title: Unexpected reversible pyrazine based methylation in a Ru(II) complex bearing a pyrazin-2'-yl-1,2,4-triazolato ligand and its effect on acid/base and photophysical properties.
abstract: The regioselective methylation of a ruthenium polypyridyl complex bearing both a 1,2,4-triazolato and a pyrazine moiety is reported. In contrast to previous studies in which methylation of the 1,2,4-triazolato ring was observed, in the present system methylation takes place exclusively at the non-coordinated nitrogen of the pyrazine ring. The monomethylation is confirmed by (1)H NMR spectroscopy and ESI-MS and the electronic properties of the methylated complexes are studied by UV/vis absorption, emission, surface enhanced, resonance and transient resonance Raman spectroscopy. Ligand deuteriation is used to simplify the (1)H NMR spectra and to assign definitively the Raman spectra. Acid-base studies show that the triazolato ring of the N-methylated complexes can be protonated at low pH and that at high pH the N-methyl group can be deprotonated reversibly. Furthermore it is shown that under conditions where the methyl group is deprotonated, demethylation occurs to recover the initial complex.
authors.affiliation: SRC for Solar Energy Conversion, School of Chemical Sciences, Faculty of Science and Health, Dublin City University, Dublin 9, Ireland.
authors.forename: Claire
authors.initials: C
authors.lastname: Brennan
authors.forename: Apparao
authors.initials: A
authors.lastname: Draksharapu
authors.forename: Wesley R
authors.initials: WR
authors.lastname: Browne
authors.forename: John J
authors.initials: JJ
authors.lastname: McGarvey
authors.forename: Johannes G
authors.initials: JG
authors.lastname: Vos
authors.forename: Mary T
authors.initials: MT
authors.lastname: Pryce
mesh_terms: D000136:Acid-Base Equilibrium; D008024:Ligands; D008745:Methylation; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D055668:Photochemical Processes; D011719:Pyrazines / Q000737:chemistry*; D012428:Ruthenium / Q000737:chemistry*; D013237:Stereoisomerism; D014230:Triazoles / Q000737:chemistry*
chemical_list: D008024:Ligands; D009942:Organometallic Compounds; D011719:Pyrazines; D014230:Triazoles; D012428:Ruthenium