Hydrolysis molybdenum complexes

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>. 

The molybdenum complex is the most unstable, and decomplexation is observed at the ketal hydrolysis stage. 

Molecular examples of trivalent molybdenum are known in mononuclear, dinuclear, and tetranuclear complexes, as illustrated in Figure 5. The hexachloride ion, MoCk (Fig- 5a) is generated by the electrolysis of Mo(VI) in concentrated HCl. Hydrolysis of MoCP in acid gives the hexaaquamolybdenum(III) ion, Mo(H20) g, which is obtainable in solution of poorly coordinating acids, such as triflic acid (17). Several molybdenum(III) organometaUic compounds are known. These contain a single cyclopentadienyl ligand (Cp) attached to Mo (Fig. 5d) (27). 

The molybdenum-mediated arylamine cyclization was also applied to the total synthesis of pyrano[3,2-a]carbazole alkaloids (Scheme 26). Reaction of the 5-aminochromene 71 with the complex salt 62 affords the complex 72, which on oxidative cyclization provides girinimbine 73, a key compound for the transformation into further pyrano[3,2-a] carbazole alkaloids. Oxidation of 73 with DDQ leads to murrayacine 74, while epoxidation of 73 using meta-chloro-perbenzoic acid (MCPBA) followed by hydrolysis provides dihydroxygirinim-bine75 [113]. 

Combination with bipyridyl hgand in carbon tetrachloride followed by hydrolysis yields a molybdenum oxychloride bipyridyl complex of formula MoOCR(bipy). When mixed with ammonium chloride in acetonitrile and water, an oxychloride-acetonitrile complex, NIRfMoOCRCHsCN], is obtained. 

MgATP hydrolysis and, 47 189-191 nitrogenase complex, 47 186-189 substrates, 47 192-202 molybdenum iron proteins, 47 161, 166-174, 176-183, 191-192 structure, 47 162-164, 166-170 nitrogen fixation role, 36 78 in nitrogen fixation systems, 27 265-266 noncomplementary reactions with Sn", 10 215... 

Tables 1 and 2 gives the numerical data for a series of vanadium (II), chromium (III), manganese (IV), molybdenum (III), rhenium (IV), iridium (VI), cobalt (II), and nickel (II) complexes. The first spin-allowed absorption band, caused by an internal transition in the partly filled shell, has the wavenumber equal to A. If spin-forbidden transitions are superposed on this band, a certain distortion from the usual shape of Gaussian error curve can be observed, and one takes the centre of gravity of intensity as the corrected wavenumber ai. One has to be careful not to confuse electron transfer or other strong bands with the internal transitions discussed here. Obviously, one has also to watch for absorption due to other coloured species, produced e. g. by oxidation or hydrolysis of the solutions. In the case of certain octahedral nickel (II), and nearly all tetrahedral cobalt (II) complexes, the first band has not actually been...

Molybdenum pentafluoride is a bright yellow solid with a melting point of 67° and an extrapolated boiling point of 211°.2 It is very susceptible to hydrolysis however, it appears quite stable in a dry, stainless-steel vessel and can be handled for short periods in a dry-box (P205). It is insoluble in most organic solvents but dissolves in dimethyl ether and acetonitrile, giving pale yellow solutions from which addition complexes are obtained.4 The solid contains a tetramer, Mo4F20. 

Wide-range pH sensors have also been made using the Eu(III) complexes of ligands 61 and 62, which are prepared from the appropriate a-haloamide of 2-methylquinoline reacting either with cyclen or with the molybdenum triearbonyl complex of cyclen (62) followed by phos-phinoxymethylation and base hydrolysis (77). 

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