Controlled mono- and double-Heck reaction catalyzed by a dicarbene dipalladium complex

Heck Migratory Insertion Catalyzed by a Single Pt Atom Site

Single-atom catalysts (SACs) have generated excitement for their potential to downsize metal particles to the atomic limit with engineerable local environments and improved catalytic reactivities and selectivities. However, successes have been limited to small-molecule transformations with little progress toward targeting complex-building reactions, such as metal-catalyzed cross-coupling. Using a supercritical carbon-dioxide-assisted protocol, we report a heterogeneous single-atom Pt-catalyzed Heck reaction, which provides the first C-C bond-forming migratory insertion on SACs. Our quantum mechanical computations establish the reaction mechanism to involve a novel C-rich coordination site (i.e., PtC4) that demonstrates an unexpected base effect. Notably, the base was found to transiently modulate the coordination environment to allow migratory insertion into an M-C species, a process with a high steric impediment with no previous example on SACs. The studies showcase how SACs can introduce coordination structures that have remained underexplored in catalyst design. These findings offer immense potential for transferring the vast and highly versatile reaction manifold of migratory-insertion-based bond-forming protocols to heterogeneous SACs.

Effect of methylene versus ethylene linkers on structural properties of tert-butyl and mesityl bis(imidazolium) bromide salts

The crystal structures of ligand precursor bis­(imidaozolium) salts 1,1′-methyl­enebis(3-tert-butyl­imidazolium) dibromide monohydrate, C₁₅H₂₆N₄⁺·2Br⁻·H₂O or [^tBuNHC₂Me][Br]₂·H₂O, 1,1′-(ethane-1,2-di­yl)bis­(3-tert-butyl­imidazolium) dibromide dihydrate, C₁₆H₂₈N₄⁺·2Br⁻·2H₂O or [^tBuNHC₂Et][Br]₂·2H₂O, 1,1′-methyl­enebis[3-(2,4,6-tri­methyl­phen­yl)imidazolium] dibromide dihydrate, C₂₅H₃₀N₄²⁺·2Br⁻·2H₂O or [^MesNHC₂Me][Br]₂·2H₂O, and 1,1′-1,1′-(ethane-1,2-di­yl)bis­[3-(2,4,6-tri­methyl­phen­yl)imidazolium] dibromide tetra­hydrate, C₂₆H₃₂N₄²⁺·2Br⁻·4H₂O or [^MesNHC₂Et][Br]₂·4H₂O, are reported. At 293 K, [^tBuNHC₂Me][Br]₂·H₂O crystallizes in the P2₁/c space group, while [^tBuNHC₂Et][Br]₂·2H₂O crystallizes in the P2₁/n space group at 100 K. At 112 K, [^MesNHC₂Me][Br]₂·2H₂O crystallizes in the ortho­rhom­bic space group Pccn while [^MesNHC₂Et][Br]₂·4H₂O crystallizes in the P2₁/c space group at 100 K.

The crystal structures of ligand precursor bis­(imidazolium) salts 1,1′-methyl­enebis(3-tert-butyl­imidazolium) dibromide monohydrate, C₁₅H₂₆N₄⁺·2Br⁻·H₂O or [^tBuNHC₂Me][Br]₂·H₂O, 1,1′-(ethane-1,2-di­yl)bis­(3-tert-butyl­imidazolium) dibromide dihydrate, C₁₆H₂₈N₄⁺·2Br⁻·2H₂O or [^tBuNHC₂Et][Br]₂·2H₂O, 1,1′-methyl­enebis[3-(2,4,6-tri­methyl­phen­yl)imidazolium] dibromide dihydrate, C₂₅H₃₀N₄²⁺·2Br⁻·2H₂O or [^MesNHC₂Me][Br]₂·2H₂O, and 1,1′-(ethane-1,2-di­yl)bis­[3-(2,4,6-tri­methyl­phen­yl)imidazolium] dibromide tetra­hydrate, C₂₆H₃₂N₄²⁺·2Br⁻·4H₂O or [^MesNHC₂Et][Br]₂·4H₂O, are reported. At 293 K, [^tBuNHC₂Me][Br]₂·H₂O crystallizes in the P2₁/c space group, while [^tBuNHC₂Et][Br]₂·2H₂O crystallizes in the P2₁/n space group at 100 K. At 112 K, [^MesNHC₂Me][Br]₂·2H₂O crystallizes in the ortho­rhom­bic space group Pccn while [^MesNHC₂Et][Br]₂·4H₂O crystallizes in the P2₁/c space group at 100 K. Bond distances and angles within the imidazolium rings are generally comparable among the four structures. All four bis­(imidazolium) salts co-crystallize with one to four mol­ecules of water.

trans-Hydroborationvs.1,2-reduction: divergent reactivity of ynones and ynoates in Lewis-base-catalyzed reactions with pinacolborane

In the presence of phosphine catalyst and pinacolborane, ynones undergo 1,2-reduction while ynoates undergotrans-hydroboration. Mechanistic insights into the two competing pathways lay grounds for control of selectivity in these processes.

Hg(ii) and Pd(ii) complexes with a new selenoether bridged biscarbene ligand: efficient mono- and bis-arylation of methyl acrylate with a pincer biscarbene Pd(ii) precatalyst

New selenoether (CSeC) bridged carbene complexes of Hg(ii) and Pd(ii) have been prepared; a pincer Pd(ii) complex showed catalytic activity in mono- and double-Heck reactions.

Palladium nanoparticles supported in a polymeric membrane: an efficient phosphine-free “green” catalyst for Suzuki–Miyaura reactions in water

Palladium(0) nanoparticles supported on a polymeric membrane, CA/Pd(0), were found to be a highly efficient “dip catalyst” (heterogeneous catalyst) for Suzuki–Miyaura cross-coupling reactions.