Diastereoselective Synthesis of New Rhodium-Based Amphiphilic Polyol-Cp Systems

The cyclopentadienide nucleophilic ring opening on the cyclopentene oxide affords diastereoselectively an efficient entry to a new polyalcoholic (1,2,4)-C5H2[CH(CH2)3CHOH]3 propeller-like, hybrid ligand CpOOO. The diastereoselective rhodium complexation gives rise almost quantitatively to a new class of racemic CpOOORh(L,L) (L,L = nbd, cod, C2H4, CO) complexes. Thermal treatment gives predominantly the air-stable CpOOORh(nbd) rac-4a (73.5%), having SP planar chirality, as determined by X-ray diffraction studies. It has also been possible to isolate its stable atropisomer rac-4c (20.5%), while the minor kinetic isomer rac-4b, showing opposite planar chirality (∼10%), has been identified by NOESY NMR experiments. The high solubility in water and benzene, evidencing the amphiphilic character, has been measured by the n-octanol/water partition coefficient. The intermolecular H-binding, due to the hydroxy groups, plays a crucial role in selecting the rhodium coordination in the reaction mixture, whereas in the solid, it determines the supramolecular organization. DFT calculations in vacuo are in agreement with the spectroscopically identified structures.