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(PA^F)₁₈]^2– (PA^F = 3,5-(CF₃)₂C₆H₃CC) with an icosahedral superatomic PdAu₁₂(8e) core underwent collision-induced sequential reductive elimination (CISRE) of 1,3-diyne (PA^F)₂ (J. Phys. Chem. C 2020, 124, 19119). The most likely scenario after the CISRE of (PA^F)₂ is the growth of the PdAu₁₂(8e) core via the fusion of the Au(0) atoms produced from the Au₂(PA^F)₃ units on the core surface. Contrary to expectation, anion photoelectron spectroscopy and theoretical calculations regarding the CISRE products [PdAu₂₄(PA^F)_{18–2<i>n</i>}]^2– (<i>n</i> = 1–6) revealed that the electronically closed PdAu₁₂(8e) core does not grow to a single superatom with (8 + 2<i>n</i>)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.