Diastereoselectivity and molecular recognition in the self-assembly of double-stranded dinuclear metal complexes of the type {M 2 {( R *, S *)-tetraphos} 2 ] (PF 6 ) 2 (M = Ag and Au)

Abstract

The ligand (R*,S*)-Ph2PCH2CH 2P(Ph)CH2CH2P(Ph)CH2CH 2PPh2, (R*,S*)-tetraphos, combines with silver(I) and gold(I) ions in the presence of hexafluorophosphate to diastereoselectively self-assemble the head-to-head (H,H) diastereomers of the double-stranded, dinuclear metal complexes [M2{(R*,S* )-tetraphos}2](PF6)2 in which the two chiral metal centers in the complexes have M (R end of phosphine) and P (S end of phosphine) configurations. The crystal and molecular structures of the compounds have been determined: (H,H)-(M,P)-[Ag2{(R*,S* )-tetraphos}2](PF6)2, monoclinic, P2 1/c, a = 10.3784(2), b = 47.320(1), c = 17.3385(4) Å, β = 103.8963(5)°, Z = 4; (H,H)-(M,P)-[Au2{(R*,S* )-tetraphos}2](PF6)2, monoclinic, P..2 1 (No. 4, c unique axis), a = 24.385(4), b = 46.175(3), c = 14.820(4) Å, Z = 8. The complexes crystallize as racemic compounds in which the unit cell in each case contains equal numbers of enantiomorphic molecules of the cation and associated anions. The cations in both structures have similar side-by-side structures of idealized C2 symmetry, the bulk helicity of each molecule in the solid state being due solely to the twist of the central ten-membered ring containing the two metal ions of opposite configuration, which has the chiral twist-boat-chair-boat conformation. When 1 equiv each of (R*,S*)-tetraphos, (R*,R*)-(± )-tetraphos, (S,S)-(+)-tetraphos, 2 equiv of Ph2PCH 2CH2PPh2 (dppe), and 7 equiv of [AuCl(SMe 2)] in dichloromethane are allowed to react for several minutes in the presence of an excess of ammonium hexafluorophosphate in water (two phases), the products are the double-stranded digold(I) complexes in which each ligand strand has recognized itself by stereoselective self-assembly, together with [Au(dppe)2]PF6.