New bis(aryloxy)–Ti(iv) complexes and their use for the selective dimerization of ethylene to 1-butene

Abstract

New titanium complexes of general formula [(ArO)(n)Ti(Oi-Pr)((4-n))] were synthesized and used as pre-catalysts for the selective dimerization of ethylene to 1-butene. The complexes were prepared in cyclohexane using [Ti(Oi-Pr)(4)] and one or two equivalents of the corresponding phenols (ArOH) at room temperature. In this work, both monodentate and chelating phenols were evaluated. For alkyl-substituted phenols, it was demonstrated that large steric hindrance at both ortho and ortho' positions selectively yielded the mono-substituted complexes [(ArO)Ti(Oi-Pr)(3)]. Substitution at only one of the ortho positions allowed both the mono- and the di-substituted Ti complexes to be isolated. When a heteroatom was introduced on the phenol backbone, di-substitution systematically occurred except with phenols presenting a hemilabile -CH(2)NR(2) group at the ortho position. Upon activation with 3 equiv. of AlEt(3) at 20 bar and 60 °C, all the complexes selectively dimerized ethylene to 1-butene (>86% of butenes among which 99% of 1-butene). An increase of the steric bulk at the ortho position of the ligand or the introduction of a functional group led to decreased activity compared to [Ti(Oi-Pr)(4)].

Role of Homogeneous Catalysis in Oligomerization of Olefins : Focus on Selected Examples Based on Group 4 to Group 10 Transition Metal Complexes

“…Noticeable differences in catalyst activity were observed when the hemilabile part was modified. This work was extended later to functionalized bis(aryloxy)-Ti(IV) complexes of general formula [(ArO-LhTi(O;PrhJ with the same catalytic tendencies [88]. ln parallel with this study, investigations on functionalized imido Ti(IV) complexes were also undertaken [89].…”

Titanium Complexes with Functional Alkoxido Ligands for Selective Ethylene Dimerization – A High Throughput Experimentation Approach

“…Most of the 1 H NMR spectra of the [Ti(OR) 2 (OiPr) 2 ] complexes presented broad signals for the H atoms in α position to the oxygen atoms and for the CH 3 protons of the isopropoxido ligands (see ESI, Figure S6 for [Ti( 5) 2 (OiPr) 2 ]). This feature may indicate the presence of di-or polynuclear species with bridging ligands, [9] as encountered in (di-aldoximato)(di-isopropoxido)titanium complexes, [16] in mono (alkoxido-amino)titanium complexes, [17] and in [Ti(μ-OPh)(O-Ph) 2 (OiPr)(OHiPr)] 2 , a (di-isopropoxido)titanium complex with non-functionalized phenoxy ligands (see ESI). In the latter, centrosymmetric complex, each Ti center is octahedrally coordinated by two bridging phenoxy ligands, one terminal phenoxy ligand trans to a μ-OPh and another cis to it, a OiPr ligand and a iPrOH molecule trans to the terminal OPh ligand (see details in ESI, Figure S34 and Table S1).…”

“…At this stage, we wanted to check whether AlEt 3 was the best co-catalyst. [5,9] Thus, a screening of various co-catalysts (AlMe 3 , AlEt 2 Cl, AlEtCl 2 , Al 2 Et 3 Cl 3 and MAO) was performed with complex [Ti( 19) 2 (OnBu) 2 ], the "lead" pre-catalyst of the secondary screening, in order to determine the best conditions for high activity, good selectivity for 1-butene without polymer formation (Table 5).…”

“…[7] Attempts to optimize the activity and the selectivity of the reaction have been essentially conducted by introducing external modifiers based on oxygen-, nitrogen-, or phosphorous-donors Lewis bases. [8] With the aims to better control and fine-tune the metal coordination sphere towards improved catalytic properties, we recently developed a promising family of titanium complexes where the modifier was incorporated in the aryloxido ligands, [9] that we extend now to alkoxido ligands. Potentially chelating ligands limit the structural diversity and sometimes difficult to control ligand rearrangements encountered in metal complexes with monodentate alkoxides.…”

Tridentate Aryloxy‐Based Titanium Catalysts towards Ethylene Oligomerization and Polymerization

“…Depending on the structure of the aryloxy ligand (steric hindrance, nature of the heteroatom and nature of the spacer group), mono‐aryloxy or bis‐aryloxy complexes can be obtained ( III and IV ; Figure 1). 6a,6b Upon activation with methylaluminoxane (MAO), catalysts derived from III and IV are poorly active towards ethylene with a selectivity oriented towards polymers (>95 %).…”