Insertion of Internal Alkynes and Ethene into Permethylated Singly Tucked-in Titanocene

Abstract

The singly tucked-in permethyltitanocene 1 reacts with an excess of internal alkynes to give the 1:1 adducts 3a−c,f−i, arising from insertion of the alkyne triple bond into the titanium−methylene bond. Only the simplest species, 2-butyne, inserted two molecules to give the known compound 2; however, at a 1:1 stoichiometric ratio the 1:1 adduct 3j was also smoothly formed. 1,4-Disubstituted conjugated diynes with CMe3 or SiMe3 substituents reacted in the same way by only one triple bond to give 3d,e, respectively. The dimethylsilylene-bridged dialkynes Me2Si(C≡CR)2 (R = SiMe3, CMe3) afforded compounds 3k,l with both triple bonds reacting. After insertion of the first triple bond, the second one underwent a rearrangement which resulted in substituent shift and formation of a silacyclobutene ring linked to the titanium atom. Alkynes bearing the bulky substituents CMe3 and SiMe3 were unreactive. Among a number of olefins and 1,3-butadiene, only ethene reacted to give cleanly the 1:1 adduct 3m. The structures ...