CONTROL OF ETA(2)-COORDINATION VS C-H BOND ACTIVATION BY RHODIUM - THE ROLE OF AROMATIC RESONANCE ENERGIES

The reactions of a series of fused polycyclic arenes with (C5Me5)Rh(PM e3)(Ph)H and (C5H5)Rh(PMe3)-(Ph)H have been examined, and the thermody namic preferences for eta2-arene coordination vs C-H bond activation h ave been determined. While naphthalene, perylene, and triphenylene giv e equilibrium mixtures of both C-H activation and eta2-complexes, phen anthrene, anthracene, 2-methoxynaphthalene, 2,6-dimethoxynaphthalene, pyrene, and fluoranthene give only eta2-complexes (C5Me5 complexes). N aphthalene and several of the polycyclic aromatics are found to give b is-eta2-complexes upon extended reaction. Electron-withdrawing groups as in p-C6H4(CF3)2 and m-C6H4(CF3)2 are also found to promote eta2-coo rdination in monocyclic arenes (C5H5 complexes). A C5H5 ligand favors eta2-coordination compared to a C5Me5 ligand, as does rhodium compared to iridium. The effects of resonance, specifically the differences in the Huckel energies of the eta2-bound vs free ligand, are believed to control the C-H activation/eta2-coordination equilibria in polycyclic systems. The perylene complex (C5Me5)Rh(PMe3)(eta2-perylene) has been found to crystallize in monoclinic space group C2/c, with a = 32.927( 10) angstrom, b = 10. 125(2) angstrom, c = 18.129(8) angstrom, 100.30( 3)degrees, V = 5946.5(6.3) angstrom3, and Z = 8.