Heterobimetallic Complexes of Rhodium Dibenzotetramethylaza[14]annulene [(tmtaa)Rh-M]: Formation, Structures, and Bond Dissociation Energetics

A rhodium­(II) dibenzotetramethylaza[14]­annulene dimer ([(tmtaa)­Rh]<sub>2</sub>) undergoes metathesis reactions with [CpCr­(CO)<sub>3</sub>]<sub>2</sub>, [CpMo­(CO)<sub>3</sub>]<sub>2</sub>, [CpFe­(CO)<sub>2</sub>]<sub>2</sub>, [Co­(CO)<sub>4</sub>]<sub>2</sub>, and [Mn­(CO)<sub>5</sub>]<sub>2</sub> to form (tmtaa)­Rh-M complexes (M = CrCp­(CO)<sub>3</sub>, MoCp­(CO)<sub>3</sub>, FeCp­(CO)<sub>2</sub>, Co­(CO)<sub>4</sub>, or Mn­(CO)<sub>5</sub>). Molecular structures were determined for (tmtaa)­Rh-FeCp­(CO)<sub>2</sub>, (tmtaa)­Rh-Co­(μ-CO)­(CO)<sub>3</sub>, and (tmtaa)­Rh-Mn­(CO)<sub>5</sub> by X-ray diffraction. Equilibrium constants measured for the metathesis reactions permit the estimation of several (tmtaa)­Rh-M bond dissociation enthalpies (RhCr = 19 kcal mol<sup>–1</sup>, RhMo = 25 kcal mol<sup>–1</sup>, and RhFe = 27 kcal mol<sup>–1</sup>). Reactivities of the bimetallic complexes with synthesis gas to form (tmtaa)­Rh-C­(O)H and M-H are surveyed.