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Abstract Exploration of the reduction chemistry of the 2,2’‐bipyridine (bipy) lanthanide metallocene complexes Cp*₂LnCl(bipy) and Cp*₂Ln(bipy) (Cp* = C₅Me₅) resulted in the isolation of a series of complexes with unusual composition and structure including complexes with a single Cp* ligand, multiple azide ligands, and bipy ligands with close parallel orientations. These results not only reveal new structural types, but they also show the diverse chemistry displayed by this redox‐active platform. Treatment of Cp*₂NdCl(bipy) with excess KC₈resulted in the formation of the mono‐Cp* Nd(III) complex, [K(crypt)]₂[Cp*Nd(bipy)₂],1, as well as [K(crypt)][Cp*₂NdCl₂],2, and the previously reported [K(crypt)][Cp*₂Nd(bipy)]. A mono‐Cp* Lu(III) complex, Cp*Lu(bipy)₂,3, was also found in an attempt to make Cp*₂Lu(bipy) from LuCl₃, 2 equiv. of KCp*, bipy, and K/KI. Surprisingly, the (bipy)¹⁻ligands in neighboring molecules in the structure of3are oriented in a parallel fashion with intermolecular C⋅⋅⋅C distances of 3.289(4) Å, which are shorter than the sum of van der Waals radii of two carbon atoms, 3.4 Å. Another product with one Cp* ligand per lanthanide was isolated from the reaction of [K(crypt)][Cp*₂Eu(bipy)] with azobenzene, which afforded the dimeric Eu(II) complex, [K(crypt)]₂[Cp*Eu(THF)(PhNNPh)]₂,4. Attempts to make4from the reaction between Cp*₂Eu(THF)₂and a reduced azobenzene anion generated instead the mixed‐valent Eu(III)/Eu(II) complex, [K(crypt)][Cp*Eu(THF)(PhNNPh)]₂,5, which allows direct comparison with the bimetallic Eu(II) complex4. Mono‐Cp* complexes of Yb(III) are obtained from reactions of the Yb(II) complex, [K(crypt)][Cp*₂Yb(bipy)], with trimethylsilylazide, which afforded the tetra‐azido [K(crypt)]₂[Cp*Yb(N₃)₄],6, or the di‐azido complex [K(crypt)]₂[Cp*Yb(N₃)₂(bipy)],7 a, depending on the reaction stoichiometry. A mono‐Cp* Yb(III) complex is also isolated from reaction of [K(crypt)][Cp*₂Yb(bipy)] with elemental sulfur which forms the mixed polysulfido Yb(III) complex [K(crypt)]₂[Cp*Yb(S₄)(S₅)],8 a. In contrast to these reactions that form mono‐Cp* products, reduction of Cp*₂Yb(bipy) with 1 equiv. of KC₈in the presence of 18‐crown‐6 resulted in the complete loss of Cp* ligands and the formation of [K(18‐c‐6)(THF)][Yb(bipy)₄],9. The (bipy)¹⁻ligands of9are arranged in a parallel orientation, as observed in the structure of3, except in this case this interaction is intramolecular and involves pairs of ligands bound to the same Yb atom. Attempts to reduce further the Sm(II) (bipy)¹⁻complex, Cp*₂Sm(bipy) with 2 equiv. of KC₈in the presence of excess 18‐crown‐6 led to the isolation of a Sm(III) salt of (bipy)²⁻with an inverse sandwich Cp* counter‐cation and a co‐crystallized K(18‐c‐6)Cp* unit, [K₂(18‐c‐6)₂Cp*]₂[Cp*₂Sm(bipy)]₂ ⋅ [K(18‐c‐6)Cp*],10. 

To advance our ability to control the electronic properties of divalent lanthanides, the interplay between deformation densities, 4f interelectronic repulsion, and ligand field effects is discussed to predict the nature of their ground states. 

Y and Nd borohydride complexes bearing 2-pyridinemethanamido ligands were synthesized, revealing a varied coordination chemistry. Nine structures were identified by X-ray diffraction, some complexes being active in the ROP of cyclic esters. 

Treatment of the scandium(II) metallocene Cpttt2Sc (Cpttt = C5H2tBu3) with CO or the isocyanide CNXyl (Xyl = C6H3Me2-2,6) yields the carbonyl complex Cpttt2Sc(CO), 1, or the isocyanide complex Cpttt2Sc(CNXyl), 2, which were identified by X-ray crystallography. Isotopic labeling with 13CO shows the CO stretch of 1 at 1875 cm−1 shifts to 1838 cm−1 in 1-13CO. The CN stretch in 2 is shifted to 1939 cm−1 compared to 2118 cm−1 for the free isocyanide. The 80.1 MHz (28.7 G) 45Sc hyperfine coupling in 1 and 74.7 MHz (26.8 G) in 2 are similar to the 82.6 MHz (29.6 G) coupling constant in Cpttt2Sc and indicate that 1 and 2 are Sc(II) complexes. A comprehensive analysis of the electronic structures of 1 and 2 using DFT calculations is reported.