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Increasing the metal-to-ligand charge transfer (MLCT) excited state lifetime of polypyridine iron(II) complexes can be achieved by lowering the ligand's π* orbital energy and by increasing the ligand field splitting. In the homo- and heteroleptic complexes [Fe(cpmp) 2 ] 2+ (1 2+ ) and [Fe(cpmp)(ddpd)] 2+ (2 2+ ) with the tridentate ligands 6,2''-carboxypyridyl-2,2'-methylamine-pyridyl-pyridine (cpmp) and N,N'-dimethyl-N,N'-di-pyridin-2-ylpyridine-2,6-diamine (ddpd) two or one dipyridyl ketone moieties provide low energy π* acceptor orbitals. A good metal-ligand orbital overlap to increase the ligand field splitting is achieved by optimizing the octahedricity through CO and NMe units between the coordinating pyridines which enable the formation of six-membered chelate rings. The push-pull ligand cpmp provides intra-ligand and ligand-to-ligand charge transfer (ILCT, LL'CT) excited states in addition to MLCT excited states. Ground and excited state properties of 1 2+ and 2 2+ were accessed by X-ray diffraction analyses, resonance Raman spectroscopy, (spectro)electrochemistry, EPR spectroscopy, X-ray emission spectroscopy, static and time-resolved IR and UV/Vis/NIR absorption spectroscopy as well as quantum chemical calculations., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Asymmetric platinum donor-acceptor complexes [(pimp)Pt(Q 2- )] are presented in this work, in which pimp=[(2,4,6-trimethylphenylimino)methyl]pyridine and Q 2- =catecholate-type donor ligands. The properties of the complexes are evaluated as a function of the donor ligands, and correlations are drawn among electrochemical, optical, and theoretical data. Special focus has been put on the spectroelectrochemical investigation of the complexes featuring sulfonyl-substituted phenylendiamide ligands, which show redox-induced linkage isomerism upon oxidation. Time-dependent density functional theory (TD-DFT) as well as electron flux density analysis have been employed to rationalize the optical spectra of the complexes and their reactivity. Compound 1 ([(pimp)Pt(Q 2- )] with Q 2- =3,5-di-tert-butylcatecholate) was shown to be an efficient photosensitizer for molecular oxygen and was subsequently employed in photochemical cross-dehydrogenative coupling (CDC) reactions. The results thus display new avenues for donor-acceptor systems, including their role as photocatalysts for organic transformations, and the possibility to introduce redox-induced linkage isomerism in these compounds through the use of sulfonamide substituents on the donor ligands., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The complex class [Fe(N^N^C)(N^N^N)] + with an Earth-abundant metal ion has been repeatedly suggested as a chromophore and potential photosensitizer on the basis of quantum chemical calculations. Synthesis and photophysical properties of the parent complex [Fe(pbpy)(tpy)] + (Hpbpy=6-phenyl-2,2'-bipyridine and tpy=2,2':6',2''-terpyridine) of this new chromophore class are now reported. Ground-state characterization by X-ray diffraction, electrochemistry, spectroelectrochemistry, UV/Vis, and X-ray spectroscopy in combination with DFT calculations proves the high impact of the cyclometalating ligand on the electronic structure. The photophysical properties are significantly improved compared to the prototypical [Fe(tpy) 2 ] 2+ complex. In particular, the metal-to-ligand absorption extends into the near-IR and the 3 MLCT lifetime increases by 5.5, whereas the metal-centered excited triplet state is very short-lived., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

New precursor chemistries for the atomic layer deposition (ALD) of aluminium oxide are reported as potential alternatives to the pyrophoric trimethylaluminium (TMA) which is to date a widely used Al precursor. Combining the high reactivity of aluminium alkyls employing the 3-(dimethylamino)propyl (DMP) ligand with thermally stable amide ligands yielded three new heteroleptic, non-pyrophoric compounds [Al(NMe 2 ) 2 (DMP)] (2), [Al(NEt 2 ) 2 (DMP)] (3, BDEADA) and [Al(NiPr 2 ) 2 (DMP)] (4), which combine the properties of both ligand systems. The compounds were synthesized and thoroughly chemically characterized, showing the intramolecular stabilization of the DMP ligand as well as only reactive Al-C and Al-N bonds, which are the key factors for the thermal stability accompanied by a sufficient reactivity, both being crucial for ALD precursors. Upon rational variation of the amide alkyl chains, tunable and high evaporation rates accompanied by thermal stability were found, as revealed by thermal evaluation. In addition, a new and promising plasma enhanced (PE)ALD process using BDEADA and oxygen plasma in a wide temperature range from 60 to 220 °C is reported and compared to that of a modified variation of the TMA, namely [AlMe 2 (DMP)] (DMAD). The resulting Al 2 O 3 layers are of high density, smooth, uniform, and of high purity. The applicability of the Al 2 O 3 films as effective gas barrier layers (GBLs) was successfully demonstrated, considering that coating on polyethylene terephthalate (PET) substrates yielded very good oxygen transmission rates (OTR) with an improvement factor of 86 for a 15 nm film by using DMAD and a factor of 25 for a film thickness of just 5 nm by using BDEDA compared to bare PET substrates. All these film attributes are of the same quality as those obtained for the industrial precursor TMA, rendering the new precursors safe and potential alternatives to TMA., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The borane-catalyzed synthesis of quinoline derivatives bearing tetrasubstituted stereocenters from vinyl anilines has been developed. Mechanistic studies and quantum-mechanical investigations support the hydride abstraction/electrocyclization/hydride addition mechanism. The products were obtained in up to 99 % yield with a diastereoselectivity of >99 % in favour for the 3a-5-cis isomer., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Non-natural oligonucleotides represent important (bio)chemical tools and potential therapeutic agents. Backbone modifications altering hybridization properties and biostability can provide useful analogues. Here, we employ an artificial nucleosyl amino acid (NAA) motif for the synthesis of oligonucleotides containing a backbone decorated with primary amines. An oligo-T sequence of this cationic DNA analogue shows significantly increased affinity for complementary DNA. Notably, hybridization with DNA is still governed by Watson-Crick base pairing. However, single base pair mismatches are tolerated and some degree of sequence-independent interactions between the cationic NAA backbone and fully mismatched DNA are observed. These findings demonstrate that a high density of positive charges directly connected to the oligonucleotide backbone can affect Watson-Crick base pairing. This provides a paradigm for the design of therapeutic oligonucleotides with altered backbone charge patterns., (© 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Identification and synthesis of intramolecularly donor-stabilized aluminium(III) complexes, which contain a 3-(dimethylamino)propyl (DMP) ligand, as novel atomic layer deposition (ALD) precursors has enabled the development of new and promising ALD processes for Al 2 O 3 thin films at low temperatures. Key for this promising outcome is the nature of the ligand combination that leads to heteroleptic Al complexes encompassing optimal volatility, thermal stability and reactivity. The first ever example of the application of this family of Al precursors for ALD is reported here. The process shows typical ALD like growth characteristics yielding homogeneous, smooth and high purity Al 2 O 3 thin films that are comparable to Al 2 O 3 layers grown by well-established, but highly pyrophoric, trimethylaluminium (TMA)-based ALD processes. This is a significant development based on the fact that these compounds are non-pyrophoric in nature and therefore should be considered as an alternative to the industrial TMA-based Al 2 O 3 ALD process used in many technological fields of application., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Highly efficient, one-step synthesis of sulfur-containing heteroacenes was achieved through palladium-catalyzed C-S cross-coupling of bis-alkynes with thioacetate as hydrogen sulfide surrogate. Heteroacenes consisting of three, five, and seven fused aromatic rings were obtained in a single catalytic step by four-, six-, and eightfold C-S bond formation., (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The autoinduced, frustrated Lewis pair (FLP)-catalyzed hydrogenation of 16-benzene-ring substituted N-benzylidene-tert-butylamines with B(2,6-F2 C6 H3 )3 and molecular hydrogen was investigated by kinetic analysis. The pKa values for imines and for the corresponding amines were determined by quantum-mechanical methods and provided a direct proportional relationship. The correlation of the two rate constants k1 (simple catalytic cycle) and k2 (autoinduced catalytic cycle) with pKa difference between imine and amine pairs (ΔpKa ) or Hammett's σ parameter served as useful parameters to establish a structure-reactivity relationship for the FLP-catalyzed hydrogenation of imines., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The frustrated Lewis pair (FLP)-catalyzed hydrogenation and deuteration of N-benzylidene-tert-butylamine (2) was kinetically investigated by using the three boranes B(C6F5)3 (1), B(2,4,6-F3-C6H2)3 (4), and B(2,6-F2-C6H3)3 (5) and the free activation energies for the H2 activation by FLP were determined. Reactions catalyzed by the weaker Lewis acids 4 and 5 displayed autoinductive catalysis arising from a higher free activation energy (2 kcal mol(-1)) for the H2 activation by the imine compared to the amine. Surprisingly, the imine reduction using D2 proceeded with higher rates. This phenomenon is unprecedented for FLP and resulted from a primary inverse equilibrium isotope effect., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A model is proposed for the drop in electronic resistance of n-type semiconducting indium oxide (In(2)O(3)) upon illumination with light (350 nm, 3.5 eV) as well as for the (light-enhanced) sensitivity of In(2)O(3) to oxidizing gases. Essential features of the model are photoreduction and a rate-limiting oxygen-diffusion step. Ordered, mesoporous In(2)O(3) with a high specific surface area serves as a versatile system for experimental studies. Analytical techniques comprise conductivity measurements under a controlled atmosphere (synthetic air, pure N(2)) and temperature-resolved in-situ Fourier transform infrared (FTIR) spectroscopy. IR measurements reveal that oxygen vacancies form a donor level 0.18 eV below the conduction band., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)