Structure Optimisation of Large Transition‐Metal Complexes with Extended Tight‐Binding Methods

Large transition‐metal complexes are used in numerous areas of chemistry. Computer‐aided theoretical investigations of such complexes are limited by the sheer size of real systems often consisting of hundreds to thousands of atoms. Accordingly, the development and thorough evaluation of fast semi‐empirical quantum chemistry methods that are universally applicable to a large part of the periodic table is indispensable. Herein, we report on the capability of the recently developed GFNn‐xTB method family for full quantum‐mechanical geometry optimisation of medium to very large transition‐metal complexes and organometallic supramolecular structures. The results for a specially compiled benchmark set of 145 diverse closed‐shell transition‐metal complex structures for all metals up to Hg are presented. Further the GFNn‐xTB methods are tested on three established benchmark sets regarding reaction energies and barrier heights of organometallic reactions.     

An Asymmetric Pathway to Dendrobine by a Transition‐Metal‐Catalyzed Cascade Process

An asymmetric pathway to the caged tetracyclic pyrrolidine alkaloid, dendrobine, is reported. The successful synthetic strategy features a one‐pot, sequential palladium‐catalyzed enyne cycloisomerization and rhodium‐catalyzed diene‐assisted pyrrolidine formation by allylic CH activation. The developed transition‐metal‐catalyzed cascade process permits rapid access to the dendrobine core structure and circumvents the handling of labile intermediates. An intramolecular aldol condensation under carefully defined reaction conditions takes place with a concomitant detosylation, followed by reductive amine methylation, to afford a late‐stage intermediate (previously identified by several prior dendrobine syntheses) in only 10 synthetic steps overall.     

Four‐Shell Polyoxometalates Featuring High‐Nuclearity Ln26 Clusters: Structural Transformations of Nanoclusters into Frameworks Triggered by Transition‐Metal Ions

A series of polyoxometalates (POMs) that incorporate the highest‐nuclearity Ln clusters that have been observed in such structures to date (Ln₂₆ , Ln=La and Ce) are described, which exhibit giant multishell configurations (Ln⊂W₆⊂Ln₂₆⊂W₁₀₀). Their structures are remarkably different from known giant POMs that feature multiple Ln ions. In particular, the incorporated Ln–O clusters with a nuclearity of 26 are significantly larger than known high‐nuclearity (≤10) Ln–O clusters in POM chemistry. Furthermore, they also contain the largest number of La and Ce centers for any POM reported to date and represent a new kind of rare giant POMs with more than 100 W atoms. Interestingly, the La₂₆‐containing POM can undergo a single‐crystal to single‐crystal structural transformation in the presence of various transition‐metal ions, such as Cu²⁺, Co²⁺, and Ni²⁺, from an inorganic molecular nanocluster into an inorganic–organic hybrid extended framework that is built from POM building blocks with even higher‐nuclearity La₂₈ clusters bridged by transition‐metal complexes.     

Coordination‐Directed Growth of Transition‐Metal–Crystalline‐Carbon Composites with Controllable Metal Composition

Transition‐metal–carbon (CTM) composites show ample activity in many catalytic reactions. However, control of composition, distribution, and properties is challenging. Now, a straightforward path for the synthesis of transition‐metal nanoparticles engulfed in crystalline carbon is presented with excellent control over the metal composition, amount, ratio, and catalytic properties. This approach uses molten monomers that coordinate metals ions at high temperature. At high temperatures, strong coordination bonds direct the growth of carbon material with homogeneous metals distribution and with negligible losses, owing to the liquid‐like reaction compared to the traditional solid‐state reaction. The strength of the approach is demonstrated by the synthesis of mono, binary, and trinary transition‐metal–crystalline‐carbon composites with tunable and precise elemental composition as well as good electrochemical properties as oxygen evolution reaction electrocatalysts.     

Dispersion Forces,Disproportionation, and Stable High‐Valent Late Transition Metal Alkyls

The transition metal tetra‐ and trinorbornyl bromide complexes, M(nor)₄ (M=Fe, Co, Ni) and Ni(nor)₃Br (nor=1‐bicyclo[2.2.1]hept‐1‐yl) and their homolytic fragmentations were studied computationally using hybrid density functional theory (DFT) at the B3PW91 and B3PW91‐D3 dispersion‐corrected levels. Experimental structures were well replicated; the dispersion correction resulted in shortened M−C bond lengths for the stable complexes, and it was found that Fe(nor)₄ receives a remarkable 45.9 kcal mol⁻¹ stabilization from the dispersion effects whereas the tetragonalized Co(nor)₄ shows stabilization of 38.3 kcal mol⁻¹. Ni(nor)₄ was calculated to be highly tetragonalized with long Ni−C bonds, providing a rationale for its current synthetic inaccessibility. Isodesmic exchange evaluation for Fe(nor)₄ confirmed that dispersion force attraction between norbornyl substituents is fundamental to the stability of these species.