π-allyl nickelate(II) and palladate(II) complexes

The homoleptic M-pi-allyl complexes M(eta(3)-C3H5)(2) (M = Ni, Pd) react with LiC3H5 and Li2C4H8 in the presence of tmeda to give the ionic pi-allyl nickelates(II) and palladates(II) [Li(tmeda)(2)](+)[(eta(3)-C3H5)M(eta(1)-C3H5)(2)](-) (M = Ni, 3a; M = Pd, 3b) and [Li(tmeda)(2)](+)[(eta(3)-C3H5)M(C4H8)](-) (M = Ni, 4a; M = Pd, 4b). Complexes 3a,b are formed by reversible addition of a further allyl group, while the formation of 4a,b occurs by replacement of one allyl group by the chelating dianionic butane-1,4-diyl ligand. The solid nickel complexes 3a and 4a are temporarily stable at ambient temperature, whereas the palladium derivatives 3b and 4b decompose above 0 degreesC. All the complexes are ionic, with square-planar metalate(II) anions containing one pi-allyl and two sigma-organyl ligands, and there is no direct interaction between the Li atom and the anion, as exemplified by low-temperature X-ray structure analyses of 3a and 4a. CP-MAS C-13 NMR spectroscopy shows that the structure of 3a is fluxional in the solid state above -93 degreesC.