Theoretical group 14 chemistry. Part 2. Si4R6: a theoretical approach

The relative energies of the isomeric compounds of Si₄R₆ (R=H, Me, Ph, 2,6-dimethylphenyl, 2,6-diisopropylphenyl) were explored with different theoretical methods including semiempirical, DFT and perturbation theory calculations. The results are compared with previous calculations and with experimental findings. On going from small substituents to bulky aryl groups the stability of the isomers is reversed from tetrasilabicyclo[1.1.0]butane (1) and tetrasilacyclobutene derivatives to the s-cis and s-trans conformers of tetrasilabuta-1,3-dienes. The concept of bond stretch isomerism of 1 and its dependence on the substituents at the central silicon atoms is also discussed.