Crystal and Molecular Structure of N-(Trifluorosilyl)trimethylphosphinimine Dimer

Abstract

N-(Trifluorosilyl)trimethylphosphinimine dimer crystallises in the monoclinic space group P21/n, Z = 2, with a= 6.314(2), b = 12.057(5), c = 10.936(4) Å, β = 95.45(2)°. The structure was solved by direct methods and refined to R 0.078 for 1117 independent reflections. The molecule is dimeric and centrosymmetric with an planar four-membered [SiN]2 ring containing trigonal-bipyramidal pentacoordinate silicon and trigonal nitrogen. Significant differences are observed in the bond lengths from silicon to its equatorial and axial ligands: Si-Neq 1.736(4), Si-Nax 1.857(4), Si-Feq1.606(4) and 1.607(3), Si-Fax 1.668(3) Å. The Si-Neq bond length is similar to that in tetracoordinate derivatives for which a (p →d) π bonding component has been postulated, while the Si-Nax distance is very much shorter than that observed in other pentacoordinate derivatives.