Insertion of Internal Alkynes and Ethene into Permethylated Singly Tucked-in Titanocene
ORGANOMETALLICS(2008)
摘要
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,I 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 of the paramagnetic [Ti-III(eta(5) -C5Me5){eta(5):eta(1)-C5Me4(CH2CR1=CR2)}] products 3a-g,k,l were determined by single-crystal X-ray diffraction analysis. These compounds and compounds 3h-j,m, whose crystal structures could not be determined, were chlorinated with PbCl2 to give the diamagnetic products [(TiCl)-Cl-IV(eta(5)-C5Me5){eta(5):eta(1)-C5Me4(CH2CR1=CR2)}] (4a-j) and the corresponding chlorotitanocene derivatives 4k-m. The solution structures of 4a-m were determined by H-1 and C-13 NMR spectroscopy, and crystal structures for 4b,e,g,l,m were found by single crystal X-ray diffraction analysis. DFT calculations threw light on the transition-state molecule for the formation of 3j and revealed a steric hindrance to be responsible for preventing the insertion of a second molecule of hex-3-yne, the closest homologue of but-2-yne, to react with 3i, forming a homologue of 2.
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