SYNTHESIS OF DELTA(2)-1,3-OXAZOLINES FROM CATIONIC PLATINUM(II) NITRILE COMPLEXES - X-RAY STRUCTURE OF TRANS-[PT(CF3)(N=C(PH)OCH2CH2)(PPH3)2]BF4-CENTER-DOT-0.5H2O-CENTER-DOT-0.25MEOH

Cationic Pt(II) nitrile complexes of the type trans-[Pt(R-)(NCR)(PPh3)2]BF4 (R' = H (1), CH3 (2), R = CH3; R'= CF3, R = CH3 (3), CH3CH2 (4), CH3CH2CH2 (5), (CH3)2CH (6), (CH3)3C (7),C6H5(8), p-CH3C6H4 (9), o-CH3Cr6H4(10), p-OCH3C6H4(11)) have been prepared by reaction of the corresponding halo complexes tans-[Pt(R')X(PPh3)2] (X = Cl, Br) with AgBF4 in the presence of a 20-30-fold excess of RCN in CH2Cl2. The complexes 1-11 readily react in THF at 0-degrees-C or below with HOCH2CH2Cl/n-BuLi (n-BuLi:complex molar ratio 1: 1) to give a mixture of products, including the oxazoline complexes trans-[Pt(R'){N=C(R)OCH2CH2}(PPh3)2]BF4 (1a-11a), the chloro complexes trans-[Pt(Cl(R')(PPh3)2, and free oxazoline N=C(r)OCH2CH2. For short reaction times (ca. 10-15 min) the oxazoline complexes 1a-1 1a could be isolated albeit in modest yield (26-49%) from the reaction mixtures and they could be separated from the corresponding chloro complexes (average yield ca. 35%) by taking advantage of the higher solubilty of the latter derivatives in benzene. For longer reaction times (>2 h), the trans[PtCl(R')(PPh3)2] species were the only isolated products. Compounds 1a-11a have been characterized by IR and multinuclear (H-1, F-19, P-31{H-1}, and C-13{H-1}) NMR spectroscopies and also by an X-ray structural determination, which has been carried out for 3a. It crystallizes in the orthorhombic space group Pna2(1), with a = 19.130(4) angstrom, b = 15-936(3) angstrom, c = 16.312(3) angstrom, V = 4973(2) angstrom3, and Z = 4. The structure was refined to R = 0.056 (R(w) = 0.065) for 2485 measured reflections with I greater-than-or-equal-to 3sigma(I). The 2-(phenyl)oxazoline ligand is almost planar and perpendicular to the mean coordination plane. A mechanism is proposed for the conversion of nitriles to 2-oxazolines in cationic Pt(II) complexes. The reactions of the isolated complexes trans-[Pt(CF3){N=C(R)OCH2CH2}(PPh3)2]BF4 (3a-11a) with excess chloride ions gave trans[ Pt(CF3)Cl(PPh3)2] and the corresponding free oxazolines, which were characterized by IR, H-1 NMR, and GC/MS techniques. Attempts to generate catalytically 2-(methyl)oxazoline have been performed using the trans-[PtX(R)(PR3)2]/CH3CN/OCH2CH2 system (PR3=PEt3, PMe2-Ph; R = H, CH3, CF3; X = Br, I). No oxazoline formation was observed between 50 and 75-degrees-C and 36 and 160 h; however, addition of LiBr and OCH2CH2 to trans-[PtBr(CH3)(PEt3)2] and trans-[PtBr(CF3)(PMe2Ph)2] (salt:complex (1.5-3):1 molar ratio) led to the formation of 2-(methyl)oxazoline, albeit not catalytically.