Molybdenum complexes benzene

One of the key factors in the syntheses of benzene molybdenum complexes is the facile preparation of large quantities of bis ( 76-benzene)molybdenum. The synthesis of this compound under sealed-tube conditions has been described elsewhere.5,6 The modified procedure described here is useful for large-scale preparations. 

Because the Si-Cl bond is sensitive to moisture, compounds containing i-Pr2SiCl are less common. However, with careful manipulation, such confounds were characterized by NMR, MS, elemental analysis, and single-crystal X-ray diffraction analysis. " For exanple, the bis(benzene)molybdenum complex was metalated with 2 equiv f-BuLi to give the diionic intermediate 10, which was subjected to react with i-Pr2SiCl2 to give complex 11 the yield of the latter step is 37% (eq 10). ... 

Molybdenum hexacarbonyl [Mo(CO)6] has been vised in combination with TBHP for the epoxidation of terminal olefins [44]. Good yields and selectivity for the epoxide products were obtained when reactions were performed under anhydrous conditions in hydrocarbon solvents such as benzene. The inexpensive and considerably less toxic Mo02(acac)2 is a robust alternative to Mo(CO)6 [2]. A number of different substrates ranging from simple ot-olefms to more complex terpenes have been oxidized with very low catalytic loadings of this particular molybdenum complex (Scheme 6.2). The epoxidations were carried out with use of dry TBHP (-70%) in toluene. 

Although solutions of molybdenum complexes A in methylcyclohexane or benzene are stable for several weeks at room temperature [416], these complexes are sensitive towards oxygen and protic solvents [813,814]. Aldehydes are quickly olefinated by complexes A, whereas variable reactivity is observed towards ketones [416,736]. With carboxylic esters usually no reaction occurs. 

The reactions of dinuclear thioaldehyde and -ketone complexes with PR3 take a different course. When the dimeric complexes 112 are treated with PMe3 a Ti-S bond in 112 is cleaved and the monomeric complexes 113 are reversibly formed (see Scheme 26), 69 The reaction of 112 with benzene-thiol led to a Ti-C cleavage and formation of 1,3-propanedithiolato-(phenylthiolato) complex.69 The reaction of binuclear p-191 rf-thioketone molybdenum complexes related to 115 (M = Mo, E = S, R = Aryl) with P(OEt)3 also gave mononuclear complexes [Mo(CO)2(Et) i72-S = C(Aryl)2 (i75-C5H5)] by a rather complicated reaction sequence. When other phosphites were employed additionally binuclear complexes derived from addition of the phosphite to one molybdenum atom were isolated.225... 

In solution the bridging fluorines are rapidly transferred between adjacent silicons, such that the 29Si spectrum features a triplet due to two equivalent fluorines (Vsi-F = 127 Hz). This triplet did not change to a doublet of doublets at the low-temperature limit in toluene-ds solution, and hence freezing out of the fluorine transfer between vicinal silicons could not be achieved. When the temperature was raised, all six fluorines became equivalent, causing the silicon resonance to be a septet ( /si-F = 43 Hz), presumably due to exchange by correlated rotation178 of the silicon substituents about the Si-benzene bonds. This rotational process was stopped when a molybdenum complex was formed (152), presumably as a result of increased steric hindrance for rotation. 

Bis(azidomethyl)oxetane, 1896 Bis(azidothiocarbonyl) disulfide, 1012a Bis(benzeneazo) oxide, 3484 Bis(jj-benzene)chromium(0), 3505 Bis(benzene)chromium dichromate, 3845 Bis(benzenediazo) sulfide, 3485 Bis(jj-benzene)iron(0), 3506 Bis(benzeneiron)—fulvalenediyl complex, 3828 Bis(jj-benzene)molybdenum(0), 3508... 

Molybdenum complexes are the most effective catalysts known for the selective epoxidation of olefins with alkyl hydroperoxides (210-212). Commonly known is the Arco or Halcon process for the large-scale manufacture of propylene oxide from propylene. This process uses t-BuOOH or ethyl benzene hydroperoxide (EBHP) as an oxidant and Mo(CO)6, for example, as a source of Mo. The Mo(CO)6 acts as a catalyst precursor, which is converted into a soluble active form by complexation with diols (3). Chemists have designed several supported versions of the catalysts for this epoxidation chemistry. A clear classification can be made on the basis of the nature of the support. 

The driving force of aromaticity can be exploited for C-C bond cleavage in prearomatic systems. Pentamethylcyclopentadienyl complexes are obtained from reactions of hexamethyl-(Dewar benzene) with RhCl3 and IrCl3 [56]. A r 4-(en-do-ethylcyclopentadienyl)molybdenum complex rearranges with breaking of the Cp-Et bond to a r 5-(cyclopentadienyl)(ethyl)molybdenum complex upon generation of a vacant coordination site on the metal [57]. 

The direct oxidation of propylene by molecular oxygen is a low-selective reaction. The propylene oxide yield can be raised by limiting the conversion rate to a low value, about 10 to 15 per cent, by using more selective catalysts, or by achieving co-oxidation with a more oxidizable compound than propylene (acetaldehyde, isobutyraldehyde etc.). Many patents have been Hied concerning this process, but without any industrial implementation. Among them is the liquid phase oxidation of propylene on a rare earth oxide catalyst deposited on silica gel (USSR), or in the presence of molybdenum complexes in chlorobenzene or benzene (JFP Instiiut Francois du Petrole. Jefferson ChemicalX vapor phase oxidation on modified silver catalysts (BP British Petroleum IFP, or on ... 

After hydrolysis of the anion of Tc(C6Hf,)2j[AlCl4], the cation was precipitated as hexafluorophosphate. The yellow-green, diamagnetic complex salt is stable in air, acids and bases [617]. Prior to the preparation of ponderable amounts, the cation was produced by irradiating h/A(benzene)molybdenum with thermal neutrons ... 

All three members of the electron transfer chain [Mo(CO)2(S2C2Me2)]" (n = 0,1, 2) were isolated and characterized. The complexes have trigonal prismatic geometries, and structural, spectral, and electrochemical properties that are consistent with the redox orbital having predominantly sulfur-ligand based character (>80%) behavior consistent also with DFT calculations. Closely related benzene- and 2,4-di-i-butyl-benzene-dithiolene complexes, [Mo(LL )(bdt)2] (L = 0, L = PPha, L = L = PMeR2 (R = Me or Ph)) were obtained by thioether S-dealkylation of appropriate dttd (22) complexes of molybdenum carbonyls and oxo species. 

Jonas and co-workers have pointed out that often a compromise must be found between sensitivity and resolution in NMR spectroscopy [76]. Line narrowing is optimum in regions of low supercritical fluid density (where the viscosity is low), but then the solubility of compounds is also low. Sometimes, admixtures with small amounts of low-viscosity solvents such as acetone may be tried to obtain a reasonable concentration of the compounds studied, i.e. coordination compounds such as (R-N=CH)2Mo(CO)4. However, line widths for this compound decrease by a factor of about four to six when comparing benzene-dg solutions to supercritical CO2 (with 8% acetone-de). The dispersion of the nitrogen chemical shift ensures identification of coordinated ligands by using NMR, in the above molybdenum complex, where A5( n) = -36 ppm) [75]. 

C ]H,o, Fluorene, iridium complex 29 232 C]3H jNO, Formanide,lV-ll-(l-naphthal-enyl)ethyl]-, rhenium complex 29 217 CijHijP, Phosphine, methyldiphenyl-, iron complex 26 61, 28 171 molybdenum complex, 27 9 nickel complex, 28 101 tungsten complexes. 27 10, 28 328,28 331 CijHio, Acetylene, diphenyl-, molybdenum complex, 26 102-105, 28 11, 13 C14H12, Benzene, 1,2-ethenediylbis-, platinum complex, 26 140 C14H14, Benzene. l,l -(l,2-ethanediyl)-bis-, 26 192... 

Arene tricarbonyl molybdenum complexes are yellow, often crystalhne compounds. They are weakly air-sensitive in the sohd state and have to be stored under inert atmosphere and out of hght. They are best purified by crystaUization. In solution, they are unstable to air. The trait that has most hampered development of the use of (arene)Mo(CO)3 complexes in organic synthesis, however, is the lability of the arene metal bond. Lewis basic solvents such as THF, DMF, DM-SO, acetone and acetonitrile rapidly displace benzene in (benzene)Mo(CO)3. This lability of the arene-Mo bond, while making handling difficult, holds promise for the catalytic use of this class of compounds. 

Hj, Hydrogen, molybdenum complex, 27 3 tungsten complex, 27 6 H2BF4l2lrC4jH34, lridium(l +X (1,2-diiodo-benzene) dihydridobis(triphenyl-phosphine)-, tetrafluoroboiate(l—X 26 125, 28 59... 

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