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

Heterometallic complexes [Cp* 2 Ln(μ- iso CO) 2 {Cr 2 (μ-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 (μ,η 2:2 -P 2 )] ( 4 ). An analogous yttrium compound [Cp* 2 Y(μ- iso CO) 2 {Cr 2 (μ-P)Cp 2 (CO) 2 }] ( 3 ) was synthesized using a three-component reaction between [Cp* 2 Y(BPh 4 )], 4 , and KC 8 . Compounds 1 - 3 were isolated as solvent-free crystalline phases; in the case of 2 , the 2·0.5C 7 H 8 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) 2 CpCr═P═CrCp(CO) 2 )} - unit, which is linked to Ln 3+ 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* 2 Sm(μ- iso CO) 2 {Cr 2 (μ-P)Cp 2 (CO) 2 }] units linked by μ- iso CO-ligands. 31 P 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 31 P 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.