Titanium and zirconium compounds stabilized by coordination of heteroscorpionate [N,N,O]-donor ligands. Synthesis, characterization and polymerization activity

The bis(pyrazol-1-yl)methane compounds [(2-hydroxyphenyl)bis(pyrazol-1-yl)methane (4) bpzmpH, (3,5-di-tert-butyl-2-hydroxyphenyl)bis(pyrazol-1-yl)methane (5) bpzmtBu2pH, (2-hydroxyphenyl)bis(3,5-dimethyl-pyrazol-1-yl)methane (6) Me2bpzmpH, (3,5-di-tert-butyl-2-hydroxyphenyl)bis(3,5-dimethyl-pyrazolyl)methane (7) Me2bpzmtBu2pH, (2-hydroxyphenyl)bis(4-methyl-pyrazolyl)methane (8) MebpzmpH and (3,5-di-tert-butyl-2-hydroxyphenyl)bis(4-methyl-pyrazolyl)methane (9) MebpzmtBu2pH] as heteroscorpionate precursor ligands have been prepared by reaction of the corresponding bis(pyrazol-1-yl)ketone (1), bis(3,5-dimethylpyrazol-1-yl)ketone (2) and bis(4-methylpyrazol-1-yl)ketone (3) with the appropriate salicylaldehyde derivative. The coordination of these molecules to titanium and zirconium compounds containing a cyclopentadienyl ligand has been studied. TiCpRCl3 (CpR = η5-C5H5 (Cp); η5-C5H4SiMe3 (Cp′); η5-C5Me5 (Cp*)) reacts with 4–9 in the presence of 2.5 equiv of NEt3, in toluene at room temperature, through an alcoholysis process to give the monocyclopentadienyl heteroscorpionate dichloro complexes TiCpRLCl2 [CpR = Cp, L = bpzmp (10), Me2bpzmtBu2p (11), MebpzmtBu2p (12); CpR = Cp′, L = Me2bpzmtBu2p (13); CpR = Cp*, L = bpzmp (14), Me2bpzmtBu2p (15)] ( Scheme 2). Treatment of TiCp*Me3 with 4, 6 and 8 affords the dimethyl complexes TiCp*LMe2 [L = bpzmp (16), Me2bpzmp (17), Mebpzmp (18)]. Analogous dichloro ZrCpLCl2 [L = bpzmp (19), bpzmtBu2p (20), Me2bpzmp (21), MebpztBu2p (22)] and dibenzyl ZrCpLBz2 [L = bpzmp (23), bpzmtBu2p (24), Me2bpzmp (25), MebpzmtBu2p (26)] zirconium complexes have also been prepared by reaction of ZrCpCl3 in THF or ZrCpBz3 in toluene with 4, 5, 6 and 8 at room temperature. From spectroscopic data tetrahedral structures in solution with a κ1-O coordination mode are suggested for the titanium complexes, while distorted octahedral geometries with a κ3-N,N,O coordination are proposed for the zirconium derivatives. Fluxional exchange between coordinated and non-coordinated pyrazolate rings is concluded in some zirconium compounds, depending on the electronic and steric effects imposed by the substituents of the heteroscorpionate ligands. Preliminary studies of catalytic activity for ethylene polymerization using sMAO as cocatalyst were performed. The complexes proved to be moderate catalysts due to loss of the scorpionate ligand.