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1. Synthesis, structural characterization and NMR studies of group 10 metal complexes with macrocyclic amine N-heterocyclic carbene ligands

   https://doi.org/10.1039/C7DT04666A  

   Lu, Taotao; Liu, Zhiming; Steren, Carlos A.; Fei, Fan; Cook, Tabitha M.; Chen, Xue-Tai; Xue, Zi-Ling (January 2018, Dalton Transactions)

   A series of Ni( ii ), Pd( ii ) and Pt( ii ) complexes [ML][PF 6 ] 2 [L = L 1 , M = Ni ( 1 ), Pd ( 2 ), Pt ( 3 ); L = L 2 , M = Ni ( 4 ), Pd ( 5 ), Pt ( 6 )] and [Pt(L 2 )(acac)] ( 7 ) have been prepared by the reactions of two tetradentate macrocyclic amine-NHC ligand precursors, [H 2 L 1 ][PF 6 ] 2 and [H 2 L 2 ][PF 6 ] 2 , with Ni(OAc) 2 ·4H 2 O, Pd(OAc) 2 and Pt(acac) 2 in the presence of NaOAc. Complex 7 is isolated along with 6 from the same reaction between [H 2 L 2 ][PF 6 ] 2 and Pt(acac) 2 . There are two atropisomers in 1–3 and two achiral conformers in 4–6 . The crystal structures of 1–3 and one conformer of 4–6 ( 4a–6a ) have been determined by single-crystal X-ray diffraction studies. The metal ion is found to reside in the cavity of the macrocyclic ring and adopts a square-planar configuration. Detailed NMR studies including variable-temperature NMR spectroscopy reveal a dynamic interconverting process between two atropisomers of 1–3 in the solutions via a ring twisting mechanism. Two conformers in the equilibrated solution of 4–6 , probably arising from the orientation of two amine N–H bonds with respect to the coordination plane, exchange slowly. Time-dependent 1 H NMR spectra show that one conformer ( 4a–6a ) in solution converts into the other ( 4b–6b ) via the inversion of the nitrogen atom. 

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2. Synthesis, Characterization, and Reactivity of Cationic Gold Diarylallenylidene Complexes

   https://doi.org/10.1002/anie.201713209  

   Kim, Nana; Widenhoefer, Ross A. (March 2018, Angewandte Chemie International Edition)

   Abstract Methoxide abstraction from gold acetylide complexes of the form (L)Au[η¹‐C≡CC(OMe)ArAr′] (L=IPr, P(^tBu)₂(ortho‐biphenyl); Ar/Ar′=C₆H₄X where X=H, Cl, Me, OMe) with trimethylsilyl trifluoromethanesulfonate (TMSOTf) at −78 °C resulted in the formation of the corresponding cationic gold diarylallenylidene complexes [(L)Au=C=C=CArAr′]⁺ OTf⁻in ≥85±5 % yield according to¹H NMR analysis.¹³C NMR and IR spectroscopic analysis of these complexes established the arene‐dependent delocalization of positive charge on both the C1 and C3 allenylidene carbon atoms. The diphenylallenylidene complex [(IPr)Au=C=C=CPh₂]⁺ OTf⁻reacted with heteroatom nucleophiles at the allenylidene C1 and/or C3 carbon atom. 

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3. Origin of the ²⁹ Si NMR chemical shift in R ₃ Si–X and relationship to the formation of silylium (R ₃ Si ⁺ ) ions

   https://doi.org/10.1039/D0DT02099K  

   Huynh, Winn; Conley, Matthew P. (November 2020, Dalton Transactions)

   null (Ed.)

   The origin in deshielding of 29 Si NMR chemical shifts in R 3 Si–X, where X = H, OMe, Cl, OTf, [CH 6 B 11 X 6 ], toluene, and O X (O X = surface oxygen), as well as i Pr 3 Si + and Mes 3 Si + were studied using DFT methods. At the M06-L/6-31G(d,p) level of theory the geometry optimized structures agree well with those obtained experimentally. The trends in 29 Si NMR chemical shift also reproduce experimental trends; i Pr 3 Si–H has the most shielded 29 Si NMR chemical shift and free i Pr 3 Si + or isolable Mes 3 Si + have the most deshielded 29 Si NMR chemical shift. Natural localized molecular orbital (NLMO) analysis of the contributions to paramagnetic shielding ( σ p ) in these compounds shows that Si–R (R = alkyl, H) bonding orbitals are the major contributors to deshielding in this series. The Si–R bonding orbitals are coupled to the empty p-orbital in i Pr 3 Si + or Mes 3 Si + , or to the orbital in R 3 Si–X. This trend also applies to surface bound R 3 Si–O X . This model also explains chemical shift trends in recently isolated t Bu 2 SiH 2 + , t BuSiH 2 + , and SiH 3 + that show more shielded 29 Si NMR signals than R 3 Si + species. There is no correlation between isotropic 29 Si NMR chemical shift and charge at silicon. 

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4. Effect of Biochar on Microbial Growth: A Metabolomics and Bacteriological Investigation in E. coli

   Rebecca A. Hill, John Hunt (April 2019, Environmental science and technology)

   ABSTRACT: Biochar has been proposed as a soil amendment in agricultural applications due to its advantageous adsorptive properties, high porosity, and low cost. These properties allow biochar to retain soil nutrients, yet the effects of biochar on bacterial growth remain poorly understood. To examine how biochar influences microbial metabolism, Escherichia coli was grown in a complex, well-defined media and treated with either biochar or activated carbon. The concentration of metabolites in the media were then quantified at several time points using NMR spectroscopy. Several metabolites were immediately adsorbed by the char, including L-asparagine, L-glutamine, and L-arginine. However, we find that biochar quantitatively adsorbs less of these metabolic precursors when compared to activated carbon. Electron microscopy reveals differences in surface morphology after cell culture, suggesting that Escherichia coli can form biofilms on the surfaces of the biochar. An examination of significant compounds in the tricarboxylic acid cycle and glycolysis reveals that treatment with biochar is less disruptive than activated carbon throughout metabolism. While both biochar and activated carbon slowed growth compared to untreated media, Escherichia coli in biochartreated media grew more efficiently, as indicated by a longer logarithmic growth phase and a higher final cell density. This work suggests that biochar can serve as a beneficial soil amendment while minimizing the impact on bacterial viability. In addition, the experiments identify a mechanism for biochar’s effectiveness in soil conditioning and reveal how biochar can alter specific bacterial metabolic pathways. 

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5. γ-Agostic interactions in ( ^Mes CCC)Fe–Mes(L) complexes

   https://doi.org/10.1039/D2CC03260K  

   Najera, Daniel C.; Peñas-Defrutos, Marconi N.; García-Melchor, Max; Fout, Alison R. (August 2022, Chemical Communications)

   Agostic interactions were observed in the bound mesityl group in a series of iron compounds bearing a bis(NHC) pincer CCC ligand. The L-type ligand on [(CCC)Fe II Mes(L)] complexes influences the strength of the agostic interaction and is manifested in the upfield shift of the 1 H NMR resonance for the mesityl methyl resonances. The nature of the interaction was further investigated by density functional theory calculations, allowing rationalization of some unexpected trends and proving to be a powerful predictive tool. 

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