Parallelograms and Ladders: Polymorphic Solid-State Structures and Solution Equilibria of Cp*GeCl

Abstract

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.