Organic Chemistry/Organometallics

From Wikibooks, open books for an open world
Jump to navigation Jump to search

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 chemistry[edit]

Alkali and akaline earths organometallic[edit]

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

Aluminium group[edit]

Silicon group[edit]

  • Si organyls
  • Ga organyls

Pb, Sb, Sn, Hg[edit]

Transition-metal organometallic chemistry[edit]

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-bonding[edit]

  1. M-alkyl

β-elimination[edit]

π-acceptor bonding[edit]

alkene complexes[edit]

Pi-d bond structure.png

Resonace structure of-pi-d..png

CO complexes[edit]

  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 complexes[edit]

Carbenes and carbynes compounds[edit]

Fischer carbenes[edit]

By treatment of a CO complex with a strong nucleophile Carbene synthesis.png

Schrock carbenes[edit]

Wittig carbene reaction.png

Catalysis by organometallic compounds[edit]

Metathesis[edit]

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]

Metathesis of olefines.svg

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

Metathesis mechanism.png

  1. ^ Grubbs, Olefin metathesis, Tetrahedron

Ziegler-Natta polymerisation[edit]

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

Ziegler Natta catal mech.png

Enantioselective hydrogenation[edit]

Wilkinson's

CatalyticCycle.png

Hydroformylation[edit]

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 Hydroformylation1.png

Fischer-Tropsch synthesis[edit]

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 systems[edit]

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

Vitamin B12