Introduction to organometallic compound

1. organometallic compounds
Dr Suhair Bani Atta

2. Part A:TOPICS:
 Introduction
 Ligands: bonding and spectroscopy
 18-electron rule
 Metalcarbonyls
 Isolobal principle
 Electron counting schemes
 Types of organometallic reactions

3. Organometallic compounds are chemical compounds that
contain at least one bond between a carbon atom of an organic
molecule and a metal. They play a crucial role in various fields,
including catalysis, organic synthesis, and materials science.

4. Organometallic compounds are typically discussed in
terms of the metal as either:
 main-group compounds: The main-group metals of organometallic
compounds are typically considered to be those of the S-block (groups 1
and 2) and the heavier elements of the p-block (groups 13–15) in the
periodic table of elements.
 transition metal compounds. The transition metals include those
elements in the d- and f-blocks (groups 3–12).


5. Hapticity of a ligand:
 The hapticity of a ligand is the number of atoms in a ligand that directly
interacts with the metal center.
 The Greek prefix ղ (eta) is commonly encountered; the letter is accompanied
by a superscript number(e.g. ղ 3).
 For example, the cyclopentadienyl ligand, C5H5- or Cp-,

6. Group 1: alkali metal organometallics
 Organic compounds such as terminal alkynes , which contain
relatively acidic hydrogen atoms, form salts with the alkali metals:

7.  Colorless alkyl derivatives of Na and K are obtained by transmetallation
reactions starting from mercury dialkyls:

8. Examples:

9. Organolithium compounds importance
 Organolithium compounds (in particular MeLi and nBuLi) are of great
importance as synthetic reagents.
 Many uses of organolithium alkyls and aryls are the conversions of boron
trihalides to organoboron compounds

10. Group 2organometallics
 Reaction types best make beryllium alkyls and aryls :
 In the vapor phase,Me2Be is monomeric, with a linear
 but in the solid-state structure is polymeric

11. The solid-state structure of Cp2Be

12. sandwich structure in which the two C5-
rings are coparallel and staggered

13. Bonding in cyclopentadienyl complexes

15. The MO diagram:

16. Magnesium
 Alkyl and aryl magnesium halides (Grignard reagents, represented by
the formula RMgX) are extremely well known on account of their uses
in synthetic organic chemistry
 1- preparation of a Grignard reagent:
 2- Transmetallation of a suitable organomercury compound is a useful
means of preparing pure Grignard reagents:

17. R = Cp-

19. Transition metal Organometallic
compounds:

20. Common types of ligand: bonding and spectroscopy
1-σ -Bonded alkyl, aryl, and related ligands
 In complexes such as WMe6, [MoMe7] , TiMe4, and MeMn(CO)5,
 the M-C-Me bond can be described as a localized 2c-2e interaction,
i.e., it parallels that for the [ղ1-Cp ligand], the Fe -CPh, Fe- CCHO
bond.

21. 2-Carbonyl ligands

22.  Bonding in one M-----CO interaction. Figure 23.1a, shows the interaction
between the highest occupied molecular orbital of CO (which has
predominantly carbon character) and a vacant orbital on the metal center.
 As a result of this interaction, an electronic charge is donated from the CO
ligand to the metal.
 Figure23.1bshows the π-interaction that leads to back-donation charge from
metal to ligand;

23. Carbon monoxide is:

24.  The traditional bonding model for an MCO
interaction emphasizes OC M-donation
and significant M CO- back-donation
leading to C –O bond weakening and a
concomitant lowering of CO.H

25. synergic effect
 “The interplay of donation and back-donation of electronic charge
between a metal and an acceptor ligand is an example .”

26. Dewar–Chatt–Duncanson model.
 This ‘donation/back-donation’


27. M-CO bonding mods
 1- terminal
 2-bridging
 3-semi-bridging

28. Evidence for a lowering of the C-O bond
 The IR spectrum of free CO, an absorption at 2143 cm-1 is assigned to the C-
O stretching mode
 The lower the value of CO, the weaker the C-O bond, and this indicates
greater back-donation of charge from metal to CO

29. Negative charge effect on the C-O bond
 the additional negative charge is delocalized onto the ligands, causing a
decrease in CO
 and weke the C-O bond
 Terminal vs bridging

30. Hydride ligands:
The charge distribution expected for an H atom
attached to a positive metal center
hydride ligands behave as protons, being removed by base or
introduced by treatment with acid

31. modes of bonding
 Hydride ligands can adopt terminal, bridging (in metal clusters) interstitial modes of
bonding
-A localized 2c-2e M—H bond is an appropriate description for the terminal hydride,
-delocalized 3c-2e or 4c-2e interactions describe վ-H and վ3-H interactions,
-7c-2e interaction is appropriate for an interstitial hydride in an octahedral cage

32. Phosphine and related ligands: are σ-donor and π-acceptor
ligands
 Monodentate organa phosphines may be tertiary (PR3),
secondary (PR2H) or primary (PRH2) and are terminally bound;
PF3 behaves similarly. Bridging modes can be adopted by [PR2]-
or [PR]-2 ligands.

33. π-Bonded organic ligands

34. metallacyclopropane ring.
 The extent of back-donation to is influenced by the
nature of R, and is enhanced by electron-withdrawing groups
such as CN. In the extreme, the π-contribution to the C-C C bond
is completely removed, and the complex metallacyclopropane
ring.

37. Dinitrogen
 The molecules N2 and CO are isoelectronic
 Complexes of N2 are not as stable as those of CO, and far
fewer examples are known
 Terminal units are linear (like a terminal
), but bridging N2 ligands do not mimic bridging CO groups
 but bridging N2 ligands do not mimic bridging CO groups

38. Dihydrogen

41. The 18-electron rule
 Low oxidation state organometallic complexes tend to obey the
18-electron rule
 This rule often breaks down for early and late d-block
metals as examples later in the chapter show: 16-electron
complexes are common, e.g., Rh(I), Ir(I), Pd(0), and Pt(0).

42. Some commonly encountered ligands donate
the following numbers of valence electrons:

43. Examples:

45. Extra exercises:

47. Self-study exercises

50. Metal carbonyls: synthesis, physical
properties and structure

51. Naming organometallic compounds follows specific
conventions based on IUPAC guidelines.
 Basic Principles:
 Identify the metal and the organic groups attached.
 Use the metal's name as a prefix or suffix, depending on its position in the compound.
 Number the carbon atoms in the organic ligand to indicate their attachment to the metal.
 Common Naming Conventions:
 Simple Organometallics: Name the organic ligand first, followed by the metal. For example,
in methyl lithium (CH3Li), "methyl" is the organic part, and "lithium" is the metal.
 Complex Ligands: Use prefixes (di-, tri-, etc.) for multiple identical ligands. For example, in
(C2H5)2Zn, it is named diethylzinc.
 Anionic Ligands: If the organic group is an anion, use the suffix "-ide" or "-ate" as
appropriate. For example, in sodium methoxide (NaOCH3), "methoxide" indicates the
anionic form of methanol.

52.  Special Cases:
 Bidentate and Polydentate Ligands: Name the ligand with its full name,
indicating its binding sites. For example, ethylenediamine is a bidentate
ligand.
 Metal Oxidation States: Indicate the oxidation state of the metal in Roman
numerals in parentheses. For example, in iron(III) acetylacetonate, the iron is
in the +3 oxidation state.

53. Ligands: bonding and spectroscopy