Effects of substituents on the formation of rhenium carbyne and η2-vinyl complexes from the reactions of ReH5(PMe2Ph)3 with terminal alkynes

Abstract

The reactions of the rhenium polyhydride complex ReH₅(PMe₂Ph)₃ with HCCAr (Ar = p-C₆H₄CF₃, o-C₆H₄CF₃, o-C₆H₄Me and o-C₆H₄Br) have been carried out. Treatment of ReH₅(PMe₂Ph)₃ with HCC(p-C₆H₄CF₃) in the presence of two equiv. of HCl produces a mixture of the carbyne complex Re(CCH₂(p-C₆H₄CF₃))Cl₂(PMe₂Ph)₃ and the η²-vinyl complex Re(η²-CH₂C(p-C₆H₄CF₃))Cl₂(PMe₂Ph)₃. Treatment of ReH₅(PMe₂Ph)₃ with HCCAr (Ar = o-C₆H₄CF₃, o-C₆H₄Me, o-C₆H₄Br) in the presence of two equiv. of HCl produces only the carbyne complexes Re(CCH₂Ar)Cl₂(PMe₂Ph)₃. The mechanism of the reactions of ReH₅(PMe₂Ph)₃ with HCCR has also been studied with the aid of DFT calculations, which suggests that the reactions are kinetically controlled and the pathways leading to the carbyne and η²-vinyl complexes are influenced by the steric and electronic effects of the substituents of the alkynes.