Complexing metal-ligand

Disiloxane, tetramesityl-, 3,206 Disproportionation iridium catalysts, 4,1159 Dissolution nuclear fuels, 6, 927 Distannene, 3,217 Distannoxane, 1,3-dichloro-, 3,207 Distibine, tetraphenyl-, 2,1008 Distibines, 2,1008 Disulfido ligands metal complexes, 2,531-540, 553 bonding, 2, 539 electron transfer, 2, 537 intramolecular redox reactions, 2,537 reactions, 2, 537... 

Numerous metal complexes have been proven to be active electrocatalysts for C02 reduction.1,66-68 These catalysts can be conveniently grouped into three main families metal complexes with polypyridyl ligands, metal complexes with macrocyclic ligands, and metal complexes with phosphorus ligands. 

Nakajima et al. (129) suggests that the stereochemistry is determined via intermediate 188 (Fig. 14). Unfortunately, nonlinear effects (78), which might be expected to shed light on the involvement of 2 equiv of ligand metal complex in the stereochemistry-determining event, were not examined in this system. 

Zhou and Pfaltz (149) note that complex 215 mirrors the behavior of van Koten s complex 210. The catalyst is trimeric in solution and solid state and displays an intricate nonlinear effect (78, 146) in the conjugate addition reaction, Fig. 19 (149). It seems likely that these ligand-metal complexes are structurally related. 

One of the most studied ligand-metal complexes is the bis(oxazoline)-ruthe-nium(ll) complex.Kurasowa and co-workers proposed that the aqua and amine complexes of bis(oxazoline)-ruthenium(ll) 17a-d also adopt a tetrahedral geometry about the metal center. These are only a few of many examples of the complexes formed between a variety of transition metals and bis(oxazoline) ligands that have been studied. ... 

Sibi s group studied a similar reaction using ligands 9b, 34a-c, and 161 with iodides 157b and 157c, tributyltin hydride 160 and A-crotonyl oxazolidinone 80a or A-cinnamoyl oxazolidinone 80b.As shown in Table 9.29 (entries 7 and 9), the inda-box ligands exhibited optimum results with yields up to 92% and selectivities up to 93% (ee). The use of the ligand-metal complexes in catalytic amounts led to lower yields and enantioselectivities (Fig. 9.50). ... 

The result is a small subset of 20-50 new catalysts. These are then synthesized and tested experimentally. The model is then updated and the cycle repeats. In theory this process can repeat indefinitely, but our results on industrial data show that the figures of merit usually converge after 5-6 cycles. This means that in principle it is possible to indicate an optimal region in a space of a million catalysts after testing less than 300 ligand-metal complexes ... 

Scheme 2.5 Self-assembly through hydrogen bonding of the 2-pyridone/2-hydroxypyridine system 1 (6-DPPon) to generate bidentate ligand metal complexes 3 for homogeneous catalysis.

Type of boron ligand Metal complex or complex unit partner Substituents at the boron Metal- boron ratio Ref. 

Figure 12-4 Structures of analytically useful chelating agents. Nitrilotriacetic acid (NTA) tends to form 2 1 (ligand metal) complexes with metal ions, whereas the others form 1 1 complexes.

Not mentioned in Table 2 (and often not in the original papers ) is the optical form (chirality) of the amino acids used. All the amino acids, except for glycine (R = H), contain an asymmetric carbon atom (the C atom). In the majority of cases the optical form used, whether l, d or racemic dl, makes little difference to the stability constants, but there are some notable exceptions (vide infra). Examination of the data in Table 2 reveals (i) that the order of stability constants for the divalent transition metal ions follows the Irving-Williams series (ii) that for the divalent transition metal ions, with excess amino acid present at neutral pH, the predominant spedes is the neutral chelated M(aa)2 complex (iii) that the species formed reflect the stereochemical preferences of the metal ions, e.g. for Cu 1 a 2 1 complex readily forms but not a 3 1 ligand metal complex (see Volume 5, Chapter 53). Confirmation of the species proposed from analysis of potentiometric data and information on the mode of bonding in solution has involved the use of an impressive array of spectroscopic techniques, e.g. UV/visible, IR, ESR, NMR, CD and MCD (magnetic circular dichroism). 

The stability of metal complex is also given by the number of chelate rings formed in the resultant ligand-metal complex. For example, desfer-rioxamine, the most widely used iron chelator, minimizes OH production by acting as a hexadentate ligand [Liu and Hider, 2002]. Unfortunately, there is not enough information on the denticity of polyphenols as metal chelators to assess the relevance of the stability of the flavonoid-metal complex formed. 

SCHEME 1 Protocol for the development and optimization of mobile phases on ligand-exchange-based CSPs. Note Use phosphate buffer only with CSPs containing ligand metal complex as the chiral selector. 

Karpishin, T. B. Stack, T. D. P. Raymond, K. N. Octahedral versus trigonal prismatic geometry in a series of catechol macrobicyclic ligand-metal complexes, J. Am. Chem. Soc. 1993,115, 182-192. 

Nickel-triarylphosphite complexes catalyze the dimerisation of butadiene to cyclooctadiene. Cyclododecatriene is an unwanted by-product, which results from trimerization catalyzed by the same catalyst. Table 3.2 shows the product yields using various ligand-metal complexes (the remainder in each case is a tarry polymeric material). 

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