New palladium complexes with rigid scorpion-type ligands. Crystal structure of complexes [Pd(η3-2-CH3-C3H 4)(bpz*mPh)](CF3SO3) and [Pd(bpz*mpy)2](BF4)2. bpz*mPh=phenyl-bis(3,5-dimethylpyrazol-1-yl)methane; Bpz*mpy=pyridin-2-yl-bis(3,5-dimethylpyrazol-1-yl)methane

Article abstract of DOI:10.1016/S0022-328X(00)00160-1

Two α-R substituted bis(3,5-dimethylpyrazol-1-yl)methane ligands (R=Ph, bpz*mPh and 2-py, bpz*mpy) have been used to synthesise new palladium(II) compounds with the general formulae PdXX′(bpz*mR) (R=Ph, X=X′=Cl; 1a, X=X′=Me; 2a, X=Cl, X′=Me; 3a, X=X′=C₆F₅; 4a or R=2-py, X=X′=Cl; 1b, X=Cl, X′=Me; 3b, X=X′=C₆F₅, 4b), [Pd(η³-2-CH₃-C₃H ₄)(bpz*mR)]X (X=PF₆^-, R=Ph, 5a; X=CF₃SO₃^-, 2-py, 5b) and [Pd(bpz*mR)₂](BF₄)₂ (R=Ph, 6a; 2-py, 6b). In all the complexes the bpz*mR ligands adopt a rigid conformation with the R group in an axial position and, as a consequence, no boat-to-boat interconversion is observed. In 1b and 3b-5b the pyridine group is uncoordinated. Complex 5b is present as a single isomer, while 5a exists as two isomers that are in equilibrium and differ in the orientation of the allyl group with respect to the NN ligand. For complex 6b the four possible anti isomers are observed in solution. The molecular structures of the major isomer of 5a and one of the isomers of 6b have been determined by X-ray structure analysis. In both structures the bpz*mR ligands are coordinated as bidentate. For 5a the ligand backbone confirms the stated rigidity. For 6b a pyridine-pyrazole coordination of the two bpz*mpy ligands is observed. The fluxional behaviour implying interconversion of the two pyrazole rings in 3b, of the two isomers in 5a and the rotation of the C₆F₅ groups in 4a and 4b has also been studied.