Mononuclear and dinuclear complexes of rhodium and iridium: pyrazole complexes and pyrazolyl bridged dimers




Bailey, James Arthur

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A series of mononuclear complexes of general formula [M(η5-C5Me5)Cl3-n(pzH)n](n-1)+ (n = 1,2) has been prepared as a result of an investigation of the reactivity of pyrazole with rhodium and iridium cyclopentadienyl and pentamethyl-cyclopentadienyl precursors. These complexes are discussed in terms of the dynamic processes that are exhibited in the 1H NMR experiment and in terms of their use as precursors to dimeric species. Dinuclear complexes of formula [M(η5-C5R5)Cl(μ-pz)]2 containing pyrazolyl bridges have been prepared from the mononuclear compounds and from the chloro-bridged dimers of formula [M(η5-C5R5)Cl2]2 by treatment with triethylamine, but not from the dipyrazole iridium cation [Ir(η5-C5Me5)Cl(pzH)2]+ 26 which has been found to be unreactive to this type of symmetrical dimer formation: the low reactivity is attributed to a relative non-lability of the pyrazole groups. The dimeric complexes have been shown to undergo a core conformational change upon chemical reduction or halide abstraction. The chair conformation of the pyrazolyl bridged complex [Rh(η5-C5ME5)Cl(μ-pz)]2 38 has been proven crystallographically. Chloride abstraction from 38 yields the binuclear product [(Rh(η5-C5ME5)(μ-pz))2(μ-Cl)]BF4 46 which is bridged by two pyrazolyl and one chloride ligand and has been structurally characterized by X-ray diffraction to contain a boat conformation for the pyrazolyl framework. Reduction of either 38 or the C5H5 analogue 40 results in the metal-metal bonded dinuclear complexes [Rh(η5-C5ME5)(μ-pz)]2 48 and 49. The C5H5 complex 49 has been crystallographically determined to possess the boat conformation. The reactivity of the metal-metal bonded products has been investigated: one and two fragment addition is discussed and a number of oxidative addition products have been structurally characterized. The mononuclear dipyrazole iridium cation 26 which contains non-labile pyrazole groups is utilized to prepare mixed-metal and mixed-oxidation state dimers with the formula [Ir(η5-C5Me5)Cl(μ-pz)MLn]. The synthesis and potential for further investigation of these complexes is discussed.



Pyrazoles, Rhodium, Iridium, Transition metal compounds