Nickel complexes dipole moments

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). 

Well-defined 1 1 and 1 2 adducts with triphenylphosphine are formed with ease 42,45, 46). The yellow 1 1 adduct is more stable than bis(acrylo-nitrile)-nickel itself (dec. p. 185° C) and represents one of the first examples of a nickel complex with the coordination number three. The 2 1 adduct is monomeric in benzene and has a dipole moment of 6 Debye units (46). Unstable bis(pyridine) adducts were also isolated, but were found to decompose at room temperature, depositing metallic nickel (46). 

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... 

It is interesting that tiiis complex, anfl related complexes of nickel, have substantial dipole moments in benzene solution (<- 1 5 D) [13, 12]. It may be that the molecules are able to bend easily about the axis through the two bridging chlorines or that some weak complex formation with benzene occurs. 

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