Versatile bonding and coordination modes of ditriazolylidene ligands in rhodium( iii ) and iridium( iii ) complexes

Metalation of novel ditriazolium salts containing a trimethylene (–CH2CH2CH2–) or dimethylether linker (–CH2OCH2–) was probed with different rhodium(III) and iridium(III) precursors. When using [MCp*Cl2]2, a transmetalation protocol via a triazolylidene silver intermediate was effective, while base-assisted metalation with MCl3via sequential deprotonation of the triazolium salt with KOtBu and addition of the metal precursor afforded homoleptic complexes. The N-substituent on the triazole heterocycle directed the metalation process and led to Ctrz,Ctrz,CPh-tridentate chelating ditriazolylidene complexes for N-phenyl substituents. With ethyl substituents, only Ctrz,Ctrz-bidentate complexes were formed, while metalation with mesityl substituents was unsuccessful, presumably due to steric constraints. Through modification of the reaction conditions for the metalation step, an intermediate species was isolated that contains a Ctrz,CPh-bidentate chelate en route to the formation of the tridentate ligand system. Accordingly, Cphenyl–H bond activation occurs prior to formation of the second metal–triazolylidene bond. Stability studies with a Ctrz,Ctrz,CPh-tridentate chelating ditriazolylidene iridium complex towards DCl showed deuterium incorporation at both N-phenyl groups and indicate that Cphenyl–H bond activation is reversible while the Ctrz–Ir bond is robust. The flexible linker between the two triazolylidene donor sites provides access to both facial and meridional coordination modes

Substantial improvement of pyridine-carbene iridium water oxidation catalysts by a simple methyl-to-octyl substitution

The substitution of a methyl to an octyl group in the ancillary triazolylidene ligand—an apparently simple variation—induces a more than 10-fold increase of activity of the corresponding iridium complex in water oxidation catalysis when using cerium(IV) as sacrificial oxidant. Detailed NMR studies suggest that various different molecular species form, all bearing the intact triazolylidene ligand. The octyl substituent is essential for inducing the association of the iridium species, thus generating extraordinarily active multimetallic catalytic sites. Their accessibility and steady-state concentration is critically dependent on the type of sacrificial oxidant and specifically on the cerium ammonium nitrate versus catayst ratio

Enhanced product selectivity promoted by remote metal coordination in acceptor-free alcohol dehydrogenation catalysis

A bimetallic [Ir3+]2 complex was synthesized based on a bridging 1,2,3-triazole ligand that coordinates to one Cp*Ir unit as N,N-bidentate chelate, and to the other as a C,C-bidentate ligand. When compared to monometallic homologues, the bimetallic complex shows greatly enhanced product selectivity for the acceptorless dehydrogenation of alcohols; spectroscopic and electrochemical analysis suggest significant alteration of the metal properties in the bimetallic system compared to the monometallic species, which offers a rationale for the observed high selectivity

Synthesis of polymeric bismuth chlorido hydroxamato complexes; X-ray crystal structure and antibacterial activity of a novel Bi(lll) salicylhydroxamato complex

Reaction of salicylhydroxamic acid (Sha) and 2-aminophenyl hydroxamic acid (2-NH2-pha) with BiCl3 affords the corresponding novel polymeric bismuth chlorido hydroxamato complexes; [BiCl2(-Sha-1H)]∞ and [BiCl3(--Pha-1H)]∞ respectively. The X-ray crystal structure of the THF-solvated polymeric bismuth chlorido salicylhydroxamato complex, [BiCl2(-Sha-1H)(THF)]∞ was solved, confirming the polymeric structure of this class of compounds and the (O,μ-O’)-bidentate bridging coordination mode of the hydroxamato ligand. The antibacterial activity of the THF-free polymeric bismuth chlorido salicylhydroxamato complex, [BiCl2(-Sha-1H)]∞, was investigated against a broad panel of bacteria, further highlighting the antibacterial properties of Bi-based compounds against Gram-positive and Gram-negative pathogenic and environmental strains of bacteria

fac-Tris(4-amino­benzohydroxamato)iron(III) ethanol solvate

In the structure of the title compound, [Fe(C7H7N2O2)3]·CH3CH2OH, the FeIII atom is in a distorted octa­hedral O6 environment with the three hydroxamate O atoms (and the three carbonyl O atoms) arranged in a fac configuration and one of the hydroxamate ligands being puckered. The methyl C atom of the ethanol solvent mol­ecule is disordered over two positions with occupancies of 0.626 (13) and 0.374 (13), respectively. The cocrystallized ethanol mol­ecule is hydrogen bonded to one of the hydroxamate O atoms. O—H⋯O and N—H⋯O inter­actions generate infinite three-dimensional networks along [100], [010] and [001]

5′,6-Dichloro-1′,3′,3′-trimethyl­spiro­[2H-1-benzopyran-2,2′-indoline]

In the crystal structure of the title compound, C19H17Cl2NO, the indoline and benzopyran ring systems are approximately perpendicular to each other. The indoline ring is in an envelope conformation with the spiro C atom as the flap. The N atom of the indoline ring forms a pyramidal environment, the sum of the angles at this atom being 352.46°

Continuous flow synthesis and antimicrobial evaluation of NHC* silver carboxylate derivatives of SBC3 in vitro and in vivo

N-heterocyclic silver carbene compounds have been extensively studied and shown to be active agents against a host of pathogenic bacteria and fungi. By incorporating hypothesized virulence targeting substituents into NHC–silver systems via salt metathesis, an atom-efficient complexation process can be used to develop new complexes to target the passive and active systems of a microbial cell. The incorporation of fatty acids and an FtsZ inhibitor have been achieved, and creation of both the intermediate salt and subsequent silver complex has been streamlined into a continuous flow process. Biological evaluation was conducted with in vitro toxicology assays showing these novel complexes had excellent inhibition against Gram-negative strains E. coli, P. aeruginosa, and K. pneumoniae; further studies also confirmed the ability to inhibit biofilm formation in methicillin-resistant Staphylococcus aureus (MRSA) and C. Parapsilosis. In vivo testing using a murine thigh infection model showed promising inhibition of MRSA for the lead compound SBC3, which is derived from 1,3-dibenzyl-4,5-diphenylimidazol-2-ylidene (NHC*).European Commission - European Regional Development FundScience Foundation IrelandSchool of Chemistry & the College of Science of University College Dubli

Synthesis, structures and antimicrobial activity of novel NHC∗- and Ph3P-Ag(I)-Benzoate derivatives

The rising threat of Antimicrobial Resistance (AMR) requires a novel approach to the treatment of infectious diseases. Covalently bonded silver, which has known antibacterial and antifungal properties and multiple mechanisms of action, may provide a treatment strategy when used alone or in combination with already known antimicrobial compounds. Here we describe the synthesis of eight novel silver(I) complexes, which were screened for in vitro activity against two pathogenic bacterial strains, Methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli (E. coli), and against two pathogenic fungal strains, Candida albicans and Candida parapsilosis. Complexes 5–8 were synthesized by reacting triphenylphosphine in relative equivalents with the relevant silver benzoates (1, 2 & 4), whilst complexes 9–12 were synthesized by generation of a free carbene NHC∗ (1,3-dibenzyl-4,5-diphenyl-imidazol-2-ylidene) and reacting this with the silver benzoates 1–4, under Schlenk conditions. Complexes 9–12 showed the strongest antimicrobial activity, resulting in 50% inhibition of growth against MRSA and C. parapsilosis at concentrations of 12.5 and 3.25 µg/mL, respectively

Atypical McMurry Cross-Coupling Reactions Leading to a New Series of Potent Antiproliferative Compounds Bearing the Key [Ferrocenyl-Ene-Phenol] Motif

In the course of the preparation of a series of ferrocenyl derivatives of diethylstilbestrol (DES), in which one of the 4-hydroxyphenyl moieties was replaced by a ferrocenyl group, the McMurry reaction of chloropropionylferrocene with a number of mono-aryl ketones unexpectedly yielded the hydroxylated ferrocenyl DES derivatives, 5a–c, in poor yields (10%–16%). These compounds showed high activity on the hormone-independent breast cancer cell line MDA-MB-231 with IC50 values ranging from 0.14 to 0.36 µM. Surprisingly, non-hydroxylated ferrocenyl DES, 4, showed only an IC50 value of 1.14 µM, illustrating the importance of the hydroxyethyl function in this promising new series. For comparison, McMurry reactions of the shorter chain analogue chloroacetylferrocene were carried out to see the difference in behaviour with mono-aryl ketones versus a diaryl ketone. The effect of changing the length of the alkyl chain adjacent to the phenolic substituent of the hydroxylated ferrocenyl DES was studied, a mechanistic rationale to account for the unexpected products is proposed, and the antiproliferative activities of all of these compounds on MDA-MB-231 cells lines were measured and compared. X-ray crystal structures of cross-coupled products and of pinacol-pinacolone rearrangements are reported.The authors wish to thank P. Herson and J. Vaissermann for three crystal structure determinations and T. Cresteil for IC50 determinations. We thank Anh N’Guyen for full discussions. K.K.’s stay in Paris was supported through an European Community Marie Curie Fellowship (HMPT-CT-2000- 00186). We thank the Agence Nationale de la Recherche for financial support (ANR 2010 BLAN 7061 blanc “Mecaferrol”) and the Ministère des Affaires Etrangères for a doctoral fellowship (M.G.)

Stress‐induced Domain Wall Motion in a Ferroelastic Mn3+ Spin Crossover Complex

Domain wall motion is detected for the first time during the transition to a ferroelastic and spin‐state ordered phase of a spin crossover complex. Single crystal X‐ray diffraction and resonant ultrasonic spectroscopy (RUS) revealed two distinct symmetry‐breaking phase transitions in the mononuclear Mn 3+ compound [Mn(3,5‐diBr‐sal 2 (323))]BPh 4 , 1. The first at 250 K, involves the space group change Cc → Pc and is thermodynamically continuous, while the second, Pc → P1 at 85 K, is discontinuous and related to spin crossover and spin‐state ordering. Stress‐induced domain wall mobility was detected as softening of the phonon modes at the Pc → P1 transition