Hybrid Iodide Perovskites of Divalent Alkaline Earth and Lanthanide Elements.

Hybrid halide perovskites AMIIX3 (A = ammonium cation, MII = divalent cation, X = Cl, Br, I) have been extensively studied but have only previously been reported for the divalent carbon group elements Ge, Sn, and Pb. While they have displayed an impressive range of optoelectronic properties, the instability of GeII and SnII and the toxicity of Pb have stimulated significant interest in finding alternatives to these carbon group-based perovskites. Here, we describe the low-temperature solid-state synthesis of five new hybrid iodide perovskites centered around divalent alkaline earth and lanthanide elements, with the general formula AMIII3 (A = methylammonium, MA; MII = Sr, Sm, Eu, and A = formamidinium, FA; MII = Sr, Eu). Structural, calorimetric, optical, photoluminescence, and magnetic properties of these materials are reported.

Dimerization and ring-opening in bis(diisopropylamino)cyclopropenylidene (BAC) mediated by [U(NR2)3(CCPh)] (R = SiMe3).

Addition of 2 equiv. of bis(diisopropylamino)cyclopropenylidene (BAC) to [U(NR2)3(CCPh)] (1, R = SiMe3), in Et2O, results in formation of [cyclo-N(iPr)C(Me)2CH(NiPr2)C{CHC3(NiPr2)2}][U(NR2)2(N(SiMe3)SiMe2CH2)(CCPh)] (2) in moderate isolated yield. Complex 2 is the result of coupling and protonation of two BAC molecules, where complex 1 contributes the required proton. It was characterized by NMR spectroscopy and X-ray crystallography and represents a new mode of reactivity of the cyclopropenylidene fragment.

Elusive Double Perovskite Iodides: Structural, Optical, and Magnetic Properties.

Halide double perovskites [A2 MI MIII X6 ] are an important class of materials that have garnered substantial interest as non-toxic alternatives to conventional lead iodide perovskites for optoelectronic applications. While numerous studies have examined chloride and bromide double perovskites, reports of iodide double perovskites are rare, and their definitive structural characterization has not been reported. Predictive models have aided us here in the synthesis and characterization of five iodide double perovskites of general formula Cs2 NaLnI6 (Ln=Ce, Nd, Gd, Tb, Dy). The complete crystal structures, structural phase transitions, optical, photoluminescent, and magnetic properties of these compounds are reported.

Ring-opening of a thorium cyclopropenyl complex generates a transient thorium-bound carbene.

The reaction of [Cp3ThCl] with in situ generated 1-lithium-3,3-diphenylcyclopropene results in the formation of [Cp3Th(3,3-diphenylcyclopropenyl)] (1), in good yields. Thermolysis of 1 results in isomerization to the ring-opened product, [Cp3Th(3-phenyl-1H-inden-1-yl)] (3) via a hypothesized carbene intermediate. This transformation represents a new mode of reactivity of 3,3-diphenylcyclopropene with the actinides, improving our ability to use this reagent as a carbene source. A combined DFT and 13C{1H} NMR analysis of 1 shows a spin-orbit induced downfield shift at Cα due to participation of the 5f orbitals in the Th-C bond.

Synthesis and electronic structure analysis of the actinide allenylidenes, [{(NR2)3}An(CCCPh2)]- (An = U, Th; R = SiMe3).

The reaction of [AnCl(NR2)3] (An = U, Th, R = SiMe3) with in situ generated lithium-3,3-diphenylcyclopropene results in the formation of [{(NR2)3}An(CH[double bond, length as m-dash]C[double bond, length as m-dash]CPh2)] (An = U, 1; Th, 2) in good yields after work-up. Deprotonation of 1 or 2 with LDA/2.2.2-cryptand results in formation of the anionic allenylidenes, [Li(2.2.2-cryptand)][{(NR2)3}An(CCCPh2)] (An = U, 3; Th, 4). The calculated 13C NMR chemical shifts of the Cα, Cß, and Cγ nuclei in 2 and 4 nicely reproduce the experimentally assigned order, and exhibit a characteristic spin-orbit induced downfield shift at Cα due to involvement of the 5f orbitals in the Th-C bonds. Additionally, the bonding analyses for 3 and 4 show a delocalized multi-center character of the ligand π orbitals involving the actinide. While a single-triple-single-bond resonance structure (e.g., An-C[triple bond, length as m-dash]C-CPh2) predominates, the An[double bond, length as m-dash]C[double bond, length as m-dash]C[double bond, length as m-dash]CPh2 resonance form contributes, as well, more so for 3 than for 4.

Synthesis of Parent Acetylide and Dicarbide Complexes of Thorium and Uranium and an Examination of Their Electronic Structures.

The reaction of [AnCl(NR2)3] (An = U or Th; R = SiMe3) with NaCCH and tetramethylethylenediamine (TMEDA) results in the formation of [An(C≡CH)(NR2)3] (1, An = U; 2, An = Th), which can be isolated in good yields after workup. Similarly, the reaction of 3 equiv of NaCCH and TMEDA with [AnCl(NR2)3] results in the formation of [Na(TMEDA)][An(C≡CH)2(NR2)3] (4, An = U; 5, An = Th), which can be isolated in fair yields after workup. The reaction of 1 with 2 equiv of KC8 and 1 equiv of 2.2.2-cryptand in tetrahydrofuran results in formation of the uranium(III) acetylide complex [K(2.2.2-cryptand)][U(C≡CH)(NR2)3] (3). Thermolysis of 1 or 2 results in formation of the bimetallic dicarbide complexes [{An(NR2)3}2(µ,η1:η1-C2)] (6, An = U; 7, An = Th), whereas the reaction of 1 with [Th{N(R)(SiMe2CH2)}(NR2)2] results in the formation of [U(NR2)3(µ,η1:η1-C2)Th(NR2)3] (8). The 13C NMR chemical shifts of the α-acetylide carbon atoms in 2, 5, and 7 exhibit a characteristic spin-orbit-induced downfield shift, due to participation of the 5f orbitals in the Th-C bonds. Magnetism measurements demonstrate that 6 displays weak ferromagnetic coupling between the uranium(IV) centers (J = 1.78 cm-1).

Synthesis and Characterization of Two "Tied-Back" Lithium Ketimides and Isolation of a Ketimide-Bridged [Cr2]6+ Dimer with Strong Antiferromagnetic Coupling.

Reaction of 1 equiv of KN(SiMe3)2 with 9-fluorenone results in the formation of (Me3Si)N═C13H8 (1) in high yield after work-up. Addition of 1 equiv of phenol to 1 results in rapid desilylation and formation of 9-fluorenone imine, HN═C13H8 (2). Subsequent reaction of 2 with 1 equiv of LiNiPr2 results in deprotonation and formation of [Li(Et2O)]4[N═C13H8]4 (3) in good yield. Reaction of 1 equiv of KN(SiMe3)2 with 2-adamantanone for 7 days at room temperature results in the formation of (Me3Si)N═C10H14 (4) in good yield. Dissolution of 4 in neat MeOH results in rapid desilylation concomitant with formation of 2-adamantanone imine, HN═C10H14 (5). Subsequent reaction of 5 with 1 equiv of LiNiPr2 results in formation of [Li(THF)]4[N═C10H14]4 (6). Both 3 and 6 were characterized by X-ray crystallography. Finally, reaction of CrCl3 with 3.5 equiv of 6 results in formation of the [Cr2]6+ dimer, [Li][Cr2(N═C10H14)7] (7), which can be isolated in modest yield after work-up. Complex 7 features a Cr-Cr bond length of 2.653(2) Å. Additionally, solid-state magnetic susceptibility measurements reveal strong antiferromagnetic coupling between the two Cr centers, with J = -200 cm-1.

Probing the Electronic Structure of a Thorium Nitride Complex by Solid-State 15N NMR Spectroscopy.

The solid-state 15N NMR powder spectra of the thorium nitride complex, [K(18-crown-6)(THF)2][(R2N)3Th(µ-15N)Th(NR2)3] ([K][1-15N], R = SiMe3), and the thorium amide complex, [Th(NR2)3(15NH2)] (2-15N), were recorded. The spectrum for [K][1-15N] represents the first reported solid-state 15N NMR data for an actinide complex. The experimentally measured tensor spans are Ω = 847 ppm for [K][1-15N] and Ω = 237 ppm for 2-15N. Both shielding tensors exhibit axial symmetry, which for [K][1-15N] is consistent with a local rotational symmetry of its 15N-labeled nitride ligand. For 2-15N, the axial asymmetry can be rationalized by a quasi-free Th-NH2 bond rotation in the solid-state. Density functional theory calculations overestimate the tensor span somewhat for [K][1-15N], but provide isotropic shifts in good agreement with both the solid-state and solution values for both complexes. Natural localized molecular orbital analyses of the nuclear shielding reveal that the larger tensor span in [K][1-15N] vs 2-15N is primarily a consequence of more pronounced covalency of the σ(N-Th) bonds and large spin-orbit coupling due to significant Th 5f orbital contribution to those bonds, impacting the principal components of the shielding tensor perpendicular to the Th-N-Th axis. Overall, our analysis confirms the involvement of the 5f orbitals in Th-N multiple bonds and further demonstrates the value of solid-state NMR spectroscopy for interrogating actinide-ligand bonding.

Coordination of Uranyl to the Redox-Active Calix[4]pyrrole Ligand.

Reaction of [Li(THF)]4[L] (L = Me8-calix[4]pyrrole]) with 0.5 equiv of [UVIO2Cl2(THF)2]2 results in formation of the oxidized calix[4]pyrrole product, [Li(THF)]2[LΔ] (1), concomitant with formation of reduced uranium oxide byproducts. Complex 1 can also be generated by reaction of [Li(THF)]4[L] with 1 equiv of I2. We hypothesize that formation of 1 proceeds via formation of a highly oxidizing cis-uranyl intermediate, [Li]2[cis-UVIO2(calix[4]pyrrole)]. To test this hypothesis, we explored the reaction of 1 with either 0.5 equiv of [UVIO2Cl2(THF)2]2 or 1 equiv of [UVIO2(OTf)2(THF)3], which affords the isostructural uranyl complexes, [Li(THF)][UVIO2(LΔ)Cl(THF)] (2) and [Li(THF)][UVIO2(LΔ)(OTf)(THF)] (3), respectively. In the solid state, 2 and 3 feature unprecedented uranyl-η5-pyrrole interactions, making them rare examples of uranyl organometallic complexes. In addition, 2 and 3 exhibit some of the smallest O-U-O angles reported to date (2: 162.0(7) and 162.7(7)°; 3: 164.5(5)°). Importantly, the O-U-O bending observed in these complexes suggests that the oxidation of [Li(THF)]4[L] does indeed occur via an unobserved cis-uranyl intermediate.

Synthesis and Crystallographic Characterization of the Tetravalent Actinide-DOTA Complexes [AnIV(κ8-DOTA)(DMSO)] (An = Th, U).

The reaction of UCl4 or ThCl4(DME)2 (DME = dimethoxyethane) with 1,4,7,10-tetrazacyclododecane-1,4,7,10-tetraacetic acid (H4DOTA), and 6 equiv of triethylamine, in dimethyl sulfoxide (DMSO) results in the formation of [AnIV(κ8-DOTA)(DMSO)] (1, An = U; 2, An = Th), which can be isolated in moderate yields after workup. Complexes 1 and 2 are the first structurally characterized actinide-DOTA complexes to feature the κ8 binding mode for the DOTA ligand. In addition, we isolated a few crystals of [U(κ4-H2DOTA)(DMSO)4][Cl]2 (3). Crystallographic characterization of this material reveals that the [H2DOTA]2- ligand in 3 is only coordinated to U4+ by its four carboxylate arms, generating an overall κ4 binding mode. Similar complexes have been previously proposed as intermediates along the H4DOTA complexation pathway, but this intermediate had not been structurally characterized until now.

Competitive, substrate-dependent reductive debromination/dehydrobromination of 1,2-dibromides with triethylamine.

The interaction of various 1,2-dibromides with NEt3 under various conditions (THF and DMF, respectively) at different temperatures was investigated. Our results from these reactions show that substrate dependent dehydrobrominations compete with reductive debrominations. A comprehensive discussion of these competitive pathways is offered.

cis-ß-Bromostyrene derivatives from cinnamic acids via a tandem substitutive bromination-decarboxylation sequence.

cis-ß-Bromostyrene derivatives were synthesized stereospecifically from cinnamic acids through ß-lactone intermediates. The synthetic sequence did not require the purification of the ß-lactone intermediates although they were found to be stable and readily purified in most cases.

Convenient synthesis of phosphonohydrazines from arylamines.

Phosphonohydrazines were prepared in good yield from corresponding arylamines by a one-pot reaction through diazotization with an organic nitrite and treatment with a trialkyl phosphite. The trialkyl phosphite is postulated to function as a nucleophile as well as a reducing agent.