C. Bianchini et al., THE MECHANISM OF THE RU-ASSISTED C-C BOND-CLEAVAGE OF TERMINAL ALKYNES BY WATER, Journal of the American Chemical Society, 118(19), 1996, pp. 4585-4594
The hydration of phenylacetylene in the presence of the complex mer, t
rans-(PNP)RuCl2(PPh(3)) in THF at 60 degrees C leads to the cleavage o
f the C-C triple bond with formation of the carbonyl complex fac, cis-
(PNP)RuCl2(CO) and toluene [PNP=CH3CH2CH2N(CH(2)CH(2)PPh(2))(2)]. A st
udy under different experimental conditions, the use of model and isot
ope labeling experiments, and the detection of several intermediates,
taken altogether, show that the C-C bond cleavage reaction comprises a
number of steps, among which the most relevant to the mechanism are 1
-alkyne to vinylidene tautomerism, conversion of a vinylidene ligand t
o hydroxycarbene by intramolecular attack of water, deprotonation of h
ydroxycarbene to sigma-acyl, deinsertion of CO from the acyl ligand, a
nd hydrocarbon elimination by protonation of the metal-alkyl moiety. T
he following intermediate species have been isolated and characterized
: the vinylidene fac,cis-(PNP)RuCl2{C=C(H)Ph}, the (aquo)(sigma-alkyny
l) complex fac-(PNP)RuCl(C=CPh)(OH2), and the (benzyl)carbonyl mer-(PN
P)RuCl(eta(1)-CH(2)Ph)(CO). Other intermediates such as the sigma-acyl
mer-(PNP)RuCl(eta(1)-COCH(2)Ph)(CO) have been intercepted by addition
of appropriate reagents, while the independent synthesis of the amino
carbene complex fac, cis-(PNP)RuCl2{C(NC5H10)(CH(2)Ph)} and its reacti
on with water have provided evidence for the intermediacy of a hydroxy
carbene species in the C-C bond cleavage reaction.