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In this contribution, we describe a post-assembly modification approach to selectively coordinate transition metals in Pd 12 L 24 cuboctahedra. The herein reported approach involves the preparation of Pd 12 L 24 nanospheres with protonated nitrogen donor ligands that are covalently linked at the interior. The so obtained Pd 12 (LH + ) 24 nanospheres are shown to be suitable for coordinative post-modification after deprotection by deprotonation. Selective formation of tetra-coordinated M B in Pd 12 M B 6 L 24 , tri-coordinated M B in Pd 12 M B 8 L 24 nanospheres and two-coordinated M B in Pd 12 M B 12 L 24 nanospheres is achieved as a result of different nitrogen donor ligands. A combination of pulsed EPR spectroscopy (DEER) to measure Cu-Cu distances in the different spheres, NMR studies and computational investigations, support the presence of the complexes at precise locations of the Pd 12 M B 6 L 24 nanosphere. The general post-assembly modification methodology can be extended using other transition metal precursors or supramolecular systems and can guide precise formation and investigation of novel transition metal-complex containing nanospheres with well-defined composition., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

There is an increasing interest in the application of metal-organic cages (MOCs) in a biomedicinal context, as they can offer non-classical distribution in organisms compared to molecular substrates, while revealing novel cytotoxicity mechanisms. Unfortunately, many MOCs are not sufficiently stable under in vivo conditions, making it difficult to study their structure-activity relationships in living cells. As such, it is currently unclear whether MOC cytotoxicity stems from supramolecular features or their decomposition products. Herein, we describe the toxicity and photophysical properties of highly-stable rhodamine functionalized platinum-based Pt 2 L 4 nanospheres as well as their building blocks under in vitro and in vivo conditions. We show that in both zebrafish and human cancer cell lines, the Pt 2 L 4 nanospheres demonstrate reduced cytotoxicity and altered biodistribution within the body of zebrafish embryos compared to the building blocks. We anticipate that the composition-dependent biodistribution of Pt 2 L 4 spheres together with their cytotoxic and photophysical properties provides the fundament for MOC application in cancer therapy., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Several metalloenzymes, including [FeFe]-hydrogenase, employ cofactors wherein multiple metal atoms work together with surrounding ligands that mediate heterolytic and concerted proton-electron transfer (CPET) bond activation steps. Herein, we report a new dinucleating PNNP expanded pincer ligand, which can bind two low-valent iron atoms in close proximity to enable metal-metal cooperativity (MMC). In addition, reversible partial dearomatization of the ligand's naphthyridine core enables both heterolytic metal-ligand cooperativity (MLC) and chemical non-innocence through CPET steps. Thermochemical and computational studies show how a change in ligand binding mode can lower the bond dissociation free energy of ligand C(sp 3 )-H bonds by ∼25 kcal mol -1 . H-atom abstraction enabled trapping of an unstable intermediate, which undergoes facile loss of two carbonyl ligands to form an unusual paramagnetic ( S = ) complex containing a mixed-valent iron(0)-iron(i) core bound within a partially dearomatized PNNP ligand. Finally, cyclic voltammetry experiments showed that these diiron complexes show catalytic activity for the electrochemical hydrogen evolution reaction. This work presents the first example of a ligand system that enables MMC, heterolytic MLC and chemical non-innocence, thereby providing important insights and opportunities for the development of bimetallic systems that exploit these features to enable new (catalytic) reactivity., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Supramolecular self-assemblies are used across various fields for different applications including their use as containers for catalysts, drugs and fluorophores. M 12 L 24 spheres are among the most studied, as they offer plenty of space for functionalization, yielding systems with unique properties in comparison to their single components. Detailed studies on the formation of M 12 L 24 structures using palladium cornerstones (that have generally dynamic coordination chemistry) aided in the development of synthetic protocols. The more robust platinum-based systems received thus far much less attention. The general use of platinum-based assemblies remains elusive as parameters and design principles of the ligand building blocks are not fully established. As platinum-based nanospheres are more robust due to the kinetically more stable nitrogen-platinum bond, we studied the sphere formation process in detail in order to develop descriptors for the formation of platinum-based nanospheres. In a systematic study, using time-dependent mass spectrometry, 1 H-NMR and DOSY NMR, we identified new kinetically trapped intermediates during the formation of Pt 12 L 24 spheres and we developed key parameters for selective formation of Pt 12 L 24 spheres. Molecular mechanics calculations and experimental result support the importance of charge and steric bulk placed at the endo -site of the ditopic linker for selective sphere formation. Applicability of these principles is demonstrated by employing various ditopic ligands with different bend-angles for the synthesis of a range of Pt 2 L 4 , Pt 3 L 6 , Pt 4 L 8 and Pt 12 L 24 polyhedra with platinum cornerstones in excellent yields, thus paving the way for future applications of well-defined robust platinum nanospheres of different shapes and sizes with the general composition Pt n L 2 n ., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Herein, we report a supramolecular rhodium complex that can form dimeric or monomeric Rh-species catalytically active in hydroformylation, depending on the binding of effectors within the integrated DIM-receptor. X-ray crystal structures, in situ (high-pressure (HP)) spectroscopy studies, and molecular modelling studies show that in the absence of effectors, the preferred Rh-species formed is the dimer, of which two ligands coordinate to two rhodium metals. Importantly, upon binding guest molecules, -effectors-, to the DIM-receptor under hydroformylation conditions, the monomeric Rh-active species is formed, as evidenced by a combination of in situ HP NMR and IR spectroscopy studies and molecular modelling. As the monomeric complex has different catalytic properties from the dimeric complex, we effectively generate a catalytic system of which the properties respond to the presence of effectors, reminiscent of how the properties of proteins are regulated in nature. Indeed, catalytic and kinetic experiments show that both the selectivity and activity of this supramolecular catalytic system can be influenced in the hydroformylation of 1-octene using acetate as an effector that shift the equilibrium from the dimeric to monomeric species.

The dinuclear ruthenium complex [Ru 2 H(μ-H)(Me 2 dad)(dbcot) 2 ] contains a 1,4-dimethyl-diazabuta-1,3-diene (Me 2 dad) as a non-innocent bridging ligand between the metal centers to give a [Ru 2 (Me 2 dad)] core. In addition, each ruthenium is bound to one dibenzo[ a , e ]cyclooctatetraene (dbcot) ligand. This Ru dimer converts H 2 to protons and electrons. It also catalyzes reversibly under mild conditions the selective hydrogenation of vitamins K 2 and K 3 to their corresponding hydroquinone equivalents without affecting the C[double bond, length as m-dash]C double bonds. Mechanistic studies suggest that the [Ru 2 (Me 2 dad)] moiety, like hydrogenases, reacts with H 2 and releases electrons and protons stepwise., (This journal is © The Royal Society of Chemistry 2019.)

The iridium(iii/iv/v) imido redox series [Ir(N t Bu){N(CHCHP t Bu 2 ) 2 }] 0/+/2+ was synthesized and examined spectroscopically, magnetically, crystallographically and computationally. The monocationic iridium(iv) imide exhibits an electronic doublet ground state with considerable 'imidyl' character as a result of covalent Ir-N t Bu bonding. Reduction gives the neutral imide [Ir(N t Bu){N(CHCHP t Bu 2 ) 2 }] as the first example of an iridium complex with a triplet ground state. Its reactivity with respect to nitrene transfer to selected electrophiles (CO 2 ) and nucleophiles (PMe 3 ), respectively, is reported.

Catalytic synthesis of substituted 1,2-dihydronaphthalenes via metalloradical activation of o -styryl N -tosyl hydrazones (( E )-2-(prop-1-en-1-yl)benzene- N -tosyl hydrazones) is presented, taking advantage of the intrinsic reactivity of a cobalt(iii)-carbene radical intermediate. The method has been successfully applied to a broad range of substrates with various R 1 substituents at the aromatic ring, producing the desired ring products in good to excellent isolated yields for substrates with an R 2 = COOEt substituent at the vinylic position (∼70-90%). Changing the R 2 moiety from an ester to other substituents has a surprisingly large influence on the (isolated) yields. This behaviour is unexpected for a radical rebound ring-closure mechanism, and points to a mechanism proceeding via ortho -quinodimethane ( o -QDM) intermediates. Furthermore, substrates with an alkyl substituent on the allylic position reacted to form E -aryl-dienes in excellent yields, rather than the expected 1,2-dihydronaphthalenes. This result, combined with the outcome of supporting DFT calculations, strongly points to the release of reactive o -QDM intermediates from the metal centre in all cases, which either undergo a 6π-cyclisation step to form the 1,2-dihydronaphthalenes, or a [1,7]-hydride shift to produce the E -aryl-dienes. Trapping experiments using TEMPO confirm the involvement of cobalt(iii)-carbene radical intermediates. EPR spectroscopic spin-trapping experiments using phenyl N-tert -butylnitrone (PBN) confirm the radical nature of the catalytic reaction.

The synthesis and tautomeric nature of three xanthene-based bisMETAMORPhos ligands ( La-Lc ) is reported. Coordination of these bis(sulfonamidophosphines) to Ir(acac)(cod) initially leads to the formation of Ir I ( L H ) species ( 1a ), which convert via formal oxidative addition of the ligand to Ir III ( L ) monohydride complexes 2a-c . The rate for this step strongly depends on the ligand employed. Ir III complexes 2a-c were applied in the base-free dehydrogenation of formic acid, reaching turnover frequencies of 3090, 877 and 1791 h -1 , respectively. The dual role of the ligand in the mechanism of the dehydrogenation reaction was studied by 1 H and 31 P NMR spectroscopy and DFT calculations. Besides functioning as an internal base, bisMETAMORPhos also assists in the pre-assembly of formic acid within the Ir-coordination sphere and aids in stabilizing the rate-determining transition state through hydrogen-bonding.