Carbonylnickelates. 3. Synthesis and chemical characterization of the [Ni12(CO)21H4-n]n- (n=2, 3, 4) clusters.

The hydrolysis of the [Ni6(CO)12]2- dianion under buffered conditions results in the synthesis of the interstitial hydride derivatives [Ni12(CO)21H2]2- and [Ni12(CO)21H]3-. The two compounds are related by an easily reversible protonation-deprotonation equilibrium. In contrast, deprotonation of [Ni12(CO)21H]3- to the corresponding [Ni12(CO)21]4- tetraanion is possible only under severe conditions. The tetraanion has been obtained as a byproduct of the synthesis of [Ni6(CO)12]2- by reduction of Ni(CO)4 in KOH-saturated methanolic solution. The [Ni12(CO)21H4-n]n- (n = 2, 3, 4) derivatives have been isolated in pure crystalline form with a variety of tetrasubstituted ammonium or phosphonium cations. All these dodecanuclear nickel carbonyl clusters are rapidly degraded by carbon monoxide (25°C, 1 atm) and possess limited thermal stability. Degradation of [Ni12(CO)21H2]2- by carbon monoxide in THF solution affords the binuclear hydride derivative [Ni2(CO)6H]- and Ni(CO)4. Degradation of [Ni12(CO)21H]3-, in addition to the former products, gives rise to [Ni5(CO)12]2-, which becomes the only product, together with Ni(CO)4, when starting from [Ni12(CO)21]4-.