Controlling two-phase self-assembly of an adenine derivative on HOPG via kinetic effects.

Large-area self-assembled structures of a nucleobase adenine derivative were successfully realized through vacuum deposition. STM images reveal two types of structures, which could be regulated by substrate temperature and the evaporation rate, indicating the relevance of kinetic effects. The results are supported by computer simulations.

Thymine and adenine tetrads formed on anisotropic metal surfaces.

The interplay of the Au(110) surface and alkyl-substituted DNA bases induces reorganization of the surface with parallel atomic grooves, while the enhanced surface anisotropy constrains the substituent alkyl chains along the grooves. Every four molecules are bound together through H-bonds while further possible H-bonds are prohibited by either the alkyl chains or the groove borders, resulting in separated tetrad structures located in the grooves.

Temperature-dependent self-assembly of adenine derivative on HOPG.

Temperature-dependent self-assembly formed by the adsorption of the nucleobase adenine derivative on a graphite surface were investigated by in situ scanning tunneling microscopy (STM). The high-resolution STM images reveal two types of structures, α phase and ß phase, which are mainly driven by either hydrogen bonding or aromatic π-π interactions between adenine bases, respectively, as well as the interactions of alkyl chains. α-Phase structures can be transformed into ß-phase structures by increasing temperature. The reverse is true for decreasing temperature. This reflects structural stabilities resulting from the different interactions. Density functional theory (DFT) calculations were performed to characterize possible arrangements of adjacent adenine moieties systematically in terms of binding energies and structural properties. Via a systematic search algorithm, all possible network structures were determined on a microscopic level. In this way, it is possible to rationalize the structural parameters as found in the STM images.

Linear alkane polymerization on a gold surface.

In contrast to the many methods of selectively coupling olefins, few protocols catenate saturated hydrocarbons in a predictable manner. We report here the highly selective carbon-hydrogen (C-H) activation and subsequent dehydrogenative C-C coupling reaction of long-chain (>C(20)) linear alkanes on an anisotropic gold(110) surface, which undergoes an appropriate reconstruction by adsorption of the molecules and subsequent mild annealing, resulting in nanometer-sized channels (1.22 nanometers in width). Owing to the orientational constraint of the reactant molecules in these one-dimensional channels, the reaction takes place exclusively at specific sites (terminal CH(3) or penultimate CH(2) groups) in the chains at intermediate temperatures (420 to 470 kelvin) and selects for aliphatic over aromatic C-H activation.

Multilevel supramolecular architectures self-assembled on metal surfaces.

We report the controllability of the complexity of surface-supported supramolecular assembly on metal surfaces. By introducing mismatch between the molecular packing and the surface atomic periodicity in the systems with comparable strength of intermolecular and molecule-substrate interactions, a homomolecular assembly exhibiting two-dimensional multilevel structures up to quaternary level was observed. In such a multiperiodicity modulated system, neither the intermolecular nor molecule-substrate interactions solely dominate the assembly, resulting in complicated multilevel structures. We further demonstrated that the multilevel assemblies can serve as templates for site-selective adsorption of guest molecules.

Chelate bis(imino)pyridine cobalt complexes: synthesis, reduction, and evidence for the generation of ethene polymerization catalysts by Li+ cation activation.

Treatment of the bis(iminobenzyl)pyridine chelate Schiff-base ligand 8 (ligPh) with FeCl2 or CoCl2 yielded the corresponding (ligPh)MCl2 complexes 9 (Fe) and 10 (Co). The reaction of 10 with methyllithium or "butadiene-magnesium" resulted in reduction to give the corresponding (ligPh)Co(I)Cl product 11. Similarly, the bis(aryliminoethyl)pyridine ligand (ligMe) was reacted with CoCl2 to yield (ligMe)CoCl2 (12). Reduction to (ligMe)CoCl (13) was effected by treatment with "butadiene-magnesium". Complex 13 reacted with Li[B(C6F5)4] in toluene followed by treatment with pyridine to yield [(ligMe)Co+-pyridine] (15). The reaction of the Co(II) complexes 10 or 12 with ca. 3 molar equiv of methyllithium gave the cobalt(I) complexes 16 and 17, respectively. Treatment of the (ligMe)CoCH3 (17) with Li[B(C6F5)4] gave a low activity ethene polymerization catalyst. Likewise, complex 16 produced polyethylene (activity = 33 g(PE) mmol(cat)(-1) h(-1) bar(-1) at room temperature) upon treatment with a stoichiometric amount of Li[B(C6F5)4]. A third ligand (lig(OMe)) was synthesized featuring methoxy groups in the ligand backbone (22). Coordination to FeCl2 and CoCl2 yielded the desired compounds 23 and 24. Reaction with MeLi gave (ligOMe)CoMe (25/26). Treatment of 25/26 with excess B(C6F5)3 gave the eta6-arene cation complex 27, where one Co-N linkage was cleaved. Activation of 25/26 with Li[B(C6F5)4] again gave a catalytically active species.