1 / 13

Ch14 Organometallic Reactions

Ch14 Organometallic Reactions. Reactions Involving Gain or Loss of Ligands Ligand Dissociation and Substitution Ligand (CO) Dissociation can be caused by heat Ligand (CO) Substitution is important for synthesis of new complexes Rate is independent of incoming ligand = D mechanism (for most)

oleg
Télécharger la présentation

Ch14 Organometallic Reactions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Ch14 Organometallic Reactions • Reactions Involving Gain or Loss of Ligands • Ligand Dissociation and Substitution • Ligand (CO) Dissociation can be caused by heat • Ligand (CO) Substitution is important for synthesis of new complexes • Rate is independent of incoming ligand = D mechanism (for most) Ni(CO)4 Ni(CO)3 18e- to 16e- (slow) Ni(CO)3 + L Ni(CO)3L 16e- to 18e- (fast) • Some organometallic substitutions show a two-term rate law i) Rate = k1[Complex] + k2[Complex][L]

  2. k1 is due to the dissociative mechanism • k2 is due to a competing associative mechanism • Larger metals show more A mechanism; smaller metals mostly D • Highly nucleophilic ligands tend to increase A mechanism • Phosphine Dissociation • Cone Angle is defined for phosphine ligands

  3. Larger cone angle = larger steric repulsion = faster ligand dissociation • Neither Dissociation nor Substitution reactions change the metal oxidation state

  4. Oxidative Addition • Coordination Number and Oxidation State of Metal Increase LnMm+ + X—Y LnM(M+2)+XY • Examples:

  5. Cyclometallations incorporate metals into organic rings; may be Ox. Add. • Reductive Elimination • Opposite of Ox. Add.; Oxidation State and Coord. Number are reduced Ox. Add Substitution

  6. Red. Elim. often results in products like: R—H, R—R’, R—X, H—H • Steric bulk of phosphine ligands can increase the rate of red. elim.

  7. Nucleophilic Displacement • Nucleophilic Ligands may displace others (Substitution) • Nucleophilic Complexes may react with electrophiles E. Summary

  8. Reactions Involving Modification of Ligands • Insertion Reactions • 1,2-Insertions • New bonds to adjacent atoms • Like 1,2-additions to alkenes in organic chemistry • May play a role in some catalyzed polymerizations

  9. 1,1-Insertions • Both new bonds are to the same atom of the inserting group • Carbonyl Insertion, Carbonyl Migration, or Alkyl Migration? • CO Insertion = direct CO insertion from external CO • CO Migration = movement of bound CO into M—R bond • Alkyl Migration = movement of bound R to bound CO

  10. Experimental Evidence • Free 13CO + complex gives no labeled acyl product This rules out mechanism #1, CO insertion • Reverse reaction gives 100% cis13CO and R Both mechanism #2 and mechanism #3 are consistent with this result

  11. Reverse reaction with 13CO cis to acyl group gives 2:1 cis:trans product Only Mechanism #3 Alkyl Migration is consistent with this data

  12. Hydride Elimination • Transfer of H from ligand to M; formation of double bond in ligand • b-elimination is most common, a and g are known • Reverse of 1,2-insertion • Coordinatively Saturated or Alkyl complexes without b-hydrogens are most stable C. Abstraction = eliminations with no change in metal coordination number + +

More Related