1 research outputs found
Reactivity of a Cationic (C<sub>5</sub>Me<sub>5</sub>)Ir<sup>III</sup>-Cyclometalated Phosphine Complex with Alkynes
The
electrophilic cationic complex [(Ī·<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)ĀIrĀ(C<sup>ā§</sup>P)]<sup>+</sup>, which contains a metalated
phosphine derived from PMeĀ(Xyl)<sub>2</sub> (Xyl = 2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub>), reacts at ā60 Ā°C with the
alkynes HCī¼CH, PhCī¼CH, and PhCī¼CMe, with formation
of the corresponding Ļ adducts [(Ī·<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)ĀIrĀ(C<sup>ā§</sup>P)Ā(Ī·<sup>2</sup>-alkyne)]<sup>+</sup>. Thermal activation of these complexes leads to products
that result from the CāC coupling of the alkyne and the Ļ
IrāC bond of the metalated phosphine, whose nature depends
markedly upon the alkyne involved. Thus, for HCī¼CH the carbonācarbon
bond -forming reaction leads to an iridium-bound alkene moiety as
the thermodynamic product, whereas the analogous complexes derived
from the bulkier PhCī¼CH and PhCī¼CMe alkynes undergo
further transformation into allylic structures. Mechanistic studies
supported by the use of PhCī¼CD demonstrate the implication
of an undetected vinylidene structure, Irī»Cī»CĀ(H)ĀPh,
in the key carbonācarbon bond-forming step of the PhCī¼CH
reaction system, whereas for the internal alkyne PhCī¼CMe a
migratory insertion mechanism is operative. However, no clear distinction
between these two routes can be made for the CāC bond-forming
reaction for which HCī¼CH is responsible