Metallic Nitrosyls

A number of other metallic nitrosyl complexes have been examined as NO-donor drugs but none have proven to be of value [38]. 

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Figure 1.46 A scrambling mechanism envisaged for the interconversion of the metal-nitrosyl linkages in [Ru(NO)2Cl(PPh3)2]+.

The report in 1968 of the first crystallographically characterized bent metal-nitrosyl linkage in [IrCl(NO)(CO)(PPh3)2]+BF4 [180],... 

Similar isomerizations have been noted for a number of complexes. As with metal nitrosyls, IR spectra can be used to indicate the manner of bonding, but there is an overlap region around 2080-2100 cm-1 where i/(C-N) is found for both N- and S-bonded thiocyanates (additionally, S-bonded thiocyanates usually give a much sharper i (C-N) band). 14N NQR has been shown to be a reliable discriminator, but X-ray diffraction is ultimately the most reliable method. 

Principles of structure, bonding and reactivity for metal nitrosyl complexes. J. H. Enemark and R. D. Feltham, Coord. Chem. Rev., 1974,13, 339-406 (126). 

Transition metal nitrosyls in organic synthesis and in pollution control. K. K. Pondey, Coord. Chem. Rev., 1983, 51, 69-98 (143). 

Recent developments in transition metal nitrosyl chemistry. N. G. Connelly, Inorg. Chim. Acta. Rev., 1972, 6, 47-89 (395). 

Metal-metal bonding, 1, 137, 169 gravimetry, 1, 525 history7, 1, 21, 23 nomenclature, 1,122, 123 Metal nitrosyls structure, 1, 16 Meta) oxides catalysts... 

Carter, O. L., McPhail, A. T. Sim, G. A. (1967) Metal-carbonyl and metal-nitrosyl complexes. Part V. The crystal and molecular structure of the tricarbonylchromium derivative of methyl benzoate, J. Chem. Soc. A, 1619-1626. 

Richter-Addo, G.B. and Legzdins, P. (1992) Metal Nitrosyls. Oxford University Press, New York. 

Ford, P.C., Bourassa, J., Miranda, K. et al. (1998) Photochemistry of metal nitrosyl complexes. Delivery of nitric oxide to biological targets, Coord. Chem. Rev., 171, 185. 

Lead(II) oxide Non-metals Lead(IV) oxide Non-metals Nitric acid Non-metals Nitrogen oxide Non-metals Nitrosyl fluoride Metals, etc. Nitryl fluoride Non-metals Oxygen difluoride Non-metals Potassium nitrite Boron Potassium nitrate Non-metals Silver difluoride Boron, etc. Sodium peroxide Non-metals... 

Iodine pentafluoride Metals Nitric acid Metals Nitrosyl fluoride Metals Perchloric acid Bismuth See other METALS... 

Dichlorine oxide Oxidisable materials Iodine pentafluoride Metals Iodine Metals Nitrosyl fluoride Metals Perchloric acid Antimony(III) compounds Potassium dioxide Metals Potassium permanganate Antimony, etc. 

Lead(II) oxide Non-metals Nitrosyl fluoride Metals, etc. Oxygen difluoride Non-metals Peroxyformic acid Non-metals Silver fluoride Non-metals... 

IV. Examples from the Chemical Biology of Metal Nitrosyl Complexes... 

Nitrosonium (NO+) is a strong oxidant and the reduction potential to NO has been measured in non-aqueous media (1.67 V vs. SCE in CH3CN), and estimated for water (Eq. (3)) (12,15). NO+ is subject to rapid hydrolysis to nitrite (2H+ + N02 ), and therefore if formed in biological media would be short-lived. However, other less water-sensitive chemical species can act as NO+ donors in reactions leading to the nitrosation of various substrates. For example, the reactions of certain metal nitrosyl complexes with nucleophiles such as R SH can lead to the transfer of NO+ as illustrated in Eq. (4). Such reactions will be discussed in greater detail below. 

Ligand substitution reactions of NO leading to metal-nitrosyl bond formation were first quantitatively studied for metalloporphyrins, (M(Por)), and heme proteins a few decades ago (20), and have been the subject of a recent review (20d). Despite the large volume of work, systematic mechanistic studies have been limited. As with the Rum(salen) complexes discussed above, photoexcitation of met allop or phyr in nitrosyls results in labilization of NO. In such studies, laser flash photolysis is used to labilize NO from a M(Por)(NO) precursor, and subsequent relaxation of the non-steady state system back to equilibrium (Eq. (9)) is monitored spectroscopically. 

Selected Reactions of Metal Nitrosyl Compounds with Nucleophiles... 

Reaction of metal nitrosyls with azide ion proceeds with formation of N2 and N20 (56). This can be viewed as the result of a nitrene transfer reaction in analogy with the Curtius rearrangement (62) and its organome-tallic counterpart (63). 

Some other reactions of metal nitrosyls LxM(NO) with various nucleophiles (Nuc) are summarized in Table III. The pattern indicated by the studies described above is repeated simple adduct formation occurs when the coordinated nitrosyls are sufficiently electrophilic and the nucleophiles sufficiently basic. The first species formed is probably the N-coordinated nucleophile nitrosyl adduct LrM(N(O)Nuc), e.g. Eq. (27). Subsequent reactions depend on the substitution lability of these species, as well as on the redox stability of the complex and of the ligand. 

The possible use of metal nitrosyls to activate the 4 -electron oxidant 02 has been of interest for some time and Scheme 7 illustrates some hypothetical pathways for accomplishing this (108,109). 

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