Design of boron-decorated bimetallic iron complexes related to the active site of [FeFe]-hydrogenases and reactivity with hydride donors

The reactivity of the 1,2-dithiolene diiron complexes [Fe₂(µ-SCHC(Ph)S)(PR₃)_<i>n</i>(CO)_6-<i>n</i>] (<i>n</i> = 0, or <i>n</i> = 1, R = Me or <i>n</i> = 1, 2, R = Ph) with the reagent HB(C₆F₅)₂ is described. With the hexacarbonyl precursor, the reaction gives an anti-Markovnikov addition product [Fe₂(µ-SCH(B(C₆F₅)₂)-CH(Ph)S)(CO)₆]. This represents a rare example of a diiron complex functionalized with a Lewis acidic borane, which has been characterized by spectroscopic measurements (NMR and IR), while an adduct with MeCN has been crystallographically analyzed. Starting from the mono-PMe₃ complex, the hydroboration is complicated by the formation of different isomers, while no hydroboration is observed with PPh₃ derivatives. In the latter case, the phosphane ligand is trapped by the boron atom. The reactivity of the diiron complexes functionalized with a Lewis acid group, -B(C₆F₅)₂, has been investigated toward dihydrogen and the hydride donor species Na[HBEt₃]. With a second equivalent of HB(C₆F₅)₂, a tetra-iron assembly {[Fe₂(µ-SCH(BH(C₆F₅))-CH(Ph)S)(CO)₆]}₂ is formed selectively from [Fe₂(µ-SCH(B(C₆F₅)₂)-CH(Ph)S)(CO)₆] through a rearrangement of substituents around the boron atoms.