Carbaborane-functionalised 2,2′:6′,2"-terpyridine ligands for metallosupramolecular chemistry:: Syntheses, complex formation, and the crystal and molecular structures of 4′-(optho-carboranyl)-2,2′:6′,2"-terpyridine and 4′-(ortho-carboranylpropoxy)-2,2′:6′,2"-terpyridine

A series of functionalised 2,2':6',2 "-terpyridine ligands, each with a closo-1,2-C(2)B(10)H(10)R (R = H or Si(t)BuMe(2)) substituent in the 4' position, either directly or indirectly attached to the heterocyclic ring, has been prepared; two members of the series, 4'-(3-ortho-carboranylpropoxy)-2,2':6',2 "-terpyridine (4) and 4'-(ortho-carboranyl)-2,2':6',2 "-terpyridine (7) have been characterised by X-ray crystallography. The reaction of ligand (7) with alcohols results in the boron decapping of the close-cage and yields a Zwitter-ionic nido-cluster-functionalised ligand. Analogous changes to the carbaborane cage have been observed in complexes in which the terpyridine domain is coordinated to ruthenium(II). However, decapping does not occur if a Si(t)BuMe(2)-protected carbaborane cage is incorporated into the terpyridine ligands. (C) 1998 Elsevier Science S.A.