title: Selective para-halogenation and dimerization of N,C,N'-arylruthenium(II) and -(III) 2,2':6',2''-terpyridine cations.
abstract: The N,C,N'-bonded arylruthenium 2,2':6',2''-terpyridine (tpy) complex salts [Ru(NCN)(tpy)](Cl) ([1a](Cl), NCN = 2,6-bis[(dimethylamino)methyl]phenyl) and [Ru(N--C--N)(tpy)](PF(6)), ([2a](PF(6)), N--C--N = 2,6-bis(2-pyridyl)phenyl) can be halogenated under very mild conditions by oxidation with copper(II) halogen salts. Halogenation occurs exclusively para to the site of metalation and yields the cations [Ru(4-R-NCN)(tpy)](+) (R = Cl, [1b](+) and R = Br [1c](+)) and [Ru(4-R-N--C--N)(tpy)](+) (R = Cl, [2b](+) and R = Br [2c](+)). In the presence of an excess of oxidant relative to [1a](+), the halogenation reaction follows first order kinetics in the oxidized ruthenium complex. However, by using a small excess of copper(II) compared to [1a](+), dimerization of the complex cation to [{Ru(tpy)}(2)(mu-NCN-NCN)](4+) ([3](4+)) is observed, which obeys second order kinetics. Both halogenation (C-X coupling) and dimerization (C-C coupling) are a result of the unique properties of the ruthenium(III) complexes compared to their parent ruthenium(II) species. According to the nature of the highest occupied spin orbital (HOSO) in DFT calculations the unpaired electron in [1a](2+) and [2a](2+) is partially localized on the para position. The involvement of the cyclometalated ligand in the HOSO is supported by redox data and electronic absorption spectroscopy. The ruthenium(III) species can best be considered a persistent organometallic radical.
authors.affiliation: Chemical Biology & Organic Chemistry, Debije Institute for Nanomaterials Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
authors.forename: Sipke H
authors.initials: SH
authors.lastname: Wadman
authors.forename: Remco W A
authors.initials: RW
authors.lastname: Havenith
authors.forename: Martin
authors.initials: M
authors.lastname: Lutz
authors.forename: Anthony L
authors.initials: AL
authors.lastname: Spek
authors.forename: Gerard P M
authors.initials: GP
authors.lastname: van Klink
authors.forename: Gerard
authors.initials: G
authors.lastname: van Koten
mesh_terms: D000042:Absorption; D019281:Dimerization; D004563:Electrochemistry; D004583:Electrons; D054879:Halogenation; D008024:Ligands; D008958:Models, Molecular; D008968:Molecular Conformation; D009584:Nitrogen / Q000737:chemistry; D009942:Organometallic Compounds / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry*; D011789:Quantum Theory; D012428:Ruthenium / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013379:Substrate Specificity; D013997:Time Factors
chemical_list: C517923:(2,2'-6',2'')-terpyridine; D008024:Ligands; D009942:Organometallic Compounds; D011725:Pyridines; D012428:Ruthenium; D009584:Nitrogen