Endohedral Plumbaspherenes of the Group 9 Metals: Synthesis, Structure and Properties of the [M@Pb<inf>12</inf>]³⁻ (M=Co, Rh, Ir) Ions

Abstract

The icosahedral [M@Pb12]3− (M=Co(1), Rh(2), Ir(3)) cluster ions were prepared 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 σ-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 σ11 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.