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Petrovic D, Bannenberg T, Randoll S, Jones PG, Tamm M: Synthesis and reactivity of copper (I) complexes containing a bis (imidazolin-2-imine) pincer ligand. Dalton Trans. 2007 Jul 14;(26):2812-22. Epub 2007 May 2.
The new pincer ligand 2,6-bis [(1,3-di-tert-butylimidazolin-2-imino) methyl] pyridine (TL (tBu)) has been prepared in high yield from 2,6-bis (hydroxymethyl) pyridine (1) and 1,3-di-tert-butylimidazolin-2-imine (3). Reaction of TL (tBu) with [Cu (MeCN) 4] PF6 affords the highly reactive copper (I) complex [(TL (tBu)) Cu] PF6, [5] PF6, which forms the stable copper (I) isocyanide complexes [6a] PF6 (nu (CN) = 2179 cm (-1)) and [6b] PF6 (nu (CN) = 2140 cm (-1)) upon addition of tert-butyl or 2,6-dimethylphenyl isocyanide, respectively. For the cations 6a and 6b, DFT calculations reveal ground-state electronic structures of the type [(TL (tBu)-kappaN (1):kappaN (2)) Cu (CNR)] with tricoordinate geometries around the copper atoms. Exposure of [5] PF6 to the air readily leads to trapping of atmospheric CO2 to form the square-planar complex [(TL (tBu)) Cu (HCO3-kappaO)] PF6, [7] PF6, with the bicarbonate ligand adopting a rarely observed monodentate coordination mode. In chlorinated solvents such as dichloromethane or chloroform, [5] PF (6) rapidly abstracts chloride by reductive dechlorination of the solvent to yield [(TL (tBu)) CuCl] PF6, [8] PF6 quantitatively. Reaction of TL (tBu) with copper (I) bromide or chloride affords complexes 9a and 9b, respectively, for which X-ray diffraction analysis, low-temperature NMR experiments and DFT calculations reveal the presence of a kappa (2)-coordinated ligand of the type [(TL (tBu)-kappaN (1):kappaN (2)) CuX]. In solution, complex 9b undergoes slow disproportionation forming the mixed-valence copper (II)/copper (I) system [(TL (tBu)) CuCl][CuCl2], [8] CuCl2 with a linear dichlorocuprate (I) counterion. |
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