AbstractThe synthesis of bis(1-tert-butyl-2 -methyl-η5 - 1 ,2 -azaborolinyl)ruthenium (1) and bis(2-methyll- trimethylsilyl-η5 - 1 ,2 -azaborolinyl)ruthenium (2) succeeds when RuCL is reacted with the corresponding 1,2-azaborolinyl lithium compounds in THF at -70 °C. Each of the sandwich complex forms two isomers with a clockwise and an anti-clockwise conformation of the azaborolinyl rings. The anti-clockwise isomer of 1 (1a ) gives colourless crystals which were investigated by singlecrystal X-ray diffraction methods. The molecular structure shows the rings in an eclipsed orientation forming an interplanar angle of 8.6 °. The isomers of 1 as well as of 2 give different 1H and 11B NMR signals.