1384182-24-4Relevant articles and documents
Mononuclear Iron(II) Dicarbonyls Derived from NNS Ligands - Structural Models Related to a Pre-Acyl Active Site of Mono-Iron (Hmd) Hydrogenase
Muthiah, Keren A. Thomas,Durgaprasad, Gummadi,Xie, Zhu-Lin,Williams, Owen M.,Joseph, Christopher,Lynch, Vincent M.,Rose, Michael J.
, p. 1675 - 1691 (2015)
We report the syntheses and characterization of dicarbonyliron complexes derived from tridentate, ortho-substituted Schiff base pyridine/thioether ligands (RNNS). Metalation reactions of RNNS (R = CH3, OCH3) at low temperature (-78 °C) with [Fe(CO)4(Br)2] afforded the desired complexes [(RNNS)Fe(CO)2Br]Br (2-COBr, 3-COBr). Reactions under similar conditions with more sterically demanding ligands [R = quinoline (Q), ClPh] afforded complex salts of the form [(RNNS)Fe(CO)2Br][Fe(CO)3(Br)3] (4-COFe and 5-COFe, respectively). Alternatively, the metalation of the RNNS ligands (for all R ≠ H) with [Fe(CO)4(Br)2] in Et2O at room temperature reliably affords the complex species of type [(RNNS)Fe(CO)2Br][Fe(CO)3(Br)3] (2-COFe, 3-COFe, 5-COFe). The metalation reactions of RNNS at only moderately low temperatures (-20 to 0 °C) result in the loss of CO to form the corresponding trigonal-bipyramidal iron(II) dibromide species of type [(RNNS)FeBr2] (2-Br, 4-Br, 5-Br; μeff ≈ 5.3 μB, S = 2). The IR spectrum of each dicarbonyl cation exhibits two ν(CO) stretches at ν ≈ 2070 and 2030 cm-1. Low-temperature 1H NMR spectroscopy measurements of 2-CO to 5-CO in CD3CN (-35 to 5 °C) revealed sharp resonances in the diamagnetic region. Under dark conditions, each dicarbonyl species is relatively stable (Me≈Q>ClPh). An examination of the structural parameters reveals that higher photostabilities correlate with shorter Fe-C(O) bond lengths, which are induced by variation of the ortho substituent of the pyridine ring. DFT calculations along the putative photolysis pathway revealed that the bulky ligand substituent (in 5-CO) destabilizes the monocarbonyl intermediate, and this is a likely explanation for its more rapid rate of CO photodissociation. Relevance to a possible apo-active site of mono-iron hydrogenase (pre-acyl formation) is discussed.
