Many applications in biotechnology and molecular biology rely on modified nucleotides. Here, we present an approach for the postsynthetic labelling of enzymatically synthesized vinyl-modified DNA by Diels-Alder reaction with inverse electron demand using a tetrazine. Labelling proceeds very efficiently and supersedes several known approaches.

A series of ruthenium styryl complexes with potentially noninnocent κ 2 [N,O] − or κ 2 [N,S] − ligands have been prepared by treatment of 5-coordinated 16-valence-electron ruthenium styryl complexes Ru(CO)Cl(P i Pr 3 ) 2 (CHCH-C 6 H 4 -4R) with deprotonated bidentate 2-hydroxy-or 2-mercaptopyridines or 2-hydroxy-or 2-mercaptoquinolines. These 6-coordinated complexes have been characterized by NMR and IR spectroscopy and by cyclic voltammetry. Moreover, the structures of complexes 1d, 2a, 3c, 5b, and 6b have been established by X-ray crystallography. Our results indicate that the pyridine-derived complexes exist as two isomers that differ with respect to the orientation of the κ 2 [N,O] − or κ 2 [N,S] − donor ligands relative to the CO and alkenyl ligands in the equatorial plane. The equilibrium between the two isomers is thermodynamically controlled. Thus, the relative amount of the minor isomer increases at higher temperatures. With the 2-hydroxyquinoline-or 2-mercaptoquinoline-derived ligands only one isomer is observed. Electrochemical studies show that these complexes undergo one or two reversible consecutive one-electron oxidations, the potentials of which respond to the electronic properties of the 4-substituent at the styryl ligand and those of the ancillary chelate ligand. Strong ligand contributions to the first oxidation of the complexes were experimentally verified by IR and EPR spectroelectrochemistry. Quantum chemical calculations reproduce our experimental results, including the positions of the Ru(CO) vibrational bands of the neutral complexes and of their corresponding radical cations. Our combined results indicate that the oxidation of all complexes is dominated by the styryl ligand, irrespective of the electronic nature of the 4-substituent and of the [N,O] − or [N,S] − chelate ligand.

We report here on ruthenium alkenyl complexes 2 and 3 derived from 2,2'-bipyridine and their Re(CO)3X adducts 4a,b and 5. Detailed electrochemical studies on these complexes and spectroscopic characterization of their oxidized forms by IR, UV/vis/NIR, and electron paramagnetic resonance spectroscopies as well as quantum chemical studies reveal sizable (bridging) ligand contributions to the redox orbitals. Engagement of the free bipy functions of complexes 2 and 3 in binding to the electron-withdrawing fac-Re(CO)3X (X = Br, Cl) moiety enhances the metal-to-ligand charge-transfer character of the optical excitations, causes sizable anodic shifts of the redox potentials, and decreases the number of observable anodic redox waves by one when compared to complexes 2 and 3. Despite the decreasing electron density at the terminal or bridging alkenyl bipyridine ligand, the anodic redox processes still maintain appreciable ligand character as is seen by the shifts of the Ru(CO) and Re(CO)3 stretching frequencies on oxidation. Binding of the fac-Re(CO)3X moiety also attenuates the degree of ground-state delocalization in the mixed-valent states.

The synthesis of two new donor−acceptor ferrocenyl derivatives with Meldrum's acid based nonplanar acceptor substituents is presented. Both compounds are obtained in high yields in a simple reaction protocol under mild conditions using either 1-acetyl-or 1,1′-diacetylferrocene and Meldrum's acid. Both products have been characterized spectroscopically, by single-crystal X-ray structure analysis, by electrochemical and UV/vis/IR spectroelectrochemical measurements, and by (TD)-DFT calculations. The spectroelectrochemical measurements disclose that the 2,2-dimethyl-1,3-dioxane-4,6-dione moiety is a moderately strong electron acceptor. Article pubs.acs.org/Organometallics

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