The molecular structure of the cation in 2 is shown in Figure . The structure is broadly similar to that of 1, with the major differences being the orientation of the The studies described here demonstrate that square-planar palladium triphosphine and PNP complexes act as strong Lewis acids in acetonitrile, imparting a dramatically lower pKa value to a coordinated solvent molecule. The coordinated acetonitrile ligands are deprotonated by bases with pKa BH+ values greater than 24.3, forming well-defined, mononuclear cyanomethyl complexes. The increase in acidity is at least 8 pKa units and likely as much as 14, with the uncertainty in these values originating from difficulties in measuring the autoionization constant of free acetonitrile. To the best of our knowledge, these reactions are the first stoichiometric demonstration of a cyanomethyl complex formed by deprotonating acetonitrile with a base whose pKa BH+ is measurably lower than that of the free solvent. These results are relevant to catalytic cyanoalkylation reactions. Structurally, the cyanomethyl complexes have similar geometries to analogous complexes with other monodentate ligands, and the bond metrics indicate a trans influence for the cyanomethyl group that is considerably larger than halide or pseudo-halide ions but less than those of phosphine ligands.