The Interaction of 1,1′‐Diphosphaferrocenes with Gold: Molecular Coordination Chemistry and Adsorption on Solid Substrates

Abstract

1,1′‐Diphosphaferrocene (1) and its 3,3′,4,4′‐tetramethyl (2), 3,3′,4,4′‐tetraphenyl (3), octamethyl (4), octaethyl (5) and octaphenyl derivative (6) have been investigated in terms of the suitability of 1,1′‐diphosphaferrocenes as adsorbate species for fabricating self‐assembled monolayers (SAMs) on gold. Compounds 3 and 6 have been structurally characterised by X‐ray diffraction. Complexes [Au(4)2][GaCl4] and [Au2(µ‐5)2][FeCl4]2 have also been prepared and are only the second and third examples to date of structurally characterised (1,1′‐diphosphaferrocene)gold complexes. [Au(4)2][GaCl4] exhibits intramolecular Au···Fe contacts compatible with Fe→Au bonding interactions, which have not been described before in ferrocene chemistry. [Au2(µ‐5)2][FeCl4]2 exhibits an intramolecular Au···Au contact indicative of aurophilic bonding, leading to a structural motif unprecedented for 1,1′‐diphosphaferrocenes. Ultrathin films obtained by chemisorption of the 1,1′‐diphosphaferrocenes from solution onto gold substrates have been investigated by X‐ray photoelectron spectroscopy and near‐edge X‐ray absorption fine‐structure (NEXAFS) spectroscopy. The results indicate that the surface binding of 1 involves the Fe atom together with both P atoms, whereas in the other cases, surface binding can be realised with just one phospholyl ring. There is no indication of any oxidative decomposition of the adsorbates on the surface. According to NEXAFS spectroscopic results 6 gives rise to SAMs of high orientational order.