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

Reaction of Fe(2)(SH)(2)(CO)(6) and HCHO, which gives Fe(2)(SCH(2))(2)NH(6) in the presence of NH(3), affords the possible intermediate Fe(2)(SCH(2)OH)(2)(CO)(6), which has been characterized crystallographically as its axial-equatorial isomer. Fe(2)(SCH(2)OH)(2)(CO)(6) was shown to react with ammonia and amines to give Fe(2)(SCH(2))(2)NR(6) (R = H, alkyl). Related hemithioacetal intermediates were generated by treatment of Fe(2)(SH)(2)(CO)(6) with RC(O)C(O)R (R = H, Ph, 4-F-C(6)H(4)) to give cycloadducts. The benzil derivative Fe(2)S(2)C(2)(OH)(2)Ph(2)(6), a C(2)-symmetric species, was also characterized crystallographically. The acylated azadithiolate Fe(2)(SCH(2))(2)NAc(6) was prepared by reaction of Li(2)Fe(2)S(2)(CO)(6) with (ClCH(2))(2)NC(O)Me. DNMR experiments show that the free energies of activation for rotation of the amide bond are the same for Fe(2)(SCH(2))(2)NAc(6) and Fe(2)(SCH(2))(2)NAc(4)(PMe(3))(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 Fe(2)(SCH(2))(2)NC(S)Me(6) does exhibit a significantly higher barrier to rotation, attributable to the increased double-bond character of the N-C(S) bond.