Exploring Cu/Al cluster growth and reactivity: from embryonic building blocks to intermetalloid, open-shell superatoms

Cluster growth reactions in the system [Cu-5](Mes)(5) + [Al-4](Cp*)(4) (Mes = mesitylene, Cp* = pentamethylcyclopentadiene) were explored and monitored by in situ LIFDI-MS and H-1-NMR. Feedback into experimental design allowed for an informed choice and precise adjustment of reaction conditions and led to isolation of the intermetallic cluster [Cu4Al4](Cp*)(5)(Mes) (1). Cluster 1 reacts with excess 3-hexyne to yield the triangular cluster [Cu2Al](Cp*)(3) (2). The two embryonic [Cu4Al4](Cp*)(5)(Mes) and [Cu2Al](Cp*)(3) clusters 1 and 2, respectively, were shown to be intermediates in the formation of an inseparable composite of the closely related clusters [Cu7Al6](Cp*)(6) (3), [HCu7Al6](Cp*)(6) (3(H)) and [Cu8Al6](Cp*)(6) (4), which just differ by one Cu core atom. The radical nature of the open-shell superatomic [Cu7Al6](Cp*)(6) cluster 3 is reflected in its reactivity towards addition of one Cu core atom leading to the closed shell superatom [Cu8Al6](Cp*)(6) (4), and as well by its ability to undergo sigma(C-H) and sigma(Si-H) activation reactions of C6H5CH3 (toluene) and (TMS)(3)SiH (TMS = tris(trimethylsilyl)).

Automated summary

The study explored cluster growth reactions in the system [Cu-5](Mes)(5) + [Al-4](Cp*)(4) and successfully isolated intermediates [Cu4Al4](Cp*)(5)(Mes) and [Cu2Al](Cp*)(3), which were shown to be crucial in the formation of larger clusters such as [Cu7Al6](Cp*)(6), [HCu7Al6](Cp*)(6), and [Cu8Al6](Cp*)(6). The radical nature of the open-shell superatomic [Cu7Al6](Cp*)(6) cluster 3 is reflected in its reactivity towards addition of one Cu core atom leading to the closed shell superatom [Cu8Al6](Cp*)(6), demonstrating its unique properties in activation reactions.