Low Coordination States Research Articles

ChemInform Abstract: Reactions of Dichlorocarbene with Phosphorus Compounds in Low Coordination (Low‐σ) States.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

かさ高い置換基を有する特異構造有機リン化合物の化学 １． ジクロロカルベンと低配位リン化合物の反応

Reactions of low coordinated phosphorus compounds with dichlorocarbene and successive conversions of the resulting phosphiranes to phosphacumulenes are reviewed. Sterically protected diphosphenes reacted with dichlorocarbene to give the corresponding dichlorodiphosphiranes, which reacted with methyllithium to give 1, 3-diphosphaallenes. Similarly, the reaction of (E) - or (Z) -2-phenyl-1- (2, 4, 6-tri- t-butylphenyl) -1-phosphaethenes with dichlorocarbene afforded trans-phosphirane, which was converted to 1-phosphaallene. In some cases, the reactions of dichlorocarbene with 1-phosphaallenes, 1, 3-diphosphaallenes, or 1-phosphabutatrienes resulted in the formation of the rearranged products. Reactions of dichlorocarbene with other phosphorus species in low coordination states such as 1-aza-3-phosphaallene, 1, 4-diphosphabutatriene, or phosphaalkyne are also described.

ChemInform Abstract: Reaction of Dichlorocarbene with Some Organo‐Phosphorus Compounds in Low Coordination States

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Reactions of Sulfur with Some Unusual Organophosphorus Compounds in Low Coordination States

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Reaction of Dichlorocarbene with Some Organo-Phosphorus Compounds in Low Coordination States

Abstract The reactions of dichlorocarbene with some organo-Phosphorus compounds in low coordination states such as diphosphenes, phosphaethylenes, phosphaallenes, phosphabutatrienes, and phosphaalkynes were carried out.

Reactions of Sulfur with Some Unusual Organophosphorus Compounds in Low Coordination States

Abstract Reactions of sulfur with some unusual organophosphorus compounds in low coordination states such as diphosphenes, phosphaallenes, and diphosphaallenes were carried out.

Use of methanol as a probe to study the adsorption sites of different MgO samples

Methanol adsorption on activated MgO has been studied by gravimetry and FT-IR spectroscopy. It gives rise to three kinds of species: 1. i) one reversibly adsorbed at room temperature (species H) coordinated to Mg 2+ sites but also strongly H-bonded to unsaturated O 2− sites; 2. ii) two methoxy species characterized by a ν(O-C) band at 1115 cm −1 (species I) and 1090 cm − (species II) resulting both from the dissociation in methanol of the O-H bond as shown by use of CH 3 18OH., Considering that faces of the (100) type are preferentially exposed, species H and I are postulated to be formed on regular faces, while species II formation involves the presence of defects, such as Mg 2+ cations in a low coordination state. Extension of the study to five MgO samples, the surface of which varies from 12 m 2 g −1 (smoke) to 565 m 2 g −1 (ex-carbonate), shows that the proportion of defects increases with the surface area, reaching more than 25 % of the total amount of methanol adsorption sites in the case of high surface area samples.

Organogermanium species with the metal in low coordination states. Recent results from the Toulouse group

Organogermanium species with the metal in low coordination states. Recent results from the Toulouse group

ChemInform Abstract: A Versatile Preparation of 2,6‐Di‐tert‐butylbromobenzene. Application to Steric Protection for Organophosphorus Compounds in Low Coordination States.

Abstract2,4,6‐Tris(tert‐butyl)bromobenzene (I) reacts with nitric acid (II) to form the monodealkylated nitro compound (IV) which is reduced to give the amine (V) and then deaminated, yielding 2,6‐di(tert‐butyl)bromobenzene (VI).

Röntgenstrukturanalyse von 2,4,6‐Tri(tert‐butyl)phenyl‐lithium · N,N,N′,N′‐Tetramethylpropan‐1,2‐diamin: Eine monomere Organolithium‐Verbindung

X‐Ray Crystal‐Structure Analysis of 2,4,6‐Tri(tert‐butyl)phenyllithium · N,N,N′,N′‐Tetramethylpropane‐1,2‐diamine: a Monomeric Organolithium CompoundTri(tert‐butyl)phenyllithium is an important reagent for the preparation of derivatives of main‐group elements with low coordination state as well as a highly hindered base for the generation of amine‐free Li‐enolates. Its monomeric nature in solution was previously deduced from NMR measurements. While Et2O, THF, and N,N,N′,N′‐tetramethylethylene‐1,2‐diamine (tmen) led to crystalline samples which were not suitable for structure analysis, the N,N,N′,N′‐tetramethylpropane‐1,2‐diamine (tmpn) gave good single crystals of the title compound from Et2O/hexane (disorder along the two‐fold crystallographic axis running through LiC(1) and C(4) of the Ph ring. The structure (Fig. 1, Table 1) has some remarkable features: (i) it is one of the very few monomeric organolithium compounds so far, (η1‐Li on aromatic ring); (ii) it has the rare trigonal‐planar coordination of the Li‐atom; iii) there are close contacts between the Li‐atom arid one of the Me groups in each ortho‐position (Fig. 3). The internal angle on the Ph‐ring ipso‐C‐atom is 114°. This angle as well as those of the other known phenyllithium (Table 2), ‐magnesium, and ‐aluminum structures are included in a plot of ipso‐angles against Pauling electronegativities (Fig. 2).

A versatile preparation of 2,6-Di-t-butylbromobenzene. Application to steric protection for organophosphorus compounds in low coordination states

Abstract 2,6-Di-t-butylbromobenzene ( 5 ) was prepared from 2,4,6-tri-t-butyl-bromobenzene by ipso nitration followed by reduction of the nitro group and deamination. The diphosphene ( 8 ) and 1,3-diphosphaallene ( 10 ) were prepared.

Activation of Methane on the MgO Surface at Low Temperatures

Abstract The C–H bond of methane is easily activated on the MgO surface even below room temperature. Active sites consist of intrinsic ion pairs, O3C2−–Mg3C2+ and O4C2+, of MgO in low coordination states on which a methane molecule adsorbs in heterolytically dissociated form.

P-coordinated group VI metal(0) pentacarbonyl complexes of multiple-bond organophosphorus compounds in the low coordination state

Group VI metal(0) carbonyl complexes of diphosphenes, phosphaethylenes, 1-phosphaallene, and 1,3-diphosphaallene with the phosphorus atom in the low coordination state were prepared, and the 31P chemical shifts of these complexes were found to correlate to one another: the structures in solution could be determined by taking into account the correlation and phosphorus-tungsten coupling constants in 31P NMR.

ChemInform Abstract: Oxygen Species Adsorbed on Ultraviolet‐irradiated Magnesium Oxide.

AbstractWährend der O2‐Adsorption unter UV‐Bestrahlung an einer bei 1123 Kentgasten MgO‐ Oberfläche bei 77 Kbilden sich die Spezies O5′ und O; zu gleichen Teilen (TPD‐ und ESR‐Untersuchungen).

Photoisomerization of benzylidenephosphine containing phosphorus in low coordination state

E -Benzylidene- P -2,4,6-tri- t -butylphenylphosphine containing phosphorus in low coordination state was irradiated to give the corresponding Z -isomer: both isomers were isolated and characterized and the reactions with chromium(O) carbonyls were described.

Oxygen species adsorbed on ultraviolet-irradiated magnesium oxide

The adsorption of oxygen, under u.v. irradiation, on the surface of MgO outgassed at 1123 K has been studied at 77 K by temperature-programmed desorption and e.s.r. spectroscopy. During adsorption ozonide and superoxide ions were formed in equal amounts. The formation of these oxygen species is explained by the reaction of oxygen molecules with a short-lived exciton produced by the absorption of a photon at a surface O2– species in a very low coordination state. Thermal decomposition of the oxygen species adsorbed at 77 K has also been studied under a dynamic vacuum. It proceeds in four steps: (i) O–3 is transformed into O– and O2 between 77 and 300 K; (ii) O– is changed into O2–2 between 77 and 473 K; (iii) O–2 is also transformed into O2–2, with the evolution of O2 between 300 and 673 K; (iv) finally O2–2 is changed into O2– and O2 between 673 and 1123 K. This mechanism is also consistent with energy considerations. The formation and thermal decomposition of superoxide ions proceeds similarly both on surfaces subjected to u.v. irradiation and on surfaces containing thermally preadsorbed hydrogen.

The study of active centers of ethylene polymerization over chromium catalysts prepared from tri- and bivalent chromium compounds

The catalysts prepared from the trivalent and divalent chromium compounds under conditions that prevented their oxidation were investigated in the reaction of ethylene polymerization. Also the reduced chromia catalyst prepared by standard method from sexivalent chromium compound was investigated. The valence and coordinate states of chromium ions in the catalysts were determined by EPR and reflectance optical spectroscopy. In all cases, the catalysts prepared from trivalent chromium ions had a large activity; whereas the catalysts from divalent chromium had no activity. The reduction of the trivalent chromium ions into divalent state sharply decreased the activity. The activity of the catalysts prepared by the standard method was also decreased under reduction. It is concluded that the exposed Cr 3+ ions in low coordination state are responsible for the catalytic activity of the catalysts.

Kinetics of liquid phase hydrochlorination of acetylene in presence of cuprous chloride

In this study, we propose gold-intercalated ordered mesoporous carbon nanosphere catalysts in which gold nanoparticles are reduced by high-temperature carbonization of the carbonaceous matrix to catalyze the selective hydrogenation of aromatic nitro compounds. A spherical morphology of particles with size approximately 90 nm and ordered mesoporous arrays was clearly observed on the surface in the high-resolution scanning electron microscopy images. The X-ray photoelectron spectra and transmission electron microscopy images showed that the dispersed metallic gold nanoparticles (2.8 nm in diameter) were intercalated into a carbon framework. The IR spectra for CO chemisorption suggested the involvement of neutral gold atoms in a low-coordination state in clusters or a stepped surface. The gold nanocatalysts intercalated into the nanospherical mesoporous carbons exhibited high activity and selectivity for the hydrogenation of nitroarenes to the corresponding amines, using H2 as a reduction agent. The initial reaction rate reached 12.7 and 6.5 min−1 in the hydrogenation of p-chloronitrobenzene and 4-nitrophenol, respectively. This catalytic performance was retained for more than five catalytic runs with no obvious activity loss or gold leaching, indicative of high stability. The trapping test using a mercapto-functionalized SBA-15 solid revealed undetected soluble gold species in the reaction solution. The high activity and stability of the ordered mesoporous carbon nanosphere-supported gold catalysts was strongly correlated to the particle morphology change by thermal reduction, which can generate new low-coordinated gold atoms for intercalated gold NPs in the matrix.