Boronic sources

Hydrocarbon Oxidation. The oxidation of hydrocarbons (qv) and hydrocarbon derivatives can be significantly altered by boron compounds. Several large-scale commercial processes, such as the oxidation of cyclohexane to a cyclohexanol—cyclohexanone mixture in nylon manufacture, are based on boron compounds (see Cylcohexanoland cyclohexanone Eibers, polyamide). A number of patents have been issued on the use of borate esters and boroxines in hydrocarbon oxidation reactions, but commercial processes apparently use boric acid as the preferred boron source. The Hterature in this field has been covered through 1967 (47). Since that time the Hterature consists of foreign patents, but no significant appHcations have been reported for borate esters. 

A demonstration of the feasibility of a reaction is illustrated in the following example regarding the formation of titanium diboride using either diborane or boron trichloride as a boron source, as shown in the following reactions ... 

TiB2 can also be obtained using diborane as a boron source as... 

Low-temperature deposition is possible from diborane as a boron sourced ll l... 

MOCVD has also been used with triethyl boron as the boron source in a hydrogen and argon atmosphere ]... 

The Group IVa borides can also be deposited with diborane as a boron source in a pressure range ofafewTorrto 1 atm as follows ... 

Thermodynamic considerations postulate BjH to be a better boron source than BCl, in CVD of TaB2Using reaction (f) at < 1200 K deposits with extremely small crystal sizes are obtained on graphite substrates . They contain amorphous B at deposition temperatures < 873 K and are substoichiometric in B above this T. Carbon from the substrate substitutes for B, thereby stabilizing the diboride structure at high deposition T... 

Boron enolates are often used for aldol reactions. Boron enolates are usually prepared from the corresponding carbonyl compounds, tertiary amine, and a boron source (e.g., dibutylboron triflates). The aldol reactions proceed via a six-membered transition state to give high diastereo-selectivity which depends upon the geometry of the boron enolates. 

In boron enolate-mediated aldol reactions, stoichiometric amounts of boron reagents are necessary. However, it has been reported that only a catalytic amount of a boron source is sufficient for boron enolate-mediated aldol reactions in water (Scheme 65).302 It should be noted that even water-sensitive boron enolates can be successfully employed in water. 

Conducting n-Si(lOO) with 0.018 fi cm (Ferrotec Silicon Corp.). Diamond powder (grain size M).5 pm, Element Six Ltd.). High-purity H2 gas (99.999%). B203 (99.98%, Sigma-Aldrich) as boron source. Acetone and methanol (Wako Pure Chemical) as carbon source. 

Substrate Carbon source Boron source Excitation source Microwave power Substrate temperature Total pressure C/H ratio Deposition time... 

Specific conductive silicon substrates have to be carefully prepared before use. For the diamond-deposition process, substrates have to be cleaned, seeded with diamond nanocrystalline seeds at high surface density, and then coated with a grown thick diamond film (from less than 1 pm up to several p,m) by hot filament chemical vapor deposition (HF-CVD). At Adamant, deposition processes are performed automatically in programmable controlled process units, which allow growing diamond on scale up to 0.5 m2. The process is performed under low pressure (1 < 0.1 bar) and high temperature (filament temperature 2,500°C and substrate temperature 800-1,000°C) with a gas mixture composed of CH4, H2 (CH4/H2 ratio <1%), and a boron source (typically trimethyl boron). 

The construction of a borole ring that is part of a metal complex from zirconium-coordinated 1,3-dienes and tris(pentafluorophenyl)borane has been recently introduced. Tris(pentafluoro-phenyl)borane is widely used as an activator of metallocene-based polymerization catalysts because of its resistance to aryl-transfer reactions, it acts as the boron source. The reaction utilizes the zwitterionic 14-electron bis(allyl)zirconium complexes 72 and 73 which are converted to the corresponding complexes 74 and 75 via activation of one of the C-H bonds of the B-CH2 moiety... 

Compounds 1, 2, 3, 4 and 5 were synthesized hydrothermally or solvothermally using H3BO3 as the boron source. All reagents were of analytical grade. The syntheses were carried out in 20 mL Teflon-lined stainless steel vessels under autogeneous pressure with a filling capacity of approximately 70%. The sole resulting crystals were collected by filtration, washed with distilled water for 1, 2 and 3 but with ethanol for 4 and 5, and dried in air at ambient temperature. 

This procednre is the method of choice for the synthesis of boronic acids. Especially good selectivity is observed with B(0 Pr)3 and XB(NR2)2 (X = Cl, Br) as the boron source. The method may also be applied to the synthesis of many diorgano-and triorganoboranes. Some recent examples of the formation of organoboranes from organolithium and organopotassium reagents, respectively, are shown in equations (3-6). ... 

Boron-doped diamond (BDD) thin films were synthesized at CSEM (Neuchatel, Switzerland) by the hot filament chemical vapor deposition technique (HF CVD) on p-type, low-resistivity (l-3mQcm), single-crystal, silicon wafers (Siltronix). The temperature of the filament was between 2440 and 2560 °C and that of the substrate was monitored at 830 °C. The reactive gas was a mixture of 1% methane in hydrogen, containing trimethylboron as a boron source (1-3 ppm, with respect to H2). The reaction chamber was supplied with the gas mixture at a flow rate of 51 min giving a growth rate of 0.24 pm h for the diamond layer. The obtained diamond film has a thickness of about 1 pm ( 10%) and a resistivity of 15mQcm ( 30%). This HF CVD process produces columnar, random textured, polycrystalline films [9]. 

An alternative boron source is diborane, which can be used for processing at reduced pressure ( 1 torr) and a much lower temperature (300-400°C) ... 

Boron halides, hydrides, arylboronic acids and corresponding esters can be employed as boron sources, when specific R on the boron atoms are requested. For example, the boron-substituted RTpx (RB(pzx)3) may be synthesized according to the following reaction (1.1) by using pyrazolate ion and excess pyrazole ... 

Diboranes(4) and dihaloboranes are the traditional boron source for the synthesis of homodinudear bridging borylene compounds. Reaction of K[( 5-C5H4Me)Mn(CO)2H] with a variety of B2R2CI2 derivatives afforded the homodimetallic manganese compounds [(/x-BX) ( 5-C5R5)Mn(CO)2 2] (R = NR 2, fBu) (23a,b-26a,b), which represent the first series of structurally authenticated borylene complexes (Scheme 10) [45-47]. 

A vertical cold wall CVD furnace was employed to prepare the B-C coatings. Boron trichloride (BCl3>99.99 vol.% and iron<10 ppm) was used as the boron source. The carbon source was provided by the methane (CH4>99.95 vol.%) and propylene (CjH6>99.95 vol.%) gas. Hydrogen (H2>99.999 vol.%) was used as a dilution gas of BCb.The deposition parameters are listed in Table 1. T-300 carbon fiber from Toray, Japan was employed as substrate. 

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