Copper-nitrosyl complex

Tolman W.B. (1995) Synthetic Modeling of the Interactions of Nitrogen Oxides with Copper Proteins Copper Nitrosyl Complexes Relevant to Putative Denitrification Intermediates, Adv. Chem. Ser., 246, 195. 

In a related observation, reported by Tanaka et al. (81), the copper(II) complex Cu(tpa)2+ (tpa = tris[(2-pyridyl)methyl] amine) was shown to serve as a catalyst for the electrochemical reduction of nitrite to N20 and traces of NO in aqueous solution. NO and/or a copper nitrosyl complex would appear to be the likely intermediates in this process (81a). 

The existence of copper-nitrosyl complexes of biological significance has been briefly discussed here (Section VII). It is worth pointing out that nitrosyl complexes of other metal-containing proteins may form, and that these may be important in understanding the effects of NO on living cells. Nitrosyl complexes of many other metals are well documented (e.g., Werner and Karrer, 1918 Moeller, 1952) and include complexes of nickel, cobalt, and ruthenium. Some such complexes may be less obvious than the paramagnetic and often colorful... 

Ruggiero, C. E., Carrier, S. M., Antholine, W. E., Whittaker, J. W., Cramer, C. J., and Tolman, W. B. (1993). Synthesis and structure and spectroscopic characterization of mononuclear copper nitrosyl complexes Models for nitric oxide adducts of copper proteins and copper exchange zeolites. J. Am. Chem. Soc. 115, 11285-11298. 

Recently several new active site model compounds have been prepared (Carrier et al., 1991) using sterically hindered tris(pyrazoyI)hydroborate (L) and tris(thioethyl)amine (L2) as ligands. The copper nitrite complex LCu11 (N02) models the enzyme substrate complex and X-ray studies confirm that the complex is tetrahedral. A mononuclear copper—nitrosyl complex similar to postulated NO adducts of copper proteins has also been prepared from LCu1 (MeCN) and NO, which has been tentatively identified as a Cu11 -NO species on the basis of IR (v NO 1711 cm 1) and ESR evidence. 

Copper Nitrosyl Complexes Relevant to Putative Denitrification Intermediates... 

This chapter focuses on the chemistry ofbiomimetic copper nitrosyl complexes relevant to the NO-copper interactions in proteins that are central players in dissimilatory nitrogen oxide reduction (denitrification). The current state of knowledge of NO-copper interactions in nitrite reductase, a key denitrifying enzyme, is briefly surveyed the syntheses, structures, and reactivity of copper nitrosyl model complexes prepared to date are presented and the insight these model studies provide into the mechanisms of denitrification and the structures of other copper protein nitrosyl intermediates are discussed. Emphasis is placed on analysis of the geometric features, electronic structures, and biomimetic reactivity with NO or NOf of the only structurally characterized copper nitrosyls, a dicopper(II) complex bridged by NO and a mononuclear tris(pyrazolyl)hydroborate complex having a Cu(I)-NO formulation. 

The first copper nitrosyl complex to be structurally characterized, 2, was prepared by treatment of a dicopper(I) compound, 1, with NO+ (47) (Scheme 2). It was also synthesized from the dicopper(I) precursor, n-Bu4N(N02), and two equivalents of HPF6-Et20 in a reaction that models the proposed initial nitrite dehydration step (Scheme 1) carried out by copper NiR (48). An X-ray crystallographic study revealed a symmetrically bound nitrosyl ligand in 2 with bond distances Cu-N = 2.036 (10) A and N-O = 1.176 (1) A. (The numbers in parenthe-... 

In the presence of metal catalysts nitrosations using nitric oxide proceed rapidly and it is clear that a very powerful nitrosating species is produced. Rate measurements on the reaction of diethylamine with nitric oxide in the presence of Cu(II) salts indicated that a copper-nitrosyl complex was that species (Brackman and Smit, 1965). Many metal-nitrosyl complexes are now known... 

Paul PP, Tyeklar Z et al (1990) Isolation and X-ray structure of a dinuclear copper-nitrosyl complex. J Am Chem Soc 112 2430-2432... 

Wright AM, Wu G, Hayton TW. Structural characterization of a copper nitrosyl complex with a CuNOflO configuration. J Am Chem Soc 2010 132(41) 14336-7. 

NO is very reactive towards copper ions, both Cu(I) and Cu(II). Until very recently only two copper nitrosyl X-ray structures were known, one possessing a bridging Cu"-rNO)-Cu" structure and formulation [v(N-O) = 1460 cm ] [78], the other being a mononuclear copper-nitrosyl complex [(Tp )Cu(NO)j (R= Bu, R = H) ... 

The copper nitrosyl complex [(Tp )Cu(NO)] was mentioned above [80]. Interestingly, Tolman and coworkers [160] found that with a less-crowded Tp h-gand (R=mesityl, R = H or R=R = Me), a corresponding Cu-NO species could be detected but ultimately NO disproportionation occurred and a Cu(II) nitrite complex and N2O were detected as products (Scheme 2.8). 

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