Molybdenum complexes polymeric

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]... 

Hydrazido and organohydrazido ligands are important intermediates in the reduction or utihzation of N2 in biological and chemical systems, and their molybdenum complexes are potential catalysts for aUcene polymerization and metathesis reactions. 

The kinetics of ADMET with complex 6 were compared to those of complex 2 by measuring the volume of ethylene liberated from ADMET reactions over time [35], Obtaining an approximate second order rate constant from the DP versus time curves, it was found that molybdenum complex 2 polymerizes 1,9-decadiene 24 times faster than ruthenium complex 6 (Tab. 6.1). 

Molybdenum is present in soil solutions as molybdate (H2M0O4, pK 5). Molybdate can reduce to MoOJ under reducing conditions. As is true for boron, molybdate forms complex polymeric ions at high concentrations in water. In soil solutions, however, only the monomer exists. 

Folin-Denis method Reduction of complex polymeric ions formed from phosphomolybdic and phospholungslic heteropoly acids to complex molybdenum-tungsten blue. detection wavelength 725 - 770 nm recommended for uniformity 765 nm complexes and reagent are unstable in alkaline solution, formation of precipitates, controlled sequence and timing of the addition of reagents (reproducibility ), deviation from Beer-Lambert law (high phenol contents), reaction is stoichiometrically predictable 105,106,110... 

Dimeric molybdenum complexes bearing metal-metal quadruple bonds have been prepared in better yield than previously reported conventionally. The tetra-carboxylate complexes Mo2(p-02CR)4 (R = Me, Et, Ph) were synthesized by heating Mo(CO)6 and the corresponding carboxylic acid at 180-200 °C for 15-32 min." The treatment of a MeOH/CH2Cl2 solution of Cu(BF4)2 H20 and 2,2 -dipyridyldisulfide at 140 °C for 2 h led to the formation of the polymeric Cu complex [Cu9(C5H5NS)8(SH)g](BF4) in 55% yield and the Cu complex [ Cu(dps)2)2(p-S)] +, dps = 2,2 -dipyridylsulfide, in 4% yield. In this unusual reaction, C-S and S-S bonds are cleaved simultaneously. 

Acyclic diene molecules are capable of undergoing intramolecular and intermolec-ular reactions in the presence of certain transition metal catalysts molybdenum alkylidene and ruthenium carbene complexes, for example [50, 51]. The intramolecular reaction, called ring-closing olefin metathesis (RCM), affords cyclic compounds, while the intermolecular reaction, called acyclic diene metathesis (ADMET) polymerization, provides oligomers and polymers. Alteration of the dilution of the reaction mixture can to some extent control the intrinsic competition between RCM and ADMET. 

Transition-metal-based Lewis acids such as molybdenum and tungsten nitro-syl complexes have been found to be active catalysts [49]. The ruthenium-based catalyst 50 (Figure 3.6) is very effective for cycloadditions with aldehyde- and ketone-bearing dienophiles but is ineffective for a,)S-unsaturated esters [50]. It can be handled without special precautions since it is stable in air, does not require dry solvents and does not cause polymerization of the substrates. Nitromethane was the most convenient organic solvent the reaction can also be carried out in water. 

Molybdenum allyl complexes react with surface OH groups to produce catalysts active for olefin metathesis.34 35 Using silica as a support for the heterog-enization of Ti and Zr complexes for the polymerization of ethylene did not give clear results.36 In these cases, HY zeolite appeared to be a more suitable support. The comparable productivity of the zeolite-supported catalyst with... 

In the case of other Group 6 metals, the polymerization of olefins has attracted little attention. Some molybdenum(VI) and tungsten(VI) complexes containing bulky imido- and alkoxo-ligands have been mainly used for metathesis reactions and the ring-opening metathesis polymerization (ROMP) of norbornene or related olefins [266-268]. Tris(butadiene) complexes of molybdenum ) and tungsten(O) are air-stable and sublimable above 100°C [269,270]. At elevated temperature, they showed catalytic activity for the polymerization of ethylene [271]. 

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