Organometallic compound and Hapticity

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                   Father of organomellic chemistry -Edward Frankland

*Definition-organometallic chemistry is the study of  chemical compounds containing at least one chemical bond between a carbon atom of an organic compound and a metal including alkaline,alkaline earth metal,transition metal and other cases...
Exception-Na-CN...There is one M-C bond ,but it is not a organometallic compound.

*Bonding in organometallic compounds-It may be ionic,coordinate,covalent....

*Classification of organometallic compounds-

  A.On the basis of Metals-
     a.Main group organometallic compounds-organometallic compound having metals of S-block and P-block.

eg.RMgX,n-BuLi,S-BuLi,,t-BuLi,Al-Et3(triethylalluminium used as cocatalyst with TiCl4 in Ziegler natta catalist)
    The first main group organometallic compound was Cacodyl oxide or Malodorous oxide.

  b.Transition metal organometallic compound-organometallic compound having metals of D-block elements.

eg.R2CuLi(Gillmann reagent),Rh(PPh3)3Cl(willikinson's catalyst),Pd(PPh3)4
 The first transition organometallic compound is Zeise's salt.

  c.Lanthanide and actinide organometallic compound-
eg.M(C8H8)-uranocene

*Hepticity( η )-The number of donor atoms from the ligand that is directaly attached with metal  is called Hepticity.

a.Monohepto(  η1 )-
  eg:-M-CH₃                                                                         
       M-CH₂-CH₃₆
       M-C6H6₆₆₆
          M-CO-R

 b.Dihepto(η2)-
eg. [ η2- C3H6], [η2- C4H6]

 c.Trihepto(η3)-
allyls show-η1 and η3
So ligand which can show more than one hepticity is called flexional ligand.
eg.allyls show both η1 and  η3,[η3-C3H3]

d.  ( η4) :-[C4H6],Cyclo-octadiene,[C4H4],[C4Ph4].

e.  ( η5) :-[C5H5].

f.   ( η6) :-[C6H6].

g.  ( η7):-[C7H7].

h.  ( η8):-eg.η2-COT,η4-COT,η6-COT.(COT:-cyclo-octatetraene)

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