Cobalt analogs

In comparison with their cobalt analogs, rhodium carbonyls are significantly more active catalysts (6). As with cobalt, aldehyde is the... 

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. 

The cobalt analog of the iron dinitrosyl iodide is prepared according to the above procedure with only minor modifications, which are outlined below. Anhydrous deoxygenated reagent-grade acetone and 35.4 g. of cobalt powderf are added to the 1000-ml. flask and allowed to react with the ether solution of iodine (38.1 g. (0.15 mole) of iodine in 300 ml. of ether) over a period of 30 minutes. Then nitric oxide is admitted to the flask. The reaction... 

In the case of rhodium, however, it was demonstrated early that in the synthesis of [Rh6C(CO)l5]2 the encapsulated carbon atom originated as chloroform, which had reacted with the rhodium carbonyl anion [Rh7(CO)l6]3- (59). In the cobalt analog, [Co6C(CO)l5]2-, the carbon atom is derived indirectly from carbon tetrachloride [via Co3(CO)9CCl] (60) Both these syntheses are performed under mild conditions, and there are apparently no examples of carbidocarbonyl clusters of cobalt or rhodium prepared directly from the metal carbonyls under pyrolysis conditions. 

The rhodium quadridentate phosphine, QP, and arsine, QAs, monocarbonyl cations (117) are more labile than the cobalt analog (117), since the rhodium s carbonyl is readily lost by halide displacement. 

The complex is readily soluble in strongly polar solvents and in chloroform and dichloromethane giving red-brown or red solutions. Voltammetric studies2 have shown that this dianion is a member of an electron-transfer series similar to its cobalt analog ... 

The electrochemistry of the polymeric and isomorphous cobalt(II) and nickel(II) methylsquarates was also studied by Iwuoha et al. In aqueous solutions, they found evidence that both the nickel(II) methylsquarate and its cobalt analog were dissociated without any reversible redox processes occurring for the metal ions. However, the cyclic and Osteryoung square wave voltammograms, obtained using a Pt electrode for solutions of these complexes in dimethylformamide and dimethylsulfoxide, contained signals attributable to both ligand-based and metal-based redox processes 142). 

Unlike cobalt, the rhodium catalyst exhibits little or no aldehyde hydrogenation activity, but it is 10 -10 limes more active than the cobalt analog. The rhodium system is also a highly active isomerization catalysts but gives rise to a low n iso ratio (about I compared to 4 of Co2(CO) ). 

By analogy with the cobalt analogs, the complexes (diene)Rh(C5Hs)... 

Third, n-allyl complexes are formed by palladium and cobalt analogous complexes of nickel and platinum are less stable, while ruthenium, rhodium, and iridium are not yet known to form them. In catalytic reactions the deuteration of cyclic paraffins over palladium has provided definite evidence for the existence of rr-bonded multiply unsaturated intermediates, while 7r-allylic species probably participate in the hydrogenation of 1,3-butadiene over palladium and cobalt, and of 1,2-cyclo-decadiene and 1,2-cyclononadiene over palladium. Here negative evidence is valuable platinum, for example does not form 7T-allylic complexes readily and the hydrogenation of 1,3-butadiene using platinum does not require the postulate that 7r-allylic intermediates are involved. Since both fields here are fairly well studied it is unlikely that this use of negative evidence will lead to contradiction in the light of future work. 

C. Thus, both [RhCp2] and [RhCp2] are considerably less stable than their cobalt analogs. 

The orange, sublimable complex formed when hydridotetrakis(tri-fluorophosphine)rhodium decomposes on standing at room temperature is believed to have the same dimeric structure as its cobalt analog 175). 

HRh6(CO)i5] is only stable at low temperatures and was one of the first clusters to be completely characterized by multinuclear NMR studies. The preparative routes are shown in Eq. (2) and it should be noted that the structure of [HRh6(CO)i5] is different from that of the cobalt analog which contains an interstitial hydride at room temperature loss of H2 occurs with subsequent dimerization (Eq. 2). 

A cobalt analog of hausmannite could be formed by the reaction 3Co2 + ViOzCaq) + 3H2O = Co304(c) + 6H ... 

The tris(ethylenediamine)chroinium(III) salts are much less stable than their cobalt analogs, and lose one molecule of ethylenediamine readily. The temperature of decomposition depends upon the nature of the anion, part of which enters the complex cation during the thermal decomposition. The reaction has been studied in detail for the... 

The iron-based catalysts are reported to be considerably more active than the cobalt analogs [21]. The yield of linear, narrow molecular weight distribution polyethylene per gram is reported to be very high [21]. 

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