Regioselective synthesis of pi-complexes of substituted polycyclic aromatic compounds. Experimental (NMR) and theoretical (DFT) studies of eta(6),eta(6)-haptotropic rearrangements in naphthalenechromiumtricarbonyl complexes

A new regioselective method for the synthesis of (eta(6)-naphthalene)chromi um tricarbonyl complexes bearing a substituent R in desired positions of ei ther the coordinated or non-coordinated ring was proposed. The kinetics of eta(6),eta(6)-haptotropic rearrangements (IRHR) was investigated by NMR spe ctroscopy for ten pairs of isomer complexes (R = D. CH3, Me3Sn. Me3Si and C l in position 1 or 2 of coordinated or non-coordinated rings). The free act ivation energies Delta G* fall into a quite narrow range of 28-31 kcal mol( -1) and are therefore relatively insensitive to the influence of substituen t R whereas equilibrium constants of IRHR change considerably from 0.03 to 17.26 within the compounds investigated, Electron donating (withdrawing) su bstituents R increase (decrease) the relative thermodynamic stability of th e isomers containing a substituent in coordinated rings. The density functi onal theory method (DFT) with extensive basis set describes quite satisfact ory the geometry and the energy of ground states and correctly predict that the least motion route of Cr(CO), from one ring to another via the center of the C-4a-C-8a bond is forbidden. The transition state for the rearrangem ent of (eta(6)-naphthalene)chromium tricarbonyl has trimsthylenemethane str ucture of C-2v-symmetry in which the Cr(CO)(3)-group is slightly shifted to the Ligand periphery. For the monosubstituted naphthalenechromium tricarbo nyls thus, there are two reaction channels of the chromium tricarbonyl grou p slippage between unsubstituted and substituted rings, one of which is pra ctically unperturbed determining the lon sensitivity of the rearrangement r ate to the effects of ligand substitution even for 1-R substituted complexe s, Calculated activation barriers are in a good accordance with the experim entally determined Delta G* values. (C) 1999 Elsevier Science S.A. All righ ts reserved.