Bis-silyl chelate ligand

BIS-SILYL CHELATE LIGAND PRECURSOR XANTSILH2 AND SOME RUTHENIUM XANTSIL COMPLEXES... 

Isonitrile ligands bound to palladium turn out to be very efficient in promoting the bis-silylation of alkenes [171], Another possibility to make oxidative addition of Si-Si bond easier is the introduction of potentially chelating functionality such as phosphino groups in the disilane (Eq. 2.74) [172],... 

In contrast with the dimeric structure of lb, an X-ray structural analysis of l,4-bis(silyl)-2,3-diphenyl-l,4-dilithio-l,3-diene le revealed a monomeric pattern with a double diUthium bridge (Jype III, Scheme 2), despite no chelating ligands such as TMEDA were used [33]. Two Li atoms were coordinated with two THF and one Et20, respectively. 

With the potentially bis-chelating 2,6-bis(/V,V-dimethylaminomethyl)phcnyl ligand, which can be attached to silicon via its lithium salt (Figure 4), Corriu et al. have prepared a number of trivalent silyl cations as their chloride salts 787-790 (Scheme 103).811... 

Evans et al. recently reported the use of structurally well-defined Sn(II) Lewis acids for the enantioselective aldol addition reactions of a-heterosubstituted substrates [47]. These complexes are readily assembled from Sn(OTf)2 and C2-symmetric bis(oxazoline) ligands. The facile synthesis of these ligands commences with optically active 1,2-diamino alcohols, which are themselves readily available from the corresponding a-amino acids. The Sn(II)-bis(oxazoline) complexes were shown to function optimally as catalysts for enantioselective aldol addition reactions with aldehydes and ketone substrates that are suited to putatively chelate the Lewis acid. For example, use of 10 mol % Sn(II) catalyst, thioacetate, and thiopropionate derived silyl ketene acetals added at -78 °C in dichloromethane to glyoxaldehyde to give hydroxy diesters in superb yields, enantioselectivity, and diastereoselectivity (Eq. 27). The process represents an unusual example wherein 2,3-ant/-aldol adducts are obtained stereoselec-tively. 

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