Quinone complexes with nickel

Benzo[6]thiophene-2,3-quinone 2-oxime 3-thiosemicarbazone forms asymmetric complexes with nickel and palladium.220... 

The observed spectra of some duroquinone-nickel complexes with olefins have been correlated by means of semiquantitative molecular-orbital theory by Schrauzer and Thy ret (48). In the case of n complexes of polynuclear hydrocarbons, such as naphthalene and anthracene, although their spectra are recorded, no conclusions have been drawn with regard to structure nor has any theoretical work been reported. Similar remarks apply to complexes of nonalternant hydrocarbons such as azulene. Although innumerable complexes of olefins with various transition metals are known and admirably reviewed (84), no theoretical discussion of even a qualitative nature has been provided of their electronic spectra. A recent qualitative account of the electronic spectra of a series of cyclopentadienone, quinone, and thiophene dioxide complexes has been given by Schrauzer and Kratel (85). 

Table 79 Nickel(H) Complexes with Quinone-Pyrocathecol-derived Ligands...

Other complexes of nickel with a number of chelate ligands of the quinone series are given in refs. 1605-1608. 

Alkylation with benzyUc halides. Chloromethylated p-quinones couple with RAIMbj by (Ph3P)2Ni which is obtained from dechlorination of the complexed nickel chloride with BuLi." An expeditious route to vitamins Kj and K2 is based on this method. 

Reaction of n-alfylmckel bromide complexes with quinones. Allylic bromides react with nickel carbonyl to afford rc-allylnickel bromide complexes formulated as (1) in the case of allyl bromide itself (2, 291 3, 210). Hegedus et al.6 have studied the reaction of... 

A similar incremental effect of porphyrin-quinone separation was observed with the systems shown in Scheme 36 which were prepared by Wittig condensation of the meso-substituted porphyrin 116 (as the nickel complex) with the phosphorus ylide 117 Demethylation, reduction of the double bonds and then oxidation furnished the free base porphyrins 118 and 119a, b. The rate of photoinduced electron transfer in such systems showed an inverse exponential dependence on the length of the chain In order to demonstrate a multistep electron transfer the bis-quinone porphyrin 120 was prepared in which the pair of quinone rings provide a redox potential gradient and may thus stabilize charge separation. Comparison with the mono-quinone etioporphyrin 119a... 

The fact that quinones may form tt complexes with transition metals was first recognized by Sternberg et al. 53), who found that butyne reacts with iron pentacarbonyl in sunlight to afford duroquinone-iron tricarbonyl (XIX). These authors also reported that manganese pentacarbonyl hydride yields durohydroquinone under similar conditions whereas nickel carbonyl did not react 53a). However, more recent work has established that duro-quinone and some other substituted quinones are capable of forming Ni(0) complexes, most of which are surprisingly stable. 

Most quinones, instead of forming rr complexes, react with nickel carbonyl yielding salt like materials. With p-benzoquinone, for instance, a nearly black, insoluble, hydroscopic and paramagnetic (ja f = 3.3 B.M.) material of composition Ni(quinone)2 was obtained which is best formulated as Ni (quinone)2 and considered as a metallic quinhydrone type of compound 54). However, duroquinone behaves exceptionally. In a smooth reaction all four molecules of carbon monoxide are evolved and red, crystalline, diamagnetic bis(duroquinone)-nickel (XX) (54) is obtained. This complex is stable in air and begins to decompose without melting at 205° C. It is nearly insoluble in all solvents except dichloromethane, in which it is monomeric. In the infrared spectrum, the quinone C=0 stretching frequency appears at 1577 cm (in free duroquinone it is 1629... 

When p-benzoquinone or toluquinone are treated with nickel carbonyl in the presence of cycloocta-l,5-diene only Ni(II)-hydroquinone or quin-hydrone salts, respectively, are formed. When the somewhat less strongly oxidizing 2,5- or 2,6-dimethyl quinones are treated with nickel carbonyl under the same conditions cycloocta-l,5-diene-dimethylquinone-Ni(0) complexes are obtained. These substances resemble their duroquinone... 

It is worth mentioning that the first transition metal complex of a natural product was obtained by treating tocopherylquinone (vitamin-E-quinone) with nickel carbonyl in the presence of cycloocta-1,5-diene. A study of its physiological properties promises to be interesting (59). 

Quinone complexes may be prepared either from acetylenes or from the quinone itself (see Figure 74). With nickel tetracarbonyl, most quinones react forming salt-like complexes which are best formulated as the oxidation products Ni2+ (quinone)2 [43,44]. These complexes are paramagnetic, insoluble and hydroscopic and do not behave like those others where the quinone is ni-bonded to the nickel. Tetramethylquinone (duro-quinone), which is a less oxidizing quinone, reacts readily with nickel tetracarbonyl forming the diamagnetic, red bis-duroquinone nickel, 8.12, m.p. 205° [48]. 

The oxidation of the metal complexes of l,10-phenanthroline-5,6-quinone is thought to proceed in a similar manner, with the first step being a benzilic acid rearrangement. Rearrangements of this type may also be followed directly in nickel(u) and cobalt(m) complexes of 2,2 -pyridil. The first step of the reaction involves nucleophilic attack on an O-bonded carbonyl group to form a hydrate, followed by a benzilic acid rearrangement. In this case, the benzilic acid rearrangement products may be isolated as metal complexes (Fig. 8-43). 

Schrauzer and Thyret have described (528, 529, 531) the synthesis of olefin-Ni(O) complexes containing a quinone, in particular, duro-quinone, as a ligand. The red, diamagnetic duroquinone complexes are obtained by reaction of nickel carbonyl with the quinone in excess olefin. They are stable in air and soluble in polar organic solvents and water. Those olefins which form the coiiqilex contain essentially parallel double bonds, e.g., norbornadiene, dicyclopentadiene, 1,5-cycloocta-diene, 1,3,5-cyclooctatriene, or cyclooctatetraene. 

With other quinones, the only olefin yielding stable complexes is 1,5-cyclooctadiene. The quinones employed have been trimethyl-p-benzoquinone, 2,5- and 2,6-dimethyl-p-benzoquinone (531), and vitamin E quinone (530). In general, these complexes show higher water solubility, higher dipole moments, and more marked paramagnetism than do the duroquinone complexes. The paramagnetism suggests that there is some electron transfer from nickel to quinone and that the nickel may indeed have an oxidation state midway between Ni(0) and Ni(II). 

The nickel(IV) oxime, bis(6-amino-3-methyl-4-azahexa-3-ene-2-one oxime)nickel(IV), and the nickel(III) oxime, (15-amino-3-methyl-4,7,10,13-tetraazapentadeca-3-ene-2-one oxime)nickel(III), complexes react with hydro-quinone. Proton-related equilibria for both the nickel complexes and the hydroquinone could be elucidated from the kinetic details. For reactions with the complexes and the hydroquinone could be elucidated from the kinetic details. For reactions with the Ni(III) complex there is evidence of an inner-sphere process. The [NiL(TCCat)] complex (TCCatH2 = tetrachlorocatechol L = 2,4,4-trimethyl-1,5,9-triazacyclododec-l-ene) forms a 1 1 adduct with tetrachloro-1,2-benzoquinone. Spectroscopic evidence suggests that this compound can be described formally as a quinone adduct of a Ni(I)-semiquinone moiety arising from inner-sphere ligand oxidation. The crystallographically determined structure (11) is shown below. Several copper complexes of a vareity of semiquinones also exist in solution in equilibrium with the corresponding catechol complexes. ... 

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