A New Class of Remote N‐Heterocyclic Carbenes with Exceptionally Strong σ‐Donor Properties: Introducing Benzo[c]quinolin‐6‐ylidene

We make the case for benzo[c]quinolin‐6‐ylidene ( 1 ) as a strongly electron‐donating carbene ligand. The facile synthesis of 6‐trifluoromethanesulfonylbenzo[c]quinolizinium trifluoromethanesulfonate ( 2 ) gives straightforward access to a useful precursor for oxidative addition to low‐valent metals, to yield the desired carbene complexes. This concept has been achieved in the case of [Mn(benzo[c]quinolin‐6‐ylidene)(CO)₅]⁺ ( 15 ) and [Pd(benzo[c]quinolin‐6‐ylidene)(PPh₃)₂(L)]²⁺ L=THF ( 21 ), OTf ( 22 ) or pyridine ( 23 ). Attempts to coordinate to nickel result in coupling products from two carbene precursor fragments. The CO IR‐stretching‐frequency data for the manganese compound suggests benzo[c]quinolin‐6‐ylidene is at least as strong a donor as any heteroatom‐stabilised carbene ligand reported.     

Acetals: a new organocatalysis chemotype for one-pot enantioselective α-amination

Conditions are described for one-pot Brønsted acid and organocatalysed enantioselective α-amination of acetals and associated functionalities. Of the organocatalysts screened, proline tetrazole gave the highest ee, while aqueous monochloroacetic acid proved to be the best Brønsted acid activator regarding minimizing racemization and maximizing product yield. The reaction opens up the way for using masked carbonyl functionalities in organocatalysis.     

Naphthalene Exchange in [Re(η6-napht)2]+ with Pharmaceuticals Leads to Highly Functionalized Sandwich Complexes [M(η6-pharm)2]+ (M=Re/99mTc)

Bis-arene sandwich complexes are generally prepared by the Fischer-Hafner reaction, which conditions are incompatible with most O- and N- functional groups. We report a new way for the synthesis of sandwich type complexes [Re(η⁶-arene)₂]⁺ and [Re(η⁶-arene)(η⁶-benzene)]⁺ from [Re(η⁶-napht)₂]⁺ and [Re(η⁶-napht)(η⁶-benzene)]⁺, with functionalized arenes and pharmaceuticals. N-methylpyrrolidine (NMP) facilitates the substitution of naphthalene with the incoming arene. A series of fully characterized rhenium sandwich complexes with simple arenes, such as aniline, as well as with active compounds like lidocaine and melatonin are presented. With these rhenium compounds in hand, the radioactive sandwich complexes [^99mTc(η⁶-pharm)₂]⁺ (pharm=pharmaceutical) can be unambiguously confirmed. The direct labelling of pharmaceuticals with ^99mTc through η⁶-coordination to phenyl rings and the confirmation of the structures with the rhenium homologues opens a path into molecular theranostics.     

Tuning Deazaflavins Towards Highly Potent Reducing Photocatalysts Guided by Mechanistic Understanding – Enhancement of the Key Step by the Internal Heavy Atom Effect

Deazaflavins are well suited for reductive chemistry acting via a consecutive photo-induced electron transfer, in which their triplet state and semiquinone – the latter is formed from the former after electron transfer from a sacrificial electron donor – are key intermediates. Guided by mechanistic investigations aiming to increase intersystem crossing by the internal heavy atom effect and optimising the concentration conditions to avoid unproductive excited singlet reactions, we synthesised 5-aryldeazaflavins with Br or Cl substituents on different structural positions via a three-component reaction. Bromination of the deazaisoalloxazine core leads to almost 100 % triplet yield but causes photo-instability and enhances unproductive side reactions. Bromine on the 5-phenyl group in ortho position does not affect the photostability, increases the triplet yield, and allows its efficient usage in the photocatalytic dehalogenation of bromo- and chloroarenes with electron-donating methoxy and alkyl groups even under aerobic conditions. Reductive powers comparable to lithium are achieved.     

A rapid heating and high magnetic field thermal analysis technique

Journal of Thermal Analysis and Calorimetry - A new thermal analysis technique is described that allows measurements to be performed on bulk samples at extreme heating and cooling rates and in high...     

Isoflavonoid-Antibiotic Thin Films Fabricated by MAPLE with Improved Resistance to Microbial Colonization

Staphylococcus aureus (Gram-positive) and Pseudomonas aeruginosa (Gram-negative) bacteria represent major infectious threats in the hospital environment due to their wide distribution, opportunistic behavior, and increasing antibiotic resistance. This study reports on the deposition of polyvinylpyrrolidone/antibiotic/isoflavonoid thin films by the matrix-assisted pulsed laser evaporation (MAPLE) method as anti-adhesion barrier coatings, on biomedical surfaces for improved resistance to microbial colonization. The thin films were characterized by Fourier transform infrared spectroscopy, infrared microscopy, and scanning electron microscopy. In vitro biological assay tests were performed to evaluate the influence of the thin films on the development of biofilms formed by Gram-positive and Gram-negative bacterial strains. In vitro biocompatibility tests were assessed on human endothelial cells examined for up to five days of incubation, via qualitative and quantitative methods. The results of this study revealed that the laser-fabricated coatings are biocompatible and resistant to microbial colonization and biofilm formation, making them successful candidates for biomedical devices and contact surfaces that would otherwise be amenable to contact transmission.     

Conceptual modelling and the project process in real simulation projects: a survey of simulation modellers

A survey was used to obtain information on the processes and methods used by simulation experts in real projects. The 102 survey respondents answered questions about their most recent simulation project. This paper presents some of the survey results, focussing mainly on conceptual modelling and the pattern of time allocation to different topics. There are a wide range of findings that include the modellers making changes to the initial conceptual model during subsequent tasks in most of the projects usually by adding complexity, model coding taking on average about twice the time of other topics, and the topics generally occurring in single blocks of time (at the resolution of the survey data collection) but with considerable overlaps. The results give an insight into the way experts approach simulation projects and their problem solving strategies. A potential application is in training novice modellers, particularly in developing ‘craft skills’. The results also provide an empirical basis for further research, especially in conceptual modelling.     

CO2 to CO: Photo- and Electrocatalytic Conversion Based on Re(I) Bis-Arene Frameworks: Synergisms Between Catalytic Subunits

Reduction of CO₂ to CO and H₂O is a two electron/two proton process. For this process, multinuclear complexes offer advantages by concentrating reduction equivalents more efficiently than mononuclear systems. We present novel complexes with [Re(η⁶-C₆H₆)₂]⁺ as scaffold conjugated to one or two catalytically active [Ru(dmbpy)(CO)₂Cl₂] subunits (dmbpy=5,5′-dimethyl-2,2′-bipyridine). The [Re(η⁶-C₆H₆)₂]⁺ scaffold was chosen due to its very high photo- and chemical stability, as well as the multiple degrees of freedom it offers for any conjugated functionalities. High efficiency and selectivity for the reduction of CO₂ to CO (over H₂ or HCOOH) is reported. TONs and TOFs were found to be comparable or higher than for the catalyst subunit without the rhenium framework. Cooperativity in photo- and electrocatalysis is observed for the complex comprising two catalytic subunits. The synergistic communication between the two catalytic subunits is responsible for the observed enhancement in both photo- and electrocatalytic performance. Confirmation of electronic communication between the two [Ru(dmbpy)(CO)₂Cl₂] subunits as well as the elucidation of a possible mechanism was supported by electrochemistry, IR-spectroelectrochemistry and DFT studies.