Organometallic Rhodium Complexes Encapsulated in Mesoporous Molecular Sieves

Abstract

Rh(III) complexes both dimmer [Cp * RhCl]2(l-Cl)2 and monomer ([RhCp * (S)3] 2+ ) were encapsulated into MCM-41 channels. All silica MCM-41 molecular sieve and aminosililated MCM-41 matrix were used for rhodium complexes accommodation. Reactivity of Cp * rhodium complexes encapsulated in meso structure was estimated on the grounds of their susceptibility to interaction with CO molecules resulting in the formation of carbonyl complexes. Formation of Cp * Rh carbonyls was recorded by means of FTIR spectra. It was found that accommodation of Rh(III) complexes in MCM-41 molecular sieves activated the complex and led to the formation of Rh(III)Cp * carbonyls as a result of contact with CO. Contact of rhodium (III) complexes encapsulated in MCM-41 matrix with CO did not result in rhodium (III) reduction, whereas in the presence of amine groups in aminosililated MCM-41 the reduction of Rh(III) to Rh(I) occurred relatively easily and formation of Cp * Rh(CO)2 complex containing Rh(I) was noted. Encapsulated rhodium complexes showed some activity in methanol carbonylation reaction carried out under heterogeneous conditions. For the most active catalyst the amount of methyl acetate reached about 8 mol.%, however, deactivation of catalyst occurred and after 2 h on stream methyl acetate was not found in the product.