Electronic structure of 2,5-dimethylazaferrocene

Electronic structures of methylated azaferrocenes and their borane adducts: Photoelectron spectroscopy and electronic structure calculations

“…Therefore, we assign the ionization energy of the nitrogen lone pair in III at 9.55 eV, consistent with the previously assigned value of 9.40 eV for the lone pair in I. 12 The ionization energy of the lone pair for pyridine is now established as 9.67 eV, 28 which is slightly greater than the azaferrocene values. On the basis of this data, one would expect I and III, in general, to be better σ-donors than pyridine.…”

“…S1-S3, ESI †). The assignment of the regions below 12 eV is based on comparison with previously reported spectra of decamethylferrocene, 22 2,5-dimethylazaferrocene (I), 12 ferrocene 22 and pyridine-borane. 17 The changes in the HeII-HeI band intensities related to the photoionization cross-sections below were also used as an aid in the assignment, especially for the bands corresponding to the ionizations from orbitals with nitrogen character and with iron 3d character.…”

“…Most recently UV Photoelectron Spectroscopy (UPS) data were reported for I, and the effect of nitrogen on the iron 3d-ligand π orbital interactions analyzed. 12 Earlier, UPS data of 2,2′,5,5′-tetra-tert-butyl-diazaferrocene were examined for evidence of interaction between the nitrogen lone pair orbitals, the hyperconjugative effects of tert-butyl groups, and comparison of the electron-withdrawing effect of N vs. P. 13 Frison et al analyzed in detail through DFT calculations the electronic structure of aza-and phosphaferrocenes in which all five C-H moieties in a Cp ring are sequentially replaced by N or P. 14 They concluded that the electronegativity of the heteroelement as well as the shape of its lone pair has profound effects on the stability and the ease of electrophilic substitution of the heteroferrocene. Their calculations also reproduce the experimentally observed greater Lewis and Brønsted basicity of the azaferrocene lone pair vs. that of phosphaferrocene.…”

“…We also report UPS data for free PMAF (III) for comparison purposes: The UPS data of DMAF (I) has previously been disclosed. 12 All four of these complexes have also been crystallographically characterized allowing a direct correlation between structural data and electronic structure. The crystal structure of the new adduct, II, is also included in this report.…”