71581-10-7Relevant academic research and scientific papers
Coordination and reactivity of benzyloxycarbonyl-Ala(CN)-OR (R = H, CH3) in complexes of platinum (II)
Campardo, Luana,Gobbo, Marina,Rocchi, Raniero,Bertani, Roberta,Mozzon, Mirto,Michelin, Rino A.
, p. 269 - 273 (2008/10/08)
The conversion of a nitrile to an oxazoline group in an amino acid side chain promoted by platinum(II) was investigated. While benzyloxycarbonyl-β-cyano-alanine (Z-Ala(CN)-OH) did not give any evidence of coordination of the nitrile group to Pt(II) in different complexes, the corresponding methyl ester Z-Ala(CN)-OCH3 readily afforded the Pt(II)-nitrile complex trans-[Pt(CF3){Z-Ala(CN)-OCH3}(PPh3) 2][BF4] in good yield by reaction with the cationic derivative trans-[Pt(CF3)(PPh3)2(solv)][BF4] (solv = CH2Cl2). The reactivity of the CN group in the complex trans-[Pt(CF3){Z-Ala(CN)OCH3}(PPh3) 2] [BF4] with ClCH2CH2O-to form the oxazoline ligand 2 was examined. The presence of the oxazoline ring in the final products was evidenced by IR, 1H and 13C NMR data and confirmed by FAB and MALDI mass spectra, but its isolation was hampered by the cleavage of the oxazoline ring under the chromatographic conditions applied.
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.
