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PHOTOCHEMISTRY OF trans ‐[Rh(BIS(DIPHENYLPHOSPHINO)ETHANE) 2 X 2 ][PF 6 ]: TRANSIENT ABSORBANCE KINETIC STUDIES OF METAL‐HALOGEN BOND HOMOLYSIS
Author(s) -
Bao Feng,
Kubiak Clifford P.
Publication year - 1992
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1992.tb04267.x
Subject(s) - chemistry , photochemistry , radical , halogen , hydride , flash photolysis , homolysis , rhodium , medicinal chemistry , metal , kinetics , catalysis , reaction rate constant , alkyl , organic chemistry , physics , quantum mechanics
— Laser flash photolysis of trans ‐[Rh(dppe) 2 X 2 ][PF 6 ] (X=Br and I; dppe=bis(diphenylphosphino)ethane) in CH 2 Cl 2 or CH 3 CN produces the d 7 Rh(II) radicals, [Rh(dppe) 2 X] + , and halogen atoms. The kinetics of the disappearance of [Rh(dppe) 2 X] + radicals in CH 2 Cl 2 or CH 3 CN were mixed order: H‐atom abstraction from solvent to produce the rhodium hydrides, [RhH(dppe) 2 X][PF 6 ], 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) 2 X][PF 6 ], formed by H‐atom abstraction were completely characterized by 31 P{ 1 H}‐NMR, 1 H‐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.