biimidazole A2, 1,1′-bis(pyridin-2-ylmethyl)-2,2′-biimidazole A3 and 1,1′-dibenzyl-2,2′-biimidazole A4) and nine symmetric aliphatic di-acids were carried out in order to determine if a ranking based on calculated molecular electrostatic potential surfaces (MEPS) can be used to effectively assign selectivity in hydrogen-bond based intermolecular interactions. Acceptors A1–A3 are asymmetric ditopic acceptors where two types of nitrogen atoms (pyridine and imidazole) are present, while A4 is a control molecule with only one type of acceptor to rule out any influence of steric factors in the observed structures. 28 of 36 experiments (78% yield) produced a co-crystal, as indicated by relevant changes in the corresponding infrared spectra. Twelve crystal structures of co-crystals of A1–A3 were obtained and every single one displayed primary OH⋯N hydrogens bonds that could be rationalized using the ranking based upon electrostatic potential maps. One crystal structure of A4 was obtained the result of which indicate that the patterns of behaviour established in this family of compounds is not a result of sterics or crystal packing; a simple electrostatic view of hydrogen-bond strength provides a reliable tool for predicting the most likely interactions in a competitive system.

77 citations

Journal ArticleDOI
TL;DR: Evidence is given that the reactivity of the pyridine nitrogen atom is essential for the biological activity of 2-substituted isonicotinic acid hydrazides and seem to support the hypothesis that isonicotonic acid derivatives are incorporated into an NAD analogue.
Abstract: Quantitative structure-activity studies have been performed for a series of 2-substituted isonicotinic acid hydrazides by correlating electronic, steric, and lipophilic properties of the substituents with the biological activity date (MIC) from serial dilution tests with Mycobacterium tuberculosis (strain H 37 Rv). The reaction rates for the quaternization of 2-substituted pyridines with methyl iodide were also determined. The rate constants show a similar dependence on the steric and electronic effects of the substituents as the antibacterial activities of the corresponding pyridine-4-carboxylic acid hydrazides. The obtained correlations give evidence that the reactivity of the pyridine nitrogen atom is essential for the biological activity of 2-substituted isonicotinic acid hydrazides and seem to support the hypothesis that isonicotinic acid derivatives are incorporated into an NAD analogue.

77 citations

Journal ArticleDOI
TL;DR: In this paper, an extensive kinetic study of this migratory alkene insertion into acyl−palladium bonds of neutral complexes containing α-diimine ligands has been carried out.

77 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023942
20221,917
2021346
2020292
2019296
2018307