Molybdenum complexes synthesis

Molybdenum, tris(phenylenedithio)-structure, 1,63 Molybdenum alkoxides physical properties, 2,346 synthesis, 2,339 Molybdenum blue liquid-liquid extraction, 1,548 Molybdenum cofactor, 6,657 Molybdenum complexes acrylonitrile, 2,263 alkoxides, 3,1307 alkoxy carbonyl reactions, 2,355 alkyl, 3,1307 alkyl alkoxy reactions, 2,358 alkyl peroxides oxidation catalyses, 6,342 allyl, 3,1306... 

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. 

Olefin-metathesis is a useful tool for the formation of unsaturated C-C bonds in organic synthesis.186 The most widely used catalysts for olefin metathesis include alkoxyl imido molybdenum complex (Schrock catalyst)187 and benzylidene ruthenium complex (Grubbs catalyst).188 The former is air- and moisture-sensitive and has some other drawbacks such as intolerance to many functional groups and impurities the latter has increased tolerance to water and many reactions have been used in aqueous solution without any loss of catalytic efficiency. 

Scheme 11). Alternatively the quaternary salts can be converted thermally into acyliron chelate complexes which can then be oxidized to azetidinones (Scheme 12). Extension of the method to the synthesis of a condensed azetidinone is illustrated in Scheme 13, but the scope of the procedure has not been evaluated. It will also be of interest to assess the utility of other cationic organometallic complexes preliminary studies have shown that molybdenum complexes behave in an analogous manner but the oxidative cyclization is inefficient (Scheme 14). 

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). 

Asymmetric Synthesis Using a Chiral Molybdenum Catalyst In olefin metathesis, a double bond is cleaved and a double bond is formed. Thus, a chiral carbon center is not constructed in the reaction. To realize the asymmetric induction by ring-closing metathesis, there are two procedures a kinetic resolution and desym-metrization of symmetric prochiral triene. Various molybdenum complexes are synthesized in order to explore the viabihty of these approaches (Figure 6.2). 

I) Simple Monomeric Molybdenum Complexes. The first report on the synthesis of simple Mo dithio complexes appeared in 1971 when Mo(IV)(R2Dtc)4 complexes were obtained by CS2 insertion into Mo(NR2)4 complexes (68). Shortly after this report, the synthesis of these complexes from MoC14 and NaR2Dtc in acetonitrile was reported (88). A variety of tetrakis R2Dtc complexes of Mo(IV) also were obtained by the oxidative decarbonyla-tion of Mo(CO)6 with tetraalkyl thiuram disulfide (481,482, 609). 

Two possible catalytic systems for olefin mclathesis are the commercially available carbene complexes 61 and 62. Molybdenum complex 62. developed by Schrock,25 was the first to be introduced. Nevertheless, it has the disadvantage of being both unstable and difficult to access. The newer Gruhbs catalyst 61 is now preferred because it is stable and also easy to synthesi/e. Both catalysts are also appropriate for starting materials containing heteroatoms (see alst) Chapter 16). 

Dithiocarbamates, in Ru and Os half-sandwiches, 6, 493 Dithiocarbenes, Pt complexes, 8, 439 Dithiocarboxy ligands, in molybdenum carbonyls, 5, 447 Dithiolate-bridged compounds in dinuclear iron compounds with Fe-Fe bonds, 6, 238 as iron-only hydrogenase biomimetic models, 6, 239 Dithiolate diamides, with Zr(IV), 4, 784 Dithiolene—uranium complexes, synthesis and characterization, 4, 212 Ditopic receptors, characteristics, 12, 489 Ditungsten complexes, associated reactions, 5, 748 Divinyllead diacetates... 

Individual carbon atoms are very uncommon ligands for transition metals. The synthesis of a molybdenum complex containing a single C radical anion, uncomplexed to any other metals or functional... 

Saussine, L., H. Mimoun, A. Mitschler, and J. Fisher. 1980. Molybdenum(VI) and vanadium(V) N,N-dialkylhydroxylamino complexes Synthesis, x-ray structure, and reactivity towards olefins. Nouv. J. Chim. 4 235-237. 

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]... 

Synthesis of 2,3,6-trisubstituted 3,6-dihydropyran 289 can be achieved in excellent yield and with high enantio-selectivity upon demetallation and hydrolysis of the hydropyranyl molybdenum complex 290 (Equation 128) <2000JA10458>. 

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

The rearrangement could be corroborated via addition and cycloaddition reactions and also by the synthesis of the (OC)5 V=SnRR, complex97. The analogous chromium complex is formed via a reaction of chromium hexacarbonyl in THF (Scheme 16)98. The molecular structure is shown in Figure 42. The molybdenum complex is formed in the same way (Scheme 16, Figure 43)98. 

Baker et al. have described the synthesis and reactions with donor ligands of the molybdenum complexes [MoClI(CO)3(NCMe)2])6° and [MoBrI(CO)3(NCMe)2],161 which are prepared by reaction offac-[Mo(CO)3 (NCMe)3]101 with C1I or BrI, respectively. Reaction of [M(CO)4(N N)J (M = Mo, W N N = bipy, phen) with ICN affords the seven-coordinate complexes [M](CN)(CO)3(N N)].162... 

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. 

T. Agapie, P. L. Diaconescu, and C. C Cummins, Methine (CH) Transfer via a Chlorine Atom Abstraction/Benzene-Elimination Strategy Molybdenum Methylidyne Synthesis and Elaboration to a Phosphaisocyanide Complex, Angew. Chem. Int. Ed. 45, 862-870 (2006). 

Simple chiral phosphines have already been mentioned (Section 3.1.3) and the macrocycle enantiomers are discussed below (Section 4.6). Current research in this area is concentrated on bidentate chiral phosphines, such as the ligands (24)-(27). Although their transition metal complexes are normally used for stereospecific synthesis, Whitmire and coworkers used the molybdenum complexes to resolve their racemic bisphosphines via flash chromatography. The phosphines were decomplexed by reductive cleavage at low temperatures (-78 °C) using sodium naphthalenide (Scheme 1). 

Allyl complexes were amongst the earliest studied nomigid complexes, and there are a number of reviews on their rearrangements. Interest has been particularly high owing to their importance in catalysis and synthesis, with palladium and molybdenum complexes playing leading roles. 

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