Abstract
Several approaches to the intramolecular activation of a pendant nitrile group attached to the group 4 metallocene framework have been probed starting with the complexes [(eta(5)-C5Me5)(eta(5)-C5H4CMe2CH2CN) MCl2] (M = Zr, 1; M = Ti, 2). A reduction induced activation of the nitrile moiety was effected for the Zr derivative either by the treatment with Mg, or by the alkylation using t-BuMgCl followed by spontaneous reductive elimination.
In both cases, the reactions finally yielded the zirconocene cyano complex with an intramolecularly tethered alkyl substituent, [(eta(5)-C5Me5)(eta(5): kappa C-1-C5H4CMe2CH2) Zr(CN-kappa C)] (4), which resulted from the CeC bond cleavage in the pendant arm. Furthermore, a by-product was isolated which contained two zirconocene fragments bridged through a MgCl2 moiety featuring a rare sigma,pi-bridging mode of the pendant nitrile group, [{(eta(5)-C5Me5)(mu-eta(5):eta(2):kappa N-C5H4CMe2CH2CN)(mu-Cl)Zr}(2)Mg] (3).
The solid-state structure of 3 was elucidated and this compound together with the product 4 and the tentative intermediate [{(eta(5)-C5Me5)(eta(5):eta(2)-C5H4CMe2CH2CN)Zr] (3') were also investigated by DFT calculations. In another approach, 1 and 2 were treated with Li[B(C6F5)(4)]center dot Et2O to generate cationic complexes.
Accidental hydrolysis of these species afforded complexes bearing an intramolecularly tethered amide group [{(eta(5)-C5Me5)(eta(5):kappa O-C5H4CMe2CH2CONH2)M], of which the Ti derivative (6) was isolated and structurally characterised. Finally, reaction of the zirconocene dimethyl complex [(eta(5)-C5Me5)(eta(5)-C5H4CMe2CH2CN)ZrMe2] (8) with (Ph3C)[B(C6F5)(4)] was studied.