New Reactions of Terminal Hydrides on a Diiron Dithiolate

Abstract

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 [(<i>term</i>-H)­(μ-H)­Fe₂(pdt)­(CO)­(dppv)₂] ([H<b>1</b>H]⁰). Spectroscopic and computational studies indicate that [H<b>1</b>H]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]⁺ ([H<b>1</b>(CO)]⁺), which undergoes substitution to afford [(μ-H)­Fe₂(pdt)­(CO)­(NCMe)­(dppv)₂]⁺ ([H<b>1</b>(NCMe)]⁺). Upon treatment of [H<b>1</b>(NCMe)]⁺ with borohydride salts, the MeCN ligand is displaced to afford [H<b>1</b>H]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 [D<b>1</b>D]⁰, but not mixed isotopomers such as [H<b>1</b>D]⁰. The dihydride undergoes oxidation with Fc⁺ under CO to give [<b>1</b>(CO)]⁺ and H₂. Protonation in MeCN solution gives [H<b>1</b>(NCMe)]⁺ and H₂. Carbonylation converts [H<b>1</b>H]⁰ into [<b>1</b>(CO)]⁰