TT-Acceptor Ligands Flashcards

Flashcards for reviewing key vocabulary related to TT-Acceptor Ligands.

π-acceptor ligands

Ligands that possess vacant low-lying orbitals (e.g., π* or d-orbitals).

Examples of π-acceptor ligands

CO, NO, PR3, Normal & Cyclo-alkenes, Acetylenes, Isonitriles, etc. with Low-valent TM’s

Metal carbonyls

The formation of the C→M σ bond using an unshared pair of electrons on the carbon atom and the formation of the M→C π bond by donation of metal dπ electrons into the π antibonding orbitals of CO.

M▬C bonds Physical Evidence

Bond lengths and Vibrational spectra (IR spectroscopy).

IR spectroscopy

Based on Hooke’s law: Used to probe the CO environment.

IR Signatures of CO Ligands Coordination Modes

Free, terminal, doubly bridging, triply bridging (H₂- bridging)(H3- bridging).

Effect of Back-bonding on νCO

Lowers the C▬O bond order & consequently the νCO.

Molecular symmetry and IR peaks

Molecular symmetry is directly proportional to the number of IR peaks.

Phosphines (:PR3) & Phosphites [:P(OR)3]

CO equivalents, but use empty 3d orbitals as acceptors Nature of R in PR3 is important: Steric/electronic effects.

Factors affecting back-donation

The identity of the donor atom (N, P), The χPauling of the groups attached to it, The overall charge on the complex ion.

Organometallic compound

Organometallic compounds of transition metals have unusual structures, and practical applications in organic synthesis and industrial catalysis.

Hapticity (η) of a ligand

Describes what portion of the ligand is coordinated to the central atom.

Dewar-Chatt-Duncanson (DCD) bonding model

The ligand donates π e-s to a metal orbital of σ symmetry directed to the centre of the ligand system, and the metal in turn back-donates e- density Into a ligand π* orbital.

Signatures of Synergism in Olefin Complexes

C─C bond distances, C─C stretching frequencies (νC-C) in IR, Chemical Reactivity.