Reactions dinitrosyl complexes

The specific goal of the mechanistic studies of DcNOx reaction is to identify the key intermediates involved in the N—N and 0—0 bonds making, discriminate them from spectator species and ascertain the sequence and conditions of their appearance. To clarify the role of the mono- and dinitrosyl complexes as intermediates or spectators of the principal mechanistic reaction steps, it is necessary to develop a more in-depth insight into the structure-reactivity relationships for both adducts, and to understand the possible ways of attaching the second NO molecule to the mononitrosyl complex. 

Molybdenum dinitrosyl complexes with the general formula Mo(NO)2(CHR) (0R )2(A1C12)2 have been found to be active in a variety of metathesis reactions [110]. New alkylidenes could be identified. Variations such as Mo(NO)2(CHMe) (RC02)2 also are known [111]. Complexes of this type are believed to be more reduced than typical d° species discussed here, although they appear to be much more active as metathesis catalysts than typical Fischer-type carbene complexes. 

An important use of dinitrosyl complexes of molybdenum has been as catalyst precursors in the alkene disproportionation reaction. Thus [MoCl2(NO)2L2] (L = PPh3 or py) together with AlCl2Et forms an active homogeneous catalyst for alkene disproportionation. The catalysis appears to require loss of NO from the metal and the field has been reviewed.19,31... 

A different homogeneous catalyst system for the carbon monoxide reduc-tition of NO is based on transition metal dinitrosyl complexes and has been investigated by both Johnson and co-workers (184,186, 235), and Ibers and co-workers (185, 236). In 1973 Johnson and Bhaduri (184) reported the separate reactions (116) and (117) which appeared to presage catalysis of NO reduction via (113). Shortly thereafter, Haymore and Ibers (185) showed that Ir(NO)2L2 + and related dinitrosyl... 

If a green solution of [Rh(N0)Cl(N02)(PPh3)2] in benzene is allowed to stand, a brown complex is precipitated.244 This may be the dinitrosyl complex which can be obtained from trans-[RhCl(CO)(PPh3)2] and nitric oxide when the reaction is carried out in carbon tetrachloride234 or toluene13 solution. 

Dinitrosyl complexes of the type [Mo (NO)2X2] were obtained by reduction of [Mo04] by hydroxylamine in the presence of added anionic hgands X, where X = dithiocarbamate, dithiocarboxylate, alkoxide, 2-NH2C6H4E" (E = O or S), hydroxamic acids. Reaction of [Mo(NO)2(dttd)]... 

Flavodi-iron proteins containing a distinctive nonheme diiron/ flavin mononucleotide active site, catalyze reductive scavenging of dioxygen and NO in air sensitive microorganisms. Anaerobic addition of NO up to one NO per diferrous rmit results in formation of a diiron mononitrosyl complex, whereas further addition of NO results in two reaction pathways, one of which produces N2O and the diferric site and the other which produces a stable diiron-dinitrosyl complex. The production of N2O upon addition of NO to the mononitrosyl deflavo-protein was interpreted in terms of the li5rponitrite mechanism (71). 

In addition, when cts-[MoCl2(NO)2(diars)] is allowed to stand in methanol, [ MoCl2diars(NO) 2(/i,2-N202)] is isolated (253), this is an example of the conversion from a d -dinitrosyl complex to a d -hyponi-trite complex. A binuclear hyponitrite complex, [Pt2(/u,-N202)-(PPh3)4]2, has also been reported as the product of the reaction of (54) with NO (254). 

Fig. 25. Possible mechanism for the reaction of dinitrosyl complexes with carbon monoxide to give N2O and COj.

Fig. 2.3 HREELS spectra after NO dosing (in Langmuir (L)) on the (3 2 x V2) R45° Sn/Pt(100) alloy at 100 K [34]. After low NO exposures, a Vj peak at 1666 cm was observed from bent-atop NO. Higher NO exposure led to the appearance of a very broad peak at 1816 cmwhich can be decomposed into two peaks centered at 1821 and 1698 cmas shown in the inset. These two peaks were assigned to a surface dinitrosyl complex. Formation of adsorbed N O from the reaction of adsorbed NO, via a dinitrosyl intermediate, occurs at 100 K, as evidenced by the peaks at 580, 1234, and 2238 cm, which are assignments for the three normal modes of linear N O molecules N-N-0 bending N-N-O stretching (v ), and N-N stretching (v ) modes, respectively.

Grundy KR, Laing KR, Roper WR (1970) Dinitrosyl complexes of ruthenium and osmium and their reaction with oxygen. J Chem Soc D 1500-1501... 

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