| Abstract
| - This report describes the preparation and structural characterization of chromium compounds supported by tris(2-pyridylmethyl)amine (TPA), including the chromium(II) complexes (TPA)CrCl2 (1) and [(TPA)CrCl]2[BPh4]2 (2) and the cationic chromium(III) derivative [(TPA)CrCl2][BPh4] (4). Further treatment of 4 with methyl and phenyl Grignard reagents yields the cationic organometallic derivatives [(TPA)CrMe2][BPh4] (5) and [(TPA)CrPh2][BPh4] (6), respectively. Each compound displays moderate polymerization activity (10−20 g/(mmol of Cr hr atm)) in the presence of methylalumoxane, yielding low to moderate molecular weight high-density polyethylene.
- This report describes the synthesis, structural characterization, and polymerization behavior of a series of chromium(II) and chromium(III) complexes ligated by tris(2-pyridylmethyl)amine (TPA), including chromium(III) organometallicderivatives. For instance, the combination of TPA with CrCl2 yields monomeric (TPA)CrCl2 (1). A similar reactionof CrCl2 with TPA, followed by chloride abstraction with NaBPh4 or NaBArF4 (ArF = 3,5-(CF3)2C6H3), provides theweakly associated cationic dimers [(TPA)CrCl]2[BPh4]2 (2A) and [(TPA)CrCl]2[BArF4]2 (2B), respectively. X-raycrystallographic analysis reveals that each chromium(II) center in 1, 2A, and 2B is a tetragonally elongated octahedron;such Jahn−Teller distortions are consistent with the observed high spin (S = 2) electronic configurations for thesechromium(II) complexes. Likewise, reaction of CrCl3(THF)3 with TPA, followed by anion metathesis with NaBPh4 orNaBArF4, yields the monomeric, cationic chromium(III) complexes [(TPA)CrCl2][BPh4] (4A) and [(TPA)CrCl2][BArF4](4B), respectively. Treatment of 4A with methyl and phenyl Grignard reagents produces the cationic chromium(III)organometallic derivatives [(TPA)Cr(CH3)2][BPh4] (5) and [(TPA)CrPh2][BPh4] (6), respectively. Similar reactions of4A with organolithium reagents leads to intractable solids, presumably due to overreduction of the chromium(III)center. X-ray crystallographic analysis of 4A, 5, and 6 confirms that each possesses a largely undistorted octahedralchromium center, consistent with the observed S = 3/2 electronic ground states. Compounds 1, 2A, 2B, 4A, 4B,5, and 6 are all active polymerization catalysts in the presence of methylalumoxane, producing low to moderatemolecular weight high-density polyethylene.
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