Identity of the Silyl Ligand in an Iron Silyl Complex Influences Olefin Hydrogenation: An Experimental and Computational Study.

In this study, we explore the selective synthesis of iron silyl complexes using the reaction of an iron mesityl complex (MesCCC)FeMes(Py) with various hydrosilanes. These resulting iron silyl complexes, (MesCCC)Fe(SiH2Ph)(Py)(N2), (MesCCC)Fe(SiMe2Ph)(Py)(N2), and (MesCCC)Fe[SiMe(OSiMe3)2](Py)(N2), serve as effective precatalysts for olefin hydrogenation. The key to their efficiency in catalysis lies in the specific nature of the silyl ligand attached to the iron center. Experimental observations, supported by density functional theory (DFT) simulations, reveal that the catalytic performance correlates with the relative stability of dihydrogen and hydride species associated with each iron silyl complex. The stability of these intermediates is crucial for efficient hydrogen transfer during the catalytic cycle. The DFT simulations help to quantify these stability factors, showing a direct relationship between the silyl ligand's electronic and steric properties and the overall catalytic activity. Complexes with certain silyl ligands exhibit better performance due to the optimal balance between the stability and reactivity of the key active catalyst. This work highlights the importance of ligand design in the development of iron-based hydrogenation catalysts.

Unlocking the Metalation Applications of TMP-powered Fe and Co(II) bis(amides): Synthesis, Structure and Mechanistic Insights.

Typified by LiTMP and TMPMgCl.LiCl, (TMP=2,2,6,6-tetramethylpiperidide), s-block metal amides have found widespread applications in arene deprotonative metalation. On the contrary, transition metal amides lack sufficient basicity to activate these substrates. Breaking new ground in this field, here we present the synthesis and full characterisation of earth-abundant transition metals M(TMP)2 (M=Fe, Co). Uncovering a new reactivity profile towards fluoroarenes, these amide complexes can promote direct M-H exchange processes regioselectively using one or two of their basic amide arms. Remarkably, even when using a perfluorinated substrate, selective C-H metalation occurs leaving C-F bonds intact. Their kinetic basicity can be boosted by LiCl or NBu4Cl additives which enables formation of kinetically activated ate species. Combining spectroscopic and structural studies with DFT calculations, mechanistic insights have been gained on how these low polarity metalation processes take place. M(TMP)2 can also be used to access ferrocene and cobaltocene by direct deprotonation of cyclopentadiene and undergo efficient CO2 insertion of both amide groups under mild reaction conditions.

Sodium mediated deprotonative borylation of arenes using sterically demanding B(CH2SiMe3)3: unlocking polybasic behaviour and competing lateral borane sodiation.

The deprotonative metalation of organic molecules has become a convenient route to prepare functionalised aromatic substrates. Amongst the different metallating reagents available, sodium bases have recently emerged as a more sustainable and powerful alternative to their lithium analogues. Here we report the study of the sterically demanding electrophilic trap B(CH2SiMe3)3 for the deprotonative borylation of arenes using NaTMP (TMP = 2,2,6,6-tetramethylpiperidide) in combination with tridentate Lewis donor PMDETA (PMDETA = N,N,N',N'',N''-pentamethyldiethylenetriamine). Using anisole and benzene as model substrates, unexpected polybasic behaviour has been uncovered, which enables the formal borylation of two equivalents of the relevant arene. The combination of X-ray crystallographic and NMR monitoring studies with DFT calculations has revealed that while the first B-C bond forming process takes place via a sodiation/borylation sequence to furnish [(PMDETA)NaB(Ar)(CH2SiMe3)3] species, the second borylation step is facilitated by the formation of a borata-alkene intermediate, without the need of an external base. For non-activated benzene, it has also been found that under stoichimetric conditions the lateral sodiation of B(CH2SiMe3)3 becomes a competitive reaction pathway furnishing a novel borata-alkene complex. Showing a clear alkali-metal effect, the use of the sodium base is key to access this reactivity, while the metalation/borylation of the amine donor PMDETA is observed instead when LiTMP is used.

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.

Intimate relationship between C-I reductive elimination, aryl scrambling and isomerization processes in Au(III) complexes.

19F NMR monitoring shows that heating trans-[AuIIIRf2I2]- solutions (Rf = C6F3Cl2-3,5) leads to formation of cis-[AuRf2I2]-, [AuRf3I]- and [AuRfI3]-via kinetic competition between isomerization and Rf/I scrambling. The system evolution is driven by the easy Rf-I reductive elimination from [AuRfI3]- (forming also [AuI2]-), which is faster than any of the Rf-Rf couplings from the coexisting species, hindering the commonly desired and thermodynamically preferred C-C coupling. A kinetic model where I- dissociation triggers both isomerization and transmetalation steps is proposed, which fits well the experimental data. DFT calculations support that the lower bond strength of AuIII-I compared to other halides produces a pathway switch that makes C-I coupling kinetically preferred. Consequently, it is better avoided in reactions looking for C-C coupling.

Problematic ArF-Alkynyl Coupling with Fluorinated Aryls. From Partial Success with Alkynyl Stannanes to Efficient Solutions via Mechanistic Understanding of the Hidden Complexity.

The synthesis of aryl-alkynyl compounds is usually achieved via Sonogashira catalysis, but this is inefficient for fluorinated aryls. An alternative method reported by Shirakawa and Hiyama, using alkynylstannanes and hemilabile PN ligands, works apparently fine for conventional aryls, but it is also poor for fluorinated aryls. The revision of the unusual literature cycle reveals the existence and nature of unreported byproducts and uncovers coexisting cycles and other aspects that explain the reasons for the conflict. This knowledge provides a full understanding of the real complexity of these aryl/alkynylstannane systems and the deviations of their evolution from that of a classic Stille process, providing the clues to design several very efficient alternatives for the catalytic synthesis of the desired ArF-alkynyl compounds in almost quantitative yield. The same protocols are also very efficient for the catalytic synthesis of alkynyl-alkynyl' hetero- and homocoupling.

γ-Agostic interactions in (MesCCC)Fe-Mes(L) complexes.

Agostic interactions were observed in the bound mesityl group in a series of iron compounds bearing a bis(NHC) pincer CCC ligand. The L-type ligand on [(CCC)FeIIMes(L)] complexes influences the strength of the agostic interaction and is manifested in the upfield shift of the 1H NMR resonance for the mesityl methyl resonances. The nature of the interaction was further investigated by density functional theory calculations, allowing rationalization of some unexpected trends and proving to be a powerful predictive tool.

Secondary Coordination Sphere Influences the Formation of Fe(III)-O or Fe(III)-OH in Nitrite Reduction: A Synthetic and Computational Study.

The reduction of nitrite (NO2-) to generate nitric oxide (NO) is a significant area of research due to their roles in the global nitrogen cycle. Here, we describe various modifications of the tris(5-cyclohexyliminopyrrol-2-ylmethyl)amine H3[N(piR)3] ligand where the steric bulk and acidity of the secondary coordination sphere were explored in the non-heme iron system for nitrite reduction. The cyclohexyl and 2,4,6-trimethylphenyl variants of the ligand were used to probe the mechanism of nitrite reduction. While previously stoichiometric addition of nitrite to the iron(II)-species generated an iron(III)-oxo complex, changing the secondary coordination sphere to mesityl resulted in an iron(III)-hydroxo complex. Subsequent addition of an electron and two protons led to the release of water and regeneration of the starting iron(II) catalyst. This sequence mirrored the proposed mechanism of nitrite reduction in biological systems, where the distal histidine residue shuttles protons to the active site. Computational studies aimed at interrogating the dissimilar behavior of the cyclohexyl and mesityl ligand systems resulting in Fe(III)-oxo and Fe(III)-hydroxo complexes, respectively, shed light on the key role of H-bonds involving the secondary coordination sphere in the relative stability of these species.

Expanding the Concepts Trans Influence and Back-Donation: Hybrid and Side Donations in [Cp*MIII(L)XY] (M = Rh, Ir) Complexes with CO, CN-, and CNR Ligands. A Window to Cis Influence.

Analysis of the bonding contributions in molecules [MIIICp*(L)XY] (M = Rh, Ir; Cp* = C5Me5; L = CO, CN-, CNR) has uncovered a rich variety of types of interaction that seem to have escaped detection so far, in spite of the continuous popularity of cyclopentadienyl transition-metal complexes since the 1970s. At variance with the M-C≡O bond in square-planar systems, which shows typical metal-to-CO π-back-donation, the nonorthogonal arrangement of the Cp* plane and Rh-C≡O fragment and the pseudooctahedral geometry lead to the observation of many direct lateral donations from other ligands that do not involve the metal orbitals, and we name side donations, for instance, Cp* → π*(CO), Cl → π*(CO), and F → π*(CO). Hybrid donations partially involving the metal, M-Caryl → π*(CO), are also observed. The summation of multiple contributions other than back-donation can easily account for about 20% of the electron donation to the π*(C≡O) orbitals.

Striking ligand-disproportionative Cl/aryl scrambling in a simple Au(III) system. Solvent role, driving forces and mechanisms.

Aryl rearrangements triggered by Cl- extraction from trans-[AuIII(Rf)2Cl2]- (Rf = C6F3Cl2-3,5), led quickly to a mixture of [Au(Rf)3(solv)], cis-[Au(Rf)2Cl(solv)] and [Au(Rf)Cl2(solv)] (solv = OEt2, OH2). 19F NMR and X-ray diffraction studies led us to identify the species present in solution and the role of the solvent in their formation, while DFT calculations confirm the thermodynamic basis of their evolution. Very different Rf-Rf coupling rates are found from (µ-Cl)2[cis-Au(Rf)2]2 or cis-[Au(Rf)2ClL] species (L = OEt2, NCMe, Cl-) depending on the coordination strength of the ligand or solvent in the fourth position.

Experimental study of speciation and mechanistic implications when using chelating ligands in aryl-alkynyl Stille coupling.

Neutral palladium(ii) complexes [Pd(Rf)X(P-L)] (Rf = 3,5-C6Cl2F3, X = Cl, I, OTf) with P-P (dppe and dppf) and P-N (PPh2(bzN)) ligands have chelated structures in the solid-state, except for P-L = dppf and X = Cl, were chelated and dimeric bridged structures are found. The species present in solution in different solvents (CDCl3, THF, NMP and HMPA) have been characterised by 19F and 31P{1H} NMR and conductivity studies. Some [Pd(Rf)X(P-L)] complexes are involved in equilibria with [Pd(Rf)(solv)(P-L)]X, depending on the solvent and X. The ΔH° and ΔS° values of these equilibria explain the variations of ionic vs. neutral complexes in the range 183-293 K. Overall the order of coordination strength of solvents and anionic ligands is: HMPA ≫ NMP > THF and I-, Cl- > TfO-. This coordination preference is determining the complexes participating in the alkynyl transmetalation from PhC[triple bond, length as m-dash]CSnBu3 to [Pd(Rf)X(P-L)] (X = OTf, I) in THF and subsequent coupling. Very different reaction rates and stability of intermediates are observed for similar complexes, revealing neglected complexities that catalytic cycles have to deal with. Rich information on the evolution of these Stille systems after transmetalation has been obtained that leads to proposal of a common behaviour for complexes with dppe and PPh2(bzN), but a different evolution for the complexes with dppf: this difference leads the latter to produce PhC[triple bond, length as m-dash]CRf and black Pd, whereas the two former yield PhC[triple bond, length as m-dash]CRf and [Pd(C[triple bond, length as m-dash]CPh)(SnBu3)(dppe)] or [Pd(C[triple bond, length as m-dash]CPh)(SnBu3){PPh2(bzN)}].

4-Pyridylisocyanide gold(i) and gold(i)-plus-silver(i) luminescent and mechanochromic materials: the silver role.

Crystallographic and DFT examination of the metalloligands [AuAr(CNPy-4)] (Ar = C6F5 (1), C6F3Cl2-3,5 (2)) and their silver complexes [Ag[AuAr(CNPy-4)]2](BF4) (3 and 4) support that the marked luminescence red-shifts observed on moving from 1 to 2, from 1,2 to 3,4, or upon grinding, are not caused by electronic differences (either by changing the aryls C6F5/C6F3Cl2, or by N coordination to silver), nor by non-existent AuAg interactions. They are always due to structural changes disturbing stronger π-π stackings in order to allow for shorter AuAu interactions.

d8d10 RhIAuI interactions in Rh 2,6-xylylisocyanide complexes with [Au(CN)2]-: bond analysis and crystal effects.

The well-known [RhL4]n(anion)n structures, with RhIRhI d8d8 interactions, are replaced by others with RhIAuI d8d10 interactions such as [{RhL4}{Au(CN)2}] (L = 2,6-xylylisocyanide) or [{RhL4}{Au(CN)2}{RhL4}{Au2(CN)3}·4(CHCl3)]∞ when the anion is [Au(CN)2]-. Orbital (RhAu), coulombic, and inter-unit π-π aryl stacking interactions stabilize these crystal structures.

RhI Ar/AuI Ar' Transmetalation: A Case of Group Exchange Pivoting on the Formation of M-M' Bonds through Oxidative Insertion.

By combining kinetic experiments, theoretical calculations, and microkinetic modeling, we show that Pf/Rf (C6 F5 /C6 Cl2 F3 ) exchange between [AuPf(AsPh3 )] and trans-[RhRf(CO)(AsPh3 )2 ] does not occur by typical concerted Pf/Rf transmetalation via electron-deficient double bridges. Instead, it involves asymmetric oxidative insertion of the RhI complex into the (Ph3 As)Au-Pf bond to produce a [(Ph3 As)Au-RhPfRf(CO)(AsPh3 )2 ] intermediate, followed by isomerization and reductive elimination of [AuRf(AsPh3 )]. Interesting differences were found between the LAu-Ar asymmetric oxidative insertion and the classical oxidative addition process of H2 to Vaska complexes.

Maternal intra- and postpartum near-miss following assisted reproductive technology: a retrospective study.

OBJECTIVE: To assess whether risk of severe maternal morbidity at delivery differs for women who conceived using assisted reproductive technology (ART), compared with those with a spontaneous conception. DESIGN: A cohort study using a prospectively maintained institutional database. SETTING: A tertiary university maternity hospital. POPULATION: All women delivering at Del Ponte Hospital, Italy, between 2005 and 2016. METHODS: Data from 650 ART-conceived pregnancies were compared with 22 803 spontaneously conceived pregnancies. We used multivariable analysis to estimate the odds of severe maternal morbidity at delivery associated with ART conception, adjusting for maternal demographic and health factors, gestational age, and mode of delivery. MAIN OUTCOME MEASURES: The World Health Organization criteria for potentially life-threatening conditions and near-miss maternal mortality were used. RESULTS: The incidence of near-miss in the entire cohort was 3.3 cases per 1000 births (95% confidence interval, 95% CI, 2.6-4.1). The crude prevalences of potentially life-threatening conditions and maternal near-miss were higher among ART than among non-ART deliveries (27.1 versus 5.7% and 2.6 versus 0.3%, respectively). The three most common causes of maternal near-miss cases were peripartum hysterectomy, transfusion of ≥5 units of red blood cells, and cardiovascular dysfunction requiring vasoactive drugs. The odds of a maternal near-miss at delivery were increased for ART-conceived pregnancies compared with non-ART-conceived pregnancies (adjusted odds ratio, aOR 3.61, 95% CI 1.61-8.09, for ART-conceived pregnancies with autologous oocytes; aOR 13.57, 95% CI 5.45-33.77, for ART pregnancies conceived with donor oocytes). CONCLUSION: Although we cannot exclude unmeasured confounding, we found that pregnancies conceived via ART, especially those conceived with donor oocytes, are at increased risk of maternal potentially life-threatening conditions and near-miss at delivery. FUNDING: This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. TWEETABLE ABSTRACT: Conceiving through assisted reproductive technology increases the likelihood of maternal near miss.

EMG activity of upper limb on spinal cord injury individuals during whole-body vibration.

Whole-body vibration (WBV) has shown positive results increasing electromyographic (EMG) activity and strength in a healthy population when applied to upper and lower limbs. The aim of this study was to verify if WBV increases the EMG signal of the upper limb muscles in patients with spinal cord injury (SCI). For this study, 15 patients with SCI were selected and one single session of WBV was applied to the upper limb. Five sessions of 30 s at 30 Hz were applied and EMG of anterior deltoid and forearm muscles was measured. The results show that EMG activity had a significant increase during WBV session compared with baseline muscle activity. These results support WBV as an efficient tool to increase the upper body EMG in individuals with SCI.

Principles for learning horizontal-planar arm movements with reversal.

PURPOSE: This study tested the hypothesis that muscle and interaction torques can be altered independently in order to improve in specific kinematics performance observed following practice. We also tested the hypothesis that a simple set of rules of EMG-control and kinetic-control models could explain the EMG and kinetic changes due to practice of movements with reversal. SCOPE: Kinematics of the upper arm with reversal, performed over three distances, was reconstructed using motion analysis. The muscle and interaction torques were calculated using inverse-dynamics. EMG activities of the major arm muscles were also recorded. The results demonstrate that improved performance is facilitated by an increase in muscle torque (and therefore acceleration) at the proximal joint (shoulder) and by an increase in the interaction torque at the distal joint (elbow). No changes were observed in the amount of muscle activity underlying these kinetic modifications, except for a decrease in the shoulder antagonist latency. CONCLUSION: The results confirm Bernstein's idea that the central nervous system takes advantage of the passive-interactive properties of the moving system. Also the modulation of the EMG patterns should be explained taking in account the reactive forces and the dual functions (maintenance of posture and generation of movement) of the muscles.