Dialkylboryl-Substituted Cyclic Disilenes Synthesized by Desilylation-Borylation of Trimethylsilyl-Substituted Disilenes.

π-Electron systems of silicon have attracted attention because of their narrow HOMO-LUMO gap and high reactivity, but the structural diversity remains limited. Herein, new dialkylboryl-substituted disilenes were synthesized by the selective desilylation-borylation of the corresponding trimethylsilyl-substituted disilenes. The dialkylboryl-substituted disilenes were fully characterized by a combination of NMR spectroscopy, MS spectrometry, single-crystal X-ray diffraction analysis, and theoretical calculations. The longest-wavelength absorption bands of boryldisilenes were bathochromically shifted compared to the corresponding silyl-substituted disilenes, indicating a substantial conjugation between π(Si=Si) and vacant 2p(B) orbitals. In the presence of 4-(dimethylamino)pyridine (DMAP), the dialkylboryl groups in the boryl-substituted disilenes were easily converted to trimethylsilyl groups, suggesting the dialkylboryl-substituted disilenes in the presence of a base serve as the surrogates of disilenyl anions (disilenides).

Tridentate thiolate ligands: application to the synthesis of the site-differentiated [4Fe-4S] cluster having a hydrosulfide ligand at the unique iron center.

We have designed new trithiols Temp(SH)(3) and Tefp(SH)(3) that can be synthesized conveniently in short steps and are useful for preparation of crystalline [3:1] site-differentiated [4Fe-4S] clusters suitable for X-ray structural analysis. The ethanethiolate clusters (PPh(4))(2)[Fe(4)S(4)(SEt)(TempS(3))] (4a) and (PPh(4))(2)[Fe(4)S(4)(SEt)(TefpS(3))] (4b) were prepared as precursors, and the unique iron sites were then selectively substituted. Upon reaction with H(2)S, (PPh(4))(2)[Fe(4)S(4)(SH)(TempS(3))] (6a) and (PPh(4))(2)[Fe(4)S(4)(SH)(TefpS(3))] (6b), which model the [4Fe-4S] cluster in the ß subunit of (R)-2-hydroxyisocaproyl-CoA dehydratase, were synthesized. Clusters 6a and 6b were further converted to the sulfido-bridged double cubanes (PPh(4))(4)[{Fe(4)S(4)(TempS(3))}(2)(µ(2)-S)] (7a) and (PPh(4))(4)[{Fe(4)S(4)(TefpS(3))}(2)(µ(2)-S)] (7b), respectively, via intermolecular condensation with the release of H(2)S. Conversely, addition of H(2)S to 7a,b afforded the hydrosulfide clusters 6a,b. The molecular structures of the clusters reported herein were elucidated by X-ray crystallographic analysis. Their redox properties were investigated by cyclic voltammetry.