Molybdenum complexes reaction with

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]. 

Molybdenum(iv) Reactions with Oxidized Pterins. Long before a pteridine was discovered in Moco, the reaction of Mo(iv) and flavin was reported in 1974 (Scheme 2.14), yielding oxo-Mo" OCl3(flavinH) (15) complex, which was characterized by spectroscopic and analytical data. This research was called into question shortly after its publication. ... 

The catalytic activity of co-ordination compounds in oxidations continues to be examined and, together with the Faraday Society Discussion, other aspects of this area of investigation have been the subject of recent reviews. Redox reactions involving bipyridyl and u-phenanthroline complexes of transition metals have been discussed and catalytic oxidations of complexes of manganese, cobalt, copper, and palladium have also been surveyed. Reviews are also available of ruthenium ammine chemistry, and redox reactions involving molybdenum complexes, together with an account of catalase and peroxidase reactivity of copper(ii) complexes. ... 

The tert-huty hydroperoxide is then mixed with a catalyst solution to react with propylene. Some TBHP decomposes to TBA during this process step. The catalyst is typically an organometaHic that is soluble in the reaction mixture. The metal can be tungsten, vanadium, or molybdenum. Molybdenum complexes with naphthenates or carboxylates provide the best combination of selectivity and reactivity. Catalyst concentrations of 200—500 ppm in a solution of 55% TBHP and 45% TBA are typically used when water content is less than 0.5 wt %. The homogeneous metal catalyst must be removed from solution for disposal or recycle (137,157). Although heterogeneous catalysts can be employed, elution of some of the metal, particularly molybdenum, from the support surface occurs (158). References 159 and 160 discuss possible mechanisms for the catalytic epoxidation of olefins by hydroperoxides. 

Molybdenum and tungsten hexacarbonyls are able to form anionic complexes (AsPli4)2[(OC)4M( -pz)2M(CO)4] upon reaction with sodium pyrazolate and PluAsCl (72CB3203). The cationic complexes [(rj -Cp)2Mo(/Lt-pz)2Mo(rj -Cp)2] " (n = 2, 3) are known as well (74HCA1988). The other representatives of the complexes containing an exobidentate ligand (26) are derived from 4//-pyrazoles [70ZAAC(379)169]. 

When methylene chloride was used as a solvent, it was found that 28 are obtained in minor amounts, while the dominating product is the -coordinated chloro-carbyne species [(> -Tp )Mo(CO)2(=CCl)], whose yield increases abruptly with substitution in the pyrazol-l-yl fragments (3-methyl-, 3,4,5-trimethyl-, and 3,5-dimethyl-4-chloro derivatives) [90AX(C)59,95JCS(D) 1709]. The tungsten analog can be prepared similarly. The chlorocarbyne molybdenum complex follows also from the reaction of the parent anion with triphenylsulfonium cation but conducted in dichloromethane. The bromo- and iodocarbyne derivatives are made similarly. 

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. 

The achiral molybdenum enolate 2 reacts with benzophenone and benzaldehyde at —78 °C to yield the x,/i-unsaturated molybdenum-acyl complexes34, which presumably arise via elimination of hydroxide from unobserved aldolate intermediates such as 3. No examples of such aldol reactions with complexes that are chiral at molybdenum have been reported. 

Stable enolates such as diethyl malonate anions react with allyl sulfones (or acetates) in the presence of nickel complexes to give a mixture of the a- and /-product83. The regioselectivity is generally poor in the nickel-catalyzed reaction, but the molybdenum-catalyzed reaction is selective for alkylation at the more substituted allylic site, thereby creating a quaternary carbon center84. 

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