Synthesis and hydrogenation of bis(imino)pyridine iron imides

Treatment of the iron bis(dinitrogen) complex, (^iPrPDI)Fe(N₂)₂ (^iPrPDI = (2,6-ⁱPr₂C₆H₃N=CMe)₂C₅H₃N), with a series of aryl azides resulted in loss of 3 equiv of N₂ and formation of the corresponding four-coordinate iron imide compounds, (^iPrPDI)Fe(NAr). These complexes, two of which (Ar = 2,6-ⁱPr₂-C₆H₃ and 2,4,6-Me₃-C₆H₂) have been characterized by X-ray diffraction, are significantly distorted from planarity. The metrical parameters in combination with Mössbauer spectroscopic and SQUID magnetic data suggest an intermediate spin iron(III) center antiferromagnetically coupled to a ligand-centered radical. Nitrene group transfer has been accomplished by addition of 1 atm of CO, yielding aryl isocyanates, ArNCO, and (^iPrPDI)Fe(CO)₂. Hydrogenation of the more sterically hindered members of the series furnished free aniline and the previously reported iron dihydrogen complex. Catalytic aryl azide hydrogenation has also been achieved, and the observed relative rates are consistent with N-H bond formation as the rate-determining step in aniline formation.