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（tris(2-pyridylmethyl)amine，TPA）及其衍生物作为四齿配体的铑(III)配合物，在加入强碱后可发生可逆去质子化反应，反应位点为TPA配体的亚甲基部分，该结论已通过光谱测量与X射线晶体学实验验证。由于对应去质子化产物配合物具备热力学稳定性，去质子化选择性地发生于轴向亚甲基位点，而非赤道面的对应位点。对去质子化的铑(III)-TPA配合物进行单电子氧化，可得到一种独特的TPA自由基配合物，该自由基通过配体中心氧化过程与铑(III)中心结合。本研究首次证实了TPA配体具有氧化还原非无辜（redox-noninnocent）的特性。