Contrasting Protonation Behavior of Diphosphido vs Dithiolato Diiron(I) Carbonyl Complexes

This paper reports on the protonation of phosphine-substituted diiron diphosphido carbonyls, analogues of diiron dithiolato centers at the active sites of hydrogenase enzymes. Reaction of the diphosphines (CH₂)_<i>n</i>(PPhH)₂ (<i>n</i> = 2 (edpH₂) and <i>n</i> = 3 (pdpH₂)) with Fe₃(CO)₁₂ gave excellent yields of Fe₂(edp)­(CO)₆ (<b>1</b>) and Fe₂(pdp)­(CO)₆ (<b>2</b>). Substitution of Fe₂(edp)­(CO)₆ with PMe₃ afforded Fe₂(edp)­(CO)₂(PMe₃)₄ (<b>3</b>; ν_CO 1855 and 1836 cm^–1). Crystallographic analysis showed that <b>3</b> adopts an idealized <i>C</i>₂ symmetry, with pairs of phosphine ligands occupying apical–basal sites on each Fe center. Relative to that in the dithiolato complex, the Fe–Fe bond (2.7786(8) Å) is elongated by 0.15 Å. Treatment of <b>3</b> with H­(OEt₂)₂BAr^F₄ (Ar^F = C₆H₃-3,5-(CF₃)₂) gave exclusively the <i>C</i>₂-symmetric μ-hydride complex [HFe₂(edp)­(CO)₂(PMe₃)₄]⁺. This result contrasts with the behavior of the analogous ethanedi<i>thiolate</i> Fe₂(edt)­(CO)₂(PMe₃)₄ (edt = 1,2-C₂H₄S₂), protonation of which gives both the bridging <i>and terminal</i> hydride complexes. This difference points to the participation of the sulfur centers in the formation of terminal hydrides. The absence of terminal hydride intermediates was also revealed in the protonation of the diphosphine diphosphido complexes Fe₂(pdp)­(CO)₄(dppv) (<b>4</b>; dppv = <i>cis</i>-1,2-C₂H₂(PPh₂)₂) and Fe₂(edp)­(CO)₄(dppbz) (<b>5</b>; dppbz = 1,2-C₆H₄(PPh₂)₂). Protonation of these diphosphine complexes afforded μ-hydrido cations with apical–basal diphosphine ligands, which convert to the isomer where the diphosphine is dibasal. In contrast, protonation of the dithiolato complex Fe₂(pdt)­(CO)₄(dppv) gave terminal hydrides, which isomerize to μ-hydrides. In a competition experiment, <b>4</b> was shown to protonate faster than Fe₂(pdt)­(CO)₄(dppv)

Barriers and facilitators to vaccination uptake against COVID-19, influenza, and pneumococcal pneumonia in immunosuppressed adults with immune-mediated inflammatory diseases: A qualitative interview study during the COVID-19 pandemic

Objectives: To explore barriers and facilitators to COVID-19, influenza, and pneumococcal vaccine uptake in immunosuppressed adults with immune-mediated inflammatory diseases (IMIDs).  Methods: Recruiting through national patient charities and a local hospital, participants were invited to take part in an in-depth, one-to-one, semi-structured interview with a trained qualitative researcher between November 2021 and January 2022. Data were analysed thematically in NVivo, cross-validated by a second coder and mapped to the SAGE vaccine hesitancy matrix.  Results: Twenty participants (75% female, 20% non-white) were recruited. Barriers and facilitators spanned contextual, individual/group and vaccine/vaccination-specific factors. Key facilitators to all vaccines were higher perceived infection risk and belief that vaccination is beneficial. Key barriers to all vaccines were belief that vaccination could trigger IMID flare, and active IMID. Key facilitators specific to COVID-19 vaccines included media focus, high incidence, mass-vaccination programme with visible impact, social responsibility, and healthcare professionals’ (HCP) confirmation of the new vaccines’ suitability for their IMID. Novel vaccine technology was a concern, not a barrier. Key facilitators of influenza/pneumococcal vaccines were awareness of eligibility, direct invitation, and, clear recommendation from trusted HCP. Key barriers of influenza/pneumococcal vaccines were unaware of eligibility, no direct invitation or recommendation from HCP, low perceived infection risk, and no perceived benefit from vaccination.  Conclusions: Numerous barriers and facilitators to vaccination, varying by vaccine-type, exist for immunosuppressed-IMID patients. Addressing vaccine benefits and safety for IMID-patients in clinical practice, direct invitation, and public-health messaging highlighting immunosuppression as key vaccination-eligibility criteria may optimise uptake, although further research should assess this.</p