Reactions of a cyanosilane with an iron(II) centre. Synthesis and crystal structure of the isocyanotriphenylborate complex trans-[FeH(CNBPh3)(Ph2PCH2CH2PPh2)2] and anodic deprotonation of the hydrogen isocyanide (CNH) analogue

Abstract

Treatment of a thf solution of trans-[FeH(Cl)(dppe)2] (dppe = Ph2PCH2CH2PPh2) with NCSiMe3, in the presence of Na[BPh4], formed trans-[FeH(CNBPh3)(dppe)2] 1 whose crystal structure was determined, whereas the use of Tl[BF4] in an acidic medium, instead of Na[BPh4], yielded trans-[FeH(CNH)(dppe)2][BF4] 2. Complex 1 is also formed by BPh3 addition to trans-[FeH(CN)(dppe)2] 3 which can be obtained by reaction of trans-[FeH(Cl)(dppe)2] with [NBu4]CN in the presence of Tl[BF4]. Complexes 1 and 3 undergo single-electron reversible oxidations upon cyclic voltammetry in an aprotic medium, and the electrochemical PL ligand parameter was estimated (–0.51 V) for the CNBPh3– ligand. Complex 2 undergoes anodically induced deprotonation to form the cyano-complex 3+ following a mechanism that has been established by digital simulation of cyclic voltammetry and allowed an estimate of the rate and acid/base equilibrium constants for the CNH/CN– interconversion in the 2/3 and 2+/3+ pairs, showing that the oxidation of 2 leads to enhancements of its acidity constant and of the rate of proton loss by factors of ca. 1.5 × 107 and 500, respectively.