Abstract
The organonickel complexes [Ni(Phbpy)X] (X = Br, OAc, CN) were obtained for the first time in a direct base-assisted arene C(sp2)–H cyclometalation reaction from the rather unreactive precursor materials NiX2 and HPhbpy (6-phenyl-2,2′-bipyridine) or from the versatile precursor [Ni(HPhbpy)Br2]2. Different from previously necessary C‒Br oxidative addition at Ni(0), an extended scan of reaction conditions allowed quantitative access to the title compound from Ni(II) on synthetically useful timescales through base-assisted C‒H activation in nonpolar media at elevated temperature. Optimisation of the reaction conditions (various bases, solvents, methods) identified 1:2 mixtures of acetate and carbonate as unrivalled synergetic base pairs in the optimum protocol that holds promise as a readily usable and easily tuneable access to a wide range of direct nickelation products. While for the base-assisted C‒H metalation of the noble metals Ru, Ir, Rh, or Pd, this acetate/carbonate method has been established for a few years, our study represents the leap into the world of the base metals of the 3d series.
Highlights
Metal-driven C(sp2 )-H activation and turnover of the resulting metalated species in catalytic processes has for a long time been the domain of heavy elements from the 4d and 5d rows, such as ruthenium, iridium and, especially, palladium
Constable et al introduced cycloruthenation, cycloplatination, and cyclopalladation through C-H activation of aryl/N-donor moieties [5,6]. This straightforward synthetic approach coupled with the potential diversity of π-conjugated derivatives of CN ligands to tailor photophysical properties led to intensive development in the field with more than 1000 congeners published today [7,8,9,10,11,12,13,14,15,16,17,18,19]
3) we identified the combination of high-boiling nonpolar solvents acetate/carbonateasas aa identified the combination of high-boiling nonpolar solvents andand acetate/carbonate homogeneous/heterogeneous base couple to enable rather rapid and very efficient homogeneous/heterogeneous base couple to enable rather rapid and very efficientnickelation
Summary
Metal-driven C(sp2 )-H activation and turnover of the resulting metalated species in catalytic processes has for a long time been the domain of heavy elements from the 4d and 5d rows, such as ruthenium, iridium and, especially, palladium. Constable et al introduced cycloruthenation, cycloplatination, and cyclopalladation through C-H activation (direct cyclometalation) of aryl/N-donor moieties [5,6]. This straightforward synthetic approach coupled with the potential diversity of π-conjugated derivatives of CN ligands to tailor photophysical properties led to intensive development in the field with more than 1000 congeners published today [7,8,9,10,11,12,13,14,15,16,17,18,19].
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