The reaction of the tetrahedral cluster Rh 4 (CO) 1 2 with two molar equivalents of trimethylamine N-oxide in the presence of an excess of cyclohexa-1,3-diene affords the hexanuclear cluster Rh 6 (CO) 1 0 (μ 3 -CO) 4 (η 4 -C 6 H 8 ) (1). This new cluster was characterized by spectroscopy and in the solid-state by a single-crystal X-ray diffraction study, and shown to be based on the structure of Rh 6 (CO) 1 2 (μ 3 -CO) 4 with two terminal carbonyl ligands replaced by a an η 4 -cyclohexadiene unit.