Decomplexative processes

Scheme 6.2 Cavity volume is minimised during the decomplexation process for flexible hosts such as unmodified calix[4]arenes.

At higher temperatures, both the diffusion and decomplexation processes are accelerated, and transport rates increase. The diffusion coefficient increases, while the extraction coefficient Kbe.x decreases with increasing temperature. 

The efforts to synthesize host molecules with larger, noncollapsing cavities for specific guest molecules resulted in the production of several families of hosts, including the cavitands, hernicarcerands. carcerands, cryptophanes, and calixarene capsules, etc. These molecules have well-defined portals for entry and exit of the guest molecules and the possibility of functionalization of the cavity interior to control the orientation and fluxionality of the guest, and the binding forces for complexation. While the cavitands provide no steric hindrance to complexation and decomplexation processes... 

Although it is assumed that transport takes place via solvent separated ions, it is seen (Table 7) that the nature of the anion affects the rate of the decomplexation process. The transport of KSCN by carrier 9 is mainly limited by diffusion, while the transport of KCIO4 is primarily kinetically controlled. 

Figure 5.14 Reversibility graph of the cage HOM-DZ (a) HOM-TMPyP (b) HOM-PR (c) and HOM-TPPS (d) nanosensors after regeneration cycles decomplexation process of analyte ions using [0.1 M] CH3 COO",...

Table 5.2 Textural parameters (Vp and Sbet) and sensing features of optical HOM nanosensors after several decomplexation processes of [Hg-TPPS]", [Sb-PRp, [Cd-TMPyP]" and [Pb-(DZ)2]" complexes using various eluants and the reuse cycles and during the recognition of 0.3 ppm analyte ions.

In another process for the synthesis of PPS, as well as other poly(arylene sulfide)s and poly(arylene oxide)s, a pentamethylcyclopentadienylmthenium(I) TT-complex is used to activate -dichlorobenzene toward displacement by a variety of nucleophilic comonomers (92). Important facets of this approach, which allow the polymerization to proceed under mild conditions, are the tremendous activation afforded by the TT-coordinated transition-metal group and the improved solubiUty of the resultant organometaUic derivative of PPS. Decomplexation of the organometaUic derivative polymers may, however, be compHcated by precipitation of the polymer after partial decomplexation. 

The interfacial transfer kinetics were then investigated by perturbing the equilibrium, through the depletion of Cu + in the aqueous phase, by reduction to Cu at an UME located in close proximity to the aqueous-organic interface. This process promoted the transfer of Cu into the aqueous phase, via the transport and decomplexation of the cupric ion-oxime complex, resulting in an enhanced steady-state current at the UME. Approach curve measurements of i/i oo) vs. d allowed the kinetics of the transfer process to be determined unambiguously [9,18]. 

Pentamethylbenzene, N-phenylpyrrole, and 1,2-diphenylindole have been decom-plexed from corresponding iron(II) complexes by use of the same GS/MW process yields were 94%, 62%, and 71%, respectively. The results showed this to be a rapid and efficient method of decomplexation. 

The [5 + 2]-cycloadditions of air-stable 7]3-pyranyl and 7]3-pyridinyl molybdenum 7T-complexes (4758 and 48,59 respectively) with alkenes reported by Liebeskind and co-workers provide a novel method for the construction of oxabicyclo[3.2.1]octenes and highly functionalized tropanes (Scheme 20). This process involves the formation of a TpMo(CO)2 complex which in the presence of EtAlCl2 reacts with an alkene in a stereoselective [5 + 21-cycloaddition to give metal-complexed cycloadducts 50 and 51 (Tp = hydridotrispyrazolylborato). Metal decomplexation via protiodemetalation or oxidation affords the products in good to excellent yields (Scheme 21). 

For crown ethers in which the H-nmr probes Ha and Hb are diastereotopic in the free crown ether too, the cation exchange process (50) becomes more complicated. For 1 1 complexes the measured free energy of activation also involves conformational inversion components (AG = AG + AG ), whereas exchange between free and complexed crown ether (2 1 ratio of crown ether to salt) only involves the free energy of activation for decomplexation (AG ). Bradshaw et al. (1979b) have recently reported AG -values for cation exchange in RNH3X complexes of crown ethers [257]. The AGf term was estimated to be 0.7, 0.5, and 1.2 kcal mol-1 for compounds [257 n = 1] with... 

Shortly after this reaction was reported, Hegedus found46 that imines undergo a similar insertion process. The products (251) are structurally very similar to the alkyne adducts (247), and decomplexation with iodine, followed by treatment with trimethylamine TV-oxide, afforded a variety of substituted pyridones in good yield. 

Generally, the reduction to the metallic state implies decomplexation of the bound ligands (hence, irreversible reduction), electrodeposition of metallic zinc on the electrode surface and consequently the anodic stripping process in the backscan. 

The conjugation in the molecular wire may be disrupted or modulated to create systems with different properties. For example, a porphyrin Ceo donor-acceptor system linked with a conjugated binaphthyl unit, has a preference for the atropi-somer where the fullerene unit is closer to the porphyrin system, thus increasing the through space interactions [82]. The charge transfer process on a dyad containing a crown ether in the linker structure can be modulated by complexation/ decomplexation of sodium cations [83] but even more interesting is the construction of supramolecular systems where the donor and acceptor moieties are... 

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