Transition-metal-oxalate complexes

Other first-row transition metal oxalate complexes behave similarly." ... 

The aim of the present chapter is to look at the structures of transition-metal-oxalate complexes with nucleobases as a valuable source of information on molecular recognition patterns controlling the formation of these systems. Therefore, we focus our attention not only on the metal-nucleobase binding modes but also on the intramolecular interligand interactions, which cooperate with the coordination bond in the stabilization of the resulting mixed-ligand complexes. 

Despite the volume of work concerned with metal-catalyzed decomposition of diazo compounds and carbenoid reactions 28>, relatively little work has been reported on the metal-catalyzed decomposition of sulphonyl azides. Some metal-aryl nitrene complexes have recently been isolated 29 31>. Nitro compounds have also been reduced to nitrene metal complexes with transition metal oxalates 32K... 

Thermogravimetric curves for solid K2[Pd(C204)2],3H20 and other transition-metal oxalates indicate that the thermal stability of the anhydrous complexes decreases with increase in electron affinity of the central metal ion. AH values were obtained for both dehydration and decomposition. Subsequent studies showed carbon dioxide as the only gaseous product, the decomposition occurring via electron transfer from a 304 ligand to the central palladium. ... 

Oxalamidinate anions represent the most simple type of bis(amidinate) ligands in which two amidinate units are directly connected via a central C-C bond. Oxalamidinate complexes of d-transition metals have recently received increasing attention for their efficient catalytic activity in olefin polymerization reactions. Almost all the oxalamidinate ligands have been synthesized by deprotonation of the corresponding oxalic amidines [pathway (a) in Scheme 190]. More recently, it was found that carbodiimides, RN = C=NR, can be reductively coupled with metallic lithium into the oxalamidinate dianions [(RN)2C-C(NR)2] [route (c)J which are clearly useful for the preparation of dinuclear oxalamidinate complexes. The lithium complex obtained this way from N,N -di(p-tolyl)carbodiimide was crystallized from pyridine/pentane and... 

Photooxidation of coordinated oxalate has been known since the earliest studies of transition metal photochemistry (42). In these reactions oxalate ligand is photooxidized to CO2, and up to two metal centers are reduced by one electron (e.g. ferrioxalate). We wondered whether the oxalate ligand could be a two-electron photoreductant, by simultaneous or rapid sequential electron transfer, with metals prone to 2e redox processes. Application of this concept to l6e square planar d complexes, Equation 15, was attractive because it should produce solvated I4e metal complexes that are inorganic analogues of... 

Surface electric potential control (or surface charge control) of the rate of flocculation is possible for any adsorptive that forms a surface complex with suspended particles, as discussed in Section 6.1 and in Chapter 4 (cf. Table 4.2). Among these adsorptives for soil colloids are oxyanions, such as phosphate or oxalate, and transition metal cations. An expression analogous to Eq. 6.78 can be developed to define points of zero charge for any such adsorptive, as illustrated in Fig. 6.9.42... 

Infrared and UV/vis data have been used by several authors to identify the C=C, C=0, and M—O stretches in the complexes synthesized 15, 18-21, 37, 38, 41, 44, 50, 54, 56, 58, 59, 64-66, 69, 74, 78, 80, 82, 103). Except in the initial research on first-row transition metal complexes of squaric acid, where these data were used in proposing structures, IR and UV/vis analysis have been used as supporting evidence for the particular coordination mode of the ligand 19,21,22, 45, 52, 59, 65). Infrared spectroscopy has also been utilized in the study of mixed oxalate/squarate complexes 118), although not to the same extent as in complexes of the oxalate ion. For example, Scott et al. studied the IR properties of Co(III) oxalate complexes with the hgand in a variety of chelating/bridging situations 119). 

Carbon dioxide, 0=C=6 , mp —57°C (5.2 atm), bp —79 °C (sublimes), is obtained from the combustion of carbon and hydrocarbons in excess air or oxygen or by the pyrolysis ( calcination ) of CaCOs (limestone). The photosynthesis in plants reduces CO2 to organic matter, but the similar reduction of CO2 in a nonliving system ( in vitro ) appears to be very difficult. However, CO2 can be reduced electrochemically to methanol, formate, oxalate, methane, and/or CO depending upon the conditions. Numerous transition metal complexes of CO2 are known,which exhibit the modes of metal-C02 bonding depicted in Figure 2. 

Figure 1 The stabihty of complexes of divalent transition metal cations. 1, Triethylenetetramine, NH2C2H4NHC2H4NHC2H4NH2 2, EDTA, ethylenediaminetetraacetic acid 3, diethylenetriamine, NH2C2H4NHC2H4NH2 4, norleucine, Me(CH2)3CH(NH2)C02H 5, 1,2,3-triaminopropane, NH2CH2CH(NH2)CH2NH2 6, ethylene-diamine, NH2C2H4NH2 7, sahcylaldehyde, 2-(HO)CgH4CHO 8, oxalic acid, HO2CCO2H. For norleucine, 4, the values for log 82 are plotted...

Metal ascorbates are frequently associated with redox chemistry, particularly when the metal is redox active, which includes most transition metal ions . The redox activity of AA also leads to decomposition of its Co(II) and Gd(III) complexes into oxalate complexes . AA is considered a major reductant for Cr(IV) to yield Cr(III) °. Reduction of CrOs with excess of AA affords a Cr(III)-ascorbate complex. However, the structure of this complex was not determined. Since Cr(III) has been demonstrated to play a role in glucose metabolism, it is thus important to investigate further the reduction of high-valent Cr species by AA and binding of AA to Cr(III). 

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