Stabilization of the Elusive Antimony(I) Cation and Its Coordination Complexes with Transition Metals

Abstract

Upon stabilization by 5,6-bis(diisopropylphosphino)acenaphthene to form compound 1, the fugitive antimony (I) cation exhibited nucleophilic behavior towards coinage metals. Compound 1 was strategically synthesized at room temperature from SbCl₃ , the bis(phosphine), and trimethylsilyl trifluoromethanesulfonate taken in a 1:2:3 ratio, whereby the bis(phosphine) plays the dual role of a reductant and a supporting ligand. The generation of 1 involves two-electron oxidation of the ligand to form a P-P bonded diphosphonium dication. Compound 1 was separated from this dication to give both products in pure form in moderate yields. Despite the overall positive charge, the Sb^I site in 1 was found to bind to metal centers, forming complexes with Au^I , Ag^I and Cu^I . Compound 1 reduced Cu^II to Cu^I and formed a coordination complex with the resulting Cu^I species. The effects of the electron-rich bis(phosphine) and the constrained peri geometry in stabilizing and enhancing the nucleophilicity of 1 have been rationalized through computational studies.

Keywords: antimony(I) cation; coordination modes; nucleophilicity; phosphine ligands; reduction.