Handout to practice: Organometallic Chemistry of Transition Metals PDF

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Topic 5. Organometallic Chemistry of Transition Metals

Synopsis I. Organometallic complexes of d-block metals, the 18 electron rule, electron count (covalent approach), common ligands, ligand hapticity, exceptions to 18e rules, geometry of the complexes, metal clusters II. The bonding of ligands to transition metal: carbon monoxide, phosphines, elkenes, polyalkenes, nitrosyls, hydrogen, alkyls; back-bonding; the influence of the bonding on the properties of both the central atom and the ligand, IR spectroscopy of complexes. III. Common and important reactions of organometallic species: oxidative addition, reductive elimination, b-hydrid elimination, migratory insertion, nucleophilic attack on coordinated ligands. Homogeneous catalysis.

Suggested textbooks: Inorganic chemistry by Catherine E. Housecroft and Alan G. Sharpe, 2012, 4th ed. E-book (Chapter 24 Organometallic chemistry: d-block elements)

Inorganic chemistry by D.F. Shriver and P.W. Atkins, any edition is good, available in our library. (Chapter 16 d- block organometallic compounds, chapter 17 homogeneous catalysis)

Definition Organometallic chemistry deals with molecules featuring ……………………………………………

Applications 

Homogeneous catalysis



Materials

O-organic

D-dye

L-……………………….

S-sensitized

E-…………………………….

S-……………………………..

D-………………………

C-………………………………….



Biomedical applications

18-electron rule A stable complex has a valence electron count of 18. (valence electron count of the next highest noble gas).

Electron count takes into account: metal valence electrons, ………………………………………..…………………………………….. ……………………………………..………………………………

Electron Count (covalent approach) = metal valence electrons + …………………………………………

………………………………

– (charge)

Number of metal valence electrons is the same as ………………………………………..

How many electrons metal donate towards total electron count of the following complexes? [Co(CO) 4]- Na+

Fe(CO)5…

Electrons provided by ligands

1 electron donors

2 electron donors

Cr(CO)6

Typical test/exam question Perform electron count for the following compounds HCo(CO)4

Fe(CO)5

Cr(CO)6

Ni(CO)4

3 electron donors

Hapticity of the ligand is the number of atoms …………………………………………………… …………………………………………………………………………………………………………

4 electron donors

5-electron donor -C5H5

6-electron donor

Perform electron count for the following compounds [Co(CO) 4]- Na+

IrCl(CO)(PPh3)2

Which of these is most likely to exist? HFe(CO)3Br(CH3)

H2Fe(CO)4

Which complex is more stable? Pd(PPh3)2

Pd(PPh3)4

Ti(-C5H5)2(-C5H5)2

Limitation of the 18 electron rule Exceptions are common on the left of the d-block due to

……………………………………

…………………………………………………………………………………………………. ………………………………………………………………………………………………….. …………………………………………………………………………………………………..

Perform electron count for the following compounds V(CO)5

W(CH3)6

[Sc(CO)7]+

Stable organometallic complexes with 16 valence electrons are common on the right of the d-block.

16-electron complexes are particularly common for d8-metals, for example Rh(….), Ir(…..),

……………………………………………………….

These complexes have …………………………………………………. geometry.

Perform electron count for the following compounds

GEOMETRY OF COMPLEXES

Perform electron count and draw the structure of Mo(CO)6

METAL CARBONYLS

Mond process, 1890 NiO (s) + H2 (g) → Ni (s) + H2O (g) ………………………………………….. ……………………………………………..

IrCl(CO)(PPh3)

Examples of neutral metal carbonyls 6

7

8

9

10 Ni(CO)4

Perform electron count and draw the structure of the following complexes Mn2(CO)10

Co2(CO)8

Perform electron count and draw the structure of the following complexes Na[Mn(CO)5]

HMn(CO)5

Fe2(CO)9

Deduce and sketch chemically reasonable structures for following complexes showing clearly the coordination mode of each ligand and the geometry at each metal. (Each complex conforms to 18 electron rule). Re2(CO)10

Ru(CO)5

Fe3(CO)12

BONDING IN ORGANOMETALLIC CHEMISTRY Carbon monoxide complexes

From which orbital CO will donate electron density?

……………………………………………….orbitals hybridise to form six………………… orbitals

………. ..orbitals are directed ……………………………………………………………….

…………… orbitals will ………………..

electrons from the CO ligands

…………… orbitals will from ……………………….-bonds with the ligands

The ……………… bond between CO and the metal can be depicted as follows:

The electron density from the metal will be ……………………………….. to ………. orbitals of CO

………….. orbitals of CO are empty and ……………. the electron density, from the metal d-orbitals.

The process of electron delocalisation other the …………… system of the ligand is known as …….………………………………………………………..

IR spectra of carbonyl compounds

As the electron density on a metal center increases ……………………………………………….. ……………………………………………………………………………………………………………

This …………………. the C-O bond by pumping more electron density into the carbonyl * orbital.

This ………………………….. the IR stretching frequency of CO absorption

Which of the following will have higher stretching frequency? [Re(CO)6]+

W(CO)6

Which of the following metal carbonyl IR spectra represents the compound with the least amount of electron density on the metal center?

IR of compound A shows CO stretching frequency at 2100cm-1 and IR of B at 1950 cm-1 Which compound will lose CO the easiest?

Which of the following metal carbonyls will have the highest CO stretching frequency? (hint F is more electron negative than Br)

The position of the carbonyl bands in the IR depends also on the bonding mode of the CO (terminal, bridging).

Not only CO stretching frequencies but also the number of CO bands are important

Number of CO bands relates to the …………………………………….. of the complexes

IR summary. the position of the carbonyl bands in the IR depends on: 1) ……………………………………………………… ……………………………………………………………………… 2) ……………………………………………………………………… ………………………………………………………………………

the number of CO bands relates to the ……………………………………………………………

Which of the following complexes display the greatest number of CO stretching bands in the IR spectrum?

The complex Ni3(5-C5H5)3(CO)2 has a single CO stretching absorption at 1771 cm-1. All 5-C5H5 ligands are in identical environment. Propose a structure of the complex....