Formation of Strong Boron Lewis Acid Sites on Silica.

Bis(1-methyl-ortho-carboranyl)borane (HBMeoCb2) is a very strong Lewis acid that reacts with the isolated silanols present on silica partially dehydroxylated at 700 °C (SiO2-700) to form the well-defined Lewis site MeoCb2B(OSi≡) (1) and H2. 11B{1H} magic-angle spinning (MAS) nuclear magnetic resonance (NMR) data of 1 are consistent with that of a three-coordinate boron site. Contacting 1 with O═PEt3 (triethylphosphine oxide TEPO) and measuring 31P{1H} MAS NMR spectra show that 1 preserves the strong Lewis acidity of HBMeoCb2. Hydride ion affinity and fluoride ion affinity calculations using small molecules analogs of 1 also support the strong Lewis acidity of the boron sites in this material. Reactions of 1 with Cp2Hf(13CH3)2 show that the Lewis sites are capable of abstracting methide groups from Hf to form [Cp2Hf-13CH3][H313C-B(MeoCb2)OSi≡], but with a low overall efficiency.

Geometry and electronic structure of Yb(III)[CH(SiMe3)2]3 from EPR and solid-state NMR augmented by computations.

Characterization of paramagnetic compounds, in particular regarding the detailed conformation and electronic structure, remains a challenge, and - still today it often relies solely on the use of X-ray crystallography, thus limiting the access to electronic structure information. This is particularly true for lanthanide elements that are often associated with peculiar structural and electronic features in relation to their partially filled f-shell. Here, we develop a methodology based on the combined use of state-of-the-art magnetic resonance spectroscopies (EPR and solid-state NMR) and computational approaches as well as magnetic susceptibility measurements to determine the electronic structure and geometry of a paramagnetic Yb(III) alkyl complex, Yb(III)[CH(SiMe3)2]3, a prototypical example, which contains notable structural features according to X-ray crystallography. Each of these techniques revealed specific information about the geometry and electronic structure of the complex. Taken together, both EPR and NMR, augmented by quantum chemical calculations, provide a detailed and complementary understanding of such paramagnetic compounds. In particular, the EPR and NMR signatures point to the presence of three-centre-two-electron Yb-γ-Me-ß-Si secondary metal-ligand interactions in this otherwise tri-coordinate metal complex, similarly to its diamagnetic Lu analogues. The electronic structure of Yb(III) can be described as a single 4f13 configuration, while an unusually large crystal-field splitting results in a thermally isolated ground Kramers doublet. Furthermore, the computational data indicate that the Yb-carbon bond contains some π-character, reminiscent of the so-called α-H agostic interaction.

A Supported Ziegler-Type Organohafnium Site Metabolizes Polypropylene.

Cp2Hf(CH3)2 reacts with silica containing strong aluminum Lewis sites to form Cp2Hf-13CH3+ paired with aluminate anions. Solid-state NMR studies show that this reaction also forms neutral organohafnium and hafnium sites lacking methyl groups. Cp2Hf-13CH3+ reacts with isotatic polypropylene (iPP, Mn = 13.3 kDa; D = 2.4; mmmm = 94%; ∼110 C3H6/Hf) and H2 to form oils with moderate molecular weights (Mn = 290-1200 Da) in good yields. The aliphatic oils show characteristic 13C{1H} NMR properties consistent with complete loss of diastereoselectivity and formation of regioirregular errors under 1 atm H2. These results show that a Ziegler-Natta-type active site is compatible in a common reaction used to digest waste plastic into smaller aliphatic fragments.

Proximal Active Optical Sensing Operational Improvement for Research Using the CropCircle ACS-470, Implications for Measurement of Normalized Difference Vegetation Index (NDVI).

Active radiometric reflectance is useful to determine plant characteristics in field conditions. However, the physics of silicone diode-based sensing are temperature sensitive, where a change in temperature affects photoconductive resistance. High-throughput plant phenotyping (HTPP) is a modern approach using sensors often mounted to proximal based platforms for spatiotemporal measurements of field grown plants. Yet HTPP systems and their sensors are subject to the temperature extremes where plants are grown, and this may affect overall performance and accuracy. The purpose of this study was to characterize the only customizable proximal active reflectance sensor available for HTPP research, including a 10 °C increase in temperature during sensor warmup and in field conditions, and to suggest an operational use approach for researchers. Sensor performance was measured at 1.2 m using large titanium-dioxide white painted field normalization reference panels and the expected detector unity values as well as sensor body temperatures were recorded. The white panel reference measurements illustrated that individual filtered sensor detectors subjected to the same thermal change can behave differently. Across 361 observations of all filtered detectors before and after field collections where temperature changed by more than one degree, values changed an average of 0.24% per 1 °C. Recommendations based on years of sensor control data and plant field phenotyping agricultural research are provided to support ACS-470 researchers by using white panel normalization and sensor temperature stabilization.

Effects of surface acidity on the structure of organometallics supported on oxide surfaces.

Well-defined organometallics supported on high surface area oxides are promising heterogeneous catalysts. An important design factor in these materials is how the metal interacts with the functionalities on an oxide support, commonly anionic X-type ligands derived from the reaction of an organometallic M-R with an -OH site on the oxide. The metal can either form a covalent M-O bond or form an electrostatic M+⋯-O ion-pair, which impacts how well-defined organometallics will interact with substrates in catalytic reactions. A less common reaction pathway involves the reaction of a Lewis site on the oxide with the organometallic, resulting in abstraction to form an ion-pair, which is relevant to industrial olefin polymerization catalysts. This Feature Article views the spectrum of reactivity between an organometallic and an oxide through the prism of Brønsted and/or Lewis acidity of surface sites and draws analogies to the molecular frame where Lewis and Brønsted acids are known to form reactive ion-pairs. Applications of the well-defined sites developed in this article are also discussed.

Cationic Tantalum Hydrides Catalyze Hydrogenolysis and Alkane Metathesis Reactions of Paraffins and Polyethylene.

Sulfated aluminum oxide (SAO), a high surface area material containing sulfate anions that behave like weakly coordinating anions, reacts with Ta(═CHtBu)(CH2tBu)3 to form [Ta(CH2tBu)2(O-)2][SAO] (1). Subsequent treatment with H2 forms Ta-H+ sites supported on SAO that are active in hydrogenolysis and alkane metathesis reactions. In both reactions Ta-H+ is more active than related neutral Ta-H sites supported on silica. This reaction chemistry extends to melts of high-density polyethylene (HDPE), where Ta-H+ converts 30% of a low molecular weight HDPE (Mn = 2.5 kg mol-1; D = 3.6) to low molecular weight paraffins under hydrogenolysis conditions. Under alkane metathesis conditions Ta-H+ converts this HDPE to a high MW fraction (Mn = 6.2 kDa; D = 2.3) and low molecular weight alkane products (C13-C32). These results show that incorporating charge as a design element in supported d0 metal hydrides is a viable strategy to increase the reaction rate in challenging reactions involving reorganization of C-C bonds in alkanes.

Abdominal aortic aneurysm and exfoliation syndrome in Utah.

PURPOSE: A pilot study of electronic medical records (EMR) in Utah was undertaken to investigate exfoliation syndrome and exfoliation glaucoma (XFS/XFG) in abdominal aortic aneurysm (AAA) patients. In a subsequent retrospective cohort study of Utah XFS/XFG patients and population controls, the risk of AAA was examined. METHODS: EMR of a statewide healthcare population were obtained from the Utah Population Database (UPDB) which links decades of medical records with Utah demographic and vital records data. In a pilot study, 7167 patients ages ≥40 years identified with AAA diagnosed from 1996 to 2015, based on International Classification of Diseases (ICD) version 9/10 codes, were included. A univariable hazards model was used to determine the risk of XFS/XFG in AAA patients. An XFS/XFG outcome based on ICD 9/10 codes in AAA patients and in 5:1 sex- and age-matched non-AAA controls was determined. A retrospective cohort of 3412 XFS/XFG patients ages ≥50 years diagnosed from 1996 to 2020 and 10 227 3:1 sex- and age-matched controls who underwent ≥1 dilated eye examination(s) were recently identified and updated diagnoses of AAA were obtained. Multivariable logistic regression was used to estimate AAA risk in XFS/XFG patients compared with controls. In a subset of XFS/XFG patients, chart reviews were conducted to confirm clinically diagnosed AAA. RESULTS: In the AAA pilot, 20 patients (0.3%) and 118 controls (0.3%) developed XFS/XFG, respectively. We observed no increased risk of XFS/XFG in AAA patients compared with non-AAA-matched controls (HR = 0.99, 95% CI 0.6-1.6). Among XFS/XFG study patients and controls, 122 patients (3.6%) and 376 controls (3.7%) had an AAA diagnosis. We likewise observed no increased risk of AAA in XFS/XFG patients (OR = 0.97, 95% CI 0.8-1.2). In 14 XFS/XFG patients with an ICD 9/10 diagnosis of AAA who underwent chart review, a clinical diagnosis of AAA was confirmed in 9 patients (64.3%). CONCLUSION: Our findings do not support an association between AAA and XFS/XFG.

Abdominal aortic aneurysm and exfoliation syndrome: A literature review comparing single site findings.

Several studies have suggested a possible relationship between exfoliation syndrome (XFS) and abdominal aortic aneurysm (AAA). A systematic literature review was undertaken to investigate this potential association. The systematic literature review was performed according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Clear definitions of XFS and AAA were used to identify eligible studies via an unrestricted search of the PubMed interface from 1979 to October 31st, 2021. After review, 876 citations were gathered and evaluated for inclusion, from which 22 articles were included. Of these 22, 16 were excluded because they did not assess the relationship between AAA and XFS or provide primary data. Ultimately, six studies were included in this literature review. Half of the studies explored AAA prevalence in a population with or without XFS, and the other half explored the opposite. Three studies supported XFS as a risk factor for the development of AAA, and the other three found this relationship to be inconclusive. This systematic review revealed inconsistent results regarding an association between AAA and XFS. A large database study including XFS and AAA patients would be useful in further determining if an association does in fact exist.

Comparative Visual Outcome Analysis of a Diffractive Multifocal Intraocular Lens and a New Diffractive Multifocal Lens with Extended Depth of Focus.

This study compares the visual and refractive performance of the TECNIS Synergy (DFR00V-DFW150-225-300-375) multifocal intraocular lens (IOL) and the AcrySof IQ PanOptix (TFAT00-30-40-50-60) multifocal IOL. Patients who underwent phacoemulsification and cataract extraction and received either a multifocal Synergy or PanOptix IOL were included. Monocular uncorrected distance (UDVA), intermediate (UIVA), near (UNVA), and corrected distance (CDVA) visual acuities were assessed at three and six months postoperatively. Secondary outcome measures of photic phenomena were also assessed. A total of 140 patients (224 eyes) were included in this study, with 69 patients (105 eyes) in the Synergy group and 71 patients (119 eyes) in the PanOptix group. There were no statistically significant differences in UIVA or CDVA measurements across all time points. When assessing UDVA, at three months postoperatively, there were more eyes in the PanOptix group with vision better than 20/40 (p = 0.04). At three and six months postoperatively, the average UNVA was superior in the Synergy group (p = 0.01, 0.002). While the Synergy group reported more night vision disturbances at one and three months (p = 0.01, 0.03), the PanOptix group had more night vision disturbances at six months (p = 0.02). Although not statistically significant, the AcrySof IQ PanOptix multifocal IOL demonstrated better UDVA and UIVA sooner postoperatively than the TECNIS Synergy multifocal IOL. The Synergy IOL provided statistically better UNVA compared to the PanOptix IOL at three and six months postoperatively. Synergy patients reported more early photic phenomena than PanOptix patients, which later diminished.

Ring Contraction of a Tungstacyclopentane Supported on Silica: Direct Conversion of Ethylene to Propylene.

The reaction of W(NAr)(13C4H8)(OSiPh3)2 (1) (NAr = 2,6-diisopropylphenylimido) with silica partially dehydroxylated at 700 °C (SiO2-700) is highly dependent on the reaction conditions. The primary product of this reaction is W(NAr)(13C4H8)(OSiPh3)(OSi(O-)3) (2) when the reaction is carried out in the dark. Grafting 1 onto SiO2-700 in ambient lab light results in the formation of 2, W(NAr)(13CH213CH2)(OSiPh3)(OSi(O-)3) (4), and one isomer of square-pyramidal W(NAr)(13CH213CH(13Me)13CH2)(OSiPh3)(OSi(O-)3) (3). Heating 2 to 85 °C for 6 h results in the formation of 3, 4, W(NAr)(13CH(13Me)13CH213CH2)(OSiPh3)(OSi(O-)3) (5), and W(NAr)((13CH2)213CH(13Me)(13CH2)2)(OSiPh3)(OSi(O-)3) (6). Photolysis of 2 with blue LEDs (λmax = 450 nm) produces 4, both isomers of 3, 5, and free ethylene. In the presence of excess ethylene and blue LED irradiation at 85 °C, 1/SiO2-700 catalyzes the direct conversion of ethylene to propylene.

Exfoliation Syndrome and Exfoliation Glaucoma in the Navajo Nation.

(1) Background: Exfoliation syndrome (XFS) is a common cause of secondary open angle glaucoma. In 1971, Faulkner et al. estimated the prevalence of XFS among 50 Navajo Nation residents as 38%. Given that XFS can cause irreversible blindness secondary to glaucoma (XFG), this study aims to identify the current prevalence of XFS among Navajo Nation residents within the Four Corners region of the U.S. (2) Methods: A retrospective chart review was conducted from 2016 to 2021 for patients aged 18 and older. All patients with XFS or XFG diagnosed by slit lamp exam were identified through chart review. (3) Results: Of the 1152 patient charts available for review, eight patients (11 eyes) were diagnosed with XFS with three patients (4 eyes) demonstrating concomitant XFG. Within this XFS population, 50% of the patients identified as male, with a mean age of 73 years. The overall prevalence of XFS was 0.7% and the overall prevalence of XFG was found to be 0.26%. The rate of XFG among patients with XFS was 37.5%. (4) Conclusion: Compared to Faulkner's study of Navajo Nation residents in 1971, our findings show a considerably lower prevalence of XFS at 0.7%. We present the largest study to date of XFS among this population.

Formation of a Strong Heterogeneous Aluminum Lewis Acid on Silica.

Al(OC(CF3 )3 )(PhF) reacts with silanols present on partially dehydroxylated silica to form well-defined ≡SiOAl(OC(CF3 )3 )2 (O(Si≡)2 ) (1). 27 Al NMR and DFT calculations with a small cluster model to approximate the silica surface show that the aluminum in 1 adopts a distorted trigonal bipyramidal coordination geometry by coordinating to a nearby siloxane bridge and a fluorine from the alkoxide. Fluoride ion affinity (FIA) calculations follow experimental trends and show that 1 is a stronger Lewis acid than B(C6 F5 )3 and Al(OC(CF3 )3 )(PhF) but is weaker than Al(OC(CF3 )3 ) and i Pr3 Si+ . Cp2 Zr(CH3 )2 reacts with 1 to form [Cp2 ZrCH3 ][≡SiOAl(OC(CF3 )3 )2 (CH3 )] (3) by methide abstraction. This reactivity pattern is similar to reactions of organometallics with the proposed strong Lewis acid sites present on Al2 O3 .

Laser-Assisted In Situ Keratomileusis (LASIK) Enhancement for Residual Refractive Error after Primary LASIK.

Background: To evaluate the safety, efficacy, and predictability of laser-assisted in situ keratomileusis (LASIK) enhancement after primary LASIK and compare to Food and Drug Administration (FDA) criteria. Methods: Patients who underwent LASIK enhancement after primary LASIK between 2002 and 2019 were compared to those who underwent LASIK without retreatment. Patient demographics, preoperative characteristics, visual outcomes, and postoperative complications were compared between groups. Epithelial ingrowth (EI) development was stratified based on duration between primary and secondary procedures. Results: We compared 901 eyes with LASIK enhancement to 1127 eyes without retreatment. Age, sex, surgical eye, sphere, cylinder, and spherical equivalent (SE) were significantly different between groups (p < 0.05). At 12 months post-enhancement, 86% of the eyes had an uncorrected distance visual acuity of 20/20 or better and 93% of eyes were within ±0.50 D of the target. Development of EI (6.1%) demonstrated an odds ratio of 16.3 in the long-term compared to the short-term (95% CI: 5.9 to 45.18; p < 0.0001). Conclusions: Older age at primary LASIK, female sex, right eye, and larger sphere, cylinder and SE were risk factors for enhancement. Risk of EI significantly increased when duration between primary and enhancement procedures exceeded five years. LASIK enhancements produce favorable outcomes and meet FDA benchmarks for safety, efficacy, and predictability.

A Heterogeneous Iridium Catalyst for the Hydroboration of Pyridines.

Sulfated zirconium oxide (SZO) capped with silylium-like ions reacts with (cod)Ir(py)Cl (cod = 1,5-cyclooctadiene; py = pyridine) to form [Ir(cod)py][SZO] (1) and Me3SiCl. 1 can also be formed in reactions of phosphonium functionalized SZO and [Ir(cod)(OSi(OtBu)3]2, which forms [Ir(cod)P(tBu)2Ph][SZO] (2), followed by reaction with pyridine to form 1. FTIR and 15N{1H} MAS NMR spectroscopy are consistent with coordination of pyridine in 1 to an electrophilic iridium. 1 is moderately active in the dearomative hydroboration of pyridine. The primary product of this reaction is 1,2-dihydropyridine, which converts to the 1,4-dihydropyridine product at long reaction times. 1 catalyzes the dearomative hydroboration of a variety of substituted pyridines and is also reactive toward pyrazines and N-methylimidazole.

Tungstacyclopentane Ring Contraction Yields Olefin Metathesis Catalysts.

Exposure of a solution of the square pyramidal tungstacyclopentane complex W(NAr)(OSiPh3)2(C4H8) (Ar = 2,6-i-Pr2C6H3) to ethylene at 22 °C in ambient (fluorescent) light slowly leads to the formation of propylene and the square pyramidal tungstacyclobutane complex W(NAr)(OSiPh3)2(C3H6). No reaction takes place in the dark, but the reaction is >90% complete in ∼15 min under blue LED light (∼450 nm λmax). The intermediates are proposed to be (first) an α methyl tungstacyclobutane complex (W(NAr)(OSiPh3)2(αMeC3H5)), and then from it, a ß methyl version. The TBP versions of each can lose propylene and form a methylene complex, and in the presence of ethylene, the unsubstituted tungstacyclobutane complex W(NAr)(OSiPh3)2(C3H6). The W-Cα bond in an unobservable TBP W(NAr)(OSiPh3)2(C4H8) isomer in which the C4H8 ring is equatorial is proposed to be cleaved homolytically by light. A hydrogen atom moves or is moved from C3 to the terminal C4 carbon in the butyl chain as the bond between W and C3 forms to give the TBP α methyl tungstacyclobutane complex. Essentially, the same behavior is observed for W(NCPh3)(OSiPh3)2(C4H8) as for W(NAr)(OSiPh3)2(C4H8), except that the rate of consumption of W(NCPh3)(OSiPh3)2(C4H8) is about half that of W(NAr)(OSiPh3)2(C4H8). In this case, an α methyl-substituted tungstacyclobutane intermediate is observed, and the overall rate of formation of W(NCPh3)(OSiPh3)2(C3H6) and propylene from W(NCPh3)(OSiPh3)2(C4H8) is ∼20 times slower than in the NAr system. These results constitute the first experimentally documented examples of forming a metallacyclobutane ring from a metallacyclopentane ring (ring contraction) and establish how metathesis-active methylene and metallacyclobutane complexes can be formed and reformed in the presence of ethylene. They also raise the possibility that ambient light could play a role in some metathesis reactions that involve ethylene and tungsten-based imido alkylidene olefin metathesis catalysts, if not others.

The coordination chemistry of oxide and nanocarbon materials.

Understanding how a ligand affects the steric and electronic properties of a metal is the cornerstone of the inorganic chemistry enterprise. What happens when the ligand is an extended surface? This question is central to the design and implementation of state-of-the-art functional materials containing transition metals. This perspective will describe how these two very different sets of extended surfaces can form well-defined coordination complexes with metals. In the Green formalism, functionalities on oxide surfaces react with inorganics to form species that contain X-type or LX-type interactions between the metal and the oxide. Carbon surfaces are neutral L-type ligands; this perspective focuses on carbons that donate six electrons to a metal. The nature of this interaction depends on the curvature, and thereby orbital overlap, between the metal and the extended π-system from the nanocarbon.

Bilateral posterior central corneal steepening with decreased visual acuity.

A 40-year-old woman was referred for the assessment of bilateral corneal opacities with gradual visual decline over the course of the past decade. Her past ocular history is significant for bilateral amblyopia and strabismus surgery in both eyes before age 5. The patient's parents were told by her childhood ophthalmologist that she had a hereditary disorder. Her systemic review was significant for anal fissure and human leukocyte antigen-B27 ankylosing spondylitis. Her past ocular record revealed corrected distance visual acuity (CDVA) of 20/80 in both eyes in 2018 with central corneal haze. On presentation, her uncorrected distance visual acuity was 20/150 in both eyes. Her CDVA was 20/100 in both eyes with manifest refraction of +0.50 -2.50 × 075 in the right eye and +5.00 -2.25 × 094 in the left eye. Corneal topography reflected keratometry of 35.75/38.97 × 171 in the right eye and 36.45/38.35 × 32 in the left eye. Central corneal thickness was 669 µm and 652 µm, respectively. External slitlamp examination revealed a central faint stromal opacity inferior to the visual axis in the right eye and a central faint stromal opacity in the left eye, and both were associated with steep posterior curvature of the cornea (Figure 1). Further findings included 0.5 corneal haze with mild guttata, normal irides, and clear lenses in both eyes. Intraocular pressure was 23 mm Hg and 26 mm Hg, respectively (Figure 2, Supplemental Figures 1 and 2, http://links.lww.com/JRS/A543). Gonioscopy was unremarkable. Dilated fundus examination revealed a 0.15 cup-to-disc ratio bilaterally, but otherwise no pertinent vitreoretinal pathologies were noted. What is the most likely diagnosis? What medical or surgical interventions would you recommend for this patient? What is the prognosis for this patient?

A Heterogeneous Palladium Catalyst for the Polymerization of Olefins Prepared by Halide Abstraction Using Surface R3 Si+ Species.

The silylium-like surface species [i Pr3 Si][(RF O)3 Al-OSi≡)] activates (N^N)Pd(CH3 )Cl (N^N=Ar-N=CMeMeC=N-Ar, Ar=2,6-bis(diphenylmethyl)-4-methylbenzene) by chloride ion abstraction to form [(N^N)Pd-CH3 ][(RF O)3 Al-OSi≡)] (1). A combination of FTIR, solid-state NMR spectroscopy, and reactions with CO or vinyl chloride establish that 1 shows similar reactivity patterns as (N^N)Pd(CH3 )Cl activated with Na[B(ArF )4 ]. Multinuclear 13 C{27 Al} RESPDOR and 1 H{19 F} S-REDOR experiments are consistent with a weakly coordinated ion-pair between (N^N)Pd-CH3 + and [(RF O)3 Al-OSi≡)]. 1 catalyzes the polymerization of ethylene with similar activities as [(N^N)Pd-CH3 ]+ in solution and incorporates up to 0.4 % methyl acrylate in copolymerization reactions. 1 produces polymers with significantly higher molecular weight than the solution catalyst, and generates the highest molecular weight polymers currently reported in copolymerization reactions of ethylene and methylacrylate.

Solid-state 11B NMR studies of coinage metal complexes containing a phosphine substituted diboraanthracene ligand.

Transition metal interactions with Lewis acids (M → Z linkages) are fundamentally interesting and practically important. The most common Z-type ligands contain boron, which contains an NMR active 11B nucleus. We measured solid-state 11B{1H} NMR spectra of copper, silver, and gold complexes containing a phosphine substituted 9,10-diboraanthracene ligand (B2P2) that contain planar boron centers and weak M → BR3 linkages ([(B2P2)M][BArF4] (M = Cu (1), Ag (2), Au (3)) characterized by large quadrupolar coupling (CQ) values (4.4-4.7 MHz) and large span (Ω) values (93-139 ppm). However, the solid-state 11B{1H} NMR spectrum of K[Au(B2P2)]- (4), which contains tetrahedral borons, is narrow and characterized by small CQ and Ω values. DFT analysis of 1-4 shows that CQ and Ω are expected to be large for planar boron environments and small for tetrahedral boron, and that the presence of a M → BR3 linkage relates to the reduction in CQ and 11B NMR shielding properties. Thus solid-state 11B NMR spectroscopy contains valuable information about M → BR3 linkages in complexes containing the B2P2 ligand.