Iridium-assisted CC bond cleavage of 1-alkyne by water: preparation of new alkyl derivatives

Abstract

Alkyl complexes IrCl₂(η¹-CH₂Ar)(CO)(PPh₃)₂ (1) [Ar = Ph (a), p-tolyl (b)] were prepared by allowing the hydride mer- or fac-IrHCl₂(PPh₃)₃ to react with terminal alkynes ArCCH in the presence of water. The complexes were characterized spectroscopically (IR and ¹H, ³¹P, ¹³C NMR) and by the X-ray crystal structure determination of 1b. The acyl complex IrCl₂{C(O)CH₂C(CH₃)₃}(PPh₃)₂ (2) was also prepared by reacting mer-IrHCl₂(PPh₃)₃ with tert-butylacetylene HCCC(CH₃)₃ in the presence of H₂O. A reaction path for the hydration of terminal alkyne in the presence of the Ir(III) complex leading to the cleavage of the CC bond, with the formation of the complexes 1 or 2 is also proposed. Acetylide complexes IrHCl(CCAr)(PPh₃)₃ (3), IrHCl(CCAr)(AsPh₃)₃ (4) [Ar = Ph (a), p-tolyl (b)] and IrHCl(CCPh){PPh(OEt)₂}(PPh₃)₂ (5) were prepared by reacting IrHCl₂L₃ (L = PPh₃, AsPh₃) or IrHCl₂{PPh(OEt)₂}(PPh₃)₂ with lithium acetylide. Protonation reaction with Brønsted acids of the acetylide 3 was also studied and led to unstable vinyl derivatives. The stable vinyl [IrCl{η²-CHC(H)COOMe}L₂]BPh₄ (6,7) [L = PPh₃ (6), AsPh₃ (7)] complexes, instead, were prepared by allowing IrHCl₂L₃ to react first with AgCF₃SO₃ and then with methyl propiolate.