Supramolecular coordination compounds bear exceptional advantages over their organic counterparts. They are available in one‐pot reactions and in high yields and display physical properties that are ...generally inaccessible with organic species. Moreover, their weak, reversible, noncovalent bonding interactions facilitate error checking and self‐correction. This Review emphasizes the achievements in supramolecular coordination chemistry initiated by serendipity and their materialization based on rational design. The recognition of similarities in the synthesis of different supramolecular assemblies allows prediction of potential results in related cases. Supramolecular synthesis obeys guidelines comparable to the “lead sheet” used by small jazz ensembles for improvisation and therefore more often leads to unpredicted results. The combination of detailed symmetry considerations with the basic rules of coordination chemistry has only recently allowed for the design of rational strategies for the construction of a variety of nanosized systems with specified size and shape.
Luck or ability? In the field of supramolecular coordination chemistry, impressive advances have been achieved by the augmentation of initial serendipitous discoveries with rational design. Detailed consideration of symmetry and of the basic principles of coordination chemistry have led to rational strategies for the construction of diverse nanostructures with specific form and size (for example, 1; Fe: white, tripodal benzene ligand: yellow).
A Pair of Cobalt(III/IV) Terminal Imido Complexes Mao, Weiqing; Fehn, Dominik; Heinemann, Frank W. ...
Angewandte Chemie (International ed.),
July 19, 2021, Letnik:
60, Številka:
30
Journal Article
Recenzirano
Odprti dostop
The reaction of the cobalt(I) complex (TIMMNmes)CoI(BPh4) (2) (TIMMNmes=tris‐2‐(3‐mesitylimidazolin‐2‐ylidene)methylamine) with 1‐adamantylazide yields the cobalt(III) imido complex ...(TIMMNmes)CoIII(NAd)(BPh4) (3) with concomitant release of dinitrogen. The N‐anchor in diamagnetic 3 features an unusual, planar tertiary amine, which results from repulsive electrostatic interaction with the filled d(z2)‐orbital of the cobalt ion and negative hyperconjugation with the neighboring methylene groups. One‐electron oxidation of 3 with FeCp2(OTf) provides access to the rare, high‐valent cobalt(IV) imido complex (TIMMNmes)CoIV(NAd)(OTf)2 (4). Despite a half‐life of less than 1 h at room temperature, 4 could be isolated at low temperatures in analytically pure form. Single‐crystal X‐ray diffractometry and EPR spectroscopy corroborate the molecular structure and the d5 low‐spin, S=1/2
, electron configuration. A computational analysis of 4 suggests high covalency within the CoIV=NAd bond with non‐negligible spin density located at the imido moiety, which translates into substantial triplet nitrene character.
Straightforward access to a cobalt(IV) terminal imido complex was provided by one‐electron oxidation of a cobalt(III) terminal imido precursor. The cobalt(IV) monoimido complex could be isolated at low temperatures in analytically pure form. Single‐crystal X‐ray diffractometry and EPR spectroscopy corroborate the molecular structure and the d5 low‐spin, S=1/2
, electron configuration.
The synthesis, characterization, and reactivity of a series of cobalt terminal imido complexes supported by an N-anchored tripodal tris(carbene) chelate is described, including a Co-supported ...singlet nitrene. Reaction of the CoI precursor (TIMMNmes)CoI(PF6) (TIMMNmes = tris-2-(3-mesityl-imidazolin-2-ylidene)-methylamine) with p-methoxyphenyl azide yields a CoIII imide (TIMMNmes)CoIII(NAnisole)(PF6) (1). Treatment of 1 with 1 equiv of FeCp2(PF6) at −35 °C affords a formal CoIV imido complex (TIMMNmes)Co(NAnisole)(PF6)2 (2), which features a bent Co–N(imido)–C(Anisole) linkage. Subsequent one-electron oxidation of 2 with 1 equiv of AgPF6 provides access to the tricationic cobalt imido complex (TIMMNmes)Co(NAnisole)(PF6)3 (3). All complexes were fully characterized, including single-crystal X-ray diffraction (SC-XRD) analyses, infrared (IR) vibrational, ultraviolet/visible (UV/vis) electronic absorption, multinuclear NMR, X-band electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), and high-energy-resolution fluorescence-detected X-ray absorption spectroscopy (HERFD XAS). Quantum chemical calculations provide additional insight into the electronic structures of all compounds. The dicationic CoIV imido complex 2 exhibits a doublet ground state with considerable imidyl character as a result of covalent Co–NAnisole bonding. At room temperature, 2 readily converts to a CoII amine complex involving intramolecular C–H bond amination. Electronically, tricationic complex 3 can be understood as a singlet nitrene bound to CoIII with significant CoIV imidyl radical character. Verifying the pronounced electrophilicity, nucleophiles such as H2O and t BuNH2 add to 3analogous to the parent free nitrenein the para position of the aromatic substituent, thus, clearly corroborating singlet nitrene-type reactivity.
A facile method for the electrodeposition of amorphous nickel oxyhydroxide is described and discussed in which well‐defined nickel complexes with pyridinedimethanol ligands are employed as ...single‐source molecular precursors. No buffering agent is required to assist the anodic deposition process. The deposited nickel oxyhydroxide shows high robustness and efficiency for electrocatalytic water oxidation.
NiOx for ox: Upon the application of an anodic potential, molecular nickel cubane 1 with 2,6‐pyridinedimethanol ligands is converted into amorphous nickel oxyhydroxide, which catalyzes water oxidation efficiently.
Two novel rhodium(III) complexes, namely, RhIII(X)Cl3 (X = 2 2,6-bis((4S,7R)-7,8,8-trimethyl-4,5,6,7-tetrahydro-1H-4,7-methanoindazol-3-yl)pyridine or ...2,6-bis((4S,7R)-1,7,8,8-tetramethyl-4,5,6,7-tetrahydro-1H-4,7-methanoindazol-3-yl)pyridine), were synthesized from camphor derivatives of a bis(pyrazolylpyridine), tridentate nitrogen-donor chelate system, giving RhIII(H2L*)Cl3 (1a) and RhIII(Me2L*)Cl3 (1b). A rhodium(III) terpyridine (terpy) ligand complex, RhIII(terpy)Cl3 (1c), was also synthesized. By single-crystal X-ray analysis, 1b crystallizes in an orthorhombic P212121 system, with two molecules in the asymmetric unit. Tridentate coordination by the N,N,N-donor localizes the central nitrogen atom close to the rhodium(III) center. Compounds 1a and 1b were reactive toward l-methionine (l-Met), guanosine-5′-monophosphate (5′-GMP), and glutathione (GSH), with an order of reactivity of 5′-GMP > GSH > l-Met. The order of reactivity of the RhIII complexes was: 1b> 1a > 1c. The RhIII complexes showed affinity for calf thymus DNA and bovine serum albumin by UV–vis and emission spectral studies. Furthermore, 1b showed significant in vitro cytotoxicity against human epithelial colorectal carcinoma cells. Since the RhIII complexes have similar coordination modes, stability differences were evaluated by density functional theory (DFT) calculations (B3LYP(CPCM)/LANL2DZp). With (H2L*) and (terpy) as model ligands, DFT calculations suggest that both tridentate ligand systems have similar stability. In addition, molecular docking suggests that all test compounds have affinity for the minor groove of DNA, while 1b and 1c have potential for DNA intercalation.
The aim of the study was to investigate the complete substitution of imported soybean meal in beef cattle diets and the consequences on performance, meat, and adipose tissue quality. Thirty growing ...crossbred Limousin bulls, with an initial bodyweight of 164 ± 13 kg and 4.3 ± 0.3 months of age, were fed a grass/maize-silage based diet with little additional concentrate (0.5:0.3:0.2). Concentrates contained either soybean meal (positive control), faba beans, pumpkin seed cake, or spirulina (Arthrospira platensis), resulting in about 226 g crude protein (CP)/kg concentrate dry matter (DM) and 158 g CP/kg total diet DM. A grain-based concentrate providing just 135 g CP/kg concentrate DM and 139 g CP/total diet DM served as a negative control. Bulls of all groups had comparable average daily gains (1.43 ± 0.1 kg) and feed intakes (6.92 ± 0.37 kg). Carcass and meat quality did not differ among groups. The fatty acid profile of meat lipids was hardly affected. These results indicate that soybean meal can be replaced by any of the tested protein sources without impairing performance or meat quality. Importantly, bulls fed the negative control achieved a fattening and slaughter performance comparable to that of the protein-supplemented groups without affecting meat and adipose tissue quality. Thus, the present findings suggest that feeding crossbred bulls a grass/maize-silage based diet does not require additional protein supplementation.
A novel rhodium(iii) complex Rh
(H
L
)Cl
(1) (H
L
= 2,6-bis(5-tert-butyl-1H-pyrazol-3-yl)pyridine) containing a pincer type, tridentate nitrogen-donor chelate system was synthesized. Single crystal ...X-ray structure analysis revealed that 1 crystallizes in the orthorhombic space group Pbcn with a = 20.7982(6), b = 10.8952(4), c = 10.9832(4) Å, V = 2488.80(15) Å
, and eight molecules in the unit cell. The rhodium center in the complex Rh
(H
L
)Cl
(1) is coordinated in a slightly distorted octahedral geometry by the tridentate N,N,N-donor and three chloro ligands, adopting a mer arrangement with an essentially planar ligand skeleton. Due to the tridentate coordination of the N,N,N-donor, the central nitrogen atom N1 is located closer to the Rh
center. The reactivity of the synthesized complex toward small biomolecules (l-methionine (l-Met), guanosine-5'-monophosphate (5'-GMP), l-histidine (l-His) and glutathione (GSH)) and to a series of duplex DNAs and RNA was investigated. The order of reactivity of the studied small biomolecules is: 5'-GMP > GSH > l-Met > l-His. Duplex RNA reacts faster with the Rh
(H
L
)Cl
complex than duplex DNA, while shorter duplex DNA (15mer GG) reacts faster compared with 22mer GG duplex DNA. In addition, a higher reactivity is achieved with a DNA duplex with a centrally located GG-sequence than with a 22GTG duplex DNA, in which the GG-sequence is separated by a T base. Furthermore, the interaction of this metal complex 1 with calf thymus DNA (CT-DNA) and bovine serum albumin (BSA) was examined by absorption (UV-Vis) and emission spectral studies (EthBr displacement studies). Overall, the studied complex exhibited good DNA and BSA interaction ability.
Easy come, easy go: The first molecular SO2 complexes of the lanthanides (Ln=Sm, Eu) have been prepared. The compounds can reversibly coordinate gaseous SO2. Concomitant with the addition and removal ...of SO2, the color of the complexes changes reversibly (see scheme). The structures of the SO2 compounds could be confirmed in solution and in the solid state.
Under anaerobic conditions, the reactions of cobalt(II) and nickel(II) acetate tetrahydrate with 2,6‐pyridinedimethanol (H2L2, 3) in anhydrous acetonitrile afforded two tetranuclear metal(II) ...complexes MII4(HL2)4(OAc)4 (4; MII = Co2+, Ni2+) with a M4(μ3‐O)44+ cubane core. X‐ray structural analyses revealed that both MII cubanes 4a·2CH3OH and 4b·2CH3OH are isostructural and crystallize in the tetragonal space group I41/acd with eight molecules in the unit cell. In the solid state, the orientation of the cubane cores of 4 and the formation of a 3D framework were controlled by π–π interactions as well as intra‐ and intermolecular O–H···O hydrogen bonds. Variable‐temperature magnetic susceptibility measurements revealed that the cubanes 4 show a ferrimagnetic coupling scheme that leads to a diamagnetic ground state for both complexes. Core‐level X‐ray photoelectron spectroscopy confirmed that the Co and Ni ions in 4a and 4b are in a divalent state. X‐ray magnetic circular dichroism was performed to extract the spin and orbital contributions to the Co and Ni magnetic moments. We compared the experimental results of the local electronic structures around the Co2+ ions in 4a and the Ni2+ ions in 4b with charge‐transfer multiplet simulations.
Starting from 2,6‐pyridinedimethanol (H2L2, 3) and metal(II) acetate tetrahydrates, divalent CoII and NiII cubanes MII4(HL2)4(OAc)4 (4) have been synthesized through self‐organization. In addition to standard methods (e.g., IR, MS, X‐ray analysis), complexes 4 were also characterized by magnetometry and X‐ray spectroscopic techniques, including XPS, XAS, and XMCD.
Starting from phenols R1,R2ArOH (5) and the anisole derivative 3,5‐di‐tert‐butyl‐2‐methoxybenzyl bromide (13), a series of new tacn‐based ligands (R1,R2ArOR3)3tacn (2) have been synthesized with ...substituents of varying bulkiness and electronic nature at the ortho and para positions with respect to the oxygen coordination site. It was observed that these groups not only determine the steric shielding and solubility properties of 2, but also deactivate the reactivity of the phenols in the modified Mannich reaction when electron‐withdrawing groups are introduced at the para position in 5. Treatment of the ligands with UCl4 in thf led to the isolation of four uranium(IV) chloro complexes {(R1,R2ArO)3tacn}UIVCl (14), which were characterized by different spectroscopic and physical methods (e.g., 1H NMR, UV/Vis, SQUID), corroborating the +4 oxidation state in 14. Single‐crystal X‐ray structure analyses revealed that 14a·CH2Cl2·CH3CN and 14b·1.25CH2Cl2 crystallize in the chiral, orthorhombic space group P212121 a = 24.934(3), b = 27.941(3), c = 9.045(1) Å, V = 6302(2) Å3, Z = 4 and the chiral, hexagonal space group P63 a = 22.097(3), c = 17.941(2) Å, V = 7587(2) Å3, Z = 4, respectively. Interestingly, complexes 14a,b self‐organize in the solid state into homochiral 1D polymeric superstructures as a result of weak intermolecular C–H···Cl contacts.
A series of tacn‐based ligands (R1,R2ArOR3)3tacn have been synthesized with substituents of varying bulkiness and electronic nature. Treatment of the ligands with UCl4 afforded uranium(IV) chloro complexes {(R1,R2ArO)3tacn}UIVCl, which self‐organize in the solid state into homochiral 1D polymeric strands as a result of weak intermolecular C–H···Cl contacts.
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