Systematic Study of the Role of Ligand Structure in the Formation of Homobinuclear Rhodium Macrocycles Formed via the Weak-Link Approach

A series of new bis-1,4-phosphinoethoxyaryl hemilabile ligands of the form (1,4-(Ph ₂PCH ₂-CH ₂O) ₂-arene), where the nature and substituent pattern of the central arene ring have been systematically varied, is reported. These ligands were prepared in two steps by one of two synthetic routes. The reaction of each of these ligands with a highly reactive Rh(I) starting material and the resulting metastable coordination isomers have been investigated. These intermediate structures have been isolated and characterized in solution, and three complexes have been characterized in the solid state by single-crystal X-ray diffraction. The reaction investigated herein is the first step in the weak-link approach to supramolecular coordination complexes. We have utilized the resulting product distribution to glean information about the relative importance of a number of stabilizing effects associated with the metastable intermediates, including the strength of the dative heteroatom-metal bonds, metal-arene interactions, and stacking interactions between arene rings.