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The 18-crown-6 (18C6) ether adduct of sodium hexachloroiridate [Na(18C6)]2[IrCl6]·xH2O (1) was found to catalyze an addition of methanol to a variety of nonfunctionalized alkynes RC≡CH (R = H, nPr, nBu, nPen, Ph, HC≡C(CH2)4) yielding the corresponding Markovnikov addition products (ketals) and in the cases of hex-1-yne and hept-1-yne also anti-Markovnikov ones (acetals, <10%). Furthermore, the reaction of methanol with octa-1,7-diyne resulted in a double Markovnikov addition to only one triple bond, yielding 7,7-dimethoxyoct-1-yne with 80% degree of conversion. On the other hand, the regioselectivity in an addition of methanol to functionalized terminal alkynes of the type RC(O)C≡CH (R = OMe, Me) was found to be towards anti-Markovnikov products (70–93%). In these two cases vinyl ether intermediates were observed NMR spectroscopically in the course of the reactions. [Copyright &y& Elsevier]

The 18-crown-6 (18C6) ether adduct of sodium hexachloroiridate [Na(18C6)]2[IrCl6]·xH2O (1) was found to catalyze an addition of methanol to a wide variety of internal alkynes RCCR′ (R/R′ = Et/Et, Me/Et, Me/nPr, Me/nBu, Me/tBu, Me/Ph, Et/nPr, Et/Ph) yielding the corresponding ketals and, due to the presence of water traces, their hydrolysis products (ketones). The regioselectivity of the addition of methanol to unsymmetrically disubstituted internal alkynes is governed by steric and electronic factors, being the highest in the case of pent-2-yne, hex-2-yne and hept-2-yne (80–85%). In the case of MeC≡CCO2Me, an alkyne having an electron-withdrawing substituent, the addition was found to be 100% regioselective, with two methoxy groups going to the side away from an ester group. Furthermore, in the analogous addition of methanol to MeO2CC≡CCO2Me, besides the vinyl ethers (E)/(Z)-MeO2CC(OMe)=CHCO2Me, a cyclotrimerization product (C6(CO2Me)6) was also observed. A comparison of the catalytic potential of other iridium compounds in the addition of methanol to hex-3-yne revealed that all examined ionic hexachloroiridates ([Na(18C6)]2[IrCl6]·xH2O, Na2[IrCl6]·6H2O, H2[IrCl6]·6H2O, Na3[IrCl6]·xH2O) were catalytically active, whereas [IrCl(CO)(PPh3)2] and [(IrCl2Cp*)2] were found to be almost inactive (degree of conversion <10%). However, the best results were obtained for the crown ether adduct 1. Moreover, in the addition of CD3OD to hex-3-yne, [Na(18C6)]2[IrCl6]·xH2O (1) was also found to catalyze a H/D exchange of protons in the neighborhood of a keto group or a quaternary carbon of a ketal with a degree of deuteration >97%. [Copyright &y& Elsevier]

The iridium dinitrogen complex [IrCl(N2)(PPh3)2] (1) was found to react with alkynylsilanes RC≡CSiR'3 to form the vinylidene iridium(I) complexes trans-[IrCl{=C=CR(SiR'3)} (PPh3)2 (R/R′=Ph/Me, 2; Me/Me, 3; Bn/Me, 4; SiMe3/Me, 5; SiEt3/Et, 6; iPr/Me, 7) and with Me3SiC≡CC(O)R to yield the iridium η2-alkyne complexes trans-[IrCl{η2-Me3SiC≡CC(O)R}(PPh3)2] (R=OEt, 9; Me, 11). Complex 9 was found to isomerize upon heating or upon UV irradiation yielding the vinylidene complex trans-[IrCl{=C=C(SiMe3)CO2Et}(PPh3)2] (10). The reaction of 1 with Me3SiC≡C—C≡CSiMe3 yielded the complex trans-[IrCl{=C=C(SiMe3)C≡CSiMe3}(PPh3)2] (8), whereas with MeO2CC≡CCO2Me the iridacyclopentadiene complex [Ir{C4(CO2Me)4}Cl(PPh3)2] (13) was formed. The complexes were characterized by means of 1H, 13C and 31P NMR spectroscopy as well as by IR spectroscopy and microanalysis. [Copyright &y& Elsevier]