Non-aqueous neptunium and plutonium redox behaviour in THF – access to a rare Np(iii) synthetic precursor

Abstract

Solvent exchange of NpCl4(DME)2 with THF proceeds simply to yield NpCl4(THF)3, whereas PuCl4(DME)2 is unstable in THF, partially decomposing to the mixed valent [PuIIICl2(THF)5][PuIVCl5(THF)] salt. Reduction of NpCl4(THF)3 with CsC8 ultimately afforded NpCl3(py)4, the only example of a structurally characterized solvated Np(iii) halide. The method demonstrates a route to a well-defined Np(iii) starting material without the need to employ scarcely available Np metal.

Synthesis and Utility of Neptunium(III) Hydrocarbyl Complex

“…Here, we report the synthesis of a stable transuranic hydrocarbyl complex, Np[ η 4 -Me2NC(H)C6H5]3, directly from NpCl4(DME)2, circumventing the need for an alkali metal reducing agent. [26] This is analogous to our recent synthesis of a uranium(III) hydrocarbyl complex, U[η 4 -Me2NC(H)C6H5]3, from reaction with UCl4. [14f] We demonstrate the utility of the Np complex and show that, unlike the uranium analog, the products maintain the trivalent oxidation state.…”

“…It should be noted that the reactivity of (C5H5)3NpCl with alkyl lithium reagents does form a significant amount of (C5H5)3Np III , which is not unexpected given the Np(IV/III) redox couple. [23] Recently, Gaunt and co-workers reported NpCl4(DME)2, [25] NpCl4(THF)3, and NpCl3(pyridine)4, [26] which has replaced NpI3(THF)4, [27] as a useful neptunium starting materials since neptunium metal is required to prepare NpI3(THF)4. Here, we report the synthesis of a stable transuranic hydrocarbyl complex, Np[ η 4 -Me2NC(H)C6H5]3, directly from NpCl4(DME)2, circumventing the need for an alkali metal reducing agent.…”

“…A potential explanation of the difference between the magnetic susceptibilities of 2 and 3, especially the greater moment of 2 is the difference the crystal fields of sulfur and oxygen-based ligands. As illustrated with chromium halides by Burdett, [26] destabilization of metal orbitals is proportional to the ligand ionization potential as well as to the overlap between the metal and ligand orbitals. Because the carboxylate orbitals involved in bonding with Np are more stable than the corresponding thiocarboxylate orbitals, the crystal field of the carboxylate ligand is expected to be greater than that of the thiocarboxylate ligand even if the overlap is similar in both complexes.…”

Synthesis and Utility of Neptunium(III) Hydrocarbyl Complex

“…It should be noted that the reactivity of (C 5 H 5 ) 3 NpCl with alkyl lithium reagents does form as ignificant amount of (C 5 H 5 ) 3 Np III ,w hich is not unexpected given the Np(IV/III) redox couple. [23] Recently,G aunt and co-workers reported NpCl 4 (DME) 2 , [25] NpCl 4 (THF) 3 ,a nd NpCl 3 (pyridine) 4 , [26] which has replaced NpI 3 (THF) 4 , [27] as au seful neptunium starting materials since neptunium metal is required to prepare NpI 3 (THF) 4 .H ere,w er eport the synthesis of as table transuranic hydrocarbyl complex, Np[h 4 -Me 2 NC-(H)C 6 H 5 ] 3 ,d irectly from NpCl 4 (DME) 2 ,c ircumventing the need for an alkali-metal reducing agent. [26] This work is analogous to our recent synthesis of au ranium(III) hydrocarbyl complex, U[h 4 -Me 2 NC(H)C 6 H 5 ] 3 ,f rom reaction with UCl 4 .…”

“…Thec hemical shifts of the mesityl methyl protons are d = 1.99 ppm and 2.36 ppm for the ortho and para methyl groups, respectively.In3,these resonances are found at d = 2.41 ppm and 2.14 ppm, respectively.I n2,t he chemical shifts are further from their diamagnetic values at d = 2.56 ppm and 1.79 ppm. Ap otential explanation of the difference between the magnetic susceptibilities of 2 and 3,especially the greater moment of 2,isthe difference the crystal fields of sulfur-and oxygen-based ligands.A sillustrated with chromium halides by Burdett, [26] destabilization of metal orbitals is proportional to the ligand ionization potential as well as to the overlap between the metal and ligand orbitals.B ecause the carboxylate orbitals involved in bonding with Np are more stable than the corresponding thiocarboxylate orbitals,t he crystal field of the carboxylate ligand is expected to be greater than that of the thiocarboxylate ligand even if the overlap is similar in both complexes.T he obvious effect of this difference is to change the energies of the low-lying excited states created by splitting ground multiplet ( 5 I 4 in RS coupling). As aresult, the shapes of the m eff vs. T curves of 2 and 3 are different.…”