Paramagnetic bis(amidinate) iron(II) complexes and their diamagnetic dicarbonyl derivatives

Reactions of two equivalents of the lithium amidinate salts Li[tBuC(NR)2] (R = iPr, cyclohexyl) with FeCl2 have been found to yield paramagnetic bis(amidinate) iron(II) compounds of the type [tBuC(NR)2]2Fe. In the case of R = cyclohexyl, the product has been characterized by single-crystal X-ray diffraction analysis as having a distorted tetrahedral geometry. The derivative with R = iPr is an oil, but its 1H and 13C NMR spectra indicate a similar monomeric structure. Both species have been found to react readily with CO to give the new diamagnetic FeII dicarbonyls [tBuC(NR)2]2Fe(CO)2. The compound with R = iPr has been structurally characterized, which showed it to have a strongly distorted octahedral structure with the carbonyls in a cis arrangement.