A Phase 2 Trial of Peresolimab for Adults with Rheumatoid Arthritis.

BACKGROUND: Peresolimab is a humanized IgG1 monoclonal antibody designed to stimulate the endogenous programmed cell death protein 1 (PD-1) inhibitory pathway. Stimulation of this pathway would be a novel approach to the treatment of patients with autoimmune or autoinflammatory diseases. METHODS: In this phase 2a, double-blind, randomized, placebo-controlled trial, we assigned, in a 2:1:1 ratio, adult patients with moderate-to-severe rheumatoid arthritis who had had an inadequate response to, a loss of response to, or unacceptable side effects with conventional synthetic disease-modifying antirheumatic drugs (DMARDs) or to biologic or targeted synthetic DMARDs to receive 700 mg of peresolimab, 300 mg of peresolimab, or placebo intravenously once every 4 weeks. The primary outcome was the change from baseline to week 12 in the Disease Activity Score for 28 joints based on the C-reactive protein level (DAS28-CRP). The DAS28-CRP ranges from 0 to 9.4, with higher scores indicating more severe disease. The primary comparison was between the 700-mg group and the placebo group. Secondary outcomes included the percentages of patients with American College of Rheumatology 20 (ACR20), ACR50, and ACR70 responses - defined as improvements from baseline of 20%, 50%, and 70% or more, respectively, in the numbers of tender and swollen joints and in at least three of five important domains - at week 12. RESULTS: At week 12, the change from baseline in the DAS28-CRP was significantly greater in the 700-mg peresolimab group than in the placebo group (least-squares mean change [±SE], -2.09±0.18 vs. -0.99±0.26; difference in change, -1.09 [95% confidence interval, -1.73 to -0.46]; P<0.001). The results of the analyses of secondary outcomes favored the 700-mg dose over placebo with respect to the ACR20 response but not with respect to the ACR50 and ACR70 responses. Adverse events were similar in the peresolimab and placebo groups. CONCLUSIONS: Peresolimab showed efficacy in a phase 2a trial in patients with rheumatoid arthritis. These results provide evidence that stimulation of the PD-1 receptor has potential efficacy in the treatment of rheumatoid arthritis. (Funded by Eli Lilly; ClinicalTrials.gov number, NCT04634253.).

Sex-Stratified Genome-Wide Association Study in the Spanish Population Identifies a Novel Locus for Lacunar Stroke.

BACKGROUND: Ischemic stroke (IS) represents a significant health burden globally, necessitating a better understanding of its genetic underpinnings to improve prevention and treatment strategies. Despite advances in IS genetics, studies focusing on the Spanish population and sex-stratified analyses are lacking. METHODS: A case-control genome-wide association study was conducted with 9081 individuals (3493 IS cases and 5588 healthy controls). IS subtypes using Trial of ORG 10172 in Acute Stroke Treatment criteria were explored in a sex-stratified approach. Replication efforts involved the MEGASTROKE, GIGASTROKE, and the UK Biobank international cohorts. Post-genome-wide association study analysis included: in silico proteomic analysis, gene-based analysis, quantitative trait loci annotation, transcriptome-wide association analysis, and bioinformatic analysis using chromatin accessibility data. RESULTS: Identified as associated with IS and its subtypes were 4 significant and independent loci. Replication confirmed 5p15.2 as a new locus associated with small-vessel occlusion stroke, with rs59970332-T as the lead variant (beta [SE], 0.13 [0.02]; P=4.34×10-8). Functional analyses revealed CTNND2 given proximity and its implication in pathways involved in vascular integrity and angiogenesis. Integration of Hi-C data identified additional potentially modulated genes, and in silico proteomic analysis suggested a distinctive blood proteome profile associated with the lead variant. Gene-set enrichment analyses highlighted pathways consistent with small-vessel disease pathogenesis. Gene-based associations with known stroke-related genes such as F2 and FGG were also observed, reinforcing the relevance of our findings. CONCLUSIONS: We found CTNND2 as a potential key molecule in small-vessel occlusion stroke risk, and predominantly in males. This study sheds light on the genetic architecture of IS in the Spanish population, providing novel insights into sex-specific associations and potential molecular mechanisms. Further research, including replication in larger cohorts, is essential for a comprehensive understanding of these findings and for their translation to clinical practice.

Tuning the Inorganic Core of a reduced Ni2Ge2 Cluster.

Tetranuclear cores (M-E)2 of transition metals (M) and tetrylenes (EII=Si, Ge, Sn) are key motifs in homogeneous and heterogeneous catalysis. They exhibit a continuum of M-M and E-E bonding within the inorganic core that leads to a variety of structures for which there are no specific synthetic methods. Herein, we report a series of highly reduced [Ni0GeII]2 squares solely stabilized by bulky terphenyl (C6H3-2,6-Ar2) ligands, for which we provide complementary and high-yielding syntheses. Reactivity studies with common Lewis bases (carbene and CO) evince that the structure of the (M-E)2 core can be transformed. We have investigated this core modification by computational means, offering a rationale to better understand the continuum of bonding across these clusters.

A Gold(I)-Acetylene Complex Synthesised using Single-Crystal Reactivity.

Using single-crystal to single-crystal solid/gas reactivity the gold(I) acetylene complex [Au(L1)(η2-HC≡CH)][BArF 4] is cleanly synthesized by addition of acetylene gas to single crystals of [Au(L1)(CO)][BArF 4] [L1=tris-2-(4,4'-di-tert-butylbiphenyl)phosphine, ArF=3,5-(CF3)2C6H3]. This simplest gold-alkyne complex has been characterized by single crystal X-ray diffraction, solution and solid-state NMR spectroscopy and periodic DFT. Bonding of HC≡CH with [Au(L1)]+ comprises both σ-donation and π-backdonation with additional dispersion interactions within the cavity-shaped phosphine.

Favipiravir in Patients With Early Mild-to-moderate Coronavirus Disease 2019 (COVID-19): A Randomized Controlled Trial.

BACKGROUND: Despite vaccination, many remain vulnerable to coronavirus disease 2019 (COVID-19) and its complications. Oral antivirals to prevent COVID-19 progression are vital. Based on perceived potency and clinical efficacy, favipiravir is widely used to treat COVID-19. Evidence from large randomized controlled trials (RCT) is lacking. METHODS: In this multicenter double-blinded placebo-controlled RCT, adults with early mild-to-moderate COVID-19 were 1:1 randomized to favipiravir or placebo. The study evaluated time to sustained clinical recovery (TT-SCR), COVID-19 progression, and cessation of viral shedding. RESULTS: Of 1187 analyzed patients across 40 centers, 83.3% were Hispanic, 89.0% unvaccinated, 70.3% severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) seronegative, and 77.8% had risk factors for COVID-19 progression. The median time from symptom presentation and from positive test to randomization was 3 and 2 days, respectively. There was no difference in TT-SCR (median of 7 days for both groups; P = .80), COVID-19 progression [11 patients each (1.9% vs 1.8%); P = .96], time to undetectable virus (median = 6 days, 95% confidence interval [CI] [6-8] vs 7 days, 95% CI [6-9]), or in undetectable virus by end of therapy (73.4% vs 72.3%; P = .94). Outcomes were consistent across the analyzed sub-groups. Adverse events were observed in 13.8% and 14.8% of favipiravir-treated and placebo-treated subjects, respectively. Uric acid elevation was more frequent among favipiravir-treated subjects (19.9% vs 2.8%). CONCLUSIONS: Favipiravir was well tolerated but lacked efficacy in TT-SCR, progression to severe COVID-19, or cessation of viral shedding and should not be used to treat patients with COVID-19. (Supported by Appili Therapeutics). CLINICAL TRIALS REGISTRATION: NCT04600895.

Donor-Acceptor Activation of Carbon Dioxide.

The activation and functionalization of carbon dioxide entails great interest related to its abundance, low toxicity and associated environmental problems. However, the inertness of CO2 has posed a challenge towards its efficient conversion to added-value products. In this review we discuss one of the strategies that have been widely used to capture and activate carbon dioxide, namely the use of donor-acceptor interactions by partnering a Lewis acidic and a Lewis basic fragment. This type of CO2 activation resembles that found in metalloenzymes, whose outstanding performance in catalytically transforming carbon dioxide encourages further bioinspired research. We have divided this review into three general sections based on the nature of the active sites: metal-free examples (mainly formed by frustrated Lewis pairs), main group-transition metal combinations, and transition metal heterobimetallic complexes. Overall, we discuss one hundred compounds that cooperatively activate carbon dioxide by donor-acceptor interactions, revealing a wide range of structural motifs.

Ischaemic stroke patients present sex differences in gut microbiota.

BACKGROUND: Gut microbiota plays a role in the pathophysiology of ischaemic stroke (IS) through the bidirectional gut-brain axis. Nevertheless, little is known about sex-specific microbiota signatures in IS occurrence. METHODS: A total of 89 IS patients and 12 healthy controls were enrolled. We studied the taxonomic differences of the gut microbiota between men and women with IS by shotgun metagenomic sequencing. To evaluate the causal effect of several bacteria on IS risk, we performed a two-sample Mendelian randomisation (MR) with inverse-variance weighting (IVW) using genome-wide association analysis (GWAS) summary statistics from two cohorts of 5959 subjects with genetic and microbiota data and 1,296,908 subjects with genetic and IS data, respectively. RESULTS: α-Diversity analysis measured using Observed Species (p = 0.017), Chao1 (p = 0.009) and Abundance-based Coverage Estimator (p = 0.012) indexes revealed that IS men have a higher species richness compared with IS women. Moreover, we found sex-differences in IS patients in relation to the phylum Fusobacteria, class Fusobacteriia, order Fusobacteriales and family Fusobacteriaceae (all Bonferroni-corrected p < 0.001). MR confirmed that increased Fusobacteriaceae levels in the gut are causally associated with an increased risk of IS (IVW p = 0.02, ß = 0.32). CONCLUSIONS: Our study is the first to indicate that there are gut microbiome differences between men and women with IS, identifying high levels of Fusobacteriaceae in women as a specific risk factor for IS. Incorporating sex stratification analysis is important in the design, analysis and interpretation of studies on stroke and the gut microbiota.

A Cavity-Shaped Gold(I) Fragment Enables CO2 Insertion into Au-OH and Au-NH Bonds.

A cavity-shaped linear gold(I) hydroxide complex acts as a platform to access unusual gold monomeric species. Notably, this sterically crowded gold fragment enables the trapping of CO2 via insertion into Au-OH and Au-NH bonds to form unprecedented monomeric gold(I) carbonate and carbamate complexes. In addition, we succeeded in the identification of the first gold(I) terminal hydride bearing a phosphine ligand. The basic nature of the Au(I)-hydroxide moiety is also explored through the reactivity toward other molecules containing acidic protons such as trifluoromethanesulfonic acid and terminal alkynes.

Unveiling the Latent Reactivity of Cp* Ligands (C5Me5-) toward Carbon Nucleophiles on an Iridium Complex.

The divergent reactivity of the cationic iridium complex [(η5-C5Me5)IrCl(PMe2ArDipp2)]+ (ArDipp2 = C6H3-2,6-(C6H3-2,6-iPr2)2) toward organolithium and Grignard reagents is described. The noninnocent behavior of the Cp* ligand, a robust spectator in the majority of stoichiometric and catalytic reactions, was manifested by its unforeseen electrophilic character toward organolithium reagents LiMe, LiEt, and LinBu. In these unconventional transformations, the metal center is only indirectly involved by means of the Ir(III)/Ir(I) redox cycle. In the presence of less nucleophilic organolithium reagents, the Cp* ligand also exhibits noninnocent behavior undergoing facile deprotonation, which is also concomitant with the reduction of the metal center. In turn, the weaker alkylating agents EtMgBr and MeMgBr effectively achieve the alkylation of the metal center. These reactive iridium(III) alkyls partake in subsequent reactions: while the ethyl complex undergoes ß-H elimination, the methyl derivative releases methane by a remote C-H bond activation. Computational studies, including the quantum theory of atoms in molecules (QTAIM), support that the preferential activation of the non-benzylic C-H bonds takes place via sigma-bond metathesis.

Genetic Architecture of Ischaemic Strokes after COVID-19 Shows Similarities with Large Vessel Strokes.

We aimed to analyse whether patients with ischaemic stroke (IS) occurring within eight days after the onset of COVID-19 (IS-COV) are associated with a specific aetiology of IS. We used SUPERGNOVA to identify genome regions that correlate between the IS-COV cohort (73 IS-COV cases vs. 701 population controls) and different aetiological subtypes. Polygenic risk scores (PRSs) for each subtype were generated and tested in the IS-COV cohort using PRSice-2 and PLINK to find genetic associations. Both analyses used the IS-COV cohort and GWAS from MEGASTROKE (67,162 stroke patients vs. 454,450 population controls), GIGASTROKE (110,182 vs. 1,503,898), and the NINDS Stroke Genetics Network (16,851 vs. 32,473). Three genomic regions were associated (p-value < 0.05) with large artery atherosclerosis (LAA) and cardioembolic stroke (CES). We found four loci targeting the genes PITX2 (rs10033464, IS-COV beta = 0.04, p-value = 2.3 × 10-2, se = 0.02), previously associated with CES, HS6ST1 (rs4662630, IS-COV beta = -0.04, p-value = 1.3 × 10-3, se = 0.01), TMEM132E (rs12941838 IS-COV beta = 0.05, p-value = 3.6 × 10-4, se = 0.01), and RFFL (rs797989 IS-COV beta = 0.03, p-value = 1.0 × 10-2, se = 0.01). A statistically significant PRS was observed for LAA. Our results suggest that IS-COV cases are genetically similar to LAA and CES subtypes. Larger cohorts are needed to assess if the genetic factors in IS-COV cases are shared with the general population or specific to viral infection.

Controlled Diels-Alder "Click" Strategy to Access Mechanically Aligned Main-Chain Liquid Crystal Networks.

Aligned liquid crystal polymers are materials of interest for electronic, optic, biological and soft robotic applications. The manufacturing and processing of these materials have been widely explored with mechanical alignment establishing itself as a preferred method due to its ease of use and widespread applicability. However, the fundamental chemistry behind the required two-step polymerization for mechanical alignment has limitations in both fabrication and substrate compatibility. In this work we introduce a new protection-deprotection approach utilizing a two-stage Diels-Alder cyclopentadiene-maleimide step-growth polymerization to enable mild yet efficient, fast, controlled, reproducible and user-friendly polymerizations, broadening the scope of liquid crystal systems. Thorough characterization of the films by DSC, DMA, POM and WAXD show the successful synthesis of a uniaxially aligned liquid crystal network with thermomechanical actuation abilities.

Biological Age Acceleration Is Lower in Women With Ischemic Stroke Compared to Men.

BACKGROUND: Stroke onset in women occurs later in life compared with men. The underlying mechanisms of these differences have not been established. Epigenetic clocks, based on DNA methylation (DNAm) profiles, are the most accurate biological age estimate. Epigenetic age acceleration (EAA) measures indicate whether an individual is biologically younger or older than expected. Our aim was to analyze whether sexual dichotomy at age of stroke onset is conditioned by EAA. METHODS: We used 2 DNAm datasets from whole blood samples of case-control genetic studies of ischemic stroke (IS), a discovery cohort of 374 IS patients (N women=163, N men=211), from GRECOS (Genotyping Recurrence Risk of Stroke) and SEDMAN (Dabigatran Study in the Early Phase of Stroke, New Neuroimaging Markers and Biomarkers) studies and a replication cohort of 981 IS patients (N women=411, N men=570) from BASICMAR register. We compared chronological age, 2 DNAm-based biomarkers of aging and intrinsic and extrinsic epigenetic age acceleration EAA (IEAA and extrinsic EAA, respectively), in IS as well as in individual IS etiologic subtypes. Horvath and Hannum epigenetic clocks were used to assess the aging rate. A proteomic study using the SOMAScan multiplex assay was performed on 26 samples analyzing 1305 proteins. RESULTS: Women present lower Hannum-extrinsic EAA values, whereas men have higher Hannum-extrinsic EAA values (women=-0.64, men=1.24, P=1.34×10-2); the same tendency was observed in the second cohort (women=-0.57, men=0.79, P=0.02). These differences seemed to be specific to cardioembolic and undetermined stroke subtypes. Additionally, 42 blood protein levels were associated with Hannum-extrinsic EAA (P<0.05), belonging to the immune effector process (P=1.54×10-6) and platelet degranulation (P<8.74×10-6) pathways. CONCLUSIONS: This study shows that sex-specific underlying biological mechanisms associated with stroke onset could be due to differences in biological age acceleration between men and women.

River Winds and Transport of Forest Volatiles in the Amazonian Riparian Ecoregion.

Volatile organic compounds (VOCs) emitted from forests are important chemical components that affect ecosystem functioning, atmospheric chemistry, and regional climate. Temperature differences between a forest and an adjacent river can induce winds that influence VOC fate and transport. Quantitative observations and scientific understanding, however, remain lacking. Herein, daytime VOC datasets were collected from the surface up to 500 m over the "Rio Negro" river in Amazonia. During time periods of river winds, isoprene, α-pinene, and ß-pinene concentrations increased by 50, 60, and 80% over the river, respectively. The concentrations at 500 m were up to 80% greater compared to those at 100 m because of the transport path of river winds. By comparison, the concentration of methacrolein, a VOC oxidation product, did not depend on river winds or height. The differing observations for primary emissions and oxidation products can be explained by the coupling of timescales among emission, reaction, and transport. This behavior was captured in large-eddy simulations with a coupled chemistry model. The observed and simulated roles of river winds in VOC fate and transport highlight the need for improved representation of these processes in regional models of air quality and chemistry-climate coupling.

Genome-Wide Studies in Ischaemic Stroke: Are Genetics Only Useful for Finding Genes?

Ischaemic stroke is a complex disease with some degree of heritability. This means that heritability factors, such as genetics, could be risk factors for ischaemic stroke. The era of genome-wide studies has revealed some of these heritable risk factors, although the data generated by these studies may also be useful in other disciplines. Analysis of these data can be used to understand the biological mechanisms associated with stroke risk and stroke outcome, to determine the causality between stroke and other diseases without the need for expensive clinical trials, or to find potential drug targets with higher success rates than other strategies. In this review we will discuss several of the most relevant studies regarding the genetics of ischaemic stroke and the potential use of the data generated.

ICA1L Is Associated with Small Vessel Disease: A Proteome-Wide Association Study in Small Vessel Stroke and Intracerebral Haemorrhage.

Small vessel strokes (SVS) and intracerebral haemorrhages (ICH) are acute outcomes of cerebral small vessel disease (SVD). Genetic studies combining both phenotypes have identified three loci associated with both traits. However, the genetic cis-regulation at the protein level associated with SVD has not been studied before. We performed a proteome-wide association study (PWAS) using FUSION to integrate a genome-wide association study (GWAS) and brain proteomic data to discover the common mechanisms regulating both SVS and ICH. Dorsolateral prefrontal cortex (dPFC) brain proteomes from the ROS/MAP study (N = 376 subjects and 1443 proteins) and the summary statistics for the SVS GWAS from the MEGASTROKE study (N = 237,511) and multi-trait analysis of GWAS (MTAG)-ICH−SVS from Chung et al. (N = 240,269) were selected. We performed PWAS and then a co-localization analysis with COLOC. The significant and nominal results were validated using a replication dPFC proteome (N = 152). The replicated results (q-value < 0.05) were further investigated for the causality relationship using summary data-based Mendelian randomization (SMR). One protein (ICA1L) was significantly associated with SVS (z-score = −4.42 and p-value = 9.6 × 10−6) and non-lobar ICH (z-score = −4.8 and p-value = 1.58 × 10−6) in the discovery PWAS, with a high co-localization posterior probability of 4. In the validation PWAS, ICA1L remained significantly associated with both traits. The SMR results for ICA1L indicated a causal association of protein expression levels in the brain with SVS (p-value = 3.66 × 10−5) and non-lobar ICH (p-value = 1.81 × 10−5). Our results show that the association of ICA1L with SVS and non-lobar ICH is conditioned by the cis-regulation of its protein levels in the brain.

Enhanced Dihydrogen Activation by Mononuclear Iridium(II) Compounds: A Mechanistic Study.

The organometallic chemistry of 4d and 5d transition metals has been vastly dominated by closed-shell states. The reactivity of their metalloradical species is though remarkable, albeit yet poorly understood and with limited mechanistic investigations available. In this work we report the synthesis and characterization of two mononuclear IrII species, including the first dinitrogen adduct. These compounds activate dihydrogen at a dissimilar rate, in the latter case several orders of magnitude faster than its IrI precursor. A combined experimental/computational investigation to ascertain the mechanism of this transformation in IrII compounds is reported.

Supported σ-Complexes of Li-C Bonds from Coordination of Monomeric Molecules of LiCH3 , LiCH2 CH3 and LiC6 H5 to Mo≣Mo Bonds.

LiCH3 and LiCH2 CH3 react with the complex [Mo2 (H)2 (µ-AdDipp2 )2 (thf)2 ] (1⋅thf) with coordination of two molecules of LiCH2 R (R=H, CH3 ) and formation of complexes [Mo2 {µ-HLi(thf)CH2 R}2 (AdDipp2 )2 ], 5⋅LiCH3 and 5⋅LiCH2 CH3 , respectively (AdDipp2 =HC(NDipp)2 ; Dipp=2,6-i Pr2 C6 H3 ; thf=C4 H8 O). Due to steric hindrance, only one molecule of LiC6 H5 adds to 1⋅thf generating the complex [Mo2 (H){µ-HLi(thf)C6 H5 }(µ-AdDipp2 )2 ], (4⋅LiC6 H5 ). Computational studies disclose the existence of five-center six-electron bonding within the H-Mo≣Mo-C-Li metallacycles, with a mostly covalent H-Mo≣Mo-C group and predominantly ionic Li-C and Li-H interactions. However, the latter bonds exhibit non-negligible covalency, as indicated by X-ray, computational data and the large one-bond 6,7 Li,1 H and 6,7 Li,13 C NMR coupling constants found for the three-atom H-Li-C chains. By contrast, the phenyl group in 4⋅LiC6 H5 coordinates in an η2 fashion to the lithium atom through the ipso and one of the ortho carbon atoms.

Divergent CO2 Activation by Tuning the Lewis Acid in Iron-Based Bimetallic Systems.

Bimetallic motifs mediate the selective activation and functionalization of CO2 in metalloenzymes and some recent synthetic systems. In this work, we build on the nascent concept of bimetallic frustrated Lewis pairs (FLPs) to investigate the activation and reduction of CO2 . Using the Fe0 fragment [(depe)2 Fe] (depe=1,2-bis(diethylphosphino)ethane) as base, we modify the nature of the partner Lewis acid to accomplish a divergent and highly chemoselective reactivity towards CO2 . [Au(PMe2 Ar)]+ irreversibly dissociates CO2 , Zn(C6 F5 )2 and B(C6 F5 )3 yield different CO2 adducts stabilized by push-pull interactions, while Al(C6 F5 )3 leads to a rare heterobimetallic C-O bond cleavage, and thus to contrasting reduced products after exposure to dihydrogen. Computational investigations provide a rationale for the divergent reactivity, while Energy Decomposition Analysis-Natural Orbital for Chemical Valence (EDA-NOCV) method substantiates the heterobimetallic bonding situation.

Coordination of LiH Molecules to Mo≣Mo Bonds: Experimental and Computational Studies on Mo2LiH2, Mo2Li2H4, and Mo6Li9H18 Clusters.

The reactions of LiAlH4 as the source of LiH with complexes that contain (H)Mo≣Mo and (H)Mo≣Mo(H) cores stabilized by the coordination of bulky AdDipp2 ligands result in the respective coordination of one and two molecules of (thf)LiH, with the generation of complexes exhibiting one and two HLi(thf)H ligands extending across the Mo≣Mo bond (AdDipp2 = HC(NDipp)2; Dipp = 2,6-iPr2C6H3; thf = tetrahydrofuran, C4H8O). A theoretical study reveals the formation of Mo-H-Li three-center-two-electron bonds, supplemented by the coordination of the Mo≣Mo bond to the Li ion. Attempts to construct a [Mo2{HLi(thf)H}3(AdDipp2)] molecular architecture led to spontaneous trimerization and the formation of a chiral, hydride-rich Mo6Li9H18 supramolecular organization that is robust enough to withstand the substitution of lithium-solvating molecules of tetrahydrofuran by pyridine or 4-dimethylaminopyridine.

Reductive C-C Coupling from Molecular Au(I) Hydrocarbyl Complexes: A Mechanistic Study.

Organometallic gold complexes are used in a range of catalytic reactions, and they often serve as catalyst precursors that mediate C-C bond formation. In this study, we investigate C-C coupling to form ethane from various phosphine-ligated gem-digold(I) methyl complexes including [Au2(µ-CH3)(PMe2Ar')2][NTf2], [Au2(µ-CH3)(XPhos)2][NTf2], and [Au2(µ-CH3)(tBuXPhos)2][NTf2] {Ar' = C6H3-2,6-(C6H3-2,6-Me)2, C6H3-2,6-(C6H2-2,4,6-Me)2, C6H3-2,6-(C6H3-2,6-iPr)2, or C6H3-2,6-(C6H2-2,4,6-iPr)2; XPhos = 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl; tBuXPhos = 2-di-tert-butylphosphino-2',4',6'-triisopropylbiphenyl; NTf2 = bis(trifluoromethyl sulfonylimide)}. The gem-digold methyl complexes are synthesized through reaction between Au(CH3)L and Au(L)(NTf2) {L = phosphines listed above}. For [Au2(µ-CH3)(XPhos)2][NTf2] and [Au2(µ-CH3)(tBuXPhos)2][NTf2], solid-state X-ray structures have been elucidated. The rate of ethane formation from [Au2(µ-CH3)(PMe2Ar')2][NTf2] increases as the steric bulk of the phosphine substituent Ar' decreases. Monitoring the rate of ethane elimination reactions by multinuclear NMR spectroscopy provides evidence for a second-order dependence on the gem-digold methyl complexes. Using experimental and computational evidence, it is proposed that the mechanism of C-C coupling likely involves (1) cleavage of [Au2(µ-CH3)(PMe2Ar')2][NTf2] to form Au(PR2Ar')(NTf2) and Au(CH3)(PMe2Ar'), (2) phosphine migration from a second equivalent of [Au2(µ-CH3)(PMe2Ar')2][NTf2] aided by binding of the Lewis acidic [Au(PMe2Ar')]+, formed in step 1, to produce [Au2(CH3)(PMe2Ar')][NTf2] and [Au2(PMe2Ar')]+, and (3) recombination of [Au2(CH3)(PMe2Ar')][NTf2] and Au(CH3)(PMe2Ar') to eliminate ethane.