Substitution reactions of diiron dithiolate complexes with phosphine or isocyanide ligands

A series of diiron dithiolate complexes bearing phosphine or isocyanide ligands, as the active site models of [FeFe]H2ases, has been prepared by carbonyl substitution and structurally characterized. While complexes [(μ-EDT)Fe2(CO)5L1] (EDT = SCH2CH2S, L1 = PPh3, 3; Ph2PCH2PPh2, 4; tBuNC, 5) were prepared by reactions of (μ-EDT)Fe2(CO)6 (1) with PPh3, Ph2PCH2PPh2 (dppm), or tBuNC in the presence of Me3NO·2H2O in MeCN in 52–82% yields, complex (μ-EDT)Fe2(CO)4(tBuNC)2 (6) was produced by reaction of 1 with 2 equivalents of tBuNC in CH2Cl2 in 42% yield. Treatment of 1 or (μ-PDT)Fe2(CO)6 (PDT = SCH2CH2CH2S) (2) with Me3NO·2H2O followed by addition of 4-PyN(PPh2)2 (Py = C5H4N) gave unexpected products (μ-EDT)Fe2(CO)5[Ph2PP(O)Ph2] (7), (μ-EDT)Fe2(CO)5(Ph2PNHPy-4) (8), (μ-PDT)Fe2(CO)5[Ph2PP(O)Ph2] (9), and (μ-PDT)Fe2(CO)5(Ph2PNHPy-4) (10) in 20–38% yields, respectively. In addition, the asymmetrically disubstituted complex (μ-EDT)Fe2(CO)4(Ph2PCH2CH2PPh2) (11) was obtained by reaction of 1 with Ph2PCH2CH2PPh2 (dppe) in refluxing xylene in 31% yield, whereas reaction of 2 with 1,1′-bis(diphenylphosphino)ferrocene (dppf) in refluxing xylene afforded the symmetrically disubstituted complex (μ-PDT)Fe2(CO)4[(η5-Ph2PC5H4)2Fe] (12) in 28% yield. The complexes 3–9, 11, and 12 were characterized by elemental analysis, IR, and NMR spectroscopy, as well as for 3–7, 9, 11, and 12 by X-ray crystallography.