Seminar by Prof. Vladimir Ya. Lee -"Towards the Silicon and Germanium Versions of Metathesis: Making M=C (M = Si, Ge) Bonds"

Speaker:
Prof. Vladimir Ya. LEE
Department of Chemistry,
Graduate School of Pure and Applied Sciences,
University of Tsukuba
E-mail: leevya@chem.tsukuba.ac.jp

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Date: Friday, December 11, 2015
Time: 11:00 – 12:00
Venue: C756, Lab 3, Level C
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Title:
“Towards the Silicon and Germanium Versions of Metathesis: Making M=C (M = Si, Ge) Bonds”

Abstract:
Transition metal carbene complexes, the key intermediates in homogeneous catalytic olefin metathesis process, are generally classified as being either Fischer or Schrock types, depending on the interaction mode between the transition metal and the carbene ligand. As for the complexes of carbene analogous of the heavier group 14 elements, mostly Fischer type complexes were known prior to our studies.¹

In this presentation, we report the rare examples of the Schrock type silylidenes and germylidenes of the group 4 metals, complexes 1, featuring loosely bound and therefore readily removable Lewis base ligands L (thf, Me₃P, ArNC) (Scheme).² This provides a vacant site for coordination of unsaturated substrates (alkynes, nitriles, etc.) at the transition metal center and results in the formation of unprecedented (sila/germa)titanocyclobutenes 2, as the “frozen” intermediates of the silicon/germanium versions of metathesis. Zirconium and hafnium analogues of 1 are also readily available, thus demonstrating a general applicability of the method to all group 4 metals. The structure, bonding nature and specific reactivity of metallacycles 2 (including their cycloreversion as the step towards the silicon/germanium metathesis) will also be discussed.

Scheme.  From Schrock type titanium silylidenes/germylidenes 1 to (sila/germa)titanacyclobutenes 2.

References:
1. Lee, V. Ya.; Sekiguchi, A. Organometallic Compounds of Low-Coordinate Si, Ge, Sn and Pb: From Phantom Species to Stable Compounds; Wiley, Chichester, 2010.
2. Lee, V. Ya.; Aoki, S.; Yokoyama, T.; Horiguchi, S.; Sekiguchi, A.; Gornitzka, H.; Guo, J.-D.; Nagase, S. J. Am. Chem. Soc. 2013, 135, 2987.