Deprotonation and dehydrogenation of Di(2-pyridylmethyl)amine with M[N(SiMe3)2]2 (M = Mn, Fe, Co, Zn) and Fe(C6H2-2,4,6-Me3)2

The reaction of di(2-pyridylmethyl)amine with FeCl2 yields [Fe{HN(CH2Py)2}2]Cl2 (1) with the tridentate amines coordinating in a facial manner at the iron(II) center. Transamination of this amine with [M{N(SiMe3)2}2] in an equimolar ratio leads to the formation of heteroleptic [(Me3Si)2N-M{μ-N(CH2Py)2}]2 [M = Mn (2a), Fe (2b), and Zn (2c)]. The metallation of di(2-pyridylmethyl)amine with dimesityl iron(II) gives [Mes-Fe{μ-N(CH2Py)2}]2 (3). At temperatures below −30 °C the transamination reaction of [Fe{N(SiMe3)2}2] with di(2-pyridylmethyl)amine in a molar ratio of 1:2 yields [Fe{N(CH2Py)2}2] (4). The reaction of [Co{N(SiMe3)2}2] with HN(CH2Py)2 leads to the formation of [Co{N(CHPy)2}2] (5b) with 1,3-di(2-pyridyl)-2-azaallyl ligands, regardless of the employed stoichiometry. The compounds 2b, 2c, 3, and 4 have to be handled and manipulated at low temperatures because they degrade already at room temperature whereas the manganese(II) derivative 2a is stable under these conditions. The degradation products [M{N(CHPy)2}2] [M = Fe (5a), Zn (5c)] contain the 1,3-di(2-pyridyl)-2-azaallyl ligands and can be considered as the dehydrogenation products of [M{N(CH2Py)2}2]. A metathetical approach via the reaction of lithium di(2-pyridylmethyl)amide with FeCl2 did not give the desired product 4 but a mixture of 1 and 5a. A 1H NMR and EPR spectroscopic pursuit of the degradation of [(Me3Si)2N-Zn{μ-N(CH2Py)2}]2 (2c) in tetrahydrofuran at temperatures between 253 and 328 K showed diminishing amounts of 2c and the appearance of 1,3-di(2-pyridyl)-2-azaallyl anions whereas the EPR experiments clearly verify the presence of di(2-pyridylmethyl)aminyl radicals in solution.

The di(2-pyridylmethyl)amides show a rather unique redox chemistry in the vicinity of late transition metals. These ligands can be deprotonated at the methylene fragments, initiating the formation of 1,3-di(2-pyridyl)-2-azaallyl anions.Figure optionsDownload as PowerPoint slide