Large Hyperfine Coupling Arising from Pseudo-S Ground States in a Series of Lutetium(II) Metallocene Complexes.

The synthesis of molecules with strong coupling between electronic and nuclear spins represents an important challenge in molecular quantum information science. Here, we report the synthesis and characterization of the divalent lutetium metallocene complexes Lu(Cp)(Cp) (Cp = pentamethylcyclopentadienyl; Cp = pentaisopropylcyclopentadienyl), Lu(Cp) (Cp = ethyltetraisopropylcyclopentadienyl), and Lu(Cp) (Cp = tetraisopropylcyclopentadienyl). The molecular structures of these complexes, as determined through single-crystal X-ray diffraction, feature a common bent sandwich geometry, with average Cp-Lu-Cp angles ranging from 159.

Alcohol-alcohol cross-coupling enabled by S2 radical sorting.

Alcohols represent a functional group class with unparalleled abundance and structural diversity. In an era of chemical synthesis that prioritizes reducing time to target and maximizing exploration of chemical space, harnessing these building blocks for carbon-carbon bond-forming reactions is a key goal in organic chemistry. In particular, leveraging a single activation mode to form a new C(sp)-C(sp) bond from two alcohol subunits would enable access to an extraordinary level of structural diversity.

Rapid and Modular Access to Quaternary Carbons from Tertiary Alcohols via Bimolecular Homolytic Substitution.

Quaternary carbons are ubiquitous in bioactive molecules; however, synthetic methods for the construction of this motif remain underdeveloped. Here, we report the synthesis of quaternary carbons from tertiary alcohols, a class of structurally diverse, bench-stable feedstocks, via the merger of photoredox catalysis and iron-mediated S2 bond formation. This alcohol-bromide cross-coupling is enabled by a novel halogen-atom transfer (XAT) reagent, which is the first reductively activated XAT reagent to be reported.

Synthesis and Crystallographic Characterization of a Reduced Bimetallic Yttrium -Metallocene Hydride Complex, [K(crypt)][(μ-Cp)Y(μ-H)] (Cp = MeSi[CH(SiMe)-3]), with a 3.4 Å Yttrium-Yttrium Distance.

The reduction of a bimetallic yttrium -metallocene hydride was examined to explore the possible formation of Y-Y bonds with 4d Y(II) ions. The precursor [CpY(μ-H)(THF)] (Cp = MeSi[CH(SiMe)-3]) was synthesized by hydrogenolysis of the allyl complex CpY(η-CH)(THF), which was prepared from (CH)MgCl and [CpY(μ-Cl)]. Treatment of [CpY(μ-H)(THF)] with excess KC in the presence of one equivalent of 2.

Divalent Lanthanide Metallocene Complexes with a Linear Coordination Geometry and Pronounced 6s-5d Orbital Mixing.

A small but growing number of molecular compounds have been isolated featuring divalent lanthanides with 4f5d electron configurations. While the majority of these possess trigonal coordination geometries, we previously reported the first examples of linear divalent metallocenes Ln(Cp) (Ln = Tb, Dy; Cp = pentaisopropylcyclopentadienyl). Here, we report the synthesis and characterization of the remainder of the Ln(Cp) () series (including Y and excluding Pm).

Ultrahard magnetism from mixed-valence dilanthanide complexes with metal-metal bonding.

Magnetic effects of lanthanide bonding Lanthanide coordination compounds have attracted attention for their persistent magnetic properties near liquid nitrogen temperature, well above alternative molecular magnets. Gould . report that introducing metal-metal bonding can enhance coercivity.

A Uranium(II) Arene Complex That Acts as a Uranium(I) Synthon.

Two-electron reduction of the amidate-supported U(III) mono(arene) complex U(TDA) () with KC yields the anionic bis(arene) complex [K[2.2.2]cryptand][U(TDA)] () (TDA = -(2,6-di-isopropylphenyl)pivalamido).

A biomimetic S2 cross-coupling mechanism for quaternary sp-carbon formation.

Bimolecular homolytic substitution (S2) is an open-shell mechanism that is implicated across a host of biochemical alkylation pathways. Surprisingly, however, this radical substitution manifold has not been generally deployed as a design element in synthetic C–C bond formation. We found that the S2 mechanism can be leveraged to enable a biomimetic sp-sp cross-coupling platform that furnishes quaternary sp-carbon centers, a long-standing challenge in organic molecule construction.

Isolation of a triplet benzene dianion.

Baird's rule predicts that molecules with 4n π electrons should be aromatic in the triplet state, but the realization of simple ring systems with such an electronic ground state has been stymied by these molecules' tendency to distort into structures bearing a large singlet-triplet gap. Here, we show that the elusive benzene diradical dianion can be stabilized through creation of a binucleating ligand that enforces a tightly constrained inverse sandwich structure and direct magnetic exchange coupling. Specifically, we report the compounds [K(18-crown-6)(THF)][M(BzN-Mes)] (M = Y, Gd; BzN-Mes = 1,3,5-tris[2',6'-(N-mesityl)dimethanamino-4'-tert-butylphenyl]benzene), which feature a trigonal ligand that binds one trivalent metal ion on each face of a central benzene dianion.

Substituent Effects on Exchange Coupling and Magnetic Relaxation in 2,2'-Bipyrimidine Radical-Bridged Dilanthanide Complexes.

Systematic analysis of related compounds is crucial to the design of single-molecule magnets with improved properties, yet such studies on multinuclear lanthanide complexes with strong magnetic coupling remain rare. Herein, we present the synthesis and magnetic characterization of the series of radical-bridged dilanthanide complex salts [(Cp*Ln)(μ-5,5'-Rbpym)](BPh) (Ln = Gd, Dy; R = NMe (), OEt (), Me (), F (); bpym = 2,2'-bipyrimidine). Modification of the substituent on the bridging 5,5'-Rbpym radical anion allows the magnetic exchange coupling constant, , for the gadolinium compounds in this series to be tuned over a range from -2.

Structure and magnetism of a tetrahedral uranium(iii) β-diketiminate complex.

We describe the functionalisation of the previously reported uranium(iii) β-diketiminate complex (BDI)UI(THF) (1) with one and two equivalents of a sterically demanding 2,6-diisopropylphenolate ligand (ODipp) leading to the formation of two heteroleptic complexes: [(BDI)UI(ODipp)] (2) and (BDI)U(ODipp) (3). The latter is a rare example of a tetrahedral uranium(iii) complex, and it shows single-molecule magnet behaviour.

Synthesis and Magnetism of Neutral, Linear Metallocene Complexes of Terbium(II) and Dysprosium(II).

The divalent metallocene complexes Ln(Cp) (Ln = Tb, Dy) were synthesized through the KC reduction of Ln(Cp)I intermediates and represent the first examples of neutral, linear metallocenes for these elements. X-ray diffraction analysis, density functional theory calculations, and magnetic susceptibility measurements indicate a 4f5d electron configuration with strong s/d mixing that supports the linear coordination geometry. A comparison of the magnetic relaxation behavior of the two divalent metallocenes relative to salts of their trivalent counterparts, [Ln(Cp)][B(CF)], reveals that lanthanide reduction has opposing effects for dysprosium and terbium, with magnetic relaxation times increasing from Tb to Tb and decreasing from Dy to Dy.

High-temperature magnetic blocking and magneto-structural correlations in a series of dysprosium(iii) metallocenium single-molecule magnets.

A series of dysprosium(iii) metallocenium salts, [Dy(Cp)][B(CF)] (R = H (), Me (), Et (), iPr ()), was synthesized by reaction of DyI with the corresponding known NaCp (R = H, iPr) and novel NaCp (R = Me, Et) salts at high temperature, followed by iodide abstraction with [H(SiEt)][B(CF)]. Variation of the substituents in this series results in substantial changes in molecular structure, with more sterically-encumbering cyclopentadienyl ligands promoting longer Dy-C distances and larger Cp-Dy-Cp angles. Dc and ac magnetic susceptibility data reveal that these structural changes have a considerable impact on the magnetic relaxation behavior and operating temperature of each compound.

Isolation of a TMTAA-Based Radical in Uranium bis-TMTAA Complexes.

We report the synthesis, characterization, and electronic structure studies of a series of thorium(IV) and uranium(IV) bis-tetramethyltetraazaannulene complexes. These sandwich complexes show remarkable stability towards air and moisture, even at elevated temperatures. Electrochemical studies show the uranium complex to be stable in three different oxidation states; isolation of the oxidized species reveals a rare case of a non-innocent tetramethyltetraazaannulene (TMTAA) ligand.

Incubation of 2-methylisoborneol synthase with the intermediate analog 2-methylneryl diphosphate.

Incubation of synthetic 2-methylneryl diphosphate (2-MeNPP, 10) with 2-methylisoborneol synthase (MIBS) gave a mixture of products that differed significantly from that derived from the natural substrate (E)-2-methylgeranyl diphosphate (3, 2-MeGPP). The proportion of (-)-2-methylisoborneol (1) decreased from 89 to 17% while that of 2-methylenebornane (4) increased from 10 to 26%, with the relative yields of the isomeric homo-monoterpenes 2-methyl-2-bornene (5) and 1-methylcamphene (6) remaining essentially unchanged (<1% each), as determined by chiral GC-MS analysis. The majority of the product mixture resulting from the MIBS-catalyzed cyclization of 2-MeNPP (10) consisted of the anomalous monocyclic homo-monoterpenes (±)-2-methylllimonene (15, 39%) and 2-methyl-α-terpineol (13, 10%), as well as the acylic derivatives 2-methylnerol (11, 7%) and 2-methyllinalool (14, <1%).

A Trinuclear Radical-Bridged Lanthanide Single-Molecule Magnet.

Assembly of the triangular, organic radical-bridged complexes Cp* Ln (μ -HAN) (Cp*=pentamethylcyclopentadienyl; Ln=Gd, Tb, Dy; HAN=hexaazatrinaphthylene) proceeds through the reaction of Cp* Ln(BPh ) with HAN under strongly reducing conditions. Significantly, magnetic susceptibility measurements of these complexes support effective magnetic coupling of all three Ln centers through the HAN radical ligand. Thorough investigation of the Dy congener through both ac susceptibility and dc magnetic relaxation measurements reveals slow relaxation of the magnetization, with an effective thermal relaxation barrier of U =51 cm .

High-yield lithiation of azobenzenes by tin-lithium exchange.

The lithiation of halogenated azobenzenes by halogen-lithium exchange commonly leads to substantial degradation of the azo group to give hydrazine derivatives besides the desired aryl lithium species. Yields of quenching reactions with electrophiles are therefore low. This work shows that a transmetalation reaction of easily accessible stannylated azobenzenes with methyllithium leads to a near-quantitative lithiation of azobenzenes in para, meta, and ortho positions.