Christiane Lang

Consecutive modular ligation as an access route to palladium containing polymers

Polymers with palladium ligating moieties in the lateral chain were synthesized via consecutive CuAAC ligation. An in-depth catalyst screening was performed to optimize the reaction conditions. The obtained polymers, quantitatively loaded with palladium complexes, feature high molar masses of up to Mn = 30 000 g mol−1. The complex formation is underpinned by model complex studies. 2,6-Bis(1-(p-tolyl)-1H-1,2,3-triazol-4-yl)pyridine was used as the model ligand. Reaction of the ligand with [Pd(cod)Cl2] resulted in the corresponding palladium model complex.

Palladium-containing polymers via a combination of RAFT and triazole chemistry

Polystyrene based copolymers with palladium-ligating side groups were obtained by RAFT polymerization of chloromethyl styrene and styrene, subsequent azide transformation and quantitative copper-mediated 1,3-dipolar cycloaddition of ethynyl pyridine. Variable copolymer compositions were synthesized ranging from 10% to 50% with respect to the fraction of the palladium-ligating comonomer. The successful loading of the polymers with PdCl2 employing [Pd(COD)Cl2] (COD = 1,5-cyclooctadiene) as the metal source was confirmed by nuclear magnetic resonance spectroscopy (NMR) and elemental analysis. Absolute molecular weights of the Pd-containing polymers ranging from Mw = 16 000 g mol−1 to 20 000 g mol−1 were determined by employing static light scattering (SLS). In order to fully clarify the incorporation of palladium into the polymers, a PdCl2 complex of a chelating N donor ligand featuring the characteristic heterocyclic donor functions used to incorporate PdCl2 in the polymer was synthesized and characterized by single crystal X-ray diffraction and NMR analysis.

Oxidative polymerization of catecholamines: structural access by high-resolution mass spectrometry

We introduce the high-resolution electrospray ionization mass spectrometric (ESI MS) structural elucidation of polymerized 3,4-dihydroxy-L-phenylalanine (L-DOPA) carrying 1-methoxy-2,2,6,6-tetramethylpiperidin-4-amide groups in the side chain. Critically, our powerful ESI MS platform unambiguously revealed the structurally diverse character of this multifunctional bio-adhesive polymer system.

Photolithographic Encoding of Metal Complexes

A platform technology for the creation of spatially resolved surfaces encoded with a monolayer consisting of different metal complexes was developed. The concept entails the light-triggered activation of a self- assembled monolayer (SAM) of UV-labile anchors, that is, phenacylsulfides, and the subsequent cycloaddition of selected diene-functionalized metal complexes at defined areas on the surface. The synthesis and characterization of the metal complexes for the UV-light assisted anchoring on the surface and a detailed study of a short-chain oligomer model system in solution confirm the high efficiency of the photoreaction. The hybrid materials obtained by this concept can potentially be utilized for the design of highly valuable catalytic or (opto-)electronic devices.

Engineering Nitroxide Functional Surfaces Using Bioinspired Adhesion

We pioneer a versatile surface modification strategy based on mussel-inspired oxidative catecholamine polymerization for the design of nitroxide-containing thin polymer films. A 3,4-dihydroxy-l-phenylalanine (l-DOPA) monomer equipped with a 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-derived oxidation-labile hydroxylamine functional group is employed as a universal coating agent to generate polymer scaffolds with persistent radical character. Various types of materials including silicon, titanium, ceramic alumina, and inert poly(tetrafluoroethylene) (PTFE) were successfully coated with poly(DOPA-TEMPO) thin films in a one-step dip-coating procedure under aerobic, slightly alkaline (pH 8.5) conditions. Steadily growing polymer films (∼1.1 nm h-1) were monitored by ellipsometry, and their thicknesses were critically compared with those obtained from atomic force microscopic cross-sectional profiles. The heterogeneous composition of surface-adherent nitroxide scaffolds examined by X-ray photoelectron spectroscopy was correlated to that examined by in-solution polymer analysis via high-resolution electrospray ionization mass spectrometry, revealing oligomeric structures with up to six repeating units, mainly composed of covalently linked dihydroxyindole along the polymer backbone. Critically, the reversible redox-active character of the nitroxide-containing polymer scaffolds was investigated by cyclic voltammetric measurements, revealing a convenient and facile access route to electrochemically active nitroxide polymer coatings with potential application in electronic devices such as organic radical batteries.