Tailoring a Dynamic Metal-Polymer Interaction to Improve Catalyst Selectivity and Longevity in Hydrogenation.

Controlling metal-support interactions is important for tuning the catalytic properties of supported metal catalysts. Here, premade Pd particles are supported on stable polymers containing different ligating functionalities to control the metal-polymer interactions and their catalytic properties in industrially relevant acetylene partial hydrogenation. The polymers containing strongly ligating groups (e.g., Ar-SH and Ar-S-Ar) can form a polymer overlayer on the Pd surface, which enables selective acetylene adsorption and partial hydrogenation to ethylene without deactivation. In contrast, polymers with weakly ligating groups (e.g., Ar-O-Ar) do not form an overlayer, resulting in non-selective hydrogenation and fast deactivation, similar to Pd catalysts on conventional inorganic supports. The results imply that tuning the metal-polymer interactions via rational polymer design can provide an efficient way of synthesizing selective and stable catalysts for hydrogenation.

Dynamic metal-polymer interaction for the design of chemoselective and long-lived hydrogenation catalysts.

Metal catalysts are generally supported on hard inorganic materials because of their high thermochemical stabilities. Here, we support Pd catalysts on a thermochemically stable but "soft" engineering plastic, polyphenylene sulfide (PPS), for acetylene partial hydrogenation. Near the glass transition temperature (~353 K), the mobile PPS chains cover the entire surface of Pd particles via strong metal-polymer interactions. The Pd-PPS interface enables H2 activation only in the presence of acetylene that has a strong binding affinity to Pd and thus can disturb the Pd-PPS interface. Once acetylene is hydrogenated to weakly binding ethylene, re-adsorption of PPS on the Pd surface repels ethylene before it is further hydrogenated to ethane. The Pd-PPS interaction enables selective partial hydrogenation of acetylene to ethylene even in an ethylene-rich stream and suppresses catalyst deactivation due to coke formation. The results manifest the unique possibility of harnessing dynamic metal-polymer interaction for designing chemoselective and long-lived catalysts.

Efficient Aluminum Catalysts for the Chemical Conversion of CO2 into Cyclic Carbonates at Room Temperature and Atmospheric CO2 Pressure.

A series of dimeric aluminum compounds [Al(OCMe2 CH2 N(R)CH2 X)]2 [X=pyridin-2-yl, R=H (PyrH ); X= pyridin-2-yl, R=Me (PyrMe ); X=furan-2-yl, R=H (FurH ); X= furan-2-yl, R=Me (FurMe ); X=thiophen-2-yl, R=H (ThioH ); X= thiophen-2-yl, R=Me (ThioMe )] containing heterocyclic pendant group attached to the nitrogen catalyze the coupling of CO2 with epoxides under ambient conditions. In a comparison of their catalytic activities with those of aluminum complexes without pendant groups at N [X=H, R=H (HH ); X=H, R=Me (HMe )] or with non-heterocyclic pendant groups [X=CH2 CH2 OMe, R=H (OMeH ); X=CH2 CH2 NMe2 , R=H (NMe2H ); X=CH2 CH2 NMe2 , R=Me (NMe2Me )], complexes containing heterocycles, in conjunction with (nBu)4 NBr as a cocatalyst, show higher catalytic activities for the synthesis of cyclic carbonates under the same ambient conditions. The best catalyst system for this reaction is PyrH /(nBu)4 NBr system, which gives a turnover number of 99 and a turnover frequency of 4.1 h-1 , making it 14- and 20-times more effective than HH /(nBu)4 NBr and HMe /(nBu)4 NBr, respectively. Although there are no direct interactions between the aluminum and the heteroatoms in the heterocyclic pendants, electronic effects combined with the increased local concentration of CO2 around the active centers influences the catalytic activity in the coupling of CO2 with epoxides. In addition, PyrH /(nBu)4 NBr shows broad epoxide substrate scope and seven terminal epoxides and two internal epoxides undergo the designed reaction.

Intriguing Indium-salen Complexes as Multicolor Luminophores.

The series of novel salen-based indium complexes (3-tBu-5-R-salen)In-Me (3-tBu-5-R-salen = N,N'-bis(2-oxy-3-tert-butyl-5-R-salicylidene)-1,2-diaminoethane, R = H (1), tBu (2), Br (3), Ph (4), OMe (5), NMe2 (6)) and [(3-tBu-5-NMe3-salen)In-Me](OTf)2 (7; OTf = CF3SO3-) have been synthesized and fully characterized by NMR spectroscopy and elemental analysis. All indium complexes 1-7 are highly stable in air and even aqueous solutions. The solid-state structures for 3-5, which were confirmed by single-crystal X-ray analysis, exhibit square-pyramidal geometries around the indium center. Both the UV/vis absorption and PL spectra of 1-7 exhibit significant intramolecular charge transfer (ICT) transitions based on the salen moieties with systematically bathochromic shifts, which depend on the introduction of various kinds of substituents. Consequently, the emission spectra of these complexes cover almost the entire visible region (λem = 455-622 nm).