Molecular structure of η5-[Pd(CH2-CH-CMeCH2CH2CH=CMe2)(MeCN)](BF4), a cationic pi -allylpalladium complex with an almost in-plane intramolecular olefin coordination.

The complex η5-[Pd(CH2CHCMeCH2CH2CHCMe2)-(MeCN)](BF4), a model for a key intermediate in diene polymerization, crystallizes in the monoclinic space group P21/c, a 11.362(2), b 13.655(4), c 10.046(2) Å, β 134.80(1)°. The structure was solved by conventional Patterson and Fourier syntheses and refined by full matrix least squares techniques to a final discrepancy index R = 0.058 for 1710 independent reflections. The palladium and nitrogen atoms, the center of gravity of the allyl triangle, and the middle point of the coordinated double bond are coplanar. The side chain of the organic moiety is located in the syn position with respect to the η3-allyl group. The orientation of the coordinated double bond, which forms an angle of 26° with the coordination plane, is novel for palladium(II) complexes.