Spectroscopic studies on adsorbed metal carbonyls. Part 1. Interaction of [Rh4(CO)12] and [Rh6(CO)16] with alumina, silica, and titania

Abstract

The interaction of [Rh₄(CO)₁₂](1) and [Rh₆(CO)₁₆](2) with Al₂O₃, TiO₂, and SiO₂ has been monitored by i.r. spectroscopy, using isotopic substitution and spectrum simulation techniques. Conversion of (1) into (2) has been demonstrated on Al₂O₃ and TiO₂. Isolated Rh^I(CO)₂ sites are considered to exist on all three oxides after oxidative fragmentation of (1) or (2). Rh(CO)_n(n= 3, or possibly 4) sites were also suggested from (1) and TiO₂ or SiO₂. Extended reaction times (TiO₂ and Al₂O₃) or exposure to the i.r. spectrometer beam (Al₂O₃) causes aggregation to metal crystallites.