Application of stopped flow techniques and energy dispersive EXAFS for investigation of the reactions of transition metal complexes in solution: activation of nickel ?-diketonates to form homogeneous catalysts, electron transfer reactions involving iron(III) and oxidative addition to iridium(I)

B. Abdul Rahman, M. Basyaruddin, Bolton, Peter R., Evans, John, Dent, Andrew J., Harvey, Ian and Diaz-Moreno, Sofia (2003) Application of stopped flow techniques and energy dispersive EXAFS for investigation of the reactions of transition metal complexes in solution: activation of nickel ?-diketonates to form homogeneous catalysts, electron transfer reactions involving iron(III) and oxidative addition to iridium(I). Faraday Discussions, 122, 211-222. (doi:10.1039/b202833f).

Abstract

Stopped-flow techniques of rapid mixing have been combined with energy dispersive X-ray absorption spectroscopy to monitor the reaction of Ni(dpm)(2) {dpm = (BuC)-C-t(O)CHC(O)Bu-t} by aluminium alkyls (AlEt2X, X = OEt and Et) to form the active species for the catalytic di- and tri-merisation of hex-1-ene. Acquisition times down to ca. 30 ms were achieved on Station 9.3 of the SRS using a photodiode array detector. The EXAFS features of the resulting solution complexes are of the form [Ni(O-O)(R) (alkene)]. In the presence of PPh3, [Ni(O-O)(R)(PPh3)] appears to be the predominant type of species. The reduction of aqueous Fe(III) by hydroquinone was investigated on ID24 at the ESRF by Fe K-edge energy dispersive EXAFS with a CCD camera as detector; spectra were obtained in 1 ms or longer. No intermediate inner sphere complex was detected prior to the formation of aqueous Fe(II). Finally the oxidative addition of CH3SO3CF3 to [IrI2(CO)(2)](-) was monitored on Station 9.3 with a silicon microstrip detector. A single acquisition of 400 mus was feasible, with spectra recorded in multiples of 1.2 ms. In that time, the first stage of the reaction had been completed, with a slower stage thereafter. The results are consistent with the two-stage ionic oxidative addition mechanism.

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