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Issue 27, 2018
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Hydrogenation of titanocene and zirconocene bis(trimethylsilyl)acetylene complexes

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Abstract

Reactions following the addition of dihydrogen under maximum atmospheric pressure to bis(trimethylsilyl)acetylene (BTMSA) complexes of titanocenes, [(η5-C5H5−nMen)2Ti(η2-BTMSA)] (n = 0, 1, 3, and 4) (1A–1D), and zirconocenes, [(η5-C5H5−nMen)2Zr(η2-BTMSA)] (n = 2–5) (4A–4D), proceeded in diverse ways and, depending on the metal, afforded different products. The former complexes lost, in all cases, their BTMSA ligand via its hydrogenation to bis-1,2-(trimethylsilyl)ethane when reacted at 80 °C for a prolonged reaction time. For n = 0, 1, and 3, the titanocene species formed in situ dimerised via the formation of fulvalene ligands and two bridging hydride ligands, giving known green dimeric titanocenes (2A–2C). For n = 4, a titanocene hydride [(η5-C5HMe4)2TiH] (2D) was formed, similarly to the known [(η5-C5Me5)2TiH] (2E) for n = 5; however, in contrast to this example, 2D in the absence of dihydrogen spontaneously dehydrogenated to the known Ti(III)–Ti(III) dehydro-dimer [{Ti(η5-C5HMe4)(μ-η15-C5Me4)}2] (3B). This complex has now been fully characterised via spectroscopic methods, and was shown through EPR spectroscopy to attain an intramolecular electronic triplet state. The zirconocene-BTMSA complexes 4A–4D reacted uniformly with one hydrogen molecule to give Zr(IV) zirconocene hydride alkenyls, [(η5-C5H5−nMen)2ZrH{C(SiMe3)[double bond, length as m-dash]CH(SiMe3)}] (n = 2–5) (5A–5D). These were identified through their 1H and 13C NMR spectra, which show features typical of an agostically bonded proton, [double bond, length as m-dash]CH(SiMe3). Compounds 5A–5D formed equilibria with the BTMSA complexes 4A–4D depending on hydrogen pressure and temperature.

Graphical abstract: Hydrogenation of titanocene and zirconocene bis(trimethylsilyl)acetylene complexes

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Supplementary files

Article information


Submitted
11 May 2018
Accepted
06 Jun 2018
First published
07 Jun 2018

Dalton Trans., 2018,47, 8921-8932
Article type
Paper

Hydrogenation of titanocene and zirconocene bis(trimethylsilyl)acetylene complexes

J. Pinkas, R. Gyepes, I. Císařová, J. Kubišta, M. Horáček, N. Žilková and K. Mach, Dalton Trans., 2018, 47, 8921 DOI: 10.1039/C8DT01909F

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