Paramagnetic intermediates in the photoinduced reaction between dodecamethylcyclohexasilane and 9,10-phenanthraquinone: Time-resolved CIDNP study

The reaction between dodecamethylcyclohexasilane (Me2Si)61 and 9,10-phenanthraquinone 2 has been studied by means of CIDNP method. In the polar solvent, the photodecomposition of 1 is shown to proceed via triplet radical ion pair formed by phenanthraquinone radical anion and cyclohexasilane radical cation. Its transformation leads to the cyclic reaction product – 10-membered cyclic dioxahexasilecine 8 – formally resulting from the addition of linear 1,6-silicon-centered biradical radical dotSi(Me)2–Si4(Me2)4-(Me)2Siradical dot to Cdouble bond; length as m-dashO bonds of quinone. Product 8 is unstable, after several hours it converts to dioxasilole 4 via sequential repeated elimination of dimethylsilylenes 3.