טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentYuliya Goldshtein
SubjectSynthesis and Reactions of Heavy Analogues of Alkenes,
R2E=CR'2(E=Si, Ge, Sn)
DepartmentDepartment of Chemistry
Supervisors ? 18? Apeloig Yitzhak
Dr. Bravo-Zhivotovs Dmitry


Abstract

The main goal of this work was to synthesize the heavy analogous of silenes - germenes and stannenes, i.e. R2E=CR’2, E = Ge and Sn, respectively, via the E-olefination reaction. We successfully synthesized the first stable germene, (t-BuMe2Si)2Ge=2-Ad, and the short-lived stannene, (t-BuMe2Si)2Sn=2-Ad, lacking resonance or heteroatom stabilization,  by the reaction of (t-BuMe2Si)3ELi•nTHF (E = Ge, n = 2; E = Sn, n = 3) with 2-adamantanone in benzene. The structure of the new germene was characterized by X-ray crystallography indicating clearly its Ge=C double bond character. The new stannene, who had a half-life of about 6 hours, was characterized by NMR spectroscopy, and its NMR chemical shifts were also supported by quantum-mechanical DFT calculations. Examination of the X-ray and calculated molecular structures of (t-BuMe2Si)2E=2-Ad (E = Si, Ge, Sn) shows that replacing the doubly-bonded Si or Ge atoms (who are very similar) by Sn atom reduces the steric protection of the E=C bond by the silyl substituents, resulting in the higher reactivity of the stannene. DFT calculations show that stannene is more polarized than silene and germene contributing to its higher reactivity.


The reactions of (t-BuMe2Si)2E=2-Ad with a carbonyl compound and with a transition metal complex were also studied. Reaction of (t-BuMe2Si)2E=2-Ad (E = Ge and Sn) with 2,6-di-t-butyl-p-quinone yields the new stable germaoxetane and short-lived stannaoxetane, respectively. The new germaoxetane was characterized by X-ray crystallography. Reaction of (t-BuMe2Si)2Sn=2-Ad, with (dmpe)Pt(PEt3)2 yields the first reported stable η2-stannene-Pt(0) complex, which was characterized by X-ray crystallography, supporting the presence of a Sn=C bond in the stannene. The geometrical parameters and the NMR chemical shifts indicate that the metallacycle form dominates this Pt-stannene complex.