A small but growing number of molecular compounds have been isolated featuring divalent lanthanides with 4f n 5d z 2 1 electron configurations. While the majority of these possess trigonal coordination geometries, we previously reported the first examples of linear divalent metallocenes Ln(Cp iPr5 ) 2 (Ln = Tb, Dy; Cp iPr5 = pentaisopropylcyclopentadienyl). Here, we report the synthesis and characterization of the remainder of the Ln(Cp iPr5 ) 2 (1-Ln) series (including Y and excluding Pm). The compounds can be synthesized through salt metathesis of LnI 3 and NaCp iPr5 followed by potassium graphite reduction for Ln = Y, La, Ce, Pr, Nd, Gd, Ho, and Er, by in situ reduction during salt metathesis of LnI 3 and NaCp iPr5 for Ln = Tm and Lu, or through salt metathesis from LnI 2 and NaCp iPr5 for Ln = Sm, Eu, and Yb. Single crystal X-ray diffraction analyses of 1-Ln confirm a linear coordination geometry with pseudo-D 5d symmetry for the entire series. Structural and ultraviolet−visible spectroscopy data support a 4f n+1 electron configuration for Ln 2+ = Sm, Eu, Tm, and Yb and a 4f n 5d z 2 1 configuration for the other lanthanides ([Kr]4d z2 1 for Y 2+ ). Characterization of 1-Ln (Ln = Y, La) using electron paramagnetic resonance spectroscopy reveals significant s−d orbital mixing in the highest occupied molecular orbital and hyperfine coupling constants that are the largest reported to date for divalent compounds of yttrium and lanthanum. Evaluation of the room temperature magnetic susceptibilities of 1-Ln and comparison with values previously reported for trigonal Ln 2+ compounds suggests that the more pronounced 6s−5d mixing may be associated with weaker 4f−5d spin coupling.

The synthesis of bimetallic molecular silicide complexes is reported, based on the use of multiple Si–H bond activations in SiH4 at the metal centers of 14-electron LCoI fragments (L = Tp″, HB(3,5-diisopropylpyrazolyl)3 –; [BP2 tBuPz], PhB(CH2P t Bu2)2(pyrazolyl)). Upon exposure of (Tp″Co)2(μ-N2) (1) to SiH4, a mixture of (Tp″Co)2(μ-H) (2) and (Tp″Co)2(μ-H)2 (3) was formed and no evidence for Si–H oxidative addition products was observed. In contrast, [BP2 tBuPz]-supported Co complexes led to Si–H oxidative additions with the generation of silylene and silicide complexes as products. Notably, the reaction of ([BP2 tBuPz]Co)2(μ-N2) (5) with SiH4 gave the dicobalt silicide complex [BP2 tBuPz](H)2CoSiCo(H)2[BP2 tBuPz] (8) in high yield, representing the first direct route to a symmetrical bimetallic silicide. The effect of the [BP2 tBuPz] ligand on Co–Si bonding in 7 and 8 was explored by analysis of solid-state molecular structures and density functional theory (DFT) investigations. Upon exposure to CO or DMAP (DMAP = 4-dimethylaminopyridine), 8 converted to the corresponding [BP2 tBuPz]Co(L)x adducts (L = CO, x = 2; L = DMAP, x = 1) with concomitant loss of SiH4, despite the lack of significant Si–H interactions in the starting complex. On heating to 60 °C, 8 underwent reaction with MeCl to produce small quantities of Me x SiH4–x (x = 1–3), demonstrating functionalization of the μ-silicon atom in a molecular silicide to form organosilanes.