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

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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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The article was received on 11 May 2018, accepted on 06 Jun 2018 and first published on 07 Jun 2018

Article type: Paper
DOI: 10.1039/C8DT01909F
Citation: Dalton Trans., 2018,47, 8921-8932
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    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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