Exploring the utility of a new chiral phosphoramidite P,N-ligand derived from (R)-BINOL and 7-azaindole in asymmetric catalysis

Abstract

Lithiation of 7-azaindole, followed by quenching with [(R)-(1,1′-binaphthalene-2,2′-diyl)]chlorophosphite afforded the new chiral phosphoramidite 1 in 92% isolated yield. Treatment of 0.5 equiv. of [(COD)MCl]2 (M = Rh, Ir; COD = η4-1,5-cyclooctadiene) with 2 equiv. of 1 afforded the corresponding [(κ1-P,N-1)(κ2-P,N-1)MCl] complexes in 68% (2a, Rh) and 72% (2b, Ir) yield, while treatment of (PPh3)3RhCl with 1 equiv. of 1 afforded [(PPh3)(κ2-P,N-1)RhCl] (3) as an analytically pure solid in 74% isolated yield. In examining the reaction of 1 with a mixture of 0.5 equiv. of [(COD)RhCl]2 and 1 equiv. of AgBF4, an inseparable mixture of [(κ2-P,N-1)2Rh]+BF4– (4a) and [(COD)(κ2-P,N-1)Rh]+BF4– (5a) was generated. Under analogous conditions employing [(COD)IrCl]2, the complex [(COD)(κ2-P,N-1)Ir]+BF4– (5b) was obtained in 86% isolated yield. Treatment of 0.5 equiv. of [(η3-allyl)PdCl]2 with 1 afforded [(η3-allyl)(κ2-P,N-1)Pd]+Cl– (6) in 86% isolated yield. The application of 1 in platinum group metal-mediated asymmetric chemical transformations, including alkene hydrogenation and hydroboration, ketone hydrosilylation, and allylic alkylation, was examined.Key words: chiral, ligand, phosphoramidite, asymmetric catalysis.