Xantphos-Capped Pd(II) and Pt(II) Macrocycles of Aryldithiolates: Structural Variation and Catalysis in C-C Coupling Reaction

Linkage Isomers of Triangular Pd Metallacycles and Catalysis in Aqueous Suzuki Coupling Reaction

The water-soluble trinuclear Pd metallacycles [Pd(tmeda)(4-Spy)]3(X)3 (tmeda = tetramethylethylenediamine, X = OTf, 2; NO3, 3) were synthesized from the ambidentate ligand 4-pyridylthiolate (Spy-) and [Pd(tmeda)X2] in 80 and 70% yield, respectively. Two possible linkage isomers are found in solution (slow interconversion found in the NMR) and in the solid state. Density functional calculations showed that the energy of the isomer with a D3-symmetric arrangement of the SPy ligand and all Pd atoms having N∧NPdSN coordination is only 7 kcal/mol lower. When reacting [Pd(tmeda)(NO3)2] with 4,4'-biphenyldithiolate (S2bph2-), the tetranuclear [{Pd(tmeda)}4(μ-S2bph)2](NO3)4 (1) was formed. A new type of undecanuclear Pd cluster was separated as a minor product from an acetone solution of 2 in air. The new complexes represent the first examples of water-soluble Pd metallacycles constructed from a pyridine-thiolate ligand. They show catalytic activity with turnover numbers ranging from 9 to 420 in aqueous Suzuki cross-coupling reactions using phenyl boronic acid and a number of aryl halides. An optimized system gave a TON of 6,900,000 and a TOF of 492,857 h-1. The catalyst could be reused eight times, and the activity has been attributed to the formation of PdNPs.

Crystal structure of a dicationic PdII dimer containing a 2-[(diisopropylphosphanyl)methyl]quinoline-8-thiolate pincer ligand

A dicationic PdII dimer, bis{2-[(diisopropylphosphanyl)methyl]quinoline-8-thiolato}palladium(II) bis(hexafluoridoantimonate) dichloromethane monosolvate, [Pd2(C32H42N2P2S2)](SbF6)2·CH2Cl2, containing a 2-[(diisopropylphos-phanyl)methyl]quinoline-8-thiolate pincer ligand, was isolated and its crystal structure determined. The title compound crystallizes in the ortho-rhom-bic space group Pbca. A dimeric structure is formed by bridging coordination of the S atoms. The geometry of the butterfly-shaped Pd2S2 core is bent, with a hinge angle of 108.0 (1)° and a short Pd⋯Pd distance of 2.8425 (7) Å. These values are the lowest measured compared to ten dicationic dimers with a Pd2S2 core featuring sulfur atoms embedded in a chelating ligand. One of the two hexa-fluorido-anti-monate anions is disordered over two sets of positions with site-occupancy factors of 0.711 (5) and 0.289 (5). The crystal structure is stabilized by many C-H⋯F and C-H⋯π inter-actions, forming a supra-molecular network.

Application of 4-pyridylselenolate palladium macrocycles in Suzuki couplings

Pd macrocycles of diphosphine were constructed employing 4-pyridylselenolate. They act as excellent catalysts in the Suzuki coupling reaction.

Synthesis and anti-proliferative activities of amine capped Pd and Pt macrocycles of 4,4′-dipyridylselenides

Symmetric macrocyclic complexes characterized as dimeric and their oligomeric form in water and the solid state exhibit high in vitro anticancer activities.

Conformational Effects of [Ni2 (μ-ArS)2 ] Cores on Their Electrocatalytic Activity

Two nickel complexes supported by tridentate NS₂ ligands, [Ni₂ (κ-N,S,S,S'-N^Ph {CH₂ (MeC₆ H₂ R')S}₂ )₂ ] (1; R'=3,5-(CF₃ )₂ C₆ H₃ ) and [Ni₂ (κ-N,S,S,S'-N^iBu {CH₂ C₆ H₄ S}₂ )₂ ] (2), were prepared as bioinspired models of the active site of [NiFe] hydrogenases. The solid-state structure of 1 reveals that the [Ni₂ (μ-ArS)₂ ] core is bent, with the planes of the nickel centers at a hinge angle of 81.3(5)°, whereas 2 shows a coplanar arrangement between both nickel(II) ions in the dimeric structure. Complex 1 electrocatalyzes proton reduction from CF₃ COOH at -1.93 (overpotential of 1.04 V, with i_cat /i_p ≈21.8) and -1.47 V (overpotential of 580 mV, with i_cat /i_p ≈5.9) versus the ferrocene/ferrocenium redox couple. The electrochemical behavior of 1 relative to that of 2 may be related to the bent [Ni₂ (μ-ArS)₂ ] core, which allows proximity of the two Ni⋅⋅⋅Ni centers at 2.730(8) Å; thus possibly favoring H⁺ reduction. In contrast, the planar [Ni₂ (μ-ArS)₂ ] core of 2 results in a Ni⋅⋅⋅Ni distance of 3.364(4) Å and is unstable in the presence of acid.