Issue 8, 2023

Nickel boryl complexes and nickel-catalyzed alkyne borylation

Abstract

The first nickel bis-boryl complexes cis-[Ni(iPr2ImMe)2(Bcat)2], cis-[Ni(iPr2ImMe)2(Bpin)2] and cis-[Ni(iPr2ImMe)2(Beg)2] are reported, which were prepared via the reaction of a source of [Ni(iPr2ImMe)2] with the diboron(4) compounds B2cat2, B2pin2 and B2eg2 (iPr2ImMe = 1,3-di-iso-propyl-4,5-dimethylimidazolin-2-ylidene; B2cat2 = bis(catecholato)diboron; B2pin2 = bis(pinacolato)diboron; B2eg2 = bis(ethylene glycolato)diboron). X-ray diffraction and DFT calculations strongly suggest that a delocalized, multicenter bonding scheme dictates the bonding situation of the NiB2 moiety in these square planar complexes, reminiscent of the bonding situation of “non-classical” H2 complexes. [Ni(iPr2ImMe)2] also efficiently catalyzes the diboration of alkynes using B2cat2 as the boron source under mild conditions. In contrast to the known platinum-catalyzed diboration, the nickel system follows a different mechanistic pathway, which not only provides the 1,2-borylation product in excellent yields, but also provides an efficient approach to other products such as C–C coupled borylation products or rare tetra-borylated compounds. The mechanism of the nickel-catalyzed alkyne borylation was examined by means of stoichiometric reactions and DFT calculations. Oxidative addition of the diboron reagent to nickel is not dominant; the first steps of the catalytic cycle are coordination of the alkyne to [Ni(iPr2ImMe)2] and subsequent borylation at the coordinated and, thus, activated alkyne to yield complexes of the type [Ni(NHC)22-cis-(Bcat)(R)C[double bond, length as m-dash]C(R)(Bcat))], exemplified by the isolation and structural characterization of [Ni(iPr2ImMe)22-cis-(Bcat)(Me)C[double bond, length as m-dash]C(Me)(Bcat))] and [Ni(iPr2ImMe)22-cis-(Bcat)(H7C3)C[double bond, length as m-dash]C(C3H7)(Bcat))].

Graphical abstract: Nickel boryl complexes and nickel-catalyzed alkyne borylation

Supplementary files

Article information

Article type
Edge Article
Submitted
22 avq 2022
Accepted
27 yan 2023
First published
27 yan 2023
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2023,14, 2215-2228

Nickel boryl complexes and nickel-catalyzed alkyne borylation

L. Tendera, F. Fantuzzi, T. B. Marder and U. Radius, Chem. Sci., 2023, 14, 2215 DOI: 10.1039/D2SC04690C

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