Dihapto binding of aromatic molecules by pi-basic transition metal complexes: development of alternatives to the {Os(NH3)(5)}(2+) fragment

Dihapto-coordination of aromatic ligands by electron-rich transition metals can effectively dearomatize the bound aromatic molecule. The pentaammineos mium(II) system forms thermally stable eta(2)-complexes with a variety of a renes and aromatic heterocycles, and has been used for a variety of organic transformations on the bound aromatic fragments. The systematic variation of isoelectronic rhenium(I) systems has provided the necessary electronic a nd steric characteristics needed for a less expensive, chiral alternative t o the {Os(NH3)(5)}(2+) system. The {TpRe(CO)(PMe3)} system has been shown t o form stable dihapto complexes with furan, thiophene and naphthalene. Acco rdingly, the {TpRe(CO)(PM3)} fragment and analogous {TpRe(CO)(L)} fragments represent the first class of asymmetric surrogates to the pentaammineosmiu m(II) system. (C) 2000 Elsevier Science S.A. All rights reserved.