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.

一种由相应的双(二氮)铁络合物(iPrPDI)Fe(N2)2合成的双(咪唑)吡啶铁中性配体衍生物系列，即(iPrPDI)FeLn（iPrPDI代表2,6-（2,6-异丙基-苯并咪唑基）-1,3-二氮杂茂基）2-苯并咪唑基，具有独特的化学性质。当L为强场配体，如叔丁基氮碳或螯合烷基二膦，如DEPE（DEPE代表1,2-双(二乙基膦基)乙烷）时，将形成五配位、抗磁性的化合物，且无光谱证据表明顺磁态的混合。将中性供体的场强降低至主要为σ型配体，如叔丁胺或THT（THT代表四氢噻吩）时，亦能获得抗磁性化合物。然而，平面双(咪唑)吡啶氢的1H NMR化学位移表现出较大的化学位移分散性，这表明了与温度无关的顺磁特性（TIP），该特性源于S = 1激发态通过自旋-轨道耦合的混合。X射线衍射的计量数据确立了双(咪唑)吡啶螯合物的还原对于每种结构类型的有效性，而穆斯堡尔参数和NMR光谱数据则区分了铁的自旋状态，并识别了来自顺磁激发态的贡献。