Cobalt, nitrosyl complexes, reaction with

Optically active organometallic complexes have been used to study stereochemical reactions. Substituted cobalt nitrosyl complexes are interesting chiral see Chiral) complexes because they exhibit tetrahedral structures, whereas most optically active organometallic complexes are half-sandwich structmes with octahedral geometries. Diastereomeric cobalt complexes of the type Co(CO)(NO)(L)( L) (L = phosphite or phosphane L = optically active phosphane or isocyanide) have been synthesized from (4) via substitution (Scheme 6). ... 

PtG. 20. The proposed mechanism for the reaction of 5-coordinate cobalt nitrosyl complexes with oxygen. 

Clarkson SG, Basolo F (1973) Study of reaction of some cobalt nitrosyl complexes with oxygen. Inorg Chem 12 1528-1534... 

General accounts of the reactivity of coordinated nitrosyls are available.106 121 124 A metal ion or metal complex is unable to generate the reactivity of ionic NO+ towards nucleophiles (i.e. OH-, RS-, RHN-) or of NO- towards electrophiles (i.e. H+, PhCH2X), but it can present NO in a less reactive form under conditions inappropriate to the free ion. Thus linear coordination with vNO > 1886 cm 1 may promote nucleophilic reactions at N, and bent coordination with the higher electron density on N (vNO < 1700cm-1) may promote electrophilic attack by H+, 02, NO and PhCHjBr.125 No cobalt nitrosyl is known to undergo nucleophilic attack on the nitrosyl group. Normally linear coordination is associated with four or five coordination and the nucleophile adds to the unsaturated metal instead. However a number of electrophilic reactions are known (Table 13). A recent discussion of these is recommended.124... 

Well-characterized complexes of the MNO 8 class are scarce (Table 7.2).62 Five-coordinate species with bound NO and square pyramidal geometries are dominant,10 18 probably related to the great trans-effect of NO-. Most common are the cobalt nitrosyl porphyrins.18 By reacting with monodentate ligands (NCS-, Cl-, Br-, etc.), six-coordinate complexes may be obtained. Reaction 7.28 describes the preparation of the first compound of this type studied by X-ray methods.13s... 

Manganese porphyrins also form nitrosyl complexes. Fast (ca. 10°M s ) reaction of Mn(II) with NO yields stable MnNO complexes (73) that show a linear Mn—N—0 geometry (74). Interestingly, no reductive nitrosylation is observed for the reaction of Mn(III) with NO (73). Cobalt porphyrins also form stable nitrosyl complexes. The CoNO species obtained, for example, by reaction of NO with Co(Il) porphyrins have been explored as isoelectronic... 

Extensive studies of the reductions of nitro substituents in the cobalt(II) cage complex, [Co(sar)] ", have been reported. These groups do not mediate electron transfer in the reactions of the metal center. The complexes [Ru(Hedta)(NO )] and [Fe(Hedta)(NO )] are catalysts in the electrochemical reduction of NOf, and the mechanism of the reaction has been investigated. Whether the product is mainly NjO or NH/ can be determined by appropriate choice of catalyst and pH. The chromium(I) complex, [Cr(N0)(H20)5] ", is resistant to oxidation. Reactions with the powerful oxidants lO and BrO are thought to be inner-sphere, with attack on the nitrosyl nitrogen atom to give nitrite and chromium(III) as products in a net two-electron reaction. ... 

Oxygen-transfer reactions have been shown to occur from cobalt(III)-nitro complexes to alkenes coordinated to palladium.472 Thus ethylene and propene have been oxidized stoichiometrically in quantitative yields to acetaldehyde and acetone respectively, with the concomitant reduction of the nitro- to the nitrosyl-cobalt analog. A catalytic transformation with turnover numbers of 4-12 can be achieved at 70 °C in diglyme. The mechanism shown in Scheme 11 has been suggested. 

Formation of Ni(CO)4 or Co(CO)4- by the cyanide method depends upon the stepwise substitution of the anion of the cyano complex by the iso-electronic carbon monoxide molecule. By treating Co2(CO)8 with potassium cyanide we obtained cyanocarbonyls of cobalt of low oxidation number (83). In reactions of the nitrosyl carbonyls of iron and cobalt, Behrens (86) substituted all the CO groups with CN to give K3[Co(NO)(CN)3] or... 

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