Intramolecular C-H oxidative addition to iridium(i) triggered by trimethyl phosphite in N, N'-diphosphanesilanediamine complexes

The reaction of Ir(SiNP)(cod)]PF6] (1]PF6]) and of IrCl(SiNP)(cod) (5) (SiNP = SiMe2{N(4-C6H4CH3)PPh2}2) with trimethyl phosphite affords the iridium(iii) derivatives of the formula IrHClx(SiNP-H){P(OMe)3}2-x](1-x)+ (x = 0, 3+; x = 1, 6) containing the ¿3C, P, P'-coordinated SiNP-H ligand (SiNP-H = Si(CH2)(CH3){N(4-C6H4CH3)PPh2}2). The thermally unstable pentacoordinated cation Ir(SiNP){P(OMe)3}(cod)]+ (2+) has been detected as an intermediate of the reaction and has been fully characterised in solution. Also, the mechanism of the C-H oxidative addition has been elucidated by DFT calculations showing that the square planar iridium(i) complexes of the formula IrClx(SiNP){P(OMe)3}2-x](1-x)+ (x = 0, 4+; x = 1, 7) should be firstly obtained from 2+ and finally should undergo the C-H oxidative addition to iridium(i) via a concerted intramolecular mechanism. The influence of the counterion of 2+ on the outcome of the C-H oxidative addition reaction has also been investigated

Divergent reactivity of 2-vinylpyridine and 1-vinylpyrazole in rhodium-phosphine systems: C-H activation and dinuclear chemistry

The Rh-I-Rh-III mixed valence dinuclear complex Rh-2-Cl-2(mu-H)(mu-eta(2),kappa(2)-C, N-NC5H4-2-(Z)CH=CH)( PPhMe2)(3) has been prepared by reaction of [Rh(mu-Cl)(eta(2)-coe)(2)](2) with 2-vinylpyridine in the presence of dimethylphenylphosphine as a result of C-H activation of the terminal olefinic proton. The X- ray structure presents anagostic Rh center dot center dot center dot HC and pi-pi interactions between aromatic rings. In contrast, 1-vinylpyrazole does not undergo a C-H activation process, resulting in the formation of dinuclear species supported by 1 vinylpyrazole bridges. Anagostic Rh center dot center dot center dot HC interactions and CH center dot center dot center dot Cl hydrogen bonds are responsible for the 3D packing of the complex. El complejo dinuclear de valencia mixta RhI-RhIII Rh2-Cl2(µ-H)(µ-¿2,¿2-C,N-NC5H4-2-(Z)CH=CH)(PPhMe2)3 ha sido preparado por reacción de [Rh(µ-Cl)(¿2-coe)2]2 con 2-vinilpiridina en presencia de dimetilfenilfosfina, como resultado de la activación C-H del protón terminal de la olefina. La estructura de rayos-X presenta enlaces anagósticos Rh···HC, así como interacciones p-p entre anillos aromáticos. Por otro lado, la reacción con 1-vinilpirazol no da lugar a una activación C-H sino que se observa la formación de una especie dinuclear soportada por ligandos 1-vinilpirazol puente. Diferentes interacciones anagósticas Rh···HC y de enlace de hidrógeno CH···Cl son responsables del empaquetamiento tridimensional del complejo

Cambios a largo plazo en la riqueza de especies en una comunidad de aves nidificantes en un pequeño archipiélago mediterráneo

We analyzed the pattern of species richness changes in a bird–breeding bird community on a small western Mediterranean archipelago (Columbretes Islands) over a 40–year period (1964–2003). The aim of this study was to qualitatively account for the relative roles of local and regional factors in shaping the community. As expected, we found that regional factors (at the metapopulation spatial scale) increased diversity whereas local factors (i.e. ecological) probably prevented further increases in diversity. We found that the archipelago gained four new species (two seabirds and two falconids) during the study period, whereas no extinctions were recorded. The community seems partially or completely closed to some groups of species (e.g. small–sized birds such as passerines and storm–petrels), probably owing to predatory exclusion by Eleonora falcons (Falco eleonorae). As newly arrived species have breeding calendars that do not fully overlap with those of resident species, competition for space in a rather saturated area is prevented. Preservation of rare species which increase gamma (regional) diversity rather than alpha diversity with common species should be the main local conservation goal.Este trabajo analiza los patrones de cambio en la riqueza de especies en una comunidad de aves nidificantes de un pequeño archipiélago mediterráneo (las islas Columbretes, Castellón) durante un periodo de 40 años (1964–2003). El estudio pretende valorar cualitativamente la influencia relativa de los factores locales y regionales. Como se esperaba, se encontró que los factores regionales (a la escala espacial de la metapoblación) aumentaron la diversidad, mientras que los factores ecológicos locales evitaron mayores incrementos. El archipiélago ganó cuatro especies durante el periodo de estudio (dos aves marinas y dos falcónidos), mientras que no se produjo ninguna extinción. La comunidad parece parcial o totalmente cerrada a ciertos grupos de especies, tales como las aves de pequeña talla (p.ej. Paseriformes y paíños) probablemente debido a la depredación excluyente por parte de los halcones de Eleonor (Falco eleanorae). Dado que las especies que son colonizadoras recientes tienen calendarios de cría que no se solapan completamente con los de las especies residentes, se evita la competencia por el espacio de cría en un área bastante saturada. La principal meta conservacionista debe ser la protección de las especies raras, que incrementan la diversidad gamma (regional), más que la diversidad alpha de las especies comunes

Preparation of Butadienylpyridines by Iridium-NHC-Catalyzed Alkyne Hydroalkenylation and Quinolizine Rearrangement

Iridium(I) N-heterocyclic carbene complexes of formula Ir(¿2O, O’-BHetA)(IPr)(¿2-coe) [BHetA=bis-heteroatomic acidato, acetylacetonate or acetate; IPr=1, 3-bis(2, 6-diisopropylphenyl)imidazolin-2-carbene; coe=cyclooctene] have been prepared by treating Ir(¿2O, O’-BHetA)(¿2-coe)2 complexes with IPr. These complexes react with 2-vinylpyridine to afford the hydrido-iridium(III)-alkenyl cyclometalated derivatives IrH(¿2O, O’-BHetA)(¿2N, C-C7H6N)(IPr) through the iridium(I) intermediate Ir(¿2O, O’-BHetA)(IPr)(¿2-C7H7N). The cyclometalated IrH(¿2O, O’-acac)(¿2N, C–C7H6N)(IPr) complex efficiently catalyzes the hydroalkenylation of aromatic and aliphatic terminal alkynes and enynes with 2-vinylpyridine to afford 2-(4R-butadienyl)pyridines with Z, E configuration as the major reaction products (yield up to 89 %). In addition, unprecedented (Z)-2-butadienyl-5R-pyridine derivatives have been obtained as minor reaction products (yield up to 21 %) from the elusive 1Z, 3gem-butadienyl hydroalkenylation products. These compounds undergo a thermal 6p-electrocyclization to afford bicyclic 4H-quinolizine derivatives that, under catalytic reaction conditions, tautomerize to 6H-quinolizine to afford the (Z)-2-(butadienyl)-5R-pyridine by a retro-electrocyclization reaction. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH Gmb

An insight into transfer hydrogenation reactions catalysed by iridium(iii) bis-n-heterocyclic carbenes

A variety of [M(L)2(L')2{kC,C'-bis(NHC)}]BF4 complexes (M = Rh or Ir; L = CH3CN or wingtip group; L' = I– or CF3COO–; NHC=N-heterocyclic carbene) have been tested as pre-catalysts for the transfer hydrogenation of ketones and imines. The conversions and TOF's obtained are closely related to the nature of the ligand system and metal centre, more strongly coordinating wingtip groups yielding more active and recyclable catalysts. Theoretical calculations at the DFT level support a classic stepwise metal-hydride pathway against the concerted Meerwein–Ponndorf–Verley (MPV) mechanism. The calculated catalytic cycle involves a series of ligand rearrangements due to the high trans effect of the carbene and hydrido ligands, which are more stable when situated in mutual cis positions. The reaction profiles obtained for the complexes featuring an iodide or a trifluoroacetate in one of the apical positions agree well with the relative activity observed for both catalysts

The dynamics of cultivation and floods in arable lands of Central Argentina

Although floods in watersheds have been associated with land-use change since ancient times, the dynamics of flooding is still incompletely understood. In this paper we explored the relations between rainfall, groundwater level, and cultivation to explain the dynamics of floods in the extremely flat and valuable arable lands of the Quinto river watershed, in central Argentina. The analysis involved an area of 12.4 million hectare during a 26-year period (1978–2003), which comprised two extensive flooding episodes in 1983–1988 and 1996–2003. Supported by information from surveys as well as field and remote sensing measurements, we explored the correlation among precipitation, groundwater levels, flooded area and land use. Flood extension was associated to the dynamics of groundwater level. While no correlation with rainfall was recorded in lowlands, a significant correlation (<i>P</i><0.01) between groundwater and rainfall in highlands was found when estimations comprise a time lag of one year. Correlations between groundwater level and flood extension were positive in all cases, but while highly significant relations (<i>P</i><0.01) were found in highlands, non significant relations (<i>P</i>>0.05) predominate in lowlands. Our analysis supports the existence of a cyclic mechanism driven by the reciprocal influence between cultivation and groundwater in highlands. This cycle would involve the following stages: (a) cultivation boosts the elevation of groundwater levels through decreased evapotranspiration; (b) as groundwater level rises, floods spread causing a decline of land cultivation; (c) flooding propitiates higher evapotranspiration favouring its own retraction; (d) cultivation expands again following the retreat of floods. Thus, cultivation would trigger a destabilizing feedback self affecting future cultivation in the highlands. It is unlikely that such sequence can work in lowlands. The results suggest that rather than responding directly and solely to the same mechanism, floods in lowlands may be the combined result of various factors like local rainfall, groundwater level fluctuations, surface and subsurface lateral flow, and water-body interlinking. Although the hypothetical mechanisms proposed here require additional understanding efforts, they suggest a promising avenue of environmental management in which cultivation could be steered in the region to smooth the undesirable impacts of floods

The Safety and Feasibility of Transitioning From Transfemoral to Transradial Access Left Ventricular Endomyocardial Biopsy

BACKGROUND: Left ventricular endomyocardial biopsy (LVEMB) is commonly performed via the transfemoral route. Radial access may help reduce vascular access complications, but there are few data on the safety and feasibility of transradial LVEMB. OBJECTIVE: Describe the safety and feasibility of transitioning from transfemoral to transradial access LVEMB. METHODS: This is a single-center, prospective, observational cohort study. Fifty procedures in 49 patients were included, 25 (50%) via the femoral route and 25 (50%) via the radial route. RESULTS: The cohort had a mean age of 47 ± 13 years and the most common indication for LVEMB was myocarditis. From June 2015 until September 2016, all procedures (n = 21) were performed via the femoral approach; thenceforth, there was a gradual transition to the radial approach. More tissue samples were obtained when the procedure was performed via the femoral approach (P<.01). The minimum sampling target of 3 specimens was not met in 4 patients (16%) via the radial approach and in 1 patient (4%) via the femoral approach. Complications occurred in 3/25 transradial procedures (12%; 2 cardiac perforations and 1 forearm hematoma) and 3/25 transfemoral procedures (12%; 1 cardiac perforation, 1 femoral artery pseudoaneurysm, and 1 ventricular fibrillation). Cardiac perforations via the transradial approach occurred during the early transition period. There were no deaths. CONCLUSIONS: Transradial LVEMB is feasible, with a similar complication profile to femoral procedures, but associated with a smaller number of specimens. Transitioning from transfemoral to transradial procedures may initially be associated with a higher risk of complications and potentially a lower diagnostic yield

First Report of Horseradish Leaf Spot Caused by Alternaria brassicae in Serbia

In July 2014, a foliar spot disease of horseradish (Armoracia rusticana) was observed in the Bačka region of Serbia (45°14′17″ N; 19°42′22″ E). The disease was observed in several small vegetable farms and disease incidence approached 20 to 40%. The symptoms first appeared on the abaxial side of older leaves as light brown concentric spots with dark margins and sometimes haloes. The spots varied in size between 0.5 and 0.9 cm. The necrotic spots gradually enlarged, tore, and dropped out. Under high humidity and temperature in 2014 in that region, development of numerous necrosis spots resulted in a rapid reduction of leaves. Small pieces taken from infected leaf tissue of diseased horseradish were treated with 1% sodium hypochlorite for 1 min, rinsed with sterile distillated water (SDW), and placed on V8 agar. Isolates were grown in pure culture at 24°C for 5 days in 12 h light/dark photoperiod. Morphological characteristics of the colony and sporulation were determined for six representative isolates. Fungal colonies were smooth, color varied from white, off white to light brown with concentric zones and intensive sporulation. Conidia were light brown, obclavate, produced singly or in short chains. Mature conidia were 16 to 38 µm wide and 73 to 158 µm long with a beak cell 79 to 120 µm long with 8 to 11 transverse septa and 0 to 4 longitudinal septa. Based on morphological characteristics, all isolates were identified as Alternaria brassicae (Berk.) Sacc (Simmons 2007). To confirm the pathogen’s identity, DNA was extracted from the fungal isolates and subjected to PCR; the internal transcribed spacer region of rDNA was amplified using primers ITS1 and ITS4 (White et al. 1990). The resulting amplicons were sequenced by Macrogen Inc. (Seoul, South Korea) and deposited in NCBI GenBank (Accession Nos. KP115599 to KP115604). BLAST analysis of revealed 100% homology with a sequence of A. brassicae strain ATCC 58169 deposited in GenBank (JX499028). Pathogenicity of six representative isolates was tested on leaves of 2-month-old horseradish seedlings by spraying with aqueous conidial suspensions (105 conidia/ml) prepared from cultures grown on V8 agar at 24°C for 5 days. Negative control plants were sprayed with SDW. Plants were covered with plastic bags and placed for 48 h in a greenhouse at 20 to 22°C. For all isolates within 10 days, inoculated plants developed brown lesions on leaves. Plants treated with SDW were symptomless. To fulfill Koch’s postulates, reisolations from all tested strains were done by streaking margins of necrotic leaf spot tissue onto V8 agar. Reisolated strains showed the same colony morphology as described above. Based on the pathogenicity test accompanied by completion of Koch’s postulates, sequence analysis, and morphological and cultural characteristics, the strains were identified as A. brassicae. According to available literature data, this is the first report of this pathogen as the causal agent of brown leaf spot of horseradish in Serbia