Deactivation Pathways of Neutral Ni(II) Polymerization Catalysts

Abstract

The novel dimethyl sulfoxide (DMSO)-coordinated complex [(N,O)Ni(CH(3))(DMSO)] {1-DMSO; (N,O) = kappa(2)-N,O-(2,6-(3,5-(F(3)C)(2)C(6)H(3))(2)C(6)H(3))-N=CH-(3,5-I(2)-2-OC(6)H(2))} was found to be a well-defined, very reactive precursor that enables direct observation of the activation and deactivation of neutral Ni(II) catalysts. Preparative reaction with ethylene afforded the ethyl complex [(N,O)Ni((alpha)CH(2)(beta)CH(3))(DMSO)] (2-DMSO). 2-DMSO is subject to interconversion of the (alpha)C and (beta)C moieties via an intermediate [(N,O)Ni(II)H(ethylene)] complex (this process is slow on the NMR time scale). Exposure of 1-DMSO to ethylene in DMSO solution at 55 degrees C results in partial reaction to form propylene (pseudo-first-order rate constant k(ins,Me) = 6.8 +/- 0.3 x 10(-4) s(-1) at an ethylene concentration of 0.15 M) and conversion to 2-DMSO, which catalyzes the conversion of ethylene to butenes. A relevant decomposition route of the catalyst precursor is the bimolecular elimination of ethane [DeltaH(double dagger) = (57 +/- 1) kJ mol(-1) and DeltaS(double dagger) = -(129 +/- 2) J mol(-1) K(-1) over the temperature range 55-80 degrees C]. This reaction is specific to the Ni(II)-Me complex; corresponding homocoupling of the higher Ni(II)-alkyls of the propagating species in catalytic C-C linkage of ethylene was not observed, but Ni(II)-Me reacted with Ni(II)-Et to form propane, as concluded from studies with 2-DMSO and its analogue that is perdeuterated in the Ni(II)-Et moiety. Under the reaction conditions of the aforementioned catalytic C-C linkage of ethylene, additional ethane evolves from the reaction of intermediate Ni(II)-Et with Ni(II)-H. This is independently supported by reaction of 2-DMSO with the separately prepared hydride complex [(N,O)NiH(PMe(3))] (3-PMe(3)) to afford ethane. Kinetic studies show this reaction to be bimolecular [DeltaH(double dagger) = (47 +/- 6) kJ mol(-1) and DeltaS(double dagger) = -(117 +/- 15) J mol(-1) K(-1) over the temperature range 6-35 degrees C]. In contrast to these reactions identified as decomposition routes, hydrolysis of Ni(II)-alkyls by added water (D(2)O; H(2)O) occurred only to a minor extent for the Ni(II)-Me catalyst precursor, and no clear evidence of hydrolysis was observed for higher Ni(II)-alkyls. The rate of the aforementioned insertion of ethylene in 1-DMSO and the rate of catalytic ethylene dimerization are not affected by the presence of water, indicating that water also does not compete significantly with the substrate for binding sites.

Gas-Phase Dimerization of Ethylene under Mild Conditions Catalyzed by MOF Materials Containing (bpy)NiII Complexes

“…suspended NU-1000-bpy-NiCl 2 as well as the appropriate controls (Table 1). Prior to the dimerization, all catalysts were pre-treated with Et 2 AlCl (70 equiv) to generate catalytically active nickel-hydrido moieties [31][32] (see SI, section S5 for experimental details and Figure S7 for a proposed catalytic cycle). For convenience of handling, the volatile products were brominated in situ prior to being analyzed by GC-FID.…”

Dimerization of ethene in a fluidized bed reactor using Ni-based Supported Ionic Liquid Phase (SILP) catalysts

“…Our observation would be in line with the assumption of a deactivation route involving the reaction of two active Ni complexes with one another in case insufficient ethene is present. 35 This aspect will be developed in more detail below.…”

“…The low reaction temperature was required to avoid thermal decomposition of the cationic Ni-complexes. 35 Under these conditions, the combination of high catalytic activity and strong exothermicity of the dimerization reaction still resulted in hot spot formation inside the fixed catalyst bed. The temperature at the top end of the fixed bed (T top ) and at the bottom end of the fixed bed (T bottom ) were measured over time using two thermocouples ( Fig.…”

Olefin Polymerization with Non-metallocene Catalysts (Late Transition Metals)

“…The Ni complex catalyze the ethylene polymerization even in water (vide infra) and in supercritical CO 2 [105,106]. The intermolecular reaction between alkyl-Ni complex and methyl-or hydride-Ni complex to form Ni bis(salicylaldimine) complex is regarded as a deactivation process of the catalyst [107]. Complex 6c (L = tmeda) catalyzes dispersion polymerization of propylene and 1-butene under aqueous media [108].…”