Lightly stabilized complexes

These lightly stabilized complexes easily undergo substitution processes in which the weakly coordinated ligand is displaced by other uncharged 18-electron metal complexes. This kind of reaction will be referred to in the next section in discussing displacement reactions. 

These lightly stabilized complexes may be then substituted by donor metal complexes by the formation of metal-metal bonds ... 

Matsuzawa Y, Tamura SI, Matsuzawa N, Ata M (1994) Light stability of a P-cyclodextrin inclusion complex of a cyanine dye. J Chem Soc Faraday Trans 90 3517-3520... 

The molecular encapsulation of flavors with cyclo-dextrins was found to improve the resistence of light sensitive flavor constituents against daylight and ultraviolet irradiation. The photodecomposition of adsorbed and complexed flavors was tested both in the solid state and in aqueous solutions. The results of the light stability tests are demonstrated in the example of complexed and adsorbed citral,beta-ionone and cinnamaldehyde formulations /Table III./. 

Formazans or their precursors, tetrazolium salts, have been used in dye-bleach systems. Certain formazans102 such as (37) can complex with metal ions to give dye images with improved light stability. 

Azo dyes with ionizable groups, or substituents with an unshared pair of electrons, next to the azo linkage form complexes with transition metals.103 Many such complexes have been described, and many have been used as fabric dyes because of their superior light stability.104... 

From the point of view of light stability and range of absorptivity, inorganic redox systems might be more interesting. Photoinduced electron transfer in an aqueous solution of tris-(2, 2 -bipyridine) ruthenium (II) has been found to decompose water in to a mixture of H2 and 02. The Complex can serve both as an electron donor and electron acceptor in the excited state. The efficiency is low because of barrier to electron transfer. SVhen spread as a monolayer on glass slides after attaching to a surfactant... 

Optical RecordingDyes (seeChapter 6). Mixtures of the nicke 1-complexed triden-tate formazans 50 are claimed to provide good light stability to optical recording layers and elements [87],... 

Light Stabilizers Pigments (carbon black, iron oxides), UV absorbers (hydroxyphenones, benzotriazoles), excited-state quenchers (organic Ni complexes), free-radical scavengers Hindered amine light stabilizers [piperidines, hindered amine light stabilizers (HALS)]... 

Complex polyphosphites such as DP12 and DP675 were shown to outperform simple phosphite esters as replacements for heavy metal components of mixed metal stabilisers for PVC. It was found that the zinc level was critical for optimisation of the performance of the phosphite blends. Synergistic performances were observed with combinations of several phosphite esters, with the additional benefit of cost effectiveness. Other properties of PVC compounds, such as clarity, light stability and plate-out resistance, also improved markedly when heavy metal components of mixed metal stabilisers were replaced with polyphosphites. 4 refs. 

The structure of the p-tolyl derivative has been determined by X-ray (30, 132). Complex (XXII) is of particular interest because it serves as a lightly stabilized model for catalytic Pd(II) chemistry (133, 134). For instance, on standing it undergoes internal cyclization analogous to insertion of Pd-C bonds into olefins (Section III, A, 4). 

Two major developments in the preparation of bimetallic allenylidene complexes involve (i) metal fragment condensation of a monomeric allenylidene complex with a lightly stabilized metal fragment and (ii) deoxygenation of the dianionic acetylide intermediates, [M2(CO)9 C=C-C( Bu2)0 ]2-, with COCI2. 

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