Synthesis and characterization of {(diene)Rh[μ-OSi(O^tBu)₃]}₂, a precursor to silica-bound rhodium

Reaction of [(diene)RhCl]2 with 2 equiv of KOSi(OtBu)3 afforded [(diene)Rh[mu-OSi(OtBu)3]]2, where diene=cod (1) and nbd (2). Multinuclear NMR studies reveal that 1 and 2 have a dimeric structure with bridging tris(tert-butoxy)siloxy ligands. These dimers are folded along the O...O axis. Complexes and reacted with PR3(R=Me, Ph) to give monomeric products, the formulae of which depend on the amount of PR3 added ((diene)Rh[OSi(OtBu)3](PR3) and Rh[OSi(OtBu)3](PMe3)3). The behavior of 1 towards water and methanol is discussed. Thermogravimetric analyses (TGAs) of 1 and 2 reveal rather sharp conversions to rhodium-containing materials. Thermolysis of 1 in toluene at 180 degrees C resulted in formation of a black precipitate, which contained rhodium nanoparticles with an average diameter of 22 nm, as determined by powder X-ray diffraction (PXRD), after calcination at 300 degrees C for 1 h.