2,2′:6′,2"-Terpyridine substituted in the 4′-poition by the solubilizing and sterically demanding tert-butyl group: a surprisingly new ligand

We describe the synthesis and characterization of 4'-tert-butyl-2,2':6',2 ''-terpyridine (4'-(t)Butpy, 1), a convergent tpy ligand that exhibits both a sterically demanding and solubilizing 4'-substituent. In the solid state, molecules of 1 pack with alternating tpy and tert-butyl domains, and the bulky alkyl substituents prevent the molecules from engaging in the face-to-face p-interactions which are typical of simple tpy ligands. Instead, the predominant packing forces involve CH center dot center dot center dot N hydrogen bonds and weak CH center dot center dot center dot pi contacts. The syntheses of the homoleptic complexes [M(1)(2)][PF6](2) (M = Fe, Co, Zn and Ru) and the heteroleptic [Ru(tpy)(1)][PF6] (2) are described. The complexes have been fully characterized in solution, including the H-1 NMR spectroscopic characterization of the paramagnetic [Co(1)(2)][PF6](2). Cyclic voltammetric data are consistent with the tert-butyl substituent being slightly electron releasing. The single crystal structures of [Zn(1)(2)][PF6](2) and [Ru(1)(2)][PF6](2) have been determined; the compounds are essentially isomorphous. The packing of the cations is such that the tert-butyl substituents are accommodated in pockets between the tpy domains of adjacent cations, and as a consequence, the {M(tpy)(2)}-embrace that is a ubiquitous feature of many related structures is not observed.