η³‐Allylnickel alkoxides and their use as homogeneous and heterogeneous catalysts for the dimerization of olefins

Abstract

η3‐Allylnickel alkoxides {η3‐C3H5NiOR}2 (R = Me, Et, i‐Pr, Ph, SiPh3) may be activated by gaseous boron trifluoride (BF3) to give active catalysts for the dimerization of propene in homogeneous phase. In CH2Cl2 at −20 °C catalytic turnover numbers of 5000 mol propene(mol Ni)−1h−1 were measured. The nature of the OR group influences both the catalytic activity and the oligomerization product distribution. The ratio of methylpentenes to dimethylbutenes in the dimer fraction may be controlled by the presence of additional phosphine ligands at the nickel atom. The nickel alkoxide precursor was heterogenized on alumina to give {Al2O3}–O–Ni–(η3‐C3H5). Subsequent activation using gaseous BF3 generates a powerful heterogeneous olefin dimerization catalyst which converts 50 × 103 mol propene (mol Ni)−1 at −10° to −5°C in a batchwise process and 143 × 103 mol propene (mol Ni)−1 continuously to give 75% dimers and 25% higher oligomers. The solvent‐free treatment of oxide supports, e.g. alumina or silica, with gaseous BF3 produces strong ‘solid acids’. The activated hydroxyl groups on the support surface serve as effective anchor sites for organometallic complexes to form heterogenous catalysts. By reaction of Ni(cod)2 with {Al2O3}O(BF3)H or {SiO2}O(BF3)H, η1, η2‐cyclo‐octenylnickel–O fragments may be fixed to the surface. In the absence of halogenated solvents, the resulting catalysts, e.g. {SiO2}O–(BF3)–Ni–(η1, η2‐C8H13), dimerize propene continuously at +5°C at the rate of 800 × 103 mol liquid propene (mol Ni)−1.

Facile Preparation and Activation of High‐Productivity Single‐Site Nickel Catalysts for Highly Linear Polyethylene

“…Associated b-diketonate-alkoxo-Ni II complexes with presumed structures similar to that of 1 have been reported by Baranwal and Mehrotra [4]. Analogous dinuclear Ni II [5] and Pd II [6] complexes with m-aryloxy bridging ligands have also been published. Perhaps most relevant are two structures, 6 and 7, that have been previously reported [7].…”

“…The return, especially to Ni, is ironic, given that the coordination oligomerization and polymerization of ethylene was originally discovered a half-century ago with adventitious Ni as the catalytic metal [13]. Several of the first-and second-row late transition metals, as well as a large variety of ligands, have now been shown to yield moderate-to-very good catalysts for olefin polymerization 5 ).…”

“…The kinetic order and an unusually high tolerance for heteroatoms leads to a proposed catalytic cycle in which the key species are heteronuclear complexes involving Ni II and a second electrophilic metal cation. The second metal center, with associated bridging ligands functions to suppress catalyst deactivation, leading to TON exceeding 10 5 . With further optimization, higher productivities are likely to be achievable.…”

The performance of methallyl nickel complexes and boron adducts in the catalytic activation of ethylene: a conceptual DFT perspective

“…Since, complex 4 proved to be the most active for the production of polyethylene when activated with B(C 6 F 5 ) 3 , it was selected as a precursor for reactions with BF 3 •OEt 2 and the following ethylene activation. BF 3 usage as co-catalyst for ethylene oligomerization has been observed before but the active species were not clearly defined [58][59][60].…”

Preparation of a Well-Defined Silica-Supported Nickel-Diimine Alkyl Complex − Application for the Gas-Phase Polymerization of Ethylene

“…The resulting species described as {SiO 2 }O-(BF 3 )-Ni-(η 1 ,η 2 -C 8 H 13 ) are active for the oligomerization of olefins. 26 We wish to report here a new method, which consists of grafting first the molecular complex 27 to obtain the well-defined [tSiO-Ni(R-diimine)(CH 2 SiMe 3 )] supported onto Aerosil SiO 2-(700) by the SOMC method. The resulting surface organometallic complex can then be activated by BF 3 to form an active catalyst for the polymerization of ethylene, which may be a cationic R-diimine nickel species obtained by coordination of the strong Lewis acid on the oxygen bound to Ni.…”