Pentamethyl- And 1,2,4-tri(tert-butyl)cyclopentadienyl containing p-block complexes - differences and similarities

Abstract

The sterically encumbered cyclopentadienyl ligand 1,2,4-(Me3C)3C5H2(Cp′′′) was used to stabilize efficiently the main group metals of Al, Ga, In, Ge and Sn, respectively. The σ-bonded gallium compounds [η1-Cp′′′Ga(μ-X)X]2(X = Cl,2; X = I,3) and indium compound [η1-Cp′′′In(μ-Br)nBu]2(7) exhibit dimers through halogen bridges. Reduction of2with 2 equivalents of KC8leads almost to the same amount of η1-Cp′′′Ga(THF)Cl2(4) and η5-Cp′′′Ga (5), respectively. The exception is compound5, which is obtained by reducing2or3with 4 equivalents of KC8. Compound5as Lewis base reacts with GaI3readily forming the Lewis acid-base adduct product η5-Cp′′′Ga → GaI3(6). Moreover, compounds with the Cp′′′ ligand stabilize heavier low-valent group 14 elements for example [η5-Cp′′′EII]+[EIICl3]−(E = Ge8, Sn9), which are π-bonded ionic compounds that possess a low-valent cation and an anion. In the cation of [η5-Cp′′′EII]+, the Cp′′′ ligand adopts an η5-coordination mode with germanium and tin, respectively, which present half-sandwich complexes. While the EIIfragment interacts with five π electrons from the Cp′′′ unit to generate an electron-octet arrangement at the respective element. All new reported structures are comparing well with the corresponding compounds containing the pentamethylcyclopentadienyl (Cp*) ligand.