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. 2020 Feb 24;25(4):997.
doi: 10.3390/molecules25040997.

Direct Base-Assisted C‒H Cyclonickelation of 6-Phenyl-2,2'-bipyridine

Nicolas Vogt  1 , Vasily Sivchik  2   3 , Aaron Sandleben  1 , Gerald Hörner  4   5 , Axel Klein  1
Affiliations

Direct Base-Assisted C‒H Cyclonickelation of 6-Phenyl-2,2'-bipyridine

Nicolas Vogt et al. Molecules. .

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.

Keywords: C–H activation; base-assisted; cyclometalation; cyclonickelation; organonickel.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Scheme 1
Scheme 1
Cyclonickelation of C(sp2)‒H bonds with monodentate and bidentate N-heterocyclic directing groups.
Scheme 2
Scheme 2
Examples of base-assisted cyclonickelations and scope of this work.
Scheme 3
Scheme 3
Cyclonickelation methods A–C and prepared compounds.
Figure 1
Figure 1
Ellipsoid view (two asymmetric units resulting in a binuclear structure) of [Ni(HPhbpy)Br2]2 (left) and crystal structure of [Ni(HPhbpy)Br2]2 viewed along the a axis (right). Ellipsoids are drawn at the 50% probability level.
Figure 2
Figure 2
Ellipsoid view of [Ni(Phbpy)(OAc)] (left) and crystal structure viewed along the c axis (right). Ellipsoids are drawn at the 50% probability level.
Figure 3
Figure 3
Yields of the cyclometalation reaction in various solvents, as monitored using UV-vis absorption spectroscopy. The traces represent the reaction entries 14, 15, 16, 18 and 19 in Table 2.
See this image and copyright information in PMC

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