Organic Chemistry/Organometallics

Organometallics is the branch of chemical science studying the chemistry of molecules that have direct carbon-metal bonds. 25% Dec 30, 2005 thumb|300px|right|s ,d, p blocks Main group organometallic chemistry Alkali and alkaline earths organometallic Li, Na, K organyls Be organyls Mg organyls Aluminium group Silicon group Si organyls Ga organyls Pb, Sb, Sn, Hg Transition-metal organometallic chemistry 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 M-alkyl β-elimination π-acceptor bonding alkene complexes 350px Image:Resonace_structure_of-pi-d..png CO complexes σ *→dσ 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 CO2143V(CO)61976Ni(CO)42057Cr(CO)62000 Arene complexes Carbenes and carbynes compounds Fischer carbenes By treatment of a CO complex with a strong nucleophile Image:Carbene_synthesis.png Schrock carbenes Image:Wittig_carbene_reaction.png Catalysis by organometallic compounds Metathesis 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 Grubbs05 File:Metathesis of olefines.svg It occurs via the carbene species nowaday known as Schrock's carbenes 600px Grubbs05 Grubbs, Olefin metathesis, Tetrahedron Ziegler-Natta polymerisation 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 450px Enantioselective hydrogenation Wilkinson's Image:CatalyticCycle.png Hydroformylation 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 450px Fischer-Tropsch synthesis 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 The only example of a biological molecule containing direct carbon-metal bonds is cobalamin, as known as vitamin B12 center|300px|Vitamin B12