Cobalt nitro complexes

Nitronate anions react with (jl-allyl)cobalt complexes prepared from acylation of 1,3-dienes by acetylcobalt tetracarbonyl to produce nitro enones (Eq. 5.50).74... 

The kinetics of base hydrolysis of several complexes of the type [Co(NH3)3L3] have been examined in order to see whether the mechanism for these uncharged complexes is the same as that operating for base hydrolysis of the standard cationic complexes (75). A comparison of kinetic parameters - a small selection is given in Table II (76,77) - suggests that all cobalt(III)-nitro-amine complexes, charged and uncharged, undergo base hydrolysis by the SnICB (Dch) mechanism. 

On the basis of these observations and conclusions it was suggested that the cobalt complexes described above might follow a related pathway. Here, however, it can be argued that the presence of base in, e.g. the reactions of Co(dmgH)2NO, leads initially to the quantitative formation of Co,(dmgH)2(NO)B. In this case attack of 02 leads first to the peroxy compounds and then, because of the absence of a suitable NO+ compound, rearrangement occurs to give the nitrito derivative. Clearly whether or not nitro or nitrato compounds are produced would depend on the concentration of base B. In some cases it is possible to obtain mixtures of such products. These oxidations are also observed for other metals, e.g. equations (37) and (38). 

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. 

Amino-acid Complexes. X-Ray crystal structures have been reported for many cobalt(m) amino-acid complexes. Potassium dinitrobis(P-alaninato)cobaltate(m) has octahedral co-ordination about the cobalt, trans nitro-groups, and a trans arrangement of amino N- and carboxylato O-donors from the bidentate P-alaninates.371 In Ca[Co(aspar-tate)2] there are two isomeric ions the cis(N)trans Os) (64) and cis(lSl)trans 06) (65),... 

Table 14 Preparations Some Cobalt(III) Nitro (N02) and Nilrito (ONO) Complexes... 

O3BF4RU2C15H13, Ruthenium(l+), jLCarbonic acid cobalt complexes, 21 120, 23 107, 112 platinum chain complex, 21 153, 154... 

NOCgHj, Benzoyl isocyanide, chromium complex, 26 32,34,35 N0C,3H,3, Formanide, N-(l-(l-naphthal-enyl)ethyll-, rhenium complex, 29 217 NOPCjsHjj, Benzamide. 2-(diphenylphos-phino)-N-phenyl-, 27 324 NOPCjjHjj, Benzamide, Af-[2-(diphenyl-phosphino)phenyl]-, 27 323 NO2CH3, Methane, nitro-, antimony complex, 29 113 cobalt complex, 29 114 NOjCjHj, 4-Pyridinecarboxylic acid, rhodium complex, 27 292 NO2P2C3JH33, Phosphorus(l-t-), p-nitrido-bis(triphenyl-, acetate, 27 296 NO2SC3H7, L-Cysteine, molybdenum complex, 29 255,258... 

A trinuclear cobalt(I) complex, PhCCo3(CO)9, can also catalyse the reduction of nitro compounds in the presence of hydroxide ion at room temperature under a normal pressure of CO [49]. Satisfactory results were obtained under phase transfer conditions. The catalyst and the aromatic nitro compounds were dissolved in benzene under carbon monoxide and an aqueous solution of sodium hydroxide containing cethyltrimethylammonium bromide was added. At a substrate/cat =10 ratio, ca. 60-80 % of amine was obtained in a 18 h reaction. The reaction also proceeded in a homogeneous phase (methanol-water, methanol, dioxane-water) but with lower conversions (less than 45 %). Cobalt complexes such as MeCCo3(CO)9 and MeCo(CO)4 were also active, but less effective. At the end of the reaction, the catalyst was recovered only in part (ca. 15 %). In the organic phase, an IR absorption at 1891 cm, attributable to [Co(CO)4] anion, was observed. Strangely enough, the preformed [Co(CO)4] anion has not been tested as catalyst. The active species was supposed to be the hydride cluster anion reported in Scheme 6. 

LCon02] + RH2— [LCo i02H]- + RH followed by reactions of the radicals and HOa. In the case of the suporoxocobalamin complex, the [LCo OaH] complex has been characterized spectroscopically. In the reactions of nitrosyl-Schiflf-base-cob dt(n) [L Co(NO)] complexes with oxygen in the presence of base, B (e.g. pyridine), the formation of nitro-complexes has been reported. Kinetic studies show the reaction to be first order in [Oa] and cobalt complex. Quantitative uptake of 0.5 mole of dioxygen per mole of complex observed is in accord with the scheme... 

---