NOBIN-based phosphoramidite and phosphorodiamiditeligands and their use in asymmetric nickel-catalysed hydrovinylation

Abstract

Phosphoramidite and P-stereogenic phosphorodiamidite ligands derived from (S_a)-2-phenylamino-2′-hydroxy-1,1′-binaphthyl (N-Ph-NOBIN) and bis(1-phenyl-ethyl)amine were synthesised, fully characterised, and the absolute configuration of the stereogenic phosphorus atoms was assigned. The phosphoramidite ligand L2 features three non-bridged substituents at phosphorus comprising the bis(1-phenylethyl)amine and two NOBIN moieties. The NOBIN units are bound to the phosphorus through the oxygen atoms with two pendant nitrogen atoms. In the Ni-catalysed hydrovinylation of styrene no conversion was observed with the phosphorodiamidites, while the phosphoramidite ligands led to active catalysts with a marked co-operative effect on selectivities. Whereas the racemic product was obtained with the (S_a,S_a,S_C,S_C) diastereomer, the (S_a,S_a,R_C,R_C) diastereomer proved to be one of the best ligands for this reaction, leading to almost perfect selectivity and ees of up to 91%.