Tantalum complexes porphyrins

An interesting C-metalation of a coordinated pyrrol ligand in a rhenium complex has been described [19a]. Methylated aromatic hydrocarbons have been activated by (ZrCU) [19b], A novel mode of electrophilic activation of an aliphatic C-H bond, assisted by porphyrin complexes ofZr(IV) and achieved by the use of hydrides of lithium, sodium or potassium, has been reported [19c]. It has been shown that the ligands 2,3,5,6-tetraphenylphenoxide and 3,5-dimethyl-2,6-diphenylphenoxide undergo intramolecular activation by tantalum alkylidene groups at rates 20 and 100 times slower than that of the simple 2,6-diphenylphenoxide ligand [19d]. 

The most studied of the Group 5 porphyrins have been compounds with vanadyl and niobium metal ions no electrochemical data have yet been reported for tantalum porphyrins. Vanadium porphyrins have been synthesized as both V(IV) and V(II) complexes. The vanadyl derivatives, represented as (P)VO, generally undergo well-defined reduction and oxidation reactions involving the porphyrin, macrocyle the lower oxidation state V(II) complexes have been prepared as (P)V (L) and (P)V (L)2 derivatives, where P = T(p-Me)PP or OEP and L = THE or PPhMe2, but these species have not been examined as to their electrochemical properties [7]. 

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