Abstract
Phenyltris(2-pyridyl)borates (Tpyb) are a promising class of tripodal “scorpionate”-type ligands with potential utility in the development of transition metal complexes with interesting optical, electronic or magnetic properties, and as building blocks to metallosupramolecular polymers. We report here a new class of “third generation”-type Tpyb ligands that contain different functional groups attached to the boron-bound aryl moiety. The synthesis, characterization and metal ion complexation behavior of ligands with iodo and trimethylsilyl groups is discussed. The electrochemical and absorption characteristics of the corresponding low-spin Fe(II) and Ru(II) complexes are compared. We demonstrate the further elaboration of the iodo derivatives with alkynes via Sonogashira-Hagihara coupling, a process that proceeds with high yield for the Fe(II) and Ru(II) complexes, but not for the free ligand. The borylation of the silyl-substituted Ru(II) complex with BBr3 was also investigated. In addition to the expected borylation product, Ru(Tpyb-Bpin)2, the replacement of one (major product) or two phenyl groups is observed, suggesting that electrophilic borylation occurs at both the C(Ph)-Si and the C(Ph)-B aromatic carbons. The successful attachment of a range of different functional groups at the periphery of the Tpyb metal complexes is expected to provide opportunities to access new polymeric materials via C-C coupling or click-type reactions.