A Pd4Br4 macrocycle trapped by cocrystallization from a highly dynamic equilibrium of eta(3)-cycloheptatrienide complexes

摘要

In the coordination chemistry of palladium, dimers bridged via halides are a common motif. Higher oligomers, however, are still rare. We report the structure of an alternating eight-membered [Pd4Br4](4-) ring framed by cycloheptatrienide ligands, which was obtained by cocrystallization of dimers and tetramers of the complex salt bromido{eta(3)-[3-(2,6-diisopropylphenyl)imidazolium-1-yl]cycloheptatrienido}palladium(II) tetrafluoroborate, namely bis[di-mu-bromido-bis({eta(3)-[3-(2,6-diisopropylphenyl)imidazolium-1-yl]cycloheptatrienido}palladium(II))] cyclotetra-mu-bromido-tetrakis({eta(3)-[3-(2,6-diisopropylphenyl)imidazolium-1-yl]cycloheptatrienido}palladium(II)) octakis(tetrafluoroborate) dichloromethane octasolvate, [Pd4Br4(C22H26N2)(4)][Pd2Br2(C22H26N2)(2)](2)(BF4)(8)center dot 8CH(2)Cl(2). These dimers and tetramers form a highly dynamic equilibrium in solution which was studied by low-temperature NMR spectroscopy. In the light of the presented results, tetrameric Pd-II species can be assumed to co-exist as a second species in many cases where by current knowledge only a dimeric compound would be expected.