Chemical Reactivity and Electrochemistry of Metal-Metal-Bonded Zincocenes

Attempts to prepare mixed-ligand zinc zinc-bonded compounds that contain bulky C5Me5 and terphenyl groups, [Zn-2(C5Me5)(Ar')], lead to disproportionation. The resulting half-sandwich Zn(II) complexes [(eta(5)-C5Me5)ZnAr'] (Ar' = 2,6-(2,6-(Pr2C6H3)-Pr-i)(2)-C6H3, 2; 2,6-(2,6-Me2C6H3)(2)-C6H3, 3) can also be obtained from the reaction of [Zn(C5Me5)(2)] with the corresponding LiAr'. In the presence of pyr-py (4-pyrrolidinopyridine) or DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), [Zn-2(eta(5)-C5Me5)(2)] reacts with C5Me5OH to afford the tetrametallic complexes [Zn-2(eta(5)-C5Me5)L(mu-OC5Me5)]2 (L = pyr-py, 6; DBU, 8), respectively. The bulkier terphenyloxide (ArO-)-O-Mes group (Ar-Mes = 2,6-(2,4,6-Me3C6H2)(2)-C6H3) gives instead the dimetallic compound [Zn-2(eta(5)-C5Me5)(OArMes)(pyr-py)(2)], 7, that features a terminal Zn-OA(Mes) bond. DFT calculations on models of 6-8 and also on the Zn-Zn-bonded complexes [Zn-2(eta(5)-C5H5)(OC5H5)(py)(2)] and [(eta(5)-C5H5)ZnZn(py)(3)](+) have been performed and reveal the nonsymmetric nature of the Zn-Zn bond with lower charge and higher participation of the s orbital of the zinc atom coordinated to the cyclopentadienyl ligand with respect to the metal within the pseudo-ZnL3 fragment. Cyclic voltammetric studies on [Zn-2(eta(5)-C5Me5)(2)] have been also carried out and the results compared with the behavior of [Zn(C5Me5)(2)] and related magnesium and calcium metallocenes.