New Reactions of Terminal Hydrides on a Diiron Dithiolate

Mechanisms for biological and bioinspired dihydrogen activation and production often invoke the intermediacy of diiron dithiolato dihydrides. The first example of such a Fe2(SR)2H2 species is provided by the complex [(term-H)(μ-H)Fe2(pdt)(CO)(dppv)2] ([H1H]0). Spectroscopic and computational studies indicate that [H1H]0 contains both a bridging hydride and a terminal hydride, which, notably, occupies a basal site. The synthesis begins with [(μ-H)Fe2(pdt)(CO)2(dppv)2]+ ([H1(CO)]+), which undergoes substitution to afford [(μ-H)Fe2(pdt)(CO)(NCMe)(dppv)2]+ ([H1(NCMe)]+). Upon treatment of [H1(NCMe)]+ with borohydride salts, the MeCN ligand is displaced to afford [H1H]0. DNMR (EXSY, SST) experiments on this complex show that the terminal and bridging hydride ligands interchange intramolecularly at a rate of 1 s–1 at −40 °C. The compound reacts with D2 to afford [D1D]0, but not mixed isotopomers such as [H1D]0. The dihydride undergoes oxidation with Fc+ under CO to give [1(CO)]+ and H2. Protonation in MeCN solution gives [H1(NCMe)]+ and H2. Carbonylation converts [H1H]0 into [1(CO)]0.