Neutral-Ligand Complexes of Bis(imino)pyridine Iron: Synthesis, Structure, and Spectroscopy

A family of bis(imino)pyridine iron neutral-ligand derivatives, (iPrPDI)FeLn (iPrPDI = 2,6-(2,6-iPr2−C6H3NCMe)2C6H3N),
has been synthesized from the corresponding bis(dinitrogen) complex, (iPrPDI)Fe(N2)2. When L is a strong-field
ligand such as  tBuNC or a chelating alkyl diphosphine such as DEPE (DEPE = 1,2-bis(diethylphosphino)ethane),
a five-coordinate, diamagnetic compound results with no spectroscopic evidence for mixing of paramagnetic states.
Reducing the field strength of the neutral donor to principally σ-type ligands such as tBuNH2 or THT (THT =
tetrahydrothiophene) also yielded diamagnetic compounds. However, the 1H NMR chemical shifts of the in-plane
bis(imino)pyridine hydrogens exhibit a large chemical shift dispersion indicative of temperature-independent
paramagnetism (TIP) arising from mixing of an S = 1 excited state via spin−orbit coupling. Metrical data from
X-ray diffraction establish bis(imino)pyridine chelate reduction for each structural type, while Mössbauer parameters
and NMR spectroscopic data differentiate the spin states of the iron and identify contributions from paramagnetic
excited states.

一类由相应的双(氮气)配合物（(iPrPDI)Fe(N2)2）合成的双(亚胺)吡啶铁中性配体衍生物（iPrPDI = 2,6-[(2,6-异丙基-1,3-二氮杂茂-2-基)甲基]苯并[1,2-b]吡啶），在合成过程中，当配体L为强场配体，如叔丁基氨基（tBuNC）或螯合烷基二膦（如DEPE，DEPE = 1,2-双(二乙基膦基)乙烷）时，会产生五配位、抗磁性化合物，且光谱学上无顺磁性状态的混合证据。降低中性供体场的强度至主要σ型配体，如叔丁胺（tBuNH2）或四氢噻吩（THT），亦能得到抗磁性化合物。然而，平面内双(亚胺)吡啶氢的1H NMR化学位移表现出显著的化学位移分散性，这表明了与温度无关的顺磁性（TIP）的存在，该顺磁性由S = 1激发态通过自旋-轨道耦合混合而产生。X射线衍射的计量数据确立了每种结构类型的双(亚胺)吡啶螯合物的还原，而莫塞鲍尔参数和NMR光谱数据则区分了铁的自旋状态，并识别了顺磁性激发态的贡献。