New acylhydrido- and diacylrhodium(III) organocomplexes derived from 8-quinolinecarbaldehyde and/or O-(diphenylphosphanyl)benzaldehyde

Article abstract of DOI:10.1002/ejic.201100904

The acylhydridorhodium(III) complex [RhHCl{PPh₂(o-C ₆H₄CO)}(py)₂] (1) reacts with 8-quinolinecarbaldehyde (C₉H₆NCHO) to afford mixed diacyl [RhCl(C₉H₆NCO){PPh₂(o-C₆H ₄CO)}(py)] (2) with acyl groups trans to chlorine and to pyridine. Complex 1 undergoes displacement of pyridine by 2-(aminomethyl)pyridine (ampy) or diphosphanes to give hydridoacyl neutral [RhHCl{PPh₂(o-C ₆H₄CO)}(LL)] [LL = ampy (3), bis(diphenylphosphanyl) methane (dppm, 5), 1,3-bis(diphenylphosphanyl)propane (dppp, 6), 1,2-bis(diphenylphosphanyl)ethane (dppe, 7)] with hydride trans to chloride. Complex 3 exchanges hydride with chloride to give [Rh(Cl)₂{PPh ₂(o-C₆H₄CO)}(ampy)] (4). The reaction of 2 with bidentate N-donor ligands yields cationic mixed diacyl [Rh(C₉H ₆NCO){PPh₂(o-C₆H₄CO)}(NN)] ⁺ species [NN = 2,2′-bipyridine (bipy, 8), ampy (9)]. Neutral or cationic diacyl complexes that contain two acylquinoline fragments can be obtained by the reaction of dimer [Rh(μ-Cl)(C₉H ₆NCO)₂]₂ (10) with pyridine to give [Rh(Cl)(C₉H₆NCO)₂(py)] (11) or with bidentate N- or P-donor ligands (LL) to afford [Rh(C₉H₆NCO) ₂(LL)]⁺ [LL = dppm (12), dppe (13), dppp (14), 1,4-bis(diphenylphosphanyl)butane (15), ampy (16), 8-aminoquinoline (17), biacetyldihydrazone (18), bipy (19)] with the acyl groups trans to LL. Complex 11 is highly fluxional in solution. At low temperatures, the acylquinoline chelate opens to allow an intramolecular exchange between 11a and 11b (δH^? = 10.1±a0.2 kcalamol^-1 and δS^? = 1.0±a0.1 calaK^-1amol ^-1), and pyridine dissociation occurs at room temperature. All the complexes were characterized spectroscopically. Single crystal X-ray diffraction analysis was performed on 2. Hydridoacylrhodium(III) (1) reacts with chelating ligands to afford new neutral acylhydrido complexes with hydride trans to chloride. The reaction with 8-quinolinecarbaldehyde affords a diacyl compound, which may give cationic diacyl derivatives with donor atoms trans to the acyl groups.