L3 Transition Metal Carbonyls - Synthesis and Structures

Features of Transition metal carbonyls

Carbonyls bond incredibly strongly thanks to backbonding and are unreactive without catalysts.

Formation of the first transition metal carbonyls

Synthesis of metal carbonyls - reductive carbonylation

Synthesis of metal carbonyls - CO gas or photochemical/thermal

The reductive method is more useful than Co gas generally

Binuclear and up complexes

When do CO bridges vs M-M bonds form

M-M bonds become more favoured as you increase orbital size

Structures of Mono and binuclear metal carbonyls

There may be multiple logical binuclear structures - any sensible one will get credit

More Binuclear structures (dont need to memorise)

Metal-CO bonding - effects on bond order

Pi backdonation into the empty pi star orbitals of the C-O bond weakens the C-O bond and is the predominant factor in strengthening the M-C bond.

There is also sigma donation from the carbon based electron pair.

How can IR spec distinguish different bonding modes

weakening bonds affects the IR frequency

Dependence on the C-O bond strength on electron density on the metal - charges on the complex

Metals don’t want a bunch of electrons so they will engage in more backbonding when they are more elctron rich - such as in -ve complexes.

Dependence on the C-O bond strength on electron density on the metal - other ligands

Ligands which donate more electrons to the metal will make it want to get rid of more electrons.

Reactions of metal carbonyls - substitution

Other reactions of metal carbonyls (3)

Reactivity of carbonyl ligands

Migratory insertion

Important to consider whether the 16e^- complex is stable enough

Monsanto process - using migratory insertion to form acetic acid