L4 Transition Metal Complexes of Higher and Cyclic Alkenes

Zeise’s salt - the first organometallic transition metal complex

Dewar-Chatt-Duncanson Model: Alkene metal bonding

(2 ways)

The DCD model - which interaction is the dominant bonding effect

The effects of backbonding in bond strength

Effect of backbonding on IR (C=C) bond stretching frequency

Increased backbonding weakens the C=C bond so the frequency drops

How does degree of backbonding affect reactivity

More backbonding drops the reactivity as you lose (some of) the double bond character in the alkene

Metal-alkenes vs metallacyclopropanes

Complexes with allyl ligands - binding modes

can either just bind as an X ligand or include the double bond to become LX

(note after eta 3, not neutral but -ve)

Cyclopentadienyl ligand binding modes

What is the Cp* and how does it affect the complex

Ring slippage - importance of the cyclopentadienyl ligand in catalysis

Note how each of the changes is a 2e^- change

Ferrocene overview

Features of first row metallocene metals

Trends for Cp₂M

Benzene as a ligand - binding modes

Complexes of 7/8-membered rings

Note that the 18 electron rule is not relevant for lanthanides and actinides.

Transition metal carbenes

Fischer carbenes - key feature

It must have a hetereoatom like in an alkoxide or amine to stabilise the rather unstable carbene.

Singlet carbene

Schrock Alkylidenes key feature

Does not have a heteroatom, instead has an aromatic or alkyl substituent and the other ligands are bulky for steric hindrance

Triplet carbene

Comparison of the two M=C types

Synthesis of carbenes and alkylidenes

Bonding in carbenes and alkylidenes

Applications of Alkylidenes : Olefin Metathesis

Ring Opening Metathesis Polymerisation