Stable platinum(II) complexed α-aminoethers derived from benzimidazole and benzoxazole
作者:A. Albinati、C. Arz、H. Berger、P.S. Pregosin
DOI:10.1016/s0020-1693(00)80240-6
日期:1991.12
A series of Schiff base compounds derived from 2-aminobenzimidazole and 2-aminobenzoxazole react with Zeise's salt in CH2Cl2/ROH (R = CH3, CH2CH3, CH(CH3)2, CH2CH2OCH3) to form a series of relatively stable alpha-aminoether complexes with coordination to Pt(II) via the heterocyclic sp2 nitrogen. The complexes, trans-PtCl2(C2H4)2-N-(CH(OR)C6II4R1)benzimidazole} (4) (R1 - 3-NO2, R = CH3, CH2CH3, CH(CH3)2; R1 = 4-Cl, R = CH3) and trans-PtCl2(C2H4)2-N-(CH(OR)C6H4R1)benzoxazole} (5) (R1 = 3-NO2, R = CH3, CH2CH3, CH2CH2OCH3; R1 = 4-Cl, 4-OCH3, 4-H, R = CH3) arise through initial coordination of the heterocyclic sp2 nitrogen followed by attack of ROH on the pendant 2-N-benzylidene moiety at the Schiff base carbon. It is suggested that withdrawal of electron density through complexation facilitates alcohol attack. In the absence of complexation the reaction can be 20-30 times slower, A Pd(II) phosphine complex can achieve the same result. H-1 NMR spectroscopy, and specifically the chemical shift of the 'CH-N' moiety, provides an indication of the polarization due to complexation. The structure of one complex, 5c, R1 - 3-NO2, R - CH2CH2OCH3, was determined by X-ray diffraction. A prismatic crystal belonging to the space group P1BAR with the following characteristics; a - 10.024(3), b = 11.242(9), c = 13.158(3) angstrom, alpha = 96.07(3), beta = 107.01(2), gamma = 109.52(3)-degrees, V = 1302 angstrom 3, Z = 2, was used to determine the structure, which was refined to R = 0.044.