The title compound (10) was prepared from the calix[4]arene precursor (11) to form the ligand 5, 11-bis (methyl(diphenylphosphino))-25,26,27,28-tetra-n-propoxy calix[4]arene (12), which was reacted with [Rh(COD)Cl](2) (COD= 1,5-cyclooctadienyl) and TIPF6 as chloride scavenger, in 31% overall chemical yield. The dimer structure in solution was demonstrated by the measurements of the P-31 NMR spin-lattice relaxation time (T-1) in comparison with the ligand itself. Computer modeling shows that the dimer macrocycle exhibits many possible conformers, including some with obvious steric hindrance about the Rh atom, but no apparent ring stress. 10 was tested for the catalytic homogeneous hydroformylation of hex-1-ene and compared with other closely related analogue systems recently reported in the literature.