Metal carbonyls are coordination complexes of transition metals with carbon monoxide ligands. They were first synthesized in 1868 by passing carbon monoxide over platinum. Metal carbonyls typically obey the 18 electron rule and are often diamagnetic. They have applications as catalysts in organic synthesis and in producing pure metals like nickel. Precautions must be taken when using metal carbonyls due to their toxicity.

1. Satyabrata Sendh
MSc part I (2017-18)
Department Of Chemistry
Berhampur University,
Odisha,India

2. INTRODUCTION
CLASSIFICATION
PREPARATION&PROPERTIES
STRUCTURE&BONDING
APPLICATIONS

3. •Metal carbonyls are coordination complexes of transition metals with carbon
monoxide ligands in low oxidation state. In this ,CO ligands acts as neutral ligands
•Metal carbonyl compounds were first synthesized in by Paul Schützenberger in 1868
by passing chlorine and carbon monoxide over platinum black, where
dicarbonyldichloroplatinum (Pt(CO)2Cl2) was formed.
•Although many compounds were produced, they couldn’t be fully characterized until
the development of X-ray diffraction, and IR and NMR spectroscopy.
•In general, these compounds obey the “18 electron rule.”
•Normally dimagnetics.
•Mononerics are colourless where polymerics are coloured.
•Poor conductors of electricity & Sublimated at low temp
•Soluble in organic solvents.

5. 1. Direct reaction of metal with carbon monoxide
Ni + 4 CO → Ni(CO)4 (1 bar, 55 °C)
Fe + 5 CO → Fe(CO)5 (100 bar, 175 °C)
2. Reduction of metal salts and oxides
CrCl3 + Al + 6 CO → Cr(CO)6 + AlCl3
3. Preparation of dinuclear carbonyls from mononuclear
carbonyls (Photolysis and thermolysis )
Fe(CO)5 → Fe(CO)9+CO

6. 1.CO substitution
M(CO)n → M(CO)n-1 + L → M(CO)n-1L
2.REDUCTIONS
Mn2(CO)10 + 2 Na → 2 Na[Mn(CO)5]
Fe(CO)5 + 2 Na → Na2[Fe(CO)4] + CO
3.Nucleophilic attack at CO
Fe(CO)5 + NaOH → Na[Fe(CO)4CO2H]
4.With electrophiles
Fe(CO)5 + X2 → Fe(CO)4X2 + CO

7. Structure of CO According to VBT & MOT

8. Formation of σ-bond:
The overlapping of empty hybrid orbital on metal atom with the filled hybrid
orbital on carbon atom of carbon monoxide molecule through lone pair
electrons results into the formation of a M←CO σ-bond.
Formation of π-bond by back donation:
This bond is formed because of overlapping of filled dπ orbitals or hybrid dpπ
orbitals of metal atom with antibonding pi orbitals on CO molecule.

9. Bridging CO groups:
In addition to the linear M-C-O groups, the carbon monoxide ligand is also known
to form bridges.
 This type of bonding is observed in some binuclear and polynuclear carbonyls.
 It is denoted by μn–CO, where n indicates the number of metals bridged. While
n=2 is the most common value, it reaches to be 3 or 4 in certain less common
carbonyls.
In a terminal M-C-O group, the carbon monoxide donates two electrons to an
empty metal orbital, while in μ2–CO group, the M-C bond is formed by sharing of
one metal electron and one carbon electron.
M----M Bond
In some carbonyls another bond develops between metal-metal due to weak
overlap of the two singly filled appropriate hybrid orbitals.
Also called fractional single bond and longer than normal single bond.

10. Ni(CO)4

11. Fe2(CO)9

12. •The C-O vibration, typically denoted νCO, occurs at 2143 cm−1 for CO gas. The
energies of the νCO band for the metal carbonyls correlates with the strength of the
carbon-oxygen bond, and inversely correlated with the strength of the π-backbonding
between the metal and the carbon.
•The π basicity of the metal center depends on a lot of factors; in the isoelectronic series
(Ti to Fe) at the bottom of this section, the hexacarbonyls show decreasing π-
backbonding as one increases (makes more positive) the charge on the metal. π-Basic
ligands increase π-electron density at the metal, and improved backbonding reduces
νCO. (As the π* orbital on CO receives electrons from the metal, the CO bond weakens
and the ν decreases.)
Compound
[Fe(CO)6]2+ 2204
[Mn(CO)6]+ 2143
Cr(CO)6 2090
[V(CO)6]- 1860
[Ti(CO)6]2- 1750
ν (cm-1)

13. The more symmetrical the structure, the fewer CO stretches
are observed in the IR spectra.
If CO ligands are cis to each
other, both the symmetric stretch
and the asymmetric stretch will
involve a change in dipole
moment, and hence two peaks will
be observed in IR spectra.
If there is a center of
symmetry, with CO ligands trans
to each other, a symmetrical
stretch will not involve a change in
dipole moment, so it will be IR
inactive. An asymmetric stretch
will be seen in the IR spectrum.
As a result, trans carbonyls give
one peak in the IR spectrum.

14. 1. DETERMINATION OF GEOMETRY OF CARBONYLS :-
TBP structure of Fe(CO)5
Calculating no of IR active bands with Raman active bands and then tally with no of
bands predicted theoretically

15. 2. DETERMINATION OF BOND ORDER:-
3. DETERMINATION OF TERMINAL & BRIDGING CARBONYL GROUP:-

16. Ligand.Metal carbonyls are useful in organic synthesis and as catalysts or
catalyst
 Precursors in homogeneous catalysis, such as hydroformylation and Reppe
chemistry.
H2 + CO + CH3CH=CH2 → CH3CH2CH2CHO
Dicobalt octacarbonyl acts as catalyst
In the Mond process, nickel carbonyl is used to produce pure nickel.
In organometallic chemistry,metal carbonyls serve as precursors for the
preparation of other ogranometalic complexes.
Metal carbonyls are toxic by skin contact, inhalation or ingestion, in part because
of their ability to carbonylate hemoglobin to give carboxyhemoglobin, which
prevents the binding of O2. That is why precaution is used before using it.
SOME OTHER APPLICATIONS