CONFORMATIONAL BEHAVIOR AND ELECTRONIC-STRUCTURE OF SILYLKETENES STUDIED WITH QUANTUM-CHEMICAL CALCULATIONS AND PHOTOELECTRON-SPECTROSCOPY

The He(I) photoelectron spectra of silylketenes (Me3Si)(2)C=C=O(1), Me 5Si2CH=C=O (2), Me2Si(CH=C=O)(2) (3), MeSi(CH=C=O)(3) (4), (SiMe2CH=C= O)(2) (5), and (CH2SiMe2CH=C=O)(2) (6) have been recorded and their st ructures and orbital energies have been calculated by ab initio method s. Orbital energies for disilanes 2 and 5 are strongly dependent on a Si-Si-C-C torsional angle due to sigma-pi orbital interaction. Compari sons between experimental and simulated spectra show that 2 and 5 pref er conformations in which the Si-Si bond and ketene group(s) are appro ximately orthogonal (113 degrees and 111 degrees, respectively). Silyl alkenes Me5Si2CH=CH2 (7) and (SiMe2CH=CH2)(2) (8), which have been inc luded in the computational study, show the same behavior as their corr esponding silylketenes. Silylbis- and trisketenes 3-6 do not exhibit p i-pi interaction of any significance. For Si-Si containing compounds, the best agreement between experimental and computed data was obtained when Becke3LYP/6-31G//HF/3-21G* was employed.