Chromium hexacarbonyl tricarbonyl

Optically active (—)-(8R)-methylcanadine was stereoselectively synthesized through selective monocomplexation of (—)-canadine (26) to chromium tricarbonyl (240). Heating of chromium hexacarbonyl with 26 effected regioselective complexation of the D ring to give the diastereomeric complexes, which were treated with n-butyllithium and trimethylsilyl chloride to give the 11-trimethylsilyl derivative 475 (Scheme 97). Methylation of this complex with methyl iodide gave stereoselectively the 8-methyl derivative 476 by preferential alkylation from the opposite face to the bulky chromium... 

Many complexes of conjugated ketones are also known, such as the iron tricarbonyl complexes of substituted cyclopentadienones 30), although reaction with chromium hexacarbonyl occurs only if phenyl substituents are available for tt complexing 31). A common difficulty of preparing complexes of heterocyclics is the ability of the heteroatom to form o bonds with the metal. 

The synthesis of 2 -methylspiro[cyclohexane-l,3 -indole] chromium tricarbonyl 1179 was carried out by treatment of 3/7-indole 1178 with chromium hexacarbonyl in THF/dioxane (1 5), under rigorous dryness, argon atmosphere and sunlight coverture, in a Strohmeier-type system, in good yield (Scheme 227) <1996JOM(522)231>. Solvent mixture was very important for the complex formation, and when Bu"20/THF (9 1) was used, a brown oil was obtained which contained the free 3/7-indole 1178 and the C=N reduction product, while complex 1179 was not detected. 

A number of substituted benzenes, naphthalenes, indans, pyridmes, and indoles form arene(tricarbonyl)chromium complexes upon thermolysis under an inert atmosphere, usually in a high boiling ether, or by irradiation of the arenes in the presence of chromium hexacarbonyl. The complexes are relatively air-stable and can usually be stored for long periods in the absence of light. Somewhat milder conditions can be used by transfer of the chromium tricarbonyl group from preformed naphthalene(tricarbonyl)chromium, tris(L)tricarbonyl chromium (L = acetonitrile, ammonia, pyridine), or tricarbonyl( -l-methylpyrrole)chromium. Enan-tiomerically pure arene(tricarbonyl)chromium complexes having two different substituents, either ortho or meta can be prepared conveniently by classical resolution of racemic... 

Complexation of dihydronaphthalene with chromium tricarbonyl facilitates the attack of a nucleophilic amine and stereoselectively directs the protonation "anti" to the metal atom. (+)-(l S,2 R)-, 2-Dihydro-7-methoxy-1,4-dimethyl-1 - 2 -[methyl(trifiuoroacetyl)amino]propyl -naphthalene [(+)-7] was treated with chromium hexacarbonyl to give a mixture of a- and /(-chromium tricarbonyl complexes in a 10 1 ratio ( H NMR). The complexes were separated and the a-isomer cyclized by base treatment and sonication. Dccomplexation gave the ben-zomorphan tricycle 8 in low yield [40%, based on recovered (+)-7]18. The trifluoroacetyl protection of the amino group was necessary to achieve both stereoselective complexation with chromium tricarbonyl and successful cyclization. 

Yet another major advance in arene-metal chemistry was made in 1957 by Fischer and Ofele 95) y who found that a sealed tube reaction involving chromium hexacarbonyl, bis(benzene)chromium, and benzene produced the half-sandwich compound benzene-chromium tricarbonyl (XXVII). 

Cuadrado and co-workers have reported the synthesis of chromium-containing organosilicon dendrimers.334 These dendrimers, 282, have chromium tricarbonyl units incorporated pendent to the terminal aromatic rings.334 Synthesized via the reaction of the silane dendrimer precursor with chromium hexacarbonyl, complete complexation was not possible due to steric hindrance at higher generations. Electrochemical studies showed that the oxidation of the chromium atoms occurred reversibly in the absence of a nucleophilic species and that the chromium tricarbonyl units behaved as isolated redox centers. 

Co(NH3)6](N03)3 Hexammineco-balt(III) nitrate, 2 218 [Co(NH3)6]2(C204)3-4H20 Hexam-minecobalt(III) oxalate, 2 220 CoNO(CO)3 Cobalt nitrosyl tricarbonyl, 2 238, 239 Co2(S04)3-18H20 Cobalt (III) sulfate 18-hydrate, 5 181 Cr(CN)sK3 Potassium hexacyano-chromate(III), 2 203 Cr (CO) t Chromium hexacarbonyl, 3 156... 

Substitution m- to the methoxy group, established earlier for arene/chromium tricarbonyl systems (ref. 119), has been used to prepare the 1-(2-dithianyl) derivative of estrone (ref.120). A solution of 2-lithio-1,3-dithian in tetrahydrofuran at -78°C treated with the chromium tricarbonyl complex of HO-protected estrol (from the protected steroid with chromium hexacarbonyl by refluxing in... 

The finding (ref. 126) that methoxyarenes complexed with chromium hexacarbonyl, thus forming arene chromium tricarbonyls, then undergo 3- rather than the anticipated 2-/4- substitution with certain nucleophiles has a potential application in the synthesis of cardanols and cardols. The method has a number of variants (refs. 127, 128) and is shown in the following scheme. Salicylates formed two isomers. 

Table 9. Calculated and experimental geometrical parameters of di-benzene-chromium, chromium-benzene-tricarbonyl, and chromium-hexacarbonyl...

Chromium, (n benzene) tricarbonyl-. See (Benzene) tricarbonylchromium Chromium hexacarbonyl. See Chromium carbonyl... 

Chromium hexacarbonyl heated at a bath temp, of 165° with benzene-diglyme (1 1) in an open system with reversed steam flow (s. original) whereby the sublimed hexacarbonyl is continuously returned by the condensed solvent benzenechromium tricarbonyl. Y 93-97%. F. e., also with cycloheptatriene, s. W. Strohmeier, B. 94, 2490 (1961). 

Synthesis of tricarbonyl[t -(methylsulfenyl)benzene]chromium(0) (Structure 2). Complexation of (methylsuifenyl)benzene (Structure 1) by thermolysis with chromium hexacarbonyl (Scheme 6.5)... 

Synthesis of tricarbonyl[/ /,/V-diniethyl-a(f )-phenylethylamine] chromium(O) (Structure 12). Complexation of chiral complex 11 by thermolysis with chromium hexacarbonyl... 

Both arene and cyclopentadienyl 7i-complexes can undergo redistribution reactions. These reactions involve the exchange of ligands between two species possessing the same or different metal. For example, the reaction of dibenzenechromium with chromium hexacarbonyl provides a method for the preparation of benzenechromium tricarbonyl (2-6). A second example of a... 

Chromium hexacarbonyl generally reacts with arenes and is stabilized as the tricarbonyl complex. Hexamethyl bicycio [2.2.0] hexa-2,5-diene chromiumtetracarbonyl is an unusual example of a stabilized chromiumtetracarbonyl. The x-ray pattern reveals a C2 symmetry (Fig. 5-13). This particular bicycio [2.2.0] diene system may effect the stabilization of the electron configuration of the complex. 

Chromium hexacarbonyl offers a highly regioselective method for the isomerization of cisoid 1,3-dienes to transoid dienes (eq 6). (Naphthalene)chromium tricarbonyl catalyzes isomerization of silyloxymethylbutadiene derivatives to silyl dienol ethers in quantitative yields via a U-shaped pentadienyl intermediate (eq7). ... 

Cyclopentadiene iron tricarbonyl has been prepared and decomposes thermally to the binuclear carbonyl [a -C5H5Fe(CO)2]2 [26o]. The binuclear iron complex may further react with cyclopentadiene or thermally decompose ( 200°) [27, 28] to give ferrocene. Monosubstituted ferrocenes may be prepared by the former reaction [27]. Chromium hexacarbonyl and cyclopentadiene at 280-350° react to give chromocene [29] the reaction is reversible since treatment of chromocene with carbon monoxide under pressure affords chromium hexacarbonyl, together with intermediate products such as [jr-CpCr(CO)3]2, [jr-Cp2Cr][3r-CpCr(CO)3] and, when hydrogen is also present, the cyclopentenyl complex jr-CsH5CrC5H7(CO)2, 4.1, is formed [30, 31, 32]. 

Refluxing thiophene with chromium hexacarbonyl gives the orange, diamagnetic, crystalline complex, C4H4SCr(CO)3 [104]. The complex is essentially isomorphous with benzenechromium tricarbonyl [105]. 

Some further examples of stereoselective deprotonation/alkylation reactions of tricarbonyl-chromium complexed (V-methyl tetrahydroisoquinolines have been reported27. Starting with the enantiomerically pure (35)-methyl tetrahydroisoquinoline reaction with hexacarbonyl-chromium led to a mixture of endo- (40%) and exo- (60%) complexes, which were deprotonated with butyllithium and subsequently methylated with iodomethane. In this way methylation occurred firstly at the 4- and secondly at the 1-position. In all cases, the methyl group entered anti to the chromium complexed face. After separation of the alkylated complexes by chromatography and oxidative decomplexation, the enantiomerically pure diastereomers (—)-(l 5,35,47 )-and ( + )-(17 ,35,45)-1,2,3,4-tetrahydro-l,2,3,4-tetramethylisoquinolme were obtained, benzylic amines such as tetrahydroisoquinoline to 2-amino-4,5-dihydrooxazoles. Deprotona... 

Density functional theory studies arene chromium tricarbonyls, 5, 255 beryllium monocyclopentadienyls, 2, 75 chromium carbonyls, 5, 228 in computational chemistry, 1, 663 Cp-amido titanium complexes, 4, 464—465 diiron carbonyl complexes, 6, 222 manganese carbonyls, 5, 763 molybdenum hexacarbonyl, 5, 392 and multiconfiguration techniques, 1, 649 neutral, cationic, anionic chromium carbonyls, 5, 203-204 nickel rj2-alkene complexes, 8, 134—135 palladium NHC complexes, 8, 234 Deoxygenative coupling, carbonyls to olefins, 11, 40 (+)-4,5-Deoxyneodolabelline, via ring-closing diene metathesis, 11, 219... 

Richard followed the course of the reactions of Cr(CO)6 and Mo(CO)6 with hexamethylborazine by UV-vis spectroscopy but although he observed that the intensity of the absorption maximum of the hexacarbonyls at around 290 nm decreased and a new band at around 350 nm appeared, he was unable to identify the new product. Experiments with other starting materials such as norborna-diene chromium and molybdenum tetracarbonyl or tris(aniline) molybdenum tricarbonyl which readily react with arenes by ligand exchange, also failed. The key to success was to use tris(acetonitrile) chromium tricarbonyl as the precursor, which in dioxan under reduced pressure afforded the desired hexamethylborazine chromium tricarbonyl as a stable crystalline solid in 90% yield. This was the breakthrough and, after we had communicated the synthesis and spectroscopic data of the complex in the January issue 1967 of Angewandte Chemie, Richard finished his work and defended his Ph.D. thesis in June 1967. Six months before, in December 1966,1 defended my Habilitation thesis in front of the faculty and became Privatdozent (lecturer) on the 1st of January 1967. 

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