TRANSITION-METAL-PROMOTED CYCLIZATION REACTIONS OF NITRILE LIGANDS IN COMPLEXES OF PLATINUM(II) - SYNTHESIS OF 2-OXAZOLINE DERIVATIVES AND X-RAY STRUCTURE OF CIS-CL2PT[N=C(PH)OCH2CH2]2

The reactions of cis- and trans-Cl2Pt(NCR)2 (R = Ph, Me) isomers with 2 equiv of -OCH2CH2Cl, generated by deprotonation of HOCH2CH2Cl with n-BuLi, afford in high yield the bis(2-oxazoline) derivatives cis- and trans-Cl2Pt[Activated N = C(R)OCH2CH2]2, respectively [cis R = Ph (1), Me (2); trans R = Ph (3), Me (4)]. No isomerization at the metal center occurs in the cyclization reactions of the nitrile ligands. Complexes 1-4 have been characterized by their elemental analyses, FAB mass spectra, and IR, H-1 NMR, C-13{H-1}, and H-1-coupled C-13 NMR spectra. The structure of 1 was established also by X-ray crystallography. It crystallizes in the monoclinic space group P2(1)/c, with a = 16.242 (3) angstrom, b = 9.438 (2) angstrom, c = 12.679 (2) angstrom, beta = 95.65 (4)degrees, V = 1934 (1) angstrom 3, and Z = 4. The structure was refined to R = 0.023 (R(w) = 0.025) for 3248 measured reflections with I greater-than-or-equal-to 2.5-sigma(I). The average N-C(R) and (R)C-O bond distances of 1.277 (6) and 1.340 (6) angstrom suggest that there is extensive electron delocalization within the N-C(R)-O system. The two oxazoline ligands are almost planar, as is the coordination geometry around Pt(II). The reactions of oxirane in the presence of variable amounts of LiCl have been examined with the nitrile complex cis-Cl2Pt(NCPh)2 by using 2-chloroethanol as solvent. From these reactions it is found that, with a nitrile complex/Cl- molar ratio in the range 1/2.1-1/0.4 and sufficiently long reaction times (46 h), complex 1 is isolated in high yield. At lower nitrile/Cl- molar ratios a mixture of 1 and the bis(imido ester) complex cis-Cl2Pt[NH = C(OCH2CH2Cl)Ph]2 (5) is formed. The latter complex could be separated in a pure form by crystallization, and the spectroscopic data are reported. A possible mechanism of the oxirane/Cl- reactions with the nitrile ligands is also discussed.