Tetra cobalt derivatives

Further substitution to give the tetra-substituted derivative is a much more delicate reaction, especially in the case of cobalt. For instance, repetition of the reported synthesis of Co4(CO)8[P(OMe)3]4 168) gave only a mixture of Co4(CO)9[P(OMe)3]3 and Co2(CO)6[P(OMe)3]2 219). 

Apart from the compounds already mentioned, vanadium, manganese, and cobalt chlorides, tetra-alkoxy derivatives of titanium, acetylacetonates of V, Cr, Mo, Mn, and Ni, Cp derivatives of Zr and Nb, and triphenyl phosphine complexes of Ti and Fe were found to be active. Later lanthanide complexes were included in the list of dinitrogen-reducing systems, the most effective being compounds of samarium and yttrium. 

Some kinetic studies involving the reactions of various cobalt carbonyl derivatives with triphenylphosphine have recently been reported. The rate constants were measured for the reactions of a variety of acylcobalt tetra-carbonyl derivatives with triphenylphosphine according to the following equation 237)... 

The organic solvent should feature a low solubility in water and a high dielectric constant. Numerous studies have been reported for liquid-liquid junctions involving DCE [43,62,70,71,73], nitrobenzene [67,68,74,75], and nitrophenyloctylether (NPOE) [56]. Various hydrophobic electrolytes have been employed in these solvents. Tetraphenylarsonium (TPAs+) [[71,75,76], bis-triphenylphosphoranylidene (BTPPA+) [43,50], and hydrophobic tetra-arylammonium [77,78] are among the cations used in the organic phase. The choice for anions has been mostly restricted to borate derivatives, tetraphenylborate (TPB ) [70,79,80], tetrakis(4-chlorophenyl)borate (TPBCH) [43,81,82], and tetrakis(penta-fluoro)phenylborate (TPFB ) [49,83], as well as dicarbollyl-cobaltate [75]. 

One obvious way in which to attach a nitroxide group to B12 is to simple alkylate Cob(I)aiamin with a suitable nitroxide derivative. This would result in having the nitroxide covalently bound to the corrinoid at the upper axial coordination position of the cobalt. Such a procedure is outlined in Fig. 19. In this reaction 4-bromoacetamido 2,2,6,6-tetra-methylpiperidine-N-oxyl is used to alkylate Cob(I)alamin. This results in a Co(III)-nitroxalkylcobalamin. The corresponding cobinamide can then be produced by hydrolyzing the ribose-phosphate linkage (119). 

The soluble metalloporphyrin-containing polymers are formed by the copolymerization of MM A or 4-VP with macrocyclic MCM — an interaction product of acrylic acid chloride with tetra-p-aminophenylporphyrinate acetate manganese [96]. Copolymers obtained by the radical copolymerization of acryloyl derivatives of cobalt phthalocyanine with 9-vinylcarbazole [97] should also be mentioned. 

As iron forms cyclobutadiene complexes preferentially in the (0) oxidation state, the best starting materials for these complexes are Fe(0) compounds such as the carbonyls. Cobalt, however, tends to form Co(I) (also cyclobutadiene complexes. The best known one (cyclopentadienyl)(tetra-phenylcyclobutadiene)cobalt (XXVIII), has been prepared from cyclo-pentadienylcobalt(I) derivatives and also from cobaltocene, a cobalt(II)... 

The influenee of peripheral substituents at the phthalocyaninato moiety on the properties of the corresponding compounds was studied with a number of octa-substituted derivatives R PcM, R PcMLj and [R PcM(pyz)] (e.g. R = CH3, m = 8, M = Fe, L=py) [83]. Substituted mononuclear and bridged phthalocyaninatoiron pyrazine complexes R PcFe(pyz)2 and [R PcFe(pyz)] are accessible according to the procedure for the corresponding unsubstituted complexes [65]. With cobalt as central metal the tetra-substituted macrocycles R PcCo (m = 4 R = f-bu, NO 2) can be prepared. They coordinate with pyridine and substituted pyridines to form the adducts R PcCoL2 [84]. With pyrazine the binuclear complex (t-bu)4PcCo(pyz)CoPc(t-bu)4 and the oligonuclear [(N02)PcCo(pyz)]n can be isolated and characterized [84]. 

Within this field, many basic investigations and proposals for practical application have been made by Shirai et al. l They have investigated tetra- and octa-carboxylic acid derivatives of iron phthalocyanine and cobalt phthalocyanine, and found that catalytic activity is affected by the states of electron spins of metal ions and inactivated by formation of the mu-oxo dimer. Iron and cobalt ion in high spin states are more reactive than that in low spin states. High spin states of metal ions are achieved by modification of ligands. Shirai et al. have applied these materials as fiber deodorizers for such odors as ammonia, trimethylamine, hydrogen sulfide, and methanethiol, in which the phthalocyanine compounds are supported on fibers of cotton, wool, rayon, and artificial fibers. 

Probably the most academically dramatic use of metal Tc-complex formation was demonstrated by the trapping of the cyclobutadiene-silver nitrite complex. Many subsequent cyclobutadiene derivatives were isolated and proved to be rather stable complexes. For example, tetraphenylcyclo-butadieneiron tricarbonyl melts without decomposition at 234° and tetra-phenylcyclobutadiene 7r-cyclopentadienyl cobalt melts at 256°C under nitrogen. Upon examination of the electronic configuration the stability of these complexes often can be predicted. 

Cobalt Halides Chang et al. s precatalytic mixture V (Figure 1.3) is also efficient for the construction of pyridines [39]. Tetra- and pentacyclic pyridines derivatives 80 were obtained by cobalt-catalyzed [2 - - 2 - - 2] cycloaddition of cyanodiynes 79 in good yields (Scheme 1.20). This time, the reaction is carried out in pure acetonitrile. The presence of a sterically demanding substituent at the alkyne terminus (R ) proved to be beneficial in most cases. 

Chang, H.T., Jeganmohan, M. and Cheng, Ch.-H. (2007) Cobalt-catalyzed intramolecular [2+2+2] cocyclotrimerization of nitrilediynes an efficient route to tetra- and pentacyclic pyridine derivatives. Organic Letters, 9(3), 505-508. 

---