Synthetic Designs and Structural Investigations of Biomimetic Ni-Fe Thiolates

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 ) â' and Ni(NS 3 ) â' (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 (PCHâ•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 , [(PCHâ•N An )Ni(μ-pdt)(Cl)Fe(dppbz)(CO)]BF 4 , [(PCH 2 NH An )Ni(μ-pdt)(Cl)Fe(dppbz)(CO)]BF 4 , [(PCHâ•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