The reaction of 2-phenyl-1H-indole with either TiCl4 or ZrCl4 was carried out under anaerobic conditions in toluene, at an elevated temperature of up to 105 degrees Celsius. At a molar ratio of PI:MCl4=2, the reaction is very efficient and complete within about 30 min yielding a single, burgundy colored product, an orthometallated complex 1, incorporating byproduct HCl. Complex 1 crystallizes after repeated washings with hexane. The same reaction, run at a molar ratio PI:MCl4=1, yields a number of different products, key among them the metallated complex in the 3-position of the indole framework 2, but no complex 1. We propose that this different reaction outcome originates from a separate mechanism pathway operating in each case, starting with the thermal transformation of an hexa-coordinated MCl4.2PI, and a penta-coordinated MCl4.PI compound, respectively, formed by mixing of the individual components at the indicated ratios, at ambient temperature. Noteworthy is the hydrogen bonding of the HCl in 1, and the ammonium salt formation in 2. Complex 1 reacts with one equivalent of triethylaluminum (TEA) to yield the bimetallic complex 3. Increasing the relative amount of TEA, we gradually substitute the Cl with Et groups on the Al. At Ti:Al molar ratio of 1:6 we have an experimentally determined statistical average of 2.5 Cl to 1.5 Et, meaning that there is an equilibrium of one mole of a Ti/Al complex containing three Cl and one Et group, per mole of a similar complex containing two Cl and two Et groups.
It has been determined that complex 1 coordinates on the 110 cut of the MgCl2 support of a polypropylene catalyst, and acts in the dual role of a modifier and a polymerization catalyst, enhancing substantially the performance of the catalytic system.
Spectroscopic and other structural evidence for the isolated products will be presented.

Direct metallation of 2-phenyl-1H-indole (PI) with MCl4 (M=Ti or Zr). Effect of the PI:MCl4 molar ratio on the formation of two different metallated complexes

ACS Spring Meeting 2021

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