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Arrhenius Parameters for the Addition of Phenols to the Silicon-Silicon Double Bond of Tetramesityldisilene
 

Summary: Arrhenius Parameters for the Addition of Phenols to the
Silicon-Silicon Double Bond of Tetramesityldisilene
Yitzhak Apeloig* and Moshe Nakash
Department of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum
Chemistry, Technion-Israel Institute of Technology, Haifa 32000, Israel
Received January 13, 1998
We have measured, for the first time for a disilene, the Arrhenius activation energies (Ea)
and preexponential factors (ln A) for an addition reaction. The addition reactions of both
p-CH3OC6H4OH and p-F3CC6H4OH to tetramesityldisilene (1) have positive Arrhenius
activation energies of 13.7 and 9.7 kcal/mol, respectively, and highly negative entropies of
activation of -34.9 and -45.3 eu, respectively (ln A ) 13.0 and 7.8 M-1 s-1, respectively).
The more negative Sq value for p-F3CC6H4OH is consistent with a more ordered type of
addition in this case. The rates of addition of phenols to 1 (k 10-4-10-2 M-1 s-1) are
dramatically slower, i.e., by a factor of ca. 109-1012, compared with the rates of addition of
alkyl alcohols to the less hindered (E)- and (Z)-1,2-dimethyl-1,2-diphenyldisilenes (3E and
3Z) and 1,2,2-trimethyl-1-phenyldisilene (4) (k 107-108 M-1 s-1).5 Steric protection of
the SidSi bond in 1 by the bulky mesityl substituents is probably responsible for this large
reactivity difference. Competition experiments support this conclusion; EtOH reacts with
3E only 1.5 times faster than i-PrOH and 19 times faster than t-BuOH (similar competition
ratios were measured for 3Z and 4),5

  

Source: Apeloig, Yitzhak - Department of Chemistry, Technion, Israel Institute of Technology

 

Collections: Chemistry