Abstract
Reactions following the addition of dihydrogen under maximum atmospheric pressure to bis(trimethylsilyl)acetylene (BTMSA) complexes of titanocenes, [(eta(5)-C5H5-nMen)(2)Ti(eta(2)-BTMSA)] (n = 0, 1, 3, and 4) (1A-1D), and zirconocenes, [(eta(5)-C5H5-nMen)(2)Zr(eta(2)-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 degrees 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 [(eta(5)-C5HMe4)(2)TiH] (2D) was formed, similarly to the known [(eta(5)-C5Me5)(2)TiH] (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(eta(5)-C5HMe4)(mu-eta(1):eta(5)-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, [(eta(5)-C5H5-nMen)(2)ZrH{C(SiMe3)=CH(SiMe3)}] (n = 2-5) (5A-5D).
These were identified through their H-1 and C-13 NMR spectra, which show features typical of an agostically bonded proton, -CH(SiMe3). Compounds 5A-5D formed equilibria with the BTMSA complexes 4A-4D depending on hydrogen pressure and temperature.