Synthesis and Reactivity of a Cyclooctatetraene‐Like Polyphosphorus Ligand Complex [Cyclo‐P8].

The thermolysis of Cp′′′Ta(CO)4 with white phosphorus (P4) gives access to [{Cp′′′Ta}2(μ,η2 : 2 : 2 : 2 : 1 : 1‐P8)] (A), representing the first complex containing a cyclooctatetraene‐like (COT) cyclo‐P8 ligand. While ring sizes of n >6 have remained elusive for cyclo‐Pn 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}4(μ4,η2 : 2 : 2 : 2 : 2 : 2 : 2 : 2 : 1 : 1 : 1 : 1‐P16)][TEF]2 (4, TEF=[Al(OC{CF3}3)4]−). Reduction, however, leads to the fission of one P−P bond in A followed by rapid dimerization to form [K@[2.2.2]cryptand]2[{Cp′′′Ta}4(μ4,η2 : 2 : 2 : 2 : 2 : 2 : 2 : 2 : 1 : 1 : 1 : 1‐P16)] (5), which features an unprecedented chain‐type P16 ligand. Lastly, A serves as a P2 synthon, via ring contraction to the triple‐decker complex [{Cp′′′Ta}2(μ,η6 : 6‐P6)] (B). [ABSTRACT FROM AUTHOR]