Insertion of 1-t-butylpropyne into singly tucked-in permethyltitanocene. Synthesis, crystal structure of product and transition-state geometry
2018
Abstrakt
The singly tucked-in titanocene [(eta(5)-C5Me5)Ti-III{eta(5):eta(1)-C5Me4(CH2)}] (1) reacted with one equivalent of 1-tert-butylpropyne to yield the propenyl-tethered regioisomer [(eta(5)-C5Me5)Ti(eta(5):eta(1)-C5Me4CH2C(t-Bu) = kappa CMe)] (3). The exclusive formation of paramagnetic 3 was proved experimentally and steric reasons were clarified by DFT calculation of transition state which involves both 7r-systems on the alkyne for bonding interaction with the metal and with sp(2) carbon atom of exomethylene group of I.
The obtained compound 3 is by 40 kJ/mol lower in energy than its hypothetical isomer having t-Bu group on C-alpha of the tether.