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

Synthesis and reactivity of an iridium complex based on a tridentate aminophosphano ligand

The iridium(iii) hydride compound IrH{¿3C, P, P'-(SiNP-H)}(CNtBu)2]PF6] (1PF6) was obtained by reaction of Ir(SiNP)(cod)]PF6] with CNtBu as the result of the intramolecular oxidative addition of the SiCH2-H bond to iridium(i) SiNP = Si(CH3)2{N(4-tolyl)PPh2}2, SiNP-H = CH2Si(CH3){N(4-tolyl)PPh2}2]. The mechanism of the reaction was investigated by NMR spectroscopy and DFT calculations showing that the pentacoordinated intermediate Ir(SiNP)(cod)(CNtBu)]PF6] (2PF6) forms in the first place and that further reacts with CNtBu, affording the square planar intermediate Ir(SiNP)(CNtBu)2]PF6] (3PF6) that finally undergoes the intramolecular oxidative addition of the SiCH2-H bond. The reactivity of 1PF6 was investigated. On one hand, the reaction of 1PF6 with N-chlorosuccinimide or N-bromosuccinimide provides the haloderivatives IrX{¿3C, P, P'-(SiNP-H)}(CNtBu)2]PF6] (X = Cl, 4PF6; Br, 5PF6), and the reaction of 5PF6 with AgPF6 in the presence of acetonitrile affords the solvato species Ir{¿3C, P, P'-(SiNP-H)}(CH3CN)(CNtBu)2]2+ (62+) isolated as the hexafluorophosphate salt. On the other hand, the reaction of 1PF6 with HBF4 gives the iridium(iii) compound IrH(CH2SiF2CH3)(HNP)2(CNtBu)2]BF4] (7BF4) as the result of the formal addition of hydrogen fluoride to the Si-N bonds of 1+ HNP = HN(4-tolyl)PPh2]. A similar outcome was observed in the reaction of 1PF6 with CF3COOH rendering 7PO2F2. In this case the intermediate IrH{¿2C, P-CH2SiMeFN(4-tolyl)PPh2}(HNP)(CNtBu)2]+ (8+) was observed and characterised in situ by NMR spectroscopy. DFT calculations suggests that the reaction goes through the sequential protonation of the nitrogen atom of the Si-N-P moiety followed by the formal addition of fluoride ion to silicon. Also, the crystal structures of SiNP, 1PF6, 4PF6 and 7BF4 have been determined by X-ray diffraction measurements. © 2022 The Royal Society of Chemistr

Cadmium exposure and cancer mortality in the Third National Health and Nutrition Examination Survey cohort.

Objective This study examined prospective data from the Third National Health and Nutrition Examination Survey (NHANES III) cohort to investigate the relationship between cadmium exposure and cancer mortality, and the specific cancers associated with cadmium exposure, in the general population. Methods Vital status and cause of death through 31 December 2006 were obtained by the National Center for Health Statistics for NHANES III participants. The cadmium concentration of spot urine samples was measured and corrected for urine creatinine (uCd). Weighted Cox proportional hazards regression with age as the time metric was applied to estimate sex-specific adjusted HRs (aHRs) of mortality associated with uCd for all cancers and the cancers responsible for the most deaths in the USA. Estimates were stratified by smoking history and adjusted for education, body mass index and race. Results uCd was associated with cancer mortality (aHR per twofold higher uCd (95% CI), men: 1.26 (1.07 to 1.48); women: 1.21 (1.04 to 1.42)). In men, mortality from lung cancer, pancreatic cancer and non-Hodgkin lymphoma was associated with uCd; an association with leukaemia mortality was suggested. In women, associations were suggested with mortality due to lung cancer, leukaemia, ovarian and uterine cancer, but evidence was weaker than in men. Conclusions Cadmium appears to be associated with overall cancer mortality in men and women, but the specific cancers associated differ between men and women, suggesting avenues for future research. Limitations of the study include the possibility of uncontrolled confounding by cigarette smoking or other factors, and the limited number of deaths due to some cancers

A dissipative environment may improve the quantum annealing performances of the ferromagnetic p-spin model

We investigate the quantum annealing of the ferromagnetic $p$-spin model in a dissipative environment ($p = 5$ and $p = 7$). This model, in the large $p$ limit, codifies the Grover's algorithm for searching in an unsorted database. The dissipative environment is described by a phonon bath in thermal equilibrium at finite temperature. The dynamics is studied in the framework of a Lindblad master equation for the reduced density matrix describing only the spins. Exploiting the symmetries of our model Hamiltonian, we can describe many spins and extrapolate expected trends for large $N$, and $p$. While at weak system bath coupling the dissipative environment has detrimental effects on the annealing results, we show that in the intermediate coupling regime, the phonon bath seems to speed up the annealing at low temperatures. This improvement in the performance is likely not due to thermal fluctuation but rather arises from a correlated spin-bath state and persists even at zero temperature. This result may pave the way to a new scenario in which, by appropriately engineering the system-bath coupling, one may optimize quantum annealing performances below either the purely quantum or classical limit.Comment: 9 Pag, 5 Fig, Submitte

Fractional differentiability for solutions of nonlinear elliptic equations

We study nonlinear elliptic equations in divergence form $${\operatorname{div}}{\mathcal A}(x,Du)={\operatorname{div}}G.$$ When ${\mathcal A}$ has linear growth in $Du$, and assuming that $x\mapsto{\mathcal A}(x,\xi)$ enjoys $B^\alpha_{\frac{n}\alpha, q}$ smoothness, local well-posedness is found in $B^\alpha_{p,q}$ for certain values of $p\in[2,\frac{n}{\alpha})$ and $q\in[1,\infty]$. In the particular case ${\mathcal A}(x,\xi)=A(x)\xi$, $G=0$ and $A\in B^\alpha_{\frac{n}\alpha,q}$, $1\leq q\leq\infty$, we obtain $Du\in B^\alpha_{p,q}$ for each $p<\frac{n}\alpha$. Our main tool in the proof is a more general result, that holds also if ${\mathcal A}$ has growth $s-1$ in $Du$, $2\leq s\leq n$, and asserts local well-posedness in $L^q$ for each $q>s$, provided that $x\mapsto{\mathcal A}(x,\xi)$ satisfies a locally uniform $VMO$ condition

Characterisation of wine yeasts isolated at different temperatures using the enrichment technique

Research NoteSaccharomyces cerevisiae strains isolated from fermenting grape must incubated at extreme fermentation temperatures (40 and 5 degrees C) were oenologically characterised. These cultures compared with S. cerevisiae wine strains, show a wider optimum temperature for growth and can ferment vigorously in a wider temperature range (27 to 35 degrees C)

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

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

Stress inversions to forecast magma pathways and eruptive vent location

When a batch of magma reaches Earth\u2019s surface, it forms a vent from which volcanic products are erupted. At many volcanoes, successive batches may open vents far away from previous ones, resulting in scattered, sometimes seemingly random spatial distributions. This exposes vast areas to volcanic hazards and makes forecasting difficult. Here, we show that magma pathways and thus future vent locations may be forecast by combining the physics of magma transport with a Monte Carlo inversion scheme for the volcano stress history. We validate our approach on a densely populated active volcanic field, Campi Flegrei (Italy), where we forecast future vents on an onshore semi-annular belt located between 2.3 and 4.2 km from the caldera center. Our approach offers a mechanical explanation for the vent migration over time at Campi Flegrei and at many calderas worldwide and may be applicable to volcanoes of any type