♣ Olefin complexes ♣ These are organometallic complexes containing unsaturated ligands such as alkenes ♣ Zeise characterized the pale yellow crystalline solid of composition K[PtCl3.(C2H4)], which is now known as zeise salt. ♣ Structure and bonding in metal olefin complexes ♣ The structure of the anion of the Zeise salt was well established in 1975 ♣ The significant features of it: 1. The 3 Cl atoms and the middle point of the ethylene double bond form a square plane 2. The Pt atom is present in the centre of the square and C=C double bond of the ethylene molecule is perpendicular to the plane containing Pt and 3 Cl atoms 3. The C2H4 group is significantly distorted from planarity ♣ The metal atom has filled and empty orbitals. The bonding occurs in two ways 1. The filled π molecular orbitals of the ethylene molecule are donated to the suitably direct vacant orbitals of the metal to form alkene ----- metal sigma bond. 2. A back bond is formed by the overlap of the filled metal hybrid orbitals with the vacant π MO of the olefin. This leads to a π bond. ♣ The back bonding will strengthen the Pt – Olefin bond but it should weaken the C – C bond in alkene ♣ Note that, metal olefin bond is essentially electronutral because donation and back donation balance the electron density.
Posted on: Sun, 04 Aug 2013 11:33:48 +0000
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