Molybdenum complexes applications

We will focus on the development of ruthenium-based metathesis precatalysts with enhanced activity and applications to the metathesis of alkenes with nonstandard electronic properties. In the class of molybdenum complexes [7a,g,h] recent research was mainly directed to the development of homochi-ral precatalysts for enantioselective olefin metathesis. This aspect has recently been covered by Schrock and Hoveyda in a short review and will not be discussed here [8h]. In addition, several important special topics have recently been addressed by excellent reviews, e.g., the synthesis of medium-sized rings by RCM [8a], applications of olefin metathesis to carbohydrate chemistry [8b], cross metathesis [8c,d],enyne metathesis [8e,f], ring-rearrangement metathesis [8g], enantioselective metathesis [8h], and applications of metathesis in polymer chemistry (ADMET,ROMP) [8i,j]. Application of olefin metathesis to the total synthesis of complex natural products is covered in the contribution by Mulzer et al. in this volume. 

Molybdenum co-factor (Moco), 77 33 Molybdenum complexes, 26 927-929, 949 Molybdenum(III) complexes, 17 26-27 Molybdenum compounds, 17 19-43 in advanced structural and heating materials, 17 38-39 in anticorrosion agents, 17 39 biological aspects of, 17 31-34 biological uses for, 17 39-40 biomedical uses for, 17 40 catalytic applications of, 17 38 chemistry of, 17 29-31... 

Despite many applications of the iron-mediated carbazole synthesis, the access to 2-oxygenated tricyclic carbazole alkaloids using this method is limited due to the moderate yields for the oxidative cyclization [88,90]. In this respect, the molybdenum-mediated oxidative coupling of an arylamine and cyclohexene 2a represents a complementary method. The construction of the carbazole framework is achieved by consecutive molybdenum-mediated C-C and C-N bond formation. The cationic molybdenum complex, required for the electrophilic aromatic substitution, is easily prepared (Scheme 23). 

Synthetic protein-like polymers containing amino acids find pharmaceutical and biological applications and display self-assembly properties [174], In this aspect, both ROMP and ADMET have been used as tools for the polymerization of amino acid-based monomers. Early ROMP examples date back to 1994 with the synthesis and ROMP of amino acid-derived homochiral norbomene monomers by Coles et al [175], The molybdenum complex [Mo(=CHCMe2Ph)(=NC6H3Pr,2-2,6)(OBu )2]... 

Sakthivel, A., Zhao, J. and Kuhn, F. E. Cyclopentadienyl molybdenum complexes grafted on zeolites - synthesis and catalytic application, Catal. Lett., 2005, 102, 115-119. 

There have been relatively few examples of the hetero-Diels-Alder reaction where the carbonyl group is part of the 4 tt component. This is mainly due to the instability of both starting materials and products to heat and acid, and consequently Lewis-acid catalysis has been of minor applicability. Yamamoto et al. have now shown, however, that the molybdenum complex [Mo02(acac)2] catalyses the... 

Sakthivel, A., Zhao, J., Hanzfik, M., et al. (2005). Heterogenization of Organometalfic Molybdenum Complexes with Siloxane Functional Groups and their Catalytic Application, Arfv. Synth. Catal., 347, pp. 473 83. 

While metallocene-derived complexes 103 deserve interest mainly because of their redox properties and applications resulting therefrom, half-sandwich complexes 104 and 105 show more diverse chemical reactions. Based on their synthesis of the fulvalene dianion 102, Smart et al. [99] prepared some molybdenum complexes such as 108 [62% yield based on Na(DME)Cp] by treatment of 102 with molybdenum hexacarbonyl followed by oxidation with bromine. Vollhardt reported the synthesis of a variety of homo- and heterodinuclear fulvalene complexes such as 109-112 by treatment of dihydrofulvalene and respective metal carbonyls. The dichromium complex 110 has some catalytic activity in the hydrogenation of conjugated dienes [110]. The authors report the reaction with iron carbonyls being unsuccessful, whereas the reaction with dicobaltoctacarbonyl resulted in the formation of fulvalene complex 112 lacking a metal-metal bond in 80% yield (Scheme 10.38) [100, 101]. Later, the diiron complex corresponding to 109 was reported [111]. Hermann et al. and Cuenca etal. prepared zirconium(IV) and zirconium(III) fulvalene complexes [112,113]. 

The first examples of catalytic RCAM for the synthesis of functionalized macrocycles were reported by Ftirstner and Seidel [7]. Two catalyst systems were employed in this study the instant system prepared by reaction of catalytic amounts of Mo(CO)6 1 with stoichiometric quantities of phenols, and the well-defined tungsten-alkylidyne 2 first prepared by Schrock in 1981 [5, 8]. Subsequent applications of RCAM, particularly in natural product synthesis, have either utilized these two systems or a molybdenum system developed by Fiirstner that employs in situ reaction of trisamido molybdenum complex 3 [9] and CH2CI2 (Figure 7.1) [10]. 

To date, applications of this system in natural product synthesis have employed the in situ generation of the catalytically active species. Molybdenum complex 3 is... 

As electrophilic substitutes for peracids, the use of borate ester induced decomposition of alkyl hydroperoxides and molybdenum VI peroxy-complexes have been reported in the recent literature. Although these reagents have led to the epoxidation of olefins in greater than 90% yield there are no reports yet of their application to steroid olefins. 

As catalysts, ruthenium- or molybdenum-alkylidene complexes are often employed, e.g. commercially available compounds of type 7. Various catalysts have been developed for special applications. " ... 

The theoretical aspects of molybdenum s corrosion behaviour are complex and there is as yet no clear cut, generally applicable picture. There are, however, a large number of literature references which include data on polarisation, passivation and potential of molybdenum under widely assorted conditions. The electrode potential of molybdenum depends on its surface condition. For example, some tests showed an of -t-0-66V when the molybdenum was passivated by treatment with concentrated chromic acid and —0-74 V after activation by cathodic treatment in sodium hydroxide. 

Abstract For many years after its discovery, olefin metathesis was hardly used as a synthetic tool. This situation changed when well-defined and stable carbene complexes of molybdenum and ruthenium were discovered as efficient precatalysts in the early 1990s. In particular, the high activity and selectivity in ring-closure reactions stimulated further research in this area and led to numerous applications in organic synthesis. Today, olefin metathesis is one of the... 

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