Preparation and activation of complexes of the type [((mesityl)NCH2CH2)(2)NX]ZrMe2 (X = H, Me) with [Ph3C][B(C6F5)(4)] or [PhNMe2H][B(C6F5)(4)]

The zirconium dimethyl complexes [N2NX]ZrMe2 (N2NX = [(MesNCH(2)CH(2))(2)NX ]; Mes = mesityl; X= H (la), Me (1b)), have "mer" structures in the solid s tate in which the amido nitrogens, occupy "axial" positions in a trigonal b ipyramid. The reaction of Ib with 1 equiv of [Ph3C] [B(C6F5)(4)] followed b y addition of diethyl ether yielded the ether adduct ([N2NMe]-ZrMe(Et2O))() (with [B(C6F5)(4)](-) as the anion), an X-ray study of which revealed it to be a fac trigonal-bipyramidal species in which the diethyl ether is coor dinated in an apical position. The reaction of Ib with 1 equiv of [PhNMe2H] [B(C6F5)(4)] led to E [N2NMe]ZrMe(NMe2Pb))-[B(C6F5)(4)], solution NMR studi es of which suggest a structure, analogous to that of (N2NMe]-ZrMe(Et2O))(). Heating solutions oft [N2NMe]ZrMe(NMe2Ph)[B(C6F5)(4)] led to C-H activat ion in one mesityl o-methyl group and formation of methane. The reaction of Ib with 0.5 equiv of [Ph3C][B(C6F5)(4)] yielded [([N2NMe]ZrMe)(2)(mu -Me)] [B(C6F5)(4)] (5b), an X-ray diffraction study of which revealed an almost linear (167.4 degrees) methyl bridge linking two distorted TBP moieties thr ough the apical positions (average Zr-C(bridge)= 2.48 Angstrom, average Zr- C(terminal) = 2.24 Angstrom). The equatorial methyl groups in 5b exchange r eadily between Zr centers, while the bridging methyl group and the equatori al methyl groups exchange relatively slowly on the NMR time scale, but stil l rapidly on the chemical time scale. Exchange of free [N2NMe]-ZrMe2 with t he [N2NMe]ZrMe2 fragment in 5b is also facile on the chemical time scale. T he reaction of Ib with 1.0 equiv or more of [Ph3C] [B(C6F5)(4)] led to form ation of a cationic species (6b), two forms of which could be observed at l ow temperature. Activation of la with [Ph3C]-[B(C6F5)(4)] yielded only one cationic form of 6a at low temperatures. Exchange of methyl groups between 6a and 6b is slow on the chemical time scale. All evidence is consistent wi th the observation of different ion pairs of 6b at low temperatures.