Ligand structures nitrosyl complexes

The syntheses, structures and properties of wide varieties of metal nitrosyl complexes have been well documented [4, 5, 20-23]. However, the bulk of the complexes reviewed previously are of academic interest and only a few of these metal nitrosyl complexes have been considered as biologically effective NO donors. It was observed that the metal nitrosyls with significant NO+ character are subject to attack from a variety of nucleophiles and have hypertensive properties. This could be due to the strong trans- labilizing effect of NO. In contrast, the metal nitrosyl compounds with the general formula [M(CN)5NO]n, where the NO ligand was either neutral (for M = Co) or anionic (for M = Cr) showed no vasodilatory effect [24]. 

In this paper author reported the reactivity of newly synthesized Co(III)-nitrosyls complexes with superoxide radical to follow nitric oxide dioxygenation. Two new Co(III)-nitrosyl complexes bearing N-tetramethylated cyclam (TMC) ligands, [(12-TMC)-Com(NO)]2+ (1) and [(13-TMC)Coin(NO)]2+ (2), were synthesized via [(TMC)Con(CH3CN)]2+ + NO(g) reactions. Spectroscopic and structural characterization showed that these compounds bind the nitrosyl moiety in a bent end-on fashion. Complexes 1 and 2 reacted with K02/2.2.2-ciyptand to produce [(12-TMC)Con(N02)]+ (3) and [(13-TMC)Con(N02)]+ (4), respectively these possess 0,0 -chelated nitrito ligands. 

Solid /8-CrPc reacts reversibly with gaseous NO at ambient temperature to give a 1 1 adduct, which reacts with both py and 02 (Scheme 117).596 No structural information is available on the oxidation product of the nitrosyl complex. In contrast to the /3 form, solid ar-CrPc is unreactive towards either 02 or NO, a difference ascribed to the solid-state structures of the two polymorphs.597 Although the distance between the phthalocyanine planes is similar (340 pm), in both cases the metal-metal distance increases from 340 to 480 pm on going from the a to the /3 form. These distances are sufficient to permit access of 02 or NO in the /8 form, while excluding them from the a form. The addition of py to CrPc(NO) causes the NO stretching band in the IR spectrum to intensify and to sharpen considerably. The diffuse nature of this band in CrPc(NO) indicates the presence of a perturbed NO ligand but the introduction of py causes lattice expansion and eliminates the perturbation. 

A parallel situation appears to obtain for the mixed allyl nitrosyl complex Ru(NO)(C3H5)L2 prepared by Schoonover and Eisenberg (231). This complex which is coordinatively saturated (NO+ and rf -allyl), forms a CO adduct which is assigned a bent nitrosyl structure (231). Further reaction under CO leads to the formation of Ru(CO)3L2 with the possible elimination of acrolein oxime. The coupling of the allyl and nitrosyl ligands can be viewed in this case as nucleophilic attack of NO- on an f/3-allyl species. Unlike in reaction (110), both of the moieties to be coupled lie within the same coordination sphere. The significance of these results is that it lends viability to the notion embodied in (109) in which a migratory insertion of nitrosyl occurs as NO-. 

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-... 

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