Cross-coupling of aryl-bromide and porphyrin-bromide on an Au(111) surface.

Cross-coupling is of great importance in organic synthesis. Here it is demonstrated that cross-coupling of aryl-bromide and porphyrin-bromide takes place on a Au(111) surface in vacuo. The products are oligomers consisting of porphyrin moieties linked by p-phenylene at porphyrin's meso-positions. The ratio of the cross-coupled versus homocoupled bonds can be regulated by the reactant concentrations. Kinetic Monte Carlo simulations were applied to determine the activation barrier. It is expected that this reaction can be employed in other aryl-bromide precursors for designing alternating co-polymers incorporating porphyrin and other functional moieties.

Palladium-Catalyzed Tandem Carbene Migratory Insertion and Intramolecular Cyclization: Synthesis of Chromeno[4,3-b]chromene Compounds.

Chromeno[4,3-b]chromene is a ubiquitous structural motif found in various pharmaceuticals and biologically active compounds. A concise palladium-catalyzed reaction of vinyl iodides and salicyl N-tosylhydrazones has been achieved to afford a series of compounds containing the chromeno[4,3-b]chromene scaffold in moderate to high yield. This tandem reaction involves palladium(II) carbene migratory insertion and intramolecular cyclization assisted by an O nucleophile and tolerates various functional groups.

Self-assembly of metal-organic coordination networks using on-surface synthesized ligands.

Supramolecular assembly and on-surface synthesis are two widely-used methods for constructing low-dimensional molecular nanostructures on surfaces. Here we describe an approach that combines both methods to create two-dimensional metal-organic networks with exceptionally large pores.

A single-molecule-level mechanistic study of Pd-catalyzed and Cu-catalyzed homocoupling of aryl bromide on an Au(111) surface.

On-surface Pd- and Cu-catalyzed C-C coupling reactions between phenyl bromide functionalized porphyrin derivatives on an Au(111) surface have been investigated under ultra-high vacuum conditions by using scanning tunneling microscopy and kinetic Monte Carlo simulations. We monitored the isothermal reaction kinetics by allowing the reaction to proceed at different temperatures. We discovered that the reactions catalyzed by Pd or Cu can be described as a two-phase process that involves an initial activation followed by C-C bond formation. However, the distinctive reaction kinetics and the C-C bond-formation yield associated with the two catalysts account for the different reaction mechanisms: the initial activation phase is the rate-limiting step for the Cu-catalyzed reaction at all temperatures tested, whereas the later phase of C-C formation is the rate-limiting step for the Pd-catalyzed reaction at high temperature. Analysis of rate constants of the Pd-catalyzed reactions allowed us to determine its activation energy as (0.41±0.03) eV.

Solvent-switched benzylic methylene functionalization: addition, ring-opening, cyclization, and unexpected cleavage of C-O and C-C bonds.

Intermolecular benzylic methylene functionalization of exo-cyclic enol ethers has been achieved using imines as reagents and potassium tert-butoxide as the catalyst. Depending on the solvent used, the reaction proceeds by two pathways. In THF, an addition/elimination reaction of exo-cyclic enol ethers with imines provides dihydroisobenzofuran derivatives in good yield. In DMSO, an addition/ring-opening/cyclization cascade reaction occurs with unexpected cleavage of C-O and C-C bonds, affording isoquinolin-1(2H)-one products in high yield under ambient reaction conditions.

Coordination self-assembly of bromo-phenyl and pyridyl functionalized porphyrins with Fe on an Au(111) surface.

Using scanning tunneling microscopy, the coordination self-assembly of a series of peripheral bromo-phenyl and pyridyl substituted porphyrins with Fe was studied on an Au(111) surface. The porphyrins functionalized with two trans-pyridyl groups afford extended hexagonal frameworks and the porphyrins functionalized with three pyridyl groups generate discrete rosette and extended chiral kagome framework structures. The self-assembly of the porphyrin derivatives in which phenyl groups are substituted by bromo-phenyl results in coordination networks exhibiting identical structures to that of the parent compounds. These structures contain nanocavities decorated with Br, which provide potential for covalent functionalization.

Steering on-surface polymerization with metal-directed template.

On-surface polymerization represents a novel bottom-up approach for producing macromolecular structures. To date, however, most of the structures formed using this method exhibit a broad size distribution and are disorderly adsorbed on the surface. Here we demonstrate a strategy of using metal-directed template to control the on-surface polymerization process. We chose a bifunctional compound which contains pyridyl and bromine end groups as the precursor. Linear template afforded by pyridyl-Cu-pyridyl coordination effectively promoted Ullmann coupling of the monomers on a Au(111) surface. Taking advantage of efficient topochemical enhancement owing to the conformation flexibility of the Cu-pyridyl bonds, macromolecular porphyrin structures that exhibit a narrow size distribution were synthesized. We used scanning tunneling microscopy and kinetic Monte Carlo simulation to gain insights into the metal-directed polymerization at the single molecule level. The results reveal that the polymerization process profited from the rich chemistry of Cu which catalyzed the C-C bond formation, controlled the size of the macromolecular products, and organized the macromolecules in a highly ordered manner on the surface.

Effects of municipal sewage sludge stabilized by fly ash on the growth of Manilagrass and transfer of heavy metals.

A greenhouse experiment was carried out to evaluate the feasibility of using an artificial soil for cultivation of Manilagrass. The transfer and transformation of heavy metals in the artificial soil-Manilagrass system were discussed at the same time. The results showed that fly ash-sludge indicated a positive effect on the growth of Manilagrass. The pots with 14% sludge and 6% fly ash mixture had the highest yield and nutrient concentrations of Manilagrass. With the increasing application of coal fly ash, the concentrations of Ni, Zn, Mn, Sb and Cu in Manilagrass decreased significantly, while Pb, V and Ti increased. Otherwise, the concentrations of Cd, As, Cr, Co, and Fe did not show a remarkable change. Except for Sb, the values of bio-concentration factor of heavy metals in Manilagrass were all below 1.0 after treated by the fly ash-sludge treatment, decreased as Sb>Ni>Zn>Cu>Pb>Mn>Co=Cr>Cd>Fe=V>Ti>As in an average for all treatments. Compared to the contrast check, the proportions of heavy metals in exchangeable, reducible and oxidizable fractions increased. Manilagrass could be used to reduce the eco-toxicity and bioavailability of Ti, V, Mn, Co, Cr and Cd in fly ash-sludge amended soil.