Solvent-dependent interconversions between Rh(I), Rh(II), and Rh(III) complexes of an aryl-monophosphine ligand.

Reaction of the aryl-monophosphine ligand alpha(2)-(diisopropylphosphino)isodurene (1) with the Rh(I) precursor [Rh(coe)(2)(acetone)(2)]BF(4) (coe=cyclooctene) in different solvents yielded complexes of all three common oxidation states of rhodium, depending on the solvent used. When the reaction was carried out in methanol a cyclometalated, solvent-stabilized Rh(III) alkyl-hydride complex (2) was obtained. However, when the reaction was carried out in acetone or dichloromethane a dinuclear eta(6)-arene Rh(II) complex (5) was obtained in the absence of added redox reagents. Moreover, when acetonitrile was added to a solution of either the Rh(II) or Rh(III) complexes, a new solvent-stabilized, noncyclometalated Rh(I) complex (6) was obtained. In this report we describe the different complexes, which were fully characterized, and probe the processes behind the remarkable solvent effect observed.