Phosphinooxazolines as assembling ligands in heterometallic complexes

Abstract

It is shown that phosphinooxazolines such as (2-oxazoline-2-ylmethyl)diphenylphosphine 1 can be used as P,N assembling ligands for the synthesis of heterometallic complexes. These were obtained in a stepwise manner from the iron carbonyl complexes containing one, [Fe(CO)₄(PCH₂-oxazoline-P)] 2, or two, trans-[Fe(CO)₃(PCH₂-oxazoline-P)₂] 6, P-bound phosphinooxazoline ligands. These metalloligands were then reacted with metal complexes. With 2, complete ligand transfer from Fe to the second metal (Pd) was sometimes observed. The metal–metal bonded complex [(OC)₄Fe(μ-PCH₂-oxazoline-P,N)PdCl₂] 3 was of limited stability, whereas the trinuclear complex trans-[{(OC)₄Fe(μ-PCH₂-oxazoline-P,N)}₂CoCl₂] 4, in which 2 functions as a N-donor metalloligand toward the tetrahedral Co(II) centre, was stable and could be fully characterised by X-ray diffraction. This complex catalyses the oligomerization of ethylene to give linear α-olefins in the range C₄–C₂₆, with a maximum of the Schulz-Flory distribution around C₆. The complex [{(OC)₄Fe(μ-PCH₂-oxazoline-P,N)}₂HgI₂] 5 was also prepared from 6. With the metalloligand 6, the Fe→Pd and Fe→Co metal–metal bonded compounds trans-[(OC)₃Fe(μ-PCH₂-oxazoline-P,N)₂Pd(NCMe)](BF₄)₂8 and trans-[(OC)₃Fe(μ-PCH₂-oxazoline-P,N)₂CoCl₂] 9 were obtained.