Reactions of trichlorogermane HGeCl3 and dichlorogallane HGaCl2 with pyridine donors

Abstract

The weak base pyridine has been found to deprotonate trichlorogermane HGeCl₃ with quantitative formation of pyridinium trichlorogermanate(II), Py-H⁺GeCl₃⁻, the pyramidal structure of the anion resembling that of the isoelectronic AsCl₃ molecule. This course of the reaction supports the assignment of an inverse polarization (−)Ge–H(+) of the bond in HGeCl₃ as compared to the (+)Si–H(−) bond in trichlorosilane HSiCl₃, which is known to form a 1 ∶ 2 adduct with pyridine instead. Germanium tetrachloride also undergoes simple addition reactions with pyridine leading ultimately e.g. to GeCl₄L₂ with L = 4-ethyl-pyridine. Dichlorogallane gives 1 ∶ 1 addition compounds (HGaCl₂L) with L = pyridine, 4-dimethylamino-pyridine, 4-cyano-pyridine, and 3,5-dimethyl-pyridine, the molecular structures of which have been determined by single crystal X-ray diffraction. Simple tetrahedral arrays of substituents around the gallium center with only minor distortions, and characteristic Ga–H stretching vibrations in the IR spectra, show that the Ga–H bond is untouched in the addition reactions. The addition of two equivalents of 3,5-dimethyl-pyridine to HGaCl₂ affords the 1 ∶ 2 complex which was shown to have a trigonal-bipyramidal geometry with the hydride ligand in an equatorial position. In order to provide benchmark data, the 1 ∶ 1 adducts GaCl₃(L) and GaH₃(L) with L = 3,5-dimethyl-pyridine were also prepared and structurally characterized. Pyridinium tetrachlorogallate(III) takes up pyridine, but the extra ligand is attached to the cation via hydrogen bonding leaving the anion unchanged: [Py-H⋯Py]⁺[GaCl₄]⁻.