154648-63-2Relevant academic research and scientific papers
Synthesis of Δ2-1,3-oxazolines from cationic platinum(II) nitrile complexes. X-ray structure of trans-[Pt(CF3){N=C(Ph)OCH2CH2}(PPh 3)2]BF4·0.5H 2O·0.25MeOH
Michelin, Rino A.,Mozzon, Mirto,Berin, Paola,Bertani, Roberta,Benetollo, Franco,Bombieri, Gabriella,Angelici, Robert J.
, p. 1341 - 1350 (2008/10/08)
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-CH3C6H4 (10), p-OCH3C6H4 (11)) have been prepared by reaction of the corresponding halo complexes trans-[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°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-11a 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 (1H, 19F, 31P{1H}, and 13C{1H}) NMR spectroscopies and also by an X-ray structural determination, which has been carried out for 3a. It crystallizes in the orthorhombic space group Pna21, with a = 19.130(4) A?, b = 15.936(3) A?, c = 16.312(3) A?, V = 4973(2) A?3, and Z = 4. The structure was refined to R = 0.056 (Rw = 0.065) for 2485 measured reflections with I ≥ 3σ(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}(PPh 3)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, 1H NMR, and GC/MS techniques. Attempts to generate catalytically 2-(methyl)oxazoline have been performed using the trans-[PtX(R)(PR3)2]/CH3CN/OCH 2CH2 system (PR3 = PEt3, PMe2Ph; R = H, CH3, CF3; X = Br, I). No oxazoline formation was observed between 50 and 75°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.
