Boron aryls

Similarly, Peters studied the coordination of the DPB ligand 80 to CuCl.15 Along with the desired anionic complex 81, a small amount (< 15%) of the neutral DPB Cu(I) complex 82 was obtained, as the result of the cleavage of a boron-aryl bond (Scheme 47). In order to get complete spectroscopic data, an... 

Before their isolation in the form of the ammonia adduct, the complexes apparently exist as a-ArPtClj and CT ArPtCUfHjO). The complexes stabilized with an ammonia ligand have been characterized by X-ray diffraction [45a] and Pt NMR spectra [45b]. The same complexes can be prepared by the reaction of HiPtClf, with mercury, tin, lead or boron aryls [46]. 

Photorearrangements of boron aryls seem to require the presence of donor solvents (92) one reason for this may be that 1,2-migrations from boron to carbon involve bridging transition states (cf. 42). Clearly in trigonal tricoordinate boron, groups that must interact are farther apart than in tetrahedral boron complexes ... 

The photochemistry of aluminum aryls bears certain features in common with boron aryls the low reactivity of the monomeric triaryl-metallic, the formation of biaryls in tetracoordinate systems having proximate aryl groups and the formation of subvalent metallic products (22-24). Thus, when irradiated at 254 nm in ethyl ether solution, triphenylaluminum ethyl etherate underwent no formation of biphenyl or aluminum metal. On the other hand, the irradiation of triphenylaluminum (99) in benzene or toluene solution, in which the aluminum aryl is largely dimeric, led to the production of biphenyl (45%) and aluminum metal. When such a reaction mixture was filtered to remove the aluminum and the filtrate treated with D2O, hydrogen gas was evolved that consisted of >98% H—D. The biphenyl now isolated was 20% undeuterated and 80% monodeuterated further spectral comparisons showed that the deuteron was at the 2-position. These findings indicated the formation of an aluminum-hydride and an o-biphenylyl aluminum bond [Eq. (47)]. The source of the hydrogen in H—D was not the... 

Isopropoxy-4/f-l,3,2-benzodioxaborin (18) has been synthesized and found to react with a variety of hydroxy compounds to replace the isopropoxy group on boron. Aryl boric acids, RB(OH)2, reportedly condense with diols of the type HO(CH a)nOH to yield oligomeric rings (19) of varying size. The reaction of allenyl borates (20) with hydrogen bromide to yield alkenes and alkynes has been published. ... 

Mark, A. R Kenneth, W. 2002. Model compounds and monomers for phenylene ether carboranylene ketone (PECK) polymer synthesis Preparation and characterization of boron-arylated oriho-carboranes bearing carboxyphenyl, phenoxyphenyl or benzoylphenyl substituents. 7. Afafer Chem., 12 1301-6. 

Aryl Arsonic Acid Aryl Boronate Aryl Bromide... 

In cases where Noyori s reagent (see p. 102f.) and other enantioselective reducing agents are not successful, (+)- or (—)-chlorodiisopinocampheylborane (Ipc BCl) may help. This reagent reduces prochiral aryl and tert-alkyl ketones with exceptionally high enantiomeric excesses (J. Chandrasekharan, 1985 H.C. Brown, 1986). The initially formed boron moiety is usually removed hy precipitation with diethanolamine. Ipc2BCl has, for example, been applied to synthesize polymer-supported chiral epoxides with 90% e.e. from Merrifield resins (T. Antonsson, 1989). 

The Suzuki coupling of arylboronic acids and aryl halides has proven to be a useful method for preparing C-aryl indoles. The indole can be used either as the halide component or as the boronic acid. 6-Bromo and 7-bromoindolc were coupled with arylboronic acids using Pd(PPh3)4[5]. No protection of the indole NH was necessary. 4-Thallated indoles couple with aryl and vinyl boronic acides in the presence of Pd(OAc)j[6]. Stille coupling between an aryl stannane and a haloindole is another option (Entry 5, Table 14.3). 

Dimethylsulfoxide Acyl and aryl halides, boron compounds, bromomethane, nitrogen dioxide, magnesium perchlorate, periodic acid, silver difluoride, sodium hydride, sulfur trioxide... 

The Balz-Schiemaim reaction is a useful laboratory and industrial method for the preparation of fluoroaromatics. The water-insoluble diazonium fluoroborate is filtered, dried, and thermally decomposed to give the aryl fluoride, nitrogen, and boron trifluoride (28—30). 

The general formula for boric acid esters is B(OR)2. The lower molecular weight esters such as methyl, ethyl, and phenyl are most commonly referred to as methyl borate [121 -43-7] ethyl borate [130-46-9J, and phenyl borate [1095-03-0] respectively. Some of the most common boric acid esters used in industrial appHcations are Hsted in Table 1. The nomenclature in the boric acid ester series can be confusing. The lUPAC committee on boron chemistry has suggested using trialkoxy- and triaryloxyboranes (5) for compounds usually referred to as boric acid esters, trialkyl (or aryl) borates, trialkyl (or aryl) orthoborates, alkyl (or aryl) borates, alkyl (or aryl) orthoborates, and in the older Hterature as boron alkoxides and aryloxides. CycHc boric acid esters, which are trimeric derivatives of metaboric acid (HBO2), are known as boroxines (1). 

The triaLkoxy(aryloxy)boranes are typically monomeric, soluble in most organic solvents, and dissolve in water with hydrolysis to form boric acid and the corresponding alcohol and phenol. Although the rate of hydrolysis is usually very fast, it is dependent on the bulk of the alkyl or aryl substituent groups bonded to the boron atom. Secondary and tertiary alkyl esters are generally more stable than the primary alkyl esters. The boron atom in these compounds is in a trigonal coplanar state with bond hybridization. A vacantp orbital exists along the threefold axis perpendicular to the BO plane. 

Boron Bromide. Approximately 30% of BBr produced in the United States is consumed in the manufacture of proprietory pharmaceuticals (qv) (7). BBr is used in the manufacture of isotopicaHy enriched crystalline boron, as a Etiedel-Crafts catalyst in various polymerization, alkylation, and acylation reactions, and in semiconductor doping and etching. Examples of use of BBr as a catalyst include copolymerization of butadiene with olefins (112) polymerization of ethylene and propylene (113), and A/-vinylcarbazole (114) in hydroboration reactions and in tritium labeling of steroids and aryl rings (5). 

Aromatic Aldehydes. Carbon monoxide reacts with aromatic hydrocarbons or aryl haHdes to yield aromatic aldehydes (see Aldehydes). The reaction of equation 24 proceeds with yields of 89% when carried out at 273 K and 0.4 MPa (4 atm) using a boron trifluoride—hydrogen fluoride catalyst (72), whereas conversion of aryl haHdes to aldehydes in 84% yield by reaction with CO + H2 requires conditions of 423 K and 7 MPa (70 atm) with a homogeneous palladium catalyst (73) and also produces HCl. 

Boron tribromide is reported to be more effective than iodotrimethylsilane for cleaving aryl methyl ethers. ... 

Selective cleavage of an aiyl methylenedioxy group, or an aryl methyl ether, by boron trichloride has been investigated. 

Thakar and Subba Rao showed that reductions with diborane give the same result regardless of whether diborane is generated externally or produced internally by the action of NaBH4 and boron trifluoride or aluminum chloride. They found that alicyclic or dialkyl ketones are not reduced beyond the alcohol stage even under drastic conditions however, diaryl ketones are hydrogenolyzed under normal conditions, while aryl ketones or a,i5-unsatu-rated ketones are hydrogenolyzed, in part, under drastic conditions. 

The aryl tin compounds are better substrates for fluorination because they give high yields of fliiorinated aromatics and they may be fluorinated with acetyl hypofluorite, cesium fluoroxysulfate, or fluorine [52, 54 (equation 28). Aryl boronic esters react with cesium fluoroxysulfate to produce fluoroaromatics [55] (equation 29). 

Boron-nitrogen heterocycles [4,5-diethyl-2,2,3-trimethyl-l-(<9-tnfluoro-methyl)phenyl-2,5-dihydro-l(-)-],2,5-azasilaboroles and -azastannaboroles] are formed in good yields The products demonstrate atropoisomensm due to the hmdered rotation about the N-aryl bond [113] (equation 88)... 

Either an aryl methyl ether or a methylenedioxy group can be cleaved with boron trichloride under various conditions. ... 

Boronic acids readily dehydrate at moderate temperatures (or over P4O10 at room temperature) to give trimeric cyclic anhydrides known as trialkyl(aryl)boroxines ... 

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