The nickel(II) carboxylate/ETHYLALUMINUM SESQUICHLORIDE (cas 12075-68-2)/benzene-1,3-butadiene homogeneous catalytic system: evidence for the existence of a square planar nickel(II) complex before monomer addition

Add time:08/01/2019    Source:sciencedirect.com

Nickel(II)carboxylate salts or nickel(II) chloride react with excess ethylaluminum sesquichloride or ethylaluminum dichloride in benzene to produce a diamagnetic orange-brown complex. The amount of this complex increases with an increase of the ethylaluminum dichloride content of the ethylaluminum compound, i.e., the amount is maximized when the Et/Al/Cl ratio is 1 : 1 : 2. This complex has d → d electronic absorption bands in the visible region at 520 nm (19 230 cm−1) and 415 nm (24 038 cm−1) with molar absorptivity coefficients of 125 ± 7 and 361 ± 25 I mol−1 cm−1, respectively. The visible band locations, molar absorptivities, and diamagnetism are characteristic of square planar nickel (II) complexes. In the absence of monomer, the predominant complex, responsible for the observed electronic absorption bands, is slowly reduced to metallic nickel. Electronic spectra obtained as a function of time can be used to show that the reaction is first order with respect to the nickel complex. Polymerization rate data indicate that the predominant nickel(II) complex is involved in the polymerization of 1,3-butadiene to highly stereospecific cis-1,4-polymer.

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