Bio-inspired iron complexes for shape-selective hydrocarbon oxidations

Abstract

Shape-selective hydrocarbon oxidation is highly important in many industrial processes particularly in petrochemical refining, but is very difficult to achieve under mild conditions. On the other hand, Nature often performs selective hydrocarbon oxidations under ambient conditions. Inspired by Nature we are interested in synthesizing complexes that can perform such shape-selective hydrocarbon oxidations and also identifying the responsible species that discriminates among substrates based on their shape. My work in particular involves modeling a class of iron enzymes, -ketoglutarate-dependent dioxygenases. -Ketoglutarate-dependent dioxygenases are a nonheme iron enzymes that perform oxygen activation under mild conditions and oxidizes hydrocarbons selectively. The best model complex reported so far involves an iron center supported by a tridentate ligand and an -ketocarboxylate, but no C-H bond oxidation (primary action of enzyme) has been observed. The intent of this research is to generate new model complexes of -ketoglutarate-dependent dioxygenases that can perform oxygen activation along with selective C-H bond oxidation. Iron complexes supported by the tridentate nitrogen donor Tp ligand (where Tp is hydrotris(pyrazolyl)borate) and various -ketocarboxylates are synthesized. Substituents on the pyrazolyl rings of the Tp are modified to generate iron complexes with different steric and electronic requirements. All of these complexes are studied for oxygen activation and their reactions with hydrocarbons are explored. It is observed that this class of complexes is very efficient in oxygen activation and can perform hydrocarbon oxidation. One of the complexes also exhibits shape-selectivity towards small, flat cyclic hydrocarbons. Oxygen activation at low temperatures is also performed to observe and characterize intermediates.