Ligands phenolate

Bis(phenolate) ligands are also present in two new lanthanide guanidinate complexes shown in Scheme 60, which were prepared by insertion of diisopropylcarbodiimide into the Ln-N bonds of appropriate neutral lanthanide amide precursors. ... 

Figure 13, indicates that the first mole of phenol is released in <30 s, the same elapsed time for the chemiluminescence to reach a maximum intensity. In fact, the measured rate constant r, for the rise in the chemiluminescence emission, is identical to the rate of the first phenol s release from the oxalate ester. Furthermore, the slower rate of release of the second phenol ligand has a rate constant that is identical to the chemiluminescence decay rate f. Thus, the model allows a quantitative analysis of the reaction mechanism, heretofore not available to us. We intend to continue this avenue of investigation in order to optimize the chemiluminescence efficiencies under HPLC conditions and to delineate further the mechanism for peroxy-oxalate chemiluminescence. 

A dinuclear iron(ll/Ill) complex bearing a hexadentate phenol ligand displayed moderate activity toward aziridination of alkenes with PhlNTs a large excess of alkene (2,000 equiv. vs PhlNTs) was required for good product yields (Scheme 22) [76]. It is noteworthy that complex 4 is active in the aziridination of aliphatic alkenes, affording higher product yields than copper (11) catalysts with tetradentate macrocyclic ligands [77]. 

There are a reasonable number of structurally characterized zinc compounds with bound THF molecules. For example, a six-coordinate zinc porphyrin complex with axial THF donors and a four-coordinate zinc center with two THF ligands and two phenolate ligands.341,357 Although less common there are other structural examples of ether solvents, such as diethyl ether, coordinated.358 The X-ray structure of zinc chloride with 1,4-dioxane ligands shows a monomeric four-coordinate zinc center with two 1,4-dioxane ligands.359... 

Brunner and Berghofer (48) investigated ligands composed of a combination of salicylaldimines and oxazolines. Intriguing effects of the electronic character of the phenol were noted. The electron poor p-nitrophenol 74b provided the trans cyclopropane in 53% ee, compared to 6% ee using the parent phenol ligand 74a. 

Figure 11. Macrocyclic phenolate ligands containing a 1,4,7-triazacyclononane backbone (see Scheme 1 for an explanation of the abbreviations used).

Figure 26. Selected phenol ligands and Cu(II) complexes thereof designed to mimick the inactive form of GO. Complexes marked with an asterisk have been crystallographically characterized.

The H64Y variant of Mb is an example of the former situation in that the tyrosyl side chain coordinates to the heme iron of the oxidized variant. As expected for a variant with an anionic phenolate ligand, the reduction potential of this variant is 40 mV lower than that of the wild-type protein (Table I). Although this change is consistent with stabilization of the oxidized form of the protein, the fact that the tyrosyl ligand is not coordinated in the reduced protein complicates quantitative interpretation of this shift in potential. 

Aresta (54) has investigated the platinum complexes formed with o-allylphenol and o-allylthiophenol. The phenolic ligand reacts with the PtCl4 ion (in a suitable acetate buffer) to form the chelate complex shown in Fig. 40. The coordinated double bonds of this compound are successively replaced by two equivalents of pyridine. 

We have utilized somewhat less-effective optional approaches to copolymer purification with attendant catalyst recovery. One of these methods involved the replacement of the f-butyl substituents on the 5-position of the phenolate ligands with poly(isobutylene) (PIB) groups, as illustrated in Fig. 14 [39]. Importantly, this chromium(III) catalyst exhibited nearly identical activity as its 3,5-di-t-butyl analog for the copolymerization of cyclohexene oxide and carbon dioxide. The PIB substituents on the (salen)CrCl catalysts provide high solubility in heptanes once the copolymer is separated from the metal center by a weak acid. 

The concept of using group I metal initiators was applied in order to minimize the toxicity generated by heavy metal residues in the end product PLAs when using metals like aluminum, tin, and lanthanides as initiators. In recent years, dinuclear lithium and macro-aggregates with phenolate ligands have attracted substantial interest, mainly due to uncommon strucmral feamres and their ability to catalyze formation of polyester and various other polymeric materials via ROP [28]. A series of lithium complexes supported with 2, 2-ethylidene-bis (4, 6-di-tert-butylphenol) (EDBP-H2) 2-6, (Scheme 6) are excellent initiators for the ROP of L-lactide in CH2CI2 at 0 °C and 25 °C [33-35]. In this case, the PDIs of the obtained PLAs were quite narrow (1.04—1.14) and a Unear relationship between and the monomer-to-initiator ratio ([M]o/[I]o) existed at 0 °C. Dimeric complexes 4 and 6 were the... 

Similarly to 3b, among the methylaluminum diphenolates examined, 3a,c-g with substituents at the ortho positions of the phenolate ligands were quite effective for accelerating the polymerization, allowing the formation of narrow MWD PMMAs with the Mn values in fair agreement with those expected from the initial mole ratio of MMA to 1 (X=Me) (Table 1, runs 1-7). In terms of both... 

The emphasis on the study of hemoproteins and the iron-sulfur proteins often distracts attention from other iron proteins where the iron is bound directly by the protein. A number of these proteins involve dimeric iron centres in which there is a bridging oxo group. These are found in hemerythrin (Section 62.1.12.3.7), the ribonucleotide reductases, uteroferrin and purple acid phosphatase. Another feature is the existence of a number of proteins in which the iron is bound by tyrosine ligands, such as the catechol dioxygenases (Section 62.1.12.10.1), uteroferrin and purple acid phosphatase, while a tyrosine radical is involved in ribonucleotide reductase. The catecholate siderophores also involve phenolic ligands (Section 62.1.11). Other relevant examples are transferrin and ferritin (Section 62.1.11). These iron proteins also often involve carboxylate and phosphate ligands. These proteins will be discussed in this section except for those relevant to other sections, as noted above. 

The transferrins belong to the iron-tyrosinate group of proteins discussed in Section 62.1.5.5.2. Charge transfer from phenolate ligands to Fem accounts for the salmon-pink colour of transferrin. The detailed coordination environment of the iron in transferrin is not known with certainty, as... 

McBride and Wesselink (1988) studied IR spectra of catechol adsorbed onto the oxide surface and found evidence that the compound was chemically altered, indicating that chemisorption was the dominant mechanism. In addition to catechols, phenols are known to adsorb onto metal oxide surfaces. This adsorption is dependent on the number and position of hydroxy substitutions on the benzene ring. Diphenolic compounds adsorb to a greater extent than monophenolic compounds, suggesting the formation of a bidentate bond with the metal oxide. This bidentate bond is formed when the two phenolic ligands coordinate with one or two surface metal ions (McBride and Wesselink, 1988). 

Boje, K. M., Sak, M. and Fung, H. L. 1988. Complexation of nifedipine with substituted phenolic ligands. Pharm. Res5 655-659. 

Another non-heme system made use of hexadentate phenol ligands [98]. However, the catalytically active species was only formed upon ligand oxidation by excess of PhI=NTs. Furthermore, a large excess of the alkene was required (2000 equiv. vs. PhI=NTs). The reaction of cyclooctene and 1-hexene gave yields of about 50%, which represents a significant improvement over the earlier described copper systems [99]. 

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