Copper nitrosyl complexes bridging

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. 

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 researchers noted that the theoretical model of the end-on terminal binding through the N (rather than 0)-atom is more consistent with the experimental spectroscopic data mode. The studies also revealed that Ru"-N20 bond is dominated by 7i back-donation, which, however, is weak compared to that found in the corresponding known ruthenium-nitrosyl complex. See further discussions below for possible bridge binding of N2O in a copper enzyme. 

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