²⁹Si NMR Spectra of Silicon-Containing Uranium Complexes

²⁹Si NMR spectra have been recorded for a series of uranium complexes containing silicon, and the data have been combined with results in the literature to determine if any trends exist between chemical shift and structure, ligand type, or oxidation state. Data on 52 paramagnetic inorganic and organometallic uranium complexes are presented. The survey reveals that, although there is some overlap in the range of shifts of U⁴⁺ complexes versus U³⁺ complexes, in general U³⁺ species have shifts more negative than those of their U⁴⁺ analogues. The single U²⁺ example has the most negative shift of all at −322 ppm at 170 K. With only a few exceptions, U⁴⁺ complexes have shifts between 0 and −150 ppm (vs SiMe₄), whereas U³⁺ complexes resonate between −120 and −250 ppm. The small data set on U⁵⁺ species exhibits a broad 250 ppm range centered near 40 ppm. The data also show that aromatic ligands such as cyclopentadienide, cyclooctatetraenide, and the pentalene dianion exhibit chemical shifts less negative than those of other types of ligands

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

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′₃Ln], <b>1-Ln</b> (Cp′ = C₅H₄SiMe₃; crypt = 2.2.2-cryptand; Ln = La, Ce, Pr, and Nd), and [K­(crypt)]­[Cp′′₃Ln], <b>2-Ln</b> [Cp′′ = C₅H₃(SiMe₃)₂]. The <b>2-Ln</b> complexes (Ce, Pr, and Nd) were synthesized by reduction of Cp′′₃Ln with potassium graphite in the presence of crypt and crystallographically characterized. The structures and UV–visible spectra of <b>2-Ln</b> are similar to those of <b>1-Ln</b>, as expected, but greater thermal stability for <b>2-Ln</b>, expected from comparisons of <b>2-U</b> and <b>1-U</b>, was not observed. The magnetic susceptibilities of <b>2-Ce</b> and <b>2-Pr</b> were investigated because those of <b>1-Ce</b> and <b>1-Pr</b> did not match simple coupling models for 4f^<i>n</i>5d¹ electron configurations. The magnetic data of the <b>2-Ln</b> complexes are similar to those of <b>1-Ln</b>, which suggests that Ce²⁺ and Pr²⁺ complexes with 4f^<i>n</i>5d¹ electron configurations may have more complex electronic structures compared to nontraditional divalent complexes of the later lanthanides. Reactivity studies of isolated samples of <b>1-Ln</b> and <b>2-Ln</b> with 1,2-dimethoxyethane (DME) were conducted to determine if methoxide products, found in previous <i>in situ</i> studies of the synthesis of <b>2-Ln</b> 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 <i>in situ</i> reduction reactions

Expanding Transuranium Organoactinide Chemistry: Synthesis and Characterization of (Cp′₃M)₂(μ-4,4′-bpy) (M = Ce, Np, Pu)

Dinuclear, organometallic, transuranium compounds, (Cp′3M)2(μ-4,4′-bpy) (Cp′– = trimethylsilylcyclopentadienide, 4,4′-bpy = 4,4′-bipyridine, M = Ce, Np, Pu), reported herein provide a rare opportunity to probe the nature of actinide–carbon bonding. Significant splitting of the f–f transitions results from the unusual coordination environment in these complexes and leads to electronic properties that are currently restricted to organoactinide systems. Structural and spectroscopic characterization in the solid state and in solution for (Cp′3M)2(μ-4,4′-bpy) (M = Np, Pu) are reported, and their structural metrics are compared to a cerium analogue

Small-Scale Metal-Based Syntheses of Lanthanide Iodide, Amide, and Cyclopentadienyl Complexes as Analogues for Transuranic Reactions

Small-scale reactions of the Pu analogues La, Ce, and Nd have been explored in order to optimize reaction conditions for milligram scale reactions of radioactive plutonium starting from the metal. Oxidation of these lanthanide metals with iodine in ether and pyridine has been studied, and LnI₃(Et₂O)_<i>x</i> (<b>1-Ln</b>; <i>x</i> = 0.75–1.9) and LnI₃(py)₄ (<b>2-Ln</b>; py = pyridine, NC₅H₅) have been synthesized on scales ranging from 15 mg to 2 g. The THF adducts LnI₃(THF)₄ (<b>3-Ln</b>) were synthesized by dissolving <b>1-Ln</b> in THF. The viability of these small-scale samples as starting materials for amide and cyclopentadienyl f-element complexes was tested by reacting KN­(SiMe₃)₂, KCp′ (Cp′ = C₅H₄SiMe₃), KCp′′ (Cp′′ = C₅H₃(SiMe₃)₂-1,3), and KC₅Me₄H with <b>1-Ln</b> generated in situ. These reactions produced Ln­[N­(SiMe₃)₂]₃ (<b>4-Ln</b>), Cp′₃Ln (<b>5-Ln</b>), Cp″₃Ln (<b>6-Ln</b>), and (C₅Me₄H)₃Ln (<b>7-Ln</b>), respectively. Small-scale samples of Cp′₃Ce (<b>5-Ce</b>) and Cp′₃Nd (<b>5-Nd</b>) were reduced with potassium graphite (KC₈) in the presence of 2.2.2-cryptand to check the viability of generating the crystallographically characterizable Ln²⁺ complexes [K­(2.2.2-cryptand)]­[Cp′₃Ln] (<b>8-Ln</b>; Ln = Ce, Nd)

Synthesis, Structure, and Reactivity of the Sterically Crowded Th³⁺ Complex (C₅Me₅)₃Th Including Formation of the Thorium Carbonyl, [(C₅Me₅)₃Th(CO)][BPh₄]

The Th³⁺ complex, (C₅Me₅)₃Th, has been isolated despite the fact that tris­(pentamethylcyclopentadienyl) complexes are highly reactive due to steric crowding and few crystallographically characterizable Th³⁺ complexes are known due to their highly reducing nature. Reaction of (C₅Me₅)₂ThMe₂ with [Et₃NH]­[BPh₄] produces the cationic thorium complex [(C₅Me₅)₂ThMe]­[BPh₄] that can be treated with KC₅Me₅ to generate (C₅Me₅)₃ThMe, <b>1</b>. The methyl group on (C₅Me₅)₃ThMe can be removed with [Et₃NH]­[BPh₄] to form [(C₅Me₅)₃Th]­[BPh₄], <b>2</b>, the first cationic tris­(pentamethylcyclopentadienyl) metal complex, which can be reduced with KC₈ to yield (C₅Me₅)₃Th, <b>3</b>. Complexes <b>1</b>–<b>3</b> have metrical parameters consistent with the extreme steric crowding that previously has given unusual (C₅Me₅)⁻ reactivity to (C₅Me₅)₃M complexes in reactions that form less crowded (C₅Me₅)₂M-containing products. However, neither sterically induced reduction nor (η¹-C₅Me₅)⁻ reactivity is observed for these complexes. (C₅Me₅)₃Th, which has a characteristic EPR spectrum consistent with a d¹ ground state, has the capacity for two-electron reduction via Th³⁺ and sterically induced reduction. However, it reacts with MeI to make two sterically more crowded complexes, (C₅Me₅)₃ThI, <b>4</b>, and (C₅Me₅)₃ThMe, <b>1</b>, rather than (C₅Me₅)₂Th­(Me)­I. Complex <b>3</b> also forms more crowded complexes in reactions with I₂, PhCl, and Al₂Me₆, which generate (C₅Me₅)₃ThI, (C₅Me₅)₃ThCl, and (C₅Me₅)₃ThMe, <b>1</b>, respectively. The reaction of (C₅Me₅)₃Th, <b>3</b>, with H₂ forms the known (C₅Me₅)₃ThH as the sole thorium-containing product. Surprisingly, (C₅Me₅)₃ThH is also observed when (C₅Me₅)₃Th is combined with 1,3,5,7-cyclooctatetraene. [(C₅Me₅)₃Th]­[BPh₄] reacts with tetrahydrofuran (THF) to make [(C₅Me₅)₃Th­(THF)]­[BPh₄], <b>2-THF</b>, which is the first (C₅Me₅)₃M of any kind that does not have a trigonal planar arrangement of the (C₅Me₅)⁻ rings. It is also the first (C₅Me₅)₃M complex that does not ring-open THF. [(C₅Me₅)₃Th]­[BPh₄], <b>2</b>, reacts with CO to generate a product characterized as [(C₅Me₅)₃Th­(CO)]­[BPh₄], <b>5</b>, the first example of a molecular thorium carbonyl isolable at room temperature. These results have been analyzed using density functional theory calculations

Synthesis, Structure, and Reactivity of the Sterically Crowded Th³⁺ Complex (C₅Me₅)₃Th Including Formation of the Thorium Carbonyl, [(C₅Me₅)₃Th(CO)][BPh₄]

The Th³⁺ complex, (C₅Me₅)₃Th, has been isolated despite the fact that tris­(pentamethylcyclopentadienyl) complexes are highly reactive due to steric crowding and few crystallographically characterizable Th³⁺ complexes are known due to their highly reducing nature. Reaction of (C₅Me₅)₂ThMe₂ with [Et₃NH]­[BPh₄] produces the cationic thorium complex [(C₅Me₅)₂ThMe]­[BPh₄] that can be treated with KC₅Me₅ to generate (C₅Me₅)₃ThMe, <b>1</b>. The methyl group on (C₅Me₅)₃ThMe can be removed with [Et₃NH]­[BPh₄] to form [(C₅Me₅)₃Th]­[BPh₄], <b>2</b>, the first cationic tris­(pentamethylcyclopentadienyl) metal complex, which can be reduced with KC₈ to yield (C₅Me₅)₃Th, <b>3</b>. Complexes <b>1</b>–<b>3</b> have metrical parameters consistent with the extreme steric crowding that previously has given unusual (C₅Me₅)⁻ reactivity to (C₅Me₅)₃M complexes in reactions that form less crowded (C₅Me₅)₂M-containing products. However, neither sterically induced reduction nor (η¹-C₅Me₅)⁻ reactivity is observed for these complexes. (C₅Me₅)₃Th, which has a characteristic EPR spectrum consistent with a d¹ ground state, has the capacity for two-electron reduction via Th³⁺ and sterically induced reduction. However, it reacts with MeI to make two sterically more crowded complexes, (C₅Me₅)₃ThI, <b>4</b>, and (C₅Me₅)₃ThMe, <b>1</b>, rather than (C₅Me₅)₂Th­(Me)­I. Complex <b>3</b> also forms more crowded complexes in reactions with I₂, PhCl, and Al₂Me₆, which generate (C₅Me₅)₃ThI, (C₅Me₅)₃ThCl, and (C₅Me₅)₃ThMe, <b>1</b>, respectively. The reaction of (C₅Me₅)₃Th, <b>3</b>, with H₂ forms the known (C₅Me₅)₃ThH as the sole thorium-containing product. Surprisingly, (C₅Me₅)₃ThH is also observed when (C₅Me₅)₃Th is combined with 1,3,5,7-cyclooctatetraene. [(C₅Me₅)₃Th]­[BPh₄] reacts with tetrahydrofuran (THF) to make [(C₅Me₅)₃Th­(THF)]­[BPh₄], <b>2-THF</b>, which is the first (C₅Me₅)₃M of any kind that does not have a trigonal planar arrangement of the (C₅Me₅)⁻ rings. It is also the first (C₅Me₅)₃M complex that does not ring-open THF. [(C₅Me₅)₃Th]­[BPh₄], <b>2</b>, reacts with CO to generate a product characterized as [(C₅Me₅)₃Th­(CO)]­[BPh₄], <b>5</b>, the first example of a molecular thorium carbonyl isolable at room temperature. These results have been analyzed using density functional theory calculations

Synthesis, Structure, and Reactivity of the Sterically Crowded Th³⁺ Complex (C₅Me₅)₃Th Including Formation of the Thorium Carbonyl, [(C₅Me₅)₃Th(CO)][BPh₄]

The Th³⁺ complex, (C₅Me₅)₃Th, has been isolated despite the fact that tris­(pentamethylcyclopentadienyl) complexes are highly reactive due to steric crowding and few crystallographically characterizable Th³⁺ complexes are known due to their highly reducing nature. Reaction of (C₅Me₅)₂ThMe₂ with [Et₃NH]­[BPh₄] produces the cationic thorium complex [(C₅Me₅)₂ThMe]­[BPh₄] that can be treated with KC₅Me₅ to generate (C₅Me₅)₃ThMe, <b>1</b>. The methyl group on (C₅Me₅)₃ThMe can be removed with [Et₃NH]­[BPh₄] to form [(C₅Me₅)₃Th]­[BPh₄], <b>2</b>, the first cationic tris­(pentamethylcyclopentadienyl) metal complex, which can be reduced with KC₈ to yield (C₅Me₅)₃Th, <b>3</b>. Complexes <b>1</b>–<b>3</b> have metrical parameters consistent with the extreme steric crowding that previously has given unusual (C₅Me₅)⁻ reactivity to (C₅Me₅)₃M complexes in reactions that form less crowded (C₅Me₅)₂M-containing products. However, neither sterically induced reduction nor (η¹-C₅Me₅)⁻ reactivity is observed for these complexes. (C₅Me₅)₃Th, which has a characteristic EPR spectrum consistent with a d¹ ground state, has the capacity for two-electron reduction via Th³⁺ and sterically induced reduction. However, it reacts with MeI to make two sterically more crowded complexes, (C₅Me₅)₃ThI, <b>4</b>, and (C₅Me₅)₃ThMe, <b>1</b>, rather than (C₅Me₅)₂Th­(Me)­I. Complex <b>3</b> also forms more crowded complexes in reactions with I₂, PhCl, and Al₂Me₆, which generate (C₅Me₅)₃ThI, (C₅Me₅)₃ThCl, and (C₅Me₅)₃ThMe, <b>1</b>, respectively. The reaction of (C₅Me₅)₃Th, <b>3</b>, with H₂ forms the known (C₅Me₅)₃ThH as the sole thorium-containing product. Surprisingly, (C₅Me₅)₃ThH is also observed when (C₅Me₅)₃Th is combined with 1,3,5,7-cyclooctatetraene. [(C₅Me₅)₃Th]­[BPh₄] reacts with tetrahydrofuran (THF) to make [(C₅Me₅)₃Th­(THF)]­[BPh₄], <b>2-THF</b>, which is the first (C₅Me₅)₃M of any kind that does not have a trigonal planar arrangement of the (C₅Me₅)⁻ rings. It is also the first (C₅Me₅)₃M complex that does not ring-open THF. [(C₅Me₅)₃Th]­[BPh₄], <b>2</b>, reacts with CO to generate a product characterized as [(C₅Me₅)₃Th­(CO)]­[BPh₄], <b>5</b>, the first example of a molecular thorium carbonyl isolable at room temperature. These results have been analyzed using density functional theory calculations

Synthesis, Structure, and Reactivity of the Sterically Crowded Th³⁺ Complex (C₅Me₅)₃Th Including Formation of the Thorium Carbonyl, [(C₅Me₅)₃Th(CO)][BPh₄]

The Th³⁺ complex, (C₅Me₅)₃Th, has been isolated despite the fact that tris­(pentamethylcyclopentadienyl) complexes are highly reactive due to steric crowding and few crystallographically characterizable Th³⁺ complexes are known due to their highly reducing nature. Reaction of (C₅Me₅)₂ThMe₂ with [Et₃NH]­[BPh₄] produces the cationic thorium complex [(C₅Me₅)₂ThMe]­[BPh₄] that can be treated with KC₅Me₅ to generate (C₅Me₅)₃ThMe, <b>1</b>. The methyl group on (C₅Me₅)₃ThMe can be removed with [Et₃NH]­[BPh₄] to form [(C₅Me₅)₃Th]­[BPh₄], <b>2</b>, the first cationic tris­(pentamethylcyclopentadienyl) metal complex, which can be reduced with KC₈ to yield (C₅Me₅)₃Th, <b>3</b>. Complexes <b>1</b>–<b>3</b> have metrical parameters consistent with the extreme steric crowding that previously has given unusual (C₅Me₅)⁻ reactivity to (C₅Me₅)₃M complexes in reactions that form less crowded (C₅Me₅)₂M-containing products. However, neither sterically induced reduction nor (η¹-C₅Me₅)⁻ reactivity is observed for these complexes. (C₅Me₅)₃Th, which has a characteristic EPR spectrum consistent with a d¹ ground state, has the capacity for two-electron reduction via Th³⁺ and sterically induced reduction. However, it reacts with MeI to make two sterically more crowded complexes, (C₅Me₅)₃ThI, <b>4</b>, and (C₅Me₅)₃ThMe, <b>1</b>, rather than (C₅Me₅)₂Th­(Me)­I. Complex <b>3</b> also forms more crowded complexes in reactions with I₂, PhCl, and Al₂Me₆, which generate (C₅Me₅)₃ThI, (C₅Me₅)₃ThCl, and (C₅Me₅)₃ThMe, <b>1</b>, respectively. The reaction of (C₅Me₅)₃Th, <b>3</b>, with H₂ forms the known (C₅Me₅)₃ThH as the sole thorium-containing product. Surprisingly, (C₅Me₅)₃ThH is also observed when (C₅Me₅)₃Th is combined with 1,3,5,7-cyclooctatetraene. [(C₅Me₅)₃Th]­[BPh₄] reacts with tetrahydrofuran (THF) to make [(C₅Me₅)₃Th­(THF)]­[BPh₄], <b>2-THF</b>, which is the first (C₅Me₅)₃M of any kind that does not have a trigonal planar arrangement of the (C₅Me₅)⁻ rings. It is also the first (C₅Me₅)₃M complex that does not ring-open THF. [(C₅Me₅)₃Th]­[BPh₄], <b>2</b>, reacts with CO to generate a product characterized as [(C₅Me₅)₃Th­(CO)]­[BPh₄], <b>5</b>, the first example of a molecular thorium carbonyl isolable at room temperature. These results have been analyzed using density functional theory calculations

Synthesis, Structure, and Reactivity of the Sterically Crowded Th³⁺ Complex (C₅Me₅)₃Th Including Formation of the Thorium Carbonyl, [(C₅Me₅)₃Th(CO)][BPh₄]

The Th³⁺ complex, (C₅Me₅)₃Th, has been isolated despite the fact that tris­(pentamethylcyclopentadienyl) complexes are highly reactive due to steric crowding and few crystallographically characterizable Th³⁺ complexes are known due to their highly reducing nature. Reaction of (C₅Me₅)₂ThMe₂ with [Et₃NH]­[BPh₄] produces the cationic thorium complex [(C₅Me₅)₂ThMe]­[BPh₄] that can be treated with KC₅Me₅ to generate (C₅Me₅)₃ThMe, <b>1</b>. The methyl group on (C₅Me₅)₃ThMe can be removed with [Et₃NH]­[BPh₄] to form [(C₅Me₅)₃Th]­[BPh₄], <b>2</b>, the first cationic tris­(pentamethylcyclopentadienyl) metal complex, which can be reduced with KC₈ to yield (C₅Me₅)₃Th, <b>3</b>. Complexes <b>1</b>–<b>3</b> have metrical parameters consistent with the extreme steric crowding that previously has given unusual (C₅Me₅)⁻ reactivity to (C₅Me₅)₃M complexes in reactions that form less crowded (C₅Me₅)₂M-containing products. However, neither sterically induced reduction nor (η¹-C₅Me₅)⁻ reactivity is observed for these complexes. (C₅Me₅)₃Th, which has a characteristic EPR spectrum consistent with a d¹ ground state, has the capacity for two-electron reduction via Th³⁺ and sterically induced reduction. However, it reacts with MeI to make two sterically more crowded complexes, (C₅Me₅)₃ThI, <b>4</b>, and (C₅Me₅)₃ThMe, <b>1</b>, rather than (C₅Me₅)₂Th­(Me)­I. Complex <b>3</b> also forms more crowded complexes in reactions with I₂, PhCl, and Al₂Me₆, which generate (C₅Me₅)₃ThI, (C₅Me₅)₃ThCl, and (C₅Me₅)₃ThMe, <b>1</b>, respectively. The reaction of (C₅Me₅)₃Th, <b>3</b>, with H₂ forms the known (C₅Me₅)₃ThH as the sole thorium-containing product. Surprisingly, (C₅Me₅)₃ThH is also observed when (C₅Me₅)₃Th is combined with 1,3,5,7-cyclooctatetraene. [(C₅Me₅)₃Th]­[BPh₄] reacts with tetrahydrofuran (THF) to make [(C₅Me₅)₃Th­(THF)]­[BPh₄], <b>2-THF</b>, which is the first (C₅Me₅)₃M of any kind that does not have a trigonal planar arrangement of the (C₅Me₅)⁻ rings. It is also the first (C₅Me₅)₃M complex that does not ring-open THF. [(C₅Me₅)₃Th]­[BPh₄], <b>2</b>, reacts with CO to generate a product characterized as [(C₅Me₅)₃Th­(CO)]­[BPh₄], <b>5</b>, the first example of a molecular thorium carbonyl isolable at room temperature. These results have been analyzed using density functional theory calculations

Identification of the Formal +2 Oxidation State of Plutonium: Synthesis and Characterization of {Pu^II[C₅H₃(SiMe₃)₂]₃}⁻

Over 70 years of chemical investigations have shown that plutonium exhibits some of the most complicated chemistry in the periodic table. Six Pu oxidation states have been unambiguously confirmed (0 and +3 to +7), and four different oxidation states can exist simultaneously in solution. We report a new formal oxidation state for plutonium, namely Pu²⁺ in [K­(2.2.2-cryptand)]­[Pu^IICp″₃], Cp″ = C₅H₃(SiMe₃)₂. The synthetic precursor Pu^IIICp″₃ is also reported, comprising the first structural characterization of a Pu–C bond. Absorption spectroscopy and DFT calculations indicate that the Pu²⁺ ion has predominantly a 5f⁶ electron configuration with some 6d mixing