Organic Chemistry/Organometallics

Organometallics is the branch of chemical science studying the chemistry of molecules that have direct carbon-metal bonds. 25% developed  as of Dec 30, 2005 (Dec 30, 2005)

s ,d, p blocks

Main group organometallic chemistryEdit

Alkali and akaline earths organometallicEdit

  • Li, Na, K organyls
  • Be organyls
  • Mg organyls

Aluminium groupEdit

Silicon groupEdit

  • Si organyls
  • Ga organyls

Pb, Sb, Sn, HgEdit

Transition-metal organometallic chemistryEdit

The organometallic chemistry of the transition elements is quite different from the main-group ones due to the availability for bonding of the n d orbitals with consequent ability for the central atom to change geometry and expand the octet.

Crystal field theory

Single σ-bondingEdit

  1. M-alkyl

β-eliminationEdit

π-acceptor bondingEdit

alkene complexesEdit

 

 

CO complexesEdit

  1. σ *→dσ
  2. dπ→π *

These interactions are synergicin increading the M-CO bond strength. In fact, the second interaction, as known as pi backbonding increases the available electron density on the CO.

The partial filling of the π* orbital leads to a weakened C-O triple bond, as showed from the stretching frequencies (in cm-1) of CO free and in M/CO complexes.

free CO 2143
V(CO)6 1976
Ni(CO)4 2057
Cr(CO)6 2000

Arene complexesEdit

Carbenes and carbynes compoundsEdit

Fischer carbenesEdit

By treatment of a CO complex with a strong nucleophile  

Schrock carbenesEdit

 

Catalysis by organometallic compoundsEdit

MetathesisEdit

Richard Schrock(MIT, USA) and Robert Grubbs (CalTech, USA) received 2005 Nobel prize for their work on the subject. Metathesis is the exchange of the termination between two alkenes [1]

 

It occurs via the carbene species nowaday known as Schrock's carbenes

 

  1. ^ Grubbs, Olefin metathesis, Tetrahedron

Ziegler-Natta polymerisationEdit

Ziegler-Natta catalyst Ziegler in the 40's worked on the oligomerisation of ethylene by aluminium alkyls via the reaction HAl-R + CH2=CH2 -> HAl-CH2CH2-R

 

Enantioselective hydrogenationEdit

Wilkinson's

 

HydroformylationEdit

Hydroformylation Hydroformylation is the process that transforms an alkene into an aldehyde by reaction with CO.

The catalyst is a hydridocarbonyl complex, HCO(CO)5 

Fischer-Tropsch synthesisEdit

Fischer-Tropsch synthesis is the heterogeneously-catalysed formation of hydrocarbons (alkanes and alkenes) from CO and hydrogen (synthesis gas). It can be seen as the inverse of synthesis gas preparation (although this is usually from methane and lighter hydrocarbons). It is the heart of the gas-to-liquids processes developed commercially by big petrochemical firms in the 90's.

Organometallics in living systemsEdit

The only example of a biological molecule containing direct carbon-metal bonds is cobalamin, as known as vitamin B12