Tungsten , coordination polymers

B. Das, M. Srilatha, B. Veeranjaneyulu, B. S. Kanth, Helv. Chim. Acta 2011, 94, 885-891. Molybdenum- and tungsten-based coordination polymers as catalysts for an efficient and rapid synthesis of hexahydro-5-oxoquinoline-3-carboxylates and 1,4-dihydropyridine-3,5-dicarboxylates. 

Rhodium, " titanium,and tungsten " complexes have also been used for this reaction. The reaction can be promoted photochemically and the rate is enhanced by the presence of primary amines.Coordinating ligands also accelerate the reaction,polymer-supported promoters have been developed " and there are many possible variations in reaction conditions.The Pauson-Khand reaction has been done under heterogeneous reaction conditions, and with... 

Historically, complex mixtures, usually based on a metal halide or oxo-halide, a tin alkyl, an alcohol, and an additive, have been used to generate the metal alkylidene in situ. However, with these initiators, usually no control is achieved and thus the polymers produced by such ill-defined systems display broad dispersities. With organometallic coordination catalyst systems containing molybdenum or tungsten, it is possible to bring about ROP of cycloolefins to linear unsaturated polymers, for example, of cyclopentene to poly (1 -pentenylene). 

The seven-coordinate compounds react rapidly at room temperature with an excess of terminal alkyne, such as PA or r-BA, to give an unsaturated polymer in high yield. All binuclear compounds of tungsten(II) polymerise PA at comparable rates that are qualitatively very fast (Table 1). 

The ROMP of norbornene catalysed by different seven-coordinate tungsten and molybdenum compounds was carried out in serum-capped flasks at the catalyst-to-monomer ratio of 1 to 100 at room temperature in toluene or dichloromethane solution. The best catalyst appears to be [(CO)4Mo( Li-Cl)3Mo(SnCl3)(CO)3]. The molecular weight of the poly-NBE formed is very high (M = ca. 10 ). The fraction of cis double bonds determined from NMR spectra varies from 27 to 70%. Unfortunately, the polymers lose their solubility with time and frequently change to intractable solids whose structure is difficult to elucidate. The polydispersities of such polymers are 2 or higher. 

Finally it is noteworthy that extended-chain metal-alkyUdyne polymers [W /r-C(4)C6H2N-3,5-Me2 (OBn )3l and [W /i-C(3)CeH4N (OBu )3] have been structurally characterized. In the 4-alkynyl-3,5-dimelhylpyridyl complex the tungstens are in the square pyramidal five-coordination but in the 3-alkynylpyridyl complex the tungstens adopt the TBP configuration. ... 

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