Metal Complex Chemistry of Low-Valent P-Block Elements

Metal Complex Chemistry of Low-Valent P-Block Elements encompasses the coordination and reactivity of compounds in which elements of groups 13–15 adopt oxidation states below their classical valences. In contrast with transition metals, these low-valent centres offer distinctive frontier orbitals that combine strong σ-donation with accessible empty p-orbitals, enabling oxidative addition and reductive elimination processes once thought exclusive to d-block chemistry. Advances in ligand design—employing bulky N-heterocyclic carbenes, boryl frameworks and multidentate phosphines—have stabilised reactive species such as acyclic silylenes, germylenes and stannylenes, allowing room-temperature activation of H₂, N–H and C–H bonds. Cooperative assemblies with transition metals further exploit ambiphilicity to promote multi-site bond cleavage, cycloaddition and migratory transformations. These developments hold promise for replacing scarce precious metals in catalysis and for sustainable feedstock conversion. In materials chemistry, low-valent p-block complexes underpin emerging semiconductors, single-source precursors for thin-film deposition and molecular devices. Interconnections between electronic structure, ligand environment and reactivity define a rapidly evolving landscape, where fundamental insights into main group multiple bonds translate into practical applications in synthesis, catalysis and materials science.

Research from Nature Portfolio

Recent studies have realised a silicon–silicon π single bond in a hexa-tert-butyl bicyclotetrasilane scaffold. The isolated compound exhibits a remarkably long 2.85 Å π interaction between bridgehead silicon atoms without an accompanying σ bond, confirmed by X-ray crystallography, electron paramagnetic resonance and ²⁹Si NMR spectroscopy. Natural bond orbital and UV/Vis analyses reveal that paired 3p electrons in a closed-shell configuration can stabilise this unprecedented π-only bond. This discovery extends the concept of π bonding to heavier p-block elements and illustrates how steric protection and orbital symmetry can yield novel bonding motifs beyond classical double-bond paradigms.

Metal Complex Chemistry of Low-Valent P-Block Elements publication trend

The graph below shows the total number of articles in metal complex chemistry of low-valent p-block elements across all publications each year (not limited to Nature Index journals).

Technical terms

Low-valent: An oxidation state of an element that is lower than its common or maximum valence, often resulting in unique reactivity.

P-block elements: The elements in groups 13–18 of the periodic table, characterised by valence electrons in p orbitals.

Oxidative addition: A reaction in which a metal centre inserts into a covalent bond, increasing its oxidation state by two.

Reductive elimination: The reverse of oxidative addition, where two ligands combine and depart from the metal, lowering its oxidation state.

σ-donor ligand: A ligand that donates electron density to a metal centre through a sigma bond, stabilising electron-deficient species.

Ambiphilicity: The property of a centre or ligand to act both as an electron donor and as an acceptor, enabling cooperative mechanisms.

References

1. Enabling and Probing Oxidative Addition and Reductive Elimination at a Group 14 Metal Center: Cleavage and Functionalization of E–H Bonds by a Bis(boryl)stannylene. Journal of the American Chemical Society (2016).
2. Main Group Multiple Bonds for Bond Activations and Catalysis. Chemistry - A European Journal (2020).
3. Small Molecule Activation by Two‐Coordinate Acyclic Silylenes. European Journal of Inorganic Chemistry (2020).
4. Acid–Base Free Main Group Carbonyl Analogues. Angewandte Chemie International Edition (2020).
5. Cooperativity in Transition Metal Tetrylene Complexes. European Journal of Inorganic Chemistry (2021).
6. Silicon–silicon π single bond. Nature Communications (2020).
7. Tin guanidinato complexes: oxidative control of Sn, SnS, SnSe and SnTe thin film deposition. Dalton Transactions (2018).