Linear boron compounds

Often Lewis acids are added to the system as a cocatalyst. It could be envisaged that Lewis acids enhance the cationic nature of the nickel species and increase the rate of reductive elimination. Indeed, the Lewis acidity mainly determines the activity of the catalyst. It may influence the regioselectivity of the catalyst in such a way as to give more linear product, but this seems not to be the case. Lewis acids are particularly important in the addition of the second molecule of HCN to molecules 2 and 4. Stoichiometrically, Lewis acids (boron compounds, triethyl aluminium) accelerate reductive elimination of RCN (R=CH2Si(CH3)3) from palladium complexes P2Pd(R)(CN) (P2= e g. dppp) [7], This may involve complexation of the Lewis acid to the cyanide anion, thus decreasing the electron density at the metal and accelerating the reductive elimination. 

Linear polyethylene can further also be considered as polymethylene. Althoguh first prepared by the thermal decomposition of diazomethane,243 244 Meerwein should be credited to have prepared it by catalytic polymerization of diazomethane effected by boron compounds (esters, halides, alkyls)245-247 taking place with concomitant dediazotation ... 

Spectra of the linear anion FHF in the gas phase were obtained by diode laser spectroscopy P = 583.6539(13) cm, uj = 1286.0284(22) cm , and 1 3 = 1331.1502(7) cm . From the resulting rotational constants an equilibrium F-F intemuclear distance of 227.771(7) pm was calculated (Kawaguchi and Hirota, 1987). In the class of binary hydrides, boron compounds are especially interesting. A recent FTIR investigation revealed the out-of-plane vibration of unstable BH3 1140.8757(39) cm (Kawaguchi et al., 1987). These data confirm the results of a recent matrix study which showed an absorption at 1132 cnr for the same vibration (Kaldor and Porter, 1971). A detailed... 

Figure 2 shows that the dependences of the specific heats of A B compounds on their molecular weights are linear for all compounds except those of boron. The points representing boron compounds are located 2.6—2.8 cal mole deg to the left of the straight lines representing compounds with the same second component. 

The modifications of boron and boron compounds are characterized by nets or chains of boron atoms bound to each other by covalent bonds. The coordination number of the boron atoms varies between 1 and 7. The nets have the form of linked icosahedra, cuboctahedra, octahedra, graphite-like planes, or linear branched boron chains. Two-electron three-center bonds in boron-cornered triangles are the rule in the lattice structure. Boron can only form ions in combination with hydrogen (BH4 ) and oxygen (BOj ). The borates (boron oxide derivatives) form covalent nets like the silicates. They are often amorphous. 

Table 4.1-30 Linear thermal expansion coefficient a of boron compounds...

The emphasis in the approaches to boron nitride [10043-11 -5] BN, precursors has been concentrated on cycHc compounds. There have been recent reports of trimethylsilyl-substituted aminoboranes being evaluated as B—N precursors. These are linear borylamines containing up to four boron atoms. Compounds were also synthesized with free —NH2 groups amenable to condensation with either dihaloboranes or dihaloborazines (65) and offering suitable monomers for linear B—N polymer synthesis and borazine-ring-linking appHcations. 

Boron hydrides add to conjugated dienes, giving linear (12) and cyclic compounds (60). The cyclic products are the result of two 1,2-additions (60). 

Similar icosahedral Bu groups are found in other modifications of boron and also in the compound BUC , in which there are linear C groups.70... 

Arsenic does not combine directly with carbon, silicon or boron. The reaction with metals to form definite arsenides or alloys is described no pp. 57-78. The presence of small quantities of arsenic or of its compounds in certain catalysts has a poisoning effect. The first traces added to the catalyst have the greatest effect thus the activity of 0-35 g. of platinum was reduced linearly by the addition of arsenic up to 0-7 mg., this quantity reducing the catalytic activity to 45 per cent, of its original value the addition of 10 mg. of arsenic, however, depressed the activity only to 26 per cent, of the original value.3 Vanadium catalysts are poisoned by the presence of arsenic, although the action is slow arsenic pentoxide is formed.4... 

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