“Third-Generation”-Type Functional Tris(2-pyridyl)borate Ligands and Their Transition-Metal Complexes

• Published in: Inorganic chemistry 2016-04, Vol.55 (7), p.3605-3615
• Main Authors: Jeong, So Yi, Lalancette, Roger A., Lin, Huina, Lupinska, Patrycja, Shipman, Patrick O., John, Alexandra, Sheridan, John B., Jäkle, Frieder
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.6b00124

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 are discussed. The electrochemical and absorption characteristics of the corresponding low-spin iron­(II) and ruthenium­(II) complexes are compared. We demonstrate the further elaboration of iodo derivatives with alkynes via Sonogashira–Hagihara coupling, a process that proceeds with high yield for the iron­(II) and ruthenium­(II) complexes but not for the free ligand. Borylation of the silyl-substituted ruthenium­(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 carbon atoms. 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.