Investigations on the Coupling of Ethylene and Alkynes in [IrTp] Compounds: Water as an Effective Trapping Agent

Abstract

Abstract:The reaction of the bis(ethylene) complex Tp Me2

Synthesis and Reactivity of Iridacycles Containing the TpMe2Ir Moiety

“…methyl propiolate HCϵCCO 2 Me (MP) in the presence of added water (10 equiv.) regioselectively yielded the iridacyclopentadiene 18 [15] (Scheme 12).…”

“…In fact, by using normally dried solvents (only adventitious water being present), the reaction did not stop in the formation of 16, but continued to give an iridacycloheptatriene (see below), with starting material remaining (Scheme 10). Scheme 10. This metallacyclopentadiene 16 could also be prepared from Tp Me2 Ir(C 2 H 4 ) 2 (4), [15] but again requiring a large excess of water. Important mechanistic information was obtained by carrying out the reaction at low temperatures and with deuterated DMAD.…”

“…[13] It is worth mentioning briefly that some adducts of 3, i. [15] where the diene is displaced by two molecules of the alkyne. This reaction will be discussed in detail in the next section.…”

“…These studies ruled out any interconversion between the iridacyclopentadiene and a bis(alkyne)Ir I species, and this was in accord with the findings observed in a related system. (17), [15] generated by a molecule of DMAD substituting one of the ethylene ligands in 4 (Scheme 11). [26] Compound 17 was stable up to 10°C, but above that temperature it reacted with a second molecule of DMAD to form either metallacycle 16, if the reaction mixture contained enough water, or an hydride-alkene species (21 in the next section) when normal anhydrous conditions were employed.…”

“…DMAD, it was displaced, to result in the iridacyclopentadiene 16. [15] This iridacycle [24] completes the 18-electron metal count by the coordination of a molecule of added water, [25] which is essential for the isolation of the iridacyclopentadiene. In fact, by using normally dried solvents (only adventitious water being present), the reaction did not stop in the formation of 16, but continued to give an iridacycloheptatriene (see below), with starting material remaining (Scheme 10).…”