Synthesis and crystal structures of novel 1-aza-2-silacyclobut-3-enes

Abstract

A crystallographic re-investigation of the structure of the 4-aryl(lithio)amino-1-aza-2-silacyclo-but-3-ene derivative, [Li{N(Ar)CC(R)SiR₂NAr}](tmen) F (R = SiMe₃, Ar = C₆H₃Me₂-2,6), formed by the treatment of [Li(SiR₃)(thf)₃] with ArNC in the presence of tmen, revealed the presence of two independent molecules within the unit cell. Its protonolysis with cyclopentadiene monomer gave the 1-aza-2-silacyclobutene, HN(Ar)CC(R)Si(R)₂NAr 2b. Replacing tmen with 1,2-bis(dimethylphosphino)ethane (dmpe), in the reaction of [Li(SiR₃)(thf)₃] with ArNC, gave either [Li{N(Ar)CC(R)Si(R)₂NAr}(thf)₂] 4 or the dimer [Li{N(Ar)CC(R)Si(R)₂NAr}(μ-dmpe)]₂3, the latter being preferred at low thf concentrations. Each of the compounds F, 2b, 3 and 4 was characterised by multinuclear NMR spectroscopy and (not 4) X-ray diffraction. The single crystal structures of 2b and 3 provide the first examples of a neutral CCSiN compound and a neutral phosphine-bound alkali metal complex, respectively. The NMR spectra revealed that 3 undergoes speciation in solution.