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

Treatment of a thf solution of trans-[FeH(Cl)(dppe)(2)] (dppe = Ph2PCH2CH2P Ph2) with N=CSiMe3, in the presence of Na[BPh4], formed trans-[FeH(CNBPh3)( dppe)(2)] 1 whose crystal structure was determined, whereas the use of Tl[B F4] 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)(dp pe)(2)] 3 which can be obtained by reaction of trans-[FeH(Cl)(dppe)(2)] wit h [NBu4]CN in the presence of Tl[BF4]. Complexes 1 and 3 undergo single-ele ctron reversible oxidations upon cyclic voltammetry in an aprotic medium, a nd the electrochemical P-L ligand parameter was estimated (-0.51 V) for the CNBPh3- ligand. Complex 2 undergoes anodically induced deprotonation to fo rm the cyano-complex 3(+) following a mechanism that has been established b y digital simulation of cyclic voltammetry and allowed an estimate of the r ate 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 enhan cements of its acidity constant and of the rate of proton loss by factors o f cn. 1.5 x 10(7) and 500, respectively.