Phosphane and phosphite unsymmetrically disubstituted diiron complexes related to the Fe-only hydrogenase active site

• A series of unsymmetrically disubstituted diiron complexes [(mu-pdt){Fe(CO)(2)L-1]{Fe(CO)(2)L-2}] [pdt = 1,3-propanedithiolato; L-1 = PMe3, L-2 = PMe2Ph, 4; PPh3, 5; PCy3, 6; P(OEt)(3), 7; L-1= PMe2Ph, L-2 = PPh3, 8; P(OEt)(3), 9; L-1 = P(OEt)(3), L-2 = PPh3, 10; PCy3, 11] and [(mu-edt){Fe(CO)(2)PMe3)}{Fe(CO)(2)PPh3}] (edt = 1, 2-ethane dithiolato, 12) were prepared by means of step-wise CO displacements of [(mu-pdt)Fe-2(CO)(6)] and [(mu-edt)-Fe-2(CO)(6)] by different tertiary phosphane and phosphite ligands. The interconversion of the irondithiacyclohexane ring and the rotation of the [Fe(CO)(2)PR3] subunit were studied using by variable-temperature P-31{H-1} NMR spectroscopy of 4, 6 and 12 in solution. The molecular structures of 4-6, 8-10 and 12 show that complexes 4-6, 8, 9 and 12 possess an apical/basal coordination mode and complex 10 has an apical/apical conformation. The X-ray analyses indicate that the PMe2Ph ligand in the apical position of the starting complex [(mu-pdt){Fe(CO)(3)}{FeCO2(PMe2Ph)}] rotates to the basal position on conversion to the products 8 and 9. Cyclic voltammograms of 4-11 were studied both under argon and CO. The influences of the phosphane and phosphite ligands on the redox properties of the unsymmetrically disubstituted diiron complexes are discussed. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Nyckelord

biomorganic chemistry

carbonyl displacement

diiron complexes

Fe-only hydrogenase

P ligands

iron hydrogenase

model complexes

electrochemical properties

coordination

exchange

ligands

evolution

analogs

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