A Comparative Investigation of Aryl Isocyanides Chemisorbed to Palladium and Gold: An ATR-IR Spectroscopic Study

The nature of the bonding interactions between aryl isocyanides and gold and palladium surfaces was investigated using attenuated total refection infrared (ATR-IR) spectroscopy. The experiments were conducted by evaporating a film of either palladium or gold onto a ZnSe internal reflection element (IRE). The studies reveal that aryl isocyanides form only σ-bonded species when coordinated to gold and that these species are bonded relatively weakly to the gold surface, evidenced by their ready removal when subjected to ultrasound (sonication). In contrast, aryl isocyanides form at least two distinct types of species when bonded to a palladium surface: one effectively σ-bonded, as with gold, but much more tenaciously, and the other species bonded strongly to the surface by a σ/π synergistic interaction. The presence of π back-donation from the palladium surface into the isocyanide π system provides a rationale for the observation that barriers to conduction are lower when diisocyanides bridge palladium electrodes than when diisocyanides or dithiols bridge gold electrodes.