Structural Features and Dynamical Behavior of Heteroleptic trans-C,C-Bisaryl-Platinum(II) and -Palladium(II) Complexes

Several heteroleptic trans-bisaryl-PtII complexes, trans-C,C-[Pt(NCN)R] (6−9), have been prepared starting from the readily available precursor [PtCl(NCN)] (1, NCN = [C6H3(CH2NMe2)2-2,6]-) and ortho-substituted phenyl- or naphthyllithium reagents, respectively. Variable-temperature 1H NMR spectroscopy shows that in solution the NCN ligand is η 3-coordinated and that rotation of the trans-aryl ligand about the Pt−Cipso bond is slow or even nonexistent on the NMR time scale. Moreover, in the temperature range −80 to +90 °C no dissociation of the Pt−N (NCN) coordination occurs. In contrast, the analogous PdII complex 13 shows fluxional behavior of the nitrogen-to-metal coordination (above 0 °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 η 3-N,C,N-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.