Transition-Metal-Stabilized Heavy Tetraphospholide Anions.

Phosphorus analogues of the ubiquitous cyclopentadienyl (Cp) are a rich and diverse family of compounds, which have found widespread use as ligands in organometallic complexes. By contrast, phospholes incorporating heavier group 14 elements (Si, Ge, Sn, and Pb) are hardly known. Here, we demonstrate the isolation of the first metal complexes featuring heavy cyclopentadienyl anions SnP 4 2- and PbP 4 2- . The complexes [(η 4 - t Bu 2 C 2 P 2 ) 2 Co 2 (μ,η 5 :η 5 -P 4 Tt)] [Tt = Sn ( 6 ), Pb ( 7 )] are formed by reaction of white phosphorus (P 4 ) with cyclooctadiene cobalt complexes [Ar'TtCo(η 4 -P 2 C 2 t Bu 2 )(η 4 -COD)] [Tt = Sn ( 2 ), Pb ( 3 ), Ar' = C 6 H 3 -2,6{C 6 H 3 -2,6- i Pr 2 } 2 , COD = cycloocta-1,5-diene] and Tt{Co(η 4 -P 2 C 2 t Bu 2 )(COD)} 2 [Tt = Sn ( 4 ), Pb ( 5 )]. While the SnP 4 2- complex 6 was isolated as a pure and stable compound, compound 7 eliminated Pb(0) below room temperature to afford [(η 4 - t Bu 2 C 2 P 2 ) 2 Co 2 (μ,η 4 :η 4 -P 4 ) ( 8 ), which is a rare example of a tripledecker complex with a P 4 2- middle deck. The electronic structures of 6 - 8 are analyzed using theoretical methods including an analysis of intrinsic bond orbitals and magnetic response theory. Thereby, the aromatic nature of P 5 - and SnP 4 2- was confirmed, while for P 4 2- , a specific type of symmetry-induced weak paramagnetism was found that is distinct from conventional antiaromatic species.