Studies of silicon–nitrogen ring formation from tetrachlorodisilanes

The addition of n equiv of MesNHLi (n = 1, 2, 3, 4) and m equiv of 12-crown-4 (m = 0.1, 1, 2, 3, 4) to (RsiCl₂)₂ (R = Mesityl; t-Butyl) in THF at −78°C resulted in higher yields and improved selectivities of cyclodisilazanes and azadisilacyclopropanes. The reaction of 2 equiv of MesNDLi with (MesSiCl₂)₂ ( I ) yielded cis-2-chloro-1,2,3,4-tetramestylcyclodisilazane ( 2a ) with 95% Si H deuteration. 2a was quantitatively chlorinated with retention of stereochemistry by N-chlorosuccinimide to give the cis dichlorocyclodisilazane ( 3 ). Variable-temperature ¹H NMR studies from −70°C to 25°C in d₈-THF were performed on 1 , 2a , 2b , and 3 . 1 exhibited little variation throughout the temperature range, whereas 2a , 2b , and 3 showed several rotational isomers. trans-2,3-Bis(mesitylamino)-1,2,3-trimesitylazadisilacyclopropane was shown to isomerize to the cis isomer in the presence of n-BuLi or MesNHLi. The molecular structures of 1 and 3 were determined by X-ray crystallography. Compound 1 crystallized in the monoclinic space group P2₁/c, with cell parameters a = 16.599(2) Å b = 14.633(2) Å, c = 16.945(2) Å, β = 92.044(13)°, V = 4113.1(8) ų, Z = 8, d (calcd) = 1.409 g/cm³, and R = 6.88%. Compound 3 ° C₆H₆ crystallized in the orthorhombic space group Pbca, with cell parameters a = 17.906(4) Å, b = 13.918(3) Å, c = 31.700(6) Å, V = 7900(3) ų, Z = 8, d (calcd) = 1.194 g/cm³, and R = 7.52%.