A family of cerium complexes featuring a redox-active ligand in different oxidation states has been synthesized, including the the iminosemiquinone (isq)1- compound, Ce(dippisq)3 (1-Ceisq), and the amidophenolate (ap)2- species CeIII(dippap)3K3 (2-Ceap), [CeIII(dippap)3K][K(18-c-6)]2 (2-Ceap 18c6), and [CeIII(dippap)3K][K(15-c-5)2]2 (2-Ceap 15c5). Treating 2-Ceap 15c5 with dioxogen furnishes the cerium(IV) derivative [CeIV(dippap)3][K(15-c-5)2]2 (3-Ceap 15c5), and an analogous synthesis can be used to generate [CeIV(dippap)3][K(crypt)]2 (3-Ceap crypt). Similarly, addition of hexamethyldisiloxane produces an interesting bis(amidophenolate) species, [(Me3SiO)2CeIV(dippap)2][K(15-c-5)2]2 (4-CeOSiMe3). Full spectroscopic and structural characterization of each derivative was performed to establish the oxidation states of both the ligands and the cerium ions. Cerium(III) complexes with redox-active ligands in oxidation states L1- and L2- have been synthesized and fully characterized. Multielectron movement has been achieved by redox chemistry at the ligands. Sequestering counterions also introduces exciting reactivity, forming Ce(IV) species with dioxygen and oxidative addition of hexamethyldisiloxane to form a bis(siloxide) cerium(IV) species. image

The synthesis and characterization of two cerium complexes of redox-active amine/amido-phenolate-type ligands are reported. A tripodal framework comprising the tris(2-(3 ',5 '-di-tert-butyl-2 '-hydroxyphenyl)amino-phenyl) amine (H(6)Clamp) proligand was synthesized for comparison of its cerium complex with a potassium-cerium heterobimetallic complex of the 4,6-di-tert-butyl-2-[(2,6-diisopropylphenyl)imino]quinone ((dipp)ap) proligand. Structural studies indicate differences in the cerium(III) cation coordination spheres, where Ce-III(CH3CN)(1.5)(H(3)Clamp) (1-Ce(H (3) Clamp)) exhibits shorter Ce-O distances and longer Ce-N bond distances compared to the analogous distances in K-3(THF)(3)Ce-III((dipp)ap)(3) (2-Ce(ap)), due to the gross structural differences between the systems. Differences are also evident in the temperature-dependent magnetic properties, where smaller chi T products were observed for 2-Ce(ap) compared to 1-Ce(H- 3 Clamp). Solution electrochemical studies for the complexes were interpreted based on ligand- and metal-based oxidation events, and the cerium(III) oxidation of 2-Ce(ap) was observed to be more facile than that of 1-Ce(H (3) Clamp), behavior that was cautiously attributed to the rigidity of the encrypted 1-Ce(H (3) Clamp) complex compared to the heterobimetallic framework of 2-Ce(ap). These results contribute to the understanding of how ligand designs can promote facile redox cycling for cerium complexes of redox-active ligands, given the large contraction of cerium-ligand bonds upon oxidation.

The synthesis and crystal structure of homoleptic tetrabenzylthorium,Th(Bn)(4) (4) (Bn = benzyl, CH2Ph),is presented herein. First reported by Thiele and co-workers 48 yearsago, the characterization of Th(Bn)(4) was limited due tothe material's sensitivity. Several other new tetrabenzyl complexeswere also crystallographically isolated and discussed here, includingTh(Bn)(4)(THF)(2) (1-THF) and Th(Bn)(4)(dme) (2-dme, dme= 1,2-dimethoxyethane). A previously isolated phosphine adduct oftetrabenzylthorium, Th(Bn)(4)(dmpe) (3-dmpe, dmpe = 1,2-bis(dimethylphosphino)ethane), is reportedwith a modified synthesis and updated structural data. A short discussionof hapticity and coordination modes of actinide benzyl ligands isalso presented. Studies on the utility of 4 as a synthonto other organothorium compounds are reported, including Th((ad)ap)(2)(pyr)(3) (5-ap)(pyr = pyridine), formed from the reaction of 4 with2-(adamantan-2-ylamino)-4,6-di-tert-butylphenol (H-2 (ad)ap). All compounds were characterized by multinuclearNMR spectroscopy and X-ray crystallography.

The first non-uranyl, f-element oxo complex synthesized from dioxygen in dry air is presented in this work. The synthesis was accomplished by treating the redox-active thorium amidophenolate complex, [Th(dippap)3][K(15-c-5)2]2 (1-ap crown), with dioxygen in dry air, forming a rare terminal thorium oxo, [O═Th(dippisq)2(dippap)][K(15-c-5)2]2 (2-oxo). Compound 1-ap crown was regenerated by treating 2-oxo with potassium graphite. X-ray crystallography of 2-oxo revealed a comparatively longer bond length for the thorium-oxygen double bond when compared to other thorium oxos. As such, several thorium-oxygen single bonds were synthesized for comparison, including Th(dippisq)2(OSiMe3)2(THF) (4-OSiMe3), Th(OSiMe3)4(bipy)2 (5-OSiMe3), and [Th(OH)2 (dippHap)4][K(15-c-5)2]2 (6-OH). Full spectroscopic and structural characterization of the complexes was performed via 1H NMR spectroscopy, X-ray crystallography, EPR spectroscopy, and electronic absorption spectroscopy as well as SQUID magnetometry, which all confirmed the electronic structure of these complexes.

A series of thorium(IV) complexes featuring the redox-active 4,6-di-tert-butyl-N-(2,6-di-isopropylphenyl)-o-iminobenzoquinone (dippiq) ligand family have been synthesized and characterized. The neutral iminoquinone ligand was used to generate Th(dippiq)Cl4(dme)2 (1-iq) and Th(dippiq)2Cl4 (2-iq), both of which show dative bonds between the thorium(IV) ion and the ligands. One electron reduction of the ligand forms the unique tris(iminosemiquinone) complex, Th(dippisq)3Cl (3-isq), which features a radical in each ligand. Further reduction furnishes the amidophenolate species, Th(dippap)3]K2(THF)2 (4-ap), which has the ligands in their dianionic form. Attempts to sequester the potassium ions with cryptand resulted in the [Th(dippap)3K][K(crypt)] (4-ap mono crypt) and [Th(dippap)3][K(crypt)]2 (4-ap crypt) species. A bis(amidophenolate) complex was accessed by incorporating bulky triphenylphosphine oxide (OPPh3) ligands to generate Th(dippap)2(OPPh)3 (5-ap). Spectroscopic and structural characterization of each derivative established the +4 oxidation state for thorium with redox chemistry occurring at the ligands rather than the thorium ion. The reported 3-isq complex is unprecedented as it is the first tri(radical) thorium complex with the highest reported magnetic moment for a thorium species as characterized by SQUID magnetometry.

Uranyl-carbon bonds are rare due to the limited numbers of synthetic routes. The synthesis of carbodicarbene uranyl complexes is reported, along with complete spectroscopic and structural characterization. These data along with a computational analysis confirm strong electron donation by the carbodicarbene ligand, as well as a single-bond order between the uranium(VI) ion and the carbon.