Hydrogallierungsreaktionen mit den Monoalkinen H 5 C 6 ‐C≡C‐SiMe 3 und H 5 C 6 ‐C≡C‐CMe 3 – cis / trans ‐Isomerie und Substituentenaustausch

Hydrogallation Reactions Involving the Monoalkynes H 5 C 6 ‐C≡C‐SiMe 3 and H 5 C 6 ‐C≡C‐CMe 3 – cis / trans Isomerisation and Substituent Exchange Phenyl‐trimethylsilylethyne, H 5 C 6 ‐C≡C‐SiMe 3 , reacted with different dialkylgallium hydrides, R 2 Ga‐H (R = Me, Et, n Pr, i Pr, t Bu), by the addition of one Ga‐H bond to its C≡C triple bond (hydrogallation). The gallium atoms attacked selectively those carbon atoms, which were also attached to trimethylsilyl groups. The cis arrangement of Ga and H across the resulting C=C double bonds resulted only for the sterically most shielded di( tert ‐butyl)gallium derivative, while in all other cases spontaneous cis / trans rearrangement occurred with the quantitative formation of the trans addition products. The diethyl compound Et 2 Ga‐C(SiMe 3 )=C(H)‐C 6 H 5 ( 2 ) gave by substituent exchange the secondary products EtGa[C(SiMe 3 )=C(H)‐C 6 H 5 ] 2 ( 7 , Z , Z ) and Ga[C(SiMe 3 )=C(H)‐C 6 H 5 ] 3 ( 8 ). Interestingly, compound 8 has two alkenyl groups with a Z configuration, while the third C=C double bond has the cis arrangement of Ga and H ( E configuration). The reversibility of the cis / trans isomerisation of hydrogallation products was observed for the first time. tert ‐Butyl‐phenylethyne gave the simple addition product, R 2 Ga(C 6 H 5 )=C(H)‐CMe 3 ( 9 ), only with di( n ‐propyl)gallium hydride.