Gold(I) Complexes of Ferrocenyl Polyphosphines: Aurophilic Gold Chloride Formation and Phosphine-Concerted Shuttling of a Dinuclear [ClAu···AuCl] Fragment

A smart steric control of the metallocene backbone in bis- and poly­(phosphino)­ferrocene ligands favors intramolecular aurophilic interactions between [AuCl] fragments in polynuclear gold­(I) complexes. We synthesized and characterized by multinuclear NMR and X-ray diffraction analysis mono-, di-, and polynuclear gold complexes of constrained ferrocenyl diphosphines, which bear either bulky <i>tert</i>-butyl groups or more flexible siloxane substituents at the cyclopentadienyl rings. The complexes <i>meso</i>-1,1′-bis­(diphenylphosphino)-3,3′-di-<i>tert</i>-butylferrocene (<b>4-m</b>), <i>rac</i>-1,1′-bis­[bis­(5-methyl-2-furyl)­phosphino]-3,3′-di-<i>tert</i>-butylferrocene (<b>5-r</b>), and <i>rac</i>-1,1′-bis­(diphenylphosphino)-3,3′-bis­[(tri-<i>iso</i>-propylsilyl)­oxy]­ferrocene (<b>6-r</b>) were used to form dinuclear gold complexes. Coordination of <i>tert</i>-butylated ferrocenyl phosphines generated aurophilic interactions in the corresponding dinuclear gold complexes, contrary to gold­(I) complexes reported with 1,1′-bis­(diphenylphosphino)­ferrocene. The structurally related tetraphosphine 1,1′,2,2′-tetrakis­(diphenylphosphino)-4,4′-di-<i>tert</i>-butylferrocene (<b>11</b>) also gave access to mononuclear, dinuclear, and the original trinuclear gold chloride aurophilic complexes in which 14e^– to 16e^– gold centers coexist. In such complexes, nonbonded (“through-space”) ³¹P–³¹P′ nuclear spin couplings were evidenced by high-resolution NMR. In these interactions nuclear spin information is transferred between the lone-pair electron of an uncoordinated phosphorus P and a phosphorus P′ that is involved in a σ covalent bond Au–P′. The dinuclear aurophilic complex displayed a concerted shuttling of its [ClAu···AuCl] fragment between the four phosphorus donors of the tetraphosphine ligand. Thus, an aurophilic Au···Au bond, which is assumed to be a weak energy interaction, can be conserved within a dynamic shuttling process at high temperature involving an intramolecular coordination–decoordination process of digold­(I) at phosphorus atoms