Synthesis and characterisation of 1-alkyl-2-imidazoline complexes of noble metals; Crystal structure of trans[PtCl2{N=C(H)N(Et)CH2CH2}(PEt3)]

Treatment of a 1-alkyl-2-imidazoline N(R)(CH2)(2)N=CH with a mu-dichloro-dirhodium(I) or -diplatinum(II) complex [{Rh(mu-Cl)(cod)}(2)] or [{Pt(mu-Cl)Cl(PEt3)}] gave the mononuclear 1-alkyl-2-imidazoline complex [RhCl{N=C(H)N(R)CH2CH2}(cod)] (R = Et la or CH2Ph Ib) 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) Angstrom; the Pt-P bond length of 2.231(4)Angstrom indicates that the imidazoline ligand has a marginally stronger trans influence than analogues of its isomer such as CN(R)(CH2)(2)NR. The rhodium complexes la and Ib have been shown to catalyse cyclopropanation of styrene and ethyl diazoacetate in high yields.