title: Carbonate formation within a nickel dimer: synthesis of a coordinatively unsaturated bis(mu-hydroxo) dinickel complex and its reactivity toward carbon dioxide.
abstract: The tridentate aminopyridine ligand bearing a bulky tert-butyl substituent at the amine nitrogen, tert-butyl-dipicolylamine (tBuDPA), occupies three coordination sites in six-coordinate complexes of nickel(ii), leaving the remaining three sites available for additional ligand binding and activation. New crystallographically characterized complexes include two mononuclear species with 1:1 metal:ligand complexation: a trihydrate solvate (1.3H(2)O) and a monohydrate biacetonitrile solvate (1.H(2)O.2CH(3)CN). Complexation in the presence of sodium hydroxide results in a bis(mu-hydroxo) complex (2), the bridging hydroxide anions of which are labile and become displaced by methoxide anions in methanol solvent, affording bis-methoxo-bridged (4). Nickel(II) centers in 2 are five-coordinate and antiferromagnetically coupled (with J = -31.4(5) cm(-1), H = -2JS(1)S(2), in agreement with Ni-O-Ni angle of 103.7 degrees). Bridging hydroxide or alkoxide anions in coordinatively unsaturated dinuclear nickel(II) complexes with tBuDPA react as active nucleophiles. 2 readily performs carbon dioxide fixation, resulting in the formation of a bis(mu-carbonato) tetrameric complex (3), which features a novel binding geometry in the form of an inverted butterfly-type nickel-carbonate core. Temperature-dependent magnetic measurements of tetranuclear carbonato-bridged revealed relatively weak antiferromagnetic coupling (J(1) = -3.1(2) cm(-1)) between the two nickel centers in the core of the cluster, as well as weak antiferromagnetic pairwise interactions (J(2) = J(3) = -4.54(5) cm(-1)) between central and terminal nickel ions.
authors.affiliation: Department of Chemistry, Tufts University, 62 Talbot Avenue, Medford, Massacusetts 02155, USA.
authors.forename: Jeffrey P
authors.initials: JP
authors.lastname: Wikstrom
authors.forename: Alexander S
authors.initials: AS
authors.lastname: Filatov
authors.forename: Elena A
authors.initials: EA
authors.lastname: Mikhalyova
authors.forename: Michael
authors.initials: M
authors.lastname: Shatruk
authors.forename: Bruce M
authors.initials: BM
authors.lastname: Foxman
authors.forename: Elena V
authors.initials: EV
authors.lastname: Rybak-Akimova
mesh_terms: D000631:Aminopyridines / Q000737:chemistry; D002245:Carbon Dioxide / Q000737:chemistry*; D002254:Carbonates / Q000737:chemistry*; D018360:Crystallography, X-Ray; D019281:Dimerization; D006900:Hydroxylation; D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry*
chemical_list: D000631:Aminopyridines; D002254:Carbonates; D008024:Ligands; D002245:Carbon Dioxide; D009532:Nickel