Synthesis and characterisation of 1-alkyl-2-imidazoline complexes of noble metals; crystal structure of trans-[PtCl2{N=C(H)N(Et)CH2CH2}(PEt 3)]

Abstract

Treatment of a 1-alkyl-2-imidazoline N(R)(CH2)2N=CH with a μ-dichloro-dirhodium(I) or -diplatinum(II) complex [{Rh(μ-Cl)(cod)}2] or [{Pt(μ-Cl)Cl(PEt3)}2] gave the mononuclear 1-alkyl-2-imidazoline complex [RhCl{N=C(H)N(R)CH2CH2)(cod)] (R = Et 1a or CH2Ph 1b) or trans[PtCl2{N=C(H)N(R)CH2CH2}(PEt3)] (R = Et 2a or CH2Ph 2b) (cod = cycloocta-1,5-diene). A single-crystal X-ray diffraction study of 2a revealed it to have a square-planar geometry about platinum, the imidazoline ring being coplanar with this plane, and a Pt-N distance of 2.088(11) Å; the Pt-P bond length of 2.231(4) Å indicates that the imidazoline ligand has a marginally stronger trans influence than analogues of its isomer such as CN(R)(CH2)2NR. The rhodium complexes 1a and 1b have been shown to catalyse cyclopropanation of styrene and ethyl diazoacetate in high yields.