Low-coordinate iron complexes based on bis(pyrazolyl)borate and their reactivity

Preparation routes for several sodium salts of diphenylbis(pyrazolyl)borates with bulky substituents are described, For a potential modelling of a-keto-acid-dependent nonheme iron enzymes, mononuclear iron compounds containing those bis(pyrazolyl)borates as ligands were synthesised and structurally characterised. The iron centres are four-coordinate (in one case only three-coordinate) thus offering room for the binding of exogenous ligands. However, reactivity studies with carboxylates and O-2 have revealed nonuniform behaviour, and the identification of a side product in one case, combined with subsequent ESI-MS studies, demonstrated that a pronounced sensitivity of the B-N bonds towards oxo nucleophiles could be a possible reason. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).