Chromium-Lanthanide Complexes Containing the Cr═P═Cr Fragment: Synthesis, Characterization, and Computational Study.

Heterometallic complexes [CpLn(μ-CO){Cr(μ-P)Cp(CO)}] [Ln = Yb (), Sm ()] were obtained in reactions of [CpLn(thf)] (Ln = Sm, Yb) with [{CpCr(CO)}(μ,η-P)] (). An analogous yttrium compound [CpY(μ-CO){Cr(μ-P)Cp(CO)}] () was synthesized using a three-component reaction between [CpY(BPh)], , and KC. Compounds - were isolated as solvent-free crystalline phases; in the case of , the solvate was also obtained. The structures of all crystalline phases were determined by single-crystal X-ray diffraction analysis. All compounds contain a unique {((CO)CpCr═P═CrCp(CO))} unit, which is linked to Ln ions through CO ligands in the isocarbonyl mode. Compounds and have a molecular structure, while compound contains polymeric chains of triangular [Cp*Sm(μ-CO){Cr(μ-P)Cp(CO)}] units linked by μ-CO-ligands. P NMR studies demonstrated similar dramatic downfield shifts for complexes -. To realize the electronic structure of - and to elucidate the nature of the high downfield chemical P shift, quantum chemical calculations were performed both for - and for related Cr- and Fe-phosphido complexes. Calculations show that the anomalously high downfield chemical shifts for - are due to the anisotropic effect of the Cr═P double bonds.