Synthesis and spectroscopic characterization of group 4 post-metallocenes bearing (σ-aryl)-2-phenolate-6-pyridyl and -isoquinolinyl auxiliaries

Abstract

A new series of group 4 bis(benzyl) complexes supported by (σ-aryl)-2-phenolate-6-pyridyl [O,C,N] ligands have been prepared, and all derivatives have been characterized by multinuclear NMR spectroscopy. In the (1)H NMR spectrum of the Ti derivative where [N] = (ortho-F)-substituted isoquinolinyl, one of the two CH2 resonances is observed as a doublet of doublets (collapsing to a normal d upon (19)F-decoupling), whereas the [(1)H,(19)F]-HMQC correlation spectrum reveals a strong crosspeak for this dd resonance only, thus indicating the presence of intramolecular C-HF-C interactions. [(1)H,(19)F]-HMBC experiments have been performed which reveal a significant scalar component for this coupling and confirm that the interactions are genuine. The contrasting NMR spectral patterns for the (ortho-F)-pyridyl Hf analogue, which exhibits two sets of non-identical doublet of doublets for the methylene resonances, have been rationalized. The activities of the isoquinolinyl-based Ti-[O,C,N] catalysts for ethylene polymerization are superior to those of pyridyl-based congeners.

Group 4 Post-Metallocenes Supported by [OCH2N,C(σ-aryl)] Auxiliaries Bearing a Seven-Membered Metallacycle: Synthesis, Characterization, and Catalysts for Olefin Polymerization

“…Spectroscopic and Structural Characterization. All complexes have been characterized and assigned using 1 H and 13 C NMR spectroscopy (including [ 1 H, 1 H]-COSY, [ 1 H, 13 C]-HSQC, and ROESY experiments), plus 19 F and [ 1 H, 19 F]-HMQC experiments for 5−9. As illustrative examples, the 1 H NMR spectra of 1 and 2 have been fully assigned (Figures S1 and S2).…”

“…For all complexes, the CH 2 (benzyl) and CH 2 (chelate) protons (denoted H a and H b respectively) are diastereotopic and appear as six discrete doublets in the alkyl region, and can be assigned using [ 1 H, 1 H]-COSY and ROESY experiments (Figures S3−S5 respectively for 2). The presence of two singlets in the 13 C and DEPT-135 spectra for the CH 2 (benzyl) groups (Figure S6 for 2), and the observation that the o-, m-, and p-Ph protons of each benzyl unit are resolved into separate resonances, are suggestive of markedly different chemical environments for the two benzyl moieties. These results confirm that, unlike [O,N,C] derivatives that exhibit C 2v symmetry (due to a virtual mirror plane through the meridional ligand), the introduction of a methylene unit into the [O,N] chelate has afforded complexes with C 1 symmetry, thus hinting at a coordination mode that deviates substantially from meridional (see crystal structure).…”

“…Furthermore, we note that these C−H•••F−C interactions have been reported for structurally related 2-phenolate-6-pyridine-(σaryl) [O,C,N] analogues. 5,13 These observations open up the possibility that such stabilizing interactions between the F atom at R 4 (ortho to Ti−C(σ-aryl) bond) and the growing polymer chain could potentially suppress β-H elimination (leading to chain termination) to afford polymers with higher M w . 6,7 Such WALPI-type C−H(β)•••F−C interactions have been invoked by Delferro and Marks, based on the appearance of 1 H••• 19 F dipolar interactions detected by [ 1 H, 19 F]-HOESY experiments, to account for the dramatically higher M w (plus lower degrees of branching) of polyolefins produced by fluorinated terphenylphenoxyimine-Ni(II) mono-and bimetallic catalysts.…”

“…Alternatively, dried toluene was added to give a 10 wt % solution that was freshly prepared before use. 1 H, 13 C (referenced to residual solvent peaks), and 19 F (external trifluoroacetic acid reference) NMR spectra were recorded at 298 K on a Bruker Avance 400 (or 300) FT-NMR spectrometer (ppm). Peak assignments were based on combinations of DEPT-135 and 2-D 1 H− 1 H, 13 C− 1 H, and NOE (plus [ 1 H, 19 F]-HMQC for 5−9) correlation NMR experiments.…”

“…8,9 Our initial studies 10,11 revealed that Ti-[O,N,C] catalysts can produce polyolefins with high M w /M n values suggestive of multisite behavior, which was subsequently ascribed to facile olefin insertion into the Ti− C(σ-aryl) bond to afford supplementary "olefin-assimilated" active species, 12 and efforts have been undertaken to modify and ameliorate polymerization characteristics. 13,14 The corresponding 2-arylamido [N,N,C]-Hf catalysts were developed by Symyx and Dow through the use of highthroughput screening, 15,16 and the analogous olefin insertion into the M−C(σ-aryl) bond of these 17,18 and related 19,20 Zr derivatives to generate olefin-assimilated (or "monomerinserted") active sites have been reported. Inspired by this unusual insertion reaction, Coates et al designed pyridylamido 21 and phenolate-amine 22 ligands bearing a pendant vinyl moiety, 23 which undergo metalation with group 4 alkyl species to afford C(sp 3 )-chelating catalysts that mediate the living isoselective polymerization of α-olefins.…”