Cationic bis-diphosphaferrocene copper and gold complexes

Abstract

The octa(ethyl)diphosphaferrocene 1 reacts with half an equivalent of [Cu(MeCN)₄][PF₆] to afford the corresponding [Cu(1)₂][PF₆] complex 2 in which 1 behaves as a chelate ligand. An X-ray crystal structural analysis reveals that the overall arrangement of the four phosphorus atoms around the Cu cation is distorted tetrahedral. The same strategy was applied to the synthesis of gold(I) complexes. Ligands 1 and the octa(n-propyl)diphosphaferrocene 4 react with two equivalents of [AuCl(SMe₂)] to yield the expected bimetallic complexes [Au₂Cl₂(1)] 3 and [Au₂Cl₂(4)] 5 respectively. In these two complexes, each phospholide unit is coordinated to an AuCl fragment. Surprisingly, crystallization of 5 affords the bis-chelate [Au(4)₂][FeCl₄] derivative. A mechanism involving oxidation of the diphosphaferrocene ligand followed by nucleophilic attack of one chloride anion has been tentatively proposed. Complexes [Au(1)₂][GaCl₄] 7 and [Au(4)₂][GaCl₄] 8 can be conventionally prepared by the direct reaction of the two ligands with [AuCl(SMe₂)] in the presence of GaCl₃ as chloride abstractor. A DFT study, coupled with a Charge Decomposition Analysis (CDA), performed on the [Cu(dpf)₂] and [Cu(dpe)₂] model complexes (dpf = C₈H₈P₂Fe, dpe = H₂PCH₂CH₂PH₂) indicates that σ-donation dominates in the two complexes. In homoleptic [M(dpf)₂] and [M(dpe)₂] complexes (M = Ni, Pd), dpf and dpe exhibit a stronger π-accepting capacity. A comparison between theoretical structures of the bis-carbonyl complexes [NiL(CO)₂] (L = dpf or dpe or Me₂PCH₂CH₂PMe₂) indicates that dpf and dpe display a similar π-accepting capacity.