The interconversion of inorganic-NOx compounds with their organo-NOx counterparts plays an important role in the global N-cycle. Heme enzymes and biomolecules are proposed to play key roles in such conversions in the environment. These interconversions may involve the formation of new carbon-nitrogen bonds from their metal-NO precursors. A pathway to such C-N bond formation involves nucleophilic attack at bound NO groups, a process that is well established in coordination chemistry. However, such reactivity in metalloporphyrin bioinorganic chemistry has lagged behind. We previously reported hydride attack at the NO ligand of ferric-NO compounds to yield Fe-HNO derivatives. We previously also demonstrated this nucleophilic attack to other carbon- and nitrogen-based nucleophiles on metalloporphyrin complexes of Fe. For example, aryl anion attack the NO ligand of [(porphyrin)Fe(NO)(L)]BF4 gives the neutral product (porphyrin)Fe(ArNO)(L), where L is a neutral nitrogeneous base. We have extended our investigations into related nucleophilic attacks at the bound NO groups in ruthenium nitrosyl porphyrins of the form [(porphyrin)Ru(NO)(L)]BF4. In our current work, we show that a similar reactivity pattern is present when C-based nucleophiles react with the Ru-NO cation to generate the neutral (porphyrin)Ru(RNO)(L) compounds that are relatively stable in air as solids. Some of these products are isolable in good yields and have been fully characterized by IR and 1H NMR spectroscopy. We also demonstrate that some N-based nucleophiles react with the bound NO groups to generate new N-N bonds. These and related reactions provide a chemical basis for understanding how heme compounds may be involved in heme-based nitrosations in nature.

Nucleophilic attack at the bound NO of cationic group 8 nitrosyl porphyrins

ACS Spring 2022

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