| Abstract
| - Meridional iridium(III) and facial rhodium(III) complexes are prepared stereoselectively via intramolecular C−H bond activation of our flexible PN ligand. The different coordination pattern of the ligand to the metal center causes the different reactivity of the complexes in the phosphine ligand exchange reactions.
- Reactions of [IrCl(coe)2]2 (coe = cyclooctene) with 1 equiv of the PN ligand (PN = o-Ph2PC6H4CH2OCH2C5H4N-2) in the presence of several phosphines or pyridine (1 equiv) at room temperature affordeda neutral iridium(III) hydride complex, (PCN-κ3P,C,N)Ir(H)(Cl)(L) (PCN = Ph2PC6H4CHOCH2C5H4N)[L = PPh3 (1a), PCy3 (1b), PBu3 (1c), PMePh2 (1d), Py (1e)] in good isolated yield. The PCN ligand iscoordinated in a meridional manner, which was confirmed by spectral analyses and X-ray analysis of 1a.The related rhodium(III) hydride complex (PCN-κ3P,C,N)Rh(H)(Cl)(L) (PCN = Ph2PC6H4CHOCH2C5H4N)[L = PPh3 (4a), PCy3 (4b)] was also prepared from the reactions of [RhCl(coe)2]2 with 1 equiv of the PNligand in the presence of 1 equiv of PPh3 or PCy3. The structure of 4a and 4b was determined by spectralanalyses and X-ray analysis of 4a. In contrast to the iridium complexes, the PCN ligand in the rhodium(III) complexes coordinated to the metal center in a facial manner. A ligand exchange reaction of thePPh3 iridium(III) complex 1a with PCy3 did not proceed well (20% conversion), while a similar reactionof the PPh3 rhodium(III) complex 4a with PCy3 afforded the PCy3 complex 4b quantitatively. We examinedthe ligand exchange reactions of the iridium(III) and rhodium(III) complexes with various phosphines toexplain the different reactivities. Using Tolman's parameter, we demonstrated that the ligand exchangereaction in the iridium(III) complexes bearing the meridional-coordinated PCN ligand is controlled bythe steric factor of the phosphines and the ligand exchange reaction in the rhodium(III) complexes bearingthe facial-coordinated PCN ligand is controlled by their electronic factors. The meridional coordinationof the PCN ligand makes the environment around the iridium center sensitive to the steric nature due tothe steric repulsion between the diphenyl group in the PCN ligand and the phosphines. The facialcoordination of the PCN ligand decreases their repulsion, and reactivity of the metal center depends onthe basicity of the phosphines.
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