Phosphaferrocenes as phosphorus ligands. Crystal and molecular structure of tetracarbonyl(3,4-dimethylphosphaferrocene-P)iron

Abstract

The structure of the title compound shows that the phospholyl ring remains fully aromatic even after phosphorus(P-) complexation of phosphaferrocene: the three C–C bond lengths are almost equal with a mean value of 1.411(3)Å and the P–C bonds are very short: 1.739(3)Å. The Fe ⋯ C₄P and Fe ⋯ C₅H₅ distances increase upon P-complexation and the configuration of the sandwich is staggered whereas it was eclipsed in free phosphaferrocene. The geometry of the P → Fe (CO)₄ moiety is a classical trigonal bipyramid with apical phosphorus. The P–Fe distance is short, 2.211 (1)Å, indicating that the bond is strong and that phosphaferrocene is a strong ligand even though it is a weak donor on the basis of the i.r. data.