Charge Transfer through Isomeric Unsaturated Hydrocarbons. Redox Switchable Optical Properties and Electronic Structure of Substituted Indenes with a Pendant Ferrocenyl

Abstract

A family of (ferrocenyl)indenes, (2-ferrocenyl)indene, (2-ferrocenyl)tetramethylindene, (2-ferrocenyl)hexamethylindene, (3-ferrocenyl)indene, and (3-ferrocenyl)hexamethylindene, and the corresponding monooxidized cations have been prepared. The results of a structural and spectroelectrochemical study are discussed. The availability of pairs of isomers with known geometries and differently methylated indenes allowed the detailed investigation of how slight geometric and electronic modifications affect their physical properties. The molecular structures have been determined by X-ray diffraction and compared with the fully optimized structures calculated with state-of-the-art DFT methods. Calculated and crystallographic structures agree in establishing the dependence of the orientation of the indene moiety and the ferrocenyl cyclopentadienyl rings on the degree of methylation. The UV−vis spectra and in particular the appearance upon oxidation of a new near-IR absorption, whose energy and intensity increase with the degree of methylation and cyclopentadienyl-indene planarity, are rationalized in the framework of the Hush theory and at quantum chemistry level by DFT and TD-DFT calculations.

Tunable electronic coupling in iron–chromium mixed-valence ions of methylated Cp-indene ligands

“…1f and its geometrical parameters are reported in Table 2. The conformation of the (2-Cp)-hexamethylindene skeleton is almost the same as that of the monometallic (2-ferrocenyl)hexamethylindene [6]. The torsion angle C1-C2-C11-C12 is around 23°, as compared with 24-25°t here observed, proving that the conformation is still controlled by the repulsive interactions between H3.…”

“…The synthetic procedure of heterobimetallic complexes 1 and 2 [4] was successfully applied to 3-5 starting from the corresponding monometallic (ferrocenyl)indenes [5]. The crystal structures of 3 and 5 have been obtained and compared with those of 1 and 2 previously reported [4] (Fig.…”

“…The crystal structures of 3 and 5 have been obtained and compared with those of 1 and 2 previously reported [4] (Fig. 1, Tables 1 and 2).…”

“…In a preliminary communication [4], we have reported on the structures and the electrochemical behaviour of two heterobimetallic isomers, g 6 -(3-ferrocenyl)indene]-Cr(CO) 3 (1) and g 6 -(2-ferrocenyl)indene]-Cr(CO) 3 (2). By combining these results with the IR and near-IR data on the mixed-valence ions 1 + and 2 + obtained at À80°C by chemical oxidation with ferrocenium-BF 4 in CH 2 Cl 2 , it was shown that electronic coupling is principally in 2 + and much less in 1 + .…”

Synthesis and Properties of Mononuclear Group 10 Alkoxy‐Biscarbene Complexes

“…The B3 LYP Hamiltonian was chosen because it was proven to provide accurate structures and reasonable UV/Vis spectra for a variety of chromophores [25] including organometallic complexes. [26] The atomic orbital occupations, bond orders, and donor-acceptor interactions have been computed by using the natural bond orbital (NBO) method. [27] The energies associated with these two-electron interactions have been computed according to the following in Equation (1) in which F is the DFT equivalent of the Fock operator and f and f* are two filled and unfilled Natural Bond Orbitals having e f and e f * energies, respectively; n f stands for the occupation number of the filled orbital.…”