Duroquinone, nickel-olefin complex

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). 

It was found that if bis(duroquinone)-nickel is thermally decomposed in the presence of cyclooctatetraene, cyclooctatetraene-duroquinone-nickel, (XXII), is obtained (56). A more convenient synthesis was found shortly thereafter in a one-step reaction of duroquinone with nickel carbonyl in the presence of the polyolefin. Using the same procedure, analogous complexes with various other olefins were made, the properties of which are listed in... 

Table I. Only olefins containing at least two roughly parallel double bonds are suitable as ligands and it follows from the NMR spectra of the complexes that they must have highly symmetrical structures, e.g., (XXIII, XXIV, and XXV) (55, 56). An X-ray structural determination of cycloocta-1,5-diene-duroquinone-nickel has been performed by Click and Dahl (56a). The space group is i (2/n) with four molecules per unit cell, a = 14.26,...

All complexes of this kind are quite polar and water soluble. The permanent dipole moments are caused by the fact that the olefinic ligands are predominantly donors and only weak acceptors so that the duroquinone molecule interacts with filled 3d orbitals of nickel even more strongly than in the case of bis(duroquinone)-nickel. Consequently, the quinone C=0 groups are more polarized than in the parent compound bis(duroquinone)-nickel (see Table I). The particularly high stability and polarity of the... 

Bis(duroquinone)-nickel readily loses a duroquinone ligand, either thermally or by displacement with olefins such as cyclo-octa-1,5-diene, cyclo-octatetraene and norbornadiene (see Figure 75) [44,48]. These olefin complexes are remarkably stable, decomposing between 120 and 200°C. Analogous complexes of the other less oxidizing quinones, such as 2,5- or 2,6-dimethylquinones, are formed by treatment of nickel... 

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). 

Since the donor strength of duroquinone is rather small, the capacity of the nickel atom in stabilizing two duroquinone molecules by dative n bonding is probably limited. The situation is similar to that in the nickel complexes of the 1,1-dicyano- and 1,1,2-tricyanoethylenes which also form only 1 1 complexes (Section IV, B, 3). During thermal decomposition of (XX) monomeric, coordinately unsaturated Ni(duroquinone) is formed. This species is evidently very reactive and rapidly associates to (XXI). It may be trapped in the monomeric state if generated in the presence of electron donors such as cyclic dienes and some phosphines. Under these conditions new complexes of composition olefin-Ni(0)-duroquinone and (phosphine)2-Ni(0)-duroquinone are formed (55, 56, 57). 

C. Complexes of Nickel with Duroquinone and Cyclic Olefins... 

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