Heterogeneous catalysis with nickel-on-graphite (Ni/C_g)

Abstract

Impregnation of nickel(II) onto graphite, upon reduction in situ, leads to a reagent that catalyzes both C-H and C-C bond formations between aryl halides, or aryl pseudo-halides, and various organometallics. Cross-couplings, most notably with tosylates, can lead to either reduced aromatics, biaryls, or styrenes as products under the influence of Ni/Cg. The catalyst is inexpensive, non-pyrophoric, and reusable.

Microwave‐Assisted Cross‐Coupling and Hydrogenation Chemistry by Using Heterogeneous Transition‐Metal Catalysts: An Evaluation of the Role of Selective Catalyst Heating

“…[13] Importantly, compared to previous studies by the same group employing conventional heating in an oil bath dating back to the late 1990s, [22] the reaction times for most of these transformations could be reduced from several hours to a few minutes by using sealedvessel microwave processing. [13][14][15]21] Choosing the Negishi cross-coupling of aryl chloride 1 with organozinc reagent 2 as our first model reaction (Scheme 1a) we wanted to see if the dramatic rate enhancement on going from 16 h employing oil-bath heating at 60 8C, [23] to 15 min under microwave conditions at 150 8C [13] was due to selective heating of the strongly microwave-absorbing Ni/C catalyst (see below), or could be rationalized by a simple thermal effect as a result of the significantly higher reaction temperature. [24] As a second example, we have selected the Cu/C-promoted Ullmann-type diaryl ether formation involving aryl bromide 4 and phenol 5 (Scheme 1b).…”

“…www.chemeurj.org tions of this type [13][14][15]21] are essentially the result of a standard thermal effect, switching from reflux conditions to a sealed-vessel microwave experiment at significantly higher temperatures. As with other related examples recently investigated in our laboratories, [25,31] we ascribe the absence of a "specific microwave effect" in these cases to the fact that although the heterogeneous metal catalyst itself can be a strongly microwave absorbing material when irradiated under suitable conditions (Figure 1), [25] for the actual reaction mixtures containing several other microwave-absorbing components (substrates, ligand, additives, bases) any effect derived from selective heating of the comparatively small quantities of heterogeneous metal catalyst will be masked.…”

“…[17,52] 1,4-Diphenyl-1-butene (12): Comparison of the 1 H NMR spectrum with literature data [53] confirmed the identity of this compound. Cholestanol (14): White crystals; m.p. 141 8C (lit.…”

Nanocatalysts for Hiyama, Stille, Kumada, and Negishi C–C Coupling Reactions

“…109 Similarly, Ni/graphite could catalyze cross-couplings between vinylic zirconocenes, derived from terminal alkynes, and aryl halides under microwave irradiation leading to stereodefined styrenes in good yields. 110 The use of ligandless "homeopathic" Pd catalysts obtained in situ from Pd(OAc) 2 was a definite attempt to use Pd-NPs as the active catalysts in Negishi coupling. It was noted in the study by Alimardanov and coworkers that the use of ligand-free Pd was possible only when the Pd-substrate ratio was kept low, typically from 0.01 to 0.1 mol%.…”

Heterogeneous nickel catalyst for selective hydration of silanes to silanols

“…Despite the fact that Ni catalysts, such as sponge Ni (Raney Ni), have been used as a promoter or heterogeneous catalyst for hydrogenation of various compounds, advances in the field of heterogeneous non-noble metal catalyzed organic synthesis is still in its infancy. Recently, Ni NPs catalysts have been introduced as a new class of heterogeneous catalysts to overcome some economic and ecological problems [1][2][3][4]. As summarized in recent reviews by Yus et al [1] and Lipshutz et al [2], Ni NPs catalyze several organic transformations which are typically implemented by noble metal-based catalysts.…”