Metal carbonyls

Introductory PPT on Metal Carbonyls having its' classification,structure and applications.This is a basic level PPT specially prepared for UG/PG Chemistry students.

1. M ETAL C ARBONYLS S atyabrata S endh MSc part I (2017-18) Department Of Chemistry Berhampur University, Odisha ,India

2. CONTENTS 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) 2 Cl 2 ) 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. INTRODUCTION

4. CLASSIFICATION

5. PREPARATIONS 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 CrCl 3 + Al + 6 CO → Cr(CO) 6 + AlCl 3 3. Preparation of dinuclear carbonyls from mononuclear carbonyls (Photolysis and thermolysis ) Fe(CO) 5 → Fe(CO) 9 +CO

6. CHEMICAL PROPERTIES 1.CO substitution M(CO) n → M(CO) n-1 + L → M(CO) n-1 L 2.REDUCTIONS Mn 2 (CO) 10 + 2 Na → 2 Na[Mn(CO) 5 ] Fe(CO) 5 + 2 Na → Na 2 [Fe(CO) 4 ] + CO 3.Nucleophilic attack at CO Fe(CO) 5 + NaOH → Na[Fe(CO) 4 CO 2 H] 4.With electrophiles Fe(CO) 5 + X 2 → Fe(CO) 4 X 2 + 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. Metal-Carbon bonding in carbonyl complexes

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. Structure of Ni(CO) 4

11. Structure of Fe 2 (CO) 9

12. CARBONYLS & IR SPECTRA The C-O vibration, typically denoted ν CO , 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. APPLICATIONS 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. H 2 + CO + CH 3 CH=CH 2 → CH 3 CH 2 CH 2 CHO 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 O 2. That is why precaution is used before using it. SOME OTHER APPLICATIONS