TMs 2 - Ch 12 - 14 - ligand effects, reaction types, catalysis

trans effect series

least substitution of trans ligand

F^-, H₂O, OH^-

< NH₃ < py

< Cl^- < Br^- < I^-

< NO₂^-, Ph^- < PR₃

< H^-, NO, CO, CN^-, C₂H₄

most substitution of trans ligand

Linear vs. bent NO

Linear = 3 e- donor

Bent = 1 e- donor

Describe the bonding in alkyne ligands

2x $\pi$ systems

Only 1 is of correct orientation to react

act same as alkenes - 2 e- donor (L type)

what metals do phosphines help stabilise?

Late TMs (Pd, Pt)

In 0 ox. state

Table of reactions between metals + ligands

ligand exchange reaction

oxidation state change in metals

rearrangement of e^- between metal + ligand

oxidative addition

reductive elimination

insertion/migration reaction

$\beta$-hydride elimination

eliminates FROM LIGAND - forms C=C

alkene insertion

GETS RID OF ALKENE!

$\sigma$- bond methathesis

d⁰ metals

Formula of Wilkinson’s catalyst. What does it do?

Catalyses hydrogenation across C=C bond

Hydrogenation catalytic cycle

Focus: Wilkinson’s Catalyst, a Rh complex.

What is a hydroformylation rxn?

Add CO + H

to C=C

Form aldehyde

Hydroformylation catalysis

Focus: migration/insertion of CO

How do you dictate formation of a linear vs. branched aldehyde in hydroformylation?

• + bulky group on catalyst (e.g. PR₃) = branched

• CO (less bulky group) = linear

STERICS not electronics dominated

What reaction is Mizoroki-Heck used for?

extending ALKENE chain

Mizoroki-Heck cross-coupling cycle

What is the selectivity of the Mizoroki-Heck reaction for terminal alkenes, H₂C=CHR?

• TS goes via R’ attack on least substituted side

• Force E (trans) due to steric clash when eliminating $\beta$ hydride

What is the selectivity of the Mizoroki-Heck reaction for 1,2 disubstituted alkenes, RHC=CHR?

• INVERSION cis $\leftrightarrow$ trans

• Only 1 elimination position possible

What reaction is Suzuki-Miyaura used for?

join 2 aromatic rings, via BORONIC ACID

Suzuki cross-coupling cycle

Mechanism for Suzuki ligand exchange step, starting from Boronic acid

What reaction is Buchwald-Hartwig used for?

Phenylamines by adding to aromatic ring

Buchwald-Hartwig cross-coupling cycle

General Pd catalytic cycle