Cooperative and non-cooperative additions involving a silicon atom and a redox-active ligand

The silylene [(dpp-bian)Si:] (1), where dpp-bian is 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene, exhibits remarkable reactivity with a variety of substrates. It reacts with chloroform and water via O-H and C-Cl bond activation to yield oxidative addition products 2 and 3, respectively. Reactions of 1 with dibenzylideneacetone and tolane involve exclusively the silicon atom and result in [4 + 1]- and [2 + 1]-cycloaddition products 4 and 6. Treatment with isoselenocyanate results in unprecedented cleavage of the CSe bond, leading to activation product 5. In contrast, treatment with acetylene and phenylacetylene leads to cooperative cycloaddition reactions, producing unique cycloadducts 7 and 8. These reactions represent a new type of cycloaddition to a tetravalent silicon atom, facilitated by a redox-active ligand. The new compounds were characterized by NMR and IR spectroscopy, elemental analysis, and X-ray diffraction studies. Their electronic structures and reaction pathways were investigated using DFT calculations.