TM Complexes With π-ligands

Question 1

Alkene bonding

Answer 1

Synergic similar to CO

Question 2

Consequences of alkene synergic bonding

Answer 2

C=C bond length increases = σ-donation decreases electron density from C=C BMO and π-back donation increases electron density in C=C π* ABMO = C=C distance approaches that of C-C
Alkenes bend
Weaker C=C = Lower νC=C
With electron poor MC σ-donation dominates = Cδ+ = susceptible to external nucleophilic attack

Question 3

Synthesis of alkene/alkyne complexes

Answer 3

Ligand substitution at low metal oxidation centres = needs to remove ligand first

Question 4

Reactivity

Answer 4

Migratory insertion, external nucleophilic attack and cyclodimerisation of alkynes