Malonate complexes

The results are sparse and in some cases inconsistent both in regard to the stoichiometry of the species formed and in relation to the values of the stability constants. Some results from a systematic study of simple phosphonates (260) are given in Table XVI together with data relating to malonate complexes for comparison purposes. 

Copper complexes of substituted malonic acids had no influence on the acute toxicity towards adult zebra fish [227], possibly due to stronger chelating groups at the gill epithelia. In contrast, hatching of zebra fish, which is already very sensitive to Cu2+ alone, was delayed in the presence of hydrophobic ra-hexade-cyl malonate, and was not influenced by the less hydrophobic benzyl malonate [227], Overall, it appeared that the toxicity of free Cu2+ and the Cu-hexadecyl malonate complex was additive [227],... 

As the size of the chelating ligand increases, a maximum in stability is normally obtained for 5 or 6 membered rings. For lanthanide complexes, oxalate forms a 5-membered ring and is more stable than the malonate complexes with 6-membered rings. In turn, the latter are more stable than the 7-membered chelate rings formed by succinate anions. 

Both CO2 activation and enolate formation are combined in the preparation of malonic acid derivatives. The reaction of CO2 with methacrylic esters or methacry-lonitrile and under visible light irradiation produced the corresponding aluminum porphyrin malonate complex. When diethylzinc was added to this system, Al(TPP)Et could be regenerated by axial ligand exchange reactions, and the malonic acid derivatives were formed catalytically with respect to the aluminum porphyrins in a one-pot photosynthetic route (Scheme 1). The first step in this... 

The enthalpies and entropies of formation of mono-mandelato-complexes have been determined and, in comparison with other hydroxycarboxylic acid complexes, the enthalpy order of stabilization is lactate > a-hydroxyiso-butyrate mandelate > glycolate, whereas the entropy order of stabilization is glycolate > a-hydroxyisobutyrate > mandelate > lactate. The stability constants and enthalpy of formation of mono- and di-malonate complexes have also been measured.The mono-1,1-cyclopentanedicarboxylato-complexes are less stable than the corresponding malonate species. 

In the orthorhombic Eu2(mal)3 8H2O (Pnma, Z=4) malonate complex, there are two independent europium ions 195). The coordination polyhedron aroimd one of the Eu(III) ions is a distorted square antiprism with average Eu—O =2.42 A. The other Eu(III) ion is nonacoordinated, with nine oxygen atoms... 

Malonate complexes, osmium, 37 286 Maltose phosphorylase, arsenate and, 44 194 compound I formation, 43 99 exogenous reduction of intermediates, 43 116-119... 

The neutral carboxyl group is not very effective in increasing the reduction rate of the complex. However, when the proton is removed from the carboxyl, the effect can increase and is greatest when the carboxyl ion is in a configuration favorable to chelation. Thus, the inverse (H+) path is not even observable for acid succinate in the same acidity range as that for which this path is important in the acid malonato reaction. The acid dissociation constants are known well enough so that the behavior difference between acid malonato and acid succinato can not be entirely ascribed to different acidities of the complexes. The results obtained with the acid malonate complexes, as reported in Table II, incidentally provide no support for the hypothesis (22) that electron transfer takes place by remote attack across hydrogen bonds. 

Zinc dibenzyl malonate complex 129, prepared by the action of Et2Zn on dibenzyl malonate, was found to be superior to alkali metal dibenzyl malonates, in terms of enantiomeric control, in the allylic substitution with ( )-130 catalysed by an in situ prepared Pd-(/ )-BINAP complex (equation 73)164. 

Solution studies of malonate complexes include the unusual observation that [(H20)sCr(Hmal)]2+ has considerable kinetic stability.924 The mechanism of ring closure has been the subject of detailed study.925 The methylenic protons of [Cr(mal)3]3- undergo bromination when a suspension of the potassium salt is treated with bromine in ether (2 h). Legg and co-workers927 have recently used a number of malonate complexes to demonstrate that the 2H NMR spectra are both readily observed and useful for solving structural problems. The resolution that may be obtained by this method may be appreciated by the fact that in the complex [Cr(mal-d2)2(bipy)]2 the geminal protons of the malonate are clearly resolved. 

Reaction 5. Another aspect of the reaction chemistry of Mn(III) is demonstrated by the classic kinetic studies of the decomposition chemistry of manganese (III) oxalate complexes (35, 36). These studies derive from an earlier discussion of the synthesis of manganese (III)-oxalate compounds (37). A similar set of kinetic and synthetic investigations, have been summarized for the manganese (III )-malonate complexes (38, 39). Both sets of studies confirm that Mn(III) has a particularly strong... 

Malonate complexes of metal ions should, on the other hand, be chelates with two equivalent bonds, i.e. one would expect values of AH ... 

Data are available for malonate complexes of the divalent ions of the first transition series from Mn2+ on, and also for H+, Table 4. For Cu2+, Zn2+ and H+, a comparison with the corresponding acetate systems is thus possible. Unfortunately, the comparison is made somewhat uncertain by the fact that the acetate and malonate data, except for H+, refer to media of very different ionic strength, which presumably has a consi-... 

Table 4. Thermodynamic functions for the formation of malonate complexes, at 1 = 0 and 25° C. All values of A H° calorimetrically determined, except for H+ (temperature coefficient 0—60° C)...

The malonate complex of Eu(III), Eu2(malonate)3 8H2O is interesting since there are two different coordination geometries, and only five of the water molecules are coordinated [167], One of the Eu ions is eight-coordinate in the form of a distorted square antiprism and the other Eu ion is nine-coordinate, distorted tricapped trigonal prism. In the analogous neodymium complex, six water molecules are coordinated because of the difference in ionic radius. The neodymium complex is nine-coordinate with monocapped antiprismatic geometry [168]. 

The catalyzed isomerization of the malonate complex was found to proceed by a different mechanism from that of the oxalate complex. The rate constants and the activation parameters are given in Table 7.24. No linear free energy relationship was found to be valid in the malonate system. 

A plot of log Ln vs log K for the malonate system is shown in Fig. 7.31. The catalyzed isomerization of the malonate complex proceeds by a different mechanism from that of the oxalato analogue because (i) lack of linear free energy relationship between the catalytic rate constants and the complex formation constants, (ii) linear relationship between catalytic rate constants (log A n) and formation constants of lanthanide malonate complexes (log K ), (iii) catalytic rate constants for the malonate system are smaller than the corresponding rate constants for the oxalate system. The proposed mechanism for... 

Fig. 7.31. log-log plot of the catalytic rate constants for the lanthanide ion catalyzed trans-cis isomerization of frans-bis(malonato)diaquochromate(III) (25°C, / = 1.5 M adjusted with NaNOj) vs. the formation constants for the lanthanide/malonate complexes (25°C, / =0.1 M) [84],... 

Bronsted LFERs also apply to reactions of metal ions (Lewis acids). Dissociation rates of Ni(II) complexes are correlated with corresponding dissociation equilibrium constants. This suggests that the reactions occur by dissociative interchange, in which breakage of the Ni(II)-ligand bond predominates over formation of the Ni(II)-water bond in the rate-determining step (Hoffmann, 1981). In addition, rates of metal-catalyzed decarboxylation of malonic acid are correlated with the stability constants for the metal-malonate complexes (Prue, 1952). 

KH Chung, E Hong, Y Do, C-H Moon. Unusual six- and eight-coordinated cadmium(II) malonate complex relevance to 113Cd NMR probe of metal binding sites on metalloproteins. J Chem Soc Chem Commun 2333—2334, 1995. 

Stoessell and Pittman (1990) concluded that, under reservoir conditions, aluminum-acetate complexes would be insignificant but that aluminum-oxalate and aluminum-malonate complexes may be significant. They also suggested that high aluminum concentrations measured in oxalic acid may be due to enhanced dissolution kinetics at low pH, not the presence of organic anions. ... 

The effect of the formation of Al-oxalate and/or malonate complexes is to increase the amount of dissolved aluminum in a water perhaps by as much as 2 to 3 orders of magnitude according to Figs. 5 and 6. Chemical model predictions are in accordance with studies of soil zone geochemistry (Lind and Hem 1975 Antweiler and Drever 1983) where elevated aluminum concentrations are measured in the presence of OAA. Conversely, reports of elevated Al in petroleum reservoir formation waters or in other deep brines are rare (Hem 1985 L.S. Land, pers. comm, to W.J.H. 1990). Normal Al concentrations may indicate lack of OAA in these waters or... 

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