Coinage metal coordination chemistry of stable primary, secondary and tertiary ferrocenylethyl-based phosphines

Abstract

Ferrocene-based phosphines constitute an important auxiliary ligand in inorganic chemistry. Utilizing the (ferrocenylethyl)phosphines (FcCH₂CH₂)_3−nH_nP (Fc = ferrocenyl; n = 2, 1; n = 1, 2; n = 0, 3) the synthesis of a series of coordination complexes [(FcCH₂CH₂)_3−nH_nPCuCl]₄ (n = 2, 1-CuCl; n = 0, 3-CuCl), [(FcCH₂CH₂)₂HPCuCl] (2-CuCl), {[(FcCH₂CH₂)H₂P]₂AgCl}₂ (1-AgCl), [(FcCH₂CH₂)₂HPAgCl] (2-AgCl), [(FcCH₂CH₂)₃PAgCl]₄ (3-AgCl), [(FcCH₂CH₂)₃PM(OAc)]₄ (M = Cu, 3-CuOAc M = Ag, 3-AgOAc), [(FcCH₂CH₂)_3−nH_nPAuCl] (n = 1, 2-AuCl; n = 0, 3-AuCl), via the reaction between the free phosphine and MX (M = Cu, Ag and Au; X = Cl, OAc), is described. The reaction between the respective phosphine with a suspension of metal–chloride or -acetate in a 1 : 1 ratio in THF at ambient temperature affords coordinated phosphine-coinage metal complexes. Varying structural motifs are observed in the solid state, as determined via single crystal X-ray analysis of 1-CuCl, 3-CuCl, 1-AgCl, 3-AgCl, 3-CuOAc, 3-AgOAc, 2-AuCl and 3-AuCl. Complexes 1-CuCl and 3-CuCl are tetrameric Cu(I) cubane-like structures with a Cu₄Cl₄ core, whereas silver complexes with primary and tertiary phosphine reveal two different structural types. The structure of 1-AgCl, unlike the rest, displays the coordination of two phosphines to each silver atom and shows a quadrangle defined by two Ag and two Cl atoms. In contrast, 3-AgCl is distorted from a cubane structure via elongation of one of the Cl⋯Ag distances. 3-CuOAc and 3-AgOAc are isostructural with step-like cores, while complexes 2-AuCl and 3-AuCl reveal a linear geometry of a phosphine gold(I) chloride devoid of any aurophilic interactions. All of the complexes were characterized in solution by multinuclear ¹H, ¹³C{¹H} and ³¹P NMR spectroscopic techniques; the redox chemistry of the series of complexes was examined using cyclic voltammetry. This class of complexes has been found to exhibit one reversible Fe(II)/Fe(III) oxidation couple, suggesting the absence of electronic communication between the ferrocenyl units on individual phosphine ligands as well as between different phosphines on the polymetallic cores.