Chromium complexes borates

Sodium triacetoxyborohydride, 283 Tetrabutylammonium iodide-Boron trifluoride etherate, 287 Tributylborane, 325 Tributyl borate, 326 Triethylborane, 33, 292 Trimethyl borate, 218 Zinc borohydride, 167 Chromium Compounds Arene(tricarbonyl)chromium complexes, 19... 

Bis(phosphoranimine) ligands, chromium complexes, 5, 359 Bis(pinacolato)diboranes activated alkene additions, 10, 731—732 for alkyl group functionalization, 10, 110 alkyne additions, 10, 728 allene additions, 10, 730 carbenoid additions, 10, 733 diazoalkane additions, 10, 733 imine additions, 10, 733 methylenecyclopropane additions, 10, 733 Bisporphyrins, in organometallic synthesis, 1, 71 Bis(pyrazol-l-yl)borane acetyl complexes, with iron, 6, 88 Bis(pyrazolyl)borates, in platinum(II) complexes, 8, 503 Bispyrazolyl-methane rhodium complex, preparation, 7, 185 Bis(pyrazolyl)methanes, in platinum(II) complexes, 8, 503 Bis(3-pyrazolyl)nickel complexes, preparation, 8, 80-81 Bis(2-pyridyl)amines... 

CHROMIUM ALKYLS WITH NITROGEN- AND OXYGEN-LIGANDS 3.1. Tris(pyrazolyl)borate complexes... 

In an attempt to change the electronics of the chromium atom, we are replacing the carbon based cyclopentadienyl ring with ligands containing harder donor atoms. For example, we have employed the tris(pyrazolyl)borate moiety, an isoclectronic replacement for Cp featuring tridentate N-coordination.[9] Figure 2 shows the molecular structure of Tp SU Cr-Ph, a representative Cr° alkyl. It will be noted, that this complex is mononuclear, due to the steric protection of the extremely bulky tris(pyrazolyl)borate. 

The obvious next step was oxidation of the tris(pyrazolyl)borate chromium alkyls to the catalytically active -t-III oxidation state. However, cyclic voltammetry experiments did not show a reversible oxidation in any case, and all attempts to prepare complexes of the type [Tp Bu,Meci-R]+X by chemical oxidation failed, yielding [Tp Cr(THF)n] X instekl. TTie reasons for the apparent instability of TpCr alkyls are not clear, and we arc continuing our efforts to isolate related compounds,... 

Qin K (2003) Dioxygen Chemistry of Hydrotris(pyrazolyl)borate Chromium(ll) Complexes. PhD Thesis, University of Delaware... 

We believe that catalysis occurs by formation of a complex between acetaldehyde, peracetic acid, and the metal ion in the 3+ oxidation state. The metal ion could be acting as a superacid as for peracetic acid decomposition, although oxidation-reduction reactions within the complex cannot be ruled out. Here again, we have found a disturbing lack of catalytic activity of other trivalent metals (aluminum, iron, and chromium). Simple acid catalysis is not as effective as proved when using p-toluenesulfonic acid and acetyl borate. This indicates that at least more than one coordination position is needed to obtain a complex of the proper configuration. 

While the first transition metal carbene complex was reported in 1964134, the first cyclopropylcarbene complex salt [(CO)5Cr=C(chromium hexacarbonyl, followed by tetramethylammonium bromide135. Subsequent reaction with trimethyloxonium fluoro-borate gave methoxycarbene complex (CO)5Cr=C(OMe)(c-Pr) (equation 62)136. 

Four main types of antioxidants are commonly used in polypropylene stabilizer systems although many other types of chemical compounds have been suggested. These types include hindered phenolics, thiodi-propionate esters, aryl phosphites, and ultraviolet absorbers such as the hydroxybenzophenones and benzotriazoles. Other chemicals which have been reported include aromatic amines such as p-phenylenediamine, hydrocarbon borates, aminophenols, Zn and other metal dithiocarbamates, thiophosphates, and thiophosphites, mercaptals, chromium salt complexes, tin-sulfur compounds, triazoles, silicone polymers, carbon black, nickel phenolates, thiurams, oxamides, metal stearates, Cu, Zn, Cd, and Pb salts of benzimidazoles, succinic acid anhydride, and others. The polymeric phenolic phosphites described here are another type. 

Apart from the di- and oligoolefm iron tricarbonyl complexes, which nowadays are frequently used in organic synthesis [71, 72], the chemistry of the readily accessible cyclohepatriene chromium and molybdenum tricarbonyls 2 and 3 was the focus of intense research efforts as well. Only a few months after the synthesis of 2 and 3 was published [58,59], both Hyp Dauben and Peter Pauson reported that these compounds react with triphenylmethyl tetrafluoro-borate in methylene chloride to give the tropylium complexes 4 and 5 in excellent yield (Scheme 7.1) [73, 74]. Later this method of hydride abstraction was also used for the preparation of the tropylium cation itself and subsequently led to the generation of several cationic rc-complexes of iron, manganese and cobalt [71, 72], The reactions of the cations of 4 and 5 with nucleophilic... 

Trivalent chromium pigments include chromium oxide (Cr203) and hydrated chromium oxide (Cr203 xH20). Chromium oxide is prepared by calcination, either by reduction of sodium bichromate (Na2Cr207) with sulfur or carbon at 750-900°C or by reduction of sodium bichromate with ammonium chloride or ammonium sulfate at 700°C. Hydrated chromium oxide is manufactured by hydrolyzing a complex chromium borate, which in turn has been produced by heating sodium bichromate with boric acid in a furnace. 

Top row the three components of the Yandulov-Schrock cycle for catalytic dinitrogen reduction. Left the catalyst with the substrate Nj coordinated to Mo (Ar refers to the aryl substituent drawn in detail for one of the nitrogens). Centre the reductant bis(pentamethylcyclopentadienyl)chromium, CpjCr. Right the proton source 2,6-lutidinium borate. Bottom row vanadium complexes with intermediates of nitrogen reduction activated dinitrogen or diazenido(2—) (46a), imide (46b) and ammonia (46c). 

Speciation of chromium (histidine/acetic acid acetate buffer/EDTA °), mercury (borate/MeOH), tin (pyridine/CTAB), lead (SDS/p-CD), arsenic (borate, phosphate or phosphate/borate, " phosphate/TTAB, phosphate andphosphate/TTAB ), sulfur (phosphate/TTAB/ACN), and selenium (histidine/acetic acid, SDS/p-CD ) by CE methods have been reported. Other examples include the analysis of beryllium (as an acetylacetone complex) in digested airborne dust and the determination of Fe(II)-, Cu(I)-, Ni(ll)-, Pd(II)-, and Pt(II)-cyano complexes and nitrate from leaching solutions of automobile catalytic converters. ... 

With allowances for the actual metal content of zirconium (a small correction is also necessary for the hafnium content of about 2 /2%) and postulation of barium zirconate formation (see Table 27), reasonable accord between calculated and measured caloric output is established. However, the situation is more complex with boron mixtures where one encounters increase of heat output with increase of the percentage of boron in the mixtures much beyond the amounts of Equation (la). Thus, even with the reasonable assumption of secondary barium borate formation, the stoichiometry and heat output of the mixtures with more than about 10% of technical boron theoretical 8%) is obscure. Chromium boride formation may be a fector. 

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