Structural features and dynamical behavior of heteroleptic trans-C,C-bisaryl-platinum(II) and -palladium(II) complexes

Several heteroleptic trans-bisaryl-Pt-II complexes, trans-C,C-[Pt(NCN)R] (6-9), have been prepared starting from the readily available precursor [PtCl(NCN)] (1, NCN = [C6H3(CH2-NMe2)(2)-2,6](-)) and ortho-substituted phenyl- or naphthyllithium reagents, respectively. Variable-temperature H-1 NMR spectroscopy shows that in solution the NCN ligand is eta(3)-coordinated and that rotation of the trans-aryl ligand about the Pt-C-ipso bond is slow or even nonexistent on the NMR time scale. Moreover, in the temperature range -80 to +90 degrees C no dissociation of the Pt-N (NCN) coordination occurs. In contrast, the analogous Pd-II complex 13 shows fluxional behavior of the nitrogen-to-metal coordination (above 0 degrees C). The dynamic properties of this type of complexes can thus be tuned by the choice of metal. The crystal structure determinations of two trans-C, C- [M(NCN)(C10H6(CH2NMe2)-2)] complexes (8 (M = Pt), 13 (M = Pd)) are reported. The most significant feature in these structures is that the eta(3)-NCN-coordinating NCN ligand present in 1 has been retained in 8 and 13; that is, the ortho-(dimethylamino)methyl group of the naphthyl ligand remains noncoordinating and cannot compete with the ortho-(dimethylamino)methyl groups of the NCN ligand.