Amidines derived from Pt(IV)-mediated nitrile - Amino alcohol coupling and their Zn(II)-catalyzed conversion into oxazolinesстатья
Статья опубликована в высокорейтинговом журнале
Информация о цитировании статьи получена из
Web of Science,
Scopus
Статья опубликована в журнале из списка Web of Science и/или Scopus
Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Аннотация:The reaction between the platinum(IV) complex trans-[PtCl4(EtCN)2] and the amino alcohols NH2CH2CH2OH, NH2C H2CH(Me)OH-(R)-(-), NH2CH(Ph)CH2OH-(R)-(-), NH2CH(Et)CH2OH-(R)-(-), NH2CH(Et)CH2OH-(S)-(+), and NH2CH(Prn)CH2OH proceeds rapidly at room temperature in CH2Cl2 to furnish the amidine complexes [PtCl4HN=C(Et)NH-OH2] (1-6) in good yield (70-80%). The related reaction between the platinum(II) complex trans-[PtCl2(EtCN)2] and monoethanolamine in a molar ratio of 1:2 in CH2Cl2 results in the addition of 4 equiv of NH2-CH2CH2OH per mole of complex to give [PtHN=C(Et)NHCH2CH2OH2 (NH2CH2CH2OH)2]2+ (7). Formulation of 1-6 is based upon satisfactory C, H, N elemental analyses, electrospray mass spectrometry, IR spectroscopy, and 1H, 13C1H, 15N, and 195Pt NMR spectroscopies, while the structures of trans-[PtCl4(Z)-NH=C(Et)NHCH2CH2-OH 2] (1), trans-[PtCl4(Z)-NH=C(Et)NHCH2CH(Me)OH-(R)-(-) 2] (2), and trans-[PtCl4(Z)-NH=C(Et)NHCH(Et)- CH2OH-(R)-(-)2] (4) were determined by X-ray single-crystal diffraction. The Z-amidine configuration of the ligands is preserved in CDCl3 solutions as confirmed by gradient-enhanced 15N,1H-HMQC spectroscopy and NOE experiments. The amidines, formed upon Pt(IV)-mediated nitrile-amino alcohol coupling, were liberated from their platinum(IV) complexes 1, 3, and 4 by reaction with Ph2PCH2CH2PPh2 (dppe) giving free NH=C(Et)NHCHRCH2OH (R = H 8, Et 9, Ph 10), with the substituents R of different types, and dppe oxides; the P-containing species were identified by 13P1H NMR spectroscopy. NOESY spectroscopy indicates that the liberated amidines retained the same configuration relative to the C=N double bond, i.e., syn-(H,Et)-NH=C(Et)NHCHRCH2OH. The liberated hydroxo-functionalized amidines 8-10 were converted into oxazolines N=C(Et)OCH2CH(R) (11-13) in the presence of a catalytic amount of ZnCl2. A similar catalytic effect has also been reached using anhydrous MSO4 (M = Cu, Co, Cd), CdCl2, and AlCl3.