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Phenanthracene nanotubes with arylene-ethynylenebutadiynylene rims and phenanthracene walls are synthesized in a modular bottom-up approach. One of the rims carries hexadecyloxy side chains, mediating the affinity to highly oriented pyrolytic graphite. Molecular dynamics simulations show that the nanotubes are much more flexible than their structural formulas suggest: In 12, the phenanthracene units act as hinges that flip the two macrocycles relative to each other to one of two possible sites, as quantum mechanical models suggest and scanning tunneling microscopy investigations prove. Unexpectedly, both theory and experiment show for 13 that the three phenanthracene hinges are deflected from the upright position, accompanied by a deformation of both macrocycles from their idealized sturdy macroporous geometry. This flexibility together with their affinity to carbon-rich substrates allows for an efficient host−guest chemistry at the solid/gas interface opening the potential for applications in single-walled carbon nanotube-based sensing, 

Cyclopentadienyl (Cp), a classic ancillary ligand platform, can be chemically noninnocent in electrocatalytic H−H bond formation reactions via protonation of coordinated η5-Cp ligands to form η4-CpH moieties. However, the kinetics of η5-Cp ring protonation, ligand-to-metal (or metal-to-ligand) proton transfer, and the influence of solvent during H2 production electrocatalysis remain poorly understood. We report in-depth kinetic details for electrocatalytic H2 production with Fe complexes containing amine-functionalized CpN3 ligands that are protonated via exogenous acid to generate via η4-CpN3H intermediates (CpN3 = 6-amino-1,4-dimethyl-5,7-diphenyl-2,3,4,6-tetrahydrocyclopenta[b]pyrazin-6-yl). Under reducing conditions, state-of-the-art DFT calculations reveal that a coordinated solvent plays a crucial role in mediating stereo- and regioselective proton transfer to generate (endo-CpN3H)Fe(CO)2(NCMe), with other protonation pathways being kinetically insurmountable. To demonstrate regioselective endo-CpN3H formation, the isoelectronic model complex (endo-CpN3H)Fe(CO)3 is independently prepared, and kinetic studies with the on-cycle hydride intermediate CpN3FeH(CO)2 under CO cleanly furnish the ring-activated complex (endo-CpN3H)Fe(CO)3 via metal-to-ligand proton migration. The on-cycle complex CpN3FeH(CO)2 reacts with acid to release H2 and regenerate [CpN3Fe(CO)2(NCMe)]+, which was found to be the TOF-determining step via DFT. Collectively, these experimental and computational results underscore the emerging importance of Cp ring activation, inner-sphere solvation, and metal−ligand cooperativity to perform proton-coupled electron transfer catalysis for chemical fuel synthesis. 

Herein is reported the structural characterization and scalable preparation of the elusive iron–phosphido complex FpP( t Bu)(F) (2-F, Fp = (Fe(η 5 -C 5 H 5 )(CO) 2 )) and its precursor FpP( t Bu)(Cl) (2-Cl) in 51% and 71% yields, respectively. These phosphide complexes are proposed to be relevant to an organoiron catalytic cycle for phosphinidene transfer to electron-deficient alkenes. Examination of their properties led to the discovery of a more efficient catalytic system involving the simple, commercially available organoiron catalyst Fp 2 . This improved catalysis also enabled the preparation of new phosphiranes with high yields ( t BuPCH 2 CHR; R = CO 2 Me, 41%; R = CN, 83%; R = 4-biphenyl, 73%; R = SO 2 Ph, 71%; R = POPh 2 , 70%; R = 4-pyridyl, 82%; R = 2-pyridyl, 67%; R = PPh 3 + , 64%) and good diastereoselectivity, demonstrating the feasibility of the phosphinidene group-transfer strategy in synthetic chemistry. Experimental and theoretical studies suggest that the original catalysis involves 2-X as the nucleophile, while for the new Fp 2 -catalyzed reaction they implicate a diiron–phosphido complex Fp 2 (P t Bu), 4, as the nucleophile which attacks the electron-deficient olefin in the key first P–C bond-forming step. In both systems, the initial nucleophilic attack may be accompanied by favorable five-membered ring formation involving a carbonyl ligand, a (reversible) pathway competitive with formation of the three-membered ring found in the phosphirane product. A novel radical mechanism is suggested for the new Fp 2 -catalyzed system.