Reactions Of Organometallic Systems Flashcards
Ligand substitution
Dissociative or associative
Dissociative ligand substitution
Initial ligand loss, rate depends on ligand loss, rate enhanced by less strongly bound ligands eg no synergic bonding, bulky ligands or heat
Associative ligand substitution
Initial ligand addition, usually 16e- complexes
Trans effect
Effect of ligand on rate of substitution at site trans to itself
Associative ligand substitution with 18e- complexes
Some ligands change binding mode and allow extra ligands to bind to MC without prior dissociation
Oxidative addition
Adds 2 ligands to metal centre, increases metal ON by 2, increases coordination number by 2, increases total e- count at MC by 2
requirements for oxidative addition
M(n+2)+ oxidation state must be accessible and as coordination number increases by 2 metal must be unsaturated or have prior ligand dissociation
Mechanisms of oxidative addition
Concerted addition of non-polar substrates giving cis-product, SN2 like nucleophilic attack of metal complex on polar substrates gives trans addition
Reductive elimination
Metal ON decreases by 2, 2 ligands eliminated, metal coordination number and total electron count reduced by 2
Requirements for reductive elimination
Mn+ oxidation state must be stable, if product X-X is a non-polar species ligands must be cis before elimination
Migratory insertion
Migration of X-type ligand onto unsaturated L-type ligand giving net insertion of L-type ligand into M-X bons
Halides and migratory insertion
No
Hydrogen transfer reactions
Transfer of H from ligand back to metal to generate M-H bond, can occur from α, β, γ or δ C but all need vacant cis metal coordination site
External nucleophilic attack on coordinated ligands
Important for CO/alkenes, synergic bonding can cause partial positive charge to build up on ligand atoms making them susceptible to external nucleophilic attack
Factors giving e- poor MC
High ON, overall positive charge on complex and e- withdrawing coligands
