Neodymium(III) Complexes Capable of Multi‐Electron Redox Chemistry

Abstract

Af amily of neodymium complexes featuring ar edox-active ligand in three different oxidation states has been synthesized,i ncluding the iminoquinone (L 0 )d erivative, ( dipp iq) 2 NdI 3 (1-iq), the iminosemiquinone (L 1À )c ompound, ( dipp isq) 2 NdI(THF) (1-isq), and the amidophenolate (L 2À )( 1-ap crown)s pecies.F ull spectroscopic and structural characterization of each derivative established the + 3n eodymium oxidation state with redox chemistry occurring at the ligand rather than the neodymium center. Oxidation with elemental chalcogens showed the reversible nature of the ligand-mediated reduction process,f orming the iminosemiquinone metallocycles, [ K(18-crown-6)]-[( dipp isq) 2 Nd(S 5 )] (2-isq crown)a nd [K(18-crown-6)(THF)]-[( dipp isq) 2 Nd(Se 5 )] (3-isq crown), whicha re characterized to contain a6 -membered twist-boat ring.

Uranyl Functionalization Mediated by Redox-Active Ligands: Generation of O–C Bonds via Acylation

“…These values suggest a stronger interaction with the nitrogen atom than the hydrogen atom of the ligand. This hyperfine pattern agrees with previously noted results. , Thus, these measurements support the presence of an iminosemiquinone ligand radical with only a weak interaction with uranium.…”

“…Finally, 3-ap shows only one absorption at 313 nm (15,313 M –1 cm –1 ) and does not absorb significantly in the visible region, consistent with its pale color. Interpretation of these data suggests that the major, color-producing peaks of the spectra can be attributed to the ligand oxidation state, as similar colors have been observed for complexes of early transition metals, lanthanides, and low valent uranium …”

“…Because solution behavior can be complicated by dynamic inner-sphere and outer-sphere cation exchange, a crown ether was employed to encapsulate the potassium ion for further studies. ,, To achieve this, two equivalents of 18-crown-6 were added to a stirring solution of 3-ap in THF. After workup, a white powder was isolated in good yield (76%).…”

“…We hypothesized that U–O uranyl bonds could undergo such a conversion with electrophilic carbon-containing substrates when mediated by reduced redox-active ligands. The iminoquinone family would be effective for such a task, as this ligand set has mediated multielectron reactions with low-valent metals − and would obviate the need for an external reductant by its ability to exist in a reduced state (Figure ). The most oxidized form of this ligand, the iminoquinone (iq 0 ), can be reduced to the iminosemiquinone (isq 1– ), which is characterized by a ligand radical.…”

Lanthanoid Complexes as Molecular Materials: The Redox Approach

“…For example Bart and co‐workers exploited the multi‐electron redox chemistry of 4,6‐di‐ tert ‐butyl‐2‐[(2,6‐diisopropylphenyl)imino]quinone ( dipp iq 0 ), with access to the iminosemiquinone ( dipp isq .− ) and amidophenolate ( dipp ap 2− ) states, to isolate a family of Nd III complexes, all exhibiting distinctly different colors: [NdI 3 ( dipp iq 0 ) 2 ] ( 54 ), [Nd( dipp isq .− ) 2 I(THF)] ( 55 ), and [K(18‐crown‐6)][Nd( dipp ap) 2 (THF) 2 ] ( 56 ) (Figure 13). [105] The reverse multi‐electron oxidation of 56 , containing the amidophenolate ( dipp ap) ligand, was tested for its capacity to act as an electron store for future reductants using elemental chalcogens (S 8 and Se), with formation of the isoquinone state (via two one‐electron oxidations) accompanied by isolation of the S 5 and Se 5 complexes [105a] . As well as for the implications for catalysis and reaction chemistry, understanding how ligand‐centered redox events can modulate the photophysical and magnetic properties of lanthanoid complexes is of interest for extending the capabilities of optically or magnetically functional lanthanoid materials.…”