Molybdenum complexes chlorides

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. 

Discussion. Molybdenum(VI) in acid solution when treated with tin(II) chloride [best in the presence of a little iron(II) ion] is converted largely into molybdenum(V) this forms a complex with thiocyanate ion, probably largely Mo(SCN)5, which is red in colour. The latter may be extracted with solvents possessing donor oxygen atoms (3-methylbutanol is preferred). The colour depends upon the acid concentration (optimum concentration 1M) and the concentration of the thiocyanate ion (1 per cent, but colour intensity is constant in the range 2-10 per cent) it is little influenced by excess of tin(II) chloride. The molybdenum complex has maximum absorption at 465 nm. 

Other molybdenum complexes able to catalyze the selective oxidation of secondary alcohols are ammonium molybdate in the presence of H202,30 benzyltrimethylammonium tetrabromooxomolybdate in the presence of r-BuOOH31 and molybdenum hexacarbonyl in the presence of catalytic cetylpyridinium chloride and stoichiometric t-BuOOH.32... 

Susuki and Tsuji reported the first Kharasch addition/carbonylation sequences to synthesize halogenated acid chlorides from olefins, carbon tetrachloride, and carbon monoxide catalyzed by [CpFe(CO)2]2 [101]. Its activity is comparable to or better than that of the corresponding molybdenum complex (see Part 1, Sect. 7). Davis and coworkers determined later that the reaction does not involve homolysis of the dimer to a metal-centered radical, which reduces the organic halide, but that radical generation occurs from the dimeric catalyst after initial dissociation of a CO ligand and subsequent SET [102]. The reaction proceeds otherwise as a typical metal-catalyzed atom transfer process (cf. Part 1, Fig. 37, Part 2, Fig. 7). 

Although Able et al. (2, 8) had originally set out to prepare 7r-cyclo-heptatrienyl complexes of metals, the cycloheptatriene complexes they actually obtained served as key intermediates in forming the former complexes. In 1958 Dauben and Honnen (61) reported that cycloheptatriene-molybdenum tricarbonyl reacted with triphenylmethyl tetrafluoroborate in methylene chloride solution with abstraction of hydride ion from the molybdenum complex. The reaction products, obtained in nearly quantitative yields, were triphenylmethane and the 7r-cycloheptatrienyl complex [(7r-C7H7)Mo(CO)3]+BF4 . 

Another type of reaction of bisarene molybdenum complexes has been observed with allyl chloride (188, 189) (arene = CgHg, MeCgHg, l,3,5-Me3CgH3) ... 

Molybdenum(V) chloride is reasonably soluble in liquid phosgene at 0 C, whereas tungsten(VI) chloride is only sparingly soluble. The results of the tensimetric titrations of molybdenum(V) chloride and tungsten(VI) chloride with phosgene at 0 C are presented in Fig. 9.8 [376] there is no evidence for complex formation. 

The formation of 1,5-diyne complexes as side-products in some reactions of cations 92 with metal alkyls [41] and the facile, regioselective reduction of a propargylic chloride complex by Zn/HOAc, used in the synthesis of the insect pheromone 5-(Z)-tetradecenyl acetate [221], provided early evidence for the intermediacy of (propargyl)Co2(CO)5 mdicals. In a similar vein, the binuclear molybdenum-complexed propargyl cations react with Na/Hg to produce... 

Interestingly, l-bromo-4-chlorobutane also cyclizes with 15 to produce [MoBr(NNCH CH CH H2)(dppe)2]Cl in which bromine is attached to molybdenum, and chloride is the anion. Recently, the secondary alkylation of alkyldiazenido complexes to form dialkylhydrazido complexes has been reported. " However, when 20 is treated with MeBr or EtBr, no alkyldiazenido complex is isolated, but instead a dialkylhydrazido complex is produced (Equation 18) ... 

Molybdenum(V) chloride, tungsten(VI) chloride, tungsten(V) chloride and tung-sten(V) bromide are reduced by acetonitrile to the tetravalent compounds MX4(AN)2, which are characterized as six coordinate complexes. Likewise vana-dium(IV) chloride is reduced to the solvate of the trichloride VCl3(AN)3 58. 

The effect of melt composition on the stability of Mo(V) chloride solutions in the melts is real but not readily attributable. At 550 C the concentration of the Mo(V) species decreased faster in LiCl-KCl melts than in NaCl-CsCI (Figure 6.11.6). This could be due to a higher stability of MoClg" complex ions in a NaCl-CsCI melt compared to a LiCl-KCl one. Small lithium cations with high ionic momentum have a greater destabilising effect on molybdenum complexes. 

Tin - A crystallographic study on [Rh(COD)(Ti -dppp)(SnCl3)] reveals two molecules in the asymmetric unit with trigonal bipyramidal and square-based pyramidal geometry about rhodium, while addition of tin dichloride to arene complexes [(T -arene)RuCI(ri -S2CPR3)] results in insertion into the ruthenium-chloride bond giving further tin trichloride complexes. A number of seven-coordinate molybdenum complexes [Mo(CX))2(PR3)Cl(r -phen)(SnRCl2)] ,... 

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