Molybdenum complexes acetylacetone

The chiral ligand (44) was prepared starting from the cyclic a-amino acid (S)-proline80). Recently, similar chiral catalysts and related molybdenum complexes involving optically active N-alkyl-P-aminoalcohols as stable chiral ligands and acetylacetone as a replaceable bidentate ligand, were designed for the epoxidation of allylic alcohols with alkyl hydroperoxides which could be catalyzed by such metal complexes 8,). 

We studied the oxidation of cyclohexene at 70°C in the presence of cyclopentadienylcarbonyl complexes of several transition metals. As with the acetylacetonates, the metal center was the determining factor in the product distribution. The decomposition of cyclohexenyl hydroperoxide by the metal complexes in cyclohexene gave insight into the nature of the reaction. With iron and molybdenum complexes the product profile from hydroperoxide decomposition paralleled that observed in olefin oxidation. When vanadium complexes were used, this was not the case. Variance in product distribution between the cyclopentadienylcarbonyl metal-promoted oxidations as a function of the metal center were more pronounced than with the acetylacetonates. Results are summarized in Table V. 

The first reaction (346) consists of hydroperoxide formation by a typical autoxidation process, and the second represents selective epoxidation by the hydroperoxide. In the absence of the autoxidation catalyst, no reaction is observed under these conditions due to efficient removal of chain-initiating hydroperoxide molecules by reaction (347). Optimum selectivities obtain when the autoxidation catalyst is of low activity, which implies a low total activity of the catalytic system. The molybdenum complexes related to Mo02(oxine)2 are among the most effective catalysts for epoxidation.496 Although the autoxidation catalysts were limited to two types (phosphine complexes of noble metals and transition metal acetylacetonates), there is no reason, a priori, why other complexes such as naphthenates should not produce similar results. 

This is by far the most stable and best-known oxidation state for chromium and is characterized by thousands of compounds, most of them prepared from aqueous solutions. By contrast, unless stabilized by M-M bonding, molybdenum(III) compounds are sparse and hardly any are known for tungsten(III). Thus Mo, but not W, has an aquo ion [Mo(H20)g] +, which gives rise to complexes [MoXg] " (X = F, Cl, Br, NCS). Direct action of acetylacetone on the hexachloromolybdate(III) ion produces the sublimable (Mo(acac)3] which, however, unlike its chromium analogue, is oxidized by air to Mo products. A black cyanide,... 

Molybdenum trioxide, intercalation into, 12, 823 Molybdocenes, as anticancer agents, 1, 892 MOMNs, see Metal-organometallic coordination networks Monisocyanides, with silver(I) complexes, 2, 223 Monitoring methods, kinetic studies, 1, 513 Mono(acetylacetonate) complexes, with Ru and Os halfsandwich rf-arenes, 6, 523 tj2-Monoalkene monodentate ligands, with platinum divalent derivatives, 8, 617 tetravalent derivatives, 8, 625 theoretical studies, 8, 625 zerovalent derivatives, 8, 612... 

Molybdenum (VI) complex compounds, nonelectrolytes, with acetylacetone, Mo02(C3H702) 2, 6 147... 

Hexacarbonylmolybdenum and /3-diketones yield the molybdenum(III) chelate complexes as shown in equation (33) for acetylacetone. 

Epoxides undergo deoxygenation upon treatment with vanadium or molybdenum acetylacetonate complexes, although their stereoselectivity is low. When the molybdenum(VI) oxo complex MoO(S2CNEt2)2 is employed, the deoxygenation proceeds with retention of configuration. For example, cw-2-butene oxide is converted to c -2-butene at 130 C in 83% yield. ... 

Among the most active transition metals are Mo and V, and both are effective in their highest oxidation state during reaction. Linden and Farona have foimd that Mo(V) is inactive for the epoxidation reaction and that V(IV) is converted to V (V) when contacted with a hydroperoxide [467]. The metals are added as compounds soluble in the reaction mixture, for example, Mo(CO)6, MoO2(acac), and VO(acac)2 (acac = monoanion of acetylacetone). Sheldon and Van Doom [266] have found that irrespective of the starting material, all molybdenum catalysts give rise to a common compound, a 1,2-diol complex (Fig. 1.11b). This is formed... 

The polyitnide bead bearing a triazole residue was used to immobilize a stable and active Mo(VI) epoxidation catalyst. The polyimide was refluxed with molybdenyl acetylacetonate in ethanol for 3days. Upon completion, a polyimide-Mo complex catalyst was filtered and extracted with ethanol in a Soxhiet apparatus for 3 days. The supported complex was dried thoroughly under vacuum. The molybdenum content was measured by inductively coupled plasma (ICP) to be l.OSmmolg for PI-DAT.Mo and l. lOmmolg for CPI-DAT.Mo. 

Trichloro(tripyridine)chromium(III), synthesis 36 Tris(3-bromoacetylacetonato)chromium(III), synthesis 37 Cyclopentadienyl tricarbonyl hydrides of chromium, molybdenum, and tungsten, synthesis 38 Trichloro(tripyridine)molybdenum(III), synthesis 39 Potassium octacyanotungstate(IV) 2-hydrate, synthesis 40 Chlorine(CP )-labeled thionyl chloride, silicon tetrachloride, boron chloride, germanium (IV) chloride and phosphorus(III) chloride, synthesis 44 Unipositive halogen complexes, synthesis 46 Monopyridineiodine(I) chloride, synthesis 47 Manganese(III) acetylacetonate, synthesis 49 Triiron dodecacarbonyl, synthesis 52... 

Molybdenum(Vl) complexes, 1256,1375-1414 alkyl, 1407 alkylidyne, 1407 alkylimido, 1396 arylimido, 1396 bipyridyldibromodioxo, 1388 bis(acetylacetonate) dioxo, 1388 catecholate dioxo, 1389 dimethyl, 1406 dinuclcar, 1408 IR spectroscopy, 1412 O or S bridge, 1411 preparation, 1411 Raman spectroscopy, 1412 single 0X0 bridge, 1408 structure, 1408 triple bridge, 1410 dioxo... 

The decomposition of cyclohexylhydroperoxide was also studied in the presence of molybdenum and chromium complexes [356]. The decomposition of cyclohexylhydroperoxide in benzene catalyzed by [Mo02(acac)2], has many characteristics of the [VO(acac)2]-catalyzed reaction [355]. The ketone/alcohol ratio in the product was 1 and the kinetic pattern of reaction is similar. When chromium(III) acetylacetonate is used, however, there is a substantial difference. The chromium complex selectively converts cyclohexyl hydroperoxide to cyclohexanone. It is suggested that in this case the extent of release of free radicals to the solution is small [356]. The ketone/alcohol ratio in this case is " 13.7. The predominant formation of cyclohexanone on decomposition of cyclohexyl hydroperoxide in the presence of [Cr(acac)3] is no doubt related to the much higher yield of ketone obtained in cyclohexane oxidation in the presence of chromium complexes than observed when Mo or V compounds are used as catalysts [356]. 

Cis-molybdenum(VI) dioxide forms biscatecholate coordination compounds. The third position is already blocked by the two cis-oriented oxo ligands. The reaction of bis(acetylacetonate) cis-dioxomolybdenum with carbonyl-substituted catecholates in the presence of lithium carbonate results in the formation of bis catecholate cis-dioxomolybdenum(VI) complexes that are in equilibrium with their dimers. 

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