Group 6 complexes as electrocatalysts of CO2 reduction: strong substituent control of the reduction path of [Mo(η3-allyl)(CO)2(x,x′- dimethyl-2,2′-bipyridine)(NCS)] (x = 4-6)

A series of complexes [Mo(η3-allyl)(CO)2)(x,x′-dmbipy)(NCS)] (dmbipy = dimethyl-2,2ʹ-bipyridine; x = 4-6) have been synthesized and their electrochemical reduction investigated using combined cyclic voltammetry (CV) and variable-temperature spectroelectrochemistry (IR/UV-vis SEC) in tetrahydrofuran (THF) and butyronitrile (PrCN), at gold and platinum electrodes. The experimental results, strongly supported by DFT calculations, indicate that the general cathodic path of these Group-6 organometallic complexes is closely related to that of the intensively studied class of Mn tricarbonyl α-diimine complexes, themselves recently identified as important smart materials for catalytic CO2 reduction. The dimethyl substitution on the 2,2ʹ-bipyridine ligand backbone has presented new insights into this emerging class of catalysts. For the first time, the 2e‒ reduced 5-coordinate anions [Mo(η3-allyl)(CO)2)(x,x′-dmbipy)]‒ were directly observed with IR SEC. The role of steric and electronic effects in determining the reduction-induced reactivity was also investigated. For the 6,6′-dmbipy, the primary 1e‒ reduced radical anions exert unusual stability radically changing the follow up cathodic path. The 5-coordinate anion [Mo(η3-allyl)(CO)2)(6,6′-dmbipy)]‒ remains stable at low temperature in strongly coordinating butyronitrile and does not undergo dimerization at elevated temperature, in sharp contrast to reactive [Mo(η3-allyl)(CO)2)(4,4′-dmbipy)]‒ that tends to dimerize in a reaction with the parent complex. The complex with the 5,5′-dmbipy ligand combines both types of reactivity. Under aprotic conditions, the different properties of [Mo(η3-allyl)(CO)2)(x,x′-dmbipy)]‒ are also reflected in their reactivity towards CO2. Preliminary CV and IR SEC results reveal differences in the strength of CO2 coordination at the free axial position. Catalytic waves attributed to the generation of the 5-coordinate anions were observed by CV, but only a modest catalytic performance towards the production of formate was demonstrated by IR SEC. For 6,6′-dmbipy, a stronger catalytic effect was observed for the Au cathode compared to Pt

Effect of the 2-R-Allyl and Chloride Ligands on the Cathodic Paths of [Mo(η3-2-R-allyl)(α-diimine)(CO)2Cl] (R = H, CH3; α-diimine = 6,6′-Dimethyl-2,2′-bipyridine, Bis(p-tolylimino)acenaphthene)

The new, formally Mo(II) complexes [Mo(η3-2-R-allyl)(6,6′-dmbipy)(CO)2Cl] (6,6′-dmbipy = 6,6′-dimethyl-2,2′-bipyridine; 2-R-allyl = allyl for R = H, 2-methallyl for R = CH3) and [Mo(η3-2-methallyl)(pTol-bian)(CO)2Cl] (pTol-bian = bis(p-tolylimino)acenaphthene) share, in this rare case, the same structural type. The effect of the anionic π-donor ligand X (Cl– vs NCS–) and the 2-R-allyl substituents on the cathodic behavior was explored. Both ligands play a significant role at all stages of the reduction path. While 2e–-reduced [Mo(η3-allyl)(6,6′-dmbipy)(CO)2]− is inert when it is ECE-generated from [Mo(η3-allyl)(6,6′-dmbipy)(CO)2(NCS)], the Cl– ligand promotes Mo–Mo dimerization by facilitating the nucleophilic attack of [Mo(η3-allyl)(6,6′-dmbipy)(CO)2]− at the parent complex at ambient temperature. The replacement of the allyl ligand by 2-methallyl has a similar effect. The Cl–/2-methallyl ligand assembly destabilizes even primary radical anions of the complex containing the strongly π-accepting pTol-Bian ligand. Under argon, the cathodic paths of [Mo(η3-2-R-allyl)(6,6′-dmbipy)(CO)2Cl] terminate at ambient temperature with 5-coordinate [Mo(6,6′-dmbipy)(CO)3]2– instead of [Mo(η3-2-R-allyl)(6,6′-dmbipy)(CO)2]−, which is stabilized in chilled electrolyte. [Mo(η3-allyl)(6,6′-dmbipy)(CO)2]− catalyzes CO2 reduction only when it is generated at the second cathodic wave of the parent complex, while [Mo(η3-2-methallyl)(6,6′-dmbipy)(CO)2]− is already moderately active at the first cathodic wave. This behavior is fully consistent with absent dimerization under argon on the cyclic voltammetric time scale. The electrocatalytic generation of CO and formate is hampered by the irreversible formation of anionic tricarbonyl complexes replacing reactive [Mo(η3-2-methallyl)(6,6′-dmbipy)(CO)2]2 along the cathodic route

One step forward towards the development of eco-friendly antifouling coatings: Immobilization of a sulfated marine-inspired compound

Marine biofouling represents a global economic and ecological challenge and few eco-friendly antifouling agents are available. The aim of this work was to establish the proof of concept that a recently synthesized nature-inspired compound (gallic acid persulfate, GAP) can act as an eco-friendly and effective antifoulant when immobilized in coatings through a non-release strategy, promoting a long-lasting antifouling effect. The synthesis of GAP was optimized to provide quantitative yields. GAP water solubility was assessed, showing values higher than 1000 mg/mL. GAP was found to be stable in sterilized natural seawater with a half-life (DT50) of 7 months. GAP was immobilized into several commercial coatings, exhibiting high compatibility with different polymeric matrices. Leaching assays of polydimethylsiloxane and polyurethane-based marine coatings containing GAP confirmed that the chemical immobilization of GAP was successful, since releases up to fivefold lower than the conventional releasing systems of polyurethane-based marine coatings were observed. Furthermore, coatings containing immobilized GAP exhibited the most auspicious anti-settlement effect against Mytilus galloprovincialis larvae for the maximum exposure period (40 h) in laboratory trials. Overall, GAP promises to be an agent capable of improving the antifouling activity of several commercial marine coatings with desirable environmental properties.This research was funded by national funds through the Foundation for Science and Technology (FCT) within the scope of research unit grants to CIIMAR (UIDB/04423/2020 and UIDP/04423/2020), to BioISI (UIDB/04046/2020 and UIDP/04046/2020) and under the project PTDC/AAG-TEC/0739/2014 (reference POCI-01-0145-FEDER-016793) supported through national funds provided by FCT and the European Regional Development Fund (ERDF) via the Programa Operacional Factores de Competitividade (POFC/COMPETE) programme and the Reforçar a Investigação, o Desenvolvimento Tecnológico e a Inovação (RIDTI; project 9471)

Determining adsorbate configuration on alumina surfaces with 13C nuclear magnetic resonance relaxation time analysis

Relative strengths of surface interaction for individual carbon atoms in acyclic and cyclic hydrocarbons adsorbed on alumina surfaces are determined using chemically resolved 13C nuclear magnetic resonance (NMR) T1 relaxation times. The ratio of relaxation times for the adsorbed atoms T1,ads to the bulk liquid relaxation time T1,bulk provides an indication of the mobility of the atom. Hence a low T1,ads/T1,bulk ratio indicates a stronger surface interaction. The carbon atoms associated with unsaturated bonds in the molecules are seen to exhibit a larger reduction in T1 on adsorption relative to the aliphatic carbons, consistent with adsorption occurring through the carbon-carbon multiple bonds. The relaxation data are interpreted in terms of proximity of individual carbon atoms to the alumina surface and adsorption conformations are inferred. Furthermore, variations of interaction strength and molecular configuration have been explored as a function of adsorbate coverage, temperature, surface pre-treatment, and in the presence of co-adsorbates. This relaxation time analysis is appropriate for studying the behaviour of hydrocarbons adsorbed on a wide range of catalyst support and supported-metal catalyst surfaces, and offers the potential to explore such systems under realistic operating conditions when multiple chemical components are present at the surface

Complex internal rearrangement processes triggered by electron transfer to acetic acid

We present negative ion formation from collisions of 100 eV neutral potassium atoms with acetic acid (CH3COOH) and its deuterated analogue molecules (CH3COOD, CD3COOH). From the negative ion time-of-flight (TOF) mass spectra, OH- is the main fragment detected accounting on average for more than 25% of the total anion yield. The complex internal rearrangement processes triggered by electron transfer to acetic acid have been evaluated with the help of theoretical calculations at the DFT levels explaining the fragmentation channel yielding OH-

Silver(I) and copper(I) complexes with ferrocenyl ligands bearing imidazole or pyridyl substituents

The reactions between five ferrocenyl derivatives containing both a CO and at least an imidazole or pyridine nitrogen atom and AgPF6, AgOTf, or [Cu(NCCH3)4]PF6 precursors were studied. The ligand {[bis(2-pyridyl)amino]carbonyl}ferrocene (L3), derived from (2-pyridyl)amine, favored tetrahedral coordination of Ag+ (with two ligands) and of Cu+ (with two acetonitrile ligands left from the precursor). In all the other ligands, both metal centers coordinated linearly to two ligands, preferring the imidazole or pyridinic nitrogen to other nitrogen atoms (amine) or oxygen donors. When the counter anions were triflate, the crystal structure showed a dimerization of the complex, with the ferrocenyl moieties occupying cis positions, by means of a weak Ag⋯Ag interaction. This was shown experimentally in the crystal structure of complex [Ag(L1)2]OTf (L1 = ferrocenylimidazole) and in the presence of peaks corresponding to {Ag2(L2)3(OTf)}+ and {Ag2(L2)4(OTf)}+ in the mass spectra of [Ag(L2)2]OTf (L2 = ferrocenyl benzimidazole). In all complexes containing PF6, there was no evidence for dimerization. Indeed, in the crystal structure of [Ag(L2)2]PF6, the ferrocenyl moieties occupy trans positions and the metal centers are far from each other. DFT calculations showed that the energy of the cis and trans conformers is practically the same and the balance of crystal packing forces leads to dimerization when triflate is present.S.Q. thanks FCT for a postdoctoral fellowship (SFRH/BPD/11463/ 2002) and M.J.C. thanks FCT, POCI, and FEDER (project PPCDT/QUI/ 58925/2004). M.C.G. and A.L. thank the Dirección General de Investigación Científica y Técnica (CTQ2007-67273-C02-01) for financial support.Peer Reviewe