Dihapto binding of aromatic molecules by π-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 pentaammineosmium(II) system forms thermally stable η²-complexes with a variety of arenes 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 and steric characteristics needed for a less expensive, chiral alternative to the {Os(NH₃)₅}²⁺ system. The {TpRe(CO)(PMe₃)} system has been shown to form stable dihapto complexes with furan, thiophene and naphthalene. Accordingly, the {TpRe(CO)(PMe₃)} fragment and analogous {TpRe(CO)(L)} fragments represent the first class of asymmetric surrogates to the pentaammineosmium(II) system.