Synthesis and Decomposition Behavior of Pallada(IV)cyclopentane Complexes

The octahedral pallada(IV)cyclopentane complexes PdX(C 4 H 8 )R(bpy) [RX = MeI ( 1 ), EtI ( 2 ), PhCH 2 Br ( 3 ), CH 2 CHCH 2 Br ( 4 ); bpy = 2,2‘-bipyridine] may be isolated on oxidative addition of organohalides to the palladium(II) complex Pd(C 4 H 8 )(bpy) in acetone at −20 °C. The complex PdBr(C 4 H 8 )(CF 3 )(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 2 − 5 adopt only the configuration with R trans to X. The complexes exhibit low stability, allowing studies of decomposition in solution under mild conditions in CDCl 3 or CD 2 Cl 2 . Formation of the major products from PdI(C 4 H 8 )Me(bpy) ( 1 ) and PdI(C 4 H 8 )Et(bpy) ( 2 ) is assumed to result from C 4 H 8 ···R coupling at Pd(IV) to give undetected Pd II CH 2 CH 2 CH 2 CH 2 R species which undergo β-elimination to form alkenes (48% of detected organic products), Pd(0), and HX, with subsequent protonation of Pd II CH 2 CH 2 CH 2 CH 2 R to give alkanes (39%). Complexes 1 and 2 also give iodopentane (∼12% from 1 ) and iodohexane (∼9% from 2 ). The complex PdBr(C 4 H 8 )(CH 2 Ph)(bpy) ( 3 ) gives phenylpentane (15%), phenylpentenes (66%), toluene (10%), and butenes (8%); PdBr(C 4 H 8 )(CH 2 CH CH 2 )(bpy) ( 4 ) and PdI(C 4 H 8 )(CF 3 )(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.