Two Synthetic Tools to Deepen the Understanding of the Influence of Stereochemistry on the Properties of Iridium(III) Heteroleptic Emitters.

Two complementary procedures are presented to prepare cis-pyridyl-iridium(III) emitters of the class [3b+3b+3b'] with two orthometalated ligands of the 2-phenylpyridine type (3b) and a third ligand (3b'). They allowed to obtain four emitters of this class and to compare their properties with those of the trans-pyridyl isomers. The finding starts from IrH5(PiPr3)2, which reacts with 2-(p-tolyl)pyridine to give fac-[Ir{κ2-C,N-[C6MeH3-py]}3] with an almost quantitative yield. Stirring the latter in the appropriate amount of a saturated solution of HCl in toluene results in the cis-pyridyl adduct IrCl{κ2-C,N-[C6MeH3-py]}2{κ1-Cl-[Cl-H-py-C6MeH4]} stabilized with p-tolylpyridinium chloride, which can also be transformed into dimer cis-[Ir(µ-OH){κ2-C,N-[C6MeH3-py]}2]2. Adduct IrCl{κ2-C,N-[C6MeH3-py]}2{κ1-Cl-[Cl-H-py-C6MeH4]} directly generates cis-[Ir{κ2-C,N-[C6MeH3-py]}2{κ2-C,N-[C6H4-Isoqui]}] and cis-[Ir{κ2-C,N-[C6MeH3-py]}2{κ2-C,N-[C6H4-py]}] by transmetalation from Li[2-(isoquinolin-1-yl)-C6H4] and Li[py-2-C6H4]. Dimer cis-[Ir(µ-OH){κ2-C,N-[C6MeH3-py]}2]2 is also a useful starting complex when the precursor molecule of 3b' has a fairly acidic hydrogen atom, suitable for removal by hydroxide groups. Thus, its reactions with 2-picolinic acid and acetylacetone (Hacac) lead to cis-Ir{κ2-C,N-[C6MeH3-py]}2{κ2-O,N-[OC(O)-py]} and cis-Ir{κ2-C,N-[C6MeH3-py]}2{κ2-O,O-[acac]}. The stereochemistry of the emitter does not significantly influence the emission wavelengths. On the contrary, its efficiency is highly dependent on and associated with the stability of the isomer. The more stable isomer shows a higher quantum yield and color purity.

Diseño y validación de 2 instrumentos para analizar y evaluar la calidad formal en el proceso de consentimiento informado de ensayos clínicos con medicamentos / Design and validation of 2 instruments to analyze and evaluate the formal quality in the informed consent process of clinical trials with medicinal products

Objetivo: la actividad de los promotores y Comités de Ética de la Investigación con medicamentos ha aumentado en los últimos años. El objetivo fue diseñar y validar 2 instrumentos para analizar y evaluar la calidad formal de la hoja de información al participante y el formulario de consentimiento informado de ensayos clínicos con medicamentos, acorde con la legislación.Métododiseño (Buenas Prácticas Clínicas y normativas europea y española); validación (método Delphi y consenso de expertos: concordancia ≥ 80%); fiabilidad (método inter-observadores, índice Kappa). 40 hojas de información al participante/consentimientos informados evaluados.Resultadosse obtuvo muy buena concordancia en ambos instrumentos (k ≥ 0,81, p < 0,001). Las versiones definitivas estaban formadas por: checklist-hoja de información al participante: 5 secciones, 16 ítems y 46 sub-ítems; checklist-consentimiento informado: 11 ítems.Conclusioneslos instrumentos desarrollados son válidos, fiables y facilitan el análisis, la evaluación y la toma de decisión sobre las hojas de información al participante/consentimientos informados de ensayos clínicos con medicamentos. (AU)

Objective: The activity of sponsors and Ethics Committees for Research with medicines has increased in recent years. The objective was to design and validate 2 instruments to analyze and evaluate the formal quality of the patient information sheet and the informed consent form of clinical trials with drugs, in accordance with the legislation.MethodDesign (Guideline for good clinical practice and European and Spanish regulations); validation (Delphi method and expert consensus: concordance ≥ 80%); reliability (inter-observer method, Kappa index). 40 patient information sheets/informed consent forms were evaluated.ResultsVery good concordance was obtained in both checklists (k ≥ 0.81, p < 0.001). The final versions consisted of checklist-patient information sheet: 5 sections, 16 items and 46 sub-items; and checklist-informed consent form: 11 items.ConclusionThe instruments developed are valid, reliable and facilitate the analysis, evaluation, and decision-making on the patient information sheets/informed consent forms of clinical trials with drugs. (AU)

[Translated article] Design and validation of two instruments to analyze and evaluate the formal quality in the informed consent process of clinical trials with medicinal products.

OBJECTIVE: The activity of sponsors and Ethics Committees for Research with medicines has increased in recent years. The objective was to design and validate 2 instruments to analyze and evaluate the formal quality of the patient information sheet and the informed consent form of clinical trials with drugs, in accordance with the legislation. METHODS: Design (Guideline for good clinical practice and European and Spanish regulations); validation (Delphi method and expert consensus: concordance ≥ 80%); reliability (inter-observer method, Kappa index). 40 patient information sheets/informed consent forms were evaluated. RESULTS: Very good concordance was obtained in both checklists (k ≥ 0.81, p b 0.001). The final versions consisted of checklist-patient information sheet: 5 sections, 16 items and 46 sub-items; and checklist-informed consent form: 11 items. CONCLUSION: The instruments developed are valid, reliable and facilitate the analysis, evaluation, and decision-making on the patient information sheets/informed consent forms of clinical trials with drugs.

Design and validation of 2 instruments to analyze and evaluate the formal quality in the informed consent process of clinical trials with medicinal products. / Diseño y validación de 2 instrumentos para analizar y evaluar la calidad formal en el proceso de consentimiento informado de ensayos clínicos con medicamentos.

OBJECTIVE: The activity of sponsors and Ethics Committees for Research with medicines has increased in recent years. The objective was to design and validate 2 instruments to analyze and evaluate the formal quality of the patient information sheet and the informed consent form of clinical trials with drugs, in accordance with the legislation. METHOD: Design (Guideline for good clinical practice and European and Spanish regulations); validation (Delphi method and expert consensus: concordance ≥ 80%); reliability (inter-observer method, Kappa index). 40 patient information sheets/informed consent forms were evaluated. RESULTS: Very good concordance was obtained in both checklists (k ≥ 0.81, p < 0.001). The final versions consisted of checklist-patient information sheet: 5 sections, 16 items and 46 sub-items; and checklist-informed consent form: 11 items. CONCLUSION: The instruments developed are valid, reliable and facilitate the analysis, evaluation, and decision-making on the patient information sheets/informed consent forms of clinical trials with drugs.

Solid state luminescence of phosphine-EWO ligands with fluorinated chalcone skeletons and their PdX2 complexes: metal-promoted phosphorescence enhancement.

Complexes trans-[PdX2L2] (X = Cl and Br), where L is 1-(PR2),2-(CHCH-C(O)Ph)-C6F4 (R = Ph, Cy, and iPr), display phosphorescent emission in the solid state, whereas due to their substantially lower lifetimes, the free ligands exhibit fluorescent behaviour. Alternatively, structurally identical derivatives with halide replaced by CN- or Pd replaced by Pt are non-emissive. DFT calculations explain this diverse behaviour, showing that the hybridization of orbitals of the MX2 moiety with those of the chalcone fragment of ligands is significant only for the LUMO of the emissive compounds. In other words, in our complexes, only MLMCT processes (LM = Metal-perturbed Ligand-centered orbital) lead to observable luminescence.

Lost in machine translation: The promises and pitfalls of machine translation for multilingual group work in global health education.

The rapid adoption of online technologies to deliver postsecondary education amid the COVID-19 pandemic has highlighted the potential for online learning, as well as important equity gaps to be addressed. For over ten years, McMaster University has delivered graduate global health education through a blended-learning approach. In partnership with universities in the Netherlands, India, Thailand, Norway, Colombia, and Sudan, experts from across the Consortium deliver lectures online to students around the world. In 2020, two courses were piloted with small groups of students from Canada and Colombia using machine translation supported by bilingual tutors. Students met weekly via video conferencing software, speaking in English and Spanish and relying on machine translation software to transcribe and translate for group members. Qualitative semi-structured interviews were conducted with students, tutors, and instructors to explore how artificial intelligence can be harnessed to integrate multilingual group work into course offerings, challenging the dominant use of English as the principal language of instruction in global health education. Findings highlight the potential for machine translation to bridge language divides, while also underscoring several key limitations of currently available technology. Further research is needed to investigate the potential for machine translation in facilitating multilingual online education as a pathway to more equitable and inclusive online learning environments.

Silyl-Osmium(IV)-Trihydride Complexes Stabilized by a Pincer Ether-Diphosphine: Formation and Reactions with Alkynes.

Complex OsH4{κ3-P,O,P-[xant(PiPr2)2]} (1) activates the Si-H bond of triethylsilane, triphenylsilane, and 1,1,1,3,5,5,5-heptamethyltrisiloxane to give the silyl-osmium(IV)-trihydride derivatives OsH3(SiR3){κ3-P,O,P-[xant(PiPr2)2]} [SiR3 = SiEt3 (2), SiPh3 (3), SiMe(OSiMe3)2 (4)] and H2. The activation takes place via an unsaturated tetrahydride intermediate, resulting from the dissociation of the oxygen atom of the pincer ligand 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene (xant(PiPr2)2). This intermediate, which has been trapped to form OsH4{κ2-P,P-[xant(PiPr2)2]}(PiPr3) (5), coordinates the Si-H bond of the silanes to subsequently undergo a homolytic cleavage. Kinetics of the reaction along with the observed primary isotope effect demonstrates that the Si-H rupture is the rate-determining step of the activation. Complex 2 reacts with 1,1-diphenyl-2-propyn-1-ol and 1-phenyl-1-propyne. The reaction with the former affords Os{C≡CC(OH)Ph2}2{=C=CHC(OH)Ph2}{κ3-P,O,P-[xant(PiPr2)2]} (6), which catalyzes the conversion of the propargylic alcohol into (E)-2-(5,5-diphenylfuran-2(5H)-ylidene)-1,1-diphenylethan-1-ol, via (Z)-enynediol. In methanol, the hydroxyvinylidene ligand of 6 dehydrates to allenylidene, generating Os{C≡CC(OH)Ph2}2{=C=C=CPh2}{κ3-P,O,P-[xant(PiPr2)2]} (7). The reaction of 2 with 1-phenyl-1-propyne leads to OsH{κ1-C,η2-[C6H4CH2CH=CH2]}{κ3-P,O,P-[xant(PiPr2)2]} (8) and PhCH2CH=CH(SiEt3).

Electronic Communication in Binuclear Osmium- and Iridium-Polyhydrides.

Reactions of polyhydrides OsH6(PiPr3)2 (1) and IrH5(PiPr3)2 (2) with rollover cyclometalated hydride complexes have been investigated in order to explore the influence of a metal center on the MHn unit of the other in mixed valence binuclear polyhydrides. Hexahydride 1 activates an ortho-CH bond of the heterocyclic moiety of the trihydride metal-ligand compounds OsH3{κ2-C,N-[C5RH2N-py]}(PiPr3)2 (R = H (3), Me (4), Ph (5)). Reactions of 3 and 4 lead to the hexahydrides (PiPr3)2H3Os{µ-[κ2-C,N-[C5RH2N-C5H3N]-N,C-κ2]}OsH3(PiPr3)2 (R = H (6), Me (7)), whereas 5 gives the pentahydride (PiPr3)2H3Os{µ-[κ2-C,N-[C5H3N-C5(C6H4)H2N]-C,N,C-κ3]}OsH2(PiPr3)2 (8). Pentahydride 2 promotes C-H bond activation of 3 and the iridium-dihydride IrH2{κ2-C,N-[C5H3N-py]}(PiPr3)2 (9) to afford the heterobinuclear pentahydride (PiPr3)2H3Os{µ-[κ2-C,N-[C5H3N-C5H3N]-N,C-κ2]}IrH2(PiPr3)2 (10) and the homobinuclear tetrahydride (PiPr3)2H2Ir{µ-[κ2-C,N-[C5H3N-C5H3N]-N,C-κ2]}IrH2(PiPr3)2 (11), respectively. Complexes 6-8 and 11 display HOMO delocalization throughout the metal-heterocycle-metal skeleton. Their sequential oxidation generates mono- and diradicals, which exhibit intervalence charge transfer transitions. This notable ability allows the tuning of the strength of the hydrogen-hydrogen and metal-hydrogen interactions within the MHn units.

Repercussion of a 1,3-Hydrogen Shift in a Hydride-Osmium-Allenylidene Complex.

An unusual 1,3-hydrogen shift from the metal center to the Cß atom of the C3-chain of the allenylidene ligand in a hydride-osmium(II)-allenylidene complex is the beginning of several interesting transformations in the cumulene. The hydride-osmium(II)-allenylidene complex was prepared in two steps, starting from the tetrahydride dimer [(Os(H···H){κ3-P,O,P-[xant(P i Pr2)2]})2(µ-Cl)2][BF4]2 (1). Complex 1 reacts with 1,1-diphenyl-2-propyn-1-ol to give the hydride-osmium(II)-alkenylcarbyne [OsHCl(≡CCH=CPh2){κ3-P,O,P-[xant(P i Pr2)2]}]BF4 (2), which yields OsHCl(=C=C=CPh2){κ3-P,O,P-[xant(P i Pr2)2]} (3) by selective abstraction of the Cß-H hydrogen atom of the alkenylcarbyne ligand with K t BuO. Complex 3 is metastable. According to results of DFT calculations, the migration of the hydride ligand to the Cß atom of the cumulene has an activation energy too high to occur in a concerted manner. However, the migration can be catalyzed by water, alcohols, and aldehydes. The resulting alkenylcarbyne-osmium(0) intermediate is unstable and evolves into a 7:3 mixture of the hydride-osmium(II)-indenylidene OsHCl(=CIndPh){κ3-P,O,P-[xant(P i Pr2)2]} (4) and the osmanaphthalene OsCl(C9H6Ph){κ3-P,O,P-[xant(P i Pr2)2]} (5). Protonation of 4 with HBF4 leads to the elongated dihydrogen complex [OsCl(η2-H2)(=CIndPh){κ3-P,O,P-[xant(P i Pr2)2]}]BF4 (6), while the protonation of 5 regenerates 2. In contrast to 4, complex 6 evolves to a half-sandwich indenyl derivative, [Os(η5-IndPh)H{κ3-P,O,P-[xant(P i Pr2)2]}][BF4]Cl (7). Phenylacetylene also provokes the 1,3-hydrogen shift in 3. However, it does not participate in the migration. In contrast to water, alcohols, and aldehydes, it stabilizes the resulting alkenylcarbyne to afford [Os(≡CCH=CPh2)(η2-HC≡CPh){κ3-P,O,P-[xant(P i Pr2)2]}]Cl (8).

Comunicación efectiva en salud: evaluación de una experiencia docente en estudiantes de medicina de Cuenca, Ecuador / Effective communication in Health: evaluation of a teaching experience in Medicine School of Cuenca, Ecuador

Introducción: La comunicación dentro del ámbito médico es esencial para obtener buenos resultados en consulta; esta habilidad debe aprenderse a lo largo de la carrera y no suponer que es innata. Luego de una revisión sistemática de la metodología de enseñanza en Ecuador y el poco desarrollo que ha tenido dentro de las universidades, vemos la necesidad de realizar un estudio evaluando las habilidades comunicacionales de los estudiantes de medicina. Metodología: se incluyó cien estudiantes de sexto año que realizan el internado en el Hospital Vicente Corral Moscoso. Se valoró las entrevistas por observación directa utilizando una lista de verificación sustentada en la Guía Calgary-Cambridge. Se analizaron los datos buscando diferencia estadística. Resultados: No hubo diferencia estadística entre los grupos. El promedio obtenido por los evaluados fue de 13,96 de 23 habilidades. Se comparó por dos grupos: estudiantes que tenían formación en comunicación médica (19) y los que no tenían ninguna (81). Se encontró que los estudiantes con formación en comunicación desarrollan entrevistas con mayor empatía, escucha efectiva, respeto por las expectativas de los pacientes y capacidad de resumir los hallazgos en busca de resultados más eficaces. Conclusión: Se observan algunas diferencias entre ambos grupos comparables con estudios internacionales. Se recomienda a las escuelas establecer un currículo formal para el aprendizaje de la comunicación como habilidad efectiva en la formación médica. El objetivo es humanizar la comunicación y favorecer una mejor relación entre médico y paciente (AU)

Introduction: Communication within the medical field is essential to obtain good results from the consultation. This skill must be learned throughout the career and not assumed to be innate. After a systematic review of teaching methodology in Ecuador and the little development it has had within medical schools, we carried out an observational study evaluating communication skills of medical students. Methodology: One hundred final-year students working at the Vicente Corral Moscoso Hospital were included. Direct observation interviews were assessed using a checklist tool supported by the Calgary-Cambridge Guide. Data were analyzed looking for statistical significance. Results: There was no statistical significance between groups. Mean score was 13.96 out of 23 skills evaluated. Two groups were randomized: students who had training in medical communication (19) and those who had none (81). Students with communication training developed empathic interviews, effective listening, respect for patient expectations and were capable to summarize findings for effective communication outcomes. Conclusion: There are some differences between both groups comparable with international studies. Ecuadorian Medical Schools are encouraged to establish a formal curriculum in learning and training communication skills. The objective is to humanize communication and to promote better relationship between doctor and patient (AU)

Introducció: La comunicació dins de l'àmbit mèdic és essencial per a obtenir bons resultats en consulta; aquesta habilitat ha d'aprendre's al llarg de la carrera i no suposar que és innata. Després d'una revisió sistemàtica de la metodologia d'ensenyament a l'Equador i el poc desenvolupament que ha tingut dins de les universitats, veiem la necessitat de realitzar un estudi avaluant les habilitats comunicacionals dels estudiants de medicina. Metodologia: Es va incloure cent estudiants de sisè any que realitzen l'internat a l'Hospital Vicente Corral Moscoso. Es va valorar les entrevistes per observació directa utilitzant una llista de verificació sustentada en la Guia Calgary-Cambridge. Es van analitzar les dades buscant diferència estadística. Resultats: No va haver-hi diferència estadística entre els grups. La mitjana obtinguda pels avaluats va ser de 13,96 de 23 habilitats. Es va comparar per dos grups: estudiants que tenien formació en comunicació mèdica (19) i els que no tenien cap (81). Es va trobar que els estudiants amb formació en comunicació desenvolupen entrevistes amb major empatia, escolta efectiva, respecte per les expectatives dels pacients i capacitat de resumir les troballes a la recerca de resultats més eficaços. Conclusió: S'observen algunes diferències entre tots dos grups comparables amb estudis internacionals. Es recomana a les escoles establir un currículum formal per a l'aprenentatge de la comunicació com a habilitat efectiva en la formació mèdica. L'objectiu és humanitzar la comunicació i afavorir una millor relació entre metge i pacient (AU)

A General Rhodium Catalyst for the Deuteration of Boranes and Hydrides of the Group 14 Elements.

Pinacolborane, catecholborane, triethylsilane, triphenylsilane, dimethylphenylsilane, 1,1,1,3,5,5,5-heptamethyltrisiloxane, triethylgermane, triphenylgermane, and triphenylstannane deuterated at the heteroatom position have been catalytically prepared in 50-70% isolated yield, through H/D exchange between the D2 molecule and the respective boranes and hydrides of the group 14 elements, in the presence of the rhodium(I)-monohydride catalyst precursor RhH{κ3-P,O,P-[xant(PiPr2)2]} (xant(PiPr2)2 = 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene).

Iridium-Promoted B-B Bond Activation: Preparation and X-ray Diffraction Analysis of a mer-Tris(boryl) Complex.

The tris(boryl) complex Ir(Bcat)3{κ3-P,O,P-[xant(PiPr2)2]} [Bcat = catecholboryl; xant(PiPr2)2 = 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene] has been prepared and characterized by X-ray diffraction analysis. The boryl ligands are disposed in a mer arrangement. The Ir-B bonds situated mutually trans are ∼0.1 Å longer than that disposed cis to the other two. An energy decomposition analysis method coupled to natural orbitals for chemical valence has revealed that the level of π-back-donation from the metal to the p z atomic orbital of the boron atom decreases ∼43% in the longer bonds with respect to the shorter one, while the level of σ-bonding interaction diminishes by only ∼8%.

Expiratory Central Airway Collapse in Adults: Corrective Treatment (Part 2).

Corrective treatment of expiratory central airway collapse (ECAC) consists of placement of airway stents or tracheobronchoplasty (TBP). The indication for corrective treatment is severe central airway collapse (>90 %), and severe symptoms that cause decline in quality of life. Patients are selected to undergo a trial of tracheal "Y" stent placement. If symptoms improve (positive trial) they undergo a TBP, provided they are good surgical candidates. Patients who are considered poor surgical candidates because of the severity of comorbidities can be offered permanent stenting to palliate symptoms. The anesthetic management of airway stent placement and TBP is complex. This article reviews the medical management and corrective treatment of ECAC, anesthetic management of airway stent placement, and considerations during TBP.

Expiratory Central Airway Collapse in Adults: Anesthetic Implications (Part 1).

Expiratory central airway collapse (ECAC) is a general term that incorporates tracheobronchomalacia (TBM) and excessive dynamic airway collapse (EDAC). TBM and EDAC are progressive, degenerative disorders of the tracheobronchial tree, causing airway collapse. Induction of general anesthesia can trigger intraoperative airway collapse in patients with these conditions. This crisis presents as the sudden inability to ventilate, which can lead to life-threatening hypoxemia and hypercapnia. This article reviews the definition, pathophysiology, diagnosis, and anesthetic implications of ECAC.

Highly enantioselective addition of dimethylzinc to fluorinated alkyl ketones, and the mechanism behind it.

Chiral-diamine catalyzed addition of ZnMe2 to PhC(O)CF2X (in dichloromethane at -30 °C) affords fluorinated alkyl tertiary alcohols in high yield (quantitative for X = H, F, Cl; 84% for X = CF3) and up to 99% ee. These conditions are similarly very efficient for other various ArC(O)CF3 molecules. A fine analysis of the results can be performed based on a double-cycle mechanism.

Cytotoxic, antioxidative, genotoxic and antigenotoxic effects of Horchata, beverage of South Ecuador.

BACKGROUND: "Horchata" is an herbal mixture infusion consumed in Southern Ecuador; 66% of its plants are anti-inflammatory medicinal plant, and 51% are analgesics. Anti-inflammatory substances can prevent carcinogenesis mediated by cytotoxic effects and can prevent DNA damage. The aim of this study was to evaluate the cytotoxicity and apoptotic/antigenotoxic effects of horchata as well as its mechanism. METHODS: Nine different varieties of horchata were prepared in the traditional way and then freeze-dried. Phytochemical screening tested for the presence of secondary metabolites using standard procedures and antioxidant activities. The cytotoxic activity was evaluated on cerebral astrocytoma (D-384), prostate cancer (PC-3), breast cancer (MCF-7), colon cancer (RKO), lung cancer (A-549), immortalized Chinese hamster ovary cells (CHO-K1), and human peripheral blood lymphocytes via a MTS assay. The pro-apoptotic effects were evaluated with Anexin V/Propidium Iodide and western blot of Bax, Bcl-2, TP53, and TP73. Induction and reduction of ROS were assessed by fluorimetry. Genotoxic and antigenotoxic effects were evaluated with a comet assay and micronuclei on binucleated cells. RESULTS: Five of nine horchatas had cytotoxic effects against D-384 while not affecting normal cells. These horchatas induce cell death by apoptosis modulated by p53/p73. In CHO-K1 cells, the horchatas decrease the damage induced by hydrogen peroxide and Mitomycin C measured in the comet and micronucleus assay respectively. CONCLUSIONS: The IC50 range of effective horchatas in D-384 was 41 to 122 µg·mL-1. This effect may be related to its use in traditional medicine (brain tonic). On the other hand, immortalized Chinese hamster ovary cells (CHO-K1) and lymphocytes did not show a cytotoxic effect. The most potent horchata induced apoptosis via a p53/p73-mediated mechanism. The horchatas present antigenotoxic properties, which may be related to the antioxidant capacity. Future studies on horchata components are necessary to understand the interactions and beneficial properties.

Ammonia Borane Dehydrogenation Promoted by a Pincer-Square-Planar Rhodium(I) Monohydride: A Stepwise Hydrogen Transfer from the Substrate to the Catalyst.

The pincer d(8)-monohydride complex RhH{xant(P(i)Pr2)2} (xant(P(i)Pr2)2 = 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene) promotes the release of 1 equiv of hydrogen from H3BNH3 and H3BNHMe2 with TOF50% values of 3150 and 1725 h(-1), to afford [BH2NH2]n and [BH2NMe2]2 and the tandem ammonia borane dehydrogenation-cyclohexene hydrogenation. DFT calculations on the ammonia borane dehydrogenation suggest that the process takes place by means of cis-κ(2)-PP-species, through four stages including: (i) Shimoi-type coordination of ammonia borane, (ii) homolytic addition of the coordinated H-B bond to afford a five-coordinate dihydride-boryl-rhodium(III) intermediate, (iii) reductive intramolecular proton transfer from the NH3 group to one of the hydride ligands, and (iv) release of H2 from the resulting square-planar hydride dihydrogen rhodium(I) intermediate.

Conclusive evidence on the mechanism of the rhodium-mediated decyanative borylation.

The stoichiometric reactions proposed in the mechanism of the rhodium-mediated decyanative borylation have been performed and all relevant intermediates isolated and characterized including their X-ray structures. Complex RhCl{xant(P(i)Pr2)2} (1, xant(P(i)Pr2)2 = 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene) reacts with bis(pinacolato)diboron (B2pin2), in benzene, to give the rhodium(III) derivative RhHCl(Bpin){xant(P(i)Pr2)2} (4) and PhBpin. The reaction involves the oxidative addition of B2pin2 to 1 to give RhCl(Bpin)2{xant(P(i)Pr2)2}, which eliminates ClBpin generating Rh(Bpin){xant(P(i)Pr2)2} (2). The reaction of the latter with the solvent yields PhBpin and the monohydride RhH{xant(P(i)Pr2)2} (6), which adds the eliminated ClBpin. Complex 4 and its catecholboryl counterpart RhHCl(Bcat){xant(P(i)Pr2)2} (7) have also been obtained by oxidative addition of HBR2 to 1. Complex 2 is the promoter of the decyanative borylation. Thus, benzonitrile and 4-(trifluoromethyl)benzonitrile insert into the Rh-B bond of 2 to form Rh{C(R-C6H4)═NBpin}{xant(P(i)Pr2)2} (R = H (8), p-CF3 (9)), which evolve into the aryl derivatives RhPh{xant(P(i)Pr2)2} (3) and Rh(p-CF3-C6H4){xant(P(i)Pr2)2} (10), as a result of the extrusion of CNBpin. The reactions of 3 and 10 with B2pin2 yield the arylBpin products and regenerate 2.

POP-pincer silyl complexes of group 9: rhodium versus iridium.

9,9-Dimethyl-4,5-bis(diisopropylphosphino)xanthene (xant(P(i)Pr2)2) derivatives RhCl{xant(P(i)Pr2)2} (1) and I rHCl{xant(P(i)Pr2)[(i)PrPCH(Me) CH2]} (2) react with diphenylsilane and triethylsilane to give the saturated d(6)-compounds RhHCl(SiR3){xant(P(i)Pr2)2} (SiR3 = SiHPh2 (3), SiEt3 (4)) and IrHCl(SiR3){xant(P(i)Pr2)2} (SiR3 = SiHPh2 (5), SiEt3 (6)). Complexes 3 and 5 undergo a Cl/H position exchange process via the MH{xant(P(i)Pr2)2} (M = Rh (8), Ir (E)) intermediates. The rhodium complex 3 affords the square planar d(8)-silyl derivative Rh(SiClPh2){xant(P(i)Pr2)2} (7), whereas the iridium derivative 5 gives IrH2(SiClPh2){xant(P(i)Pr2)2} (9), which is stable. In agreement with the formation of 7, the reactions of 8 with silanes are a general method to prepare square planar d(8)-rhodium-silyl derivatives. Thus, the addition of triethylsilane and triphenylsilane to 8 initially leads to the dihydrides RhH2(SiR3){xant(P(i)Pr2)2} (SiR3 = SiEt3 (10), SiPh3 (11)), which lose molecular hydrogen to afford Rh(SiR3){xant(P(i)Pr2)2} (SiR3 = SiEt3 (12), SiPh3 (13)). Treatment of 7 with NaBAr(F)4·2H2O leads to the cationic five-coordinate d(6)-species [RhH{Si(OH)Ph2}{xant(P(i)Pr2)2}]BAr(F)4 (14) through a silylene intermediate. According to the participation of the latter in the formation of 14, this cation is an efficient catalyst precursor for the monoalcoholysis of diphenylsilane with a wide range of alcohols, reaching turnover frequencies at 50% of conversion between 4000 and 76 500 h(-1). The X-ray structures of 3, 6, 7, 9, 12, and 14 are also reported.