Conversion of nitriles into Δ2-1,3-oxazolines in platinum(II) complexes. Crystal structure of trans-[PtCl2{NC(But)OCH2CH2}2]

Abstract

The reactions of cis- and trans-[PtCl₂(NCR)₂](R =p-MeC₆H₄, p-CF₃C₆H₄, o-MeC₆H₄, Et, Prⁿ, Prⁱ or Bu^t) complexes with 2 equivalents of ^–OCH₂CH₂Cl, generated by deprotonation of HOCH₂CH₂Cl with LiBuⁿ, afford in high yield the bis(Δ²-1,3-oxazoline) derivatives cis-and trans-[PtCl₂{[graphic omitted]H₂}₂]. The complexes have been characterized by their elemental analyses, IR, ¹H NMR, ¹³C-{¹H} NMR and FAB mass spectra. The structure of trans-[PtCl₂{[graphic omitted]H₂}₂] was established also by X-ray crystallography: monoclinic, space group P2₁/n, a= 11.233(2), b= 8.741(2), c= 9.394(2)Å, β= 101.61(3)° and Z= 2; R= 0.038 (R′= 0.042) for 2514 measured reflections with I 3σ(I). The N–C(R) and (R)C–O bond distances of 1.284(5) and 1.335(5)Å suggest that there is extensive electron delocalization within the N–C(R)–O system. The co-ordination geometry around Pt^II is planar and the oxazoline rings are only slightly twisted. The formation of Δ²-1,3-oxazolines from platinum(II)-co-ordinated nitriles has also been examined using HOCH₂CH₂Cl in the presence of the weak base NEt₃. These reactions proceed through the initial formation of the bis(imido ester) complexes [PtCl₂{NHC(R)OCH₂CH₂Cl}₂], present as their (Z,Z), (E,E) and (E,Z) conformers, which slowly convert to the final cyclic Δ²-1,3-oxazoline derivatives.