Synthesis\nof [Fe<sub>2</sub>[(μ-SeCH<sub>2</sub>)<sub>2</sub>NH](CN)<sub>2</sub>(CO)<sub>4</sub>]<sup>2–</sup> and Related Iron Selenoates

The dianion [Fe<sub>2</sub>[(μ-SeCH<sub>2</sub>)<sub>2</sub>NH](CN)<sub>2</sub>(CO)<sub>4</sub>]<sup>2–</sup> ([<b>2</b>]<sup>2–</sup>) is of interest for the preparation\nof the selenide analog of the active site of the [FeFe]-hydrogenases.\nThe obvious route for its synthesis by cyanation of Fe<sub>2</sub>[(μ-SeCH<sub>2</sub>)<sub>2</sub>NH](CO)<sub>6</sub> (<b>3</b>) fails for reasons that this paper explains and resolves.\nWe show that CN<sup>–</sup> cleaves Se–C bonds in <b>3</b>. For example, treatment of Fe<sub>2</sub>[(μ-SeCH<sub>2</sub>)<sub>2</sub>NH](CO)<sub>6</sub> with NEt<sub>4</sub>CN followed\nby CH<sub>3</sub>I gives substantial amounts of Fe<sub>2</sub>(μ-SeCH<sub>3</sub>)<sub>2</sub>(CO)<sub>6</sub>. Authentic [<b>2</b>]<sup>2–</sup> can be obtained by cyanation of Fe<sub>2</sub>[(μ-SeCH<sub>2</sub>)<sub>2</sub>NH](CO)<sub>5</sub>(pyridine). The <sup>77</sup>Se NMR data for [<b>2</b>]<sup>2–</sup> and <b>3</b> are reevaluated and explained. Attempts to prepare Fe<sub>2</sub>[(μ-SeCH<sub>2</sub>)<sub>2</sub>NH](PPh<sub>3</sub>)<sub>2</sub>(CO)<sub>4</sub> (<b>9</b>) by Me<sub>3</sub>NO-induced decarbonylation\nof <b>3</b> also suffers from degradation of the organoselenium\nligand. Complex <b>9</b> was prepared instead by photosubstitution.\nThe protonation of [<b>2</b>]<sup>2–</sup> and [Fe<sub>2</sub>[(μ-SCH<sub>2</sub>)<sub>2</sub>NH](CN)<sub>2</sub>(CO)<sub>4</sub>]<sup>2–</sup> are compared: the selenium compounds\nare more basic. The structure of [HFe<sub>2</sub>[(μ-SCH<sub>2</sub>)<sub>2</sub>NH](CN)<sub>2</sub>(CO)<sub>4</sub>]<sup>−</sup> was determined crystallographically.