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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. The curious cases of tetrahydrosalen-type ligands interacting with Ni( ii ): structures and ligand-based oxidation reactions

   https://doi.org/10.1039/d3dt02023a  

   Xu, Vivian; Pandey, Bedraj; Jayawardhena, J. P.; Krause, Jeanette A.; Guan, Hairong (August 2023, Dalton Transactions)

   This work centers around the nickel complexes derived from two tetrahydrosalen-type proligands: N , N ′-bis(2-hydroxybenzyl)- o -phenylenediamine (H 2 salophan) and N , N ′-bis(2-hydroxy-3-methylbenzyl)- o -phenylenediamine (H 2 salophan_Me). The reaction of H 2 salophan with Ni(OAc) 2 ·4H 2 O generates a dinuclear complex Ni 2 (Hsalophan) 2 (OAc) 2 or Na[Ni 2 (salophan) 2 (OAc)] when NaOH is added to assist ligand deprotonation. The reaction of H 2 salophan_Me with Ni(OAc) 2 ·4H 2 O, however, yields a mononuclear complex Ni(Hsalophan_Me) 2 . Unlike the corresponding salen-type nickel complexes, these tetrahydrosalen-type complexes are paramagentic and air sensitive (in solution). Oxidation by O 2 or peroxides results in dehydrogenation of the ligand backbone to form the salen-type complexes. 

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3. Pd‐Catalyzed Regiodivergent N ⁶ versus C ^vinyl Arylation of 8‐Vinyl Adenine Nucleosides, Sequential Diarylation, Fluorescence Properties, and Computational Evaluations**

   https://doi.org/10.1002/chem.202501477  

   Akula, Hari_K; Ghosh, Goutam; Greer, Alexander; Pradhan, Padmanava; Lakshman, Mahesh_K (July 2025, Chemistry – A European Journal)

   Abstract Palladium‐catalyzed aryl amination and Heck arylation reactions are complementary transformations, generally requiring a suitable catalyst combination and a base. With substrates containing both an amino group and a vinyl moiety, control of C─N versus C─C reactivity can lead to regiodivergent functionalizations. With this focus, reactions of silyl‐protected 8‐vinyl 2'‐deoxyadenosine and adenosine with aryl bromides and iodides have been studied. Pd(OAc)₂, Pd₂(dba)₃, and preformed dichloro[1,1′‐bis(di‐t‐butylphosphino)ferrocene]palladium (II) (Pd‐118) were evaluated as metal sources. Ligands tested were Xantphos, DPEphos, BIPHEP, and DPPF, with Cs₂CO₃and K₃PO₄as bases. In toluene as solvent, the Pd(OAc)₂/Xantphos/Cs₂CO₃combination was uniquely capable of predominantN⁶arylation. Aryl bromides and iodides gave comparable product yields. Replacement of Cs₂CO₃with K₃PO₄redirected arylation from the nitrogen atom to the vinyl carbon atom, and all other catalyst, ligand, and base combinations gave C^vinylarylation as well. Simply switching from Pd(OAc)₂to Pd₂(dba)₃resulted in loss of theN⁶‐selectivity and C^vinylarylation was favored. Based upon these results, using two structurally similar catalytic systems sequential C^vinylandN⁶arylations of the nucleosides were accomplished. Some of the products were converted to other novel nucleoside analogues. Because some compounds were fluorescent, their photophysical properties were assessed experimentally and computationally. 

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4. Purinyl N -directed aroylation of 6-arylpurine ribo- and 2′-deoxyribonucleosides, and mechanistic insights

   https://doi.org/10.1039/D4OB00689E  

   Lakshman, Mahesh K; Malinchak, Casina T; Shank, Nathaniel; Neary, Michelle C; Stahl, Lothar (August 2024, Organic & Biomolecular Chemistry)

   The purinyl nitrogen atom is an effective metalation director, which in the presence of Pd(OAc)₂,t-BuOOH, and aryl aldehydes, leads to acylation of the aryl ring at the C6 position of the purine. 

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5. Reaction Mechanism Underlying Pd(II)-Catalyzed Oxidative Coupling of Ethylene and Benzene to Form Styrene: Identification of a Cyclic Mono-Pd ^II Bis-Cu ^II Complex as the Active Catalyst

   https://doi.org/10.1021/acs.organomet.2c00183  

   Musgrave, Charles B.; Bennett, Marc T.; Ellena, Jeffrey F.; Dickie, Diane A.; Gunnoe, T. Brent; Goddard, William A. (July 2022, Organometallics)

   A recent advance in the synthesis of alkenylated arenes was the demonstration that the Pd(OAc)2 catalyst precursor gives >95% selectivity toward styrene from ethylene and benzene under optimized conditions using excess Cu(II) carboxylate as the in situ oxidant [ Organometallics 2019, 38(19), 3532−3541]. To understand the mechanism underlying this catalysis, we applied density functional theory (DFT) calculations in combination with experimental studies. From DFT calculations, we determined the lowest-energy multimetallic Pd and Pd–Cu mixed metal species as possible catalyst precursors. From the various structures, we determined the cyclic heterotrinuclear complex PdCu2(μ-OAc)6 to be the global minimum in Gibbs free energy under conditions of excess Cu(II). For cyclic PdCu2(μ-OAc)6 and the parent [Pd(μ-OAc)2]3, we evaluated the barriers for benzene C–H activation through concerted metalation deprotonation (CMD). The PdCu2(μ-OAc)6 cyclic trimer leads to a CMD barrier of 33.5 kcal/mol, while the [Pd(μ-OAc)2]3 species leads to a larger CMD barrier at >35 kcal/mol. This decrease in the CMD barrier arises from the insertion of Cu(II) into the trimetallic species. Because cyclic PdCu2(μ-OAc)6 is likely the predominant species under experimental conditions (the Cu to Pd ratio is 480:1 at the start of catalysis) with a predicted CMD barrier within the range of the experimentally determined activation barrier, we propose that cyclic PdCu2(μ-OAc)6 is the Pd species responsible for catalysis and report a full reaction mechanism based on DFT calculations. For catalytic conversion of benzene and ethylene to styrene at 120 °C using Pd(OAc)2 as the catalyst precursor and Cu(OPiv)2 (OPiv = pivalate) as the oxidant, an induction period of ∼1 h was observed, followed by catalysis with a turnover frequency of ∼2.3 × 10–3 s–1. In situ1H NMR spectroscopy experiments indicate that during the induction period, Pd(OAc)2 is likely converted to cyclic PdCu2(η2-C2H4)3(μ-OPiv)6, which is consistent with the calculations and consistent with the proposal that the active catalyst is the ethylene-coordinated heterotrinuclear complex cyclic PdCu2(η2-C2H4)3(μ-OPiv)6. 

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