1073193-20-0Relevant articles and documents
Insertion of internal alkynes and ethene into permethylated singly tucked-in titanocene
Pinkas,Cisarova,Gyepes,Horacek,Kubista,Cejka,Gomez-Ruiz,Hey-Hawkins,Mach
, p. 5532 - 5547 (2009/03/12)
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 of the paramagnetic [TFiIII- (η5-C5Me5)(η5: η1-C5Me4(CH2CR2)}] 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 [TiIVCl(η5-C5Me 5){η5:η1-C5Me 4(CH2CR1=CR2)}] (4a-j) and the corresponding chlorotitanocene derivatives 4k-m. The solution structures of 4a-m were determined by 1H and 13C 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.
