The chemistry of spin-coated rhodium-ferrocenyl complexes supported on silanol-capped silicon wafers

Abstract

A series of rhodium β-diketonato complexes [Rh(FcCOCHCOR)(CO)2] and [Rh(FcCOCHCOR)(CO)(PPh3)] with R = CF3, CH3, Ph = C6H5 and Fc (ferrocenyl = FeII(C5H5)(C5H4)) were spin-coated on two-dimensional silanol-functionalised silicon wafers. Chemical reactions were observed that do not occur in ethanol solutions. Si-OH fragments on the wafers substituted ligands and oxidatively added to the Rh(I) centres. A multitude of different surface species could be identified with X-ray photoelectron spectroscopy (XPS). These included the parent spin-coated rhodium(I) complexes and rhodium(I) species that resulted from β-diketonato displacement from parent rhodium complexes by surface silanol OH’s to generate [wafer-(O)2-Rh-(CO)2]⊝ and [wafer-(O)2-Rh-(CO)(PPh3)]⊝ units. Several RhIII surface species that inter alia resulted from oxidative addition of surface Si-OH groups to surface-coordinated RhI core atoms were also identified. Efficacy of β-diketonato ligand substitution by the silanol surfaces is a kinetically driven process and can be related to the rate of solution-phase β-diketonato substitution by 1,10-phenanthroline from parent [Rh(FcCOCHCOR)(CO)2] and [Rh(FcCOCHCOR)(CO)(PPh3)] complexes. The binding energies of the RhI and RhIII 3d5/2 photoelectron lines were found to be functions of Gordy scale R-group electronegativities and they are also linearly related to electrochemically determined RhI oxidation potentials.