Electronic effects in homogeneous indenylzirconium Ziegler-Natta catalysts

A series of new bis(indenyl)zirconium(IV) complexes of the general formula (\u3b75-4,7-X2C9H5) 2ZrCl2 and (\u3b75-4,7-X2C9H5) 2Zr(CH2C6H5)2 (where X = H, CH3, OCH3, and F) were synthesized in order to investigate the electronic effects of substituents on the nature of the catalytic species in homogeneous Ziegler-Natta catalysts. By use of poly(methylaluminoxane) as cocatalyst, the activity of these complexes as catalyst precursors in the polymerization of ethylene was examined. The substitution with electron-withdrawing groups resulted in a decrease of both molecular weights and productivity, whereas in the case of electron donors, like methyl groups, no significant change in productivity and average molecular weight was observed. These effects support the hypothesis of a polar or ionic character of the catalytic species. The molecular structure of (\u3b75-4,7-F2C9H5) 2Zr(CH2C6H5)2 was determined by X-ray diffraction. The complex crystallizes in space group P21/c (No. 14) with cell parameters a = 10.786 (1) \uc5, b = 11.084 (2) \uc5, c = 21.602 (2) \uc5, \u3b2 = 98.30 (1)\u302, Z = 4, R = 0.0220, and Rw = 0.0295. \ua9 1990 American Chemical Society

Crystal structures and solution conformations of the meso and racemic isomers of (ethylenebis(1-indenyl))zirconium dichloride

The crystal and molecular structures of the C2 symmetric rac-(EBI)ZrCl2 (1r) [monoclinic, space group I2/c, No. 15, a = 11.957(1) \uc5, b = 10.627(1) \uc5, c = 13.775(2) \uc5, \u3b2 = 106.06(1)\ub0] and of its meso isomer (1m) [monoclinic, space group P21/n, No. 14, a = 11.119(3) \uc5, b = 10.467(1) \uc5, c = 14.949(2) \uc5, \u3b2 = 100.94(2)\ub0] have been solved. 1r is in the indenyl-forward (\u3a0) conformation, as is the case for most of the chiral ansa ethylene-bridged bisindenyl-type metallocenes. In solution however, already at room temperature there is a rapid (NMR time scale) interconversion between the two \u3a0 and Y (indenyl-backward) conformations, as shown by conformational analysis on the proton spectra of the bridge methylenes. This equilibrium is shifted toward the lower energy conformation \u3b4 at lower temperatures and is influenced by both the solvent and the \u3c3-ligands. The solid state structure of 1m shows that this meso form is actually in a chiral conformation (C1 symmetry) because of the staggered placement of the two indenyl ligands (Ind 27Ind = 10.0\ub0). In solution this aspecific zirconocene gives a perfectly symmetric 1H NMR spectrum, indicating that, as in the case of the rac-isomer, there is a rapid interconversion between the two equienergetic, mirror-image limit conformations. \ua9 1995 American Chemical Society

Simple and efficient synthesis of 4,7-dimethoxy-1(H)-indene

Stirring 4,7-dimethoxy-1-indanol in chloroform at room temperature in the presence of a catalytic amount of p-toluenesulfonic acid gave 4,7-dimethoxy-1(H)-indene in quantitative yield. Other solvents, including benzene, which was the most frequently used one for this reaction, gave mostly polymeric materials. The new method was also effective for dehydration of other electron-rich benzylic alcohols. Copyright © Taylor & Francis Group, LLC