A phosphino-oxazolineligand as a P,N-bridge in palladium/cobalt or P,N-chelate in nickel complexes: catalytic ethylene oligomerization

Abstract

The Pd(II) complex [PdCl(2)(1)] [1 = ({oxazolin-2-yl}methyl)diphenylphosphine] was obtained by the 1:1 reaction of 1 with [PdCl(2)(NCPh)(2)]. Although this neutral complex is stable in the solid-state and in solution, it reacts with the dinuclear complex [CoCl(2)(μ-1)](2) to afford the heterometallic zwitterionic complex [{PdCl(1)}(+)(μ-1)(CoCl(3))(-)] (2). Under inert atmosphere, two equivalents of 1 reacted with [NiCl(2)(dme)] to give trans-[NiCl(2)(1)(2)] (3) in CH(2)Cl(2) but cis-[NiCl(2)(1)(2)] (4) in CHCl(3). When the latter reaction was performed in air, trans-[NiCl(2)(5)(2)] (6) [5 = ({oxazolin-2-yl}methyl)diphenylphosphine oxide] was obtained. All metal complexes, 2, 3, 4 and 6, have been structurally characterized by X-ray diffraction. Complexes 3, 4 and 6 have been evaluated as precatalysts for ethylene oligomerisation in the presence of AlEtCl(2) as cocatalyst. Complexes 3 and 6 yielded a turnover frequency (TOF) of 60,700 and 62,600 mol of C(2)H(4)/((mol of Ni)·h), respectively, in the presence of 10 equiv. of AlEtCl(2). In the presence of only 6 equiv. of cocatalyst, these Ni complexes yielded TOF values of 41,500 and 58,000 mol of C(2)H(4)/((mol of Ni)·h), respectively.

Pyrazolyl‐phosphinoyl nickel (II) complexes: synthesis, characterization and ethylene dimerization studies

“…[17] Single crystals of Ni1 suitable for X-ray diffraction studies were grown from a concentrated dichloromethane solution of the compound at low temperature. [17,18] The chelate bite angle of the pyrazolyl-phosphinoyl ligand [O(1)-Ni(1)-N(2) 88.30(4)°], as well as the other bond lengths and angles, confirm the distorted octahedral geometry. The X-ray diffraction analysis of Ni1 shows that the central nickel atom is chelated by two pyrazolyl-phosphinoyl ligands.…”

“…Similar trends were also observed for others phosphinoyl-coordinated nickel complexes already described in the literature. [17] Single crystals of Ni1 suitable for X-ray diffraction studies were grown from a concentrated dichloromethane solution of the compound at low temperature. The molecular structure of Ni1 is shown in Figure 3 and the main crystallographic data and structure refinement parameters are reported in Table 1.…”

“…[17] More recently, Ojwach et al has also try to design unsymmetrical pyrazolyl-phosphine transition metal complexes containing a pyrazolyl unit and a secondary donor atom. The comparison between the performances of B and C illustrates the combined influence of a different donor atom and ring size of the metal chelates in the catalytic activity of the complexes.…”

“…The comparison between the performances of B and C illustrates the combined influence of a different donor atom and ring size of the metal chelates in the catalytic activity of the complexes. [17] More recently, Ojwach et al has also try to design unsymmetrical pyrazolyl-phosphine transition metal complexes containing a pyrazolyl unit and a secondary donor atom. However, attempts to synthesize the phosphine ligand was also hampered by in situ oxidation to the phosphine oxide ligands in very high yields.…”

Recent advances in Ni-mediated ethylene chain growth: Nimine-donor ligand effects on catalytic activity, thermal stability and oligo-/polymer structure

“…By contrast, pyridinylimine-based N^N-nickel pre-catalysts, in the main, promote the conversion of ethylene to α-olefins with the ligand structure, substitution effects and process conditions playing an important role on the catalytic activity and product distribution [24,25,29]. Elsewhere, Braunstein and co-workers have made significant contributions in the field of catalytic ethylene oligomerization [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] and, in particular, with regard to the preparation and application of P^N [30][31][32]34,36], P^P [38,40], N^P^N [37] and SHOP-type [35,38] nickel complexes for olefin oligomerization. In general, however, it still remains difficult to achieve performance characteristics that can compete with industrial catalysts.…”