Diastereoselective synthesis of coordination compounds: a chiral tripodal ligand based on bipyridine units and its ruthenium(II) and iron(II) complexes

The enantiomerically pure chiral tris-chelating ligand (+)-(7S, 10R)- L (L) comprising three 4,5-pinenobipyridine subunits connected through a mesityl spacer has been synthesized. Complexes of L with Ru-II and Fe-II have been prepared and characterised. NMR spectroscopy indicates that only one diastereoisomer is formed, and the CD spectra show that the complexes have the Lambda configuration on the metal centre. The X-ray crystal structure of the iron complex shows that in the octahedral complex, the ligand L coils around the metal and confirms the absolute configuration. The Ru-II and Fe-II compounds were also characterised by mass spectrometry, electronic absorption, and, in the case of Ru(II), fluorescence spectroscopy. The photostability of the ruthenium compound was checked by photochemical experiments.