Iron Complexes of a Proton-Responsive SCS Pincer Ligand with Sensitive Electronic Structure

SCS pincer ligands have an interesting combination of strong-field and weak-field donors that is also present in the nitrogenase active site. Here, we explore the electronic structures of iron(II) and iron(III) complexes with such a pincer ligand, bearing a monodentate phosphine, thiolate S donor, amide N donor, ammonia, or CO. The ligand scaffold features a protonresponsive thioamide site, and the protonation state of the ligand greatly influences the reduction potential of iron in the phosphine complex. The N–H bond dissociation free energy can be quantitated as 56 ± 2 kcal/mol. EPR spectroscopy and SQUID magnetometry measurements show that the iron(III) complexes with S and N as the fourth donors have an intermediate spin (S = 3/2) ground state with large zero field splitting, and X-ray absorption spectra show high Fe–S covalency. The Mössbauer spectrum changes drastically with the position of a nearby alkali metal cation in the iron(III) amido complex, and DFT calculations explain this phenomenon through a change between having the doubly-occupied orbital as dz2 or dyz, as the former is more influenced by the nearby positive charge.

On the Amine-Catalyzed Suzuki-Miyaura Coupling Using a Catalysis-Based Fluorometric Method

<p>The Suzuki-Miyaura coupling is one of the most frequently used reactions in organic synthesis. Recent work by others suggested that an arylamine, prepared by palladium catalysis and tricyclohexylphosphine, could catalyze Suzuki-Miyaura coupling reactions without transition metals. Herein, we used a fluorometric quantification method for palladium previously developed in our laboratory to unambiguously conclude that there is a correlation between the palladium content in the arylamine and the rate of a Suzuki-Miyaura coupling. Also, our mass spectroscopic analysis of the arylamine revealed the presence of a palladium-phosphine complex. When Pd(OAc)₂ was used as a catalyst for the same Suzuki-Miyaura coupling, tricyclohexylphosphine was detrimental to the coupling and that the arylamine played negligible role. This study demonstrates the utility of the fluorometric technology for catalysis research.<br></p>

On the Amine-Catalyzed Suzuki-Miyaura Coupling Using a Catalysis-Based Fluorometric Method

<p>The Suzuki-Miyaura coupling is one of the most frequently used reactions in organic synthesis. Recent work by others suggested that an arylamine, prepared by palladium catalysis, could catalyze Suzuki-Miyaura coupling reactions without transition metals. Herein, we used a fluorometric quantification method for palladium previously developed in our laboratory to unambiguously conclude that there is a correlation between the palladium content in the arylamine and the rate of a Suzuki-Miyaura coupling. Also, our mass spectroscopic analysis of the arylamine revealed the presence of a palladium-phosphine complex. We discovered that the phosphine was detrimental to the palladium catalysis and that the arylamine played negligible role. This study demonstrates the utility of the fluorometric technology for catalysis research.</p>

On the Amine-Catalyzed Suzuki-Miyaura Coupling Using a Catalysis-Based Fluorometric Method

<p>The Suzuki-Miyaura coupling is one of the most frequently used reactions in organic synthesis. Recent work by others suggested that an arylamine, prepared by palladium catalysis, could catalyze Suzuki-Miyaura coupling reactions without transition metals. Herein, we used a fluorometric quantification method for palladium previously developed in our laboratory to unambiguously conclude that there is a correlation between the palladium content in the arylamine and the rate of a Suzuki-Miyaura coupling. Also, our mass spectroscopic analysis of the arylamine revealed the presence of a palladium-phosphine complex. We discovered that the phosphine was detrimental to the palladium catalysis and that the arylamine played negligible role. This study demonstrates the utility of the fluorometric technology for catalysis research.</p>

In vitro evaluation of antileishmanial activity of copper (I) complexes

In the research for the development of new drugs for the therapy of American tegumentary leishmaniasis, copper has been studied for its antileishmania activity. This study aims to report the activity of three copper(I) complexes on parasites of the species L. amazonensis and L. guyanensis. The metal complexes were tested according to in vitro antileishmanial assays, against promastigote and amastigote forms of the most prevalent species in the state of Amazonas, Brazil. Cytotoxicity of the complexes was evaluated in murine macrophage-like cell line (MJ774). The results of the in vitro assays indicated that, among the copper complexes tested, the homoleptic phosphine complex [Cu(thp)4][PF6](thp=tris-hydroxymethylphosphine) presented promising activity against the evolutionary forms of L. amazonensis, and obtained a IC50 of 26.45 and 24.61 µM in a period of 48 and 72 h, respectively. The results for copper complex at concentration 160 µM in amastigote forms showed a decrease in the infection index (32% of infected cells) and, in the cytotoxicity assay with MJ774, 52.43% of cell viability was observed. The results showed that the complex [Cu(thp)4][PF6] presented significant biological activity, indicating a need for future in vivo studies.

A five-coordinate cobalt bis(dithiolene)–phosphine complex [Co(pdt)2(PTA)] (pdt = phenyldithiolene; PTA = 1,3,5-triaza-7-phosphaadamantane)

The title compound, bis(1,2-diphenyl-2-sulfanylideneethanethiolato-κ2 S,S′)(1,3,5-triaza-7-phosphaadamantane-κP)cobalt(II) dichloromethane hemisolvate, [Co(pdt)2(PTA)]·0.5C2H4Cl2 or [Co(C14H10S2)2(C6H12N3P)]·0.5C2H4Cl2, contains two phenyldithiolene (pdt) ligands and a 1,3,5-triaza-7-phosphaadamantane (PTA) ligand bound to cobalt with the solvent 1,2-dichloroethane molecule located on an inversion center. The cobalt core exhibits an approximately square-pyramidal geometry with partially reduced thienyl radical monoanionic ligands. The supramolecular network is consolidated by hydrogen-bonding interactions primarily with nitrogen, sulfur and chlorine atoms, as well as parallel displaced π-stacking of the aryl rings. The UV–vis, IR, and CV data are also consistent with monoanionic dithiolene ligands and an overall CoII oxidation state.

Facile synthesis of a nickel(0) phosphine complex at ambient temperature

The reaction of the bis(methoxy)-2-pyridyl-phosphine (MeO)2P(2-py) with [Ni(MeCN)6](BF4)2 leads to the unexpected, single-step reduction of NiII and the formation of a tetrahedral nickel(0) complex.