The effect of outer-sphere environment on alkene epoxidation catalysis using an organic hydroperoxide oxidant is demonstrated for calix[4]arene-Ti single-sites grafted on amorphous vs crystalline delaminated zeotype (UCB-4) silicates as supports. A chelating calix[4]arene macrocyclic ligand helps enforce a constant Ti inner-sphere, as characterized by UV-visible and X-ray absorption spectroscopies, thus enabling the rigorous comparison of outer-sphere environments across different siliceous supports. These outer-sphere environments are characterized by solid-state H NMR spectroscopy to comprise proximally organized silanols confined within 12 membered-ring cups in crystalline UCB-4, and are responsible for up to 5-fold enhancements in rates of epoxidation by Ti centers.

Mo(0), W(0), Fe(0), Ru(0), Re(0), and Zn(0) nanoparticles—essentially base metals—are prepared as a general strategy by a sodium naphthalenide ([NaNaph])-driven reduction of simple metal chlorides in ethers (1,2-dimethoxyethane (DME), tetrahydrofuran (THF)). All the nanoparticles have diameters ≤10 nm, and they can be obtained either as powder samples or long-term stable suspensions. Direct follow-up reactions (e.g., Mo(0)+S8, FeCl3+AsCl3, ReCl5+MoCl5), moreover, allow the preparation of MoS2, FeAs2, or Re4Mo nanoparticles of similar size as the pristine metals (≤10 nm).

Although essentially molecular noble metal species provide active sites and highly tunable platforms for the design of supported catalysts, the susceptibility of the metals to reduction and aggregation and the consequent loss of catalytic activity and selectivity limit opportunities for their application. Here, we demonstrate a new construct to stabilize supported molecular noble-metal catalysts, taking advantage of sterically bulky ligands on the metal that serve as surrogate supports and isolate the active sites under conditions involving steady-state catalytic turnover in a reducing environment. The result is demonstrated with an iridium pair-site catalyst incorporating P-bridging calix[4]arene ligands dispersed on siliceous supports, chosen as prototypes because they offer weakly interacting surfaces on which metal aggregation is prone to occur. This catalyst was used for the hydrogenation of ethylene in a flow reactor. Atomic-resolution imaging of the Ir centers and spectra of the catalyst before and after use show that the metals resisted aggregation and deactivation, remaining atomically dispersed and accessible for catalysis. This strategy thus allows the stabilization of the catalysts even when they are weakly anchored to supports.

Tungsten nanoparticles were obtained from liquid-ammonia-based synthesis via reduction of WCl6 with dissolved sodium. The W(0) nanoparticles exhibit a diameter of 1-2 nm and can be dispersed in alkanes, showing a grayish-orange color due to red-shifted plasmon resonance absorption.

Metallic titanium (Ti(0)) nanoparticles, 1.5 ± 0.4 nm in diameter, are obtained via lithium naphthalenide ([LiNaph])-driven reduction of TiCl4× 2THF in tetrahydrofuran (THF). HRTEM, fast Fourier transformation (FFT), optical spectra and X-ray absorption near edge structure (XANES) confirm their chemical composition. Besides their pyrophoric properties, their high reactivity is validated by direct transformation of Ti(0) into TiC maintaining the size.

Although oxygen is a common ligand in supported-metal catalysts, its coordination has been challenging to elucidate. Using a well-defined Ir-dimer cluster that incorporates a µ-η 1 :η 1-peroxo ligand, we observe a FT-Raman band at 756 cm-1 assigned to the 16 O-16 O stretch, and a greatly enhanced intensity at 788 cm-1. The frequency of this latter band does not change upon 18 O labeling, suggesting it arises due to a change in symmetry accompanying bridging peroxo-ligand incorporation. We also investigate reaction of oxygen with a silica-supported tetrairidium carbonyl cluster protected with bulky electron-donating phosphine ligands (p-tert-butylcalix[4]arene(OPr)3(OCH2PPh2; Ph = phenyl; Pr = propyl), and observe the same Raman band at 788 cm-1 , which is associated with formation of similar bridging peroxo ligands on the tetrairidum frame. IR spectra recorded as the supported cluster was decarbonylated in sequential exposures to (i) H2, (ii) O2, (iii) H2, and (iv) CO are consistent with two bridging peroxo ligands bonded irreversibly per supported tetrairidium cluster, replacing bridging carbonyl ligands, without altering either the cluster frame or bound phosphine ligands. X-ray absorption near edge and infrared spectra recorded as the cluster reacted with O2 include isosbestic points signifying a stoichiometrically simple reaction, and mass spectra of the effluent gas identify CO2 formed by oxidation of one terminal CO ligand per cluster and H2 (not H2O)-evidence that hydride ligands had been present on the cluster. The results demonstrate that O2 reacts with intact ligated metal polyhedra on supports-an inference that pertains broadly to oxidation catalysis on supported noble metals.

Delamination of layered zeolite precursor B-SSZ-70 succeeds in an aqueous solution of Zn(NO3)2 and Bu4NF without need for sonication.

Small Co(0) nanoparticles catalyze hydrogenations of alkenes, alkynes, imines, and heteroarenes; the magnetic properties enabled catalyst separation and multiple recyclings.