Chromium 6-benzene tricarbonyl

The first publication in a journal of xSR of organometallics was in 1997 by Jayasooriya et al. [4], where studies of tetraphenyl lead, benzene chromium tricarbonyl and ruthenocene were discussed. 

The most complete conclusions were drawn from the results on benzene chromium tricarbonyl. This compound crystallizes in the monoclinic space group P2 /m with two symmetry related molecules per unit cell, with almost undistorted benzene rings at room temperature [16]. Measurements at 78 K using both X-ray and neutron diffraction showed a lowering of the benzene 

The faster relaxing component was not further investigated at the time [18]. These additional radicals that are formed showing Arrhenius parameters which have no closed-shell counterparts are discussed later in this chapter. 

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Among the compounds that form complexes with silver and other metals are benzene (represented as in 9) and cyclooctatetraene. When the metal involved has a coordination number >1, more than one donor molecule participates. In many cases, this extra electron density comes from CO groups, which in these eomplexes are called carbonyl groups. Thus, benzene-chromium tricarbonyl (10) is a stable compound. Three arrows are shown, since all three aromatic bonding orbitals contribute some electron density to the metal. Metallocenes (p. 53) may be considered a special case of this type of complex, although the bonding in metallocenes is much stronger. 

X-ray dipole moments of formamide, of sulfamic acid, of benzene chromium tricarbonyl, and of water, obtained from /c-refinements, are in good agreement with those from other physical techniques. When hydrogen-atom positions are of crucial importance, as in the case of the water molecule, the availability of positional information from neutron diffraction becomes essential if accurate moments are to be obtained. In other cases, extension of the X-H bond to accepted values provides a reasonable alternative. 

Studies on various derivatives of ferrocene, cymantrene, benzene-chromium tricarbonyl, and butadieneiron tricarbonyl were recently reported (174, 176). Carbonyl derivatives containing the COR group lose CO to give an ion probably containing the R group attached to the metal, e.g. 

Complexes of Cr, W, Mo, Fe, Ru, V, Mn and Rh form stable, isolable arene if -complexes. Among them, arene complexes of Cr(CO)3 have high synthetic uses. When benzene is refluxed with Cr(CO)6 in a mixture of dibutyl ether and THF, three coordinated CO molecules are displaced with six-7r-electrons of benzene to form the stable i/fi-benzene chromium tricarbonyl complex (170) which satisfies the 18-electron rule (6 from benzene + 6 from Cr(0) + 6 from 3 CO = 18). Complex formation is facilitated by electron-donating groups on benzene, and no complex of nitrobenzene is formed. Complex formation has a profound effect on reactivity of arenes, and the resulting complexes are used in synthetic reactions. The metal-free reaction products can be isolated easily after decomplexation by mild oxidation using low-valent Cr. Cycloheptatriene also forms a stable complex with Cr(CO)3 and its synthetic applications are discussed below. 

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). 

The centrosymmetric structure proposed for benzene-chromium tricarbonyl was subsequently confirmed by x-ray analysis 8, 52). 

Following this initial discovery, several additional routes to benzene-chromium tricarbonyl and related complexes were developed, the most convenient of which involves the simple refluxing of the metal carbonyl and arene with concurrent loss of carbon monoxide 96, 97,184, 187). 

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). 

The lithiated derivative (LiCgH5)Cr(CO)3 has been prepared in high yield by the reaction of [(CO)3Cr](CaHgHgC6H5)[Cr(CO)3] with re-butyl lithium. Complexes, such as 2-phenylpyridine chromium tricarbonyl and (Ph2PCgHg)Cr(CO)3, which are not otherwise obtainable were prepared by the reaction of the lithiated derivative with pyridine and PhaPCl, respectively 348). Benzene chromium tricarbonyl has been metalated by treatment with re-butyl lithium in THF and after carbona-tion yielded w-benzoic acid chromium tricarbonyl 304). 

The only electrophilic substitution of arene chromium tricarbonyl complexes so far achieved is Friedel-Crafts acetylation. Benzene and substituted benzene chromium tricarbonyls undergo this reaction under mild conditions giving the corresponding acetyl-substituted complexes 109, 176, 218, 233, 234, 355). Substituent and conformational effects play an important role in directing the position of acetylation in arene chromium tricarbonyl complexes 176, 218, 233, 234). 

The third approach to obtain diarylmethylpiperazine derivatives uses the highly stereospecific chiral oxazaborolidine-catalyzed reduction, using catecholborane as the reductant of the 4-bromobenzophenone chromium tricarbonyl complex, as described by Corey and Helal [59], followed by the stereospecific displacement of the hydroxyl benzyl group by the /V-substituted-piperazine [44]. As outlined in Scheme 2, Delorme et al. [44] used this approach for the enantioselective synthesis of compound 31, (+)-4-[ (aS)-a-(4-benzyl-l-piperazinyl)benzyl]-lV,lV-diethylben-zamide. Lithiation of the readily available benzene chromium tricarbonyl with n-BuLi in the presence of TMEDA in THF at —78 °C, followed by addition of... 

Strohmeier 469> reported the photoinduced exchange of unlabeled benzene chromium tricarbonyl with 14C-labeled benzene (57% in 3 hrs., 366 nm irradiation). 

Alcoholates are produced from benzene chromium tricarbonyl 81) and Cr(CO) 79) according to Eq. (34). 

Miscellaneous Systems Other systems have been described [li,m] ferrocene/ carbon tetrachloride (a trichloromethyl radical is formed), ferrocene/carbon tetrabromide, metal carbonyl/onium salts (e.g., the [cyclopentadienyl Fe (CO)2]2/ diaryliodonium hexafluorophosphate combination where a phenyl radical is generated), benzene chromium tricarbonyl/halide derivative, and so on. 

Table 12. The vibrational frequencies of benzene-chromium-tricarbonyl ... 

This set of calculations represents a successful new area of application for density functional theory. These calculations provide the first complete force fields for ferrocene, dibenzene-chromium, and benzene-chromium-tricarbonyl. 

Benzene, 1-chloro-3-(trifluoromethyl)-. Seem-Chlorobenzotrifluoride Benzene, 1-chloro-4 (trifluoromethyl). Seep-Chlorobenzotrifluoride Benzene chromium tricarbonyl Benzenechromotricarbonyl. See (Benzene) tricarbonylchromium... 

Benzenethiol. See Thiophenol (Benzene) tricarbonylchromium CAS 12082-08-5 EINECS/ELINCS 235-146-6 Synonyms Benzene chromium tricarbonyl Benzenechromotricarbonyl Chromium, (benzene) tricarbonyl- Chromium, (n benzene) tricarbonyl- n Benzenetricarbonylchromium Tricarbonylbenzene chromium Empirical CgHeCrOs... 

Benzene) Chromium tricarbonyl (a piano stool complex)... 

The geometric (size and shape) complementarity between the cyclodextrin host and the organometallic guest determines a well manifested selectivity in the formation of inclusion complexes and can be used for the separation of ferrocene from dime-thylferrocene (only the latter forms a complex with y5-CD) [471], and of (benzene)-chromium tricarbonyl, (7 -C6H6)Cr(CO)3 from (hexamethylbenzene)-chromium tricarbonyl, ( y -C6Me6)Cr(CO)3 (only the latter forms a complex with y-CD) [471], Cyclodextrin host-guest complexation also affords the resolution of hydroxyethylferrocene enantiomers [489]. 

Synthesis of Diphenylhydantoin Bearing a Bendirotrene (Benzene chromium Tricarbonyl) Entity... 

Figure 7.7 Arrhenius plot of reciprocal correlation times extracted from the longitudinal muon spin relaxation measurements of benzene chromium tricarbonyl compared with QENS data [4]. Reproduced from Hyperfine Interactions 106, 27-32 (1997), U. A. Jayasooriya, I A. Stride, G. M. Aston, G. A. Hopkins, S. F. J. Cox, S. P. Cottrell and C. A. Scott, Figure 2, Kluwer, with kind permission of Kluwer Academic Publishers.

For monosubstituted arenes, kinetically controlled discrimination between the two enantiotopic ortho hydrogens of the planar chiral benzene chromium tricarbonyl complex leads to nonracemic products. Asymmetric lithiation is more efficient when one or more oxygen atoms, such as ether linkages, are present in the starting prochiral complex (Scheme 26.14). Treatment of Cr(CO)j-anisole complex 52 with the chiral lithium amide 53, in the presence of TMSCl under ISQ conditions, affords (+)-orfho-silylated complex 54 with good chemical yield and ee value [143-145]. The isobenzofuran system 55 reacts as well to give a-sUylated product 56 [146]. 

Scheme 29.18 Reactions of single-walled carbon nanotubes with (jj -benzene)chromium tricarbonyl.

Assuming the most symmetrical structure that is chemically reasonable, deduce the point group of an isolated molecule of benzene chromium tricarbonyl. How many symmetry-independent Cr—C, C—O, C—C and C—H bond lengths will there be ... 

Crystals of benzene chromium tricarbonyl are monoclinic with a = 6.17, h = 11.07, c = 6.57 A, 101.5°, and the density is 1.650gcm. Calculate the volume of the unit cell and the number of molecules per unit cell. 

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