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 tert-butyl groups or more
flexible siloxane substituents at the cyclopentadienyl rings. The
complexes meso-1,1′-bis­(diphenylphosphino)-3,3′-di-tert-butylferrocene (4-m), rac-1,1′-bis­[bis­(5-methyl-2-furyl)­phosphino]-3,3′-di-tert-butylferrocene (5-r), and rac-1,1′-bis­(diphenylphosphino)-3,3′-bis­[(tri-iso-propylsilyl)­oxy]­ferrocene (6-r) were used
to form dinuclear gold complexes. Coordination of tert-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-tert-butylferrocene (11) 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.