Scandium complexes addition

Addition of Sc-R moieties to metal coordinated carbon monoxide was ascribed to the high Lewis acidity of the organometallic scandium complexes [281b]. R-Substituted scandoxycarbene complexes of type Cp2M=C(R)OScCpf (M = Mo, W R = H, Me) and CpM(CO)[=C(R)OScCpf] (M = Co,Rh, R = H, Me, CH2CH2Ph, NMe2) were obtained. The molecular structure of... 

In recent years, many chiral catalysts for the enantioselective synthesis of optical active 1,5-dicarbonyl compounds have been developed, such as chiral crown ethers with potassium salt bases and chiral palladium complexes, including bimetallic systems. Nakajima and coworkers reported on enantioselective Michael reactions of S-keto esters to a,/3-unsaturated carbonyl compounds in the presence of a chiral biquinoline N,N dioxide-scandium complex, which catalyzed the additions in high yields and with enan-tioselectivities up to 84% ee . Kobayashi and coworkers found that the combination of Sc(OTf)3 with the chiral bipyridine ligand 149 (equation 41) was also effective as a chiral catalyst for asymmetric Michael additions of 1,3-dicarbonyl compounds 147 to a,/3-unsaturated ketones 148. The corresponding Michael adducts 150 were obtained in good to high yields with excellent enantiomeric excesses in most cases (Table 10). 

Additional catalytic investigation of p-diketiminate scandium complexes by Piers and coworkers showed that well-characterized complexes 121 and 122 with the bulky ligand L27 were highly active catalysts for intramolecular hydroamination to form nitrogen heterocycles. The catalytic reaction was monitored by determining starting material and product with NMR. Both the neutral complex 121 and the CIP complex 122 are effective catalysts (10 mol%) for the intramolecular hydroamination of 5-phenyl-4-pentyl-l-amine (R = H, R = Ph, n = 1 in Scheme 42). However, they are not active catalysts for the potential application to the intermolecular hydroamination of 1-hexyne with alkylamines [82],... 

Metal vapour s)mthesis in rare-earth chemistry has been used as early as 1977 to prepare rare-earth butadiene and alk)me complexes by interaction of butadienes and alk)mes (respectively) with vaporised metals (Evans, 1987 Evans et al., 1977), and we have seen in Section 3 that low-valent scandium complexes can also be made by this technique. Additionally, condensation of rare-earth vapours with a 7i-acceptor such as 1,4-di-(t-Butyl)diazadiene (DAD) has produced compounds of general formula [R(DAD)3], except with scandium where the composition is [Sc(DAD)2]. Extensive metal-ligand electron transfer is effective in these molecules so the real oxidation state of the rare earth (at least at room temperature) is in fact + 3. Note that the first structurally characterised organosamarium(II)... 

Compound 24, the corresponding IV,]V -dioxide of 23, presents enhanced fluorescence when complexed with Sc(OTf)3. 24 forms a strong Sc[( )-24]2 complex whose fluorescence disappears upon addition of amino alcohols. Optically pure scandium complex formed with optically pure 24, Sc[(+)-24]2 generates diastereomeric complexes with a racemic aminoalcohol such as alaninol. The fluorescence signal could be switched off enantioselectively and it was exploited for sensing purpose. The enantiomers of 24 were obtained by chromatography on (R,R)-Whelk-01 (08JOC4267). 

The catalytic asymmetric Michael reaction using silyl enol esters (Mukaiyama-Michael reaction) as the pronucleophiles has been reported using a titanium/BINOL catalyst (in up to 90% ee). Considering furan (11.36) as a silyl enol ether, this has been shown to undergo nucleophilic addition to the Michael acceptor (11.37). The product (11.38) canbe obtained with excellent diastereocon-trol with the scandium complex of hgand (11.39), or with excellent enantiocontrol... 

The Friedel-Crafts reaction of electron-rich aromatic and heteroaromatic compounds with carbonyl acceptors is one of the fundamental reactions for forming carbon-carbon bonds. In recent years, several enantioselective approaches have been described utiMzing copper and scandium complexes as catalysts. In addition, the use of organocatalytic approaches has been considerably expanded. 

TBP (3.4 to 2.9), 50% TBP solution in CCI4 (2.4 to 2.8), and TVEX-TBP (2.8-1.9) and has fractional value indicating simnltaneous formation of several scandium complexes in organic phase and different ratio between them. In addition, the ASN value depends on the metal concentration in the resin phase and decreases for TVEX-TBP resins and increases for 50% TBP solution in CCI4 with scandium content increase. 

Chiral scandium-bis(oxazolinyl)pyridine (Sc-pybox) complexes catalyze various catal5dic asymmettic addition reactions with carbonyl compounds. The first report of this complex was addition and annulation reactions of allenylsi-lanes with etiiyl glyoxylate using the scandium complex. The application of these complexes was expanded to various catalytic asymmetric transformations such as aldol reactions, allylation, and ene reactions. ... 

Rare earth arene complexes are good precursors for difficult-to-synthesize rare earth compounds (Bochkarev, 2002) and the same was true for the scandium arene complexes supported by NN . Hessen previously showed that a scandium complex of the 2,2 -bipyridyl radical anion could be readily accessed from a reduced 1,3-diene scandium complex (Beetstra et al., 2003). Similarly, the addition of 2,2 -bipyridine to a CeDs solution of Sc2-naph (Scheme 3A) led to the formation of the previously reported radical anionic bipyridyl complex (NN )Sc(2,2 -bipyridine) (Williams et al., 2010). 

Scandium A computational study on the C-H addition of a-picoline (2-MeC5H3N) and other pyridine derivatives to terminal olefins RCH=CH2, catalysed by cationic scandium complexes, has demonstrated that the reaction rate is controlled by generation of the active metal-pyridyl species and an insertion step. In agreement with the experimental observation, formation of the branched product 6-[RCH(Me)-(2-MeC5H3N)] is both kinetically and energetically favourable over that of the linear product. ... 

In these procedures 1 litre of seawater was shaken with 60 mg charcoal for 15 min. Complexing agents were added in amounts of 1 mg, dissolved in 1 ml of acetone. The pH was 5.5, or it was adjusted to 8.5 by addition of 0.1 M ammonia. The charcoal was filtered off and irradiated. Results of three sets of experiments with charcoal alone, charcoal in the presence of dithizone, and charcoal in the presence of sodium diethyldithiocarbamate are compared. The following elements are adsorbed to an extent from 75 to 100% silver, gold, cerium, cadmium, cobalt, chromium, europium, iron, mercury, lanthanum, scandium, uranium, and zinc. The amount of sodium is reduced to about 10 6, bromine to about 10 5, and calcium to about 10 2. 

Allenyltrimethylsilanes add to ethyl glyoxalate in the presence of a chiral pybox scandium triflate catalyst to afford highly enantioenriched homopropargylic alcohols or dihydrofurans, depending on the nature of the silyl substituent (Tables 9.39 and 9.40) [62]. The trimethylsilyl-substituted silanes give rise to the alcohol products whereas the bulkier t-butyldiphenylsilyl (DPS)-substituted silanes yield only the [3 + 2] cycloadducts. A bidentate complex of the glyoxalate with the scandium metal center in which the aldehyde carbonyl adopts an axial orientation accounts for the observed facial preference ofboth additions. 

Analogous addition with scandium-(5, 5 -2,6-bis(oxazolinyl)pyridine) complex resulted in lower enantioselectivity. A chiral heterobimetallic complex of Y(OTf)3 and Li-BINOL provided high ee in addition of 0-methylhydroxylamine to enones of type 55 (equation 36) . ... 

The complexation constants Ki for interaction of Sc3+ ions with substituted and unsubstituted carboxylates in aqueous solution have been determined potentiometrically at 25 °C and 0.1 MKN03 ionic background. They are listed in Table 1, the AH values being derived with the aid of additional measurements at 40°C.61 These values for scandium are greater than those for the lanthanides by roughly one order of magnitude.62... 

Like the hydroxides of the Rare earth, scandium hydroxide, Sc(OH)3, is precipitated by addition of alkalies to solutions of scandium salts however, the latter is precipitated at pH 4.9, while the former require pH 6.3 or more, a property which is utilized in one method of separation. Upon heating the hydroxide (or certain oxyatid salts), scandium oxide. Sc>C>3 is produced. Scandium hydroxide is less acidic than aluminum hydroxide, requiring boiling KOH solution to form the complex potassium compound, K2[Sc(OH)5 H 0] 3H 0. 

A series of trivalent lanthanoid complexes, scandium, and ytterbium tris-(R)-(-)-1,1 -binaphthyl-2,2 -diyl phosphonate, have been introduced as new chiral and stable Lewis acids for the asymmetric hetero Diels-Alder reaction of Danishefsky s diene and aldehydes. 2,6-Lutidine was found to be an effective additive to improve the enantioselectivity up to 89% ee [66] (Eq. 8A.42). 

Kobayashi reported an asymmetric Diels-Alder reaction catalyzed by a chiral lanthanide(III) complex 24, prepared from ytterbium or scandium triflate [ Yb(OTf)3 or Sc(OTf)3], (Zf)-BINOL and tertiary amine (ex. 1,2,6-trimethylpiperidine) [30], A highly enantioselective and endose-lective Diels-Alder reaction of 3-(2-butenoyl)-l,3-oxazolidin-2-one (23) with cyclopentadiene (Scheme 9.13) takes place in the presence of 24. When chiral Sc catalyst 24a was used, asymmetric amplification was observed with regard to the enantiopurity of (/ )-BINOL and that of the endoadduct [31 ]. On the other hand, in the case of chiral Yb catalyst 24b, NLE was affected by additives, that is, when 3-acetyl-l,3-oxazolidin-2-one was added, almost no deviation was observed from linearity, whereas a negative NLE was observed with the addition of 3-pheny-lacetylacetone. 

Enantiopure amide derivatives (64) of -unsaturated a-hydroxy acids have been made by addition of a vinylsilane, R2R1C=(4ISiMe3, to /V-phcnylglyoxamide.181 The reaction is catalysed by scandium(III) triflate complexed to a C2-symmetric PYBOX ligand derived from (f )-norephedrine. 

The asymmetric conjugate addition of thiophenol to ( >3-crotonoyloxazolidin-2-one, catalysed by the scandium(III) triflate complex of Ph-PYBOX, gave the corre- sponding adduct in 66% ee. Lanthanoid triflates gave lower enantioselectivities (<28% ee).132... 

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