Oligomerization of 1-butene with a homogeneous catalyst system based on allylic nickel complexes

Abstract

The oligomerization of 1-butene with a nickel-based catalyst system constitutes an elegant synthesis method for obtaining linear octenes from readily available chemicals. It is well known that the bis-(cyclooctadiene)nickel(0)-complex (Ni(COD) 2 ) can be used in combination with 1,1,1,5,5,5-hexafluoroacetylacetone (hfacac) forming [Ni-1] as a catalyst for the dimerization of 1-butene, which produces a linear octene yield of 75-83% at reaction temperatures between 70-80 C. We are the first to demonstrate that it is also possible to use allylic nickel complexes in combination with hfacac to produce linear octenes with a selectivity of 70% under very mild reaction conditions and at low catalyst concentrations. Additionally the catalyst can be formed simply by adding the activator hfacac to a solution of the allylic nickel complex. No complicated synthesis or purification is needed.

Nickel Hydride Complexes

“…120 277 A recent study demonstrates that methallyl complex {(η 3 -C 4 H 7 )Ni(μ-Cl)} 2 mixed with hfacac-H is also an active catalyst for the oligomerization of 1-butene. 278 The reaction temperature in this case is lower (30 °C), while the selectivity still favors the linear dimers (67% C8 vs 21% C12). In both catalytic systems, the catalytically active species is the 3coordinate (hfacac)NiH.…”

“…Mixing Ni­(COD) 2 with hfacac-H (hfacac-H = CF 3 COCH 2 COCF 3 ) generates (hfacac)­Ni­(cyclooctenyl) (analogous to those shown in Scheme ), which catalyzes the oligomerization of 1-butene at 70–80 °C to linear octenes in 75–83% yield . A recent study demonstrates that methallyl complex {(η 3 -C 4 H 7 )­Ni­(μ-Cl)} 2 mixed with hfacac-H is also an active catalyst for the oligomerization of 1-butene . The reaction temperature in this case is lower (30 °C), while the selectivity still favors the linear dimers (67% C8 vs 21% C12).…”

Tracing Active Sites in Supported Ni Catalysts during Butene Oligomerization by Operando Spectroscopy under Pressure

“…Under 1-butene, two additional signals appear: site 3 ( g ∥ = 2.219, g ⊥ = 2.012) is attributed to Ni I , which coordinates to a π-system, since a similar shift to lower g -values has been found for Ni I interacting with π-electrons of unsaturated hydrocarbons. , It may arise from a Ni site that forms a π-complex with 1-butene. The g ⊥ value of signal 4 ( g ∥ = 2.233, g ⊥ = 2.090) is much larger, in comparison to those of signals 1–3, suggesting that signal 4 does not arise from a π-complex of Ni I with 1-butene but rather from a Ni I –(CH 2 ) 3 CH 3 complex formed by insertion of 1-butene into the Ni–H bond, which is commonly assumed to be the first step in the reaction cycle. − Signals 1 and 2 decrease with rising butene pressure, in favor of signals 3 and 4 (see Figure b, as well as Table S1), indicating that those Ni I species (Ni I ···Cp and/or Ni I ···COD) are converted to species 3 (Ni I ···π) and 4 (Ni I –(CH 2 ) 3 CH 3 ).…”

Role of Surface Acidity in Formation and Performance of Active Ni Single Sites in Supported Catalysts for Butene Dimerization: A View inside by Operando EPR and In Situ FTIR Spectroscopy

“…Nickel-based catalysts have been established as the most effective catalysts due to their high activity and selectivity to linear C 8 alkenes used as comonomers in the production of polyethylene and plasticizers. − In the homogeneous DIMERSOL oligomerization process, a nickel complex catalyst activated by an organoaluminum compound is used. This catalyst, however, cannot be separated and frequently suffers from deactivation by traces of nitrogen and/or oxygen-containing polar compounds, present in the used solvents. ,, In contrast, the heterogeneous OCTOL process uses bifunctional supported nickel catalysts, is more environmentally friendly, and is easier to use. This process produces up to 50% methylheptenes and up to 20% n -octene as desired products, implying that there is still much potential for selectivity improvements.…”

“…This catalyst, however, cannot be separated and frequently suffers from deactivation by traces of nitrogen and/or oxygen-containing polar compounds, present in the used solvents. 1,4,5 In contrast, the heterogeneous OCTOL process uses bifunctional supported nickel catalysts, is more environmentally friendly, and is easier to use. This process produces up to 50% methylheptenes and up to 20% noctene as desired products, implying that there is still much potential for selectivity improvements.…”