Scandium complexes pyridine

Reaction of Cp LuH with pyridine yielded the orthometallated (C,N->/2) pyridine complexes under release of hydrogen [205]. The scandium complexes CpfScR (R = H, CH3, C6H5, CH2C6H5) show a similar reaction [206]. 

When a chiral scandium complex of 2,6-bis-(oxazolinyl)pyridine, [Sc(/f)-py-box](OTf)3, 0Tf=0S02CE3, is employed instead of Sc(OTf)3, a 2 2 chiral Jt-dimer complex of 1,4-napthosemquinone radical anion (NQ ) with Sc (R)-... 

Scheme 48 A direct, enantioselective alkylation of pyridines by a cationic half-sandwich scandium complex.

A number of pyridines can be alkylated by alkenes with a cationic halfsandwich scandium complex in an enantioselective manner (Scheme 48). The alkylation occurs at C-2 with high yields and high enantiometric excess (ee).The pyridines can be substituted with alkyl, aryls, and halides with no effect of the yields or selectivity. The reaction also occurs on isoquinolines. A number of alkenes will react with 2-picoline with high selectivity and yields (14JA12209). 

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. ... 

Scheme 18 Coupling between two pyridine ligands on a scandium complex by Diaconescu et al.

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. ... 

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) . ... 

Much work in the review period has concerned enantioselective substitution in five-membered heterocyclics. The enantioselective alkylation of some pyrroles by unsaturated 2-acylimidazoles catalysed by the bis(oxazolinyl)pyridine-scandium(in) triflate complex (31) has been reported.39 Compound (33) is formed in 98% yield and 94% ee from the 2-acylimidazole (32) and pyrrole at —40 °C. A series of enantiomer- ically pure aziridin-2-ylmethanols has been tested as catalysts in the alkylation of /V-mclhylpyrrolc and (V-methylindole by ,/l-unsalura(cd aldehydes.40 Enantiomeric excesses of up to 75% were observed for the alkylation of /V-mcthylpyrrole by ( >crotonaldehyde using (2.S ,3.S )-3-mclhylazirin-2-yl(diphenyl)methanol TFA salt as catalyst to form (34). 

Simple bis(oxazoline) ligands, especially azabis(oxazolines), can catalyse the addition of indoles to benzylidene malonates in up to 99% ee, provided that excess of the chiral ligand is avoided.166 The paradigm followed in many asymmetric catalytic reactions that an excess of the chiral ligand with respect to the metal should improve enantioselectivity because the background reaction catalysed by a free metal is suppressed, was shown not to be applicable here,166 which might call for revisiting some of the many copper(II)-bis(oxazoline)-catalysed processes known. Enantioselective additions of pyrroles and indoles to ,/9-unsaturated 2-acylimidazoles catalysed by the bis(oxazolinyl)pyridine-scandium(III) triflate complex have been accomplished.167... 

Enantioselective additions of a,f)-unsaturated 2-acyl imidazoles, catalyzed by bis(oxazolinyl)pyridine-scandium(III)triflate complex, were used for the asymmetric synthesis of 3-substituted indoles. The complex 114 was one of the most promising catalysts. The choice of acetonitrile as the solvent and the use of 4 A molecular sieves were also found to be advantageous. The 2-acyl imidazole residue in the alkylation products of u,(i-unsaturated 2-acyl imidazoles could be transformed into synthetically useful amides, esters, carboxylic acid, ketones, and aldehydes (Scheme 32) [105]. Moreover, the catalyst 114 produced both the intramolecular indole alkylation and the 2-substituted indoles in good yield and enantioselectivity (Scheme 33) [106]. The complex... 

Chiral 2-(3-oxoalkyl)pyrroles and 3-(3-oxoalkyl)indoles can also be accessed by reaction in the presence of 10 mol% of chiral bis(oxazoline)/metal complexes in CH2C12 in very high yields and with ee values over 90% <2005JA4154>. Alkylation of pyrrole and of substituted indoles with, -unsaturated acyl phosphonates <2003JA10780> or 2-acyl N-methylimidazoles catalyzed by a chiral bis(oxazolinyl)pyridine (pybox)/scandium(III) triflate complex also exhibits good enantioselectivity over a broad range of substrates <2005JA8942>. 

Enantioselective Michael-type indole Friedel-Crafts reaction with a,P-unsaturated acyl thiazole has been disclosed <07JA10029>. Reaction of indole 127 and 128 in the presence of 10% mol of bis(oxazolinyl)pyridine-scandium(III) triflate complex 129 in acetonitrile at -40 °C affords 130 with high level of enantioselectivity. 

The Friedel-Crafts alkylation of the parent pyrrole and of substituted indoles with a,P-unsaturated acyl phospho-nates 468 <2003JA10780> and 2-acyl iV-methylimidazoles 469 catalyzed by the chiral bis(oxazolinyl)pyridine (pybox)/scandium(lIl) triflate complex 467 exhibits good enantioselectivities over a broad range of substrates (Scheme 97, Equation 113) <2005JA8942>. The desired alkylation products 470-472 were formed in good yields and enantioselectivities. 

Reaction of the anhydrous SCX3 (X = Cl, Br) with pyridine yields Sc(py)4X3, which possibly have one molecule of pyridine in the lattice, as it is lost in vacuo. Sc(py)3(NCS)3 also exists. Using bidentate ligands, SCL2X3 (L = phen, bipy) have been made, sometimes in two forms they are believed to be [ScL2X2]+X and it is possible that cis and trans-isomers may exist, but there is no stmctural confirmation. Similar ethylenediamine complexes have been made by removal of a ligand molecule in vacuo from Sc(en)3X3 (X = Cl, Br). Of the complexes of tridentate N-donors, the best characterized is Sc(terpy)(N03)3, which has nine-coordinate scandium, but with one rather long Sc-0 bond. 

In 1998, Kempe and coworkers [34] reported the first aminopyridinato rare-earth metal complexes. 4-Methyl-2-[(trimethylsilyl)amino]pyridine(HLl) was utilized in this complex. The reaction of lithiated LI and YCI3 in ether and pyridine led to the ate complex [Y(Ll)4(LiPy)] (Py = pyridine) (1). The complex 1 catalytically mediated a ligand transfer reaction to form [Pd(Ll)2] and [Y(Ll)3(py)] (2) from [Pd(cod)Cl2] (cod = cyclooctadiene). The LI ligand transfer from yttrium to palladium and the regeneration of 1 are significant in the efficient synthesis of the very strained amido palladium complexes (Scheme 2). Lithiated LI underwent a salt metathesis reaction with ScCb, at low temperature in THF, to yield the homoleptic complex [Sc(L1)3] (3) (Scheme 2). 3 is the first reported scandium aminopyridinato complex [35]. 

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