S. Lafolleebezzenine et al., REACTION OF AMINOCARBENE COMPLEXES OF CHROMIUM WITH ALKYNES 10 - FROMLARGE TO SMALL CYCLIC AMINES - SINGLE VERSUS DOUBLE ALKYNE INSERTIONS, Journal of organometallic chemistry, 567(1-2), 1998, pp. 83-100
For the purpose of comparing the reaction of various aminocarbene comp
lexes of chromium with alkynes and to ascertain several points of the
mechanism of their interaction, a series of complexes derived from lar
ge cyclic amines, HN(CH2)(n) (n greater than or equal to 6) and from a
small cyclic amine (n = 2) was synthesized. In the case of the larger
amines, all the complexes examined herein, led to the expected bridge
head lactams 12 as the major product, providing strong evidence for a
concerted rearrangement of an intermediate nitrogen-ylid complex such
as 4. The X-ray structure of the lactam complex 12d (n = 12) has been
established in order to confirm the ring opening and the migration of
the twelve carbon-atom alkyl chain from nitrogen to the gamma-carbon.
Interestingly, the last possibility, the migration from nitrogen to ox
ygen in 4, which had so far not been observed but which according to c
alculations should also be possible, took place in the case of complex
10b (n = 7), giving rise, yet in low yield, to an alkoxypyrrole 14. M
inor products resulting from annulation reactions without CO insertion
s, were also observed. For aminocarbene complexes derived from methyla
ziridine (n = 2), important results, which substantiate previous obser
vations, have been obtained especially as far as the mechanism of the
insertion reaction is concerned: the regioselectivity of the ring-open
ing reaction could be established by X-ray crystallography on two isom
eric complexes 25 and 26, the timing of the various steps could be det
ermined by the examination of the reactivity of vinyl-aziridinyl carbe
ne complexes 31 and 35 which led surprisingly to aziridinyl phenols 33
and 36. Finally, an unexpected product, the structure of which could
also be established by X-ray crystallography as 27, and resulting from
the oxidation at the a position of the carbonyl in complexes 25 or 26
was isolated during the interaction of complex 23 with diphenylacetyl
ene. (C) 1998 Elsevier Science S.A. All rights reserved.