Complexes of Boron

71 Complexation is believed to be involved in the first step of the hydrobo-ration of alkenes and alkynes rearrangement reactions of organoboranes most likely involve intermediates of a rc-complex type. However, the stability of such complexes is generally too low to allow their isolation (112). However, evidence for 7t-complex formation has been obtained by the device of anchoring the alkene function to the metal atom in question by means of a 

The structure of these complexes has been unambiguously proved by 11B-, 1H-, and, 3C-NMR spectroscopic and other analytical data. Spin 

The electron counting rules of Wade (S3), Williams (117), and Rudolph (118) can serve as a useful concept to explain structure and bonding in a variety of systems which at first glance are very different Zintl phases, boranes and carboranes, transition metal n complexes and carbonyl clusters, nonclassical carbocations, and also n complexes of main-group elements. According to 

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Organic ring systems are named by replacement nomenclature. Three- to ten-membered mono-cyclic ring systems containing uncharged boron atoms may be named by the specialist nomenclature for heterocyclic systems. Organic derivatives are named as outlined for substitutive nomenclature. The complexity of boron nomenclature precludes additional details the text by Rigaudy and Klesney should be consulted. 

Coumarone—Indene Kesins. These should be called polyindene resins (17) (see Hydrocarbon resins). They are derived from a close-cut fraction of a coke-oven naphtha free of tar acids and bases. This feedstock, distilling between 178 and 190°C and containing a minimum of 30% indene, is warmed to 35°C and polymeri2ed by a dding 0.7—0.8% of the phenol or acetic acid complex of boron trifluoride as catalyst. With the phenol complex, tar acids need not be completely removed and the yield is better. The reaction is exothermic and the temperature is kept below 120°C. When the reaction is complete, the catalyst is decomposed by using a hot concentrated solution of sodium carbonate. Unreacted naphtha is removed, first with Hve steam and then by vacuum distillation to leave an amber-colored resin. It is poured into trays, allowed to cool, and broken up for sale. 

Catalytic curing agents initiate resin homopolymerization, either cationic or anionic, as a consequence of using a Lewis acid or base in the curing process. The Lewis acid catalysts frequently employed are complexes of boron trifluoride with amines or ethers. 

COMPLEXATION OF BORON WITH THE REAGENTS OF BERYLLON HI GROUP... 

Complexes of boron trifluoride and amines such as monoethylamine are of interest because of the very long pot lives possible. The disadvantages of these complexes are their hygroscopic nature and the corrosive effects of BF3 liberated during cure. 

Organometallic Complexes of Boron, Silicon, and Phosphorus Analogues of Azoles... 

The first chapter covers organometallic complexes of boron, silicon, and phosphorus analogs of azoles. This chapter continues the series by A. P. Sadimenko (Fort Hare, South Africa) in which he is treating comprehensively organometallic complexes of heterocyclic compounds. So far, he has covered, in the volumes of AHC indicated, complexes of the following heterocycles ... 

Discussion. The method is based upon the complexation of boron as the bis(salicylato)borate(III) anion (A), (borodisalicylate), and the solvent extraction into chloroform of the ion-association complex formed with the ferroin. 

Anionic complexes of boron (boronates, borinates, etc.) have been introduced as convenient reagents in cross-coupling reactions of broad scope, particularly interesting for the transfer of alkynyl and primary alkyl residues, which cannot be accomplished using the standard protocols of the Suzuki-Miyaura reaction. Readily available Ph4BNa can be used as a convenient reagent for phenylation in place of the much more expensive PhB(OH)2, and all four phenyl groups can be utilized when the reaction is carried out with a phosphine-free catalyst in aqueous solutions.244... 

Figure 7.4. Crystal structure of the 1,1-bimetallic complex of boron and zirconium 22. Adapted by the authors.

These figures are based on published and submitted papers. Among others, carboranes, donor-acceptor complexes of boron, ring molecules with silicon, phosphoranes, sul-fones have received much attention. The lack of gas-phase structural studied of other classes of compounds, e. g., sulfuranes, is also noteworthy. The above elements were selected as most typical. Much interest is concentrated however on other elements as well, which may have been somewhat neglected in the past. The increase of the amount of structural data is also facilitating demand for further extension of the circle of compounds studied. 

Borane (BH3), boron trichloride (BCI3) and boron trifluoride (BF3) are known as Lewis acids, because boron has a vacant d orbital that accepts a pair of electrons from a donor species. For example, diethyl ether acts as a Lewis base towards BCI3 and forms a complex of boron trichloride. 

In practice the amine curing reactions are often accelerated by the addition of Lewis acids, especially amine complexes of boron trifluoride. Such materials can also initiate epoxide homopolymerisation in which chain propagation occurs through a carbocation ... 

Ethene does not polymerize by the cationic mechanism because it does not have sufficiently effective electron-donating groups to permit easy formation of the intermediate growing-chain cation. 2-Methylpropene has electron-donating alkyl groups and polymerizes much more easily than ethene by this type of mechanism. The usual catalysts for cationic polymerization of 2-methylpropene are sulfuric acid, hydrogen fluoride, or a complex of boron... 

Important aviation and motor alkylate gasoline processes are the jet-type sulfuric acid process, the Kellogg sulfuric acid autoref rigeration process, the UOP hydrofluoric acid process, and the Stratford effluent refrigeration process. Petrochemical alkylation includes various processes using as catalysts solid phosphoric acid, aluminum chloride, hydrofluoric acid, boron trifluoride, and phenol and ether complexes of boron trifluoride (1). 

A comparison of catalytic activity of the triphenyl phosphate complexes of boron trifluoride,boron trichloride and boron tribromide showed that comparable rates of polymerization were obtained using the chloride or bromide complexes. The fluoride complex gave about half the rate of the bromide or chloride comparable molecular weights were obtained in all three cases. 

Until recently, very little had been reported on the important area of metal borate complexation in aqueous solution. The effect of salts on the ionization of boric acid (358, 375) has been mentioned above, and subsequent research suggests that complexation of borate with, for example, calcium ions can account for the enhanced acidity of H O Literature on cationic complexes of boron was reviewed in 1970 (376). 

The significant interest that the prospects of transition metal complexes of boron received over the past few years is not only due to a hitherto unknown type of metal-boron linkage. Boryl complexes in particular became a highly rewarding target due to their potential application for the functionalisation of hydrocarbons. They are well known to be key intermediates in the metal catalysed hydroboration and related reactions,58 65... 

The strong tendency to filling up the sextet is seen from the formation of complexes of boron trifluoride with argon although neither of the two components possesses a dipole... 

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