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Metal carbonyl and related complexes (dative ligands). Textbook H: Chapter 2.1 – 2.2.7 Textbook A: Chapter 7.1 – 7.4. Stable binary carbonyls. Synthesis of metal carbonyl complexes. From CO Directly from reaction with the metal Ligand substitution Reductive carbonylation

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metal carbonyl and related complexes dative ligands

Metal carbonyl and related complexes (dative ligands)

Textbook H: Chapter 2.1 – 2.2.7

Textbook A: Chapter 7.1 – 7.4

synthesis of metal carbonyl complexes
Synthesis of metal carbonyl complexes
  • From CO
    • Directly from reaction with the metal
    • Ligand substitution
  • Reductive carbonylation
  • Deinsertion: not very common
bonding in co
Bonding in CO

13C NMR features, d: 180 – 250 ppm

bonding in co complexes
Bonding in CO complexes
  • Bonding in CO
    • The transfer of electrons from the lone pair of O to C leads to a C--O+ polarization, which is almost cancelled out by the C+-O- polarization (O electronegativity).
    • HOMO of CO is the C-lone pair (O orbitals are deeper-lying).
    • LUMO of CO (p*) is polarized toward C.
  • CO binds through C
    • s-bond removes electron density from C.
    • p-backbond increases electron density both at C and O.
  • Polarization of CO on binding
    • C more positive, O more negative
    • Dependent on the other ligands present
      • C is more electrophilic when good p acceptors are present or when the complex is cationic (s-bond is enhanced, p-backbond is weakened)
      • O is more nucleophilic when good p donors are present or when the complex is anionic
    • Can be followed by IR
      • The more important the p-backbond contribution, the weaker the C-O bond, the lower the stretching frequency.
backbonding
Backbonding

Experimental support for backdonation:

  • X-ray: in (C5H5)Mo(CO)3Me, M-C is 2.38 Å, M=C is 1.99 Å (>0.07 Å)
  • IR, n(CO):
    • free CO, 2149 cm-1
    • H3B-CO, 2178 cm-1
    • Cr(CO)6, 2000 cm-1
    • V(CO)6-, 1860 cm-1
    • Mn(CO)6+, 2090 cm-1
    • Cr(tren)(CO)3, 1880 cm-1 (tren = H2NCH2CH2NHCH2CH2NH2)
co frequency and phosphine ligands
CO frequency and phosphine ligands

p-Acid character: PMe3 ~ P(NR2)3 < PAr3 < P(OMe)3 < (POAr)3 < PCl3 < CO ~ PF3

phosphine ligands bonding
Phosphine ligands: bonding

As the electronegativity of the atom

attached to the phosphorus increases,

the s* orbital becomes lower in energy

and the phosphine is a better p-acceptor.

monodentate phosphines cone angles
Monodentate phosphines: cone angles

Reference: Tolman, C. A. Chem. Rev. 1977, 77, 313

nitrosyl no complexes binding
Nitrosyl (NO) complexes: binding
  • Two different coordination modes
electronic structure
Electronic Structure
  • Non-innocent ligand
  • M–N–O can range from 120–180°

+ e–

– e–

NO

NO+

NO–

Isoelectronic with O2

Isoelectronic with CO

binding modes and ir spectroscopy

Bent

Linear

Binding Modes and IR spectroscopy
  • Multiple binding modes
  • Effect on the NO stretching frequency

1900

1800

1700

1600

1500

1400

2000

νNO (cm-1)

enemark and feltham notation
Enemark and Feltham Notation

{M(NO)n}m

  • m = number of electrons in the metal d orbitals and the π*(NO) orbital

Allows to circumvent assigning oxidation states in difficult molecules

NO0 = 1 π*(NO) electron

Co0 = 9 d electrons

{CoNO}10

If considered NO+ the oxidation state is Co( –1)

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