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)

Which phosphine ligand has similar pi-acceptor ability to CO?

PF₃ - EWG present

all others are WORSE PI ACCEPTORS

what metals do phosphines help stabilise?

Late TMs (Pd, Pt)

In 0 ox. state

What phsophine is a good sigma donor

P^tBu₃

can electronics + sterics of phosphines be tuned independently?

NO

Table of reactions between metals + ligands

cyclooligomerisation

form benzene ligand from alkynes

what happens to the NMR on complexation of a benzene?

LOCALISED bonding character increases

lower ring current

lower shift

how can Cp be made?

1. deprotonate CpH

REMEMBER Cp- is the ligand!!!!

weak base is ok

2. Use NaCp - salt crashes out to provide driving force

Cp vs Cp*

Cp* better donor

what reactions can ferrocene and cobaltocene catalyse/be used in?

Ferrocene: friedel-crafts acylation of cp

cobaltocenIUM (+ charge): oxidation of CpMe to CPCOOH

reactions involving a single electron carrier (easy to oxidise/reduce reversibly)

How do bipy ligands aid electron transfer?

strong pi-acceptors

stabilise a $\pm$ 1 change in oxidation state

oxidative addition

AB adds cis as 2x X type ligands

What is the TS for OA of H2?

alkene-like:

sigma donation from H-H sigma

pi acceptance from H-H sigma star

How does OA of HX (HCl etc.) depend on solvent?

non polar - cis addition, concerted

polar = trans addition (stabilise ions)

insertion/migration reaction

insertion = 1 ligand inserts into another

migration = 1 group removed from another ligand and goes back onto metal

via 3-centre (triangle) TS

$\beta$-hydride elimination

eliminates FROM LIGAND - forms C=C

alkene insertion

GETS RID OF ALKENE!

how can we catalyse alkene polymerisation?

insertion rxn

$\sigma$- bond methathesis

d⁰ metals

match up sets of $\delta -, \delta +$

M R1 + H R2 $\rightarrow$ H M + R1 R2 or the other connectivity

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