Synthesis and Decomposition Behavior of Pallada(IV)cyclopentane Complexes

Allan J. Canty,* Jason L. Hoare, Noel W. Davies, and Peter R. Traill
Department of Chemistry and Central Science Laboratory, University of Tasmania, Hobart, Tasmania, Australia 7001
Organometallics, 1998, 17 (10), pp 2046–2051
DOI: 10.1021/om980005t
Publication Date (Web): April 17, 1998
Copyright © 1998 American Chemical Society

Abstract

The octahedral pallada(IV)cyclopentane complexes PdX(C4H8)R(bpy) [RX = MeI (1), EtI (2), PhCH2Br (3), CH2CHCH2Br (4); bpy = 2,2‘-bipyridine] may be isolated on oxidative addition of organohalides to the palladium(II) complex Pd(C4H8)(bpy) in acetone at −20 °C. The complex PdBr(C4H8)(CF3)(bpy) (5) has been generated in solution but was too unstable to permit isolation as a solid. Complex 1 occurs as a mixture of isomers in a 4:1 ratio, where the dominant isomer has the methyl group trans to bpy and the minor isomer has 2-fold symmetry with the methyl group trans to the iodo ligand. Complexes 25 adopt only the configuration with R trans to X. The complexes exhibit low stability, allowing studies of decomposition in solution under mild conditions in CDCl3 or CD2Cl2. Formation of the major products from PdI(C4H8)Me(bpy) (1) and PdI(C4H8)Et(bpy) (2) is assumed to result from C4H8···R coupling at Pd(IV) to give undetected PdIICH2CH2CH2CH2R species which undergo β-elimination to form alkenes (48% of detected organic products), Pd(0), and HX, with subsequent protonation of PdIICH2CH2CH2CH2R to give alkanes (39%). Complexes 1 and 2 also give iodopentane (12% from 1) and iodohexane (9% from 2). The complex PdBr(C4H8)(CH2Ph)(bpy) (3) gives phenylpentane (15%), phenylpentenes (66%), toluene (10%), and butenes (8%); PdBr(C4H8)(CH2CHCH2)(bpy) (4) and PdI(C4H8)(CF3)(bpy) (5) give predominantly cyclobutane, together with minor amounts of butenes (4, 5) and propene (4). Deuteration studies implicate the occurrence of intermolecular hydrogen atom transfer for elimination of alkenes and alkanes, except for cyclobutane.

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History

  • Published In Issue May 11, 1998
  • Received January 6, 1998

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