Monocyclopentadienyl Bis(phenoxo-imino) Zirconium Complexes as Precatalyst Species for Olefin Polymerization. Stereospecific Methylation of an Imino Group with Formation of a Zirconium−amido Bond

Abstract

The Schiff base N,N ‘-o-phenylenebis(3,5-di-tert-butyl-salicylideneimine) (1; t Bu4salophenH2) reacts with 1 equiv of Zr(η5-C5H5)Cl3·DME in the presence of 2.2 equiv of NEt3 in pentane to give the monocyclopentadienyl bis(phenoxo-imino) monochloro zirconium derivative Zr(η5-C5H5)[C6H4-1,2-{NCH(3,5- t Bu2C6H2-2-O)}2]Cl (2). Moreover, 2 equiv of the monolithiated reagent derived from 3-tert-butyl-N-ethylsalicylaldimine by reaction with Li n Bu in hexane reacts at −78 °C with 1 equiv of Zr(η5-C5H5)Cl3·DME in THF to yield the corresponding monocyclopentadienyl bis(phenoxo-imino) monochloro zirconium complex Zr(η5-C5H5)[CH3CH2NCH{(3- t BuC6H3-2-O)}]2Cl (5) after elimination of LiCl. Methylation of 2 with MgClMe in pentane or toluene at −78 °C affords Zr(η5-C5H5)[1,2-C6H4{NCH(3,5- t Bu2C6H2-2-O)}{NCH(Me)(3,5- t Bu2C6H2-2-O)}] (3) as a result of the reduction of one of the CN bonds of the coligand. The hydrolysis of 3 gives the new organic compound [C6H4{NCH(3,5- t Bu2C6H2-2-OH)}{NCH(Me)(3,5- t Bu2C6H2-2-OH)}] (4), which was also quantitatively isolated by reaction of 1 with MgClMe followed by treatment with a saturated solution of NH4Cl in water. All of the reported compounds were characterized by the usual analytical and spectroscopic methods, and the molecular structure of 5 was determined by X-ray diffraction analysis from suitable single crystals. The catalytic activities of 2, 3, and 5 for ethylene polymerization using MAO as cocatalyst were determined.

Synthesis, crystal structure and ethylene polymerization activity of zirconium complexes bearing mono-Cp and tridentate Schiff base [ONO] ligands

“…The Zr-N(1) bond (2.341(3) Å ) is slightly shorter than that of FI zirconium complexes (2.355-2.38 Å ), which indicates significant coordination of imino nitrogen atom to metal center in the solid state [21]. The Zr-O(2) bond length (1.993(2) Å ) is in the range of the structurally related mono-Cp zirconium complexes (1.954-2.040 Å ) [13,14]. As expected for the weak methoxy donor, the…”

“…Among them, mixed ligands titanium complexes of the type Cp 0 Ti(L)X 2 containing cyclopentadienyl ligand and non-Cp ligand have attracted considerable attention, because this type of catalyst has been expected to exhibit unique characteristics as olefin polymerization catalyst that would combine the merits of metallocene and non-Cp catalyst type [6][7][8][9][10][11][12]. However, there have been only a few reports on the use of mixed ligands zirconium complexes for the olefin polymerization [13,14].Schiff base ligands represent one of the most widely utilized classes of ligands in metal coordination chemistry. Their complexes have shown many important catalytic applications, ranging from asymmetric epoxidation [15,16], Lewis acid assisted organic transformations [17], to various types of polymerization [18,19].…”

“…Among them, mixed ligands titanium complexes of the type Cp 0 Ti(L)X 2 containing cyclopentadienyl ligand and non-Cp ligand have attracted considerable attention, because this type of catalyst has been expected to exhibit unique characteristics as olefin polymerization catalyst that would combine the merits of metallocene and non-Cp catalyst type [6][7][8][9][10][11][12]. However, there have been only a few reports on the use of mixed ligands zirconium complexes for the olefin polymerization [13,14].…”

Synthesis of novel zirconium complexes bearing mono‐Cp and tridentate Schiff base [ONO] ligands and their catalytic activities for olefin polymerization

“…21 -23 The mixed ligands group 4 complexes are mainly focused on titanium metal, and there have been only a few reports on the use of mixed ligands zirconium complexes for the olefin polymerization. 24,25 Schiff base ligands represent one of the most widely utilized classes of ligand in metal coordination chemistry. Their complexes have shown many important catalytic applications, ranging from asymmetric epoxidation 26,27 and Lewis acid-assisted organic transformations, 28 to various types of polymerization.…”

“…35 There are some examples of the use of monochloro complexes for ethylene polymerization. 25,36 The polymerization was run at different temperatures • C) to probe the catalyst's thermal stability. The polymerization temperature has a remarkable effect on the catalytic behavior, as demonstrated in Table 3.…”