High catalytic activity and selectivity in hydrosilylation of new Pt(II) metallosupramolecular complexes based on ambidentate ligands

Multi-Stimuli-Responsive Network of Multicatalytic Reactions using a Single Palladium/Platinum Catalyst

Given her unrivalled proficiency in the synthesis of all molecules of life, nature has been an endless source of inspiration for developing new strategies in organic chemistry and catalysis. However, one feature that remains thus far beyond chemists' grasp is her unique ability to adapt the productivity of metabolic processes in response to triggers that indicate the temporary need for specific metabolites. To demonstrate the remarkable potential of such stimuli-responsive systems, we present a metabolism-inspired network of multicatalytic processes capable of selectively synthesising a range of products from simple starting materials. Specifically, the network is built of four classes of distinct catalytic reactions-cross-couplings, substitutions, additions, and reductions, involving three organic starting materials-terminal alkyne, aryl iodide, and hydrosilane. All starting materials are either introduced sequentially or added to the system at the same time, with no continuous influx of reagents or efflux of products. All processes in the system are catalysed by a multifunctional heteronuclear PdII/PtII complex, whose performance can be controlled by specific additives and external stimuli. The reaction network exhibits a substantial degree of orthogonality between different pathways, enabling the controllable synthesis of ten distinct products with high efficiency and selectivity through simultaneous triggering and suppression mechanisms.

Enhanced catalytic performance derived from coordination-driven structural switching between homometallic complexes and heterometallic polymeric materials

A bifunctional ligand 4,4-dimethyl-1-(pyridin-4-yl)pentane-1,3-dione (HL) able to provide two distinct coordination sites, i.e. anionic β-diketonate (after deprotonation) and neutral pyridine, has been used in the synthesis of Ag(I), Pd(II) and Pt(II) complexes that then have been applied as metalloligands for the construction of new heterometallic polymeric materials. The ambidentate nature of L- enables switching between different modes of coordination within mononuclear complexes or their conversion into polymeric species in a fully controllable way. The coordination-driven processes can be triggered by various stimuli, i.e. a metal salt addition or acid-base equilibria, and presents an efficient strategy for the generation of metallosupramolecular materials. As a consequence of self-assembly, new multimetallic coordination aggregates have been synthesized and characterized in depth in solution (¹H NMR, ESI-MS) as well as in the solid state (XPS, SEM-EDS, FTIR, pXRD, TGA). Furthermore, the Pd-based assemblies have been found to be efficient catalyst precursors in the Heck cross-coupling reaction, demonstrating a direct impact of compositional and morphological differences on their catalytic activity.

Electronic structure comparisons of isostructural early d- and f-block metal(iii) bis(cyclopentadienyl) silanide complexes

We report the synthesis of the U(iii) bis(cyclopentadienyl) hypersilanide complex [U(Cp'')₂{Si(SiMe₃)₃}] (Cp'' = {C₅H₃(SiMe₃)₂-1,3}), together with isostructural lanthanide and group 4 M(iii) homologues, in order to meaningfully compare metal-silicon bonding between early d- and f-block metals. All complexes were characterised by a combination of NMR, EPR, UV-vis-NIR and ATR-IR spectroscopies, single crystal X-ray diffraction, SQUID magnetometry, elemental analysis and ab initio calculations. We find that for the [M(Cp'')₂{Si(SiMe₃)₃}] (M = Ti, Zr, La, Ce, Nd, U) series the unique anisotropy axis is conserved tangential to ; this is governed by the hypersilanide ligand for the d-block complexes to give easy plane anisotropy, whereas the easy axis is fixed by the two Cp'' ligands in f-block congeners. This divergence is attributed to hypersilanide acting as a strong σ-donor and weak π-acceptor with the d-block metals, whilst f-block metals show predominantly electrostatic bonding with weaker π-components. We make qualitative comparisons on the strength of covalency to derive the ordering Zr > Ti ≫ U > Nd ≈ Ce ≈ La in these complexes, using a combination of analytical techniques. The greater covalency of 5f³ U(iii) vs. 4f³ Nd(iii) is found by comparison of their EPR and electronic absorption spectra and magnetic measurements, with calculations indicating that uranium 5f orbitals have weak π-bonding interactions with both the silanide and Cp'' ligands, in addition to weak δ-antibonding with Cp''.

Pd(II) Complexes with Pyridine Ligands: Substituent Effects on the NMR Data, Crystal Structures, and Catalytic Activity

A wide range of functionalized pyridine ligands have been employed to synthesize a variety of Pd(II) complexes of the general formulas [PdL₄](NO₃)₂ and [PdL₂Y₂], where L = 4-X-py and Y = Cl^– or NO₃^–. Their structures have been unambiguously established via analytical and spectroscopic methods in solution (NMR spectroscopy and mass spectrometry) as well as in the solid state (X-ray diffraction). This in-depth characterization has shown that the functionalization of ligand molecules with groups of either electron-withdrawing or -donating nature (EWG and EDG) results in significant changes in the physicochemical properties of the desired coordination compounds. Downfield shifts of signals in the ¹H NMR spectra were observed upon coordination within and across the complex families, clearly indicating the relationship between NMR chemical shifts and the ligand basicity as estimated from pK_a values. A detailed crystallographic study has revealed the operation of a variety of weak interactions, which may be factors explaining aspects of the solution chemistry of the complexes. The Pd(II) complexes have been found to be efficient and versatile precatalysts in Suzuki–Miyaura and Heck cross-coupling reactions within a scope of structurally distinct substrates, and factors have been identified that have contributed to efficiency improvement in both processes.

A wide range of pyridine derivatives have been employed to synthesize a variety of di- and tetrasubstituted Pd(II) complexes of square-planar geometry. This in-depth characterization has shown that the functionalization of ligand molecules with groups of either electron-withdrawing or -donating nature results in significant changes in the physicochemical properties of the coordination compounds. Moreover, the complexes have been found to be of practical utility as efficient precatalysts for both Suzuki−Miyaura and Heck cross-coupling reactions.

Charge Neutral [Cu2L2] and [Pd2L2] Metallocycles: Self-Assembly, Aggregation, and Catalysis

A range of morphologically distinct metallosupramolecular Cu(II) and Pd(II) complexes has been constructed, based on the tritopic ligand 1,1',1″-(benzene-1,3,5-triyl)tris(4,4-dimethylpentane-1,3-dione) (H₃L). By control of the reaction conditions, it is possible to generate distinct coordination assemblies possessing either macrocyclic or polymeric structures and more importantly distinct activity in catalysis of the Suzuki-Miyaura cross-coupling.

f-Element silicon and heavy tetrel chemistry

The last three decades have seen a significant increase in the number of reports of f-element carbon chemistry, whilst the f-element chemistry of silicon, germanium, tin, and lead remain underdeveloped in comparison. Here, in this perspective we review complexes that contain chemical bonds between f-elements and silicon or the heavier tetrels since the birth of this field in 1985 to present day, with the intention of inspiring researchers to contribute to its development and explore the opportunities that it presents. For the purposes of this perspective, f-elements include lanthanides, actinides and group 3 metals. We focus on complexes that have been structurally authenticated by single-crystal X-ray diffraction, and horizon-scan for future opportunities and targets in the area.

Intrinsic Effect of Pyridine-N-Position on Structural Properties of Cu-Based Low-Dimensional Coordination Frameworks

Metal-organic assemblies have received significant attention for catalytic and other applications, including gas and energy storage, due to their porosity and thermal/chemical stability. Here, we report the synthesis and physicochemical characterization of three metallosupramolecular assemblies consisting of isomeric ambidentate pyridyl-β-diketonate ligands L1–L3 and Cu(II) metal ions. It has been demonstrated that the topology and dimensionality of generated supramolecular aggregates depend on the location of the pyridine nitrogen donor atom in L1–L3. This is seen in characterization of two distinct 2D polymeric assemblies, i.e., [Cu(L1)₂]_n and [Cu(L2)₂]_n, in which both β-diketonate and pyridine groups are coordinated to the Cu(II) center, as well as in characterization of the mononuclear 1D complex Cu(L3)₂, in which the central atom is bound only by two β-diketonate units.