Nucleophilic Substitution of η⁵-Pyrrolyl Ligands in Ruthenium(II) Complexes

The reaction of RuCl₂(PPh₃)₃ with pyrrolyllithium results in the formation of the pyrrolyl complex (NC₄H₄)RuCl(PPh₃)₂, 1, which has been characterized by an X-ray diffraction study. The structure confirms the η⁵-bonding mode for the pyrrolyl ligand. Ligand substitution reactions with 1 have led to the facile synthesis of related η⁵-pyrrolyl ruthenium complexes with other suppporting ligands. Reactions of the PEt₃ derivatives (NC₄H₄)RuX(PEt₃)₂, X = Cl and I, with aryl- and alkyllithium reagents resulted in nucleophilic substitution of the pyrrolyl ligand accompanied by hydrogen transfer to the metal ion, forming (2-RNC₄H₃)RuH(PEt₃)₂. The hydride products could be converted to the corresponding chloride derivatives in chlorinated solvents, and the complex (2-PhNC₄H₃)RuCl(PEt₃)₂ has been structurally characterized. A second nucleophilic substitution reaction on the coordinated pyrrolyl ligand has been characterized in some cases, and protonation of the substituted pyrrole complex led to isolation of the free substituted pyrrole with recycling of the ruthenium complex. The nucleophilic substitutions are sensitive to the electronic features of the supporting ligands in the complex and to the strength of the nucleophiles.