Ethene Complexes of Bulky Titanocenes, Their Thermolysis, and Their Reactivity toward 2-Butyne
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- 作者：Ji艡铆 Pinkas ; Ivana C铆sa艡ov谩 ; R贸bert Gyepes ; Ji艡铆 Kubi拧ta ; Michal Hor谩膷ek ; Karel Mach
- 刊名：Organometallics
- 出版年：2012
- 出版时间：August 13, 2012
- 年：2012
- 卷：31
- 期：15
- 页码：5478-5493
- 全文大小：628K
- 年卷期：v.31,no.15(August 13, 2012)
- ISSN：1520-6041
文摘
Ethene complexes of titanocenes [Ti(II)(畏2-C2H4)(Cp鈥?2] for Cp鈥?= 畏5-C5Me5 (1), 畏5-C5Me4t-Bu (2), 畏5-C5Me4SiMe3 (3), and 畏5-C5HMe4 (4) were prepared by reduction of corresponding titanocene dichlorides with magnesium in THF in the presence of ethene. Thermolysis of 1鈥?b>3 in toluene solution at a maximum of 100 掳C resulted in elimination of ethane, affording cleanly doubly tucked-in titanocene compounds 5鈥?b>7, respectively. Experiments with 2 and 3 in NMR tubes proved that symmetrical isomers 6a and 7a were formed first, and these thermally isomerized to thermodynamically more stable asymmetrical isomers 6b and 7b. The energy difference between 7a and 7b calculated by DFT methods was 15.3 kJ/mol. Thermolysis of 4 in m-xylene required a temperature of 135 掳C, affording a mixture of 8b > 8a and 鈥渄imeric dehydro-titanocene鈥?9 as a concurrent product of hydrogen abstraction. In contrast to thermolysis in solvents, heating of 1 and 2 in high vacuum to 135 掳C resulted in sublimation of known titanocenes [Ti(C5Me5)2] (10) and [Ti(畏5-C5Me4t-Bu)2] (13) (Chirik et al. J. Am. Chem. Soc.2004, 126, 14688鈥?4689), respectively. The former isomerized in hexane solution to the tucked-in hydride [TiH{C5Me4(CH2)}(C5Me5)] (10A) as described by Bercaw (J. Am. Chem. Soc.2004, 126, 14688鈥?4689). A mixture of 10/10A decayed within days to give major paramagnetic products [TiH(C5Me5)2] (11) and singly tucked-in titanocene [Ti{C5Me4(CH2)}(C5Me5)] (12) and minor diamagnetic 5 and its so far unknown, less stable isomer [Ti{C5Me4(CH2)}2] (10B), identified by NMR spectra and corroborated by DFT calculations. Solid 3 eliminated ethene at only 80 掳C, leaving titanocene 14, whereas compound 4 sublimed at 135 掳C mostly without decomposition. Cocrystals of 10 with [TiCl(C5Me5)2] (1:2) (10C) afforded an X-ray single-crystal structure with linear geometry for 10. The ethene complexes 1鈥?b>4 differed in their reactivity toward but-2-yne: compounds 1 and 4 yielded the respective [Ti(IV)(畏1: 畏1-CH2CH2CMe鈺怌Me)(Cp鈥?2] 2,3-dimethyltitanacyclopent-2-ene complexes 15 and 16, whereas 2 and 3 replaced ethene with but-2-yne, affording the [Ti(II)(畏2-MeC鈮Me)(Cp鈥?2] complexes 17 and 18, respectively. Crystal structures of 2, 4, 10C, 15, 17, and 18 have been determined by X-ray crystallography.