Hydroboration. 97. Synthesis of new exceptional chloroborane--Lewis base adducts for hydroboration. Dioxane--monochloroborane as a superior reagent for the selective hydroboration of terminal alkenes

Several less volatile oxygen-containing Lewis bases, such as tert-butyl methyl ether, dioxane, anisole, ethyl acetate, beta-chloroethyl ether, and monoglyme, were examined as prospective mono- and dichloroborane carriers. Dioxane, ethyl acetate, and beta-chloroethyl ether form relatively stable boron trichloride adducts, but the boron trichloride adduct of monoglyme is not very stable and must be used immediately. On the other hand, tert-butyl methyl ether and anisole fail to form stable boron trichloride adducts and the corresponding ether-cleaved products are obtained. Among the selected oxygen-containing Lewis bases, only dioxane forms stable and reactive mono- and dichloroborane adducts. Monoglyme and beta-chloroethyl ether give stable dichloroborane adducts requiring excess of diborane. Convenient methods for the preparation of mono- and dichloroborane adducts of dioxane from dioxane-BCl(3) and NaBH(4) in the presence of catalytic amounts of tri- or tetraglyme were developed. The dioxane--monochloroborane adduct hydroborates representative olefins cleanly and rapidly. The corresponding alcohols were obtained in quantitative yields after oxidation. Also, the hydroboration of several terminal olefins with dioxane--monochloroborane were highly regioselective and the primary alcohols were obtained almost exclusively (>99.5%), after oxidation. Accordingly, dioxane-monochloroborane should serve as a reagent of choice for such hydroborations. The dioxane--dichloroborane adduct showed remarkable selectivity toward 2-substituted terminal olefins, such as 2-methyl-1-butene and beta-pinene, when compared to simple terminal and hindered olefins, giving a unique tool for selective hydroborations. Dichloroborane adducts of monoglyme and beta-chloroethyl ether also showed high reactivity, even at room temperature, toward simple unhindered olefins. However, hydroboration of hindered olefins is slow and requires either higher temperatures or the addition of 1 equiv of boron trichloride to liberate free dichloroborane, as in the case of the previously known dichloroborane adducts of methyl sulfide and diethyl ether.     

Chlorination of Aromatic Rings by PCL5

Abstract

The reaction products of PCl₅ with 2,6-dimesityl-aniline and with naphthalene-1,5-diamine are 4-chloro-2,6-dimesityl-aniline and (2,4,6,8-tetrachloronaphthalene-1,5-diyl)bis(phosphor­imidic trichloride), respectively, and were characterized by X-ray crystallographic analyses. The phosphazene shows π-stacking, extremely large C–N–P angles, and extremely short P–N distances.     

A spirocyclic system comprising both phosphazane and phosphazene rings

The reaction of hexakis(cyclohexylamino) cyclotriphosphazene [NP(CyNH)(2)](3), 1, with phosphorus trichloride yields [NP(CyN)(2)PCl](3), 2, which contains three four-membered phosphazane rings fused in spirocyclic fashion to a central six-membered phosphazene ring and constitutes the first structurally characterized compound that comprises both phosphazene and phosphazane rings. The peripheral P atoms feature stereoactive lone pairs, and, thus, 2 exists in isomeric C(3h) and C(s) forms. The spirocyclic phosphazene-phosphazane derivative 2 carries three reactive PCl functions in peripheral positions, promising an interesting precursor molecule for the synthesis of extended phosphorus nitrogen structures of high rigidity. Extension of the PN moiety can be achieved by reaction of 2 with a primary amine yielding [NP(CyN)(2)PN(H)(t)Bu](3), 3, which features a central scaffold of 6 phosphorus and 12 nitrogen centers and aggregates via N-H...P hydrogen bonds in the solid state. On the contrary, the reaction of 1 with SbCl(3) undergoes incomplete proton abstraction, resulting in the formation of the tricyclic compound N(3)P(3)(CyNH)(4)(CyNSbCl(2))(2), 4, which contains two four-coordinate Sb centers chelated by N(exo)-N(ring) sites of the phosphazene.     

Disulfidation of alkynes and alkenes with gallium trichloride

[reaction: see text] Treatment of diphenyl disulfide and terminal alkynes with gallium trichloride afforded (E)-1,2-diphenylthio-1-alkenes selectively (E/Z > 20/1). Alkenes also underwent this reaction to form trans adducts.     

Controlled ROP of β‐Butyrolactone Simply Mediated by Amidine,Guanidine, and Phosphazene Organocatalysts

Basic organocatalysts of the guanidine (1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene, TBD), amidine (1,8‐diazabicyclo[5.4.0]‐undec‐7‐ene, DBU), and phosphazene (2‐tert‐butylimino‐2‐diethylamino‐1,3‐dimethylperhydro‐1,3,2diazaphosphorine, BEMP) type do effectively polymerize β‐butyrolactone (BL). Poly(3‐hydroxybutyrate)s (PHBs) with controlled molecular features, that is, controlled molar masses, narrow molar mass distributions, and well‐defined functional end groups are thus formed at 60 °C from bulk monomer, with up to 21 500 g mol⁻¹. The formation of α,ω‐guanidine/amidine/phosphazene,crotonate functionalized PHBs, as demonstrated by NMR, SEC, and MALDI–ToF mass spectrometry analyses, mechanistically suggests the formation of N‐acyl‐α,β‐unsaturated propagating species that originate from 1:1 guanidine/amidine/phosphazene:BL adducts.     

Phosphazene cations

Cations derived from (NPCl2)3, hexachloro-cyclo-triphosphazene, the weakly basic precursor of phosphazene polymers, have been prepared using strongly electrophilic reagents based on carborane anions. N-protonated, N-methylated, and N-silylated adducts of (NPCl2)3 have been isolated and characterized by X-ray crystallographic and spectroscopic methods. The normally potent chloride-abstracting silyl reagents of the type R3Si(carborane) are unable to abstract chloride from (NPCl2)3, even though the coordinatively unsaturated N2P2Cl5+ cation is widely accepted as a reactive intermediate in the ring-opening polymerization of (NPCl2)3.     

Staudinger’s phosphazene as an efficient esterifying reagent

A new application of Staudinger’s phosphazene as an efficient esterifying reagent is reported. Staudinger’s phosphazene formed in situ by the reaction of organic mono-azide with triphenylphosphine, which is trapped by carboxylic acid, to afford amide exclusively. In contrast, interestingly the same phosphazene behaves in a different way as an efficient esterifying reagent, affording ester under a solvent-free microwave-assisted protocol wherein alcohol is added as the another component in addition to the other reactants. This discovery adds yet another new application of Staudinger’s phosphazene to synthetic chemistry.     

Ring Enlargement of Phospholenes to Phosphorin Derivatives Through Dichlorocarbene Adducts

Abstract

The ring enlargement of ready available phospholenes by dichlorocarbene addition to the double bond and subsequent opening of the cyclopropane ring is discussed. Adductcs of phospholene wih dichlorocarbene (2)can be synthetised under liquid-liquid phase transfer circumstances. The simplest bray to open the cyclopropane ring in the adducts is thermal transformation giving the two regioisomers of the appropriate dihydrophosphorin (3). Electrophilic reagents can also be used for -the opening of the cyclopropane ring. On heating with silver nitrate in water or in alcohols the adducts are transformed to the -two rcgioisomers of the hydroxy- or the alkoxy -tetrahydrophosphorins, respectively (4, Y=H, CH₃ C₂H₅) In the reaction of adducts with mercury acetate-acetic acid the corresponding acetoxy-derivatives (4, Y=CH₃CO) are formed. The Friedl Crofts reaction of the adducts with benzene iii the presence of aluminium trichloride yields diarylated product.     

Balancing Donor-Acceptor and Dispersion Effects in Heavy Main Group Element π Interactions: Effect of Substituents on the Pnictogen⋅⋅⋅π Arene Interaction

High-level ab initio calculations using the DLPNO-CCSD(T) method in conjunction with the local energy decomposition (LED) were performed to investigate the nature of the intermolecular interaction in bismuth trichloride adducts with π arene systems. Special emphasis was put on the effect of substituents in the aromatic ring. For this purpose, benzene derivatives with one or three substituents (R=NO₂, CF₃, OCHO, OH, and NH₂) were chosen and their influence on donor-acceptor interaction as well as on the overall interaction strength was examined. Local energy decomposition was performed to gain deeper insight into the composition of the interaction. Additionally, the study was extended to the intermolecular adducts of arsenic and antimony trichloride with benzene derivatives having one substituent (R=NO₂ and NH₂) in order to rationalize trends in the periodic table. The analysis of natural charges and frontier molecular orbitals shows that donor-acceptor interactions are of π→σ* type and that their strength correlates with charge transfer and orbital energy differences. An analysis of different bonding motifs (Bi⋅⋅⋅π arene, Bi⋅⋅⋅R, and Cl⋅⋅⋅π arene) shows that if dispersion and donor-acceptor interaction coincide as the donor highest occupied molecular orbital (HOMO) of the arene is delocalized over the π system, the M⋅⋅⋅π arene motif is preferred. If the donor HOMO is localized on the substituent, R⋅⋅⋅π arene bonding motifs are preferred. The Cl⋅⋅⋅π arene bonding motif is the least favorable with the lowest overall interaction energy.     

Isolation, X-ray structures, and electronic spectra of reactive intermediates in Friedel-Crafts acylations

[reaction: see text] Reactive intermediates in the Friedel-Crafts acylation of aromatic donors are scrutinized upon their successful isolation and X-ray crystallography at very low temperatures. Detailed analyses of the X-ray parameters for the [1:1] complexes of different aliphatic and aromatic-acid chlorides with the Lewis acids antimony pentafluoride and pentachloride, gallium trichloride, titanium and zirconium tetrachlorides provide unexpected insight into the activation mechanism for the formation of the critical acylium carbocations. Likewise, the X-ray-structure examinations of aliphatic and aromatic acylium electrophiles also isolated as crystalline salts point to the origins of their electrophilic reactivity. Although the Wheland intermediates (as acylium adducts to arene donors) could not be isolated in crystalline form owing to their exceedingly short lifetimes, transient (UV-vis) spectra of benzenium adducts of acylium carbocations with hexamethylbenzene can be measured and directly related to Wheland intermediates with other cationic electrophiles that have been structurally established via X-ray studies.     

Linear, cyclic and polymeric phosphazenes

An assessment of the diversity of phosphazene chemistry is presented with an emphasis on recent developments and their significance. Fundamental properties of phosphazenes are examined such as structure, nomenclature and bonding, and the various synthetic procedures are catagorized. In addition, the more important reactivity patterns are detailed and analysed. The review compares all systems containing the phosphazene bond, and makes extensive reference to previous reviews on specific types of phosphazene.     

THE DIELS-ALDER REACTION OF DIPHENYL(1,2-PROPADIENYL)PHOSPHINE OXIDE AND DIPHENYL(1-PROPYNYL)PHOSPHINE OXIDE WITH CYCLOPENTADIENE

The Diels-Alder reaction of diphenyl(1,2-propadienyl)phosphine oxide 1 and diphenyl(1-propynyl)phosphine oxide 2 with cyclopentadiene is reported. 1 reacts smoothly at room temperature in the presence of one equivalent of aluminum trichloride to give the corresponding adducts endo 3a and exo 3b (90:10 ratio) whose structure was attributed on the basis of their ¹³C NMR spectra, whereas 2 is a poor dienophile, affording the corresponding adduct in low yield even under harsh conditions.     

Diels-Alder reactions of acyclic α-cyano α,β-alkenones: a new approach to highly substituted cyclohexene system

The Diels-Alder reactions of a variety of acyclic α-cyano α,β-unsaturated ketones 8 have been investigated. With the assistance of boron trichloride, these compounds were found to undergo the cycloaddition readily with dienes to give the corresponding adducts 9 in good to high yields. In addition, some of 9 could be further subjected to the reductive alkylation reactions using lithium naphthalenide (LN) and an appropriate alkylating agent, thus allowing for the generation of highly substituted cyclohexenes 10 with the replacement of the cyano group with an alkyl substituent.     

Tris(tetramethylguanidinyl)phosphine: The Simplest Non-ionic Phosphorus Superbase and Strongly Donating Phosphine Ligand

We report the synthesis and properties of the much sought-after tris(1,1,3,3-tetramethylguanidinyl) phosphine P(tmg)₃, a crystalline, superbasic phosphine accessible through a short and scalable procedure from the cheap and commercially available bulk chemicals 1,1,3,3-tetramethylguanidine, tris(dimethylamino)-phosphine and phosphorus trichloride. The new phosphine exhibits exceptional electron donor properties and readily forms transition metal complexes with gold(I), palladium(II) and rhodium(I) precursors. The formation of zwitterionic Lewis base adducts with carbon dioxide and sulfur dioxide was explored. In addition, the complete series of phosphine chalcogenides was prepared from the reaction of P(tmg)₃ with N₂O and the elemental chalcogens.     

Rheological behavior and microstructure of 2,2′‐dioxy‐ 1,1′‐binaphthylphosphazene R/S random copolymer

Solutions of a binaphthoxy phosphazene copolymer (containing chiral 2,2′‐dioxy‐1,1′‐binaphthyl units with 50% R and S configurations distributed along the chains) in N‐methyl pyrrolidone were studied by means of continuous flow experiments and small amplitude oscillatory flow tests. A sudden viscosity decrease was observed in the polymer concentration range (39–40 wt %), evidencing a liquid‐crystalline polymer behavior. This has been confirmed by other rheological methods which have demonstrated that, for a sufficiently high concentration, the solutions of the binaphthoxy phosphazene copolymer give rise to a lyotropic system with formation of rigid rods (axial ratio of 10) stacked parallel to each other. The lyotropic properties of our binaphthoxy phosphazene copolymer are compatible with a regular helical structure, similar to that found for a homoleptic binaphthoxy phosphazene, which contains only S configuration. This suggests that the chains of 50% R/S binaphthoxy phosphazene copolymer are, in average, close to the strictly alternating R‐S copolymeric structure of the syndiotactic isomer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Darstellung von Selten-Erd-Trichloriden über chemischen Transport mit Aluminiumtrichlorid

Preparation of Rare Earth Trichlorides by Chemical Transport with Aluminium Trichloride The preparation of rare earth trichlorides by reaction of rare earth oxides with aluminium trichloride and their purification by means of chemical vapour phase transport with aluminium trichloride is described. By the method used especially rare earth doted rare earth trichlorides are obtainable in one step. The method furthermore allows a simple preparation of europium trichloride, which is not easy to prepare in another way. Two modifications of terbium trichloride can be prepared depending on the exact temperature conditions of the chemical vapour phase transport.     

Iodine trichloride in glacial acetic acid as an oxidizing titrant

A systematic study of the redox reactions of iodine trichloride with various inorganic ions in glacial acetic acid medium is described. Sodium sulphite, arsenic trichloride, antimony trichloride, iron(II) perchlorate and mecury(I) perchlorate were examined. Potentiometric and amperometric methods were used to follow the reduction of iodine trichloride, which yields different products according to the type of reductant.     

C(alpha),C(ortho)-Dimetalated phosphazene complexes

The first C(alpha),C(ortho) dilithium complex of a phosphazene has been synthesized as a single stereoisomer and has been structurally characterized in solution; the complex is monomeric, with the dianion acting as an N-C(ortho) and O-C(alpha) chelate. Transmetallation with Me(3)SnCl and PhHgCl afforded the first C(alpha),C(ortho) homo- and hetero-bimetallic phosphazene complexes, which contain a desymmetrised Ph(2)PN moiety.     

The determination of antimony(iii) and free HCl in mixtures

Antimony trichloride in a boiling aqueous solution reacts quantitatively with alkali yielding the trioxide Sb₂O₃. This can be employed for alkalimetric titration of antimony trichloride. When the method is combined with the iodimetric titration of antinony(lll), free hydrochloric acid can be determined in presence of the trichloride.     

Catalytic Action of Water during Nucleophilic Substitution of Halogen in Hexachlorocyclotriphosphazatriene with Pyridine <Emphasis Type="Italic">N</Emphasis>-Oxide

The data on the kinetics of the reaction between hexachlorocyclotriphosphazatriene (the phosphazene) with pyridine N-oxide in mixed organic solvents in the presence of water are presented. The reaction of the phosphazene with pyridine N-oxide leads to the formation of the onium salt. It has been found that water catalyzes this reaction, the catalytic action resulting from the solvation of the polar transition state due to the formation of the phosphazene complex with hydrogen bonding, thus facilitating the rupture of the phosphorus bond with the leaving anion.