Choice Of Reaction Solvent Research Articles

Solvent Coligand-Induced Spin State Variation in Iron(II) Complexes Bearing Pentadentate N5 Ligand Toward the Construction of an N5O Spin Crossover Center

Three iron(II) complexes having a 1,2,3-triazole-containing linear pentadentate N5 ligand L3-Me-3Me and different monodentate solvent coligand X, [Fe(L3-Me-3Me)X](BPh4)2 [L3-Me-3Me = bis(N,N′-1-methyl-1H-1,2,3-triazol-4-yl-methylideneaminopropyl)methylamine; X = MeCN (1), dimethylformamide (DMF) (2), and dimethyl sulfoxide (DMSO) (3)] have been selectively prepared by the choice of reaction solvent. Along the well-known spectrochemical series, the strong-field solvent ligand MeCN generates a low-spin (LS) complex 1, the weak-field ligand DMSO generates a high-spin (HS) complex 3, and the complex 2 coordinated by the medium-field ligand DMF exhibits gradual and reversible one-step HS↔LS spin crossover (SCO) with T1/2 = 173 K in the temperature range of 400–5 K. This spin state variation among LS 1, HS 3, and SCO 2 has been investigated by the combination of temperature-dependent magnetic susceptibilities measurements, single-crystal X-ray diffraction (SCXRD) studies, Hirshfeld surface analyses, and density functional theory calculations. In addition, the details of structural change between HS and LS states of an N5O iron(II) center upon SCO are revealed for the first time by the variable-temperature SCXRD studies for 2 at nine different temperatures in which the difference of Fe–O bond length between the two spin states is shorter than that of any other Fe–N bond lengths.

Mechanistic Guidance Leads to Enhanced Site-Selectivity in C–H Oxidation Reactions Catalyzed by Ruthenium bis(Bipyridine) Complexes

The development of an operationally simple C–H oxidation protocol using an acid-stable, bis(bipyridine)Ru catalyst is described. Electronic differences remote to the site of C–H functionalization are found to affect product selectivity. Site-selectivity is further influenced by the choice of reaction solvent, with highest levels of 2° methylene oxidation favored in aqueous dichloroacetic acid. A statistical model is detailed that correlates product selectivity outcomes with computational parameters describing the relative “electron-richness” of C–H bonds.

Gas Adsorption in R2‐MOF‐5 Difunctionalized with Alkyl Groups

AbstractZinc terephthalate metal−organic framework (MOF) MOF‐5 and some of its dialkylated derivatives (R2‐MOF‐5; R=Me, Et, Pr, Bu) were obtained from a solvothermal synthesis using 2,5‐dialkyl‐1,4‐benzenedicarboxylic acids with zinc nitrite. The effect of the solvent on the solvothermal synthesis of R2‐MOF‐5 was investigated. For R=H and Me, interpenetrating or non‐interpenetrating MOFs obtained depending on the choice of reaction solvent, while for R=Et, Pr, and Bu, no such solvent effect was observed, and only jungle‐gym‐type MOFs were generated. All compounds were fully characterized using powder X‐ray diffraction analysis (PXRD), Fourier‐transform infrared (FT‐IR) spectroscopy, and thermogravimetric analysis (TGA). After activation, all these compounds exhibit significant porosity, as confirmed by N2‐, H2‐, and CO2‐sorption experiments. The N2‐adsorption capacity of these compounds depends on the size of the attached alkyl groups, while the H2‐uptake values tend to increase for the alkyl‐functionalized MOFs relative to the unfunctionalized parent MOFs and exhibit a maximum value for Pr2‐MOF‐5.

Solvent-Controlled Divergent Syntheses of Polycyclic N-Fused Heteroaromatics

Due to a growing interest in aza-fused polyaromatic systems among various sciences, enormous attention has been continuously paid to design and synthesize novel chemotypes of N-fused hetero­cycles. During the course of continued efforts in this line, it was found that divergent access to new polycyclic N-fused heteroaromatics was enabled by choice of reaction solvent. Described herein are solvent-controlled selective approaches to three novel N-fused azacycles, benzo-[d]imidazole-pyrrolo[1,2-a]pyrazine hybrids, under mild conditions. The plausible reaction mechanism for each class of compound is suggested as well.

The Palladium-Catalyzed Ullmann Cross-Coupling Reaction: A Modern Variant on a Time-Honored Process.

Cross-coupling reactions, especially those that are catalyzed by palladium, have revolutionized the way in which carbon-carbon bonds can be formed. The most commonly deployed variants of such processes are the Suzuki-Miyaura, Mizoroki-Heck, Stille, and Negishi cross-coupling reactions, and these normally involve the linking of an organohalide or pseudohalide (such as a triflate or nonaflate) with an organo-metallic or -metalloid such as an organo-boron, -magnesium, -tin, or -zinc species. Since the latter type of coupling partner is often prepared from the corresponding halide, methods that allow for the direct cross-coupling of two distinct halogen-containing compounds would provide valuable and more atom-economical capacities for the formation of carbon-carbon bonds. While the venerable Ullmann reaction can in principle achieve this, it has a number of drawbacks, the most significant of which is that homocoupling of the reaction partners is a competitive, if not the dominant, process. Furthermore, such reactions normally occur only under forcing conditions (viz., often at temperatures in excess of 250 °C). As such, the Ullmann reaction has seen only limited application in this regard, especially as a mid- to late-stage feature of complex natural product synthesis. This Account details the development of the palladium-catalyzed Ullmann cross-coupling reaction as a useful method for the assembly of a range of heterocyclic systems relevant to medicinal and/or natural products chemistry. These couplings normally proceed under relatively mild conditions (<100 °C) over short periods of time and, usually, to the exclusion of (unwanted) homocoupling events. The keys to success are the appropriate choice of coupling partners, the form of the copper metal employed, and the choice of reaction solvent. At the present time, the cross-coupling partners capable of engaging in the title reaction are confined to halogenated and otherwise electron-deficient arenes and, as complementary reactants, α- or β-halogenated, α,β-unsaturated aldehydes, ketones, esters, lactones, lactams, and cycloimides. Nitro-substituted (and halogenated) arenes, in particular, serve as effective participants in these reactions, and the products of their coupling with the above-mentioned carbonyl-containing systems can be manipulated in a number of different ways. Depending on the positional relationship between the nitro and carbonyl groups in the cross-coupling product, the reduction of the former group, which can be achieved under a range of different conditions, provides, through intramolecular nucleophilic addition reactions, including Schiff base condensations, access to a diverse range of heterocyclic systems. These include indoles, quinolines, quinolones, isoquinolines, carbazoles, and carbolines. Tandem variants of such cyclization processes, in which Raney cobalt is used as a catalyst for the chemoselective reduction (by dihydrogen) of nitro and nitrile groups (but not olefins), allow for the assembly of a range of structurally challenging natural products, including marinoquinoline A, (±)-1-acetylaspidoalbidine, and (±)-gilbertine.

Intramolecular dehydro-Diels-Alder reaction affords selective entry to arylnaphthalene or aryldihydronaphthalene lignans.

Intramolecular dehydro-Diels–Alder (DDA) reactions are performed affording arylnaphthalene or aryldihydronaphthalene lactones selectively as determined by choice of reaction solvent. This constitutes the first report of an entirely selective formation of arylnaphthalene lactones utilizing DDA reactions of styrene-ynes. The synthetic utility of the DDA reaction is demonstrated by the synthesis of taiwanin C, retrohelioxanthin, justicidin B, isojusticidin B, and their dihydronaphthalene derivatives. Computational methods for chemical shift assignment are presented that allow for regioisomeric lignans to be distinguished.

Controlled Regioselective Anilide Formation from Aspartic and Glutamic Acid Anhydrides

The regioselectivity of the reaction of aniline with a series of N-protected aspartic and glutamic acid anhydrides was controlled through the choice of reaction solvent. In benzene, the formation of aspartic or glutamic acid α-anilides was favored, with α:(β or γ) regioselectivities as high as 100:0. On the other hand, in DMSO, the formation of either aspartic acid β-anilide or glutamic acid γ-anilide was favored, with α:(β or γ) regioselectivities as high as 0:100. This regioselectivity was not observed for alkylamines, amino acids, thiols, or alcohols. However, the high yields of the aniline reactions and the ability to specify their regioselectivities demonstrate the usefulness of our method for the formation of aspartic and glutamic acid anilide bonds.

Reactions of the polyhydride complex ReH7(dppe) (dppe = Ph2PCH2CH2PPh2) with pyridine-2-carboxylic acid, 1-isoquinolinecarboxylic acid, 2-hydroxy-6-methylpyridine and 2-mercaptoquinoline. synthesis and structural characterization of seven-coordinate monohydrido complexes of rhenium(iii)

The thermal reactions of ReH7(dppe) (dppe = Ph2PCH2CH2PPh2) with pyridine-2-carboxylic acid (Hpic), 1-isoquinolinecarboxylic acid (Hisoquin), 2-hydroxy-6-methylpyridine (Hmhp) and 2-mercaptoquinoline (Hmq) in refluxing benzene afforded the monohydridorhenium(III) species ReH(L)2(dppe) [L = pic (1a), isoquin (1b), mhp (1c), mq (1d)]. While analogous complexes have been prepared previously from ReH7(PPh3)2 in the case of L = pic, isoquin and mhp, the reactions between ReH7(PPh3)2 and the ligands 2-hydroxyquinoline and 2-mercaptoquinoline are dependent on the choice of reaction solvent; the rhenium hydride complexes ReH4(L)(PPh3)2 (L = hq or mq) and ReH(hq)2 (PPh3)2 have been isolated in a pure state. 1H and 31P NMR spectral measurements on the seven-coordinate species 1a-d show that these compounds are stereochemically rigid at room temperature. The solution structures are in accord with the solid state structures of 1c and 1d, as determined by X-ray crystallography. Copyright © 1996 Elsevier Science Ltd