Chromium-mesitylene complexes

The preceding analysis gives the following rate constants (M s ) for Eq. (20) at 20°C Cr (1 x 10 ), Mo (5 x 10 ), W (1 x 10 ). This translates into the relative reactivity order Mo > W > Cr (5 x 10 10 1). Because of the ethyl groups in 7, this series has a steric component, but it is likely that the same qualitative order will always obtain because studies with [(mesitylene)M(CO)3] indicate that W > Cr by ca. 10 1. In dissociative reactions of 18-electron chromium triad complexes, the normal reactivity order is Mo > Cr > W. Steric effects only serve to increase the rate for Cr compared to W. The much greater rate of W compared to Cr for associative reactions at 17-electron centers is likely due to the greater size of W (and Mo). In any event, it is apparent that the reactivity of 17-electron complexes can be very dependent on the metal within a triad. 

The formation of the inclusion compounds was selective. /3-CD formed 1 1 inclusion compounds with benzene, toluene, and o-xylene chromium tricarbonyl complexes, and not with w-xylene, />-xylene, guaiacol, methyl anthrani-late mesitylene, or hexamethylbenzene chromium tricarbonyl complexes. Whereas a-CD did not form inclusion complexes with any arene chromium complexes, 7-CD formed 1 1 inclusion complexes with all arene chromium... 

Both dimesitylchromium(II) 166) and trimesitylchromium(III) (167) (isolated as tctrahydrofuranates) undergo simple hydrolysis to mesitylene and chromium salts without formation of the 77-mesitylene complex. Pyrolysis of the a-mesityl compounds leads to complete decomposition. Electron-withdrawing substituents (e.g., halogen) that destabilize the TT-complexes also prevent the tr-aryl to tr-arene conversion (168). 

At constant temperature on the SE-30 column, the separation of para- and meta-xylenetricarbonylchromiums is poor the complexes of orthoxylene and ethylbenzene are eluted in the same time and are not completely resolved from the mesitylene complex. The selectivity of the Apiezon L column is greater for the xylene derivatives and the separation of o-xylene and ethylbenzene complexes is improved but the resolution of mesitylene- and pseudocumeme-tricarbonyl-chromiums is bad. Figure 215 shows a chromatogram of a benzene solution of the thirteen derivatives, obtained at 140°C with a SE-30 column. 

Chromium atoms provide a unique route to 7r-pyridine complexes. No simple product has been isolated from the reaction of pyridine and chromium atoms, but 2,6-dimethylpyridine and chromium atoms give a low yield of (i 8-2,6-dimethylpyridine)2chromium characterized by a crystal structure showing essentially planar pyridine rings (103). A mixture of pyridine with either PF3 or mesitylene gives a 7r-C5H5N complex ... 

The chromium analogue of 16, [(mesitylene)Cr(CO)3] (17) also undergoes a net two-electron oxidation in MeCN, but the chemistry involved is entirely different for the two complexes. With 17+, attack by solvent leads to rapid loss of arene and CO ligands, accompanied by further oxidation. (At fast scan rates, the 17+/17 couple becomes a reversible one-electron process.) A comparison of the relative reactivity of the 17-electron complexes 16+ and 17+ toward associative attack by MeCN led to the rate order W > Cr (ratio of ca. 104 1). It was suggested that this reactivity order reflects less steric congestion for nucleophilic attack at the... 

Support for this step was obtained by us in experiments where M was shown to add directly to bis(arene)metal complexes to give M2L2 (45, 46). Maximum nuclearity and stability of these species depends on the element, atom deposition rate, temperature and the type of arene. Mono-alkyl and -silyl substituted arenes give compounds that are unstable above 0 C. On the other hand, single crystals of a related triple-decker sandwich of mesitylene and chromium have been obtained (47),... 

The very air-sensitive compounds [Mo(terpy)2] (purple) and [W(terpy)2] (green) have been described by a number of workers 44,174). The chromium compound may be prepared by the reaction of [Cr(CO)g] 44), [Cr(CN)g] 42,47), [Cr(CO)3(C6H6)] 47), or [Cr(bipy)3] 44) with two equivalents of terpy. The molybdenum 44,174) and tungsten 44) compounds have been prepared from [M(CO)g] in a similar manner. Electrochemical studies on [Mo(terpy)2] indicate three one-electron oxidations 8). Photosubstitution reactions of [M(CO)g] in the presence of limited amounts of terpy lead to the formation of [M(CO)4(terpy)] (M = Cr, Mo, or W) 205). It is unlikely that these compounds are seven-coordinate, and they may well provide examples of a bidentate terpy. [Mo(CO)3(terpy)] may be prepared by the reaction of terpy with [Mo(CO)3(mesitylene)], but attempts to prepare the other group VI complexes of this stoichiometry lead to the formation of [M(CO)4(terpy)] 205). 

The second procedure for an axial isomerization is thermal conditions. Refluxing of syn biphenyl chromium complexes 65 in high boiling aromatic solvent, e.g., toluene, xylene, mesitylene, for 2 h gave the antz-biphenyl chromium complexes 66 (Eq. 55) [59b,cj. 

An overview of the effect of catalyst in the reaction of arenes with chromium hexacarbrmyl has been published. The reactivity of 17-, 18-, and 19-etectron catkMis generated electrochemically from mesitylene-tungsten tricarbonyl has been examined. The gas phase ion chemistry of a range of arene tricarbonylchromium complexes has been investigated by F.T. mass spectrometry. An improved synthesis of substituted naphthalene chromium carbonyls has appeared. ... 

Resolution of o and m-substituted benzylalcohol chromium tricarbonyls by reduction of the corresponding aldehydes using bakers yeast has been achieved. The regioselective complexation of 1,2 9,10-dibenzo[2.2]paracyclophane-1,9-diene with Cr(CX))3 has been described. The diasteteoselective nuclec hilic 1,2-addition reactions of N-benzylidene-1--methylaniline chromium tricarbonyl has been achieved. A range of hetetobimetallic complexes of substituted mesitylene chromium iricarbonyls has been prepared. ... 

In the case of mesitylene, it reacts with chromium at lO Torr by heating with tungsten filaments to afford a triple-decker sandwich complex (see Figure 13.2) besides (r/ -(l,3,5-MeC6H3))2Cr as shown in eq. (13.14) [24]. 

Figure 206 illustrates a separation of the four-component mixture, fluorobenzene tricarbonylchromium and benzene, mesitylene and methylbenzoate tricarbonylchromiums. The fluorobenzene chromium complex elutes prior to the benzene complex, and is the only complex to do so. The methylbenzoate complex elutes with approximately the same retention time as durene tricarbonylchromium. Methylbenzoate... 

Gas chromatographic separation of FTC, BTC, MTC, MBTC, (fluorobenzo, benzene, mesitylene, and methyl benzoate tricarbonyl chromium complexes). 

Bisarene Complexes The new triple-decker-sandwich complex (46) has been proposed as a product of a metal vapour synthesis of chromium with mesitylene.The metal vapour technique has also led to the isolation of (C5H5AS)2Cr. 

Tricarbonyl(6,6-diphenylfulvene)chromium(0) (52) was obtained by reaction of 6,6-diphenylfulvene with hexacarbonylchromium in 64% yield [56]. Later it was shown that almost quantitative yields can be obtained under photochemical reaction conditions starting from (benzene)Cr(CO)3 or from (mesitylene)Cr(CO)3 as the complexation reagent [63]. The corresponding molybdenum and tungsten complexes were prepared by treatment of the ligands with tris(acetonitrile)M(CO)3 (M = Mo, W) [64]. Olefin complex 53 was obtained by Wilkinson and Altman in 51% yield from 6,6-diphenylfulvene and bis(dicarbonylchlororhodium). Similar complexes were prepared with other rhodium reagents [58]. Hiibel and Weiss [59] prepared the diene tri-carbonyliron complex 54 (11-30%) in addition to the dinuclear complex, in which either one of the endocyclic double bonds is coordinated at Fe(CO)4 (49-66%). 

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