Cyclopropenation and Related Reactions of Ruthenium Vinylidene Complexes

Facile deprotonation of a number of cationic ruthenium vinylidene
complexes, followed by cyclopropenation,
is accomplished in acetone. The deprotonation of
[Ru]C(Ph)CH2R+, ([Ru] =
(η5-C5H5)(PPh3)2Ru)
by n-Bu4NOH induces a novel cyclization reaction and yields the neutral
cyclopropenyl complexes
[Ru]−CC(Ph)CHR
(3b, R = CN; 3c, R = Ph; 3d, R =
CHCH2; 3e, R = CHCMe2).
Complex
[Ru]−CC(C6H9)CHCN+
(3k) is
similarly prepared. Protonation of 3b−3e
regenerates the corresponding vinylidene complexes. Deprotonation
of
[Ru]CC(Ph)CH2COOMe+
(2h) by n-Bu4NOH induces a
different type of cyclization and yields the neutral furan
complex
[Ru]−CC(Ph)CHC(O)OMe
(4h). The cyclopropenyl complex containing a methoxy
substituent cannot
be prepared from
[Ru]CC(Ph)CH2OCH3+
(2i), but F- of
n-Bu4NF attacks the Cα of
2i to produce the unstable
vinyl complex [Ru]C(F)C(Ph)CH2OCH3
(5). Complex
[Ru]−CC(Ph)C(CN)OCH3
(9b) was indirectly prepared
from the addition of TCNQ to 3b, giving
[Ru]CC(Ph)CH(CN)TCNQ (6b)
followed by methanolysis. Unlike 3,
complex 9b is not converted to vinylidene complex, instead,
removal of the methoxy substituent by acid gives the
cationic cyclopropenylium complex
[Ru]−CC(Ph)C(CN)+
(10b). Complex
[Ru]−CC(Ph)C(COOMe)+
(10h)
is similarly prepared from 4h via a TCNQ complex
6h followed by a methoxy-substituted complex 9h.
In the
presence of allyl iodide, opening of the three-membered ring of
3b, followed by a subsequent oxidative coupling
reaction, gives a dimeric dicationic product
{[Ru]CC(Ph)−CHCN}22+
(11). Proton abstraction of 11 by
n-Bu4NF gives the biscyclopropenyl complex
{[Ru]−CC(Ph)CCN}2
(12). Molecular structures of complexes 3b,
3f,
4h, 6b, 9b, and 11 have
been confirmed by X-ray diffraction analysis.