Scandium amides

Scandium amides are described in more detail in Chapter 4. 

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. 

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... 

The enantioselective total synthesis of (-)-hemiasterlin, a marine tripeptide with cytotoxic and antimitotic activity, was achieved by E. Vedejs and co-workers. The asymmetric Strecker reaction was used to construct the key tetramethyltryptophan subunit. The aldehyde substrate was first converted to the corresponding chiral imine with (R)-2-phenylglycinol under scandium triflate catalysis. The addition of tributyltin cyanide resulted in the formation of a-amino nitriles as an 8 1 mixture of diastereomers. Subsequently the cyano group was converted to a primary amide, and the chiral auxiliary was removed under catalytic hydrogenation conditions. 

CCC (1987) contains a section on sulfoxides, amide, amine oxides, and related ligands that have sections on phosphine oxides and arsine oxides.159 Phosphine and arsine oxide complexes of yttrium and the lanthanides were highlighted in CCC (1987).1 Scandium and yttrium phosphine oxide complexes have been reinvestigated and characterized by multinuclear NMR and X-ray... 

Studies of the bonding in some transition-metal complexes have identified a similarity between the He(I) photoelectron spectra of three-co-ordinate homoleptic bis(trimethylsilyl) amides of scandium and those of open-shell compounds. The two bands at ionization potential <9 eV were assigned to lone-pair orbitals. Bands corresponding to ionization from the metal 3d orbitals were considered to lie at ionization potentials >9eV or to be masked by the bands resulting from nitrogen lone-pair orbitals (> 8.1 eV). 

Ionic systems - less susceptible to deleterious dimerization - are accessible with a Judicious choice of ancillary ligand. The /3-diketoiminate scandium dimethyl complex (7) (Figure 11 Ar = 2,6-diisopropylphenyl), activated by B(C6Fs)3 leads to a structurally characterizable ionic complex which polymerizes ethylene. The neutral 1,4,7-triazocyclononane ligand was used to prepare a scandium trimethyl complex (8), which polymerizes ethylene when B(CeF5)3 is used as a cocatalyst. A derivative pendant amide arm leads to the yttrium bis (trimethylsilylmethyl) compound (9), which exhibits modest activity in the presence of [HNMe2Ph][B(C6F5)4l.= ... 

Scandium complexes, 1059-1116 alkoxides, 1065 amides, 1062,1066 amine oxides, 1065 amines, 1060 amino acids, 1066 aromatic amines, 1061 arsenic compounds, 1065 2,2 -bipyridyl, 1061... 

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