Endohedral Plumbaspherenes of the Group 9 Metals: Synthesis, Structure and Properties of the [M@Pb12]3‐ (M = Co, Rh, Ir) Ions

The icosahedral [M@Pb12]3 from K4Pb9 and Co(dppe)Cl2 (dppe = 1,2-Bis(diphenylphosphino)ethane) / Rh(PPh3)3Cl / [Ir(cod)Cl]2 (cod = 1,5-cyclooctadiene), respectively, in the presence of 18-crown-6 / 2,2,2-cryptand in ethylenediamine / toluene solvent mixtures. The [K(2,2,2-cryptand)]+ salt of 1 and the [K(18-crown-6)]+ salt of 3 were characterized via X-ray crystallography; the ions 1 and 3 are isostructural and isoelectronic to the [Rh@Pb12]3- (2) ion as well as to the group 10 clusters [M'@Pb12]2- (M' = Ni, Pd, Pt). The ions are all 26-electron clusters with near perfect icosahedral Ih point symmetry. Clusters 1-3 show record downfield 207Pb NMR chemical shifts due to sigma-aromaticity of the cluster framework. Calculated and observed 207Pb NMR chemical shifts and 207Pb-xM J-couplings (xM = 59Co, 103Rh, 193Ir) are in excellent agreement and DFT analysis shows that the variations of 207Pb-NMR chemical shifts for the [M@Pb12]2,3- ions (M = Co, Rh, Ir, Ni, Pd, Pt) are mainly governed by the perpendicularly oriented s11 component of the chemical shift anisotropy tensor. The laser desorption ionization time-of-flight (LDI-TOF) mass spectra contain the molecular ions as well as several new gas phase clusters derived from the parents. The DFT minimized structures of these ions are described.