Synthesis and coordination chemistry of a 14-membered macrocyclic ligand containing one phosphorus, two sulfur and one ambidentate sulfoxide donor sets

Abstract

The macrocyclic ligand PhP(CH₂CH₂SCH₂CH₂CH₂)₂SO (L) was obtained from the reaction between bis(3-chloropropyl) sulfoxide and bis(2-mercaptoethyl)phenylphosphine in the presence of caesium carbonate. The ligand is stable in the solid state but rearranges slowly into the isomeric phosphine oxide S(CH₂CH₂CH₂SCH₂CH₂)₂P(O)Ph in solution. In the presence of molecular iodine, the oxygen migration process occurred spontaneously and the phosphine oxide was obtained quantitatively within several minutes. When treated with [MCl₂(CH₃CN)₂] (where M = Pd, Pt), the sulfinyl-substituted macrocycle functions as a bidentate ligand via its phosphorus and one of the thioether sulfur donor atoms giving the corresponding neutral square-planar complexes cis-[M(L-P,S)Cl₂]. In both complexes, the sulfoxide group is not involved in metal complexation. However, when the dichloro complexes were treated with silver perchlorate, the corresponding tetradentate complexes [M{L-P,S,S,S}][ClO₄]₂ were formed. In both the perchlorate salts, the ambidentate sulfoxide functions are coordinated to the metal centre via their sulfur donor. In contrast to the previously reported acyclic analogues, the sulfoxide–metal bonds are kinetically stable.