Rhodium (II) dibenzotetramethylaza[14]annulene dimer ([(tmtaa)Rh]2) reacts with carbon monoxide and hydrogen in toluene to form (tmtaa)Rh-H and (tmtaa)Rh-C(O)H at room temperature and low reagent gas pressures. The rhodium formyl complex was isolated and the molecular structure determined. Equilibrium constants at 298K were measured for reactions of the rhodium hydride with CO to make the formyl species ((tmtaa)Rh-C(O)H) in toluene (Ktol = 10.8 (1.0) x103) and pyridine (Kpy = 2.2(0.2) x 103). The reaction to make the formyl complex is proposed to occur though alternate radical and ionic pathways depending on the solvent medium. In toluene the metallo-radical ((tmtaa)RhII�) activates CO by electron donation to the p* of CO while in pyridine it is a metallo-anion ((tmtaa)RhI�) that acts as the s donor to CO. DFT calculations for CO complexes of (tmtaa)RhII� and (tmtaa)RhI� show bent CO units that are consistent with the proposed mechanism.

Reaction of [(tmtaa)Rh]<sub>2</sub> with CO and H<sub>2</sub> to form a rhodium formyl complex: Rhodium s donor activation of CO

248th National Meeting (2014)

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Reaction of [(tmtaa)Rh]2 with CO and H2 to form a rhodium formyl complex: Rhodium s donor activation of CO

Reaction of [(tmtaa)Rh]₂ with CO and H₂ to form a rhodium formyl complex: Rhodium s donor activation of CO