Stable Four-Coordinate Guanidinatosilicon(IV) Complexes with SiN3El Skeletons (El = S, Se, Te) and Si=El Double Bonds

To get information about the reactivity profile of the donor-stabilized guanidinatosilicon(II) complexes 2 and 3, a series of oxidative addition reactions was studied. Treatment of 2 and 3 with S8, Se, or Te afforded the respective four-coordinate silicon(IV) complexes 8-10 and 12-14, which contain an SiN3 El skeleton (El = S, Se, Te) with an Si=El double bond. Treatment of 2 with N2O yielded the dinuclear four-coordinate silicon(IV) complex 11 with an SiN3O skeleton and a central four-membered Si2O2 ring. Compounds 8-14 exist both in the solid state and in solution. They were characterized by elemental analyses, NMR spectroscopic studies in the solid state and in solution, and crystal structure analyses. The reactivity profile of 2 was compared with that of the structurally related bis[N,N'-diisopropylbenzamidinato(-)]silicon(II) (1), which is three-coordinate in the solid state and four-coordinate in solution (1'). In contrast, as shown by state-of-the-art relativistic DFT analyses and experimental studies, silylene 2 is three-coordinate both in the solid state and solution. The three-coordinate species 2 is 9.3 kcal mol(-1) more stable in benzene than the four-coordinate isomer 2'. The reason for this was studied by bonding analyses of 2 and 2', which were compared with those of 1 and 1'. The gas-phase proton affinities of the relevant species in solution (1' and 2) amount to 288.8 and 273.8 kcal mol(-1), respectively.