Synthesis and Reactivity of a Cyclooctatetraene-Like Polyphosphorus Ligand Complex [Cyclo-P ].

The thermolysis of Cp'''Ta(CO) with white phosphorus (P ) gives access to [{Cp'''Ta} (μ,η -P )] (A), representing the first complex containing a cyclooctatetraene-like (COT) cyclo-P ligand. While ring sizes of n >6 have remained elusive for cyclo-P structural motifs, the choice of the transition metal, co-ligand and reaction conditions allowed the isolation of A. Reactivity investigations reveal its versatile coordination behaviour as well as its redox properties. Oxidation leads to dimerization to afford [{Cp'''Ta} (μ ,η -P )][TEF] (4, TEF=[Al(OC{CF } ) ] ). Reduction, however, leads to the fission of one P-P bond in A followed by rapid dimerization to form [K@[2.2.2]cryptand] [{Cp'''Ta} (μ ,η -P )] (5), which features an unprecedented chain-type P ligand. Lastly, A serves as a P synthon, via ring contraction to the triple-decker complex [{Cp'''Ta} (μ,η -P )] (B).