TM-Carbonyls

Question 1

CO X or L

Answer 1

L

Question 2

TM-CO complex structures

Answer 2

Metals with even number of electrons = mononuclear
Metals with odd number of electrons = make M-M bonds to satisfy 18e- rule

Question 3

Synergic bonding in TM-CO

Answer 3

σ-donation from CO 3σ* to vacant eg TM orbital
π-back donation (across 2 axes) from occupied M t2g to CO 2π*

Question 4

Consequences of synergic bonding

Answer 4

σ-donation = more electron density on M = more M π-back donation = strengthens and shortens M-CO = better σ….
σ-donation removes electron density from slightly ABMO CO 3σ* so slightly strengthens CO bond
π-back donation increases electron density in strong ABMO CO 2π* so weakens CO bond (major)

Question 5

Evidence for synergic bonding

Answer 5

CO only forms addicts with MG LA
As MC becomes more electron rich metal t2g AO destabilised therefore energy mismatch decreases and π-back donation increases = weaker CO bond

Question 6

External Nu- attack of M-CO complexes

Answer 6

CO ligands compete for electron density = each CO receives little π-back donation so σ-donation dominates = net flow of electron density from CO to TM = Cδ+ and Nu- attack