Neutral Pentacoordinate Silicon Fluorides Derived from Amidinate, Guanidinate, and Triazapentadienate Ligands and Base-Induced Disproportionation of Si2Cl6 to Stable Silylenes

Pentacoordinate silicon fluorides L1SiF3 (2a), L2SiF3 (2b), and (L3SiF2)2 (2c)2 based on amidinate (L1 = PhC(NtBu)2), guanidinate (L2 = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinate), and triazapentadienate (L3 = NC(NMe2)NC(NMe2)NAr; Ar = 2,6-iPr2C6H3) ligands were prepared by fluorination of the corresponding chlorosilanes L1SiCl3 (1a), L2SiCl3 (1b), and L3SiCl2 (1c) with Me3SnF at ambient temperature. Compounds 1b, 1c, 2a, 2b, and (2c)2 were characterized by 1H, 13C, 19F, and 29Si NMR spectroscopic studies. Molecular structures of 1b, 1c, 2a, and (2c)2 were determined by single crystal X-ray structural analysis. Invariom refinement involving non-spherical scattering factors of the Hansen-Coppens multipole model was performed for 1b. Compound L3SiF2 (2c) is dimeric both in the solid state and in solution, whereas its chloro-analogue 1c is monomeric. The attempted synthesis of diamidinatotetrachlorodisilane by reaction of lithium amidinate with Si2Cl6 led to the formation of the silane (1a) and the silylene L1SiCl (3). Reaction of Si2Cl6 with N-heterocyclic carbenes (NHC) afforded NHC adducts of dichlorosilylene and SiCl4. A one pot method for the preparation of base-stabilized silylenes from Si2Cl6 is discussed.