Redox-Noninnocent Behavior of Tris(2-pyridylmethyl)amine Bound to a Lewis Acidic Rh(III) Ion Induced by C–H Deprotonation

Rh­(III) complexes having tris­(2-pyridylmethyl)­amine (TPA) and its derivative as tetradentate ligands showed reversible deprotonation at a methylene moiety of the TPA ligands upon addition of a strong base as confirmed by spectroscopic measurements and X-ray crystallography. Deprotonation selectively occurred at the axial methylene moiety rather than equatorial counterparts because of the thermodynamic stability of corresponding deprotonated complexes. One-electron oxidation of the deprotonated Rh­(III)–TPA complex afforded a unique TPA radical bound to the Rh­(III) center by a ligand-centered oxidation. This is the first example to demonstrate emergence of the redox-noninnocent character of the TPA ligand.

以三(2-吡啶甲基)胺（TPA）及其衍生物作为四齿配体的铑(III)配合物，在加入强碱后可于TPA配体的亚甲基位点发生可逆去质子化，该过程经光谱测量与X射线晶体学验证。由于对应去质子化配合物的热力学稳定性优势，去质子化选择性发生于轴向亚甲基位点，而非平位位点。对去质子化的铑(III)-TPA配合物进行单电子氧化，可得到一类经配体中心氧化后与铑(III)中心结合的独特TPA自由基配合物。这是首例证实TPA配体具备氧化还原非无辜（redox-noninnocent）特性的研究案例。