Trimethylsilyl versus Bis(trimethylsilyl) Substitution in Tris(cyclopentadienyl) Complexes of La, Ce, and Pr: Comparison of Structure, Magnetic Properties, and Reactivity

Abstract

To evaluate the effect of cyclopentadienyl ligand substitution in complexes of new +2 ions of the lanthanides, comparisons in reactivity and spectroscopic and magnetic properties have been made between [K(crypt)][Cp′ 3 Ln], 1-Ln (Cp′ = C 5 H 4 SiMe 3 ; crypt = 2.2.2-cryptand; Ln = La, Ce, Pr, and Nd), and [K(crypt)][Cp′′ 3 Ln], 2-Ln [Cp′′ = C 5 H 3 (SiMe 3 ) 2 ]. The 2-Ln complexes (Ce, Pr, and Nd) were synthesized by reduction of Cp′′ 3 Ln with potassium graphite in the presence of crypt and crystallographically characterized. The structures and UV−visible spectra of 2-Ln are similar to those of 1-Ln, as expected, but greater thermal stability for 2-Ln, expected from comparisons of 2-U and 1-U, was not observed. The magnetic susceptibilities of 2-Ce and 2-Pr were investigated because those of 1-Ce and 1-Pr did not match simple coupling models for 4f n 5d 1 electron configurations. The magnetic data of the 2-Ln complexes are similar to those of 1-Ln, which suggests that Ce 2+ and Pr 2+ complexes with 4f n 5d 1 electron configurations may have more complex electronic structures compared to nontraditional divalent complexes of the later lanthanides. Reactivity studies of isolated samples of 1-Ln and 2-Ln with 1,2-dimethoxyethane (DME) were conducted to determine if methoxide products, found in previous in situ studies of the synthesis of 2-Ln by Lappert and co-workers, would form. Methoxide products were not observed, which shows that the chemistry of the isolated complexes differs from that of the in situ reduction reactions.

Evaluating Electron‐Transfer Reactivity of Complexes of Actinides in +2 and +3 Oxidation States by using EPR Spectroscopy

“…TwoE PR active products are also observable in Figure 2, which shows the EPR spectrum of the products of Equation (8). The EPR spectra of the products of Equations (9) and (10) (Supporting Information, Figures S2 andS 3, respectively) show only the rare-earth signals as expected.…”

“…As ignal for another La II speciesm aking am inor contribution (g = 1.96, A( 139 La) = 143.5 G) is also observed. TwoE PR active products are also observable in Figure 2, which shows the EPR spectrum of the products of Equation (8). TwoE PR active products are also observable in Figure 2, which shows the EPR spectrum of the products of Equation (8).…”

“…Specifically, the first crystallographically-characterizable examples of Y II ,L a II ,C e II ,P r II , Gd II ,T b II ,H o II ,E r II ,L u II ,T h II ,U II ,N p II ,a nd Pu II have been isolated from reductionso ft ris(silylcyclopentadienyl) complexesa s shown in Equation (1). [1][2][3][4][5][6][7][8][9][10] Additionally,e xamples of these new ions in other ligand environments have also been reported. [11][12][13][14][15][16][17][18][19] When an ew oxidation state is identified, one of the characteristics to be defined is the redox potential by which it is formed.…”

“…Cp'' 3 Th III also absorbss trongly at 650 nm (5000 m À1 cm À1 ), but there are other peaks in the range 470-650 nm of as imilari ntensity that can be used to identify the Th III complex if it is present. The reverse reactions of Equations (7) and (8) were probedb yU V/Vis spectroscopya nd Equations (11) and (12) (7) and (8) show that in these ligand sets, Th II ,L a II ,a nd Y II all have similar reducing abilities.…”

Rare‐Earth Metal(II) Aryloxides: Structure, Synthesis, and EPR Spectroscopy of [K(2.2.2‐cryptand)][Sc(OC6H2tBu2‐2,6‐Me‐4)3]

“…The reductive chemistry of the rare-earth elements has been investigated along two lines in recent years. LnA 3 /M reduction reactions (Ln = Sc, Y, lanthanides;A= anionic ligand;M= alkali metal) have been conducted under argon to isolate complexes of new Ln II ions, [1][2][3][4][5][6][7][8][9] for example, with A = C 5 H 4 SiMe 3 and C 5 H 3 (SiMe 3 ) 2 in [Eq. (1)],a nd under dinitrogen to make reduced dinitrogenc omplexes of (N 2 ) 2À ,[ Eq.…”