Anionic chelating ligands

Until recently only complexes of low stability were known for AC s even in the case of anionic chelating ligands (especially in water Table 7). Numerous and much more stable chelate complexes of AEC s with multidentate anionic ligands are known however (see Table 7). The complexation constants (3) always follow the stability sequence Ca2+ > Sr2+, Ba2+ and are in general difficult to modify in a progressive, stepwise fashion. It is obviously of interest to be able to control both stability and selectivity of AC and AEC complexes, especially the former. 

Analogous to the work on dipicolinic acid reported in Section 31.5.2, a range of titanium(IV) peroxo complexes (35) have been prepared which encompass an oxygen-nitrogen anionic chelating ligand and hexamethylphosphortriamide.171 The crystal structure of... 

Scheme 4.4 Use of an inert Ru(II) centre to organise an anion chelate ligand.

The bidentate coordination behaviour of Lewis acid anion chelating ligands such as 4.69-4.78 suggests that very strong anion binding might be achieved with those Lewis acid groups as part of a macrocyclic... 

Figure 3.36 Imino/enamino tautomerism and coordination as an anionic chelate ligand.

Substitution of the trans halide ligand together with only one equatorial ligand by anionic chelate ligands is rare. Stone synthesized complex 102 by reaction of 101 with the bispyrazolylborate anion (7/6). One of the remaining two mutually trans carbon monoxide ligands is subject to further substitution [Eq. (81)]. 

Table 6 Nickel alkyl and aryl complexes containing anionic chelating ligands, Ni(R)(chelate)(L)...

Complexes prepared from [Rh(CO)2Cl]2 include (a) five-coordinate [Rh(CO)2L2CI] (L = many imidazoles), (b) [Rh(CO)2(bid)), [Rh(CO) P(OPh)(bid)] and [Rh(CO)(PPh )(bid)] (bid = the anionic chelate ligands, 2-carboxyquinolinato, 1,1,1-trifluoro - 5,5,5-tri-methylpentanedionato, N-hydroxy-N-nitrosobenzenaminato, oxinate derivatives, and the Schiff bases derived from condensations of 3-diketones with N-methyl-S-methyldithiocarbazates),(c) [ Rh(CO)2)2 -L4] (L4 = tetradentate azine dianions e.g. 0CgH4CH=NN=CHCgH40 ),... 

With sodium acetate as the source of the anionic chelating ligand, the precipitation of NaCl is slow and other factors may also be important in driving the reaction to completion. Attempts to generate the ruthenium(IV) complex [Ru(02CMe)Cl(r 3 ri -CioHi6)] using acetic acid failed. ... 

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