Chromium-Lanthanide Complexes Containing the CrUPUCr Fragment: Synthesis, Characterization, and Computational Study

Heterometallic complexes [Cp*(2)Ln(& mu;-(CO)-C- iso )(2){Cr-2(& mu;-P)Cp-2(CO)(2)}] [Ln = Yb (1), Sm (2)] were obtained in reactions of [Cp*(2)Ln(thf)(2)] (Ln = Sm, Yb) with [{CpCr(CO)(2)}(2)(& mu;,& eta;(2:2)-P-2)] (4). An analogous yttriumcompound [Cp*Y-2(& mu;-(CO)-C- iso )(2){Cr-2(& mu;-P)Cp-2(CO)(2)}] (3) was synthesized using a three-component reactionbetween [Cp*Y-2(BPh4)], 4, and KC8. Compounds 1-3 were isolatedas solvent-free crystalline phases; in the case of 2,the 2 & BULL;0.5C ( 7 ) H ( 8 ) solvate was also obtained. The structuresof all crystalline phases were determined by single-crystal X-raydiffraction analysis. All compounds contain a unique {((CO)(2)CpCr UP UCrCp(CO)(2))}(-) unit,which is linked to Ln(3+) ions through CO ligands in theisocarbonyl mode. Compounds 1 and 3 havea molecular structure, while compound 2 contains polymericchains of triangular [Cp*Sm-2(& mu;-(CO)-C- iso )(2){Cr-2(& mu;-P)Cp-2(CO)(2)}] units linked by & mu;-(CO)-C- iso -ligands. P-31 NMR studies demonstrated similar dramaticdownfield shifts for complexes 1-3. To realize the electronic structure of 1-3 and to elucidate the nature of the high downfield chemical P-31 shift, quantum chemical calculations were performed bothfor 1-3 and for related Cr- and Fe-phosphidocomplexes. Calculations show that the anomalously high downfield chemicalshifts for 1-3 are due to the anisotropiceffect of the Cr UP double bonds. Reductionof [{CpCr(CO)(2)}(2)(& mu;,& eta;(2:2)-P-2)] by [Cp*(2)Ln(thf)(2)](Ln = Yb, Sm) or by KC8 in the presence of [Cp*Y-2(BPh4)] leads to the complexes [Cp*(2)Ln(& mu;-(CO)-C- iso )(2){Cr-2(& mu;-P)Cp-2(CO)(2)}] (Ln = Yb, Sm, and Y). These compounds representthe first examples of complexes containing an almost linear heterocumuleneCr UP UCr fragment. P-31 NMR spectra of theLn/Cr complexes display an anomalously high downfield chemical shiftdue to the anisotropic effect of the Cr UP double bonds.