UBC Theses and Dissertations
Iron carbonyl complexes of the mixed ligands Chia, Lian Sai
A number of iron carbonyl complexes has been prepared from the mixed ligands F₄AsP and F₆AsP and the iron carbonyls Fe(CO)₅ , Fe₂(C0)₉ and Fe₃(C0)₁₂. They are isolated by chromatographic methods and characterized by spectroscopic techniques. These complexes, which can be classified into ten groups, are the only series of iron complexes of organo-bridged mixed ligands known so far. The complex (F₄AsP)₂Fe(CO)₃ is probably the first example of a L₂Fe(CO)₃ compound in which the two polydentate ligand molecules behave as mono-dentates and occupy the two trans positions of a trigonal bipyramidal structure. The isolation of P-bonded complexes F₄AsPFe(CO)₄, F₆AsPFe(CO)₄ and (F₄AsP)₂FeCO)₃ and the complete absence of the corresponding As-bonded complexes clearly illustrate that the PPh₂ group is a better coordinating group than the AsMe₂ⁿ group. The novel complexes LmLFe₂(CO)₅ (Lm = monodentate ligand), LbLFe₂(CO)₄ (Lb = bridging group) and Lc LFe₂(CO)₄ (Lc = chelating group) are derived from the very stable LFe₂(C0)₆ complexes (L = F₄AsP, F₆AsP). The structures of these are unusual in that they contain two types of ligand molecules, one acting as a tri-dentate group while the other acting as a mono-dentate group, a bridging group or a chelating group. It is interesting to note that the F₄AsP forms two complexes of the same molecular formula, namely, (F₄AsP)b F₄AsPFe₂(CO)₄ and (F₄AsP)c F₄AsPFe₂(CO)₄, which can be distinguished by infrared and Mossbauer data. Moreover, two additional complexes of the same molecular formula, (F₄AsP)b F₆AsPFe₂(CO)₄ and (F₆AsP)c F₄AsPFe₂(CO)₄ ՚ are obtained from F₄AsP and F₆AsP The method of preparation and the spectroscopic properties of the mixed ligands and their complexes are discussed. The factors which affect the formation of the iron carbonyl complexes are investigated and the possible reaction mechanisms for their formation are proposed.
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