om500121p_si_003.pdf (2.08 MB)
Titanocene and Zirconocene Complexes with Diaminoacetylenes: Formation of Unusual Metallacycles and Fulvene Complexes
journal contribution
posted on 2014-04-14, 00:00 authored by Òscar Àrias, Alex R. Petrov, Thomas Bannenberg, Kai Altenburger, Perdita Arndt, Peter G. Jones, Uwe Rosenthal, Matthias TammThe reaction of dipiperidinoacetylene
(pipCCpip, pip = NC5H10, 1a) with [Cp2Ti(η2-btmsa)] (2) or with [Cp2Zr(η2-btmsa)(py)] (4) (btmsa = bis(trimethylsilyl)acetylene, py = pyridine) afforded
the metallacyclopentadienes [Cp2M(C4pip4)] (3, M = Ti; 5, M = Zr), which
in the solid state exhibit twisted five-membered metallacycles with
an unusual half-chair conformation. In contrast, the sterically more
demanding decamethyltitanocene (Cp*2Ti) and -zirconocene
(Cp*2Zr) complex fragments can only accommodate one alkyne
ligand. Thus, the titanacyclopropene [Cp*2Ti(C2pip2)] (7) was isolated from the reaction
of 1a with [Cp*2Ti(η2-btmsa)]
(6) or with [Cp*2TiCl] in the presence of
magnesium, whereas the zirconacyclopropenes [Cp*2Zr(C2X2)] (8a, X = pip; 8b, X = NC5H9-4-Me; 8c, X = NEt2) were prepared by the reduction of [Cp*2ZrCl2] with magnesium in the presence of 1a, bis(4-methylpiperidino)acetylene
(1b), and bis(diethylamino)acetylene (1c), respectively. NMR studies showed that complexes 8 are in equilibrium with their tucked-in tetramethylpentafulvene–diaminovinyl
isomers [Cp*(η6-C5Me4CH2)Zr(CX=CHX)] (9) in solution, which are formed
by intramolecular C–H-bond activation and hydrogen transfer
from one Cp* methyl group to the alkyne ligand. Thermodynamic and
kinetic parameters were derived by variable-temperature NMR spectroscopy
and DFT experiments. The molecular structures of 3, 5, 7, 8a, [8a·MgCl2]2, 8b, and 8c were established
by X-ray diffraction analyses.