Pyrrole, alkylation organometallics

Organometallic chemistry of pyrrole is characterized by a delicate balance of the ti N)- and -coordination modes. Azacymantrene is an illustration of the considerable nucleophilicity of the heteroatom. However, azaferrocene can be alkylated at C2 and C3 sites. Ruthenium and osmium, rhodium, and iridium chemistry revealed the bridging function of pyrroles, including zwitterionic and pyrrolyne complex formation. The ti (CC) coordination of osmium(2- -) allows versatile derivatizations of the heteroring. 

The second structural type found for organometallic cobalt porphyrins contains an organic fragment bridged between the cobalt and one pyrrolic nitrogen. Cobalt complexes of N-alkyl- or N-arylporphyrins arc well established (but will not be specifically addressed here). The bridged complexes are derivatives of these where the N-alkyl group also forms a cr-bond to cobalt. They are also related to the axially... 

Alkyl substituents can also be built up by organometallic additions to acylindoles and pyrroles, followed by reduction of the resulting carbinols. Pyrrole-2-carboxaldehyde, for example, reacts with aryllithium reagents to give carbinols which can be reduced to 2-benzylpyrroles in situ. In this case, reduction was done by distilling liquid ammonia into the reaction mixture, followed by addition of lithium metal (Equation (89)) <8UOC5060>. 

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