EFFECTS OF ISOLOBAL SUBSTITUTION IN CYCLOPENTADIENYL LIGANDS - THE AZACYCLOPENTADIENYL SYSTEM C4R4N - COMPARATIVE PHOTOELECTRON-SPECTRA OF THE TETRA-TERT-BUTYL FERROCENE DERIVATIVES

The He(I) photoelectron (PE) spectra of tetra-tert-butylferrocene (7) and tetra-tert-butyl-diazaferrocene (8) are reported. A comparison wit h the PE spectrum of ferrocene and pyridine reveals that (i) the hyper conjugative donor effect of a tert-butyl group is about twice that of a methyl or trimethylsilyl group, (ii) the electron-withdrawing potent ial of the nitrogen atom is very similar to that of the phosphorus ato m in diphosphaferrocenes, (iii) there is no significant interaction be tween the nitrogen lone-pair orbitals. An explanation for the marked i nstability of diazaferrocenes compared to stable diphosphaferrocenes i s offered. The PE spectra of 7 and 8 could be reproduced with an INDO/ S theoretical calculation.