PHOTOCHEMISTRY OF trans-[Rh(BIS(DIPHENYLPHOSPHINO)ETHANE)2X2][PF6]: TRANSIENT ABSORBANCE KINETIC STUDIES OF METAL-HALOGEN BOND HOMOLYSIS |
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| Authors: | Feng,Bao Clifford P.,Kubiak &dagger |
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| Affiliation: | Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA |
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| Abstract: | Abstract— Laser flash photolysis of trans -[Rh(dppe)2X2][PF6] (X=Br and I; dppe=bis(diphenylphosphino)ethane) in CH2Cl2 or CH3CN produces the d7 Rh(II) radicals, [Rh(dppe)2X]+, and halogen atoms. The kinetics of the disappearance of [Rh(dppe)2X]+ radicals in CH2Cl2 or CH3CN were mixed order: H-atom abstraction from solvent to produce the rhodium hydrides, [RhH(dppe)2X][PF6], and Rh/X recombination. In the poor H-atom donor solvent, benzonitrile, Rh/Br recombination was observed to be uncomplicated by competing H-atom abstraction. The hydride complexes [RhH(dppe)2X][PF6], formed by H-atom abstraction were completely characterized by 31P{1H}-NMR, 1H-NMR, and mass specrometry. Cyclohexene was used as an effective trap for photogenerated Br atoms and yielded bromocyclohexane and 3-bromocyclohexene in a relative yield, 1:9. The photochemical mechanism is discussed in light of the transient absorbance and trapping studies. |
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