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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. 

To expand the range of donor atoms known to stabilize 4fⁿ5d¹Ln(ii) ions beyond C, N, and O first row main group donor atoms, the Ln(iii) terphenylthiolate iodides, Ln^III(SAr^iPr6)₂I (Ar^iPr6= C₆H₃-2,6-(C₆H₂-2,4,6-ⁱPr₃)₂, Ln = La, Nd) were reduced to Ln^II(SAr^iPr6)₂complexes. 

The synthesis of previously unknown bis(cyclopentadienyl) complexes of the first transition metal, i.e., Sc(II) scandocene complexes, has been investigated using C5H2(tBu)3 (Cpttt), C5Me5 (Cp*), and C5H3(SiMe3)2 (Cp″) ligands. Cpttt 2ScI, 1, formed from ScI3 and KCpttt, can be reduced with potassium graphite (KC8) in hexanes to generate dark-red crystals of the first crystallographically characterizable bis(cyclopentadienyl) scandium(II) complex, Cpttt 2Sc, 2. Complex 2 has a 170.6° (ring centroid)-Sc-(ring centroid) angle and exhibits an eight-line EPR spectrum characteristic of Sc(II) with Aiso = 82.6 MHz (29.6 G). It sublimes at 200 °C at 10−4 Torr and has a melting point of 268−271 °C. Reductions of Cp*2ScI and Cp″2ScI under analogous conditions in hexanes did not provide new Sc(II) complexes, and reduction of Cp*2ScI in benzene formed the Sc(III) phenyl complex, Cp*2Sc(C6H5), 3, by C−H bond activation. However, in Et2O and toluene, reduction of Cp*2ScI at −78 °C gives a dark-red solution, 4, which displays an eight-line EPR pattern like that of 1, but it did not provide thermally stable crystals. Reduction of Cp″2ScI, in THF or Et2O at −35 °C in the presence of 2.2.2-cryptand, yields the green Sc(II) metallocene iodide complex, [K(crypt)][Cp″2ScI], 5, which was identified by X-ray crystallography and EPR spectroscopy and is thermally unstable. The analogous reaction of Cp*2ScI with KC8 and 18-crown-6 in Et2O gave the ligand redistribution product, [Cp*2Sc(18- crown-6-κ2O,O′)][Cp*2ScI2], 6, as the only crystalline product. Density functional theory 

Although there are few reduced dinitrogen complexes of scandium, this metal has revealed a new structural type in reductive dinitrogen chemistry by reduction of bis(pentamethylcyclopentadienyl) scandium halides under N2. 

The importance of the specific trialkylsilyl substituent in the cyclopentadienyl chemistry of C5H4SiR3 ligands has been demonstrated by the synthesis of low oxidation-state thorium complexes. Although the structure of the disilyl-substituted cyclopentadienyl Th(III) complex, [C5H3(SiMe3)2]3ThIII (Cp″3ThIII), was reported in 1986, no monosilyl-substituted analogues, (C5H4SiR3)3ThIII (R = alkyl, aryl), have been isolated to date, even though analogues are well known in U(III) chemistry. We now report that crystalline tris(monosilyl-substituted cyclopentadienyl) Th(III) and Th(II) complexes can be isolated when R = isopropyl, i.e., using the (triisopropylsilyl)cyclopentadienyl ligand, C5H4SiiPr3 (CpTIPS). The salt metathesis reaction between three equiv of KCpTIPS and ThIVBr4(DME)2 (DME = 1,2-dimethoxyethane) afforded the colorless Th(IV) complex, CpTIPS3ThIVBr, 1, which was identified spectroscopically and crystallographically. KC8 reduction of 1 in THF produced dark blue CpTIPS3ThIII, 2, in crystalline form. The complex was identified by X-ray crystallography, EPR, and UV–visible spectroscopy in contrast to ″(C5H4SiMe3)3ThIII,″ which has never been isolated due to its instability. This Th(III) complex can be reduced further with KC8 in the presence of 2.2.2-cryptand (crypt) to make [K(crypt)][CpTIPS3ThII], 3, which is only the second crystallographically characterized Th(II) complex isolated since (Cp″3ThII)1– was discovered in 2014. Spectroscopic, crystallographic, and density functional theory (DFT) analyses are consistent with 6d1 and 6d2 electron configurations for the Th(III) and Th(II) complexes, respectively. The importance of the triisopropylsilyl substituent and the role that steric factors play in the successful isolation of Th(III) and Th(II) complexes were evaluated by Guzei solid angle calculations and electrochemical studies. The results suggest that both electronic and steric effects should be considered in the isolation of Th(III) and Th(II) complexes. 

The salt metathesis reaction between one equivalent of SmI2(THF)2 and two equivalents of K(C5Me4H) in THF afforded single crystals of the unusual, toluene-soluble, and asymmetric bimetallic Sm(II)/Sm(II) complex, (C5Me4H)2SmII(μ-η3:η5-C5Me4H)SmII(C5Me4H)(THF)2, instead of the expected product, (C5Me4H)2SmII(THF)2. The toluene-insoluble products of this reaction can be worked up in 1,2-dimethoxyethane (DME) to provide X-ray quality crystals of the monomeric Sm(II) metallocene, (C5Me4H)2SmII(DME). (C5Me4H)2SmII(DME) can also be synthesized directly by the reaction between one equivalent of SmI2(THF)2 and two equivalents of K(C5Me4H) in neat DME. The isolation and characterization of the bimetallic Sm(II)/Sm(II) complex provides supporting evidence for the possible oligomerization that may occur during the synthesis of Sm(II) complexes with cyclopentadienyl ligands that are less sterically bulky and less solubilizing than (C5Me5)1−. 

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.