Cobalt derivatives

The coordination modes of the nitrate ligand in the complexes [TpBut]M(N03) (M = Cu, Ni, Co, Zn) are summarized in Fig. 46. (171, 184). Evidently, the coordination mode varies from unidentate for Zn to symmetric bidentate for Ni and Cu, with the cobalt derivative exhibiting an anisobidentate coordination mode. Moreover, the related cadmium derivative [TpBut,Me]Cd(N03) also exhibits bidentate coordination of the nitrate ligand, with Cd-0 bond lengths of2.272(6) A and 2.295(7) A (91). Such symmetric bidentate coordination contrasts with the significantly different Zn-0 interactions [1.978(3) A and 2.581(3) A] in unidentate [TpBut]Zn(N03). The coordination modes for a variety of [TpRR ]M(N03) complexes are summarized in Table VIII. 

Several copper, silver, ruthenium, rhodium, and cobalt compounds (e.g., Ru-Cl3 aq, [RuC h(l)ipy) (bipy=2,2 -bipyridine), RhCl3 aq, fotx(dimelbylglyoxima-to)cobalt derivatives (cobaloximes), etc.) have been found to catalyze hydrogenations in aqueous solutions [9]. Although important for the early research into homogeneous catalysis, these catalysts did not gain synthetic significance. 

The chemistry of the 1 1 and 1 2 complexes differs with respect to hydrogenation (84,89). The 1 2 derivatives are inert to hydrogenation, while the 1 1 compounds are smoothly transformed into an ethylidene complex (see Scheme 1). This difference in behavior may well reflect the cause of differences in behavior of olefins on metal surfaces toward hydrogenation. The ethylidene complex may be converted back to the olefin adduct by reaction with trityl ion. The ethylidene adduct was first obtained for ruthenium by interaction of ethylene with H RujfCO) (89), and is structurally related to the corresponding cobalt derivatives, Co3(CO)9RC. As discussed above, the structure has been established in detail and involves a capping of the metal triangle... 

Dimethyl(trimethylsilyl)phosphine (63) reacts with aluminium chlorides with cleavage of the silicon-phosphorus bond,58 as shown for aluminium trichloride. The same phosphine (63) reacts with the cobalt derivative (64) as shown.59... 

Another cobalt derivative with CoN6 coordination is [Co(sep)]3+. This is the complex formed by Co(III) with the ligand 1,3,6,8, 10,13,l,6,19-octaazabicyclo[6.6.6]eicosane, which is related to the diamino-sarcophagine seen for the chromium complexes, and is called sepulcrand . Figure 90 shows the octahedral structure of this complex.135... 

For the route A, acyl radicals donors like iS are readily generated from acyl selenides (ISa) or acyl cobalt derivatives (iSb) and radicals acceptors 2S are usually multiple bonds as in methyl vinyl ketone (2Sa) -although some homolytic substitutions are possible. On the other hand, nitriles GSal are useful acceptors (3S) in radical cyclisations and 4Sa is an obvious synthon equivalent of radical donor 4S (See Table 7.2). 

The reaction is reversible (33). The cobalt derivatives are considerably more reactive than the corresponding manganese compounds. Acetylcobalt tetracar-bonyl dissociates about 2250 times more rapidly than the corresponding acetylmang-anese pentacarbonyl does (33). 

Solid-state sulfide compounds MMo2S4 (M = V, Cr, Fe, Co) contain infinite chains of Mo4S6 clusters with intracluster Mo-Mo distances (2.756-2.989 A) and intercluster distance (2.960 A) for the cobalt derivative (112). As the valence of M is +2, judging from magnetic measurements, and the average oxidation state of molybdenum +3, the CVE for M2Mo4S8 is 12. This agrees with five intracluster and one intercluster... 

Let us now consider the cobalt derivative. The FCM curve increases rapidly below 38 K, and reaches a plateau below 28 K. The derivative, dFCM/dT, has its extremum at 36.2 K, whereas the REM vanishes at a slightly higher temperature, 37.2 K. The x u and Zm curves have peak-like shapes, with maximum values at 37 K and 36.7 K, respectively. The critical temperature of this compound is taken as Tc=37 K. 

We have mentioned that the structural parameters of C2H4 bridged compounds can vary over a wide range. Whereas most examples reported do not have metal-metal bonds, there is one conspicuous exception. Theopold and Bergman succeeded in synthesizing the propane-1,3-d iyl cobalt derivative 125 from the radical anion [(t) ,-C5H5)Co(/z-CO)12 and 1,3-dibromopropane (98, 295) in 40 5 yield. This compound is best described as a dimetallacyclopentane, and its chemistry (thermolysis and reaction with CO and phosphines Scheme 34) supports this view. Formation of cyclopropane (100°C or I2/25°C) is probably the most remarkable feature of this cyclic system. Simple C—C bond formation has never been observed before in ligand-induced or thermal reactions of either mono- or binuclear cyclopentadienylcobalt complexes. The architectural details of... 

Rather high stability is observed for the nickel and cobalt derivatives containing the [M4( i3-OMe)4] cubane-like core and heteroligands such as acac, OAr, OC6H4CHO, [M(CO) ],and so on [1771, 1097, 698, 642, 276]. 

The value of J is not known in the case of the copper-nickel derivative. However, the same line of discussion should hold for this derivative, whose spectrum is shown in Fig. 6.8B [29]. It is noteworthy that the R values of the protons of the copper domain are smaller in this case than in the cobalt case. This is probably due to a shorter electronic relaxation time of tetrahedral nickel(II) than tetrahedral cobalt(II) (see Section 3.3). In this respect it may be interesting to note that in the case of the cobalt-cobalt derivative we have a tetrahedral and a square pyramidal cobalt(II) ion [30,31]. The former has longer electronic relaxation times. Upon establishment of magnetic coupling, the electronic relaxation times of the tetrahedral cobalt(II) ion decrease and tend to reach the values of the square pyramidal cobalt(II) ion. This is evident by comparing the spectra of the protein containing only the tetrahedral cobalt(H) ion with those containing both ions (Fig. 6.9). 

The 1,19-substituted octadehydrocorrin complexes have been isolated as crystalline materials and characterized. In the case of the 1-substituted species only the nickel complex turned out to be stable, while the cobalt derivative showed a very high reactivity and all attempts of purification afforded a mixture of compounds [56, 57]. 

The principal chromophores in pseudo sulfur dyes are copper and cobalt phthalocyanines, e.g., in C.I. Sulphur Green 25 (16), and the perylene tetracar-boxylic diimide structure in C.I. Sulphur Red 14 [81209-07-6] and C.I. Solubilised Sulfur Red 11 [61969-41-3] (17). In contrast to the sulfur dye made from Cu phthalocyanine, the cobalt derivative can be applied with dithionite. 

Several effects are related to the nature of the silicon halide. Hydrido halides usually react readily with a range of anions, while organosilicon halides may not for instance, HgSiCU reacts with Co(CO)J in ether giving good yields of silicon-cobalt derivatives (2), while MesSiCl does not (336). This is probably related in the main to the electron-accepting... 

In several other cases, compounds have been synthesized that contain potentially reactive groups attached to silicon, although their functionality has not yet been exploited. These include the methyl-chlorosilyl cobalt derivatives Cl Me3-nSiCo(CO)4 (re = 1,2) (215) and platinum complexes such as fra/is-lEtaPIsPtCXISiHjPISiHals (168) (cf. Table VI, entries 8-10). 

The most studied reaction involves the replacement of carbonyl groups by tertiary phosphines. This proceeds most readily in the case of cobalt derivatives, manganese compounds must usually be heated, and iron compounds require irradiation (except in the case of entry 13). 

In the case of disubstituted cobalt derivatives, it is believed that representatives of the three isomers (XXVIII)-(XXX) can be prepared by reaction (86) (entry 25), reaction (87) (entry 31), and reaction 88 (Table IV, entry 33). 

JA similar cobalt derivative is prepared from [(OC)3Cr-7)6-C6H5]Me2SiH W). andCo2(CO)8. 

Eventually we formed carbonyls in the liquid phase by redox disproportionation of nickel and cobalt derivatives of organic thioacids. In the reaction between nickel(II) dithiobenzoate and carbon monoxide in the presence of HS ion we assumed the formation of a sulfur-bridged nickel(IV) complex (VII, 32). More recent investigations (84), however, have shown that half the nickel appears as a monomeric nickel(II) complex of the same empirical formulation, formed by insertion of a sulfur atom in the dithio ligand, the other half of the nickel being reduced to nickel(O) by the sulfide. 

The reaction of a Co(I) nucleophile with an appropriate alkyl donor is used most frequently for the formation of a Co-C bond, which also can be formed readily by addition of a Co(I) complex to an acetylenic compound or an electron-deficient olefin (5). The nu-cleophilicity of Co(I) in Co(I)(BDHC) is expected to be similar to that in the corrinoid complex, as indicated by their redox potentials. The formation of Co-C a-bond is the attractive criterion for vitamin Bi2 models. Sodium hydroborate (NaBH4) was used for the reduction of Co(III)(CN)2(BDHC) in tetrahydrofuran-water (1 1 or 2 1 v/v). The univalent cobalt complex thus obtained, Co(I)(BDHC), was converted readily to an organometallic derivative in which the axial position of cobalt was alkylated on treatment with an alkyl iodide or bromide. As expected for organo-cobalt derivatives, the resulting alkylated complexes were photolabile (17). 

Bis[2,3-butanedione dioximato(l-)] cobalt derivatives (cobaloximes(I)) appear in most respects to be good model systems for the cobalamins of the vitamin B12 coenzyme.1 The central cobalt atom exhibits three stable oxidation states... 

Cobalt-catalyzed epoxidation of alkenes has been carried out with the cobalt derivative of (174), employing iodosylbenzene as the oxidant. Epoxidation of cfa- -methylstyrene furnishes exclusively the cis-epoxide (equation 62). The reaction proceeds through an active oxo-cobalt(IV) species, and is mote selective than reactions proceeding through oxo-chromium or oxo-manganese species. The catalyst can be recovered unchanged by simple filtration. 

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