Nickel complexes quinone

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). 

No isomers were detected in the copper and nickel complexes of the strongly polarized o,o -dihydroxyazobenzene (89), the l-(2-hydroxyphenylazo)-2-naphthols (90), or the 1-phenyl-3-methyl-4-(2-hydroxyphenylazo)-5-pyrazolones (91). These compounds exist predominantly in the quinone hydrazone (92 and 93) and ketone hydrazone (94) forms, respectively (Section... 

Nickel complexes in transformations of heterocycles 90YGK370. Palladium salts and complexes in reactions of heterocycles 90S739. Quinones and quinone methides in chemical modification of heterocyclic fragments in biopolymers 89AG(E)555. 

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). 

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 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. ... 

In the last few years the design and use of various disilane compounds has gained importance because of the reactivity of the Si-Si bond and the large potential for organic synthesis involved with it. Many publications offer us numerous examples of possible reactions at the silicon-silicon bond such as addition reactions with C-C double bonds or C-C triple bonds [1, 2], addition reactions with C-element multiple bonds (e.g. aldehydes, quinones, isocyanides) [3-5] or metathesis [6, 7] and cross-metathesis [8]. In the most cases the existence of a catalyst (palladium, platinum or nickel complexes) for activation of the silicon-silicon a bond is indispensable for a successful transformation [9-11]. 

In contrast to the transition metal catalysts above, nickel complexes have been studied intensely for the polymerization of CHD and its derivatives. jr-Allylnickel-based complexes were employed by Dolgoplosk et al. for CHD polymerization. They used n-alkenylnickel halides, for example, K-metallyl nickel dichloride and it-allyl nickel dibromide, combined with electron acceptors such as chloranil (tetrachloro-/ -quinone) or nickel trichloroacetate. Unfortunately, the true propagating species of the above catalytic systems are not clear, but they were moderately active for CHD polymerization and the polymer obtained appeared to have a predominantly 1,4-linked structure. However, the stereoregularity of the polymer was not very high based on its Tm (270 °C). 

All the duroquinone-nickel complexes are diamagnetic. Attempts to prepare similar compounds with o-quinones have failed. It is also impossible to prepare bis(trimethylquinone)-nickel. Instead, the Ni(II) salt of tri-methylquinone is isolated (55). Evidently a slight increase in the electron affinity of the quinone -n system is sufficient to induce oxidation of nickel. 

C=0 Stretching Frequencies and Decomposition Points of Cycloocta-1,5-diene-Nickel Complexes of Some Quinones ... 

The alkylation of quinones by jr-allyl nickel complexes is another interesting synthetic route to vitamin K and coenzyme Q, the selectivity of this process being remarkably improved relatively to the classical approach based on acid-catalyzed addition of phytol to quinones. 

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

Ni(phenanthrenequinone)2Br2 is the only complex which seems to contain the neutral ligand coordinated to nickel(II). 3 The complex has been synthesized by reacting NiBr2 and the quinone in methanol-acetic acid solution. 

The neutral complexes Nil or NiL2B2 (B = py or ibipy) have been conveniently synthesized by reacting the quinone ligand and Ni(CO)4 in apolar solvents (n-pentane, n-hexane, benzene).1 0,1601 The use of anaerobic conditions gives the best results. In one case, that of Ni(C6H402)2, the complex was obtained by the peroxodisulfate oxidation of an aqueous solution of nickel(II) acetate and pyrocatechol. 

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

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

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). 

Scheme 7.2 Preparation of bis(duroquinone) nickel(O) (10) and the related 1,5-cyclooctadiene(duroquinone) complex 11 (the methyl groups of the quinone ligands are omitted for clarity)...

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. 

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... 

---