Mixed-ligand reactivity

Gnmwald-Winstein analysis, 505 Chromium(III) complexes doublet excited states reactions, 400 emission rules, 395 ligand field states reactivity, 397 magnetic behavior, 272 mixed-ligand reactivity, 398 nitrito... 

Mixed ligand reagent Reactivity and properties Reference... 

Mixed-ligand Crm complexes have a particularly rich substitutional photochemistry in that two (or more) reaction modes are normally observed. Data for the well-studied class of acidoamine complexes are presented in Table 2. The dominant photochemical reaction for [CrX(NH3)5]2+ complexes in aqueous solution is NH3 aquation, with X- aquation occurring to a lesser extent (equation 31). In contrast, the latter pathway is the favored thermal reaction of these compounds. Such behavior again illustrates that the reactivity of ligand field excited states can differ sharply from that of the ground state. 

These oxidized species, 2, 3, and 4, were used to prepare series of mixed ligand complexes and thus made available catalyst systems in which reactivity and selectivity can be carefully controlled. 

Sigman and Jorgenson490 have found that zinc(II) catalyzes the transesterification reaction between N- (/3-hydroxy ethyl) ethylenediamine and 4-nitrophenyl picolinate. This reaction involves a reactive mixed ligand complex (152) in which the zinc(II) ion perturbs the p/fa of the hydroxyethyl group of N-(/3-hydroxyethyl)ethylenediamine to provide a high effective concentration of the nucleophile. Intramolecular nudeophlic attack then occurs at the carbonyl group of p-nitrophenyl picolinate. This system provides a somewhat unique example of intramolecular... 

The reaction involves the catalyst-substrate complex (158). Molecular models show that in the mixed ligand complex (158), the N—O- group is in a position to attack the acetyl group of (157). The zinc complex (156) is also an excellent catalyst for the hydrolysis of p-nitrophenyl acetate in fact it is comparable in reactivity to hydroxide ion, although its p.Ka is only 6.5, (Table 29). 

The interaction of the metal alkoxides with the salts of carboxylic acids or with p-diketonates of other metals is especially attractive for the synthesis of bimetallic molecular precursors in the cases, when the preparation of the alkoxide of the other metal is somehow hindered or it is insoluble or irreactive under the conditions applied. This method has been widely used for the sol-gel preparation of HTSC materials (because of low solubility and reactivity of Cu(OR)2) and lead-containing ferroelectrics (in the view of difficult synthesis and low stability of Pb(OR)2). It should be mentioned that the reaction between a metal alkoxide and a functional derivative does far not always lead to the formation of a mixed-ligand bimetallic complex ... 

The coordinatively unsaturated complexes [M(CO)i(hfN)]2 are extremely reactive. With polydentate N and P ligands, new mono- or di-nuclear bridged mixed-ligand complexes are formed by fission of the CO bridges. Examples are given in Table VII (171, 172). 

The aziridination catalysis was carried out in situ with mixed ligand and silver salt, which gives results similar to those obtained using the pure [Ag2(iBu3tpy)2(N03)] (N03) crystal. The (Bu3tpy ligand shows superior reactivity over other pyridine... 

The chemistry of Os with PR3, AsRs, and ShRs ligands is very extensive and rich, and is based largely about the substitution chemistry of octahedral, mixed ligand Os complexes, although there are examples extending from Os , for example, [Os(NO)2(PPh3)2], to Os , for example, [0s02(en)(PR3)2] +. Scheme 5, in which reactivity depends upon L (= tertiary phosphine) and LL (= chelate phosphine), illustrates aspects of the substitution chemistry of Os-phosphine complexes. 

Mixed-ligand precursors are also frequently employed in CSD processing. For example, titanium tetraisopropoxide, which is too reactive to be directly employed in most CSD routes, may be converted into a more suitable precursor by a reaction with either acetic acid or acetylacetone (Hacac). Such reactions are critical in dictating precursor characteristics and have been studied extensively. - Using these reactions, crystalline compounds of known stoichiometry and structure have been synthesized that may subsequently be used as known precursors for film fabrication.Mixed-hgand molecules (carboxylate-alkoxide and diketonate-alkoxide ) represent complexes that are not easily hydrolyzed. A typical structure for one of these compounds is shown in Figure 27.3e. 

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