Parallelograms and ladders: Polymorphic solid-state structures and solution equilibria of CpGeCl

Two polymorphic structures of Cp*GeCl were determined by single-crystal X-ray diffraction analysis: (I) a dimer in the form of a parallelogram in solid state (yellow crystals, P2₁/n) and (II) an infinite ladder of alternating parallelograms (colorless crystals, C2/c). Melting experiments in X-ray capillary tubes revealed that the C2/c polymorph converts to the P2₁/n polymorphic structure. Variable-temperature and concentration-dependent ¹H NMR spectroscopy suggest an equilibrium between a monomer and either a dimer or higher oligomer species. Variable-temperature ¹H NMR (from 25 to -80 °C) of Cp*GeCl (P2₁/n) dissolved in toluene-d₈ indicates that lower temperature favors the dimers and/or oligomers. Increasing concentration (from 0.05 to 0.65 M) also favors the dimer or oligomer structure. The addition of chloride ions (from 0.1 to 1.0 equiv) via the addition of tetrabutylammonium chloride to solutions prepared from Cp*GeCl resulted in the formation of Cp*₂Ge. Addition of increasing amounts (from 5 to 42 mg) of Cp*GeCl to a sample of Cp*₂Ge gave no evidence of exchange by ¹H NMR spectroscopy. Similarly, the addition of one equivalent of methyl mesylate to various concentrations of Cp*GeCl (0.06, 0.09, and 1.8 M) did not result in the formation of methyl chloride, indicating that an equilibrium involving chloride ions is not operative.