Fluoride-promoted cross-coupling of chloro(mono-, di-, or triphenyl)germanes with aryl halides in "moist" toluene. Multiple transfer of the phenyl group from organogermane substrates and comparison of the coupling efficiencies of chloro(phenyl)germanes with their corresponding stannane and silane counterparts

The trichlorophenyl-, dichlorodiphenyl-, and chlorotriphenylgermanes undergo Pd-catalyzed cross-couplings with aryl bromides and iodides in the presence of tetrabutylammonium fluoride in toluene with addition of the measured amount of water. One chloride ligand on the Ge center allows efficient activation by fluoride to promote transfer of one, two, or three phenyl groups from the organogermanes. The corresponding chlorophenylstannanes were found to be more reactive than chlorophenylsilanes, which in turn were more effective than chlorophenylgermanes. One chloride ligand on the Ge or Si center allows efficient activation by fluoride to promote transfer of up to three aryl groups from germane or silicon. However, no haloligand was necessary to be present on the Sn center, since tetraphenyltin efficiently transferred up to four phenyl groups during fluoride-promoted couplings with aryl halides. (19)F NMR studies suggested formation of the fluorophenylgermanes and the hypervalent germanate species as possible intermediates.