Ligand cone angle

Ligand cone angle measures a ligand’s steric bulk as the angle of a cone enclosing its atoms when viewed from a coordinated metal center.

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Tolman cone angle: A standardized ligand cone angle estimated from a space-filling model around a metal–phosphorus bond. Tolman’s construction supplies the best-known operational definition of this measure.
Ligand sterics: The spatial effects of a ligand’s size and shape on bonding and reactions at a coordination center. Cone angle is a compact descriptor within the broader study of ligand sterics.
Solid angle: A three-dimensional angular measure describing the portion of space subtended by an object from a point. It is a spatial alternative to expressing a ligand’s steric envelope as a planar cone angle.
Chadwick A. Tolman: An American chemist known for developing quantitative steric and electronic descriptors for phosphine ligands. Tolman introduced the influential cone-angle framework for comparing phosphines.
Steric hindrance: Reduced reactivity or accessibility caused when atoms or groups occupy space near a reactive site. Cone angle quantifies one geometric source of hindrance at a metal center.
Phosphine ligand: A ligand containing phosphorus that donates a lone pair to a metal center. Phosphines are the ligand family for which cone angles became widely used.
Sterimol parameters: Ligand steric descriptors that quantify widths and lengths along a defined bond axis. They distinguish directional dimensions that one cone-angle value combines.
Tolman electronic parameter: A carbonyl stretching-frequency measure used to compare the electronic donor strength of phosphine ligands. Tolman developed this companion descriptor alongside his steric measure.
Metal–ligand bond: A chemical bond between a metal center and an atom or group acting as a ligand. The bond axis is the viewpoint from which the ligand’s cone is measured.
Catalytic selectivity: The preference of a catalyst for forming one product or pathway over competing outcomes. Ligand bulk can steer which substrates or reaction trajectories reach the metal.