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)n(CO)6-n] (n = 0, or n = 1, R = Me or n = 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.