Studies on the Condensation Pathway to and Properties of Diiron Azadithiolate Carbonyls

Reaction of Fe2(SH)2(CO)6 and HCHO, which gives Fe2[(SCH2)2NH](CO)6 in the presence of NH3,
affords the possible intermediate Fe2(SCH2OH)2(CO)6, which has been characterized crystallographically
as its axial−equatorial isomer. Fe2(SCH2OH)2(CO)6 was shown to react with ammonia and amines to
give Fe2[(SCH2)2NR](CO)6 (R = H, alkyl). Related hemithioacetal intermediates were generated by
treatment of Fe2(SH)2(CO)6 with RC(O)C(O)R (R = H, Ph, 4-F-C6H4) to give cycloadducts. The benzil
derivative Fe2[S2C2(OH)2Ph2](CO)6, a C2-symmetric species, was also characterized crystallographically.
The acylated azadithiolate Fe2[(SCH2)2NAc](CO)6 was prepared by reaction of Li2Fe2S2(CO)6 with
(ClCH2)2NC(O)Me. DNMR experiments show that the free energies of activation for rotation of the
amide bond are the same for Fe2[(SCH2)2NAc](CO)6 and Fe2[(SCH2)2NAc](CO)4(PMe3)2, which implies
that the ligands on the iron centers do not strongly affect the basicity of the nitrogen. As a control, we
showed that the thioamide Fe2[(SCH2)2NC(S)Me](CO)6 does exhibit a significantly higher barrier to
rotation, attributable to the increased double-bond character of the N−C(S) bond.