Organic ligand transfer between transition metals

ORGANIC LIGAND TRANSFER BETWEEN TRANSITION METALS... 

The Taft relation Ej 2 = P 2a + x, which was found to hold for organic compounds and some transition metal complexes can also be of use here (37). Phenyl compounds do not fit the relation. This is probably due to a mesomeric effect that depends on the dihedral angle between the phenyl and the NCS2 planes. For bulky substituents deviations are also found which could be caused by widening of the CNC angle, changing the hybridisation of the N. The low values of p indicate that the M.O. s involved in the electron transfer have little ligand contribution. 

The effect of transition metals on the thermo-oxidative stability of polymers is ascribed to reactions such as initiation, in which electron or ligand transfer between organic substrate and transition metal ion takes place. In these reactions the transition metal ions may act either as electron donors or as electron acceptors. 

Many complexes of metals with organic ligands absorb in the visible part of the spectrum and are important in quantitative analysis. The colours arise from (i) d- d transitions within the metal ion (these usually produce absorptions of low intensity) and (ii) n->n and n n transitions within the ligand. Another type of transition referred to as charge-transfer may also be operative in which an electron is transferred between an orbital in the ligand and an unfilled orbital of the metal or vice versa. These give rise to more intense absorption bands which are of analytical importance. 

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