A zero-valent palladium cluster-organic framework

Regioselective Suzuki-Miyarua Cross-Coupling for Substituted 2,4-Dibromopyridines Catalyzed by C3-Symmetric Tripalladium Clusters

Multipalladium clusters possess peculiar structures and synergistic effects for reactivity and selectivity. Herein, C3-symmetric tripalladium clusters (1, 0.5 mol %) afford C2-regioselective SMCC of 2,4-dibromopyridine with phenylboronic acids or pinacol esters (C2:C4 up to 98:1), in contrast to Pd(OAc)2 in ligand-free conditions. In addition, similar C2-selectivity was achieved in Sonogashira, Negishi, and Kumada coupling reactions. This method highlights their powerful catalytic ability, exclusive C2-selectivity, broad substrate scope, efficient amplification, and multiple ligand-exchange feasibility and demonstrates that the conventional sites could be successfully regulated or even reversed by catalysts.

Photo-Assisted Bottom-Up Synthesis of Orange Phosphorus

A tubular strand of phosphorus composed of vectorially aligned pentagons has been theoretically predicted as a new allotrope of phosphorus with a polar structure, expecting potential applications. However, it has not been successfully synthesized yet due to the difficulty of creating isolated strands to avoid interchain bonding. Here, such an allotrope named "orange phosphorus" was successfully produced using a photo-assisted synthesis from an amorphous film of solution-processable Na2P16 precursors. A green laser irradiation initiated the phase transition of precursors, inducing chemical reactions like topochemical polymerization and rearrangement, creating a 1D chain of orange phosphorus. 3D electron diffraction crystallography showed that the molecular structure of orange phosphorus consists of one-dimensional polar pentagonal-tubes made up of [P8]P2[ repeat units. Orange phosphorus demonstrates excellent piezoresistivity due to its high strain-sensitive 1D chain structure, showing strain-induced Raman shifts. Its gauge factor exceeds those of 2D materials such as black phosphorus and transition metal dichalcogenides. These findings indicate that orange phosphorus has great potential for use in strain sensor applications.

A coordination polymer with a silylene-supported Pd6 core as an efficient heterogeneous hydrogenation catalyst

A hexanuclear palladium cluster supported by two silylene units was readily linked by molecules of a linear ditopic isocyanide to afford a coordination polymer that retained the core Pd6(SiPh2)2Cl2 framework. The obtained coordination polymer exhibited good performance as a heterogeneous catalyst in the hydrogenation of various alkenes in common organic solvents and in protic solvents such as H2O. Furthermore, the obtained coordination polymer showed sufficient stability during the hydrogenation in order for it to be recycled and reused.

Two-Dimensional Silver-Isocyanide Frameworks

Metal-organic frameworks (MOFs) have been widely studied due to their versatile applications and easily tunable structures. However, heteroatom-metal coordination dominates the MOFs community, and the rational synthesis of carbon-metal coordination-based MOFs remains a significant challenge. Herein, two-dimensional (2D) MOFs based on silver-carbon linkages are synthesized through the coordination between silver(I) salt and isocyanide-based monomers at ambient condition. The as-synthesized 2D MOFs possess well-defined crystalline structures and a staggered AB stacking mode. Most interestingly, these 2D MOFs, without π-π stacking between layers, exhibit narrow band gaps down to 1.42 eV. As electrochemical catalysts for converting CO2 to CO, such 2D MOFs demonstrate Faradaic efficiency over 92 %. Surprisingly, the CO2 reduction catalyzed by these MOFs indicates favorable adsorption of CO2 and *COOH on the active carbon sites of the isocyanide groups rather than on silver sites. This is attributed to the critical σ donor role of isocyanides and the corresponding ligand-to-metal charge-transfer effect. This work not only paves the way toward a new family of MOFs based on metal-isocyanide coordination but also offers a rare platform for understanding the electrocatalysis processes on strongly polarized carbon species.

Heterogenization of Palladium Trimer and Nanoparticles Through Polymerization Boosted Catalytic Efficiencies in Recyclable Coupling and Reduction Reactions

The development of heterogeneous palladium catalysts has shown continuous vitality in the field of catalysis and materials. In this work, we report one concise free radical polymerization approach to accomplish the aromatic palladium trimer functionalized polymers PSSy-[Pd3]+ (2) and its derived palladium nanoparticles (3). Full characterizations could confirm the successful combination of cationic [Pd3]+ or nanoparticles with poly(p-sulfonated styrene) skeleton. Compared to their monomeric tri-palladium precursor (1) and common Pd(dba)2, Pd(PPh3)4, Pd(OAc)2, heterogeneous PSSy-[Pd3]+ (2) shows much superior catalytic activities (0.15 mol %, TOF=1333.3 h-1) in the SMCC reaction. The identically ligated PdNPs (3) are formed in-suit in the presence of NaBH4 and accomplish quantitative reduction of 4-nitrophenol in just 320 s (0.50 mol %, TOF=2250 h-1). Moreover, these heterogeneous catalysts are reused for 5-6 times without significant loss of catalytic activity. Their superior catalytic ability is probably attributed to the synergistic effect of polymer entanglement and the tri-palladium fragment. This work enlightens that the immobilization of palladium clusters or nanoparticles by polymerization could offer multiple advantages in stability, efficiency and recyclability for their involved catalyses and show far-reaching future implications.

Pd8(PDip)6: Cubic, Unsaturated, Zerovalent

Atomically precise nanoclusters hold promise for supramolecular assembly and (opto)electronic- as well as magnetic materials. Herein, this work reports that treating palladium(0) precursors with a triphosphirane affords strongly colored Pd8(PDip)6 that is fully characterized by mass spectrometry, heteronuclear and Cross-Polarization Magic-Angle Spinning (CP-MAS) NMR-, infrared (IR), UV-vis, and X-ray photoelectron (XP) spectroscopies, single-crystal X-Ray diffraction (sc-XRD), mass spectrometry, and cyclovoltammetry (CV). This coordinatively unsaturated 104-electron Pd(0) cluster features a cubic Pd8-core, µ4-capping phosphinidene ligands, and is air-stable. Quantum chemical calculations provide insight to the cluster's electronic structure and suggest 5s/4d orbital mixing as well as minor Pd─P covalency. Trapping experiments reveal that cluster growth proceeds via insertion of Pd(0) into the triphosphirane. The unsaturated cluster senses ethylene and binds isocyanides, which triggers the rearrangement to a tetrahedral structure with a reduced frontier orbital energy gap. These experiments demonstrate facile cluster manipulation and highlight non-destructive cluster rearrangement as is required for supramolecular assembly.

Significantly enhanced catalytic performance of Pd nanocatalyst on AlOOH featuring abundant solid surface frustrated Lewis pair for improved hydrogen activation

The catalytic performance of a catalyst is significantly influenced by its ability to activate hydrogen. Constructing frustrated Lewis pairs (FLPs) with the capacity for hydrogen dissociation on non-reducible supports remains a formidable challenge. Herein, we employed a straightforward method to synthesize a layered AlOOH featuring abundant OH defects suitable for constructing solid surface frustrated Lewis pair (ssFLP). The results indicated that the AlOOH-80 (synthesized at 80 °C) possessed an appropriate crystalline structure conducive to generating numerous OH defects, which facilitated the formation of ssFLP. This was further evidenced by the minimal water adsorption in the AlOOH-80, inversely correlated with the quantity of defects in the catalyst. As expected, the Pd loaded onto AlOOH (Pd/AlOOH-80) exhibited excellent catalytic activity in hydrogenation reactions, attributed to abundant defects available for constructing ssFLP. Remarkably, the Pd/AlOOH-80 catalyst, with larger-sized Pd nanoparticles, displayed notably superior activity compared to commercial Pd/Al2O3 and Pd/C, both featuring smaller-sized Pd nanoparticles. Evidently, under the influence of ssFLP, the size effect of Pd nanoparticles did not dominate, highlighting the pivotal role of ssFLP in enhancing catalytic performance. This catalyst also exhibited exceptionally high stability, indicating its potential for industrial applications.