Search results for "steric"
showing 10 items of 476 documents
Exploiting Pressure To Induce a "Guest-Blocked" Spin Transition in a Framework Material.
2016
A new functionalized 1,2,4-triazole ligand, 4-[(E)-2-(5-methyl-2-thienyl)vinyl]-1,2,4-triazole (thiome), was prepared to assess the broad applicability of strategically producing multistep spin transitions in two-dimensional Hofmann-type materials of the type [FeIIPd(CN)4(R-1,2,4-trz)2]·nH2O (R-1,2,4-trz = a 4-functionalized 1,2,4-triazole ligand). A variety of structural and magnetic investigations on the resultant framework material [FeIIPd(CN)4(thiome)2]·2H2O (A·2H2O) reveal that a high-spin (HS) to low-spin (LS) transition is inhibited in A·2H2O due to a combination of guest and ligand steric bulk effects. The water molecules can be reversibly removed with retention of the porous host f…
Understanding the molecular mechanism of the [3 + 2] cycloaddition reaction of benzonitrile oxide toward electron-richN-vinylpyrrole: a DFT study
2016
The [3 + 2] cycloaddition (32CA) reaction of benzonitrile oxide, BNO 2, with an electron-rich N-vinylpyrrole derivative, NVP 3a, in the presence of dichloromethane, has been theoretically studied using density functional theory (DFT) methods at the B3LYP/6-31G(d) level. This 32CA reaction presents a relatively high activation Gibbs free energy as a result of the low polar character of this zwitterionic-type (zw-type) reaction. Analyses of the calculated relative Gibbs free energies and transition state geometries indicate that the studied 32CA reaction, in excellent agreement with experimental outcomes, takes place in a complete regioselective manner as a consequence of the steric repulsion…
Supramolecular arrangements of novel clickable 4-substituted 3,6-bis(2′-pyridyl)pyridazine molecules
2020
Abstract The clickable reaction between the starting 3,6-bis(2′-pyridyl)-1,2,4,5-tetrazine (bptz) with a series of terminal alkynes-containing functional biomolecules [prop-2-yn-1-ol, 4-(prop-2′-yn-1′-yl)morpholine and D-galactose] by means of an inverse electron demand Diels-Alder pathway has been studied and four new 4-substituted 3,6-bis(2′-pyridyl)pyridazine derivatives (4-Rdppn) were isolated, namely 4-(hydroxymethyl)-3,6-di(pyridin-2-yl)pyridazine (1), 4-((prop-2-yn-1-yloxy)methyl)-3,6-di(pyridin-2-yl)pyridazine (2) obtained by post-etherification reaction of 1, 4-(morpholinemethyl)-(3,6-dipyridin-2-yl)pyridazine monohydrate (3) and 3,6-di(pyridin-2-yl)-4-((2,2,7,7-tetramethyltetrahyd…
Stability of Dinuclear Phosphane Palladium(III) Complexes: A DFT Approach
2018
Computational density functional theory studies have been carried out for the dinuclear ortho-metalated palladium(III) compounds [Pd2{μ-(C6H4)PPh2}2{μ-(X1-X2)}2Cl2]. These studies have shown that the electronic and steric properties of the auxiliary ligands (X1-X2 = bridging (carboxylato) or chelating (phenolato/acetylacetonato) O,O-donor ligands, bridging N,N-donor ligands (triazenido/formamidinato/pyrazolato), and bridging N,S-donor ligands) lead to systematic trends in their stability, highlighting that (a) the electronic nature of the donor atoms trans to the P has a clear trend, the replacement of hard donor atoms (O, N) by softer S donors generally reducing the stability of the compou…
Assessing the reactivity of sodium alkyl-magnesiates towards quinoxaline : single electron transfer (SET) vs. nucleophilic alkylation processes
2015
By exploring the reactivity of sodium butyl-magnesiate (1) supported by the bulky chelating silyl(bisamido) ligand {Ph2Si(NAr*)2}(2-) (Ar* = 2,6-iPr2-C6H3) towards Quinoxaline (Qx), the ability of this bimetallic system to effectively promote SET processes has been disclosed. Thus 1 executes the single-electron reduction of Qx affording complex (2) whose structure in the solid state contains two quinaxolyl radical anions Qx˙ stabilised within a dimeric magnesiate framework. Combining multinuclear NMR and EPR measurements with DFT calculations, new insights into the constitution of 2 in solution and its magnetic behaviour have been gained. Further evidence on the SET reactivity of 1 was foun…
Synthesis of bodinieric acids A and B, both C-18 and C-19-functionalized abietane diterpenoids: DFT study of the key aldol reaction
2020
[EN] The first synthesis of C-18- and C-19-bifunctionalized abietane diterpenoids, bodinieric (or callicapoic) acids, via an aldol reaction has been developed. This key aldol reaction was very sensitive to steric hindrance. This fact has been studied by deuterium exchange experiments and DFT methods. Optimization of this reaction led to the synthesis of anti-inflammatory bodinieric acids A and B, starting from abietic acid
A Density Functional Study of Open-Shell Cyclopentadienyl−Molybdenum(II) Complexes. A Comparison of Stabilizing Factors: Spin-Pairing, Mo−X π Bonding…
2000
International audience; The dissociation of PH3 from the 18-electron system CpMoX(PH3)3 to afford the corresponding 16-electron CpMoX(PH3)2 fragment has been investigated theoretically by density functional theory for X = H, CH3, F, Cl, Br, I, OH, and PH2. The product is found to prefer a triplet spin state for all X ligands except PH2, the singlet−triplet gap varying between 1.7 kcal/mol for OH to 8.7 kcal/mol for F. The Mo−PH3 bond dissociation energy to the 16-electron ground state varies dramatically across the series, from 4.5 kcal/mol for OH to 23.5 kcal/mol for H, and correlates with experimental observations on trisubstituted phosphine derivatives. Geometry-optimized spin doublet Cp…
Concave macrobicycles: Absorption spectra, luminescence properties, and endocavital complexation of neutral organic guests
1996
By a mild modified Eglinton coupling a series of diynebridged macrobicyclic hosts capable of endocavital complexation were synthesized and their structures and complexation properties investigated by X-ray analysis. The inclusion of DMSO in 7 suggests a direct correlation between steric fit and orientation of the guest. On the basis of this hypothesis, the orientation of acetone in an endocavital inclusion of 2 was predicted and verified by X-ray analysis. Comparison of the single-crystal X-ray structures of the vacant macrobicycle 3 and of a family of macrobicycles showing endocavital or “pocket” complexation of neutral organic guests suggests that torsion of the cavities upon complexation…
Halogenomercury Salts of Sterically Crowded Triazenides - Convenient Starting Materials for Redox-Transmetallation Reactions
2010
Diaryl-substituted triazenides Ar(Ar′)N3HgX [Ar/Ar′ = Dmp/Mph, X = Cl (2a), Br (3a), I (4a); Ar/Ar′ = Dmp/Tph, X = Cl (2b), I (4b) with Mph = 2-MesC6H4, Mes = 2,4,6-Me3C6H2, Tph = 2′,4′,6′-triisopropylbiphenyl-2-yl and Dmp = 2,6-Mes2C6H3] were synthesized by salt-metathesis reactions in ethyl ether from the readily available starting materials Ar(Ar′)N3Li and HgX2. These compounds may be used for redox-transmetallation reactions with rare-earth or alkaline earth metals. Thus, reaction of 4b or 2b with magnesium or ytterbium in tetrahydrofuran afforded the triazenides Dmp(Tph)N3MX(thf) (5b: M = Mg, X = I; 6b: M = Yb, X = Cl) in good yield. All new compounds were characterized by melting poin…
Allylpalladium( II ) Complexes with Aminophosphane Ligands: Solution Behaviour and X‐ray Structure of cis ‐[Pd(η 3 ‐CH 2 CHCHPh){Ph 2 PCH 2 CHPhNH(2,…
2004
A new β-aminophosphane L2 [Ph2PCH2CH(Ph)NH(2,6-C6H3iPr2)], bearing an asymmetric carbon atom and a vicinal prochiral nitrogen centre and (η3-allyl)palladium complexes of general formula [Pd(η3-C3H4R){η2-Ph2PCH2CH(Ph)NHAr}][PF6] (1−6) (R = H, Me or Ph and Ar = Ph or 2,6-C6H3iPr2) have been synthesised. NMR spectroscopic studies and a crystal structure analysis of complex 6 (R = Ph, Ar = 2,6-C6H3iPr2) confirmed the highly diastereoselective coordination of the nitrogen atom. Because of the allyl fluxionality and the presence of asymmetric centres, all the complexes exist in solution as mixtures of up to four diastereomers. For the monosubstituted allyl complexes [Pd(η3-C3H4R){Ph2PCH2CH(Ph)NHA…