Lead cobalt complex

CoCl(PPh3)3], Reaction of [Co(TIMEN )]Cl 9 with oxygen in the presence of NaBPh leads to the formation of the peroxo-complex [Co(r -02)(TIMEN 5 )] BPh 10, which is a rare example of a side-on r -peroxo cobalt complex (the majority of Co-O -adducts are rj -O -complexes, i.e. end-on). The authors also showed that 10 is capable of converting molecular oxygen to benzoylchloride. 

The intermolecular Pauson-Khand reaction of the resulting S/P-cobalt complexes with norbornadiene was studied under thermal and A -oxide activation conditions. Thus, heating the diastereomerically pure complex (R = Ph, R = Cy) with ten equivalents of norbornadiene at 50 °C in toluene afforded the corresponding exo-cyclopentenone in a quantitative yield and with an enantio-selectivity of 99% ee. Under similar conditions, the analogous trimethylsilyl complex (R = TMS, R = Cy) afforded the expected product in a high yield but with a lower enantioselectivity of 57% ee. In order to increase this enantio-selectivity, these authors performed this reaction at room temperature in dichloromethane as the solvent and in the presence of NMO, which allowed an enantioselectivity of 97% ee to be reached. These authors assumed that the thermal activation promoted the isomerisation of the S/P ligand leading to a nonstereoselective process. 

Clearly, from inspection of Table 4.14, there is a good correlation between the steric bulk of R and L and the non-coincidence angle a. Furthermore, analysis of the hyperfine parameters leads to the conclusion that only about 25% of the electron spin resides in Co orbitals (mainly dxz), and crystal structures of the R = CF3, L = PPh3 and P(OPh)3 complexes do indeed show distortions. The difference between iron and cobalt is just one electron, but this electron occupies a dithiolene 7i orbital, which makes the cobalt complexes much more easily distorted. 

Reduction of low-spin Fe(m) imide 165 with hydrogen (1 atm, 20 °C) proceeds stepwise leading first to anilido complex 168 and then to 77-cyclohexadienyl complex 169 via hydrogenolysis of the Fe=NR linkage (Scheme 64). It should be mentioned that the similar low-spin cobalt complex [PhB(CH2PPh2)3]Co N-/>-Tol is stable to hydrogen pressure (1-3 atm) up to 70 °C <2004JA4538>. 

The reaction of cobaltocene with organoboron dihalides RBX2 (R = Me, Ph and X = Cl, Br mainly) and boron trihalides (BC13, BBr3) leads essentially to three types of (boratabenzene) cobalt complexes, 19,20, and 21 (7,57). CoCp2 plays a dual role in part it acts as a reductant, in part it... 

Cfs-butene should lead initially to the anti form trrms-butene should lead initially to the syn form and 1-butene should give rise initially to both. The equilibrium distribution of syn and anti forms usually differs greatly from the equilibrium distribution of cis- and frans-butene for cobalt complexes 59, 60) the syn form, precursor of irans-butene, is by far the most stable. By way of contrast for the corresponding carbanion, the cis anion seems by far the more stable. This preference for the cis carbanion is presumed to be the source of the high initial cis-to-trans ratio in the initial products of base catalyzed isomerization. In the base catalyzed isomerization of more complex cf-s-olefins (cfs-S-methyl-stilbene), the ions corresponding to syn and anti are not interconvertible and cis-trans isomeriza-... 

Fig. 13 A two-dimensional infinite network is formed via pairs of (+)N-H -N(+) interactions in the [PF6] salt of the cobalt complex Co(terpy)22+ (top), while a quarter of the potential HB interactions are not formed leading to a broken network in the case of the [BF4] salt (bottom) [46]... 

Aryl methyl ketones have been obtained [4, 5] by a modification of the cobalt-catalysed procedure for the synthesis of aryl carboxylic acids (8.3.1). The cobalt tetracarbonyl anion is converted initially by iodomethane into the methyltetra-carbonyl cobalt complex, which reacts with the haloarene (Scheme 8.13). Carboxylic acids are generally obtained as by-products of the reaction and, in several cases, it is the carboxylic acid which predominates. Unlike the carbonylation of haloarenes to produce exclusively the carboxylic acids [6, 7], the reaction does not need photoinitiation. Replacement of the iodomethane with benzyl bromide leads to aryl benzyl ketones in low yield, e.g. 1-bromonaphthalene produces the benzyl ketone (15%), together with the 1-naphthoic acid (5%), phenylacetic acid (15%), 1,2-diphenylethane (15%), dibenzyl ketone (1%), and 56% unchanged starting material [4,5]. a-Bromomethyl ketones dimerize in the presence of cobalt octacarbonyl and... 

The electrochemical processes involving cobalt complexes have already been thoroughly investigated [62, 66], Additional results have been reported with cobalt complexes different from vitamin Bxj and also with nickel ligated to tetradentated macrocyclic ligands. Both series of complexes lead to radicals. 

However, cobalt complexes, treated with a tenfold excess of Grignard or lithium reagents lead to the formation of anionic species (Scheme 5) ... 

It is suggested that this occurs by interaction of the isopropyl side chain with the cobalt complexes in solution, leading to C—C bond cleavage and subsequent hydrogenation (97). 

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). 

The fluorescence properties of two fulvic acids, one derived from the soil and the other from river water, were studied. The maximum emission intensity occurred at 445-450 nm upon excitation at 350 nm, and the intensity varied with pH, reaching a maximum at pH 5.0 and decreasing rapidly as the pH dropped below 4. Neither oxygen nor electrolyte concentration affected the fluorescence of the fulvic acid derived from the soil. Complexes of fulvic acid with copper, lead, cobalt, nickel and manganese were examined and it was found that bound copper II ions quench fulvic acid fluorescence. Ion-selective electrode potentiometry was used to demonstrate the close relationship between fluorescence quenching and fulvic acid complexation of cupric ions. It is suggested that fluorescence and ion-selective electrode analysis may not be measuring the same complexation phenomenon in the cases of nickel and cobalt complexes with fulvic acid. 

The thermolysis of cobalt complex 116 in the presence of copper powder at 190 °C gave 10-membered cyclic acetylene 117 (Scheme 4) <2002AGE1181>. The reaction was iterated to lead to belt-like macrocycles. The same procedure was also utilized to synthesize twofold CpCo-capped bis(cyclopentadieno)superphane <20000M1578>. 

At the same time, according to x-ray data for zinc chelate 909, the nitrogen atom is turned to the side of the metal. The distance Npy-Zn is 2.80 A, that allows us to consider the possible participation of the examined donor center in binding with the metal, leading to formation of a hexacoordinated structure (two-capped tetrahedron) [243]. In relation with this result, let s pay attention to the data reported in Refs. 244 and 248. The tetrahedral configuration without coordination of the nitrogen atom of pyridine is attributed to the cobalt complex 907 (X = NTs, M — Co), although this N atom is rotated to the side of the metal [244]. The pentacoordinated complex 910 is described in Ref. 248, in which only one pyridine substituent is coordinated (the distance Npy-Co is 2.45 A) ... 

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