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A yet-outstanding supramolecular chemistry challenge is isolation of novel varieties of stacked complexes with finely-tuned donor-acceptor bonding and optoelectronic properties, as herein reported for binary adducts comprising two different cyclic trinuclear complexes (CTC@CTC'). Most previous attempts focused only on 1-2 factors among metal/ligand/substituent combinations, resulting in heterobimetallic complexes. Instead, here we show that, when all 3 factors are carefully considered, a broadened variety of CTC@CTC' stacked pairs with intuitively-enhanced intertrimer coordinate-covalent bonding strength and ligand-ligand/metal-ligand dispersion are attained (d M-M' 2.868(2) Å; ΔE>50 kcal/mol, an order of magnitude higher than aurophilic/metallophilic interactions). Significantly, CTC@CTC' pairs remain intact/strongly-bound even in solution (K eq 4.67×10 5  L/mol via NMR/UV-vis titrations), and the gas phase (mass spectrometry revealing molecular peaks for the entire CTC@CTC' units in sublimed samples), rather than simple co-crystal formation. Photo-/electro-luminescence studies unravel metal-centered phosphorescence useful for novel all metal-organic light-emitting diodes (MOLEDs) optoelectronic device concepts. This work manifests systematic design of supramolecular bonding and multi-faceted spectral properties of pure metal-organic macrometallacyclic donor/acceptor (inorganic/inorganic) stacks with remarkably-rich optoelectronic properties akin to well-established organic/organic and organic/inorganic analogues., (© 2024 Wiley-VCH GmbH.)

Manganese-catalyzed hydrogenation reactions have aroused widespread interest in recent years. Among the catalytic systems described, especially PNP- and NNP-Mn pincer catalysts have been reported for the hydrogenation of aldehydes, ketones, nitriles, aldimines and esters. Furthermore, NNP-Mn pincer compounds are efficient catalysts for the hydrogenolysis of less reactive amides, ureas, carbonates, and carbamates. Herein, the synthesis and application of specific imidazolylaminophosphine ligands and the corresponding Mn pincer complexes are described. These new catalysts have been characterized and studied by a combination of experimental and theoretical investigations, and their catalytic activities have been tested in several hydrogenation reactions with good to excellent performance. Especially, the reduction of N-heterocycles can be performed under very mild conditions., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The degradation pathways of highly active [Cp*Ir(κ 2 -N,N-R-pica)Cl] catalysts (pica=picolinamidate; 1 R=H, 2 R=Me) for formic acid (FA) dehydrogenation were investigated by NMR spectroscopy and DFT calculations. Under acidic conditions (1 equiv. of HNO 3 ), 2 undergoes partial protonation of the amide moiety, inducing rapid κ 2 -N,N to κ 2 -N,O ligand isomerization. Consistently, DFT modeling on the simpler complex 1 showed that the κ 2 -N,N key intermediate of FA dehydrogenation (I NH ), bearing a N-protonated pica, can easily transform into the κ 2 -N,O analogue (I NH2 ; ΔG ≠ ≈11 kcal mol -1 , ΔG ≈-5 kcal mol -1 ). Intramolecular hydrogen liberation from I NH2 is predicted to be rather prohibitive (ΔG ≠ ≈26 kcal mol -1 , ΔG≈23 kcal mol -1 ), indicating that FA dehydrogenation should involve mostly κ 2 -N,N intermediates, at least at relatively high pH. Under FA dehydrogenation conditions, 2 was progressively consumed, and the vast majority of the Ir centers (58 %) were eventually found in the form of Cp*-complexes with a pyridine-amine ligand. This likely derived from hydrogenation of the pyridine-carboxiamide via a hemiaminal intermediate, which could also be detected. Clear evidence for ligand hydrogenation being the main degradation pathway also for 1 was obtained, as further confirmed by spectroscopic and catalytic tests on the independently synthesized degradation product 1 c. DFT calculations confirmed that this side reaction is kinetically and thermodynamically accessible., (© 2020 Wiley-VCH GmbH.)

Invited for the cover of this issue is the group of Cristiano Zuccaccia at the Università degli Studi di Perugia. The image depicts a relation of the nuances of chemical bonding to the diverse ways that animals "bind" to their natural surroundings. Read the full text of the article at 10.1002/chem.201905699., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Heterobimetallic complexes with inequivalent bridging alkyl chains are very often invoked as key intermediates in many catalytic processes, yet their interception and structural characterization are lacking. Such complexes have been prepared from reactions of the cationic cyclometalated hafnocene [Cp Pr Cp CH 2 CH 2 CH 2 Hf][B(C 6 F 5 ) 4 ] (1) with main group metal alkyls to afford the corresponding hetero-bridged cationic products, [Cp Pr Cp CH 2 CH 2 ( μ - CH 2 ) Hf(μ-R)E(R) n ][B(C 6 F 5 ) 4 ] (E=Al or Zn; R=Me, Et, or iBu). NMR and DFT studies demonstrate that both bridging alkyls establish agostic interactions with Hf, which are appreciably stronger for ethyl rather than methyl groups. Hf-Al and Hf-Zn distances are surprisingly short and only slightly longer than computed Hf-Al or Hf-Zn single bond lengths (2.80 Å). Finally, a reaction of [Cp Pr Cp CH 2 CH 2 ( μ - CH 2 ) Hf(μ-Me)Zn(Me)][B(C 6 F 5 ) 4 ] with excess ZnMe 2 yields an unprecedented heterotrimetallic species, [(Cp Pr ) 2 Hf(μ-Me)(ZnMe)(μ 3 -CH 2 )ZnMe][B(C 6 F 5 ) 4 ], the detailed structure of which is elucidated by a combination of NMR spectroscopic methods and molecular calculations., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Measuring accurate translational self-diffusion coefficients (D t ) by NMR techniques with modern spectrometers has become rather routine. In contrast, the derivation of reliable molecular information therefrom still remains a nontrivial task. In this paper, two established approaches to estimating molecular size in terms of hydrodynamic volume (V H ) or molecular weight (M) are compared. Ad hoc designed experiments allowed the critical aspects of their application to be explored by translating relatively complex theoretical principles into practical take-home messages. For instance, comparing the D t values of three isosteric Cp 2 MCl 2 complexes (Cp=cyclopentadienyl, M=Ti, Zr, Hf), having significantly different molecular mass, provided an empirical demonstration that V H is the critical molecular property affecting D t . This central concept served to clarify the assumptions behind the derivation of D t =ƒ(M) power laws from the Stokes-Einstein equation. Some pitfalls in establishing log (D t ) versus log (M) linear correlations for a set of species have been highlighted by further investigations of selected examples. The effectiveness of the Stokes-Einstein equation itself in describing the aggregation or polymerization of differently shaped species has been explored by comparing, for example, a ball-shaped silsesquioxane cage with its cigar-like dimeric form, or styrene with polystyrene macromolecules., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

An efficient heterogenized water oxidation catalyst (2_TiO2 ) has been synthesized by immobilizing the Kläui-type organometallic precursor [Cp*Ir{P(O)(OH)2 }3 ]Na (2, Cp*=1,2,3,4,5-pentamethylcyclopentadienyl ligand) onto rutile TiO2 . Iridium is homogeneously distributed at the molecular and atomic/small cluster level in 2_TiO2 and 2'_TiO2 (solid catalyst recovered after the first catalytic run), respectively, as indicated by STEM-HAADF (scanning transmission electron microscopy - high angle annular dark field) studies. 2'_TiO2 exhibits TOF values up to 23.7 min(-1) in the oxidation of water to O2 driven by NaIO4 at nearly neutral pH, and a TON only limited by the amount of NaIO4 used, as indicated by multiple run experiments. Furthermore, while roughly 40 % leaching is observed during the first catalytic run, 2'_TiO2 does not undergo any further leaching even when in contact with strongly basic solutions and completely maintains its activity for thousands of cycles. NMR studies, in combination with ICP-OES (inductively coupled plasma optical emission spectrometry), indicate that the activation of 2_TiO2 occurs through the initial oxidative dissociation of PO4 (3-) , ultimately leading to active centers in which a 1:1 P/Ir ratio is present (derived from the removal of two PO4 (3-) units) likely missing the Cp* ligand., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Herein a combined NOE NMR/DFT methodology to discriminate between adducts held together by halogen bonding (XB) and other noncovalent interactions (non-XB, such as lone pair/π), based on the determination of the XB donors' and acceptors' relative orientation, is proposed. In particular, (19) F,(1) H HOESY NMR spectroscopy experiments and DFT calculations on different XB donors, such as perfluorohexyl iodide (I1), iodopentafluorobenzene (I2) and bromopentafluorobenzene (Br), combined with different Lewis bases, such as 1,4-diazabicyclo[2.2.2]octane (DABCO) and 2,4,6-trimethylpyridine (Me3 Py), were performed. The results clearly show that in the case DABCO/I1 the XB adduct is practically the only one present in solution, whereas for the other pairs a certain amount of non-XB adduct is present. Combining DFT and HOESY results, the amount of non-XB adducts can be roughly quantified under our experimental conditions as 4 % for DABCO/I2, between 10 and 20 % for Me3 Py/I1 and Me3 Py/I2, and 44 % for DABCO/Br., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The reaction of [Cp*Ir(bzpy)NO3 ] (1; bzpy=2-benzoylpyridine, Cp*=pentamethylcyclopentadienyl anion), a competent water-oxidation catalyst, with several oxidants (H2 O2 , NaIO4 , cerium ammonium nitrate (CAN)) was studied to intercept and characterize possible intermediates of the oxidative transformation. NMR spectroscopy and ESI-MS techniques provided evidence for the formation of many species that all had the intact Ir-bzpy moiety and a gradually more oxidized Cp* ligand. Initially, an oxygen atom is trapped in between two carbon atoms of Cp* and iridium, which gives an oxygen-Ir coordinated epoxide, whereas the remaining three carbon atoms of Cp* are involved in a η(3) interaction with iridium (2 a). Formal addition of H2 O to 2 a or H2 O2 to 1 leads to 2 b, in which a double MeCOH functionalization of Cp* is present with one MeCOH engaged in an interaction with iridium. The structure of 2 b was unambiguously determined in the solid state and in solution by X-ray single-crystal diffractometry and advanced NMR spectroscopic techniques, respectively. Further oxidation led to the opening of Cp* and transformation of the diol into a diketone with one carbonyl coordinated at the metal (2 c). A η(3) interaction between the three non-oxygenated carbons of "ex-Cp*" and iridium is also present in both 2 b and 2 c. Isolated 2 b and mixtures of 2 a-c species were tested in water-oxidation catalysis by using CAN as sacrificial oxidant. They showed substantially the same activity than 1 (turnover frequency values ranged from 9 to 14 min(-1) )., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

New [(N(-),N,N(-))ZrR2] dialkyl complexes (N(-),N,N(-)=pyrrolyl-pyridyl-amido or indolyl-pyridyl-amido; R=Me or CH2Ph) have been synthesised and tested as pre-catalysts for ethene and propene polymerisation in combination with different activators, such as B(C6F5)3, [Ph3C][B(C6F5)4], [HNMe2Ph][B(C6F5)4] or solid AlMe3-depleted methylaluminoxane (DMAO). Polyethylene (M(w)>2 MDa and M(w)/M(n)= 1.3-1.6) has been produced if pre-catalysts were activated with 1000 equivalents of DMAO (based on Al) [activity >1000 kg(PE)(mol([Zr]) h mol atm)(-1)] or by using a higher pre-catalyst concentration and a mixture of [HNPhMe2][B(C6F5)4] (1 equiv) and AliBu2H (60 equiv). In the case of propene polymerisation, activity has been observed only if pre-catalysts were treated with an excess of AliBu2H prior to addition of DMAO, which led to highly isotactic polypropylene ([mmmm]>95%). Neutral pre-catalysts and ion pairs derived from their activation have been characterised in solution by using advanced 1D and 2D NMR spectroscopy experiments. The detection and rationalisation of intercationic NOEs clearly showed the formation of dimeric species in which some pyrrolyl or indolyl π-electron density of one unit is engaged in stabilising the metal centre of the other unit, which relegates the counterions in the second coordination sphere. The solid-state structure of the dimeric indolyl-pyridyl-amidomethylzirconium derivative, determined by X-ray diffraction studies, points toward a weak Zr···η(3)-indolyl interaction. It can be hypothesised that the formation of dimeric cationic species hampers monomer coordination (especially of less reactive α-olefins) and that addition of AliBu2H is crucial to split the homodimers., (Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

New multicationic organoruthenium dendrimers (RuPF(6)-Dabn, n = 2, 4, 8, 16) have been synthesized by coupling of [Ru(eta(6)-p-cymene)(kappa(3)-dpk-OCH(2)CH(2)OH)]X (1PF(6), dpk = 2,2'-dipyridyl ketone, X = PF(6)) with 1,4-diaminobutane (DAB) and polypropylenimine dendrimer DAB-dendr-(NH(2))(n) {n=4, 8, 16} mediated by 1,1'-carbonyldiimidazole (CDI). The intermediate in the synthesis, [Ru(eta(6)-p-cymene)(kappa(3)-dpk-OCH(2)CH(2)OC(O)Im]X (2PF(6), Im = imidazole, X = PF(6)) has been isolated and characterized by single-crystal XRD. The intra- and supramolecular structures in a solution of RuPF(6)-Dabn dendrimer have been investigated by multidimensional and multinuclear NMR techniques. Diffusion NMR experiments on dilute solutions indicated that the linear distance between two metal centers (14.9-22.1 A depending on the dendrimer generation) is much greater than the diameter of 1PF(6) (9.9 A). (19)F,(1)H-HOESY NMR experiments (HOESY = heteronuclear Overhauser effect spectroscopy) showed that the counterion is positioned on the surface of the dendrimers and assumes the same relative anion-cation orientation as in 2PF(6). Diffusion NMR experiments on RuPF(6)-Dabn dendrimers in CD(2)Cl(2) at different concentrations revealed a process of supramolecular assembly of dendrimers to megamers that is strongly favored for the highest generations. Megamer formation is coupled with an increased fraction of free ions (alpha) and a consequent reduction in ion-paired ruthenium centers. Graphs of alpha versus C(Ru) (the concentration of ruthenium centers) showed a minimum for RuPF(6)-Dab4, RuPF(6)-Dab8, and RuPF(6)-Dab16 at a position coinciding with the significant presence of supramolecular dendritic dimers. The tendency to ion pairing decreases as the dendrimer generation increases.

The catalytic activity and stereoselectivity of complexes [Pd(eta(1),eta(2)-C(8)H(12)OMe)(Ar--N==C(R')--C(R')==N--Ar)]X in the copolymerization of CO and p-methylstyrene have been correlated with their interionic structure in solution and in the solid state, as determined by (19)F,(1)H-HOESY NMR spectroscopy and X-ray diffraction studies, respectively. The highest productivity is obtained with unhindered diimine ligands bearing electron-donating substituents and with the least coordinating counterion. Copolymers with a microstructure ranging from atactic to predominantly isotactic are obtained. The degree of isotacticity increases as the steric hindrance in the apical positions and the coordinating ability of the counterion increase. The counterion is located close to the diimine in both solution and the solid state but it moves toward the palladium as the steric hindrance in the apical positions decreases. When the latter is small the counterion competes with the substrate for apical coordination, and consequently it affects the productivity. In the case of ortho-dimethyl-substituted ligands the counterion is confined in the back, above the N==C(R')--C(R')==N moiety, and does not affect the productivity. However, it contributes to increasing the stereoregularity of the copolymer by making the aryl moieties more rigid. With R'=Me and Ar=o-Me(2)C(6)H(3) an ll of 81 % and 72 % was obtained with X(-)=CF(3)SO(3) (-) or BArF(-), respectively. The isotacticity of the copolymers produced by ortho-monosubstituted catalysts depends greatly on the counterion and ranges from 30 % to 59 % with X(-)=BArF(-) and X(-)=CF(3)SO(3) (-), respectively, with Ar=o-EtC(6)H(4) and R'=Me. Based on the interionic structural results, this effect can be explained by a greater reduction of the copolymerization rate of C(s)-symmetric isomers with respect to their C(2)-symmetric counterparts.