Nucleophilic T-Shaped (LXL)Au(I)-Pincer Complexes: Protonation and Alkylation

Abstract

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Tipping the Balance between Ligand and Metal Protonation due to Relativistic Effects: Unusually High Proton Affinity in Gold(I) Pincer Complexes

“…However, when relativistic effects are switched on, the two protonation sites in 1‐Au compete with each other with a difference of only 25–30 kJ mol −1 (with/without THF) in the proton affinities. This is in nice agreement with the observed proton‐exchange mechanism between the Au center and the N‐1 site . Moreover, in the non‐relativistic case, the proton affinities of the coinage metal atom sites follow the trend 1‐Ag < 1‐Cu ≈ 1‐Au .…”

“…Similar large effects occur in the chemistry of mercury, for example, see the latest paper by Kozlowsky and co‐workers . The question therefore naturally arises if the high basicity of gold observed in these (LXL)Au I –pincer complexes is due to relativistic effects. To find an answer to this interesting question, we decided to perform quantum chemical calculations to determine the proton affinity for the (LXL)M I –pincer complexes (M=Cu, Ag and Au) with and without relativity and solvent effects for tetrahydrofuran (THF) included.…”

“…In a recent paper, Kleinhans et al. reported the synthesis and reactivity of unusual T‐shaped (LXL)Au I –pincer complexes (Scheme ) . With a formal oxidation state of +1 at the gold atom, we would naively expect protonation on some of the electron‐rich nitrogen sites.…”

“…However, Kleinhans et al. found that the strong electron‐donating properties of the ligand makes the Au I center reactive towards oxidative addition of electrophiles, such as protons, leading to an unusual cationic Au III hydride …”

“…For the T‐shaped pincer M I complexes (M=Cu, Ag and Au), we utilized model systems with less bulky substituents as shown in Figure . The structures were optimized with the ORCA 3.0.3 program package, using density functional theory (DFT) employing the B3PW91 functional together with the def2‐TZVPP basis set and D3 dispersion correction including Becke‐Johnson damping .…”