New studies on the apparent allyl rotation in scorpion-like palladium complexes.: The influence of non-directly bonded groups.: X-ray molecular structures of [Pd(η 3-2-Me-C3H4)L]TfO, L = bpzmArOMe and bpz*mCy

New cationic 2-Me-allylpalladium complexes were prepared with the N,N-donor chelate ligands bis(pyrazol-1-yl)(R)methane (R=anisol-2-yl. bpzmArOMe: 2-hydroxyphenyl, bpznlArOH) and bis(3,5-dimethylpyrazol-1-yl)(R)methane (R=anisol-2-yl, bpz*mArOMe; cyclohexyl. bpz*mCy and ferrocenyl, bpz*mFc). The bpz'mR ligands adopt a rigid boat conformation after coordination to the Pd center and the R group is in the axial position of the metallacycle. The new complexes exhibit two isomeric forms in solution that differ in the relative orientation of the 2-Me-allyl group with respect to the bpz'mRPd fragment. The fluxional behavior of the new complexes, mainly in the context of the isomerization process, has been analyzed. Conclusions concerning the influence on this isomerization of the R group and the pyrazole substituents in positions 3 and 5 are discussed. The isomerization process was found to be affected by the presence of coordinating anions (Cl-) or by a change in the complex concentration. The molecular structures of the complexes [Pd(eta(3)-2-Me-C3H4)(bpzmArOMe)]TfO and [Pd(eta(3)-2-Me-C3H4)(bpz*mCy)]TfO have been determined by X-ray diffraction studies. (C) 2002 Elsevier Science B.V. All rights reserved.