Phosphine Ligands

Flashcards about Phosphine Ligands

What is the primary interaction between phosphines and a metal center?

Phosphines (PR3) donate a lone pair in a σ-donation to a metal center.

What is the secondary interaction between phosphines and a metal center?

Back-donation from a filled metal d-orbital into a π-acceptor orbital involving the P-R σ* orbital.

How do R groups on phosphines affect back-bonding?

The degree of stabilization from back-bonding depends on the R groups attached to phosphorus; PF3 is a better π-acceptor than PMe3.

Why can phosphorus be chiral in phosphine ligands?

Phosphorus has a lone pair and a higher inversion barrier than N, allowing for chirality.

How are phosphines generally synthesized?

Metathesis reactions of Grignard reagents/organolithiums with phosphorus chlorides.

What spectroscopic technique is useful for identifying and characterizing phosphines and metal phosphines?

31P NMR spectroscopy.

Besides electronics, what other factor is important for phosphines?

Sterics or Cone Angle

What property quantifies the steric bulk of a phosphine ligand?

The ligand cone angle (θ).

What is the benefit of large phosphine ligands in reactions?

Steric bulk allows selectivity for reactions.

What complexes are formed when Palladium metal (Pd0) reacts with an excess of three tertiary phosphine ligands?

Pd(PMe3)4, Pd(PPh3)3, Pd(PCy3)2

How does the bulk of phosphines impact substitution reactions and catalysis?

Steric strain is avoided by ligand dissociation.

What defines the bite angle in bidentate phosphines?

The angle defined by P-M-P.

What are the intended learning outcomes?

Intended Learning Outcomes: Describe the bonding of phosphines to a metal centre as both a σ-donor and a π-acceptor. Use cone angles and bite angles to explain the reactivity and reactions of simple reactions of metal phosphine complexes. Explain the effect of steric bulk on the dissociation of ligands and the creation of coordinative unsaturation