om9b00509_si_002.xyz (91.48 kB)
From Dialkyltitanium Species to Titanacyclopropanes: An Ab Initio Study
dataset
posted on 2019-10-15, 19:33 authored by Philippe BertusAlthough the dialkoxytitanacyclopropanes
are presented as important
reagents in organic synthesis, the mechanism of their generation from
dialkyltitanium species is not firmly established, as shown by the
various propositions cited in the literature. An ab initio study of
these transformations was investigated, namely, β-H elimination,
β-H abstraction, epimetalation, as well as the related α-H
abstraction. The results tend to show that the formation of a titanium
hydride intermediate is unlikely, but, most probably, a direct hydrogen
transfer (β-H abstraction) would occur. Compared to titanocene
analogues, the α-H and β-H abstraction reactions were
less favorable with dialkoxytitanium complexes. The overall reaction
was found to be more favorable in the case of dialkoxydialkyltitanium
complexes by the prior formation of bimetallic intermediates, underlining
the importance of titanium ate complexes in this chemistry. A prior
agostic interaction between the ethyl moiety and the metal was found
to facilitate the hydrogen transfer and the formation of the metallacyclopropane.
This phenomenon was illustrated by an easier β-H abstraction
from a complex bearing an agostic interaction in its ground state.
The intrinsic bond orbital method was used throughout this work to
better visualize the electronic processes involved in these transformations.