Scandium cations

Saponins la 7,411,430 -, bioautographic determination la 109 Sarcosine Ia435 lbl24 Scandium cations, detection la 144 Scanner, optical trains la 30,39 S-Chamber (small chamber) la 126,127 SCHiFF s bases lb 52 Scintillators la 12 Scopolamine lb 231,252,255,323 Scopoletin lb 216-218,365 Screening process lb 45 Sebacic acid la 178,233,249,308 Sebuthylazine lb 418 Selectivity, enhancement by derivatiza-tion la 55... 

Sandwich chamber 126,127 Sapogenins 43,195, 206, 411 -, steroid 69, 206 -, trifluoroacetates 69 Saponins 7,109, 411, 430 Sarcosine 435 Scandium cations 144 Scanners, optical trains 30, 39 S-chamber see Sandwich chamber Scintillators 12 Sebacic acid 178,233,249, 308 Selectivity... 

Scheme 3 Reaction of D-ribose with dimedone catalyzed by scandium cation-exchanged mont-morillonite or scandium triflate...

Interestingly, the use of Sc(OTf)3 as the promoter gave hydroxyalkyl-6,7-dihydrobenzofuran-4(57/)-one derivatives 17 from D-ribose (9), whereas scandium cation-exchanged montmorillonite (Sc -mont) afforded hydroxyalkyl-3,3,6,6,-tetramethyl-3,4,5,6,7,9-hexahydro-l//-xanthene-l,8(27/)-dione (18) in good yield [97] (Scheme 3). 

The surfactant-aided Lewis acid catalysis was first demonstrated in the model reaction shown in Table 13.1 [22]. While the reaction proceeded sluggishly in the presence of 10 mol% scandimn triflate (ScfOTOs) in water, a remarkable enhancement of the reactivity was observed when the reaction was carried out in the presence of 10 mol% Sc(OTf)3 in an aqueous solution of sodium dodecyl sulfate (SDS, 20 mol%, 35 mM), and the corresponding aldol adduct was obtained in high yield. It was found that the type of surfactant influenced the yield, and that Triton X-100, a non-ionic surfactant, was also effective in the aldol reaction (but required longer reaction time), while only a trace amount of the adduct was detected when using a representative cationic surfactant, cetyltrimethylammonium bromide (CTAB). The effectiveness of the anionic surfactant is attributed to high local concentration of scandium cation on the surfaces of dispersed organic phases, which are surroimded by the surfactant molecules. 

Figure 8.21 Synthesis of scandium cation with contact ion pair structure.

Under these conditions, HCl was also found to promote the reaction, indicating that the rate-determining step, accelerated by HCl, was not the catalyst turnover step (Scheme 3.60). These results would suggest that the scandium cation and proton cooperatively act as a combined catalyst in the nucleophilic addition of the silyl enol ether to benzal-dehyde. ... 

Determine the total cation charge and show that it matches the total anion charge. The LU cation has a 1-I- charge and the Al + cation has a 3-1- charge for a total of 4-I-, which matches the anion charge. Each scandium cation has a charge of 3-1- for a total of 6-1-, which matches the anion charge. 

The importance of the Lewis acid cation in this process was shown from the lack of activity of pristine H-USY in the model aza-Diels-Alder of A-benzylidenaniline with cyclopentadiene leading to the tetrahydroquinoline product (Equation (8.48)) [136]. The immobilization of the scandium cation inside the pores of this zeolite with oidy a coordination position occupied by a triflate group changed completely the behavior of this zeolite affording an almost total yield in the condensation product. 

In a systematic study, it was demonstrated that, using a specially designed bulky benzamidinate ligand, it is possible to isolate mono(amidinato) dialkyl complexes over the full size range of the Group 3 and lanthanide metals, i.e., from scandium to lanthanum. The synthetic methods leading to the neutral and cationic bis(alkyls) are summarized in Scheme 56. Figure 18 displays the molecular structures of the cations obtained with Sc, Gd, and La. ... 

The guanidinate-supported titanium imido complex [Me2NC(NPr02l2Ti = NAr (Ar = 2,6-Me2C6H3) (cf. Section IILB.2) was reported to be an effective catalyst for the hydroamination of alkynes. The catalytic activity of bulky amidinato bis(alkyl) complexes of scandium and yttrium (cf. Section III.B.l) in the intramolecular hydroamination/cyclization of 2,2-dimethyl-4-pentenylamine has been investigated and compared to the activity of the corresponding cationic mono(alkyl) derivatives. 

For any cation, the empty 4 S orbital is slightly higher in energy than the partially filled 3 d orbital. Thus, the isoelectronic V and Cr cations both have the [Ar] 3 d configuration. On the other hand, the isoelectronic neutral atom scandium has the configuration [Ar]4 3 d ... 

Scott Oakes et al. (1999a, b) have shown how adoption of SC conditions can lead to a dramatic pressure-dependent enhancement of diastereoselectivity. In the case of sulphoxidation of cysteine derivatives with rert-butyl hydroperoxide, with cationic ion-exchange resin Amberlyst-15 as a catalyst, 95% de was realized at 40 °C and with SC CO2. By contrast, with conventional solvents no distereoselectivity was observed. Another example is the Diels-Alder reaction of acrylates with cyclopentadiene in SC CO2 at 50 °C, with scandium tris (trifluoromethanesulphonate) as a Lewis acid catalyst. The endoiexo ratio of the product was as high as 24 1, while in a solvent like toluene it was only 10 1. 

The enthalpies of solution and solubilities reviewed here provide much of the experimental information required in the derivation of single-ion hydration and solvation enthalpies, Gibbs free energies, and entropies for scandium, yttrium, and lanthanide 3+ cations. 

In studies of the concentrations of arsenic, bromine, chromium, copper, mercury, lead and zinc in south-eastern Lake Michigan, it was shown that these elements concentrated near the sediment water interface of the fine-grained sediments. The concentration of these elements was related to the amount of organic carbon present in the sediments (161). However, it was not possible to correlate the concentration of boron, berylium, copper, lanthanum, nickel, scandium and vanadium with organic carbon levels. The difficulty in predicting the behaviour of cations in freshwater is exemplified in this study for there is no apparent reason immediately obvious why chromium and copper on the one hand and cobalt and nickel on the other exhibit such variations. However, it must be presumed that lanthanium might typify the behaviour of the trivalent actinides and tetravalent plutonium. 

Organolithium compounds of structure 275 can been applied as transfer agents for transition metal ions, for example, as shown in equation 54 for scandium(III) with tetrahedral coordination (276). The structure of these complexes, elucidated by XRD crystallography, shows the transition metals forming part of an anionic entity, paired to solvated lithium cations. Further structural information can be obtained from H, and "B NMR spectroscopies. ... 

Another approach to the "greening of catalysts has been the use of rare-earth compounds known as inflates. The term inflate is an abbreviation for the trifluoromethanesulfonate (SO3CF3) cation. Some typical triflates that have been used in research include the lanthanides, scandium, and hafnium. These triflates act as Lewis acids (electron acceptors) and can, therefore, be substituted for stronger mineral acids (such as sulfuric acid) with undesirable environmental... 

Hi. Zeolites exchanged with transition metal ions. In the first row, scandium-, titanium-, cobalt-, and nickel-exchanged zeolites have been the most studied. Cobalt-exchanged zeolites are discussed in Section IV,E since they lead to oxygen adducts on adsorption of oxygen. There are several cases where copper and particularly iron ions are found as impurity cations which affect the oxygen adsorption properties of the zeolite. 

This chapter consists of a description of the ions formed in aqueous solutions by the transition elements - the d-block elements - and a discussion of the variations of their redox properties across the Periodic Table from Group 3 to Group 12. There is particular emphasis on the first transition series from scandium to zinc in the fourth period, with summaries of the solution chemistry of the second (Y to Cd) and third (Lu to Hg) series. The d-block ions in solution are those restricted solely to aqua complexes of cations, e.g. [Fe(H20)f,]" +, and the various oxocalions and oxoanions formed, e.g. V02+ and MnCXj". Oxidation states that are not well characterized are omitted or referred to as such. 

Scandium complexes with chloride ion in aqueous solution, and there is ion-exchange evidence for anionic species, presumably ScClJ aq, in concentrated hydrochloric acid,119 while values of K = 90 and K2 - 37 for the first two association constants have been reported.1211 Solid salts of the anions ScClt-, St Cll- and ScCl2- have been isolated with alkali metal cations.121,122 It seems likely that both the first two species are octahedral and bridged-octahedral respectively, in line with Cs2NaScCl6 which has an X-ray powder pattern in accord with a face-centred cubic structure.123... 

The dehydration of aldoximes with 2-methylene-l,3-dioxepane has been found to proceed smoothly in the presence of a catalytic amount of scandium(III) triflate to give the corresponding nitriles. The authors608 proposed that coordination of Sc(OTf)3 to the oxygen atom of the 1,3-dioxepane ring induces C—O bond cleavage to form a cationic... 

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