Stereoisomerism of bis(σ-Zincane) Complexes: Evidence for an Intramolecular Pathway

The Continuum Between Hexagonal Planar and Trigonal Planar Geometries

New heterometallic hydride complexes that involve the addition of {Mg-H} and {Zn-H} bonds to group 10 transition metals (Pd, Pt) are reported. The side-on coordination of a single {Mg-H} to Pd forms a well-defined σ-complex. In contrast, addition of three {Mg-H} or {Zn-H} bonds to Pd or Pt results in the formation of planar complexes with subtly different geometries. We compare their structures through experiment (X-ray diffraction, neutron diffraction, multinuclear NMR), computational methods (DFT, QTAIM, NCIPlot), and theoretical analysis (MO diagram, Walsh diagram). These species can be described as snapshots along a continuum of bonding between ideal trigonal planar and hexagonal planar geometries.

Synthesis and reactivity of heterometallic complexes containing Mg- or Zn-metalloligands

Heteronuclear metal complexes comprising main group metals and transition metals have attracted widespread attention from researchers due to their applications in stoichiometric and catalytic activation of small molecules with possible cooperative effects. Herein, the advances of heterometallic complexes containing Mg- or Zn-metalloligands over the past ten years are reviewed. They consist of two parts: (i) synthetic approaches to heterometallic complexes. Only a brief discussion is made on the different Mg/Zn precursors since they have been summarized before. (ii) Stoichiometric and catalytic reactivities of heterometallic complexes containing Mg/Zn metalloligands. The exploration of the cooperative catalytic reaction of heterometallic complexes is still in its infancy, promising but challenging; thus, further investigations are required in the future.

Molecular Main Group Metal Hydrides

This review serves to document advances in the synthesis, versatile bonding, and reactivity of molecular main group metal hydrides within Groups 1, 2, and 12-16. Particular attention will be given to the emerging use of said hydrides in the rapidly expanding field of Main Group element-mediated catalysis. While this review is comprehensive in nature, focus will be given to research appearing in the open literature since 2001.

Metathesis by Partner Interchange in σ-Bond Ligands: Expanding Applications of the σ-CAM Mechanism

In 2007 two of us defined the σ‐Complex Assisted Metathesis mechanism (Perutz and Sabo‐Etienne, Angew. Chem. Int. Ed. 2007, 46, 2578–2592), that is, the σ‐CAM concept. This new approach to reaction mechanisms brought together metathesis reactions involving the formation of a variety of metal–element bonds through partner‐interchange of σ‐bond complexes. The key concept that defines a σ‐CAM process is a single transition state for metathesis that is connected by two intermediates that are σ‐bond complexes while the oxidation state of the metal remains constant in precursor, intermediates and product. This mechanism is appropriate in situations where σ‐bond complexes have been isolated or computed as well‐defined minima. Unlike several other mechanisms, it does not define the nature of the transition state. In this review, we highlight advances in the characterization and dynamic rearrangements of σ‐bond complexes, most notably alkane and zincane complexes, but also different geometries of silane and borane complexes. We set out a selection of catalytic and stoichiometric examples of the σ‐CAM mechanism that are supported by strong experimental and/or computational evidence. We then draw on these examples to demonstrate that the scope of the σ‐CAM mechanism has expanded to classes of reaction not envisaged in 2007 (additional σ‐bond ligands, agostic complexes, sp²‐carbon, surfaces). Finally, we provide a critical comparison to alternative mechanisms for metathesis of metal–element bonds.

Palladium-Catalysed C-H Bond Zincation of Arenes: Scope, Mechanism, and the Role of Heterometallic Intermediates

Catalytic methods that transform C-H bonds into C-X bonds are of paramount importance in synthesis. A particular focus has been the generation of organoboranes, organosilanes and organostannanes from simple hydrocarbons (X=B, Si, Sn). Despite the importance of organozinc compounds (X=Zn), their synthesis by the catalytic functionalisation of C-H bonds remains unknown. Herein, we show that a palladium catalyst and zinc hydride reagent can be used to transform C-H bonds into C-Zn bonds. The new catalytic C-H zincation protocol has been applied to a variety of arenes-including fluoroarenes, heteroarenes, and benzene-with high chemo- and regioselectivity. A mechanistic study shows that heterometallic Pd-Zn complexes play a key role in catalysis. The conclusions of this work are twofold; the first is that valuable organozinc compounds are finally accessible by catalytic C-H functionalisation, the second is that heterometallic complexes are intimately involved in bond-making and bond-breaking steps of C-H functionalisation.

Transition metal-induced dehydrogenative coupling of zinc hydrides

Transition metal-induced dehydrogenative homocoupling of zinc(ii) hydrides to a zinc–zinc bonded complex has been achieved.