Configurationally homogeneous diastereomers of a linear hexa(tertiary phosphine): Enantioselective self-assembly of a double-stranded parallel helicate of the type ( P )-[Cu 3 (hexaphos) 2 ](PF 6 ) 3

Abstract

Three configurationally homogeneous diastereomers of the linear hexa(tertiary phosphine) Ph2PCH2CH2P(Ph) CH2CH2P(Ph)CH2 CH2P-(Ph)CH2CH2P(Ph)CH2 CH2PPh2 (hexaphos) have been isolated in enantiomerically pure form, namely (R,S,S,R)-, (R,S,S,S)-, and (S,S,S,S)-hexaphos. The strongly helicating (R,S,S,R)-(-) form of the ligand combines with copper(I) ions to generate by stereoselective self-assembly the P enantiomer of a parallel helicate of the type [Cu3(hexaphos)2](PF6)3, which has been characterized by x-ray crystallography. Theoretical modeling of the cation indicates that it is the relationship between the helicities of the two 10-membered rings containing the three copper ions, each of which has the twist-boat-chair-boat conformation, and the configurations of the three chiral, tetrahedral copper stereocenters of P configuration that determines the stereochemistry of the parallel and double α-helix conformers of the double-stranded trinuclear metal helicate. Show more