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 (1)H-NMR. Feedback into experimental design allowed for an informed choice and precise adjustment of reaction conditions and led to isolation of the intermetallic cluster [Cu(4)Al(4)](Cp*)(5)(Mes) (1). Cluster 1 reacts with excess 3-hexyne to yield the triangular cluster [Cu(2)Al](Cp*)(3) (2). The two embryonic [Cu(4)Al(4)](Cp*)(5)(Mes) and [Cu(2)Al](Cp*)(3) clusters 1 and 2, respectively, were shown to be intermediates in the formation of an inseparable composite of the closely related clusters [Cu(7)Al(6)](Cp*)(6) (3), [HCu(7)Al(6)](Cp*)(6) (3H) and [Cu(8)Al(6)](Cp*)(6) (4), which just differ by one Cu core atom. The radical nature of the open-shell superatomic [Cu(7)Al(6)](Cp*)(6) cluster 3 is reflected in its reactivity towards addition of one Cu core atom leading to the closed shell superatom [Cu(8)Al(6)](Cp*)(6) (4), and as well by its ability to undergo σ(C–H) and σ(Si–H) activation reactions of C(6)H(5)CH(3) (toluene) and (TMS)(3)SiH (TMS = tris(trimethylsilyl)).