Dehydrogenative Ga-Ga coupling and hydrogallation in gallium hydride complexes of 3,5-dimethylpyridine

Stefan D. Nogai, Hubert Schmidbaur

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The 2:1 complex of 3,5-dimethylpyridine (L′) and dichlorogallane, (L′)2GaHCl2, undergoes dehydrogenative Ga-Ga coupling in boiling toluene to give high yields of (L′)Cl 2Ga-GaCl2(L′). The structure of the dinuclear product (which has C2h symmetry) has been determined [Ga-Ga′ 2.4000(8) Å]. By contrast, the 1:1 complex of L′ and gallium trihydride, (L′)GaH3, on prolonged standing at 20°C or when treated with excess ligand L′, is converted into the hydrogallation product, (L′)(L′H)GaH2. In this product, the gallium atom is attached to a pyridine donor ligand L′ and a 4-hydropyridyl substituent, as proven by a crystal structure determination and by NMR and IR spectral studies. The Ga-N bond length is very significantly shorter for the hydropyridyl as compared to the pryridine group, and the carbon atom C 4 of the former has become the center of an aliphatic CH2 group with its 1H and 13C resonances shifted into the corresponding upfield regions. The C3-C4 and C 4-C5 linkages have been converted into single bonds, with double bonds localized at C2-C3 and C5-C 6 of the (L′H) heterocycle. While the N-Ga-N angle is very small at only 103(1)°, the H-Ga-H angle is exceedingly large at 127(2)°, indicating a strong steric pressure of the seemingly small hydride ligands and that hydride functions thus are to be considered as bulky substituents.

Original languageEnglish
Pages (from-to)5877-5880
Number of pages4
Issue number24
StatePublished - 22 Nov 2004
Externally publishedYes


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