Inorganic reaction mechanisms

What does it mean for a reagent compound to be stable?

has a thermodynamic energy state that is more favorable than the product, lower ΔG for reagents compared to products

What does it mean for a reagent compound to be labile?

undergoes rapid ligand exchange; low ΔG between reagents and intermediate

Effective nuclear charge (decreases/increases) across a period and (decreases/increases) down a group.

Effective nuclear charge (decreases/increases) across a period and (decreases/increases) down a group.

As Zeff increases, size (decreases/increases), ionisation energy (decreases/increases), electron affinity (decreases/increases).

As Zeff increases, size (decreases/increases), ionisation energy (decreases/increases), electron affinity (decreases/increases).

Octahedral metal complex orbitals

Tetrahedral metal complex orbitals

LFSE formula

LFSE= [n_e(-0.4) + n_e(0.6)]Δ + P

• number of electrons in t2g orbitals

• number of electrons in eg orbitals

• number of orbitals in which paired electrons exist

Spectrochemical series

I^- < Br^- < S₂– < SCN– < Cl^- < NO₃^- < F^- < OH^- < C₂O₄^2- < OH₂ < NCS^- < CH₃CN < py < NH₃ < en < bipy < phen < NO₂^- < PPh₃ < CN^- < CO

*strong field ligands have increased sterics or has C or N donor (EXCEPT NO₃^-)

What spin configuration do tetrahedral complexes usually have?

high spin

How do 4d and 5d orbitals compare to 3d orbitals and how does it affect ligand interactions?

They are larger/extended, leading to significant penetration of core electrons and increased ligand orbital overlap, lower pairing energy

TRUE OR FALSE: All 4d and 5d transition metal octahedral complexes are low spin

TRUE

What causes Jahn-Teller distortion?

uneven electronic occupation of the orbitals, especially the eg orbitals

What is required for square planar complexes? (3) (Also commit figure to memory)

• d⁸ electron configuration

• heavy metals (4d or 5d)

• strong field ligands (for 3d)

Organometallic compounds

contain a metal tocarbon bond or interaction

Do organometallic or non-organometallic/classical complexes experience pi backbonding?

organometallic

What effects does pi backbonding have? (3)

• the metal is electron rich (low formal oxidation states)

• The metal to ligand bonds are more covalent

• modifies ligand reactivity

Do octahedral complexes with pi accepting ligands have a greater or lower Δ and why?

greater (lower t2g) because pi acceptor ligand orbitals ABOVE d_t2g also have t2g symmetry and can interact with the t2g d orbitals

Do octahedral complexes with pi accepting ligands have a greater or lower Δ and why?

lower (raised t2g) because pi acceptor ligand orbitals BELOW d_t2g also have t2g symmetry and can interact with the t2g d orbitals

How does pi back bonding act on CO ligands in terms of a) reactivity and b) bonds?

a) The empty antibonding π* orbitals of CO accept electron density from the metal t2g orbitals making C^δ+ and O^δ-

b) weakening the carbonyl bond and strengthening the metal bond

How can electron donating/accepting capability of trans ligands to CO be rationalized?

A stronger electron-donating (less accepting) trans ligand increases electron density on the metal, enhancing CO backbonding, which weakens the C-O bond and lowers the infrared stretching frequency

Why does the large HOMO-LUMO gap between t2g and eg result in the complex being kinetically stable?

It is difficult to remove electrons from the t2g orbitals or add electrons to the eg orbitals to form low energy intermediates or transition states.

Why are 18 electron compounds stable?

all bonding molecular orbitals are filled, and antibonding unoccupied

What complexes deviate from the 18 electron rule?

d8 square planar organometallics: d_x²-y² orbital is very high in energy (16 electron configuration)

Early transition metal compounds: low number of metal valence electrons and difficulty avoiding steric conflicts

Electron counting (4 steps)

1. Treat metal and ligand as neutral

2. Count all valence electrons (4s, 3d) of the metal

3. Classify the ligands and include all electrons donated. Consider M-M bonding and bridging ligands

4. Adjust for the overall charge on the complex

What are the two types of ligand electron donors (neutral configurations)?

L type: 2 electron donor

X type: 1 electron/radical donor

What is the oxidation state of a) L and b) X type ligands?

a) 0

b) -1; also applies to L_nX

TRUE OR FALSE: early transition metal complexes are unstable due to lower electron counts

SOMEWHAT FALSE: Very sterically demanding ligands can be used to stabilise them

How many electrons do the following cyclopentadienyl orientations donate?

alkali metal halide elimination

How does length of the C=C bond in an η2 -alkene complex compare to the free alkene and why?

Longer due to use of bonding electrons to coordinate metal

M-(η2-Ligand) + nucleo/electrophile → ?

Bis(benzene) Chromium d-orbital splitting

Piano Stool Complexes Preparation

Ferrocene d-orbital splitting

As Zeff increases for metallocenes, M-C bond length…

decreases

Nucleophilic substitution

Friedel-Crafts acylation

How does hydrogen bond to a metal

σ-lone pair donor (X type) or as dihydrogen (L type)

Metal Hydride Formation (2 steps)

1. bonding of H-H to metal centre

2. Backbonding from electron rich complex breaks H-H bond

R_n-M-H (hydride) + RC=CR (alkene/alkyne) → ?

R_n-M-RC-CR-H

TRUE OR FALSE: Electron poor complexes can form metal hydride complexes if they have a heavy metal

FALSE: more likely to yield dihydrogen complex (pictured)

Incorporating H₂ into metal complex (decreases/increases) acidity and (lengthens/shortens) the H-H bond

Incorporating H₂ into metal complex (decreases/increases) acidity and (lengthens/shortens) the H-H bond

What changes does oxidative addition to a metal result in? (4)

• +2 coordination number

• Mⁿ⁺ to M⁽ⁿ⁺²⁾⁺

• n+2 electrons; usually tending to 18 → increased stabilisation

• molecule generates a compound with X and Y cis to one-another

Oxidative Addition

where X and Y must have an electronegativity greater than the metal

metal nucleophilic attack

• SN2

• common for polar molecules

• trans addition

a) What is the mechanism for reductive elimination and b) what structural feature does it require?

a) exact opposite to oxidative addition

b) eliminated molecules cis to one another

TRUE OR FALSE: Oxidative addition and reductive elimination exist in an equilibrium

TRUE, BUT one direction is thermodynamically favoured

C-H bond activation

Irradiation or heat can leads to the loss of H₂ producing a 16 electron intermediate (by reductive elimination) which can undergo oxidative addition of C-H bonds

1,1-migratory insertion

primarily with CO ligands

What effect does migratory insertion have?

• -1 coordination number

• -2 electrons at metal center

1,2-Insertion

primarily with η2 -coordinated alkenes or alkynes

In what circumstances is β-elimination not common?

When the β-carbon to M has less than 2H

Wilkinson’s catalyst

[RhCl(PPh3 )3 ]; used to convert alkenes to alkanes with < 1 atm H₂

Enantioselective reactions require a (__) substrate

Enantioselective reactions require a prochiral substrate

How can branching (pictured) be prevented?

partial replacement of a catalyst’s ligand to induce steric effects

How is the nature of the interactions between the main group metal ion and the water molecules described?

predominantly electrostatic, non-directional

Covalency of interactions transition (__) main group metals

Covalency of interactions transition > main group metals

How many H₂O molecules in the first hydration sphere of metals?

typically six, except Li⁺ which has four due to its small size and low charge

What increases hydrated ionic radii?

increased charge density (small ion, large charge)

TRUE OR FALSE: neutral ligands result in more stable complexes for both transition and main group metals

FALSE: less stable for main group. Same effect as for large polarisable ions (eg. Br-)

stability of a complex with a Group 1 (__) Group 2 metal ion with same ligands

stability of a complex with a Group 1 < Group 2 metal ion

Put in order of complex stability with a) small donor ligands and b) multidentate ligands: Ca²⁺, Li⁺, Mg²⁺, Na⁺

Mg²⁺ > Ca²⁺ > Li⁺ > Na⁺

Ca²⁺ > Mg²⁺ > Na⁺> Li⁺

TRUE OR FALSE: chelating ligands provide stability

TRUE

Macrocyclic ligands form strong complexes with the Group(s) (__) elements

Macrocyclic ligands form strong complexes with the Group 1 elements

How can macrocyclic ligands be used for “selection”?

matching the cavity size with the “ionic” radius of elements

macrocyclic effect

the cyclic ligands are pre-organised, so the entropy change on ligation is even more positive therefore favourable than for chelating ligands

f orbitals

there are 7 with 3 angular nodes each

The term given to the f orbitals due to the electrons being kept away from the nucleus

non-penetrating

In what order are the orbitals after 4p filled?

5s, 4d, 5p, 4f