More Like this

1. Replacing Trimethylsilyl with Triisopropylsilyl Provides Crystalline (C ₅ H ₄ SiR ₃ ) ₃ Th Complexes of Th(III) and Th(II)

   https://doi.org/10.1021/acs.organomet.3c00343  

   Nguyen, Joseph Q; Anderson-Sanchez, Lauren M; Moore, William_N G; Ziller, Joseph W; Furche, Filipp; Evans, William J (October 2023, Organometallics)

   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. 

   more » « less
2. Synthesis and characterization of a tert- butyl ester-substituted titanocene dichloride: ^t-BuOOC Cp ₂ TiCl ₂

   https://doi.org/10.1107/S2056989020011834  

   McCarthy, Jackson S.; McMillen, Colin D.; Pienkos, Jared A.; Wagenknecht, Paul S. (October 2020, Acta Crystallographica Section E Crystallographic Communications)

   null (Ed.)

   Bis[η 5 -( tert -butoxycarbonyl)cyclopentadienyl]dichloridotitanium(IV), [Ti(C 10 H 13 O 2 ) 2 Cl 2 ], was synthesized from LiCp COO t -Bu using TiCl 4 , and was characterized by single-crystal X-ray diffraction and 1 H NMR spectroscopy. The distorted tetrahedral geometry about the central titanium atom is relatively unchanged compared to Cp 2 TiCl 2 . The complex exhibits elongation of the titanium–cyclopentadienyl centroid distances [2.074 (3) and 2.070 (3) Å] and a contraction of the titanium–chlorine bond lengths [2.3222 (10) Å and 2.3423 (10) Å] relative to Cp 2 TiCl 2 . The dihedral angle formed by the planes of the Cp rings [52.56 (13)°] is smaller than seen in Cp 2 TiCl 2 . Both ester groups extend from the same side of the Cp rings, and occur on the same side of the complex as the chlorido ligands. The complex may serve as a convenient synthon for titanocene complexes with carboxylate anchoring groups for binding to metal oxide substrates. 

   more » « less
3. Evaluating electrochemical accessibility of 4f ⁿ 5d ¹ and 4f ⁿ⁺¹ Ln( ii ) ions in (C ₅ H ₄ SiMe ₃ ) ₃ Ln and (C ₅ Me ₄ H) ₃ Ln complexes

   https://doi.org/10.1039/D1DT02427B  

   Trinh, Michael T.; Wedal, Justin C.; Evans, William J. (October 2021, Dalton Transactions)

   The reduction potentials (reported vs. Fc + /Fc) for a series of Cp′ 3 Ln complexes (Cp′ = C 5 H 4 SiMe 3 , Ln = lanthanide) were determined via electrochemistry in THF with [ n Bu 4 N][BPh 4 ] as the supporting electrolyte. The Ln( iii )/Ln( ii ) reduction potentials for Ln = Eu, Yb, Sm, and Tm (−1.07 to −2.83 V) follow the expected trend for stability of 4f 7 , 4f 14 , 4f 6 , and 4f 13 Ln( ii ) ions, respectively. The reduction potentials for Ln = Pr, Nd, Gd, Tb, Dy, Ho, Er, and Lu, that form 4f n 5d 1 Ln( ii ) ions ( n = 2–14), fall in a narrow range of −2.95 V to −3.14 V. Only cathodic events were observed for La and Ce at −3.36 V and −3.43 V, respectively. The reduction potentials of the Ln( ii ) compounds [K(2.2.2-cryptand)][Cp′ 3 Ln] (Ln = Pr, Sm, Eu) match those of the Cp′ 3 Ln complexes. The reduction potentials of nine (C 5 Me 4 H) 3 Ln complexes were also studied and found to be 0.05–0.24 V more negative than those of the Cp′ 3 Ln compounds. 

   more » « less
4. Crystal structure of the [(THF)Cs(μ-η ⁵ :η ⁵ -Cp′) ₃ Yb] _n oligomer

   https://doi.org/10.1107/S2056989020008051  

   Huh, Daniel N.; Ziller, Joseph W.; Evans, William J. (July 2020, Acta Crystallographica Section E Crystallographic Communications)

   null (Ed.)

   The green compound poly[(tetrahydrofuran)tris[μ-η 5 :η 5 -1-(trimethylsilyl)cyclopentadienyl]caesium(I)ytterbium(II)], [CsYb(C 8 H 13 Si) 3 (C 4 H 8 O)] n or [(THF)Cs(μ-η 5 :η 5 -Cp′) 3 Yb II ] n was synthesized by reduction of a red THF solution of (C 5 H 4 SiMe 3 ) 3 Yb III with excess Cs metal and identified by X-ray diffraction. The compound crystallizes as a two-dimensional array of hexagons with alternating Cs I and Yb II ions at the vertices and cyclopentadienyl groups bridging each edge. This, based off the six-electron cyclopentadienyl rings occupying three coordination positions, gives a formally nine-coordinate tris(cyclopentadienyl) coordination environment to Yb and the Cs is ten-coordinate due to the three cyclopentadienyl rings and a coordinated molecule of THF. The complex comprises layers of Cs 3 Yb 3 hexagons with THF ligands and Me 3 Si groups in between the layers. The Yb—C metrical parameters are consistent with a 4 f 14 Yb II electron configuration. 

   more » « less
5. The importance of the counter-cation in reductive rare-earth metal chemistry: 18-crown-6 instead of 2,2,2-cryptand allows isolation of [Y ^II (NR ₂ ) ₃ ] ¹⁻ and ynediolate and enediolate complexes from CO reactions

   https://doi.org/10.1039/C9SC05794C  

   Ryan, Austin J.; Ziller, Joseph W.; Evans, William J. (February 2020, Chemical Science)

   The use of 18-crown-6 (18-c-6) in place of 2.2.2-cryptand (crypt) in rare earth amide reduction reactions involving potassium has proven to be crucial in the synthesis of Ln( ii ) complexes and isolation of their CO reduction products. The faster speed of crystallization with 18-c-6 appears to be important. Previous studies have shown that reduction of the trivalent amide complexes Ln(NR 2 ) 3 (R = SiMe 3 ) with potassium in the presence of 2.2.2-cryptand (crypt) forms the divalent [K(crypt)][Ln II (NR 2 ) 3 ] complexes for Ln = Gd, Tb, Dy, and Tm. However, for Ho and Er, the [Ln(NR 2 ) 3 ] 1− anions were only isolable with [Rb(crypt)] 1+ counter-cations and isolation of the [Y II (NR 2 ) 3 ] 1− anion was not possible under any of these conditions. We now report that by changing the potassium chelator from crypt to 18-crown-6 (18-c-6), the [Ln(NR 2 ) 3 ] 1− anions can be isolated not only for Ln = Gd, Tb, Dy, and Tm, but also for Ho, Er, and Y. Specifically, these anions are isolated as salts of a 1 : 2 potassium : crown sandwich cation, [K(18-c-6) 2 ] 1+ , i.e. [K(18-c-6) 2 ][Ln(NR 2 ) 3 ]. The [K(18-c-6) 2 ] 1+ counter-cation was superior not only in the synthesis, but it also allowed the isolation of crystallographically-characterizable products from reactions of CO with the [Ln(NR 2 ) 3 ] 1− anions that were not obtainable from the [K(crypt)] 1+ analogs. Reaction of CO with [K(18-c-6) 2 ][Ln(NR 2 ) 3 ], generated in situ , yielded crystals of the ynediolate products, {[(R 2 N) 3 Ln] 2 (μ-OCCO)} 2− , which crystallized with counter-cations possessing 2 : 3 potassium : crown ratios, i.e. {[K 2 (18-c-6) 3 ]} 2+ , for Gd, Dy, Ho. In contrast, reaction of CO with a solution of isolated [K(18-c-6) 2 ][Gd(NR 2 ) 3 ], produced crystals of an enediolate complex isolated with a counter-cation with a 2 : 2 potassium : crown ratio namely [K(18-c-6)] 2 2+ in the complex [K(18-c-6)] 2 {[(R 2 N) 2 Gd 2 (μ-OCHCHO) 2 ]}. 

   more » « less