Isomeric complexes

Chemical Properties. Higher a-olefins are exceedingly reactive because their double bond provides the reactive site for catalytic activation as well as numerous radical and ionic reactions. These olefins also participate in additional reactions, such as oxidations, hydrogenation, double-bond isomerization, complex formation with transition-metal derivatives, polymerization, and copolymerization with other olefins in the presence of Ziegler-Natta, metallocene, and cationic catalysts. All olefins readily form peroxides by exposure to air. 

Similar considerations have been invaluable in devising synthetic routes to numerous other isomeric complexes of Pt" but. as can be seen in Hg. A, other considerations such as the relative stabilities of the different Pt-ligand bonds arc also involved. 

In—W bond. Use of Ph3Al leads to a complex in which the oxygen atom of a carbonyl ligand is the site of electron pair basicity in a WC=OAl link. Solutions of [n-Bu4N][Ph3GaCpW(CO)3] in CH2CI2 contain, in addition to free [CpW(CO)3], two isomeric complexes a metal-metal-bonded species and a C- and O-bonded adduct of the type found in the Ph3Al case. 

An especially important case is the enantioselective hydrogenation of a-amidoacrylic acids, which leads to a-aminoacids.29 A particularly detailed study has been carried out on the mechanism of reduction of methyl Z-a-acetamidocinnamate by a rhodium catalyst with a chiral diphosphine ligand DIPAMP.30 It has been concluded that the reactant can bind reversibly to the catalyst to give either of two complexes. Addition of hydrogen at rhodium then leads to a reactive rhodium hydride and eventually to product. Interestingly, the addition of hydrogen occurs most rapidly in the minor isomeric complex, and the enantioselectivity is due to this kinetic preference. 

Fig. 29. Isomeric complexes [TeO(DMSA)2] with the meso (a) and racemic (b) ligand...

Even under the most inert atmosphere conditions, the 31CP/MAS spectrum of the immobilized ligand showed a major signal at 6 = 42 ppm (wrt 85% H3POO characteristic of phosphine oxide rather than phosphine. This could be quantitatively reduced by HSiCl3 and this surface reaction monitored by NMR but the subsequent exchange reaction (equation [5]) generated substantial quantities of phosphine oxide and a number of different isomeric complexes were f ormed. 

Data for a series of [Ru(ri6-arene)Cl(en)](PF6) complexes with the isomeric p-, o-, and m-terphenyls mirrored these observations (74). The complex with the most extended arene (p-terphenyl, 14) was the most potent, with potency similar to cisplatin, but is not cross-resistant, and has a much higher activity than its isomeric complexes. Again, no cross-resistance with cisplatin was observed for these complexes (74). 

In confirmation, however, of the delicate electronic effects present in these complexes, the two-electron oxidized mixed-valent isomeric complex [MnIV(3,6-di-Butcat)(3,6-di-Butsq)2] has been isolated and structurally characterized.59... 

As happens for other physico-chemical techniques, one must first ask if an electrochemical investigation is able to distinguish geometric isomers of the type cisjtrans or facjmer metal complexes. In principle, this is possible since, as mentioned previously, the redox potential of an electron transfer is influenced also by steric effects. For instance, we have seen in Chapter 5 that some octahedral complexes of the scorpiand diammac display different electrochemical responses, depending on whether the two outer amino groups assume cis or trans arrangements. One must keep in mind, however, that the differences in the electrochemical response of isomeric complexes can sometimes be quite small, so may escape a first examination. 

Insight into the forces intervening in the supersonically expanded isomeric complexes of (2R,3R)-(Mrr), (2S,3S)-(Mss), and (2R,35)-butanediols (M ) with Cr is achieved by lcR2Pl-TOF experiments. " Fig. 10 illustrates the corresponding excitation spectra together with that of bare Cr. 

There is no general theoretical study for trialkyl-substituted cations R3E, which investigates the relationship of the classical planar trigonal structure to isomeric complexes RE /R2 and its relative energy compared to the dissociation products, the singly coordinated four-valence-electron species R E and the hydrocarbon R2. The only exceptions are 7-norbornadienyl cations 37 for which the germyl and silyl cation has been intensively studied theoretically by Radom and Nicolaides. ... 

However, salt 3 is unstable at room temperature as a solid and in olution and rearranges to the Isomeric complex in which the iron center is bound to the carbonyl group of the substituted cyclohexanone. 

These two isomeric complex salts differ in colour, the former being green and the latter red. Also, the former are neutral in reaction, whilst the latter have an acid reaction in solution.2... 

Two isomeric complexes, 60 and 61, have been analyzed by Cl MS (reagent gas CH4), producing [M -b I] and [M -b 29]+ ions. Electron ionization mass spectrometry was applied in the analysis of the product of the reaction between Zn(CF3)Br-2CH3CN (62) and 4-(Af,Af-dimethylamino)pyridine (DMAP). The El (20 eV) mass spectrum of the product, Zn(CF3)Br DMAP (63), was recorded at 280 °C and consisted mainly of [C6H3BrF2NZn]+, [ZnBr2]+ and [ZnBr]+ ions. At lower temperatures, this compound did not yield any Zn-containing ions, and the spectra were dominated by the peaks of the [DMAPJ+ and [C2HgN]+ ions . 

Solvent or ligand Interactions with tight Ion pairs produce externally complexed tight Ion pairs and/or ligand separated Ion pairs. The stability of the complexes depends on solvent, temperature, type of crown and the nature of the cation. For example, In ethereal solvents benzo-15-crown-5 and fluorenyl sodium (Fl-.Na ) form the two Isomeric complexes I and II depicted In reaction 1, but the ratio I/II Is highly solvent sensitive (9) (If the bound solvent In II Is Included In the structure of II, the two complexes of course can actually not be considered Isomeric). 

From a mechanistic point of view (see below) it is important to note that the chloropalladation of labeled 2,2-diphenyl-l-methylenecyclopropane-3,3-d2 gave only two isomeric complexes, with absence of the isomer in which both the phenyl and deuterium reside on the allylic moiety (equation 323). This allows the exclusion of a symmetrically bound >/4-trimethylenemethane (TMM) intermediate or rapidly equilibrating >/3-TMM species,... 

The introduction of more than one C- or jV-substituted en ring into the coordination sphere considerably increases the isomeric complexity. Many of these ligands are now unsymmetrical and their complexes may exhibit geometric isomerism dependent upon the end-for-end orientation.257 Thus there are 24 distinct configurational and conformational forms expected for Co(R,5-pn)3+, 258 Table 6 lists a variety of C- and JV-substituted ethylenediamine type ligands that have been investigated. 

With substituted 1,4-dienes, such as (15), (18) and (22), the isomerization/complexation reaction invariably produces mixtures of complexes. Although these can often be separated chromatographically, it... 

Look at the colors of the isomeric complexes in Figure 20.17, and predict which is the stronger field ligand, nitro (-N02) or nitrito (-ONO) Explain your reasoning. 

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