Do ν(CO) Stretching Frequencies in Metal Carbonyl Complexes Unequivocally Correlate with the Intrinsic Electron‐Donicity of Ancillary Ligands?

Abstract

Schön bunt: Fluoreszenzsonden mit unterschiedlichen Farbstoffeinheiten, die auf der Grundlage einer Fluoreszenzlöschung durch eine Excitonenwechselwirkung funktionieren, fluoreszieren bei der Hybridisierung mit ihrer Zielnucleinsäure in unterschiedlichen Farben. Im Bild ist die simultane Fluoreszenz in drei Farben in einem Zellkern zu sehen, der drei unterschiedliche microRNA‐Stränge im Überschuss enthält. Links: Differenzinterferenzkontrastbild.

Synthesis, Structure, and Electronic Properties of Extended π‐Conjugated Group 6 Fischer Alkoxy–Bis(carbene) Complexes

“…Moreover and as expected, the ethoxy group directly attached to the carbene carbon atom adopts the socalled anti conformation (i.e., the CH 2 group is oriented towards the CO wall of the metal fragment), which is the preferred conformation for most of the alkoxy Fischer carbene complexes in the gas phase and in the solid state. [17] Another important geometrical feature revealed by this experimental-computational study is the high planarity exhibited by these bisA C H T U N G T R E N N U N G (carbene) complexes (see also Figure 1 S in the Supporting Information), which plays a crucial role in their electronic structures (see below). www.chemeurj.org Electronic structure and optical properties: Figure 3 show the UV/Vis spectra of all chromium(0) bisA C H T U N G T R E N N U N G (carbene) complexes 2 aa-2 al recorded at room temperature in hexane with a concentration of approximately 1 10 À5 mol L À1 (see also Table 1).…”

“…[24] The assignment of the excitation energies to the experimental bands was performed on the basis of the energy values and oscillator strengths. The B3LYP Hamiltonian was chosen because it was proven to provide reasonable UV/Vis spectra for a variety of chromophores [25] including Fischer carbene complexes [17] and other organometallic species. [26] Despite that, the B3LYP functional sometimes underestimate the energy of the charge-transfer (CT) excited states.…”

The Doping Effect of Fluorinated Aromatic Solvents on the Rate of Ruthenium‐Catalysed Olefin Metathesis

“…The observed faster decomposition of Gru-II in solutions containing FAH may seem surprising in the light of the invariably better yields reported for reactions in these solvents, as well as in the presence of oxygen (see Table 7). We suggest that the facile dissociation/oxidation reaction of the phosphine ligand in FAHs allows faster and irreversible formation of catalytically active 14-electron species, which can be subsequently stabilised by p-p stacking interactions between an electron-donating moiety (N-mesityl or benzylidene) and electron-poor solvent molecules, [23,26] or even by direct fluorine-ruthenium interactions. [27] In the case of phosphine-free Hoveyda type systems, similar stabilisation of the propagating species can be suggested.…”

“…[27] In the case of phosphine-free Hoveyda type systems, similar stabilisation of the propagating species can be suggested. We postulate that the interactions with fluorinated solvent molecules can modify the through-space transfer of electron density between the Ru=CHR unit and the aromatic rings on the Nsubstituents of the NHC ligand, thereby accelerating the rate of the metathesis reaction, [26] such that high TONs can be achieved even for very challenging substrates.…”

On the relation between carbonyl stretching frequencies and the donor power of chelating diphosphines in nickel dicarbonyl complexes

“…2,3 TEP is based on the position of the A 1 carbonyl stretching-frequency band in the spectrum of [Ni(CO) 3 L], where L is a phosphine ligand, with respect to the stretching vibration of free CO as recorded in the gas phase, which has a value of 2143 cm –1 . 4 In classical mononuclear carbonyl complexes, the A 1 carbonyl stretching frequency lies in the range 2125–1850 cm –1 , 5 and the observed red shift with respect to free CO is taken as a measure of the overall donor ability of L. Though the validity of such approach has been recently questioned (see for instance ref. 6, where evidence is given for intramolecular interactions interfering with the carbonyl stretching response to the ligand–metal interaction) and alternative, more sophisticated parameters have been proposed, 7 TEP still represents a traditional and widespread method for assessing and comparing the electronic properties of the ligands.…”