Synthetic Designs and Structural Investigations of Biomimetic Ni-Fe Thiolates.

Described are the syntheses of several Ni(μ-SR)Fe complexes, including hydride derivatives, in a search for improved models for the active site of [NiFe]-hydrogenases. The nickel(II) precursors include (i) nickel with tripodal ligands: Ni(PS) and Ni(NS) (PS = tris(phenyl-2-thiolato)phosphine, NS = tris(benzyl-2-thiolato)amine), (ii) traditional diphosphine-dithiolates, including chiral diphosphine R,R-DIPAMP, (iii) cationic Ni(phosphine-imine/amine) complexes, and (iv) organonickel precursors Ni( o-tolyl)Cl(tmeda) and Ni(CF). The following new nickel precursor complexes were characterized: PPh[Ni(NS)] and the dimeric imino/amino-phosphine complexes [NiCl(PCH═N)] and [NiCl(PCHNH)] (P = PhPCH-2-). The iron(II) reagents include [CpFe(CO)(thf)]BF, [Cp*Fe(CO)(MeCN)]BF, FeI(CO), FeCl(diphos)(CO), and Fe(pdt)(CO)(diphos) (diphos = chelating diphosphines). Reactions of the nickel and iron complexes gave the following new Ni-Fe compounds: Cp*Fe(CO)Ni(NS), [Cp(CO)Fe(μ-pdt)Ni(dppbz)]BF, [( R,R-DIPAMP)Ni(μ-pdt)(H)Fe(CO)]BAr, [(PCH═N)Ni(μ-pdt)(Cl)Fe(dppbz)(CO)]BF, [(PCHNH)Ni(μ-pdt)(Cl)Fe(dppbz)(CO)]BF, [(PCH═N)Ni(μ-pdt)(H)Fe(dppbz)(CO)]BF, [(dppv)(CO)Fe(μ-pdt)]Ni, {H[(dppv)(CO)Fe(μ-pdt)]Ni]}BF, and (CF)Ni(μ-pdt)Fe(CO)(dppv) (DIPAMP = (CHP(CH-2-OMe)); BAr = [B(CH-3,5-(CF)])) Within the context of Ni-(SR)-Fe complexes, these new complexes feature new microenvironments for the nickel center: tetrahedral Ni, chirality, imine, and amine coligands, and Ni-C bonds. In the case of {H[(dppv)(CO)Fe(μ-pdt)]Ni}, four low-energy isomers are separated by ≤3 kcal/mol, one of which features a biomimetic HNi(SR) site, as supported by density functional theory calculations.