Design of Boron-Decorated Bimetallic Iron Complexes Related to the Active Site of [FeFe]-Hydrogenases and Reactivity with Hydride Donors

Abstract

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 diiron complex functionalized with a Lewis acidic borane which has been characterized by spectroscopic measurements (NMR, 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 this last case, the phosphane ligand is trapped by the boron atom. The reactivity of the diiron complexes functionalized by a Lewis acid group -B(C6F5)2 has been investigated with 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.