4-Isopropyltropolone, complexation

Maiti B, Desai SR. 1986. High-performance liquid chromatographic separation of beryllium, cobalt, nickel and chromium as the (3-isopropyltropolone complexes and its application to the determination of chromium in air samples. Analyst 111 809-811. 

The formation constants of an actinium isopropyltropolonate complex were determined. Thermochemically relevant studies of thorium enolates generally involve bis(pentamethyl-cyclopentadienyl)thorium derivatives. Cp 2Th(Cl)(C(0)CFl2Bu-f) with an anionic acyl group that readily rearranges to the isomeric enolate Cp 2Th(Cl)OCH=CHBu-t. The Z-isomer is formed upon heating and the -isomer upon catalysis with Cp 2ThH2. Is the E or Z enolate thermodynamically more stable For the simple alkyl enolates MeCH=CHOR, the equilibration reaction of the Z- and E-isomers is nearly thermo-neutral . Consider the two species Cp 2Th(H)OCH(Bu-t)2 and Cp 2Th(H)0-2,6-C6H3 (Bu-f)2. The reversible addition of CO yields the rp- formyl derivative in reactions that are 19 4 and 25 6 kJmoR exothermic. These formyl species dimerize to form the classical enediolate, Cp 2Th(OR)OCH=CHO(OR)ThCp 2. This product is formed as the Z-isomer, plausibly thermodynamically preferred over the -isomer, much as (Z)-MeOCH=CHOMe is preferred over its E-counterpart by 6.0 0.2 kJmoR. ... 

Several amine adducts of j -isopropyltropolone complexes of nickel(ii) have been isolated NiL2(py)2, NiL2(y-pic)2, NiLjfa-pic), NiLjY (Y = piperidine, or diethyl-amine /I = 1 or 2). The complexes are octahedral and probably trimeric. The crystal structure of bis(diphenyldipyrazolylborato)nickel(ii), (Ph2B(C3H3N2)2 Ni has been determined. ... 

K. Ishihara, S. Funahashi and M. Tanaka, Inorg. Chem. 22, 194 (1983) with Fe(III) complexing with 4-isopropyltropolone, the assessment is made on the basis of A values. 

The complexes MLa (M = Th, U) with HL = oc-, /J- or y-isopropyl tropolone are also known. Molecular weight determinations (benzene solution) for the thorium compounds indicate that the a compound is close to a dimer, whereas the 0 and y derivatives are approximately trimeric. The corresponding uranium(IV) complexes are all monomers. All three thorium compounds readily form monohydrates and the structure of the hydrated y-isopropyltropolonate is described on p. 1144. 

A neutral complex NiLj has been reported with L = 5-isopropyltropolonate.1599 The complex is paramagnetic in dilute solution as indicated by NMR measurements. 

For case (b) original data are reported. Complexation of Zr in aqueous phase by yff-isopropyltropolone cannot be excluded. Due to the missing documentation on method (a), the confirmation of the stoichiometry by two independent extraction methods is considered only as Indication for the presence of ZrOH as the dominant solution species and, as sueh, the presence of Zr" at the high acidities used cannot be completely ruled out. 

This paper follows on from the early work by these authors (see discussion of [74TRI/SCH] in this Appendix). In this and the earlier work, the authors used the solvent extraction technique with y isopropyltropolone to study the complexation of Zr. In this work, they studied the complex formation of zirconium with chloride, thiocyanate, sulphate, oxalate and phosphate. On the basis of their earlier work, they proposed that reactions of the type... 

Anionic pentakis tropolonato complexes, M [M (trop)s], are known for M = Th (M = Li, Na or K), M = Pa or U (M = Li). TTie thorium compounds are prepared by heating Th(trop)4 with H trop and M OH in a mixture (1 1 2 by volume) of ethanol, water and methyl cyanide. Li[Pa(trop)s] has been obtained from Pa(trop)4 in the presence of Li(trop) in DMF, and Li[U(trop)5] has been prepared by both of the above methods. Sodium salts, Na[ThLs], are also known for HL = a- and y-isopropyltropolone. 

Inhibitors of COMT are frequently competitive substrates, such as pyrogallol. No potent irreversible inhibitors of the enzyme are available. Figure 8 shows some of the substances which are effective inhibitors in vitro. 8-hydroxyquinoline is slightly more potent than pyrogallol as an inhibitor, but other metal chelating substances, such as EDTA, are inactive. The tropolone compounds, 4-methyl-tropolone and 4-isopropyltropolone ( -thujaplicin) are isosteric with catechols and can probably form a complex with magnesium ions and the active centre of the enzyme. 3,4 Dihydroxy-a-methylpropiophenone (U-0521) has recently been found to be a powerful competitive inhibitor both in vitro and in vivo. 

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