Synthetic Designs and Structural Investigations of Biomimetic Ni-Fe Thiolates

摘要

Described are the syntheses of several Ni(mu-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(PS3)(-) and Ni(NS3)(-) (PS33- = tris(phenyl-2-thiolato)phosphine, NS33- = tris(benzy1-2-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(C6F5)(2). The following new nickel precursor complexes were characterized: PPh4[Ni(NS3)] and the dimeric imino/amino-phosphine complexes [NiCl2(PCH=N-An)](2) and [NiCl2(PCH2NHAn)](2) (P = Ph2PC6H4-2-). The iron(II) reagents include [CpFe(CO)(2)(thf)]BF4, [Cp*Fe(CO)(MeCN)(2)]BF4, FeI2(CO)(4), FeCl2(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(NS3), [Cp(CO)Fe(mu-pdt)Ni(dppbz)]BF4, [(R,R-DIPAMP)Ni(mu-pdt)(H)-Fe(CO)(3)]BAr4F, [(PCH=N-An)Ni(mu-pdt)(Cl)Fe(dppbz)(CO)]BF4, [(PCH2NHAn)Ni(mu-pdt)(Cl)Fe(dppbz)(CO)]BF4, [(PCH=N-An)Ni(mu-pdt)(H)Fe(dppbz)(CO)]BF4, [(dppv)(CO)Fe(mu-pdt)](2)Ni, {H[(dppv)(CO)Fe(mu-pdt)](2)Ni]BF4, and (C6F5)(2)Ni(mu-pdt)Fe(CO)(2)(dppv) (DIPAMP = (CH2P(C6H4-2-OMe)(2))(2); BAr4F- = [B(C6H3-3,5-(CF3)(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(mu-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.