Reactivity of Iron Complexes binding with a Tris(thiolato)phosphine Ligand

Abstract

Two mononuclear non-heme FeIII complexes supported by a tris(benzenethiolato)phosphine derivative [FeIII(PS3”)(OCH3)]- (the anion of 1) and [FeIII(PS3”)(Cl)]- (the anion of 2) have been synthesized and characterized The FeIII centers adopt trigonal-bipyramidal geometry with a methoxide or a chloride binding in the axial position The bound methoxide in FeIII-OCH3 complex is labile and can be replaced by a CH3CN molecule The forming FeIII-CH3CN species can be further reduced by cobaltocene quantitatively to a stable FeII-CH3CN complex [Fe(PS3”)(CH3CN)]- that was synthesized and characterized previously in our laboratory The axial ligand bound chloride in 2 is relatively inert and stays ligated in donor solvents One electron oxidation of [FeIII(PS3”)(Cl)]- (the anion of 2) by ferrocenium gave a FeIV analogue [FeIV(PS3”)(Cl)] Importantly FeIII-OCH3 moiety in complex 1 acts as a strong nucleophile that activates the C-Cl bond in CH2Cl2 leading to the formation of FeIII-Cl complex (2) quantitatively The nucleophilic reactions of complex 1 with other electrophiles benzyl chloride and benzyl bromide were also evidenced The chemistry shows that a FeIII bound base in a sulfur-rich ligation environment can have strong nucleophilicity and perform a nucleophilic reaction While the pathway of nitrile hydratase has not been clearly determined our example reported here provides a conjecture that the activation of nitrile could be through a nucleophilic attack of a FeIII bound hydroxide in the enzyme In addition complex 1 might undergo hydrogen atom abstraction in substract such as xanthene flourene and DHA More interestingly the complex 1 in DMF reacts with H2O to evolve dihydrogen Overall the work demonstrates that a FeIII center binding with a tetradentae tris(thiolato)phosphine ligand provides a versatile reactivity in the axial site of trigonal bipyramidal geometry The reactivity described at this work is summarized in the following scheme

Date of Award	2016 Apr 6
Original language	English
Supervisor	Hua-Fen Hsu (Supervisor)