Synthesis, and Structural and Spectroscopic Analysis of Trielyl-Derived Complexes of Iron

Abstract

The reactivity of group 13 anions of the form [(NON)E]− (NON=4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethyl-xanthene, E=Al, Ga, In) towards Fe(CO)5 has been investigated. In the case of the aluminyl system, both reaction outcome and product structure are highly sensitive to the availability of the potassium counterion; sequestration by 18-crown-6 is necessary to yield a species featuring a direct, unsupported Al−Fe bond. 2.2.2-Cryptand, by contrast, yields a species featuring bridging carbonyl ligands, while the use of no sequestering agent at all leads to isocarbonyl bridging to aluminium. Owing to their lower oxophilicity, the heavier congeners gallium and indium more straightforwardly deliver Fe−E bonded adducts (E=Ga, In). The series of trielyl iron complexes has been interrogated by structural and computational analyses, as well as by IR and Mössbauer spectroscopies, revealing a consistent shift in bond polarity and electron richness at iron as group 13 is descended. This in turn is consistent with the diminishing donor strength of the trielyl ligand with increasing atomic number.