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

摘要

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 _2Cl _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 60700 and 62600 mol of C _2H _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 41500 and 58000 mol of C _2H _4/((mol of Ni).h), respectively.