Homoleptic ‘sandwich’ complexes of substituted tris(methimazolyl)borate ligands with ruthenium, rhodium and palladium

The pursuit of heteroleptic 'half-sandwich' complexes of boron substituted anionic and charge-neutral tris(methimazolyl)borate ligands is described. The formation of the homoleptic 'sandwich' complexes was found to be favoured when the metal precursor contains labile ligands. When unable to form these homoleptic complexes Tm is shown to preferentially coordinate in a κ²-[S,S] fashion. This study reinforces previous assertions that the Tm ligand preferentially adopts the κ²-[S,S] mode when coordinated to electron rich metal centres and demonstrates the strong electron donor properties of substituted Tm ligands.