Alumanyl-Samarium(II): Synthesis, Characterization, and Reactivity Studies.

Metal-metal bonded species involving lanthanides are intriguing but rare. The recently reported salt metathesis reaction of an Al anion and SmI2(thf)2 yields novel heterometallic compound possessing two distinctive Al-Sm bonds. Although the Al-Sm bonds were considerably long [3.518(1) and 3.543(1) Å], DFT calculations indicated polar character of the Alδ--Smδ+ bonds. This is the first example of lanthanide species containing X-type Al ligands. Reactivity studies have demonstrated that the introduction of Sm(II) produces unique reactivity. The reaction with carbodiimide led to an insertion of carbodiimide into the Al-Sm bonds and reductive coupling of carbodiimide to create an oxalamidinate moiety, facilitated by Sm(II). Exposure of the Al-Sm-Al complex toward ethylene furnished a Sm(II) salt of anionic aluminacyclopropane that was spontaneously isomerized to a 1,4-dialuminacyclohexane derivative. The important role of Sm(II) to facilitate the ring expansion through an alkyl-relay mechanism was elucidated by DFT calculations.

Alkali Chloride Adducts of Acyclic Acylaluminum: Synthesis, Structure, and Reactivity Studies.

Two acyclic acylaluminums and one cyclic acylaluminum dimer were synthesized by reaction of the recently reported Al-anion with acyl chloride. The reaction of the acylaluminums with TMSOTf and DMAP gave a ring-expanded iminium-substituted aluminate and a 2-C-H cleaved product. In the reaction of acylaluminums toward C=O and C=N bonds, acyclic acylaluminums reacted as an acyl nucleophile, while the cycilc dimer showed no reactivity. Amide-bond forming ligation using acyclic acylaluminums and hydroxylamines was further demonstrated. Throughout the study, acyclic acylaluminums exhibited higher reactivity than that of the cyclic dimer.

Complexes Featuring a cis-[M → → ${{\rm{ \mathbin{{\stackrel{\textstyle\rightarrow} { {\smash{\rightarrow}\vphantom{_{\vbox to.5ex{\vss}}}} } }} }}}$ U ← ← ${{\rm{ \mathbin{{\stackrel{\textstyle\leftarrow} { {\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}} } }} }}}$ M] Core (M=Rh, Ir): A New Route to Uranium-Metal Multiple Bonds.

Although examples of multiple bonds between actinide elements and main-group elements are quite common, studies of the multiple bonds between actinide elements and transition metals are extremely rare owing to difficulties associated with their synthesis. Here we report the first example of molecular uranium complexes featuring a cis-[M → → ${{\rm{ \mathbin{{\stackrel{\textstyle\rightarrow} { {\smash{\rightarrow}\vphantom{_{\vbox to.5ex{\vss}}}} } }} }}}$ U ← ← ${{\rm{ \mathbin{{\stackrel{\textstyle\leftarrow} { {\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}} } }} }}}$ M] core (M=Rh, Ir), which exhibits an unprecedented arrangement of two M → → ${{\rm{ \mathbin{{\stackrel{\textstyle\rightarrow} { {\smash{\rightarrow}\vphantom{_{\vbox to.5ex{\vss}}}} } }} }}}$ U double dative bond linkages to a single U center. These complexes were prepared by the reactions of chlorine-bridged heterometallic complexes [{U{N(CH3 )(CH2 CH2 NPi Pr2 )2 }(Cl)2 [(µ-Cl)M(COD)]2 }] (M=Rh, Ir) with MeMgBr or MeLi, a new method for the construction of species with U-M multiple bonds. Theoretical calculations including dispersion confirmed the presence of two U ← ← ${{\rm{ \mathbin{{\stackrel{\textstyle\leftarrow} { {\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}} } }} }}}$ M double dative bonds in these complexes. This study not only enriches the U ← ← ${{\rm{ \mathbin{{\stackrel{\textstyle\leftarrow} { {\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}} } }} }}}$ M multiple bond chemistry, but also provides a new opportunity to explore the bonding of actinide elements.

Al-Sc Bonded Complexes: Synthesis, Structure, and Reaction with Benzene in the Presence of Alkyl Halide.

An alumanyl anion possessing N,N'-bis(2,6-diisopropylphenyl)-1,3-propanediamine ligand was synthesized and characterized. Transmetalation of this Al anion with diaminoscandium chloride precursors afforded the corresponding Al-Sc complexes possessing an unprecedented Al-Sc bond. The Al-Sc[N(SiMe3)2] complex underwent intramolecular C-H cleavage to form a bridged dinuclear complex with µ-hydrido and µ-methylene ligands. The Al-Sc(NiPr2)2 complex reacted with benzene in the presence of alkyl bromide to furnish a 1,4-dialuminated cyclohexadiene product with a concomitant formation of the alkyl-alkyl coupled product. Although the latter product seems to form through the radical mechanism, DFT calculations revealed an ionic mechanism involving bimetallic reaction pathways to react with alkyl bromide and benzene, which provides new insight into the chemistry of metal-metal bonded compounds.

Tunable Construction of Sandwich-Type Double-[1 + 1] and Half-Folded [2 + 2] Schiff-Base Complexes Controlled by the Combination of Primary and Secondary Template Effects.

The first-row transition-metal ions Mn2+-Cu2+ could serve as effective templates to construct three types of double-[1 + 1], [2 + 2], and [1 + 1] Schiff-base dinuclear macrocyclic complexes in the presence of dialdehydes with different pendant arms and a common 1,8-diamine. The extremely flexible nature of macrocyclic ligands allows for the multiple template-directed syntheses, but the final products could be finely tuned by the subtle variations of Mn2+-Cu2+ ions in a 3d-electronic configuration, radius, and coordination number/geometry as well as the auxiliary (pendant-armed and anionic) template effect at the same time. Two borderlines are observed at the Co2+ ion for forming double-[1 + 1] and [2 + 2] metallacycles involving the H2pdd precursor and the [1 + 1] Cu2+ complex for double-[1 + 1] and [2 + 2] macrocycles containing the H2hpdd unit, respectively. The structural diversity is originated from the non-perfect match between [1 + 1]/[2 + 2] Schiff-base macrocycles and dinuclear metal centers; hence, a compromise between the metal coordination modes and alterations of the ligand conformation takes place.

Identification of a uranium-rhodium triple bond in a heterometallic cluster.

The chemistry of d-block metal-metal multiple bonds has been extensively investigated in the past 5 decades. However, the synthesis and characterization of species with f-block metal-metal multiple bonds are significantly more challenging and such species remain extremely rare. Here, we report the identification of a uranium-rhodium triple bond in a heterometallic cluster, which was synthesized under routine conditions. The uranium-rhodium triple-bond length of 2.31 Å in this cluster is only 3% longer than the sum of the covalent triple-bond radii of uranium and rhodium (2.24 Å). Computational studies reveal that the nature of this uranium-rhodium triple bond is 1 covalent bond with 2 rhodium-to-uranium dative bonds. This heterometallic cluster represents a species with f-block metal-metal triple bond structurally authenticated by X-ray diffraction. These studies not only demonstrate the authenticity of the uranium-metal triple bond, but also provide a possibility for the synthesis of other f-block metal-metal multiple bonds. We expect that this work may further our understanding of the bonding between uranium and transition metals, which may help to design new d-f heterometallic catalysts with uranium-metal bonds for small-molecule activation and to promote the utilization of abundant depleted uranium resources.

Heterometallic Clusters with Multiple Rare Earth Metal-Transition Metal Bonding.

Although a series of complexes with rare earth (RE) metal-metal bonds have been reported, complexes which have multiple RE-Rh bonds are unknown. Here we present the identification of the first example of a molecule containing multiple RE-Rh bonds. The complex with multiple Ce-Rh bonds was synthesized by the reduction of a d-f heterometallic molecular cluster Ce{N[(CH2CH2NPiPr2)RhCl(COD)]3} with excess potassium-graphite. The oxidation state of Ce in 3a appears to be a mixture of Ce(III) and Ce(IV), which was confirmed by X-ray photoelectron spectroscopy, magnetism, and theoretical investigations (DFT and CASSCF). For comparison, the analogous species with multiple La(III)-Rh and Nd(III)-Rh bonds were also constructed. This study provides a possible route for the construction of complexes with multiple RE metal-metal bonds and an investigation of their potential properties and applications.

Polar Ketone-Functionalized Metal-Organic Framework Showing a High CO2 Adsorption Performance.

The incorporation of various functionalities into porous metal-organic frameworks (MOFs) represents an efficacious strategy to improving their gas adsorption properties. In this work, a carbonylated tetracarboxylic acid ligand (5,5'-carbonyldiisophthalic acid) was synthesized, and a ketone-functionalized MOF with exposed metal sites based on this ligand was formed successfully. Structural analysis reveals that the new MOF possesses channels decorated by the carbonyl groups and rhombicuboctahedral cages, with open CuII sites pointing toward the cage center. The framework exhibits exceptionally high CO2 (46.7 wt % at 273 K and 1 bar) and H2 (2.8 wt % at 77 K and 1 bar) uptake. Furthermore, it displays high selectivities of CO2 adsorption over N2 and CH4 at 298 K.

Two Types of Anion-Induced Reconstruction of Schiff-Base Macrocyclic Zinc Complexes: Ring-Contraction and Self-Assembly of a Molecular Box.

Two 46-membered [2 + 2] Schiff-base macrocyclic dinuclear Zn(II) complexes (1a and 1b) were investigated deeply by the postmodification strategy, and two types of supramolecular processes (ring-contraction and self-assembly) have been achieved after the addition of specific anions as stimulus for the equilibrium of Schiff-base macrocyclic complexes. Namely, in the presence of linear three-atom SCN(-), 1a was degraded into two 23-membered [1 + 1] Schiff-base macrocyclic complexes simultaneously (mononuclear Zn(II) complex 2 and dinuclear Zn(II) complex 3). In contrast, 1b was only transformed into the macrocyclic mononuclear complex 5. More interestingly, in the case of pseudolinear five-atom N(CN)2(-), supramolecular self-assembly took place instead of the above-mentioned ring-contraction. Finally, 1a was assembled into a unique molecular box 4 with two 46-membered [2 + 2] Schiff-base macrocyclic heteronuclear Zn4Na4 substrates and double µ2-N(CN)2(-) bridges, while no similar assembly process was observed for 1b. The geometry of anions and pH values slightly adjusted by the pendant arms on the macrocyclic skeletons are believed to be the critical factors for the different supramolecular processes originating from the dynamic covalent chemistry of Schiff-base imine bonds.

Construction of Chiral [4 + 4] and [2 + 2] Schiff-Base Macrocyclic Zinc(II) Complexes Influenced by Counterions and Pendant Arms.

Chiral and racemic 68-membered [4 + 4] tetranuclear and 34-membered [2 + 2] dinuclear Schiff-base macrocyclic zinc(II) complexes 1-10 can be selectively synthesized based on the secondary template effects of counterions and pendant arms, when [(S,S), (R,R), (±)]-1,2-diaminocyclohexane precursors are first used to react with a pair of extended dialdehydes with different pendant arms via zinc(II) ion template-assisted imine condensation.

Solvent-controlled self-assembly of tetrapodal [4 + 4] phosphate organic molecular cage.

Two flexible subcomponents, namely tris(4-formylphenyl)phosphate and tris(2-aminoethyl)amine, are assembled into a tetrapodal [4 + 4] cage depending on the solvent effect. Single-crystal structure analysis reveals that the caivity is surrounded by four phosphate uints. Good selectivity of CO2 adsorption over CH4 is demonstrated by the gas adsorption experiment.

Construction of heterometallic clusters with multiple uranium-metal bonds by using dianionic nitrogen-phosphorus ligands.

Compared with the prevalent metal-metal bond in transition metals, examples of the actinide-metal bond in heterometallic clusters are rare. Herein, a series of heterometallic clusters with multiple uranium-metal bonds has been prepared based on two newly synthesized nitrogen-phosphorus ligands L1 {O[(CH2)2NHP(iPr)2]2} and L2 {[CH2O(CH2)2NHP(iPr)2]2}. Different P-P distances, 6.069 and 4.464 Å, are observed in the corresponding uranium complexes 1 {O[(CH2)2NP(iPr)2]2UCl2} and 2 {[CH2O(CH2)2NP(iPr)2]2UCl2}, respectively, and lead to the different coordination modes with transition metals. The reactions of zero-valent group 10 metal compounds with complex 1 generate heterometallic clusters (3-U2Ni2 and 4-U2Pd2) featuring four uranium-metal bonds; whereas reactions with 2 afford one-dimensional metal-chain 5-(UNi)n, bimetallic species 6-UPd, and a tri-platinum bridged diuranium molecular cluster 7-U2Pt3. Complex 5-(UNi)n represents the first infinite chain containing the U-M bond and 7-U2Pt3 is the first species with multiple U-Pt bonds. This study further highlights the important role of ligands in the construction of multiple uranium-metal bonds and may allow the synthesis of novel d-f heterometallic clusters and the investigation of their applications in catalysis and small-molecule activation.

Transition-metal-bridged bimetallic clusters with multiple uranium-metal bonds.

Heterometallic clusters are important in catalysis and small-molecule activation because of the multimetallic synergistic effects from different metals. However, multimetallic species that contain uranium-metal bonds remain very scarce due to the difficulties in their synthesis. Here we present a straightforward strategy to construct a series of heterometallic clusters with multiple uranium-metal bonds. These complexes were created by facile reactions of a uranium precursor with Ni(COD)2 (COD, cyclooctadiene). The multimetallic clusters' cores are supported by a heptadentate N4P3 scaffold. Theoretical investigations indicate the formation of uranium-nickel bonds in a U2Ni2 and a U2Ni3 species, but also show that they exhibit a uranium-uranium interaction; thus, the electronic configuration of uranium in these species is U(III)-5f26d1. This study provides further understanding of the bonding between f-block elements and transition metals, which may allow the construction of d-f heterometallic clusters and the investigation of their potential applications.

Air-oxidation from sulfur to sulfone-bridged Schiff-base macrocyclic complexes showing enhanced antimicrobial activities.

Two embedded sulfur atoms in a novel [2 + 2] Schiff-base macrocyclic dinuclear Zn(II) complex were found to be easily autoxidized to the sulfone units on air exposure, and the resultant sulfone-functionalized macrocyclic complex was obtained by the post-modification strategy exhibiting enhanced antimicrobial activities because of the presence of dual active sites in comparison with the sulfur-containing Schiff-base macrocycle.

Cavity partition and functionalization of a [2+3] organic molecular cage by inserting polar P[double bond, length as m-dash]O bonds.

The cavity of a [2+3] organic molecular cage was partitioned and functionalized by inserting inner-directed P[double bond, length as m-dash]O bonds, which shows CO2 capture and CH4 exclusion due to the size-matching and polarity effects. Computational results demonstrate that the successful segmentation via polar P[double bond, length as m-dash]O bonds facilitates the CO2 molecules to reside selectively inside the cavity.