Nitro complexes

The 4-hydroxy-1-alkene (homoallylic alcohol) 81 is oxidized to the hetni-acetal 82 of the aldehyde by the participation of the OH group when there is a substituent at C3. In the absence of the substituent, a ketone is obtained. The hemiacetal is converted into butyrolactone 83[117], When Pd nitro complex is used as a catalyst in /-BuOH under oxygen, acetals are obtained from homoallylic alcohols even in the absence of a substituent at C-3[l 18], /-Allylamine is oxidized to the acetal 84 of the aldehyde selectively by participation of the amino group[l 19],... 

Mn2(H2P202)2) is the stable product in the potentiometric deterrnination of manganese. Manganese(III) does not coordinate with amines or nitro complexes, but it does make manganicyanides of the types M2(Mn(CN)g) and M2(Mn(CN) (OH)), which are similar to the ferricyanides. The K", Na", LC and manganicyanides have been prepared and slowly hydroly2e in water to MnO(OH). 

A typical value for the N O distance in nitro complexes is 124 pm whereas in nitrito complexes the terminal N-O (121pm) is shorter than the internal N-O(M) 129 pm. In the bidentate chelating mode (iii) the 2 M O distances may be fairly similar as in [Cu(bipy)2(02N)]N03 or quite different as in [Cu(bipy)(02N)2] ... 

Other nitrosyl compounds such as, K[NOBr5lr], K2[NOCLsRu] and [NO(NH3)sRu]Cl3, have also shown vasodilatory activity, presumably by releasing NO, but are too toxic for clinical use. A nitro complex, [Cl(02NXbpy)2Ru], which probably releases NOJ, exhibited higher activity than sodium nitrite [38]. 

Nitroprusside reacts with hydroxide to yield the corresponding nitro complex. The rate is first order in both reactants and probably involves nucleophilic attack by OH on the NO followed by proton ionization. Infrared studies on 0-labeled compounds indicate the NOJ to be bound as nitro (-NO2) rather than as nitrito (-ONO) [3, 116]. 

Hydroxide attack on complexes of the type cis-[(NO)L(bpy)2Ru ] also yields the corresponding nitro complex [118]. The equilibrium constants for these reactions are a strong function of the cis-ligand and increased by 10 on changing L from a jr-donor (Cl ) to a rr-acceptor (py) [98]. The ability of the nitro complexes to transfer an oxygen atom to a reductant such as triphenyl-phosphine is also a function of the cis-ligand [98]. 

Table III also shows the values of the equilibrium constants, KVAp for the conversion of iron nitrosyl complexes into the corresponding nitro derivatives. Keq decreases downwards, meaning that the conversions are obtained at a lower pH for the complexes at the top of the table. Thus, NP can be fully converted into the nitro complex only at pHs greater than 10. The NO+ N02 conversion, together with the release of N02 from the coordination sphere, are key features in some enzymatic reactions leading to oxidation of nitrogen hydrides to nitrite (14). The above conversion and release must occur under physiological conditions with the hydroxylaminoreductase enzyme (HAO), in which the substrate is seemingly oxidized through two electron paths involving HNO and NO+ as intermediates. Evidently, the mechanistic requirements are closely related to the structure of the heme sites in HAO (69). No direct evidence of bound nitrite intermediates has been reported, however, and this was also the case for the reductive nitrosylation processes associated with ferri-heme chemistry (Fig. 4) (25).

In the above instance the kinetically favored nitrito complex isomenzes to the thermodynamically favored nitro complex in seconds. 

Nitrite complexes can be simply prepared by metathetical replacement with nitrite ion.1163 The structure of n-anj-Pt(N02)2 P-(p-tol)3 2 has a Pt—N distance of 2.030(5) A and N—O distances of 1.228(8) A and 1.98(7) A.11 4 Chemical shift (5 Pt) and coupling constant data have been tabulated for a large group of platinum(II) and (IV) nitro complexes. Both chemical shift and coupling constant changes upon ligand substitution are dominated by the nature of the trans ligand/165... 

In (95), the initial formation of the bent nitrosyl species [Co(NO)(en)2Cl]+ (220) is followed by electrophilic attack of free NO and then by reaction with a second NO molecule leading to products. Since the nitro complex produced in this reaction has the same stereochemistry as the reactant Co111—NO- species, it has been proposed that the Co—N(nitrosyl) bond remains intact throughout the reaction sequence, thus requiring free NO to attack via its oxygen end (193). This proposal requires further proof. 

Hydroxide ion attack, again leading to a nitro complex, has been observed in a ruthenium system. The process is reversed in the presence of H+ (equation 21). 

In one instance, however, clear evidence has been obtained to suggest the formation of a peroxynitrate intermediate. Thus, the nickel complex Ni(NO)CI(diphos) reacts with 02 either in dimethylformamide or on irradiation in dichloromethane to form the nitro complex Ni(N02)Cl(di-phos). Evidence for the formation of a d9 nickel(I) intermediate came from ESR studies. This intermediate was considered to be the peroxy-bridge species (4) and the reaction sequence was believed to follow the sequence shown in Scheme 1. 

Oxidation of Alkenes by Palladium(II)- and Rhodium(III)-Nitro Complexes 373... 

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