Synthesis and Reactivity of a Cyclooctatetraene-Like Polyphosphorus Ligand Complex [Cyclo-P8

Abstract

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).