Using a bis(N-heterocyclic carbene) ligand system, we have synthesized magnesium complexes bearing redox-active α-diimines and observed structural rearrangements promoted by dynamic N-heterocyclic carbene (NHC) dissociation. The reduction of a bis(NHC)-stabilized magnesium dihalide (iPrNHC)2MgBr2 (1; iPrNHC = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) with KC8 in the presence of the respective diimine, affords the doubly reduced compounds (iPrNHC)2Mg(MesDABMe) (2), (iPrNHC)2Mg(MesDABH) (3), and (iPrNHC)2Mg(DippDABMe) (4) (MesDABMe = N,N′-bis(2,4,6-trimethylphenyl)-2,3-dimethyl-1,4-diaza-1,3-diene, MesDABH = N,N′-
bis(2,4,6-trimethylphenyl)-1,4-diazabutadiene, DippDABMe = N,N′-bis-(2,6-diisopropylphenyl)-2,3-dimethyl-1,4-diaza-1,3-diene) as mononuclear five-membered magnesacycles. In contrast to the κ2-diamide coordination in 2−4, (iPrNHC)2Mg(DippDABH) (5; DippDABH = N,N′-bis(2,6-diisopropylphenyl)-1,4-diazabutadiene), prepared under similar conditions, crystallizes as the dinuclear 10-membered magnesacycle [(iPrNHC)Mg(μ DippDABH)]2 (6), where the bridging η1:η1-enediamide ligands are involved in cooperative bonding interactions with the NHC ligands. The diradical complex Mg(DippDABH)2 (7) was also obtained from a solution of 5, which supports an equilibrium between 5 and 6. The rearrangement of 6 to 5 results in an Mg(DAB)2− species that is not stabilized by a Lewis base, which can undergo a disproportionation reaction to form the stable Mg(DAB•−)2 diradical (7). The mechanism for the formation of 6 was evaluated, and a comparative mono(NHC) stabilization of the methylated DAB analogue Mg(DippDABMe) afforded the solid-state coordination polymer [(iPrNHC)Mg-(DippDABMe)·KBr]n (8). The observation of a KBr interaction with the magnesacycle highlights the accessibility to a more Lewis acidic magnesium center upon carbene dissociation from bis(NHC)-stabilized species.

N‐Heterocyclic carbene (NHC)‐ and cyclic (alkyl)(amino)carbene (CAAC)‐stabilized borafluorene radicals have been isolated and characterized by elemental analysis, single‐crystal X‐ray diffraction, UV/Vis absorption, cyclic voltammetry (CV), electron paramagnetic resonance (EPR) spectroscopy, and theoretical studies. Both the CAAC–borafluorene radical (2) and the NHC–borafluorene radical (4) have a considerable amount of spin density localized on the boron atoms (0.322 for 2 and 0.369 for 4). In compound 2, the unpaired electron is also partly delocalized over the CAAC ligand ^carbeneC and N atoms. However, the unpaired electron in compound 4 mainly resides throughout the borafluorene π‐system, with significantly less delocalization over the NHC ligand. These results highlight the Lewis base dependent electrostructural tuning of materials‐relevant radicals. Notably, this is the first report of crystalline borafluorene radicals, and these species exhibit remarkable solid‐state and solution stability.

The synthesis and reactivity study of the first isolable boraphosphaketene, cyclic(alkyl)(amino) carbene (CAAC)-borafluorene-P=C=O (2), is described. Photolysis of compound 2 results in the formation of CAAC-stabilized BP-doped phenanthryne (3) through tandem decarbonylation, monoatomic phosphide insertion, and ring-expansion. Notably, while BN-doped phenanthryne was previously discussed as a reactive intermediate which could not be isolated, the heavier BP-doped analogue exhibits remarkable solution and solid-state stability. The reactivity of 2 with stable carbenes was also explored. Addition of CAAC to 2 led to migration of the original CAAC ligand from boron to phosphorus and coordination of the added CAAC to carbon, affording compound 4. Reaction of 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (NHC) with 2 resulted in N-C bond activation to give the unusual spiro-heterocyclic compound (5).

A detailed investigation was conducted on the reaction of a 1,1′-bi-2-naphthol–coumarin-based fluorescent probe with amino acids. On the basis of the studies, including fluorescence spectroscopy, ¹H NMR, UV–vis, mass spectroscopy, single-crystal X-ray analysis, and molecular modeling, it was found that the distinctively different fluorescent responses of the probe toward the amino acid at the two excitation wavelengths are due to two different reaction pathways that generate different intermediates and products.

A second-row transition metal complex {MoTp(NO)(DMAP)} (DMAP = 4-(dimethylamino)pyridine; Tp = tris(pyrazolyl)borate) is shown to form dihapto-coordinate complexes with a range of substituted pyridines bearing both electron-withdrawing and electron-donating substituents. Subsequent reactivity of the pyridine ligand is demonstrated by protonation and nucleophilic addition reactions.

Dihapto-coordinate 1,2-dihydropyridine complexes of the metal fragment {WTp(NO)(PMe₃)} (Tp = tris(pyrazolyl)borate), derived from pyridine, are demonstrated to undergo protonation at C6 followed by regioselective amination at C5 with a variety of primary and secondary amines. The addition takes place stereoselectively anti to the metal center, producing exclusively cis-disubstituted products. The resulting 1,2,5,6-tetrahydropyridines can be successfully liberated by oxidation, providing a route to novel molecules of potential medicinal interest.

Interest in beryllium, the lightest member of group 2 elements, has grown substantially within the synthetic community. Herein, we report the synthesis and crystal structure of a heteroleptic haloberyllium borohydride bis(1-isopropyl-3-methyl-benzimidazol-2-ylidene)methane ‘carbodicarbene’ (CDC) complex [(CDC)BeCl(BH₄)]. Crystallographic data: Triclinic space group P1̅, a = 8.8695(14), b = 12.394(2), c = 16.844(3) Å, α = 102.395(4), β = 96.456(4), γ = 99.164(4)°, wR2 (all data) = 0.2706 for 6720 unique data and 357 refined parameters.

Metal–organic frameworks (MOFs) are an emerging class of microporous materials that have potential applications in a wide range of areas. As a subclass of MOFs, ionic MOFs, especially charge-separated MOFs, have been relatively less studied but possess unique features including strong host–guest interactions from the exposed charged centers. We report the synthesis and single-crystal structural characterization of five new charge-separated MOFs (UNM 1–5) based on two tetrapodal borate ligands: tetrakis(4-(4-pyridineethynyl)-2,3,5,6-tetrafluorophenyl)borate (T1) and tetrakis(4-(4-pyridyl)-2,3,5,6-tetrafluorophenyl)borate (T2) having rigid arms of different lengths and pyridine groups at the end of each arm. Coordination of these tetrapods with Cu(I), Cu(II), and Ag(I) ions under specific conditions led to a series of new charge-separated MOFs in single crystalline forms. UNM-1 and UNM-2/UNM-3, which crystallize respectively in tetragonal I4̅ space group and monoclinic C2/c space group, are derived from Cu(CH₃CN)₄BF₄ and Cu(NO₃)₂ upon coordination with T1. On the other hand, coordination of T2 with Cu(CH₃CN)₄BF₄ and AgBF₄ respectively yielded UNM-4 and UNM-5 in the monoclinic I2/a space group. All these MOFs possess several degrees of interpenetration that are correlated with the arm lengths of ligands. Noticeably, UNM-1 is 4-fold interpenetrated, leading to the highest stability among all five MOFs, while still displaying an impressive Brunauer–Emmett–Teller (BET) surface area (SA_BET) of ca. 621 m²/g. Our findings highlight the versatility of tetrapodal borate ligands in engineering charge-separated MOFs with diverse structures and controlled functionality.

The hydrogen isotopes deuterium (D) and tritium (T) have become essential tools in chemistry, biology and medicine¹. Beyond their widespread use in spectroscopy, mass spectrometry and mechanistic and pharmacokinetic studies, there has been considerable interest in incorporating deuterium into drug molecules¹. Deutetrabenazine, a deuterated drug that is promising for the treatment of Huntington’s disease², was recently approved by the United States’ Food and Drug Administration. The deuterium kinetic isotope effect, which compares the rate of a chemical reaction for a compound with that for its deuterated counterpart, can be substantial^1,3,4. The strategic replacement of hydrogen with deuterium can affect both the rate of metabolism and the distribution of metabolites for a compound⁵, improving the efficacy and safety of a drug. The pharmacokinetics of a deuterated compound depends on the location(s) of deuterium. Although methods are available for deuterium incorporation at both early and late stages of the synthesis of a drug^6,7, these processes are often unselective and the stereoisotopic purity can be difficult to measure^7,8. Here we describe the preparation of stereoselectively deuterated building blocks for pharmaceutical research. As a proof of concept, we demonstrate a four-step conversion of benzene to cyclohexene with varying degrees of deuterium incorporation, via binding to a tungsten complex. Using different combinations of deuterated and proteated acid and hydride reagents, the deuterated positions on the cyclohexene ring can be controlled precisely. In total, 52 unique stereoisotopomers of cyclohexene are available, in the form of ten different isotopologues. This concept can be extended to prepare discrete stereoisotopomers of functionalized cyclohexenes. Such systematic methods for the preparation of pharmacologically active compounds as discrete stereoisotopomers could improve the pharmacological and toxicological properties of drugs and provide mechanistic information related to their distribution and metabolism in the body.

Key steps in the functionalization of an unactivated arene often involve its dihaptocoordination by a transition metal followed by insertion into the C–H bond. However, rarely are the η²-arene and aryl hydride species in measurable equilibrium. In this study, the benzene/phenyl hydride equilibrium is explored for the {WTp(NO)(PBu₃)} (Bu = n-butyl; Tp = trispyrazoylborate) system as a function of temperature, solvent, ancillary ligand, and arene substituent. Both face-flip and ring-walk isomerizations are identified through spin-saturation exchange measurements, which both appear to operate through scission of a C–H bond. The effect of either an electron-donating or electron-withdrawing substituent is to increase the stability of both arene and aryl hydride isomers. Crystal structures, electrochemical measurements, and extensive NMR data further support these findings. Static density functional theory calculations of the benzene-to-phenyl hydride landscape suggest a single linear sequence for this transformation involving a sigma complex and oxidative cleavage transition state. Static DFT calculations also identified an η²-coordinated benzene complex in which the arene is held more loosely than in the ground state, primarily through dispersion forces. Although a single reaction pathway was identified by static calculations, quasiclassical direct dynamics simulations identified a network of several reaction pathways connecting the η²-benzene and phenyl hydride isomers, due to the relatively flat energy landscape.