Transition metal nitroso complexes

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Structure of the dye Naphthol Green B, which features of nitroso ligand bound to Fe(III). NaphtholGreenB.svg
Structure of the dye Naphthol Green B, which features of nitroso ligand bound to Fe(III).

Transition metal nitroso complexes are coordination complexes containing one or more organonitroso ligands (RNO). [1]

Contents

Structure and bonding

Organic nitroso compounds bind to metals in several ways, but most commonly as monodentate N-bonded ligands. Also known are O-bonded, η2-N,O-bonded. Dimers of organic nitroso compounds also bind in a κ2--O,O bidentate manner. Illustrative are Ru(acac)2(C6H5NO)2, where a pair nitrosobenzenes are monodentate, and [Ru(acac)2(μ−C6H5NO)]2 where two nitrosobenzenes bridge. [2]

Chelating nitroso ligands

Trapping of 1,2-dinitrosobenzene by Ru(II) BenzofuroxanRu.svg
Trapping of 1,2-dinitrosobenzene by Ru(II)

Arylnitroso compounds with a flanking hydroxy group are a well-developed, e.g. 1-nitroso-2-naphthol. They are precursors to anionic N,O chelating ligands. Chelating dinitrosoarenes are uncommon but have been investigated. [3]

Synthesis

Organic nitroso complexes can be prepared from preformed organic nitroso precursors. These precursors usually exist as N-N bonded dimers, but the dimer dissociates readily. This direct method is used to give W(CO)5(tert-BuNO) (where tert-Bu is (CH3)3C). [4] The Fe-porphyrin complex depicted below is prepared by this route. More complicated but more biorelevant routes involve degradation of precursors such as nitrobenzene and phenylhydroxylamine. [5]

Ni(PEt3)4 + i−PrNO2 → Ni(PEt3)2(η2-i−PrNO) + PEt3 + OPEt3 (Et = C2H5, i-Pr = (CH3)2CH)

The coupling of organic ligands and nitric oxide is yet another route. [1]

Connection to methemoglobinemia

Structure of Fe(octaethylporphyrin)(C6H5NO)(imidazole). This synthetic complex is thought to resemble heme inhibited by nitroso benzene. Color code: red = O, blue = N, Fe, gray = C, white = H. CSD CIF FAVGUE.png
Structure of Fe(octaethylporphyrin)(C6H5NO)(imidazole). This synthetic complex is thought to resemble heme inhibited by nitroso benzene. Color code: red = O, blue = N, Fe, gray = C, white = H.

Methemoglobinemia is a disorder where a large fraction of hemoglobin in one's blood has converted to inactive forms, generically called methemoglobin. Since methemoglobin is not an oxygen-carrier, methemoglobinemia is a serious disorder, sometimes fatal. Exposure to nitrobenzene, aniline, and their derivatives cause this disorder, which is attributed to their conversion to nitrosobenzene (and derivatives), which inactivate hemoglobin by forming a complex with the Fe center, precluding binding of O2. [6]

As indicated by the applications in dyeing, chelating aryl nitroso compounds often form deeply colored complexes

References

  1. 1 2 Lee, Jonghyuk; Chen, Li; West, Ann H.; Richter-Addo, George B. (2002). "Interactions of Organic Nitroso Compounds with Metals". Chemical Reviews. 102 (4): 1019–1066. doi:10.1021/cr0000731. PMID   11942786.
  2. ↑ Dey, Sanchaita; Panda, Sanjib; Ghosh, Prabir; Lahiri, Goutam Kumar (2019). "Electronically Triggered Switchable Binding Modes of the C -Organonitroso (ArNO) Moiety on the {Ru(acac)2} Platform". Inorganic Chemistry. 58 (2): 1627–1637. doi:10.1021/acs.inorgchem.8b03191. PMID   30615436.
  3. ↑ Chan, Siu-Chung; England, Jason; Wieghardt, Karl; Wong, Chun-Yuen (2014). "Trapping of the putative 1,2-dinitrosoarene intermediate of benzofuroxan tautomerization by coordination at ruthenium and exploration of its redox non-innocence". Chem. Sci. 5 (10): 3883–3887. doi:10.1039/C4SC01185F. hdl: 10356/107442 .
  4. ↑ Pilato, R. S.; McGettigan, C.; Geoffroy, G. L.; Rheingold, A. L.; Geib, S. J. (1990). "tert-Butylnitroso Complexes. Structural Characterization of W(CO)5(N(O)Bu-tert) and [CpFe(CO)(PPh3)(N(O)Bu-tert)]+". Organometallics. 9 (2): 312–17. doi:10.1021/om00116a004.
  5. ↑ Berman, R. S.; Kochi, J. K. (1980). "Kinetics and Mechanism of Oxygen Atom Transfer from Nitro Compounds Mediated by Nickel(0) Complexes". Inorganic Chemistry. 19: 248–254. doi:10.1021/ic50203a050.
  6. ↑ Godbout, Nathalie; Sanders, Lori K.; Salzmann, Renzo; Havlin, Robert H.; Wojdelski, Mark; Oldfield, Eric (1999). "Solid-State NMR, Mössbauer, Crystallographic, and Density Functional Theory Investigation of Fe−O2and Fe−O2Analogue Metalloporphyrins and Metalloproteins". Journal of the American Chemical Society. 121 (16): 3829–3844. doi:10.1021/ja9832820.
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