Surface-derived metal species from M(III) β-diketonato precursors on amine-capped 2-D silica wafers: XPS characterisation and apparent catalytic activity in urethane synthesis

Metal-containing two-dimensional surfaces were prepared by exposing amine-capped silicon wafers to Mn(β-diketonato) 3 precursors [β-diketonato = acetylacetonato, dibenzoylmethanato, trifluorofuroylacetonato or hexafluoroacetylacetonato] or M(acac) 3 (M = Co, Rh or Ir). X-ray photoelectron spectroscopy (XPS) confirmed metal deposition. For the Mn-containing surfaces, strongly sub-stoichiometric F:Mn ratios for fluorinated precursors and broad, oxide-range Mn 2p envelopes indicate extensive ligand loss and heterogeneous, predominantly oxide-like Mn environments; the spectra do not uniquely establish individual Mn compounds or intact surface complexes. Metal:N ratios were therefore used only to estimate total XPS-detected metal surface densities, not molecular complexes or catalytically active sites. The surfaces promoted the reaction of ethanol with hexamethylenediisocyanate (HDI) to form hexamethylenediurethane (HDU). Total-metal-normalised apparent turnover frequencies (TOF app ) were approximately 5–127 s −1 . Rh-derived surfaces gave the highest TOF app . The qualitative association with precursor-metal Pauling electronegativity in this limited series is not proof of the electronic structure or mechanism of the active species.