Iridium(III) complexes with a trifunctional pincer ligand containing protic N-heterocyclic carbene (pNHC), pyridine, and imine donor groups were obtained in two sequential steps: (i) protonation of 2-(1-(2,6-diisopropylphenyl-imino)ethyl)-6-(1-imidazolyl)pyridine (L-CH; the superscript imidazole ring) with HBF4-Et2O to give the imidazolium salt specifies the position of the tautomerizable H atom in the [HLCH](+)[BF4](-) (protonation always occurs at the imidazole N atom) and (ii) metalation of the latter with [Ir(cod)(mu-Cl)](2) to give the hydrido pincer complex [Ir(H)(Cl)(NCMe){L-NH-kappa N-3(imine),NPy,CNHC}](+)[BF4](-) (3(+)[BP4](-)). Substitution of MeCN in 3(+)[BF4](-) by treatment with triisopropylphosphine gave the analogue [Ir(H)(COP(i-Pr)(3){L-NH-kappa N-3(imine),N-py,C-NHC}](+)[BF4](-)(4(+)BF(4)](-)). Chloride abstraction from 3(+)[BF4](-) by AgBF4 gave [Ir(H)(NCMe)(2){L-NH-kappa(Nimine,Npy,CNHC)-N-3}](2+) [BF4-](2) (5(2+)[BF4-](2)). The centrosymmetric dinuclear Ir(III) complex [Ir(H)(NCMe){mu-(L-CH-H)-kappa N-3(imine),N-py,C2,kappa N3}](2)(2+)[B-(C6F5)(3)F-](2) (6(2+)[B(C6F5)(3)F-](2)) was obtained after deprotonation of 5(2+)[BF4-](2) with KO-t-Bu, followed by addition of B(C6F5)(3). It contains two Ir pincer moieties, each with a N-imine,N-py,C2 donor set, which are connected by the Ir-N bonds involving the imidazolide rings, leading to a mu-C,N bridging mode for the latter. Remarkably, all of the donor atoms in the tetradentate bridging chelating ligands are chemically different. The molecular structures of 3(+)[BF4](-)center dot CH2Cl2, 4(+)[BF4](-)center dot CH2Cl2, 5(2+)[BF4-](2)center dot 2CH(2)Cl(2), and 6(2+)[B(C6F5)(3)F-]2 center dot 4CH(2)Cl(2) have been determined by X-ray diffraction.
Oligomerisation of ethylene to linear α-olefins by tetrahedral cobalt(II) precursors stabilised by benzo[b]thiophen-2-yl-substituted (imino)pyridine ligands
摘要:
On activation by MAO, 2-(imino)pyridine cobalt dichlorides bearing a benzo[b]thiophen-2-yl substituent in the 6-position of the pyridine ring oligomerise ethylene to alpha-olefins with turn-over-frequencies as high as 1.5 x 10(6) mol of C2H4 converted (mol of Co x h)(-1) and productivities as high as 3769 kg of oligomers (mol of Co x h x bar)(-1). Aldimine precursors are more active than ketimine analogues, yet ketimines give higher molecular weight oligomers. (C) 2003 Elsevier B.V. All rights reserved.