Chromium carbonyl arenes

Arene Chromium Carbonyl Arenes are generally protected with the Cr(CO)3 group, but as this complexation leads to a number of other important changes in the chemical properties of the arene, in particular making it much more susceptible to nucleophilic attack, we will study this reagent in detail in Section 14.7. 

Scheme 1 Use of a chromium carbonyl arene complex as a linker...

In equation 1, the Grignard reagent, C H MgBr, plays a dual role as reducing agent and the source of the arene compound (see Grignard reaction). The Cr(CO)g is recovered from an apparent phenyl chromium intermediate by the addition of water (19,20). Other routes to chromium hexacarbonyl are possible, and an excellent summary of chromium carbonyl and derivatives can be found in reference 2. The only access to the less stable Cr(—II) and Cr(—I) oxidation states is by reduction of Cr(CO)g. 

Fig. 12. Polystyrene anchored arene-chromium carbonyl complex...

The carbonyl complexes listed in Table V are of two types tricarbonyl-chromium rj6-arene 77-complexes, and pentacarbonyltungsten <7-pyridine complexes, with both complex types having relatively low y. Nonlinearities increase on arene or pyridine 77-system lengthening, and on proceeding from acceptor to donor substituent on the tricarbonylchromium-coordinated arene ring. Relative magnitudes and trends thus mirror those observed with quadratic nonlinearities of these complexes (see Ref. 1)... 

The deoxygenation of arene oxides have also been achieved by using chromium carbonyl complexes. The aromatic hydrocarbons produced are partially converted to chromium complexes. Formation of 246 in methanol suggests Rh-catalyzed solvolysis, resulting in nucleophilic addition of meth-... 

Arasabenzene, with chromium, 5, 339 Arcyriacyanin A, via Heck couplings, 11, 320 Arduengo-type carbenes with titanium(IV), 4, 366 with vanadium, 5, 10 (Arene(chromium carbonyls analytical applications, 5, 261 benzyl cation stabilization, 5, 245 biomedical applications, 5, 260 chiral, as asymmetric catalysis ligands, 5, 241 chromatographic separation, 5, 239 cine and tele nucleophilic substitutions, 5, 236 kinetic and mechanistic studies, 5, 257 liquid crystalline behaviour, 5, 262 lithiations and electrophile reactions, 5, 236 as main polymer chain unit, 5, 251 mass spectroscopic studies, 5, 256 miscellaneous compounds, 5, 258 NMR studies, 5, 255 palladium coupling, 5, 239 polymer-bound complexes, 5, 250 spectroscopic studies, 5, 256 X-ray data analysis, 5, 257... 

Carbonyl complexes with actinides, 4, 192 (7 5-acyclic)Re(CO)3 complexes, 5, 919 allylation, 10, 663 with allylic tins, 9, 354 into 7 3-allyl palladium complexes, 8, 364 arene chromium carbonyls... 

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... 

Electric arcs, in metal vapor synthesis, 1, 224 Electric-field-induced second harmonic generation Group 8 metallocenes, 12, 109 for hyperpolarizability measurement, 12, 107 Electrochemical cell assembly, in cyclic voltammetry, 1, 283 Electrochemical irreversibility, in cyclic voltammetry, 1, 282 Electrochemical oxidation, arene chromium carbonyls, 5, 258 Electrochemical properties, polyferrocenylsilanes, 12, 332 Electrochemical reduction, bis-Cp Zr(III) and (IV) compounds, 4, 745 Electrochemical sensors biomolecule—ferrocene conjugates... 

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... 

If the issue of n-complex formation with PMDA-ODA polyimide seems confused, the results of model compound studies have, in places, exacerbated the problem. Several research groups have turned to reactions of formally zerovalent chromium to model the chemistry of PMDA-ODA/Cr (58e, 60. 62) The studies assume that the chemistry of atomic Cr and of certain chromium carbonyl complexes is coextensive. Since atomic chromium has not been available as a benchtop reagent, popular sources of formally zerovalent chromium, disguised as Cr(CO)6 and (CH3CN)3Cr(CO)3, have been used. These compounds readily form (arene)Cr(CO)3 complexes (71). 

The chromium carbonyl linkers 1.40 (98) and 1.41 (99) were prepared from commercial triphenylphospine resin and respectively from pre-formed p-arene chromium carbenes and Fischer chromium amino carbenes. Their SP elaboration is followed by cleavage with pyridine at reflux for 2 h (1.40) and with iodine in DCM for 1 h at rt (1.41) both linkers produce the desired compounds in good yields. A similar cobalt carbonyl linker 1.42 (100) was prepared as a mixmre of mono- (1.42a) and bis- (1.42b) phosphine complex, either from pre-formed alkyne complexes on triphenylphosphine resin or by direct alkyne loading on the bisphosphine cobalt complex traceless cleavage was obtained after SP transformations by aerial oxidation (DCM, O2, hp, 72 h, rt) and modified alkynes were released with good yields and... 

Hexacarbonylchromium(O) is readily attacked by chlorine giving CrCb, CO, and COCI2. Bromine and iodine do not attack Cr(CO)6 to any substantial extent at room temperature. The chromium tricarbonyl arene complexes, Cr(CO)3( -arene), are readily oxidized at room temperature by I2 to give Cris this is a conveitient preparative method for the anhydrous iodide. Although the oxidation of the tricarbonyl arene derivatives of chrontium with I2 does not show evidence of intermediate carbonyl complexes in oxidation states >0, the corresponding molybdenum(O) compounds give a series of carbonyl iodides of molybdenum(II), for example, the ionic [Mo(CO)3 ( ) -arene)]I. 

The diverse chemistry of chromium carbonyl complexes has its origin in the discovery of Cr(CO)6 in 1926 by Job and Cassal. Early developments in this area included the preparation of the (jj -arene)Cr(CO)3 family of organometallics by Nicholls and Whiting in 1959, the synthesis of the first structurally characterized carbene complex by Fischer and Maasbdl (1965), and a... 

Decomplexation of ArCr CO)3. The chromium carbonyl complexes of arenes are useful for activation of the aryl group to nucleophilic attack (6, 28, 125-126 7, 71-72). Decomplexation has been effected with iodine or by photochemical oxidation with destruction of the expensive Cr(CO)3 unit. A more recent method involves reflux with pyridine to form Py3-Cr(CO)3 in yields of 70-100%. The pyridine complex in the presence of BF3 can be reused for preparation of ArCr(CO)3. Isomerization of 1,3-dienes. Ergosteryl acetate (1) is isomerized by chromium carbonyl to ergosteryl 83 acetate (2) in 81% yield. Under the same conditions ergosteryl 83 acetate (3) is isomerized to ergosteryl 81 acetate (4). 80th reactions involve isomerization of a cisoid diene to a transpid diene. In contrast iron carbonyl isomerizes steroidal transoid 3,5- and 4,6-dienes to 2,4-dienes. ... 

Detailed vibrational assignments have been carried out on arene chromium and arene molybdenum tricarbonyl complexes (18, 19). Splitting of the E band in the carbonyl region was observed for substituted benzene chromium tricarbonyl complexes but not in (CgHg)Cr(CO)3 itself, showing that the concept of local symmetry (Cg ) is of very restricted validity when discussing the C—O stretching vibrations in such complexes (18). 

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