Regioselective synthesis of π-complexes of substituted polycyclic aromatic compounds.: Experimental (NMR) and theoretical (DFT) studies of η6,η6-haptotropic rearrangements in naphthalenechromiumtricarbonyl complexes

A new regioselective method for the synthesis of (eta(6)-naphthalene)chromium tricarbonyl complexes bearing a substituent R in desired positions of either the coordinated or non-coordinated ring was proposed. The kinetics of eta(6),eta(6)-haptotropic rearrangements (IRHR) was investigated by NMR spectroscopy for ten pairs of isomer complexes (R = D. CH3, Me3Sn. Me3Si and Cl in position 1 or 2 of coordinated or non-coordinated rings). The free activation energies Delta G* fall into a quite narrow range of 28-31 kcal mol(-1) and are therefore relatively insensitive to the influence of substituent R whereas equilibrium constants of IRHR change considerably from 0.03 to 17.26 within the compounds investigated, Electron donating (withdrawing) substituents R increase (decrease) the relative thermodynamic stability of the isomers containing a substituent in coordinated rings. The density functional theory method (DFT) with extensive basis set describes quite satisfactory 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 rearrangement of (eta(6)-naphthalene)chromium tricarbonyl has trimsthylenemethane structure of C-2v-symmetry in which the Cr(CO)(3)-group is slightly shifted to the Ligand periphery. For the monosubstituted naphthalenechromium tricarbonyls thus, there are two reaction channels of the chromium tricarbonyl group slippage between unsubstituted and substituted rings, one of which is practically unperturbed determining the lon sensitivity of the rearrangement rate to the effects of ligand substitution even for 1-R substituted complexes, Calculated activation barriers are in a good accordance with the experimentally determined Delta G* values. (C) 1999 Elsevier Science S.A. All rights reserved.