On-surface synthesis of 2D COFs on Cu(111) via the formation of thermodynamically stable organometallic networks as the template.

Template-directed polymerization is an effective approach used to afford regular 2D covalent organic frameworks (COFs), thus the regularity of the template is crucial for the quality of the resulting 2D COFs. For the Ullmann reactions on Cu(111), aryl iodides and bromides are activated at low temperature to form organometallic C-Cu-C structures, which lead to kinetic trapping and irregular organometallic networks. Therefore, the subsequent annealing step can only afford irregular 2D COFs. In this manuscript, the molecule 4,4''-dibromo-5'-(4-chlorophenyl)-1,1':3',1''-terphenyl incorporated two Br terminals and one Cl terminal has been used to demonstrate different reactivities of a C-Cl bond and a C-Br bond via the hierarchical activation of the C-Br bond and the C-Cl bond on Cu(111). At room temperature, zigzag, armchair, and ring-like organometallic chains formed due to the activation of the C-Br bond to generate a C-Cu-C structure while C-Cl remained intact, illustrating that the C-Cl bond is more stable than C-Br. Further annealing at 433 K activated the C-Cl bond to produce regular organometallic networks as the thermodynamic product. Using the simpler molecule 1,3,5-tris(4-chlorophenyl)benzene as the precursor, the self-assembly of the intact molecules was observed on Cu(111) at 300 K without activation of the C-Cl bond. After annealing at 433 K, similar thermodynamically stable organometallic networks formed directly, which were used as a template to generate regular 2D COFs upon further annealing at 510 K.

Diverse supramolecular structures self-assembled by a simple aryl chloride on Ag(111) and Cu(111).

Diverse self-assembled structures were obtained on Cu(111) and Ag(111) surfaces by using a simple and small 4,4''-dichloro-1,1':4',1''-terphenyl molecule. Surprisingly, a complicated supramolecular self-assembled vortex structure, composed of 15 molecules in a large unit, was realized through the collaboration of hydrogen bonding and halogen bonding.

On-surface reactions of aryl chloride and porphyrin macrocycles via merging two reactive sites into a single precursor.

The reaction of aryl chloride and porphyrin macrocycles, which are merged into a single precursor, has been achieved on Cu(111). Scanning tunneling microscopy analysis of the oligomer products showed that the adjacent porphyrin moieties linked mainly by the phenyl group with the porphyrin macrocycle.

On-Surface Heck Reaction of Aryl Bromides with Alkene on Au(111) with Palladium as Catalyst.

The on-surface Heck reaction of aryl bromides with terminal alkene has been achieved for the first time. With palladium as the catalyst, cross-coupling of porphyrin-derived aryl bromides with terminal alkene proceeds with high selectivity on an Au(111) surface, as determined by scanning tunneling microscopy at the single molecular level. Density functional theory calculations suggest that the on-surface Heck reaction proceeds via debromination of aryl bromide, addition to the C═C bond, and elimination of hydrogen, ultimately affording the cross-coupling product.

Ullmann coupling reaction of aryl chlorides on Au(111) using dosed Cu as a catalyst and the programmed growth of 2D covalent organic frameworks.

The efficiency of Ullmann reaction of aryl chlorides on an Au(111) surface has been substantially increased by using dosed Cu as a catalyst. The different reactivity of aryl bromides and aryl chlorides has been exploited to design a programmed, on-surface synthesis to form 2D covalent organic frameworks.

Ullmann Reaction of Aryl Chlorides on Various Surfaces and the Application in Stepwise Growth of 2D Covalent Organic Frameworks.

On-surface Ullmann coupling reaction of aryl chlorides has been achieved on Cu(111), Ag(111), and Au(111), and the mechanism has been investigated on the single molecule level using scanning tunneling microscopy and density functional theory. The different reactivity of the aryl halides was utilized to design a stepwise on-surface synthesis, which affords a zigzag template and then converts to 2D porous networks.

Transition metal-free cascade reactions of alkynols to afford isoquinolin-1(2H)-one and dihydroisobenzofuran derivatives.

Transition metal-free cascade reactions of alkynols with imines have been achieved using potassium tert-butoxide as catalyst. Switching the reaction solvent gives two kinds of products in good yield: isoquinolin-1(2H)-one derivatives and dihydroisobenzofuran derivatives. This approach was used to generate the natural product 8-oxypseudopalmatine in a two-step procedure from commercially available starting materials. Additionally, multicomponent reactions of alkynols, aldehydes, and amines were also successfully achieved to afford isoquinolin-1(2H)-one derivatives.

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.