A pyrazolyl-terminated 2,2':6',2''-terpyridine ligand : Iron(II), ruthenium(II) and palladium(II) complexes of 4'-(3,5-dimethylpyrazol-1-yl)-2,2':6',2''-terpyridine

The preparation of 4`-(3,5-dimethylpyrazol-1-yl)-2,2`:6`,2 ``-terpyridine (2) under acidic conditions results in the formation of the salts [H(2)2][MeOSO3](2) and [H(2)2][EtOSO3](2), treatment of which with base leads to neutral 2. The structure of [H(2)2][EtOSO3](2) center dot H2O has been established by single crystal X-ray diffraction. The complexes [Fe(2)(2)][PF6](2) and [Ru(2)(2)][PF6](2) have been prepared and characterized, and the single crystal structure determination of [Ru(2)(2)][PF6](2) is reported; [Fe(2)(2)][PF6](2) is isostructural with [Ru(2)(2)][PF6](2). Treatment of [Fe(2)(2)](2+) with PdCl2 produces [Pd(2)Cl](+), isolated and structurally characterized as the hexafluoridophosphate salt, illustrating that metal exchange within the tpy-binding domain occurs in preference to palladium(II) coordination by the N-donor atom of the pendant 3,5-dimethylpyrazol-1-yl unit in 2. [Pd(2)Cl](2+) can also be prepared from PdCl2 and [H(2)2][MeOSO3](2) in refluxing methanol.