THEORETICAL COMPARISON OF THE BONDING OF CHALCOCARBONYL LIGANDS

Abstract

Fenske-Hall molecular orbital calculations on the complexes CpFe(CO)₂(CX)⁺ (X = O, S, Se, and Te) have been used to quantify the nature of bonding between the CX ligands and the metal atom. In addition, conclusions have been reached about the reactivity of the complexes under both nucleophilic and electrophilic attack. The previously established trend of increasing metal—ligand bond strength as X changes from O to S to Se is demonstrated by our molecular orbital calculations, and found to extend to Te. The mechanism for nucleophilic attack, variously explained in the past by either charge control or orbital control, is quantitatively ascribed to orbital control only. The nature of electrophilic attack on these complexes is also found to begin with orbital control.     

Reaction of 4-Nitrobenzenesulfenamide with Liquid Ammonia

Abstract

Although numerous investigations on the chemistry of organic sulfenamides, for example, studies on the S–N torsional barrier,¹ the electronic nature of the S–N bond² and some nucleophilic substitutions on sulfur or nitrogen atom³ have been known, no example of nucleophilic substitution on arylcarbon of aromatic sulfenamides has been reported.     

VICARIOUS NUCLEOPHILIC SUBSTITUTION WITH SULFUR CONTAINING CARBANIONS

Abstract

Carbanions stabilized with sulfur containing substituents are versatile intermedi-ates in organic synthesis. The great value and importance of such carbanions is connected with specific properties of the sulfur atom which is capable to exist in a variety of valent states and to form many functional groups. These various sulfur-containing groups exert different carbanion stabilizing effects and can also serve as leaving groups in nucleophilic substitution or elimination reactions. Taking into account numerous types of sulfur containing functional groups and a variety of reactions they can promote, it is well understandable that reactions of sulfur-containing carbanions have been thoroughly studied and widely exploited in organic synthesis. The reactions of such carbanions with aliphatic electrophilic partners: alkylating agents, carbonyl compounds and Michael acceptors consist a major section of this field and were subject of numerous studies as well as many monographs.¹ Contrary to that, not very much was known about reactions of such carbanions with electrophilic aromatic compounds. Actually, there are only few reports on nitroarylation of sulfur-containing carbanions via replacement of halogen orfho- or para- to the nitro group in halonitrocornpounds.² There are also some reports on the alkylation of nitroarenes and heterocyclic compounds in the reaction with sulfonium3 and sulfoxonium4 ylides, dimethylsulfoxide carbanion,⁵ and dialkyl or alkyl aryl sulfones carbanions.⁶     

An Efficient Preparation of Hexamethyldisilane

The striking reactivity conferred by silicon on organic molecules of widely diverse structural type has prompted considerable interest during the last decade in methods for the generation of silicon-carbon bonds and the subsequent transformations of the resultant organosilicon compounds. The highly nucleophilic silyl anions seem particularly suited to serve as precursors to these organosilicon compounds, although, in some cases, they have been postulated to react as one-electron transfer reagents.¹ Although silyl anions have been known for some time², only recently have efficient in situ methods been devised for the preparation of trimethylsilyllithium³, -sodium⁴ and -potassium⁵ from hexamethyldisilane (1) and methyllithium, sodium methoxide and potassium methoxide, respectively. These trimethylsilyl anions undergo reaction     

Reactivity of Dicoordinated Stannylones (Sn0) versus Stannylenes (SnII): An Investigation Using DFT‐Based Reactivity Indices

The reactivity of dicoordinated Sn⁰ compounds, stannylones, is probed using density functional theory (DFT)‐based reactivity indices and compared with the reactivity of dicoordinated Sn^II compounds, stannylenes. For the former compounds, the influence of different types of electron‐donating ligands, such as cyclic and acyclic carbenes, stannylenes and phosphines, on the reactivity of the central Sn atom is analyzed in detail. Sn⁰ compounds are found to be relatively soft systems with a high nucleophilicity, and the plots of the Fukui function f^? for an electrophilic attack consistently predict the highest reactivity on the Sn atom. Next, complexes of dicoordinated Sn compounds with different Lewis acids of variable hardness are computed. In a first part, the double‐base character of stannylones is demonstrated in interactions with the hardest Lewis acid H⁺. Both the first and second proton affinities (PAs) are high and are well correlated with the atomic charge on the Sn atom, probing its local hardness. These observations are also in line with electrostatic potential plots that demonstrate that the tin atom in Sn⁰ compounds bears a higher negative charge in comparison to Sn^II compounds. Stannylones and stannylenes can be distinguished from each other by the partial charges at Sn and by various reactivity indices. It also becomes clear that there is a smooth transition between the two classes of compounds. We furthermore demonstrate both from DFT‐based reactivity indices and from energy decomposition analysis, combined with natural orbitals for chemical valence (EDA‐NOCV), that the monocomplexed stannylones are still nucleophilic and as reactive towards a second Lewis acid as towards the first one. The dominating interaction is a strong σ‐type interaction from the Sn atom towards the Lewis acid. The interaction energy is higher for complexes with the cation Ag⁺ than with the non‐charged electrophiles BH₃, BF₃, and AlCl₃.     

THE CHEMISTRY OF OPTICALLY ACTIVE SULFUR COMPOUNDS PART III

Abstract

The chemistry of optically active sulfur compounds has proven to be one of great interest and challenge as demonstrated by the prolific publications in this area. An ever larger number of different types of compounds with sulfur as center of chirality are being synthesized and it is expected that in future publications additional members of this group will be described. Thus far the following chiral sulfur compounds have been prepared:     

Water-promoted unprecedented chemoselective nucleophilic substitution reactions of 1,4-quinones with oxygen nucleophiles in aqueous micelles

Unique nucleophilic substitution and addition reactions of nitrogen and sulfur nucleophiles with 1,4-quinones in aqueous suspension with amines and thiols have recently been demonstrated by us.² However, the reactivity of oxygen nucleophiles toward nucleophilic substitution compared to nitrogen and sulfur nucleophiles ‘on water’ is not facile. An unprecedented economical, green methodology approach using ordinary laundry detergent (LD; washing powder, 0.5 mol %, reusable)/SDS as surfactant ‘in water’ for nucleophilic substitution by oxygen nucleophiles in 1,4-quinones in excellent yields has been demonstrated.     

Phosphorylation of Amine Compounds with Sodium Cyclo-triphosphate

Abstract

Among inorganic linear and cyclic phosphates, cyclo-triphosphate has drawn special attention for its high reactivity with various amine compounds. A ring opening reaction to produce N-alkylamidotriphosphate derivatives proceeds under moderate conditions, e.g., at room temperature in aqueous solution. In spite of its potentiality as a phosphorylating agent for amino groups, a systematic investigation on the reaction mechanism has not fully carried out. This may be due to the lack of analytical methods which allow the quantitative examination of the reactions. In this work, HPLC with an anion-exchanger column developed for phosphate compounds together with ³¹P-NMR were applied to a kinetic study. It has been clarified that; 1) the reactivity of amine compounds is primarily correlated with the basisity of the amino groups, i.e., pKa values of its conjugate acids, though, branching at α carbon of the amino group greatry retards the reaction rate because of steric hindrance, and 2) some bifunctional reagents, such as ethylenediamine, propanediamine, ethanol-amine, and some α-amino acids produce heterocycles which contain P-N bond through an intramolecular reaction following the ring opening of cyclo-triphosphate. Ba or Mg salts of N-alkylamidotriphosphate derivatives have been prepared from mono amines, diamines, aminoalcohols, and aminoacids.     

Synthesis and antioxidant screening of new 2-cyano-3-(1,3-diphenyl-1H-pyrazol-4-yl)acryloyl amide derivatives and some pyrazole-based heterocycles

Abstract

The high functionality compound namely 2-cyano-3-(1,3-diphenyl-1H-pyrazol-4-yl)acryloyl chloride (1) was utilized as a building block synthon via reactions with some nitrogen and sulfur nucleophilic reagents. The present work was planned to study the effect of 2-cyano group on the reactivity and stability of C₂–C₃ double bond toward different strong-to-weak nucleophiles, in addition to its facility of nucleophilic addition at C₂–C₃ double bond to construct new heterocyclic derivatives. The proclivity toward some mono-, 1,2-, 1,3-, 1,4-, and 1,5-binucleophiles was investigated. The reaction with 2-cyanoacetohydrazide was mainly dependent on the reaction conditions. Some new heterocycles integrated with pyrazole scaffold were successfully synthesized, such as benzoxazinone, indoline, isoindoline, pyrazolone, chromene, and pyrimidopyrimidine derivatives. Some of the newly synthesized compounds were screened for their antioxidant activity using ABTS method, and the results revealed that some compounds exhibited promising inhibitory antioxidant activity.     

Phase Transfer Catalysed Synthesis of Methyl α-Bromomethylacrylate

Methyl α-bromomethylacrylate 1 is an important intermediate both as a starting material for specifically functionalized polymers and for use in general organic synthesis. As an example of the former it has been used to prepare polymeric anthraquinoid dyes¹. Synthetically, its bifunctional reactivity towards nucleophilic attack has made it useful in the preparation of both spiro² and bicyclic^3,4 ring systems. Several reports of synthetic methods leading to α-methylenelactones, having potential antitumor activity, have also been reported which use α-bromomethylacrylate as a starting point⁵.     

Synthesis and Chemical Behavior of the N-Morpholino- O-Alkyl-3-Methyl-1,2-Butadienephosphonic Acid Esters

Abstract

The synthesis and the reactivity of the titled compounds towards electrophilic and nucleophilic reagents have been discussed.     

AM1 calculations of parts of the enthalpy surfaces for additions of active methylene nitriles to α β-unsaturated nitriles

The nucleophilic additions of active methylene nitriles (MNs), R₁R₂CH⁻, where R₁=CN and R₂=CN, and CSNH₂, to acetaldehyde and to the resultant α, β-unsaturated nitriles have been studied theoretically by the AM1 semiempirical MO method. The additions of MNs anions to acetaldehyde are found to be endothermic with late productlike transition states (TSs) on the reaction coordinate. Their additions to α,β-unsaturated nitriles may conceivably proceed via two pathways: addition to the C=C double bond and addition to the C≡N triple bond. It has been found that the nucleophilic attack at the &alpha,β-unsaturated linkage is exothermic, while that at the nitrile group is endothermic and has a relatively high enthalpy barrier. Both additions have late productlike transition states. The reactivity of the nucleophilic attack has been discussed in the light of the frontier molecular orbital theory and in terms of the HOMO–LUMO two-electron interaction. The calculations have been compared with experimental results. © 1997 John Wiley & Sons, Inc.     

Origin of the oxygen in the oxidation of triphenylphosphine by potassium persulfate—application of the 18O isotope effect in 31P NMR

Potassium persulfate oxidizes triphenylphosphine to triphenylphosphine oxide in 60% aqueous acetonitrile. It has been suggested that the oxygen of the product, triphenylphosphine oxide, might originate from solvent water, following nucleophilic attack on an intermediate phosphonium ion. We have investigated the origin of the oxygen in the oxidation of triphenylphosphine by potassium persulfate in 60% aqueous acetonitrile containing 20% [¹⁸O]water. The product was analyzed by using the ¹⁸O isotope effect in ³¹P NMR spectroscopy. The magnitude of the ¹⁸O isotope-induced shift was determined by synthesizing triphenylphosphine [¹⁸O]oxide and was found to be 0.038 ppm upfield. The product of the oxidation reaction in 20% [¹⁸O]water displayed no ¹⁸O isotope effect. The origin of the oxygen in the oxidation reaction is the persulfate ion, consistent with an alternative mechanism involving nucleophilic attack by water at the sulfur atom of a phosphonium peroxysulfate intermediate.     

Thermal and photochemical reactivity of phosphaalkenes

Abstract

The reactivity of acyclic dicoordinated phosphorus derivatives has intensively been studied. Nevertheless, up to date, a very few examples of photochemical reactivity of these compounds have been described. We wish to report here some thermal and photochemical reactions of phosphaalkenes 1–4. ¹     

Nucleophilic Reactivity of the Thiophosphoryl Group

The difference in the nucleophilic reactivities of the and groups can be satisfactorily explained on the basis of Pearson's acid-base concept^[21]. The thiophosphoryl sulfur is a typical “soft base”, and reacts preferentially with sub-group B metals, halogens, and sp³ hybridized carbon, whereas it is largely inert to “hard acids” such as protons, carbonyl carbon, and tetrahedral phosphorus. Since a nucleophilic attack by the thiophosphoryl sulfur leads to a decrease in the charge density of the phosphorus atom, the latter (or the α-carbon atom in O-alkyl esters) becomes more open to nucleophilic attack. This reaction principle forms the basis of sulfur exchange, dealkylation, isomerization, and the Pistschimuka and Michalski reactions.     

The effect of cations on nucleophilic additions to carbonyl compounds: carbonyl complexation control versus ionic association control. application to t

The fundamental influence of cations in nucleophilic additions to carbonyl compounds is discussed in terms of either carbonyl complexation or ionic association with the nucleophile. Since loose ion pairs react essentially under complexation control while tight ion pairs react under association control, an experimental criterion is proposed to determine which factor controls the reactivity (complexation or association) based on the kinetic effects of cryptand or crown-ether addition.An application of this duality is then examined for the regioselectivity of nucleophilic additions to α-enones and correlated with perturbational arguments based on abinitio calculations. Under complexation control, attack at carbon 2 is favoured, especially when a soft nucleophile is involved and the counter-ion is Li⁺ rather than Na⁺. Under association control two cases are considered according to whether the cation is directly bound or not to the nucleophilic center; in addition, the influence of hard or soft metals and the possibility of a cationic bridge in the transition state have been discussed. Several kinetic controlled reactions have been examined and interpreted in this way. An extension of this concept to other reactions will be considered.     

Olefin‐Supported Rhenium(III) Terminal Oxo Complexes Generated by Nucleophilic Addition to a Cyclopentadienyl Ligand

The reactivity of the oxo Re^V β‐diketiminate, OReCl₂(BDI), with various cyclopentadienide (Cp) sources has been investigated. As a result, we have developed a route to a new class of terminal oxo complexes of Re^III supported by olefin moieties of substituted cyclopentadienes. The success of this pathway is due to the electrophilic nature of the Cp ligand in the cation, [ORe(η⁵‐Cp)(BDI)]⁺ ( 3⁺ ), which allows for nucleophilic attack by a variety of reagents under mild conditions. In contrast, ^tBuNC was found to attack at the oxo moiety to produce isocyanate by oxygen atom transfer.     

Décontamination chimique. Destruction rapide,douce, totale de toxiques organophosphorés et organosoufrés par une nouvelle série de ω-phtalimidoperacides

The chemical decontamination of toxic organophosphorus (pesticides or warfare agents) and sulfur compounds is of increasing importance. These products are destroyed by nucleophilic substitution for organophosphorus and oxidation of sulfur compounds. Peroxyacids, in micellar medium, are interesting for their reactivity on both families. We show here the interest of a new family: the phtalimidoperoxyacids.     

Quantum Chemical Study of Mechanisms of Organic Reactions: VII. Reaction of Ethane-1,2-dithiol with 1,3-Dichloropropene in the System Hydrazine Hydrate–KOH

A mechanism has been proposed for the reaction of 1,3-dichloropropene with ethane-1,2-dithiol in the system hydrazine hydrate–potassium hydroxide on the basis of DFT quantum chemical calculations [B3LYP/6-311++G(d,p)]. The proposed mechanism involves several consecutive steps, in particular nucleophilic substitution of chlorine at the sp³-hybridized carbon atom by sulfur, prototropic allylic rearrangement of the monosubstitution product with double bond migration toward the sulfur atom, dithiolane ring closure via nucleophilic attack of the second thiolate group on the carbon atom in the γ-position with respect to the second chlorine atom, and prototropic allylic rearrangement of 2-vinyl-1,3-dithiolane to more stable 2-ethylidene-1,3-dithiolane.     

REACTION OF α-CHLOROTOLUENE WITH ELEMENTAL SULFUR IN LIQUID AMMONIA

Abstract

α-Chlorotoluene (1) reacts with elemental sulfur in liquid ammonia affording dibenzyl disulfide (2), dibenzyl trisulfide (3), dibenzyl tetrasulfide (4), dibenzyl pentasulfide (5) and benzylidene benzylimide (6) at a low temperature such as 20°C. This reaction is presumed to be initiated by the nucleophilic attack of ammonium thioaminohydroxylate, “H₂NS^-NH₄ ⁺,” or dithioaminohydroxylate, “H₂NSS^-NH₄,” formed upon treating elemental sulfur in liquid ammonia, on α-chlorotoluene (1). Benzylidene benzylimide (6) is presumed to be formed from benzylamine, which can be formed by treatment of α-chlorotoluene (1) with ammonia.