Complexes, stability

Dimethyl acetylenedicarboxylate (DMAD) (125) is a very special alkyne and undergoes interesting cyclotrimerization and co-cyclization reactions of its own using the poorly soluble polymeric palladacyclopentadiene complex (TCPC) 75 and its diazadiene stabilized complex 123 as precursors of Pd(0) catalysts, Cyclotrimerization of DMAD is catalyzed by 123[60], In addition to the hexa-substituted benzene 126, the cyclooctatetraene derivative 127 was obtained by the co-cyclization of trimethylsilylpropargyl alcohol with an excess of DMAD (125)[6l], Co-cyclization is possible with various alkenes. The naphthalene-tetracarboxylate 129 was obtained by the reaction of methoxyallene (128) with an excess of DMAD using the catalyst 123[62],... 

This vibrational cooling is sufficient to stabilize complexes that are weakly bound by van der Waals or hydrogen-bonding forces. The pure rotational spectra and structure of species such as... 

Kumada has extended hydrosilylation by phosphine-stabilized complexes into nickel chemistry (173). The most effective catalyst is (XXX). This... 

With the successful chemistry of the cymantrenes and the (cyclobuta-diene)tricarbonyl iron, the quest for tetraethynylated cyclobutadienes based on CpCo-stabilized complexes arose. Why would they be interesting Whereas all derivatives of 63 and 68 exhibit reasonable stability when their alkynyl substituents are protected by either an alkyl or a trimethylsilyl group, the desilylated parents are isolated only with difficulty and are much more sensitive. 

The (CjHsl ion can also function as a Lewis acid, forming collision-stabilized complexes or molecular ion adducts ... 

While 52 stands for simple base-stabilized complexes 148), 53 is an example of a chelated base-stabilized stannylene coordinated with a transition metal149). 54 144) and 55 150) illustrate that the aggregation state of the stannylene remains unchanged in the complexes. 

From the standpoint of stabilization, complex formation is certainly an advantage. It means namely that the HALS stabilizer is already located preferentially at the site where degradation is initiated. 

Oupicky D, Parker AL, Seymour LW (2002) Laterally stabilized complexes of DNA with linear reducible polycations strategy for triggered intracellular activation of DNA delivery vectors. J Am Chem Soc 124 8-9... 

Caamano, C.A., Fernandez, H.N., and Paladani, A.C. (1983) Specificity of covalently stabilized complexes of 1251-labeled human somatotropin and components of the lactogenic binding sites of rat liver. Biochem. Biophys. Res. Comm. 115, 29-37. 

The kinetically-stabilized complexes of the cage ligands normally yield redox reagents free of the exchange problems often associated with simple complexes. Indeed, the redox chemistry of the complexes shows a number of unusual features for example, saturated cages of the type mentioned in Chapter 3 are able to stabilize rare (monomeric) octahedral Rh(n) species (d7 electronic configuration) (Harrowfield etal., 1983). In a further study, radiolytical or electrochemical reduction of the Pt(iv) complexes of particular cages has been demonstrated to yield transient complexes of platinum in the unusual 3+ oxidation state (Boucher et al., 1983). 

The use of alkali and alkaline earth group metal ions, especially those of sodium, potassium, magnesium, and calcium, for maintenance of electrolyte balance and for signaling and promotion of enzyme activity and protein function are not discussed in this text. Many of these ions, used for signaling purposes in the exciting area of neuroscience, are of great interest. In ribozymes, RNAs with catalytic activity, solvated magnesium ions stabilize complex secondary and tertiary molecular structure. Telomeres, sequences of DNA at the ends of chromosomes that are implicated in cell death or immortalization, require potassium ions for structural stabilization. 

Structure 1031 illustrates an internally base-stabilized complex, in which the stabilizing unit is part of the added metal fragment. This contrasts to the other molecules in this section where the chelating function is part of the organic group attached to E. 

Table 7 Formally monovalent ligand-stabilized complexes of the form LnM E(X)(L )... 

A particularly interesting piece of evidence concerning the nature of this sequence has been presented by Barluenga et al.21 When the vinylcarbene complex 14 was heated, decarbonylation afforded the alkene-stabilized complex 15. Upon treatment with dimethyl acetylenedicarboxylate, the alkyne-insertion product 16 was isolated. This complex proved to be unstable in solution at room temperature and decomposed readily to 17, the expected product of a Dotz reaction with an aminovinylcarbene. 

TPD and EELS experiments have shown coadsorbed NO/NH3 to form a surface stabilized complex on Pt(lll). This assertion was based in part on the very large vibrational shifts observed for the neat (NO or NH3) systems compared to the mixed system, and in part on the simultaneous desorption of NO and NH3 from the mixed system at values of Tg higher than typical of desorption from the neat systems at comparable initial coverage Kinetit y, desorption from this system has been characterized as reaction limited,... 

Many compounds of technetium and rhenium are of analogous composition and of corresponding physical and chemical properties. Because of the very similar ionic radii, isotypic crystal structure formation of analogous compounds could often be observed. Technetium remarkably differs from manganese by the high stability of pertechnetate compared with permanganate. Moreover, divalent technetium does not exist as a hydrated ion but only as a stabilized complex. 

The structures of the colored products of the reactions between polynitroaromatic compounds and bases were first suggested by Meisenheimer [12]. They are usually described as resonance-stabilized complexes known as Meisenheimer complexes. Thus, the red-colored product of a reaction between TNB and sodium methoxide was assigned the following formula (1) ... 

The chelate effect also favors oxidative addition of the C2—H bonds of imidazo-lium salts because it provides stabilized complexes. The reaction of a pyridine-imidazolium salt with [lrCl(cod)]2 yields the oxidative addition product, even in the absence of a base (Scheme 3.9), thus confirming that the oxidative addition of an imidazolium salt should be considered as a vahd process for the preparation of NHC—M—H complexes [24]. 

An alternative application of flash photolysis to study myoglobin electron transfer kinetics has been employed by Hofifinan and co-workers 156). In this approach, the photoactive zinc-substituted derivative of Mb is mixed with an equivalent amoimt of ferricytochrome bs to form an electrostatically stabilized binary complex. Upon transient irradiation, the strongly reducing Zn-Mb intermediate is formed, and the kinetics of ferricytochrome reduction within the preformed complex can be monitored spectrophotometrically. The resulting kinetics represents a mixed-order process consistent with electron transfer both within the electrostatically stabilized complex and between the dissociated components of the complex. 

Application of the steady-state approximation to the initially formed, chemically activated complex yields the rate equation for disappearance of the bare chloride ion and formation of the collisionally stabilized Sfj2 intermediate. Equation (7). The apparent bimolecular rate constant for the formation of the stabilized complex... 

Dihydrogen complexes, osmium, 37 3(X)-301 Dihydroxo-bridged complexes acid-base equilibria, 32 108-110 quantitative considerations, 32 115-118 binuclear, 32 66-67 crystallographic data, 32 61, 63 stability complexes, 32 103-104... 

For instance, ti-donor substituents R in [(CO)5Cr=(C)xR2] should stabilize complexes with an odd number of carbon atoms x and, conversely, complexes with an even number of carbon atoms should be stabilized by 7t-acceptor substituents [11]. 

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