Abstract
Described are the syntheses of several Ni(μ-SR)(2)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(3))(-) and Ni(NS(3))(-) (PS(3)(3-) = tris(phenyl-2-thiolato)phosphine, NS(3)(3-) = 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(C(6)F(5))(2). The following new nickel precursor complexes were characterized: PPh(4)[Ni(NS(3))] and the dimeric imino/amino-phosphine complexes [NiCl(2)(PCH═N(An))](2) and [NiCl(2)(PCH(2)NH(An))](2) (P = Ph(2)PC(6)H(4)-2-). The iron(II) reagents include [CpFe(CO)(2)(thf)]BF(4), [Cp*Fe(CO)(MeCN)(2)]BF(4), FeI(2)(CO)(4), FeCl(2)(diphos)(CO)(2), and Fe(pdt)(CO)(2)(diphos) (diphos = chelating diphosphines). Reactions of the nickel and iron complexes gave the following new Ni-Fe compounds: Cp*Fe(CO)Ni(NS(3)), [Cp(CO)Fe(μ-pdt)Ni(dppbz)]BF(4), [( R,R-DIPAMP)Ni(μ-pdt)(H)Fe(CO)(3)]BAr(F)(4), [(PCH═N(An))Ni(μ-pdt)(Cl)Fe(dppbz)(CO)]BF(4), [(PCH(2)NH(An))Ni(μ-pdt)(Cl)Fe(dppbz)(CO)]BF(4), [(PCH═N(An))Ni(μ-pdt)(H)Fe(dppbz)(CO)]BF(4), [(dppv)(CO)Fe(μ-pdt)](2)Ni, {H[(dppv)(CO)Fe(μ-pdt)](2)Ni]}BF(4), and (C(6)F(5))(2)Ni(μ-pdt)Fe(CO)(2)(dppv) (DIPAMP = (CH(2)P(C(6)H(4)-2-OMe)(2))(2); BAr(F)(4)(-) = [B(C(6)H(3)-3,5-(CF(3))(2)](4)(-))) Within the context of Ni-(SR)(2)-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)](2)Ni}(+), four low-energy isomers are separated by ≤3 kcal/mol, one of which features a biomimetic HNi(SR)(4) site, as supported by density functional theory calculations.