Cobalt complexes dicarboxylates

Whereas the cyclobutane rings in (8 X = O or S) are planar, that in (9) is puckered, and two short Br Br distances of 3.55=A are observed in the crystals. Planarity is also seen in ds-cyclobutene-3,4-dicarboxylic acid and in substituted cyclopentadi-enyl cobalt complexes of tetraphenylcyclobutadiene, in which each metal atom is sandwiched between parallel, planar fo ir- and five-membered rings. Crystal structures have been obtained for a variety of polycyclic compounds containing cyclobutane rings. ... 

Spicer has reported that dimethylacetylene dicarboxylate reacted with norbomene at room temperature in the presence of TMANO to give the cyclopentenone in 73% yield. However, the cobalt complex is thermally unstable and mild PKR conditions were required for success. The intramolecular and inter-molecular PKR of alkynones has been reported by Hoye in 30-90% yields. In the intramolecular examples, improved yields were observed when a geminal dimethyl was incorporated into the tether. In the intermolecular examples, the ketone was found in the 3-position of the cyclopentenone. The vinylogous 48 ynone cyclised in 62% yield to provide the tricyclic product 49 as a 2.7 1 mixture of cis/trans isomers. An interesting intramolecular example was disclosed by de Meijere in which ketone 50 produced the spirocyclopropane 51 in 63% yield. ... 

The kinetics of the oxidations of the mixed-metal cuboidal complexes [MojNiS4(H20)io] -" and [Mo3FeS4(H20)io] + by [Co(dipic)2] (dipic =pyridine-2,6-dicarboxylate) and [Fe(H20)6] have been studied as a function of acid concentration/ The oxidations by the cobalt complex are acid-independent and outer-sphere, whereas the oxidations by Fe " (aq) proceed by outer-sphere acid-independent ([Fe(H20)j] " ) and inner-sphere (OH -bridged) add-dependent ([Fe(H20)50H] ) pathways. 

In an interesting study, phthalocyanine complexes containing four anthraquinone nuclei (5.34) were synthesised and evaluated as potential vat dyes and pigments [18]. Anthraquinone-1,2-dicarbonitrile or the corresponding dicarboxylic anhydride was reacted with a transition-metal salt, namely vanadium, chromium, iron, cobalt, nickel, copper, tin, platinum or lead (Scheme 5.6). Substituted analogues were also prepared from amino, chloro or nitro derivatives of anthraquinone-l,2-dicarboxylic anhydride. 

The electrophilic reactions of co-ordinated 1,10-phenanthrolines are not always as simple as might be expected. Thus, the nitration of cobalt(m) 1,10-phenanthroline complexes yields 5-nitro-1,10-phenanthroline derivatives at low temperature, but prolonged reaction in hot solution leads to further reaction and oxidation of the ligand to give excellent yields of 1,10-phenanthroline-5,6-quinone complexes (Fig. 8-40). Even after the formation of the quinone, the complexes may exhibit further reaction. For example, reaction of the l,10-phenanthroline-5,6-quinone complexes with base results in the formation of a complex of 2,2 -bipyridine-3,3 -dicarboxylic acid (Fig. 8-41)... 

The formation of hydrated cobalt(n) complexes of pyridine carboxylic acids and the subsequent thermal decomposition to lower hydrates has been documented.82,83 Cobalt(n) halides react with 6-methylpicolinic acid (6-mpaH), picolinic acid (paH), nicotinic acid (naH), and pyridine-2,6-dicarboxylic acid (2,6-py) to form Co(6-mpa) (6-mpaH)X (X = Cl, Br, or NCS), Co(naH)nX2 (n = 2, X = Cl, Br n = 3, X = NCS), and Co(pa)(paH)X, EtOH (X = Cl, Br, or NCS) which are all probably octahedral.83 6-Methylpicolinic acid also formed Co(6-mpaH)4X2,2HX (X = Cl or Br) which were formulated [(6-mpaH)2H]2[CoX4], since the electronic spectra show absorptions characteristic of tetrahalogenocobaltate(n) ions.83... 

The X-ray crystal structures of pyrazine V.JV -dioxide (134) <02AX(E)1253>, the P-polymorph of phenazine (135) <02AX(C)181>, cobalt(III) complexes of pyrazine-2,6- and pyridine-2,6-dicarboxylic acids <02JIC458>, and bis-urea-substituted phenazines <02ZN(B)937> were reported. Fluorescent pyrido[l,2-a]quinoxalines 136 prepared as pH indicators were examined by X-ray crystallography <02JCS(P2)181>, as were macrocyclic quinoxaline-bridged porphyrinoids obtained from the condensation of dipyrrolylquinoxalines 137 and 1,8-diaminoanthracene... 

Table 60 Preparations Some Bridged Monocarboxylate and Dicarboxylate Cobalt(III) Complexes...

Chromium(ii) reductions of Co(NH3)g complexes of various dicarboxylic acid derivatives of pyridine have been studied in order to determine the effect of placing the cobalt centre at different positions relative to the ring nitrogen. It is found that in general complexes with cobalt attached to carboxyl in the 2-position react 10—10 times faster than those with cobalt attached at a more remote position. This is attributed to chelation in the transition state. 

Reaction of chromium(ii) with pyridine-2,4-dicarboxylic acid yields two radical complexes of Cr, one of which is active in reducing cobalt(iii) complexes, the other not. The inactive form is formed in reversible equilibrium, and is believed to be the chelate (30), with apparent formation constant A app = /sT/[H+]x 50 at 20 °C in I.2M-HCIO4. The active form, possibly (31), is not detected as such, but is an intermediate postulated in the reaction [Co(NH3)spy] + + Cr +, when accelerated by the presence of the organic acid. ... 

Bicyclo[5,3,0]dec-l(7)-en-2-one was obtained by anodic oxidation of bicyclo-[4,4,0]decane-l,6-diol in methanol containing tetraethylammonium p-toluenesul-phonate. The dicarboxylic acid (68), used in the synthesis of methymycin, was obtained by oxidative cleavage of 8-formylbicyclo[4,2,l]nona-2,4-dien-7-one. Autooxidation of (-t-)-car-3-ene in the presence or absence of cobalt stearate gave a complex mixture of products including eucarvone (up to 11.5 %) and 3,6,6-trimethylcyclohepta-2,4-dienone (up to 48 %). 3-Methylene-4-cholestene gave a 40% yield of 3,3-diazido-A-homochoIest-5-ene when treated with Pb(OAc)4 (N3) . ... 

Multidentate Leaving Groups.— The decomposition of dicarboxylate complexes of cobalt(in), particularly of [Co(ox)3] , has long been established to involve an internal redox step. Several papers published during the past couple of decades have concluded that the initial step is the charge-transfer or redox... 

---