A phosphino-oxazoline ligand as a P,N-bridge in palladium/cobalt or P,N-chelate in nickel complexes: catalytic ethylene oligomerizationCCDC reference numbers 831824831827. For crystallographic data in CIF or other electronic format see DOI: 10.1039/c1dt11352f

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 (- 1 )] 2 to afford the heterometallic zwitterionic complex [{PdCl( 1 )} + (- 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 60700 and 62600 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 41500 and 58000 mol of C 2 H 4 /((mol of Ni)h), respectively. Using a P,N-phosphino-oxazoline ligand, the Pd( ii )/Co( ii ) zwitterionic complex [{PdCl( 1 )} + (- 1 )(CoCl 3 ) ] ( 2 ) and octahedral Ni( ii ) complexes were obtained, the latter show reversible solvent-dependent isomerism between all-trans - 3 and all-cis - 4 .