Effect of Pnictogen Ligand Substitution on a Tripalladium Ditropylium Core

A combination of multinuclei NMR, UV−vis spectroscopy, and single crystal X-ray diffraction was used to characterize a new series of tripalladium ditropylium sandwich complexes [Pd3Tr2(E)3][BF4]2 (E = PPh3, AsPh3, and SbPh3 and PEt3). Ligand substitution leads to a systematic shift of the 1H and 13C NMR tropylium resonances and is correlated with the electron donating properties of the substituent group. Replacement of the ligand increases the palladium-pnictogen bond length in the order P < As < Sb; however, this only slightly alters the internal Pd−Pd bond lengths, supporting the hypothesis that there are only weak Pd−Pd bonding interactions.