C-H and C-N Activation at Redox-Active Pyridine Complexes of Iron.

Pyridine activation by inexpensive iron catalysts has great utility, but the steps through which iron species can break the strong (105-111 kcal mol-1 ) C-H bonds of pyridine substrates are unknown. In this work, we report the rapid room-temperature cleavage of C-H bonds in pyridine, 4-tert-butylpyridine, and 2-phenylpyridine by an iron(I) species, to give well-characterized iron(II) products. In addition, 4-dimethylaminopyridine (DMAP) undergoes room-temperature C-N bond cleavage, which forms a dimethylamidoiron(II) complex and a pyridyl-bridged tetrairon(II) square. These facile bond-cleaving reactions are proposed to occur through intermediates having a two-electron reduced pyridine that bridges two iron centers. Thus, the redox non-innocence of the pyridine can play a key role in enabling high regioselectivity for difficult reactions.