A dynamic {AuI⋯AuI}-coupling cluster-based coordination capsule for photocatalytic benzylamine oxidation

Abstract

Coordination chemistry driven by aurophilic interactions has generated numerous unique supramolecular architectures with tunable structures and innovative functions. In this work, a dimeric cluster-based capsule [C1]₂·6PF₆⁻ ([(dppmAu₂)₃L¹]₂·6PF₆⁻) with a dynamic cavity was self-assembled. The dppmAu₂Cl₂ dinuclear gold(I) complex was used as the coordination corner and the K₃L¹ (1, 3, 5-tri(1-bicarbodithiolate piperazinyl)-2,4,6-triethylbenzene potassium salt) tripodal cavitand acted as the organic linker in a multiple-component modular synthesis strategy. A tetranuclear gold(I) corner with a continuous Au^I⋯Au^I bonding motif was formed during the self-assembly and crystallization process of a [Au₆L¹]-type semispherical monomeric cluster that was spontaneously aggregated into a [Au₆L¹]₂-type dimeric capsule. The Au^I⋯Au^I coupling molecular capsule exhibited excellent photophysical properties and electron–hole separation ability. Accordingly, the photocatalytic performance for the benzylamine oxidation coupling reaction was outstanding. For ten aromatic amine substrates, the catalytic yield reached 88–96% under irradiation. In addition, the recycled catalytic yield remained above 86% after three runs due to the high chemical stability and tolerance of the [C1]₂·6PF₆⁻ cluster catalyst. In the photocatalytic mechanism, the primary amines formed holes, thereby triggering amine substrate oxidation, reactive oxygen species (ROS)-induced C–N bond activation, and imine condensation. Here, the formation of the intermediate benzaldehyde was detected using real-time ¹H-NMR monitoring and electrospray ionization mass spectroscopy (MS), and then further confirmed by density functional theory (DFT) calculations. This dynamic gold(I) cluster-based capsule can potentially be utilized as a photocatalyst via selective host-guest recognition associated with cooperative multi-metal aurophilic interaction.