@article{TenderaSchaubKrahfussetal.2020,
  author    = {Tendera, Lukas and Schaub, Thomas and Krahfuss, Mirjam J. and Kuntze-Fechner, Maximilian W. and Radius, Udo},
  title     = {Large vs. Small NHC Ligands in Nickel(0) Complexes: The Coordination of Olefins, Ketones and Aldehydes at [Ni(NHC)\(_{2}\)]},
  series = {European Journal of Inorganic Chemistry},
  volume    = {2020},
  journal   = {European Journal of Inorganic Chemistry},
  number    = {33},
  doi       = {10.1002/ejic.202000493},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-216058},
  pages     = {3194 -- 3207},
  year      = {2020},
  abstract  = {Investigations concerning the reactivity of Ni(0) complexes [Ni(NHC)\(_{2}\)] of NHCs (N-heterocyclic carbene) of different steric demand, Mes\(_{2}\)Im (= 1,3-dimesitylimidazoline-2-ylidene) and iPr\(_{2}\)Im (= 1,3-diisopropyl-imidazoline-2-ylidene), with olefins, ketones and aldehydes are reported. The reaction of [Ni(Mes\(_{2}\)Im)\(_{2}\)] 1 with ethylene or methyl acrylate afforded the complexes [Ni(Mes\(_{2}\)Im)\(_{2}\)(η\(^{2}\)-C\(_{2}\)H\(_{4}\))] 3 and [Ni(Mes\(_{2}\)Im)\(_{2}\)(η\(^{2}\)-(C,C)-H\(_{2}\)C=CHCOOMe)] 4, as it was previously reported for [Ni\(_{2}\)(iPr\(_{2}\)Im)\(_{4}\)(µ-(η\(^{2}\):η\(^{2}\))-COD)] 2 as a source for [Ni(iPr\(_{2}\)Im)\(_{2}\)]. In contrast to 2, complex 1 does not react with sterically more demanding olefins such as tetramethylethylene, 1,1-diphenylethylene and cyclohexene. The reaction of [Ni(NHC)\(_{2}\)] with more π-acidic ketones or aldehydes led to formation of complexes with side-on η\(^{2}\)-(C,O)-coordinating ligands: [Ni(iPr\(_{2}\)Im)\(_{2}\)(η\(^{2}\)-O=CH\(^{t}\)Bu)] 5, [Ni(iPr\(_{2}\)Im)\(_{2}\)(η\(^{2}\)-O=CHPh)] 6, [Ni(iPr\(_{2}\)Im)\(_{2}\)(η\(^{2}\)-O=CMePh)] 7, [Ni(iPr\(_{2}\)Im)\(_{2}\)(η\(^{2}\)-O=CPh\(_{2}\))] 8, [Ni(iPr\(_{2}\)Im)\(_{2}\)(η\(^{2}\)-O=C(4-F-C\(_{6}\)H\(_{4}\))\(_{2}\))] 9, [Ni(iPr\(_{2}\)Im)\(_{2}\)(η\(^{2}\)-O=C(OMe)(CF\(_{3}\)))] 10 and [Ni(Mes\(_{2}\)Im)\(_{2}\)(η\(^{2}\)-O=CHPh)] 11, [Ni(Mes\(_{2}\)Im)\(_{2}\)(η\(^{2}\)-O=CH(CH(CH\(_{3}\))\(_{2}\)))] 12, [Ni(Mes\(_{2}\)Im)\(_{2}\)(η\(^{2}\)-O=CH(4-NMe\(_{2}\)-C\(_{6}\)H\(_{4}\)))] 13, [Ni(Mes\(_{2}\)Im)\(_{2}\)(η\(^{2}\)-O=CH(4-OMe-C\(_{6}\)H\(_{4}\)))] 14, [Ni(Mes\(_{2}\)Im)\(_{2}\)(η\(^{2}\)-O=CPh\(_{2}\))] 15 and [Ni(Mes\(_{2}\)Im)\(_{2}\)(η\(^{2}\)-O=C(4-F-C\(_{6}\)H\(_{4}\))\(_{2}\))] 16. The reaction of 1 and 2 with these simple aldehydes and ketones does not lead to a significantly different outcome, but NHC ligand rotation is hindered for the Mes\(_{2}\)Im complexes 3, 4 and 11-16 according to NMR spectroscopy. The solid-state structures of 3, 4, 11 and 12 reveal significantly larger C\(_{NHC}\)-Ni-C\(_{NHC}\) angles in the Mes\(_{2}\)Im complexes compared to the iPr\(_{2}\)Im complexes. As electron transfer in d\(^{8}\)- (or d\(^{10}\)-) ML\(_{2}\) complexes to π-acidic ligands depends on the L-M-L bite angle, the different NHCs lead thus to a different degree of electron transfer and activation of the olefin, aldehyde or ketone ligand, i.e., [Ni(iPr\(_{2}\)Im)\(_{2}\)] is the better donor to these π-acidic ligands. Furthermore, we identified two different side products from the reaction of 1 with benzaldehyde, trans-[Ni(Mes\(_{2}\)Im)\(_{2}\)H(OOCPh)] 17 and [Ni\(_{2}\)(Mes\(_{2}\)Im)\(_{2}\)(µ\(_{2}\)-CO)(µ\(_{2}\)-η\(^{2}\)-C,O-PhCOCOPh)] 18, which indicate that radical intermediates and electron transfer processes might be of importance in the reaction of 1 with aldehydes and ketones.},
  language  = {en}
}