Gallium(III) Tetraphenylporphyrinates Containing Hydrosulfide and Thiolate Ligands: Structural Models for Sulfur-Bound Iron(III) Hemes

Gallium­(III)
tetraphenylporphyrinates (TPP) containing anionic sulfur ligands have been
prepared and characterized in the solid state and solution. The complexes
serve as structural models for iron­(III) heme sites containing sulfur
coordination that otherwise prove challenging to synthesize due to
the propensity for reduction to iron­(II). The compounds prepared include
the first well-characterized example of a trivalent metalloporphyrinate containing a
terminal hydrosulfide ligand, [Ga­(SH)­(TPP)], as well as [Ga­(SEt)­(TPP)],
[Ga­(SPh)­(TPP)], and [Ga­(SSiiPr3)­(TPP)]. The stability of these compounds toward reduction has permitted
an investigation of their solid-state structures and electrochemistry.
The structural features and reaction chemistry of the complexes in
relation to their iron­(III) analogs is discussed.