Introducing Novel Redox-Active Bis(phenolate) N-Heterocyclic Carbene Proligands: Investigation of Their Coordination to Fe(II)/Fe(III) and Their Catalytic Activity in Transfer Hydrogenation of Carbonyl Compounds.

A simple and efficient procedure for synthesizing novel pincer-type tridentate N-heterocyclic carbene bisphenolate ligands is reported. The synthesis of pincer proligands with N,N'-disubstituted imidazoline core, 5 and 6, was carried out via triethylorthoformate-promoted cyclization of either N,N'-bis(2-hydroxy-3,5-di-tert-butylphenyl)cyclohexanediamine, 3, or N,N'-bis(2-hydroxyphenyl)cyclohexanediamine, 4, in the presence of concentrated hydrochloric acid. Cyclic voltammograms of the ligands revealed ligand-centered redox activity, indicating the noninnocent nature of the ligands. The voltammograms of the ligands exhibit two successive one-electron oxidations and two consecutive one-electron reductions. In contrast to previous reports, the redox-active ligands in this study exhibit one-electron oxidation and reduction processes. All products were thoroughly characterized by using 1H and 13C NMR spectroscopy. The base-promoted deprotonation of the proligands and subsequent reaction with iron(II) and iron(III) chlorides yielded compounds 7 and 8. These compounds are binuclear and tetranuclear iron(III) complexes that do not contain carbene functional groups. Complexes 7 and 8 were characterized by using elemental analysis and single-crystal X-ray crystallography. At low catalyst loadings, both 7 and 8 exhibited high catalytic activity in the transfer hydrogenation of selected aldehydes and ketones.

Phosphite-imidazole catalyzed N-formylation and N-acylation of amines.

A novel and convenient method for the N-formylation reaction of amines with DMF as a formylating agent has been developed, utilizing a catalytic amount of diethyl phosphite/imidazole. Diethyl phosphite, as a nucleophilic catalyst, plays a significant role in this conversion. The presented method has a broad substrate scope, and various N-formyl products were obtained in good to excellent yields. Moreover, by using DMA instead of DMF, the N-acetylation reaction was also successful. The reaction of o-phenylenediamines with DMF afforded the corresponding benzimidazoles. Furthermore, N-sulfonyl amidines were obtained in good to excellent yields by the reaction of sulfonamides with DMF under similar conditions.

Heteroleptic Silver(I) and Gold(I) N-Heterocyclic Carbene Complexes: Structural Characterization, Computational Analysis, Tyrosinase Inhibitory, and Biological Effects.

Derivatization of (NHC)M-Cl (M = Ag, Au) with selected sulfur donors from the family of dialkyldithiophosphates and bis(2-mercapto-1-methylimidazolyl)borate ligands gave a series of heteroleptic mononuclear complexes. In single-crystal X-ray diffraction analysis, Ag(I) complexes adopted a trigonal planar geometry, while Au(I) complexes are near-linear. TD-DFT and hole-electron analyses of the selected complexes gave insight into the electronic features of the metal complexes. In vitro cellular tests were conducted on the human cancerous breast cell line MCF-7 using 2 and 8. The antibacterial activities of complexes 1, 2, 3, 7, 8, and IPr-Ag-Cl were also screened against Gram-positive (Staphylococcus aureus PTCC 1112) and Gram-negative (Escherichia coli PTCC 1330) bacteria. Antityrosinase and hemolytic effects of the selected compounds were also determined.

Correction to "Homobimetallic Au(I)-Au(I) and Heterotrimetallic Au(I)-Fe(II)-Au(I) Complexes with Dialkyldithiophosphates and Phosphine Ligands: Structural Characterization, DFT Analysis, and Tyrosinase Inhibitory and Biological Effects".

[This corrects the article DOI: 10.1021/acsomega.3c00645.].

Homobimetallic Au(I)-Au(I) and Heterotrimetallic Au(I)-Fe(II)-Au(I) Complexes with Dialkyldithiophosphates and Phosphine Ligands: Structural Characterization, DFT Analysis, and Tyrosinase Inhibitory and Biological Effects.

The role of bridging and terminal ligand electronic and steric properties on the structure and antiproliferative activity of two-coordinated gold(I) complexes was investigated on seven novel binuclear and trinuclear gold(I) complexes synthesized by the reaction of either Au2(dppm)Cl2, Au2(dppe)Cl2, or Au2(dppf)Cl2 with potassium diisopropyldithiophosphate, K[(S-OiPr)2], potassium dicyclohexyldithiophosphate, K[(S-OCy)2], or sodium bis(methimazolyl)borate, Na(S-Mt)2, which afforded air-stable gold(I) complexes. In 1-7, the gold(I) centers adopt a two-coordinated linear geometry and are structurally similar. However, their structural features and antiproliferative properties highly depend upon subtle ligand substituent changes. All complexes were validated by 1H, 13C{1H}, 31P NMR, and IR spectroscopy. The solid-state structures of 1, 2, 3, 6, and 7 were confirmed using single-crystal X-ray diffraction. A density functional theory geometry optimization calculation was used to extract further structural and electronic information. To investigate the possible cytotoxicities of 2, 3, and 7, in vitro cellular tests were carried out on the human cancerous breast cell line MCF-7. 2 and 7 show promising cytotoxicity.

Recent Advances in Catalysis Involving Bidentate N-Heterocyclic Carbene Ligands.

Since the discovery of persistent carbenes by the isolation of 1,3-di-l-adamantylimidazol-2-ylidene by Arduengo and coworkers, we witnessed a fast growth in the design and applications of this class of ligands and their metal complexes. Modular synthesis and ease of electronic and steric adjustability made this class of sigma donors highly popular among chemists. While the nature of the metal-carbon bond in transition metal complexes bearing N-heterocyclic carbenes (NHCs) is predominantly considered to be neutral sigma or dative bonds, the strength of the bond is highly dependent on the energy match between the highest occupied molecular orbital (HOMO) of the NHC ligand and that of the metal ion. Because of their versatility, the coordination chemistry of NHC ligands with was explored with almost all transition metal ions. Other than the transition metals, NHCs are also capable of establishing a chemical bond with the main group elements. The advances in the catalytic applications of the NHC ligands linked with a second tether are discussed. For clarity, more frequently targeted catalytic reactions are considered first. Carbon-carbon coupling reactions, transfer hydrogenation of alkenes and carbonyl compounds, ketone hydrosilylation, and chiral catalysis are among highly popular reactions. Areas where the efficacy of the NHC based catalytic systems were explored to a lesser extent include CO2 reduction, C-H borylation, alkyl amination, and hydroamination reactions. Furthermore, the synthesis and applications of transition metal complexes are covered.

A Borane Platinum Complex Undergoing Reversible Hydride Migration in Solution.

Reaction of [Pt(κ2-C,N-ppy)(dmso)Cl], 1 (Hppy = 2-phenylpyridine), with Na[H2B(mb)2] (Hmb = 2-mercapto-benzimidazole) smoothly afforded the complex {[(κ3-S,B,S-HB(mb)2]Pt(κ2-C,N-ppy)H}, 2, featuring a strong reverse-dative Pt → B σ interaction in the solid state. When dissolved in thf (or acetone) solution, 2 undergoes a reversible Pt-H bond activation, establishing an equilibrium between the hexacoordinated 2 and the tetracoordinate complex {[(κ2-S,S-H2B(mb)2]Pt(κ2-C,N-ppy)}, 3, as ascertained by multinuclear NMR. Hydrolysis of the B-N bond in 2/3 resulted ultimately in the formation of a dimeric half-lantern platinum(II,II) complex [{Pt(κ2-C,N-ppy)(µ2-κ2-N,S-mb)}2], 4. The SC-XRD structures of 2 and 4 are reported.

Biocompatible 3D Liquid Crystal Elastomer Cell Scaffolds and Foams with Primary and Secondary Porous Architecture.

3D biodegradable and highly regular foamlike cell scaffolds based on biocompatible side-chain liquid crystal elastomers have been prepared. Scaffolds with a primary porosity characterized by spatially interlaced, interconnected microchannels or an additional secondary porosity featuring interconnected microchannel networks define the novel elastomeric scaffolds. The macroscale morphology of the dual porosity 3D scaffold resembles vascular networks observed in tissue. 3D elastomer foams show four times higher cell proliferation capability compared to conventional porous templated films and within the channels guide spontaneous cell alignment enabling the possibility of tissue construct fabrication toward more clinically complex environments.

Biocompatible, biodegradable and porous liquid crystal elastomer scaffolds for spatial cell cultures.

Here we report on the modular synthesis and characterization of biodegradable, controlled porous, liquid crystal elastomers (LCE) and their use as three-dimensional cell culture scaffolds. The elastomers were prepared by cross-linking of star block-co-polymers with pendant cholesterol units resulting in the formation of smectic-A LCEs as determined by polarized optical microscopy, DSC, and X-ray diffraction. Scanning electron microscopy revealed the porosity of the as-prepared biocompatible LCEs, making them suitable as 3D cell culture scaffolds. Biodegradability studies in physiological buffers at varying pH show that these scaffolds are intact for about 11 weeks after which degradation sets in at an exponential rate. Initial results from cell culture studies indicate that these smectic LCEs are compatible with growth, survival, and expansion of cultured neuroblastomas and myoblasts when grown on the LCEs for extended time periods (about a month). These preliminary cell studies focused on characterizing the elastomer-based scaffolds' biocompatibility and the successful 3D incorporation as well as growth of cells in 60 to 150-µm thick elastomer sheets.

Mono-anionic acetophenone imine ligands: synthesis, ortho-lithiation and first examples of group (V) metal complexes.

A series of niobium and tantalum imido complexes with mono-anionic ortho-metallated acetophenone imine ligands have been prepared and characterized using NMR spectroscopy, mass spectrometry and elemental analysis. These low symmetry complexes are produced with only one or two structural isomers in all cases and display interesting correlations between the steric bulk of the ligands employed and the isomers formed. Crystal structures of several new niobium and tantalum complexes are presented as confirmation of the connectivity in these structural isomers.

Titanium imido complexes utilizing orthometallated derivatized acetophenone and piperonal imine ligands: synthesis, isolation, and characterization.

A series of five ortho-lithiated imines (Li-L(n); n = 1-5) was synthesized via the reaction of an aryl or alkyl acetophenone imine with n-butyllithium. The ortho-lithiated imines were subsequently reacted with Ti(NR)Cl(2)py(3) (R = C(CH(3))(3), 2,6-Me(2)C(6)H(3), 2,6-Et(2)C(6)H(3), or 2,6-(i)Pr(2)C(6)H(3)), yielding complexes of the form (L(n))(2)Ti(NR). Several of the resulting complexes [(L(1))(2)Ti(NC(CH(3))(3)), 1a; (L(3))(2)Ti(N-2,6-Me(2)C(6)H(3)), 3b; and (L(5))(2)Ti(NC(CH(3))(3)), 5a] were structurally characterized using small molecule X-ray diffraction. The C(2) symmetric complexes produced in these reactions displayed a distorted square pyramidal geometry. In each complex the titanium center was located above the square plane of the two coordinated bidentate ligands and the chelating C approximately N ligands were folded away from the metal center. When a less sterically demanding alkylimine was used (L(4)), the resulting complex was isolated as an equilibrium mixture of cis and trans isomers of the empirical formula (L(4))(2)Ti(NC(CH(3))(3))py (cis/trans 4a).

Tris(1,10-phenanthroline-kappa2N,N')cobalt(III) tris(trifluoromethanesulfonate) dihydrate.

The title compound, [Co(C(12)H(8)N(2))(3)](CF(3)SO(3))(3) x 2 H(2)O, crystallizes to form infinite chains of complex cations that are connected through offset face-to-face and edge-to-face interactions between their phenanthroline ligands. The chains are themselves interconnected through weak offset face-to-face ligand interactions. The three trifluoromethanesulfonate anions of the asymmetric unit are connected with one another through the two water molecules by hydrogen bonds. One of the trifluoromethanesulfonate anions is described by a disorder over three positions, with occupancies of 0.35, 0.35 and 0.3 in the refined model.