Cyclopentadienyl molybdenum di- and tricarbonyl dimer and cyclopentadienyl tungsten di- and tricarbonyl dimer complexes were added to silica as precursors to supported metal dimers. These complexes are shown to yield metal dimers following attachment to the silica and carbonyl ligand removal. Reductive carbonyl coupling of acetaldehyde and acetone was used as a molecular probe to determine whether dimers formed, with each metal atom being in the 4+ oxidation state. Acetaldehyde and acetone reductively coupled to produce cis- and trans-2-butenes and 2,3-dimethyl-2-butene, respectively. Diolates formed as intermediate products during the coupling reaction. Infrared bands were observed at 2969, 2925, and 2859 cm(-1) that correspond to nu(asym)(CH3), nu(CH), and nu(sym)(CH3), respectively, for the 2,3-butanediolate formed from acetaldehyde. The hydrogens on the methyl groups for the acetone reductive coupling intermediate, 2,3-dimethyl-2,3-butanediolate, were not equivalent, resulting in the appearance of three C-H stretching frequencies at 2977, 2939, and 2891 cm(-1) that are assigned to A(asym)’, A ", A(sym)’ Of CH3, respectively. Extended X-ray absorption fine structure (EXAFS) spectroscopy was used to characterize a sample prepared from cyclopentadienyl tungsten dicarbonyl dimer on silica. The EXAFS data showed that there were W-O bonds with lengths of 1.96 and 2.26 Angstrom. The EXAFS data are also consistent with W-W interactions at an average length of 2.96 Angstrom.