Five Possible Isocyanoazulenes and Electron-Rich Complexes Thereof:  A Quantitative Organometallic Approach for Probing Electronic Inhomogeneity of the Azulenic Framework

Abstract

Efficient syntheses of all five possible isocyanoazulenes, the four isomeric archetypal compounds CN1Az, CN2Az, CN4Az, and CN6Az, as well as the 1,3-di-tert-butyl derivative of CN5Az (Az = azulenyl), are described. Compounds CN1Az and CN2Az show unexpected shifts of the S0 → S1 transition in their electronic spectra relative to azulene. The origins of these “anomalous” shifts have been addressed by DFT calculations, cyclic voltammetry, and comparison of the electronic spectra of isocyanoazulenes with those of the corresponding isomeric cyanoazulenes. Despite the high propensity of the azulenic nucleus to undergo multihapto coordination and C−C coupling in the presence of low-valent metals, the isocyanoazulenes react with 1/6 equiv of Cr(η6-naphthalene)2 to afford thermally stable Cr(CN x Az)6 (x = 1, 2, 4, 6), which contain six discrete azulenyl groups separated from the Cr center by isocyanide linkers. All Cr(CN x Az)6 species undergo oxidation to form the corresponding paramagnetic cations [Cr(CN x Az)6]+, which have been crystallographically characterized. Changing the atom of attachment of the azulenyl groups to the “Cr(CN)6” core substantially alters the donor/acceptor properties of the isocyanoazulene ligands. The half-wave Cr0/+ and Cr+/2+ redox potentials for [Cr(CN x Az)6] z form the “electrochemical series” that constitutes a quantitative measure of electronic inhomogeneity of the azulenic framework. Unpaired spin delocalization within the azulenic moieties of [Cr(CN x Az)6]+ has been observed by multinuclear NMR. The CrI(dπ)→CN x Az(pπ*) interaction has been shown to be an important contributor to the mechanism of unpaired electron delocalization in [Cr(CN x Az)6]+.

Multi-state extrapolation of UV/Vis absorption spectra with QM/QM hybrid methods

“…50 The results for these molecules are shown in Figure 8 layer (substituent). However, they are interesting because they allow us to study the effect of different substituents on the absorption of the main chromophore.…”

“…Indeed, azulene is a particularly versatile compound whose photochemical characteristics can be finely tuned by substitution in any of the eight possible positions. 50 Here we want to probe how our approach handles relatively small differences due to similar substituents. We considered 100 states for the target and each subcalculation to simulate the spectrum.…”

Interaction of Mono- and Diisocyanoazulenes with Gold Surfaces: First Examples of Self-Assembled Monolayer Films Involving Azulenic Scaffolds

“…Angles ∆ and Ψ are consistent with expectations for a nonabsorbing film of ∼10-50 Å thickness, 43 which is not surprising considering that the extinction coefficients for the azulenic compounds studied are quite small at the laser wavelength. 29,31 b. FTIR Measurements on Films. The grazing incidence reflection absorption Fourier transform infrared spectroscopy data were collected on a nitrogen-purged Thermo Nicolet 670 FTIR spectrometer with a VeeMax grazing angle accessory typically set at an angle of 70°.…”

Reaction of the heteronuclear cluster RuOs3(μ-H)2(CO)13 with azulenes

“…The spike Ru(4)eRu(5) bond is long despite being bridged by a carbonyl group; usually the shortest metalemetal bond is associated with a bridging CO. The two longest metalemetal edges in each of the metal tetrahedra, Os(1)eOs (2) and Os (2) A similar reaction of 1 with guaiazulene afforded, besides 2, a yet different pentanuclear cluster Ru 2 Os 3 (CO) 11 (m 3 ,h 5 :h 3 :h 3 -C 10 H 5 Me 2 i Pr) (6), which has also been completely characterised by spectroscopic, elemental and a single-crystal X-ray crystallographic analyses. An ORTEP plot showing the molecular structure of 6, together with selected bond parameters, is given in Fig.…”

“…In addition, the naturally occurring derivative guaiazulene (7-isopropyl-1,4-dimethylazulene) is an essential ingredient in many cosmetics and lotions. More recently, azulene derivatives have found important applications as reagents in synthesis as well as components in advanced polymers, optical materials and liquid crystals [1,2]. This has led to a resurgence of interest in azulene-ligated organometallic clusters, which were first reported in the 1960s [3e7].…”