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

Heterometallic complexes [Cp*2Ln(µ-isoCO)2{Cr2(µ-P)Cp2(CO)2}] [Ln = Yb (1), Sm (2)] were obtained in reactions of [Cp*2Ln(thf)2] (Ln = Sm, Yb) with [{CpCr(CO)2}2(µ,η2:2-P2)] (4). An analogous yttrium compound [Cp*2Y(µ-isoCO)2{Cr2(µ-P)Cp2(CO)2}] (3) was synthesized using a three-component reaction between [Cp*2Y(BPh4)], 4, and KC8. Compounds 1-3 were isolated as solvent-free crystalline phases; in the case of 2, the 2·0.5C7H8 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)2CpCr═P═CrCp(CO)2)}- unit, which is linked to Ln3+ ions through CO ligands in the isocarbonyl mode. Compounds 1 and 3 have a molecular structure, while compound 2 contains polymeric chains of triangular [Cp*2Sm(µ-isoCO)2{Cr2(µ-P)Cp2(CO)2}] units linked by µ-isoCO-ligands. 31P NMR studies demonstrated similar dramatic downfield shifts for complexes 1-3. To realize the electronic structure of 1-3 and to elucidate the nature of the high downfield chemical 31P shift, quantum chemical calculations were performed both for 1-3 and for related Cr- and Fe-phosphido complexes. Calculations show that the anomalously high downfield chemical shifts for 1-3 are due to the anisotropic effect of the Cr═P double bonds.