Rare-Earth Supported Nickel Catalysts for Alkyne Semihydrogenation: Chemo- and Regioselectivity Impacted by the Lewis Acidity and Size of the Support

Abstract

Bimetallic catalysts of nickel(0) with a trivalent rare-earth ion or Ga­(III), NiML3 (where L is [iPr2PCH2NPh]−, and M is Sc, Y, La, Lu, or Ga), were investigated for the selective hydrogenation of diphenylacetylene (DPA) to (E)-stilbene. Each bimetallic complex features a relatively short Ni–M bond length, ranging from 2.3395(8) Å (Ni–Ga) to 2.5732(4) Å (Ni–La). The anodic peak potentials of the NiML3 complexes vary from −0.48 V to −1.23 V, where the potentials are negatively correlated with the Lewis acidity of the M­(III) ion. Three catalysts, Ni–Y, Ni–Lu, and Ni–Ga, showed nearly quantitative conversions in the semihydrogenation of DPA, with NiYL3 giving the highest selectivity for (E)-stilbene. Initial rate studies were performed on the two tandem catalytic reactions: DPA hydrogenation and (Z)-stilbene isomerization. The catalytic activity in DPA hydrogenation follows the order Ni–Ga > Ni–La > Ni–Y > Ni–Lu > Ni–Sc. The ranking of catalysts by (Z)-stilbene isomerization initial rates is Ni–Ga ≫ Ni–Sc > Ni–Lu > Ni–Y > Ni–La. In operando 31P and 1H NMR studies revealed that in the presence of DPA, the Ni bimetallic complexes supported by Y, Lu, and La form the Ni­(η2-alkyne) intermediate, (η2-PhCCPh)­Ni­(iPr2PCH2NPh)2M­(κ2-iPr2PCH2NPh). In contrast, the Ni–Ga resting state is the Ni­(η2-H2) species, and Ni–Sc showed no detectable binding of either substrate. Hence, the mechanism of Ni-catalyzed diphenylacetylene semihydrogenation adheres to two different kinetics: an autotandem pathway (Ni–Ga, Ni–Sc) versus temporally separated tandem reactions (Ni–Y, Ni–Lu, Ni–La). Collectively, the experimental results demonstrate that modulating a base-metal center via a covalently appended Lewis acidic support is viable for promoting selective alkyne semihydrogenation.

Recent Advances in 2D Rare Earth Materials

“…[ 37,41–46 ] Briefly, RE ions have two ground‐state electron configurations including [Xe]4f n and [Xe]4f n −1 5d 1 . [ 41,47–49 ] The 4f electrons in 4f n configuration are localized core‐like and have a strong correlationship with n . [ 50–55 ] Localized 4f transitions including the f–d interconfigurational and f–f intraconfigurational transitions endow RE with atomic‐like optical transitions, which can be observed as sharp and various absorption or luminescence bands.…”

“…[37,[41][42][43][44][45][46] Briefly, RE ions have two ground-state electron configurations including [Xe]4f n and [Xe]4f n−1 5d 1 . [41,[47][48][49] The 4f electrons in 4f n configuration are localized core-like and have a strong correlationship with n. [50][51][52][53][54][55] Localized 4f transitions including the f-d interconfigurational and f-f intraconfigurational transitions endow RE with atomic-like optical transitions, which can be observed as sharp and various absorption or luminescence bands. [54,[56][57][58][59][60][61] In this way, RE has been widely applied in areas such as light emitting diode (LED), lasers, and bioimaging, whether as hosts or dopants.…”

Converting copper sulfide to copper with surface sulfur for electrocatalytic alkyne semi-hydrogenation with water

“…This transformation is also a classical model reaction to evaluate the performance of a newly developed catalyst or hydrogenation method [1][2][3][4][5][6][7][8] . Although significant progress has been achieved, current reports are still mainly relying on the expensive noble-metal catalysts (e.g., Pt, Pd, Ru, or their related alloys) [9][10][11][12][13] or complicated metal complexes [14][15][16][17] with gaseous hydrogen (H 2 ) or expensive and/or toxic organic hydrogen sources, causing severe concerns on the cost, safety, and sustainability. To solve these problems, an electrochemical strategy has been recently developed by our group for selective semi-hydrogenation of alkynes over a Pd-P cathode by using H 2 O as the hydrogen source 18 .…”

Rare‐Earth‐Based Metal–Organic Frameworks as Multifunctional Platforms for Catalytic Conversion

“…With the shielding effect of the filled 5s and 5p orbits, the unfilled 4f orbits are insensitive to the surrounding chemical environments, leading to well-defined electronic energy levels. [10][11][12][13] Due to their special structure, RE element-based materials display unique properties in many fields such as luminescence, [14][15][16][17][18] magnetic materials, [19] catalysis, [20][21][22][23][24] and energy conversion. [25][26][27] Compared with the well-constructed fabrication strategies of transition metal-based MOFs, RE-MOFs or RE-doped MOFs are less studied but can display satisfactory performance for catalysis.…”