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, [Zn2(C5Me5)(Ar′)], lead to disproportionation. The resulting half-sandwich Zn(II) complexes [(η5-C5Me5)ZnAr′] (Ar′ = 2,6-(2,6-iPr2C6H3)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), [Zn2(η5-C5Me5)2] reacts with C5Me5OH to afford the tetrametallic complexes [Zn2(η5-C5Me5)L(μ-OC5Me5)]2 (L = pyr-py, 6; DBU, 8), respectively. The bulkier terphenyloxide ArMesO– group (ArMes = 2,6-(2,4,6-Me3C6H2)2-C6H3) gives instead the dimetallic compound [Zn2(η5-C5Me5)(OArMes)(pyr-py)2], 7, that features a terminal Zn–OArMes bond. DFT calculations on models of 6–8 and also on the Zn–Zn-bonded complexes [Zn2(η5-C5H5)(OC5H5)(py)2] and [(η5-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 [Zn2(η5-C5Me5)2] have been also carried out and the results compared with the behavior of [Zn(C5Me5)2] and related magnesium and calcium metallocenes.