Amino Group Functionalized N‑Heterocyclic 1,2,4-Triazole-Derived Carbenes: Structural Diversity of Rhodium(I) Complexes

The synthesis of the amino group functionalized NHC precursor 1-<i>tert</i>-butyl-4-(2-((dimethylamino)­methyl)-phenyl)-3-phenyl-4<i>H</i>-1,2,4-triazol-1-ium perchlorate has been developed. The generation and bonding properties of the NHC ligand have been evaluated in reactions toward three Rh­(I) complexes[Rh­(COD)­Cl]₂, [Rh­(cyclooctene)₂Cl]₂, and [Rh­(ethylene)₂Cl]₂, respectively. For the first complex, [(NHC)­RhCl­(COD)], the coordination of the dangling amino group was not observed because of the fully occupied coordination neighborhood of the Rh atom. On the other hand, in the case of [(NHC)­RhCl­(ethylene)], [(NHC)­RhCl­(cyclooctene)], [(NHC)­Rh­(COD)]⁺[BF₄]⁻, and [(NHC)­RhCl­(CO)] a strong intramolecular coordination of the amino nitrogen atom was revealed, thus forming the unusual seven-membered diazametallacycle. All of the products of these reactions were characterized in solution by NMR spectroscopy as well as in the solid state by X-ray diffraction analysis

Palladium(II) Complexes of 1,2,4-Triazole-Based <i>N</i>‑Heterocyclic Carbenes: Synthesis, Structure, and Catalytic Activity

Six palladium­(II) complexes bearing three different triazole-based N-heterocyclic carbene (NHC) ligands, [1-<i>tert</i>-butyl-4-{2-[(<i>N</i>,<i>N</i>-dimethylamino)­methyl]­phenyl}-3-phenyl-1<i>H</i>-1,2,4-triazol-4-ium-5-ide, 1-<i>tert</i>-butyl-4-(2-methoxyphenyl)-3-phenyl-1<i>H</i>-1,2,4-triazol-4-ium-5-ide, and 1-<i>tert</i>-butyl-4-(4-methylphenyl)-3-phenyl-1<i>H</i>-1,2,4-triazol-4-ium-5-ide], were synthesized and fully characterized. NMR spectroscopy and X-ray diffraction analysis revealed that the amino-group-substituted NHC ligand is coordinated in bidentate fashion, forming a monocarbene chelate complex with an additional intramolecular Pd ← N bond with the nitrogen donor atom. The 4-methylphenyl- and 2-methoxyphenyl-substituted NHC ligands coordinate as C-monodentate donors, forming simple biscarbene Pd­(II) complexes. The evaluation of the catalytic performance in the Suzuki–Miyaura cross-coupling reaction revealed very promising performance of the intramolecularly coordinated monocarbene complexes under relatively mild conditions even in direct comparison with the commercially available PEPPSI catalyst. In contrast, the biscarbene complexes proved inactive in this catalytic process. According to theoretical calculations (EDA and NOCV analysis), functionalization of the 1,2,4-triazole-based NHC with the 2-[(<i>N</i>,<i>N</i>-dimethylamino)­methyl]­phenyl group has a significant effect on the stability of the NHC–metal bond

Combined NMR and DFT Study on the Complexation Behavior of Lappert’s Tin(II) Amide

The complexation chemistry of the stannylene Sn­{N­[Si­(CH₃)₃]₂}₂, first reported by Lappert in the 1970s, was investigated by ¹¹⁹Sn NMR chemical shift measurements. To this end, experimental NMR data and theoretical density functional theory (DFT) calculations were combined to get an insight into the interaction between the stannylene and various solvent molecules with σ- and/or π-coordinating power. Small variations in the measured ¹¹⁹Sn chemical shifts revealed a donor–acceptor interaction with the solvent molecules. In comparison to the noncoordinating solvent cyclohexane taken as a reference, a weak coordination was observed with aromatic solvent molecules (benzene and toluene) and a much stronger coordination with the σ-donors THF and pyridine. Pyridine was confirmed to be the strongest donor, as evidenced by its large upfield chemical shift Δδ­(¹¹⁹Sn) of 635 ppm. The experimental chemical shifts were reproduced by DFT (NMR) calculations, demonstrating similar trends in the interaction strength with the σ- and π-donors. The stannylene Sn­{N­[Si­(CH₃)₃]₂}₂ showed the ability to react with Fe­(CO)₅ and Fe₂(CO)₉ in the molar ratio 1/1 to provide L₂SnFe­(CO)₄ complexes. With a molar excess of Fe₂(CO)₉, L₂Sn­[Fe­(CO)₄]₂ was generated irreversibly. Upon prolonged UV irradiation in the presence of W­(CO)₆, in the molar ratio 1/1, a mixture of L₂SnW­(CO)₅ and two (L₂Sn)₂W­(CO)₄ complexes was generated

Heterocycles Derived from Generating Monovalent Pnictogens within NCN Pincers and Bidentate NC Chelates: Hypervalency versus Bell-Clappers versus Static Aromatics

Generating monovalent pnictogens within NCN pincers has resulted in the isolation of three distinct types of 1,2-azaheteroles, highly aromatic nitrogen analogues like pyrazole-based <b>5</b>, aromatic yet fluxional P- and As-derived bell-clappers <b>1</b> and <b>2</b>, and hypervalent Sb and Bi derivatives <b>3</b> and <b>4</b>, which are supported by 3-center, 4-electron N–E–N bonds. Careful analysis of the solid-state structures of <b>1</b>–<b>5/[5-Me]­[OTf]</b> in combination with NICS calculations (at the GIAO/M06/cc-pVTZ­(-PP) level) and other computational methods (NBO) suggest that simpler NC chelates may support new phosphorus- and arsenic-containing heterocycles. Indeed, reduction of ECl₂ (E = P or As) derivatives supported by <i>N</i>-Dipp (Dipp = 2,6-diisopropylphenyl) substituted NC bidentate ligands produced 1,2-benzoazaphosphole <b>11</b> and 1,2-benzoazaarsole <b>12</b>. NICS calculations revealed <b>11</b> and <b>12</b> had aromatic character on par with that of pyrazole-based <b>5</b>