Structural Probing on the Sn-Cc5 ring Bond of the Sn(Ⅱ) Metallocenes in Both the Solid State and the Temperature-dependent Solution Relaxation State

摘要

Various bond modes of the M-Cc5 ring exist in metallocene compounds of group 14 heavier elements,mostly due to an intricate interaction between the lone electron pairs at the M center and the 6 π-electrons of the C5 ring.The tin(Ⅱ) metallocene complexes LSnR (L =HC[CMe(N-2,6-iPr2C6H3)]2,R =cyclopentadienyl,C5H5 (1);indenyl,C9H7 (2);fluorenyl,C13H9 (3)) stabilized by the β-diketiminato ligand were prepared and utilized in the study on their solid and solution state structures.X-ray single-crystal diffraction data revealed an η1-mode of the Sn-Cc5 ring bond in each 1～3.However,the room temperature 1H NMR spectral studies disclosed such a fluxional bonding mode in solution.The 119Sn NMR studies suggested a quadruple coordination nature of the Sn center in 1 while the triple coordination manner was for the Sn atom in both 2 and 3.Then the variable-temperature (25～-75 ℃) 1H NMR spectral studies for each 1～3 were performed,which detected the relaxation state structures of 1 ～3 at lower temperature.All of these results indicate a stereochemical activity of the lone electron pairs at the tin(Ⅱ) atom that definitely has an electronic interaction with the 6 π-electrons of the C5 ring.The observed Sn-Cc5 ring bond modes appear influenced by either the metallocene size or the compound state existed.