Hume–Rothery Phase-Inspired Metal-Rich Molecules: Cluster Expansion of [Ni(ZnMe)6(ZnCp*)2] by Face Capping with Ni0(η6‑toluene) and NiI(η5‑Cp*)

The novel all-hydrocarbon ligand-stabilized binuclear clusters of metal–core composition Ni2Zn7E, [(η5-Cp*)­Ni2(ZnMe)6(ZnCp*)­(ECp*)] (1-Zn, E = Zn; 1-Ga, E = Ga) and [(η6-toluene)­Ni2(ZnCp*)2(ZnMe)6] (2; Cp* = pentamethylcyclopentadienyl), were obtained via Ga/Zn and Al/Zn exchange reactions using the starting compounds [Ni2(ECp*)3(η2-C2H4)2] (E = Al/Ga) and an excess of ZnMe2 (Me = CH3). Compounds 1-Zn and 1-Ga are very closely related and differ only by one Zn or Ga atom in the group 12/13 metal shell (Zn/Ga) around the two Ni centers. Accordingly, 1-Zn is EPR-active and 1-Ga is EPR-silent. The compounds were derived as a crystalline product mixture. All new compounds were characterized by 1H and 13C NMR and electron paramagnetic resonance (EPR) spectroscopy, mass spectrometric analysis using liquid-injection field desorption ionization, and elemental analysis, and their molecular structures were determined by single-crystal X-ray diffraction studies. In addition, the electronic structure has been investigated by DFT and QTAIM calculations, which suggest that there is a Ni1–Ni2 binding interaction. Similar to Zn-rich intermetallic phases of the Hume–Rothery type, the transition metals (here Ni) are distributed in a matrix of Zn atoms to yield highly Zn-coordinated environments. The organic residues, ancillary ligands (Me, Cp*, and toluene), can be viewed as the “protecting” shell of the 10-metal-atom core structures. The soft and flexible binding properties of Cp* and transferability of Me substituents between groups 12 and 13 are essential for the success of this precedence-less type of cluster formation reaction.