Resistance of a PdAu12(8e) Core to Growth in Collision-Induced Sequential Reductive Elimination of (CCR)2 from [PdAu24(CCR)18]2–

Previous studies have reported that [PdAu24(PAF)18]2– (PAF = 3,5-(CF3)2C6H3CC) with an icosahedral superatomic PdAu12(8e) core underwent collision-induced sequential reductive elimination (CISRE) of 1,3-diyne (PAF)2 (J. Phys. Chem. C 2020, 124, 19119). The most likely scenario after the CISRE of (PAF)2 is the growth of the PdAu12(8e) core via the fusion of the Au(0) atoms produced from the Au2(PAF)3 units on the core surface. Contrary to expectation, anion photoelectron spectroscopy and theoretical calculations regarding the CISRE products [PdAu24(PAF)18–2n]2– (n = 1–6) revealed that the electronically closed PdAu12(8e) core does not grow to a single superatom with (8 + 2n)e but assembles with Au2(2e) units. Characterization of the CISRE products of other alkynyl-protected Au clusters suggested that even the non-superatomic Au17(8e) core was resistant to growth due probably to rigidification by PA ligands. We propose that there is a kinetic bottleneck in the growth process of protected Au clusters at the stage where they are electronically closed and/or lose their structural fluxionality by ligation.