Chromium complexes alkoxides

The complex [Cr(OCBu3)2 LiCl(THF)2], which was obtained according to Scheme 15,77 has a unique structure. The metal ion is three-coordinate, and the donor atoms outline a distorted T (22). It is not obvious how the reduction occurs because the BuLi is added in stoichiometric quantity to the alcohol and this solution then added to the CrCl3 suspension. Since LiCl is eliminated on the addition of hexane to give [Cr(OCBu3)2(THF)2], Scheme 15 may provide a simpler route to chromium(II) alkoxides than that from the very air- and moisture-sensitive complex [Cr N(SiMe3)2 2(THF)2]. 

The insertion of various isocyanates into chromium(lll) alkoxide M—O bonds has been reported.737 The complexes are prepared by refluxing the isocyanates with a suspension of the alkoxide in benzene. No structural data were given for the products. Unusual bimetallic alkoxides have recently been prepared738 by the reaction of Cr[Al(OPr )4]3 with alcohols and acetylacetone (166). A wide range of spectroscopic methods were used to study them. In general, the results were in accord with a monomeric formulation similar to (166) below Cr[Al(OMe)4]3 was grossly insoluble the small size of the methyl groups may permit extensive polymerization. 

Chromium activation allows a strategy for aryl ether synthesis in four stages (i) electrophilic chlorination (ii) chromium coordination (iii) alkoxide substitution for chloride and (iv) oxidative decomplexa-tion.33 The process is effective for the synthesis of 6-methoxytetrahydroquinolines and 5-methoxydihydroindole derivatives, for example. Chlorination of iV-acetyltetrahydroquinoline with SO2CI2 followed by deacetylation provides 6-chlorotetrahydroisoquinoline in 77% yield (equation 11).33 Complexation with [Cr(CO)6] in diglyme-cyclohexane at 125 °C for 53 h using the Strohmeier apparatus gave the chromium complex (13) in 85% yield, based on 40% recovery of starting material. The unre-... 

As with the analogous chromium complexes (420), anions (R ) such as hydride, cyanide, alkoxide, etc., add to cyclohexa- or cyclohepta-dienyliron complexes to form the sub.stituted species of structure (107) (299). Reduction of the cycloheptadienyliron cation with zinc dust... 

The molecular structure of a chromium(II) complex [Cr(OC-f-Bu3)2 LiCl(thf)2] (281) is shown in Fig. 45. The structure is noteworthy in several respects, being a rare example of three-coordinate chromium(II) alkoxide. The geometry at chromium with a wide 0(1)—Cr—0(2) angle of 157.2(2)° may be considered as T-shaped. All five atoms forming the core 0(1), 0(2), Cr, Cl, and Li are coplanar. The geometry around the lithium atom is a severely... 

The methods for the preparation of chromium(IV) alkoxides are well illustrated by Scheme 118, which shows the preparations of adamantoxo (1-adamantanol = adoH, 285) and bis((-butylmethoxo) complexes of Cr and Cr v 1319,1320 chromium(IV) complex Cr(l-... 

Fluorochemicals used in water- and oil-repellent finishes have been monomeric or polymeric. The first fluorochemical repellents used commercially were monomeric. In analogy to repellents with a hydrocarbon hydrophobe (see Section 12.1), perfluoroalkanoic acids, and phosphate esters have been applied as chromium complexes [121-123], zirconium or titanium alkoxides or salts [124-126] or have been converted to quaternary amines [127,128] ... 

Reaction of haloafene chromium tricarboriyl complexes [Cr(CO)3ArX] with alkoxide anions... 

Also non-heteroatom-substituted tungsten [440,443,444,451,452,461], molybdenum [437], and chromium carbene complexes [440] have been prepared by a-abstraction of alkoxide. 

Chromatography cyclophosphazenes, 21 46, 59 technetium, 11 48-49 Chromites, as spinel structures, 2 30 Chromium, see Tetranuclear d-block metal complexes, chromium acetylene complexes of, 4 104 alkoxides, 26 276-283 bimetallics, 26 328 dimeric cyclopentdienyl, 26 282-283 divalent complexes, 26 282 nitrosyls, 26 280-281 trivalent complexes, 26 276-280 adamantoxides, 26 320 di(/ >rt-butyl)methoxides, 26 321-325 electronic spectra, 26 277-279 isocyanate insertion, 26 280 substitution reactions, 26 278-279 [9]aneS, complexes, 35 11 atom... 

Pair-of-dimer effects, chromium, 43 287-289 Palladium alkoxides, 26 316 7t-allylic complexes of, 4 114-118 [9JaneS, complexes, 35 27-30 112-16]aneS4 complexes, 35 53-54 [l5]aneS, complexes, 35 59 (l8)aneS4 complexes, 35 66-68 associative ligand substitutions, 34 248 bimetallic tetrazadiene complexes, 30 57 binary carbide not reported, 11 209 bridging triazenide complex, structure, 30 10 carbonyl clusters, 30 133 carboxylates... 

Many polymeric chromium(III) complexes in this general class exist. For the general formula [Cr(L)(0PRR 0)2] , compounds have been prepared involving hydroxide, perfluorocarboxy-late, alkoxide, aryloxide and carboxylates.849,850... 

As indicated in Scheme 27, indoles may be alkylated by their acid-catalyzed reaction with alcohols. Similarly, r-butylation of pyrroles has been effected by the acid-catalyzed reaction with t- butyl acetate (B-77MI30502), and the diarylmethylation of 1-methylpyrrole from the acid-catalyzed reaction with the chromium trichloride complex of the diarylcarbinol has been described (78JA4124). The alkylation of indoles by alcohols in the presence of the aluminum alkoxide and Raney nickel appears to be efficient for the synthesis of 3-substituted indoles, but is less successful in the alkylation of 2-methylindole (79JHC501). The corresponding isopropylation of pyrrole produces 2,5-diisopropylpyrrole and 1-isopropylpyrrolidine, as the major products (79JHC501). 

The alcoholysis of derivatives that do not initially contain alkoxide ligands is of special importance for the preparation of alkoxide halids. It is also an efficient synthetic route to mixed-ligand complexes of chromium [538, 523, 1189] ... 

The most important feature of the chromium compounds, as well as of the other derivatives of early transition 3difference between the derivatives of different oxidation states (T able 12.18). The alkoxides of chromium (II and HI) are in the majority the insoluble and non-volatile polymers. The most important exclusion from this rule appears to be the volatile chelate Cr(OCMe2CH2OMe)3 complex, and in the future, possibly, the number of the representatives of this family will increase. The derivatives of chromium (IV and VI) are monomers highly soluble in organic solvents. The lack of volatility for Cr(VI) compounds in contrast to those of Cr(IV) is caused apparently by the high electronegativity of the central atom, leading to thermal destruction and not to evaporation. 

These same alkoxy compounds are also the primary products in the oxidation of alcohols with high oxidation state metal oxo complexes. In a typical process, the reaction of an alcohol with the chromium(vi) compound [HCr04] is shown in Fig. 9-16. The intermediate is often described as a chromate ester, but it is in all respects identical to the alkoxide complexes that we described earlier. 

Bis(adamantylimido) compounds, with monomeric chromium(VI) complexes, 5, 348 Bis(alkene) complexes conjugated, Rh complexes, 7, 214 mononuclear Ru and Os compounds, 6, 401 -02 in Ru and Os half-sandwich rj6-arenes, 6, 538 with tungsten carbonyls and isocyanides, 5, 685 Bis(u-alkenylcyclopentadienyl) complexes, with Ti(II), 4, 254 Bis(alkoxide) nitrogen-donor complexes, with Zr(IV), 4, 805 Bis(alkoxide) titanium alkynes, in cross-coupling, 4, 276 Bis(alkoxo) complexes, with bis-Cp Ti(IV), 4, 588 Bis[alkoxy(alkylamino)carbene]gold complexes, preparation, 2, 288... 

Heterometal alkoxide precursors, for ceramics, 12, 60-61 Heterometal chalcogenides, synthesis, 12, 62 Heterometal cubanes, as metal-organic precursor, 12, 39 Heterometallic alkenes, with platinum, 8, 639 Heterometallic alkynes, with platinum, models, 8, 650 Heterometallic clusters as heterogeneous catalyst precursors, 12, 767 in homogeneous catalysis, 12, 761 with Ni—M and Ni-C cr-bonded complexes, 8, 115 Heterometallic complexes with arene chromium carbonyls, 5, 259 bridged chromium isonitriles, 5, 274 with cyclopentadienyl hydride niobium moieties, 5, 72 with ruthenium—osmium, overview, 6, 1045—1116 with tungsten carbonyls, 5, 702 Heterometallic dimers, palladium complexes, 8, 210 Heterometallic iron-containing compounds cluster compounds, 6, 331 dinuclear compounds, 6, 319 overview, 6, 319-352... 

Ligand exchange reactions of monodentate amides, iodides, or alkoxide complexes with other amides, alkoxides as well as sulfides, and carbon ligands has been documented [23,25]. A rather unique reaction of a trimethylsilylmethyl ligand bound to a chromium nitride has been reported thus, reaction of tert-butyl isocyanide with 52 is reported to furnish 53 (Eq. (17)). 

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