Synthesis of [Fe2[(μ-SeCH2)2NH](CN)2(CO)4]2- and Related Iron Selenoates.

The dianion [Fe2[(μ-SeCH2)2NH](CN)2(CO)4]2- ([2]2-) is of interest for the preparation of the selenide analog of the active site of the [FeFe]-hydrogenases. The obvious route for its synthesis by cyanation of Fe2[(μ-SeCH2)2NH](CO)6 (3) fails for reasons that this paper explains and resolves. We show that CN- cleaves Se-C bonds in 3. For example, treatment of Fe2[(μ-SeCH2)2NH](CO)6 with NEt4CN followed by CH3I gives substantial amounts of Fe2(μ-SeCH3)2(CO)6. Authentic [2]2- can be obtained by cyanation of Fe2[(μ-SeCH2)2NH](CO)5(pyridine). The 77Se NMR data for [2]2- and 3 are reevaluated and explained. Attempts to prepare Fe2[(μ-SeCH2)2NH](PPh3)2(CO)4 (9) by Me3NO-induced decarbonylation of 3 also suffers from degradation of the organoselenium ligand. Complex 9 was prepared instead by photosubstitution. The protonation of [2]2- and [Fe2[(μ-SCH2)2NH](CN)2(CO)4]2- are compared: the selenium compounds are more basic. The structure of [HFe2[(μ-SCH2)2NH](CN)2(CO)4]- was determined crystallographically.