Metal-assisted coupling of oximes and nitriles: a synthetic, structural and theoretical study
作者:Maxim L. Kuznetsov、Nadezhda A. Bokach、Vadim Yu. Kukushkin、Tapani Pakkanen、Gabriele Wagner、Armando J. L. Pombeiro
DOI:10.1039/b006168i
日期:——
Chlorination of [Ph3PCH2Ph][PtCl3(EtCN)], obtained from the reaction of [PtCl2(EtCN)2] with [Ph3PCH2Ph]Cl, formed the platinum(IV) complex [Ph3PCH2Ph][PtCl5(EtCN)] which, at ambient temperature and both in solution and in the solid phase, hydrolyses to the ammonia compound [Ph3PCH2Ph][PtCl5(NH3)] and undergoes nucleophilic addition by ketoximes or amidoxime HONCR1R2 [R1R2 = Me2, C4H8, C5H10, C9H16, C9H18 or Ph(NH2)] to give the corresponding iminoacylated product [Ph3PCH2Ph][PtCl5HNC(Et)ONCR1R2}]. All compounds were characterized by elemental analyses, FAB mass spectrometry, IR and 1H, 13C-1H}, 31P-1H} and 195Pt NMR spectroscopies. A crystal structure determination of [Ph3PCH2Ph][PtCl5NHC(Et)ONC(C9H16)}] disclosed amidine one-end rather than the N,N-bidentate co-ordination mode of the N-donor ligand. The iminoacylation by oximes was investigated by ab initio methods (at RHF level using quasi-relativistic pseudopotentials for platinum) for [PtCl5(NCMe)]− which were also applied to the related neutral platinum(IV) [PtCl4(NCMe)2] and platinum(II) [PtCl2(NCMe)2] complexes. The calculations included geometry optimization of the starting and final complexes, location of possible transition states for the reaction discussed and intrinsic reaction coordinate calculations for one reaction. The results obtained provided an interpretation, on the basis of kinetic (activation energies) and thermodynamic (reaction energies) effects, for the order of reactivity observed [neutral PtIV > anionic PtIV > neutral PtII] and indicated that a mechanism based on nucleophilic addition of the protic nucleophile (undeprotonated oxime), to form a transition state with a four-membered NCOH ring, is energetically favoured relative to the alternative one involving prior deprotonation of the oxime, unless base-catalysed conditions are operating.
由[PtCl2(EtCN)2]与[Ph3PCH2Ph]Cl反应得到的[Ph3PCH2Ph][PtCl3(EtCN)]氯化反应生成了铂(IV)络合物[Ph3PCH2Ph][PtCl5(EtCN)]、在常温下,该复合物在溶液和固相中都会水解为氨化合物 [Ph3PCH2Ph][PtCl5(NH3)],并与酮肟或脒肟 HONCR1R2 [R1R2 = Me2、C4H8、C5H10、C9H16、C9H18 或 Ph(NH2)]发生亲核加成反应,生成相应的亚氨基酰化产物 [Ph3PCH2Ph][PtCl5HNC(Et)ONCR1R2}]。所有化合物都通过元素分析、FAB 质谱、红外光谱和 1H、13C-1H}、31P-1H} 和 195Pt NMR 光谱进行了表征。[Ph3PCH2Ph][PtCl5NHC(Et)ONC(C9H16)}]的晶体结构测定结果表明,N-供体配体的一端为脒基,而不是 N,N-配位模式。我们采用 ab initio 方法(在 RHF 水平上使用铂的准相对论假势)研究了[PtCl5(NCMe)]--肟的亚氨基酰化作用,该方法也适用于相关的中性铂(IV)[PtCl4(NCMe)2]和铂(II)[PtCl2(NCMe)2]配合物。计算包括起始和最终配合物的几何优化、所讨论反应的可能过渡态的位置以及一个反应的内在反应坐标计算。所获得的结果在动力学(活化能)和热力学(反应能)效应的基础上解释了所观察到的反应性顺序[中性 PtIV > 阴离子 PtIV > 中性 PtII],并表明除非在碱催化条件下,否则基于亲核体(未去质子化的肟)亲核加成以形成具有四元 NCOH 环的过渡态的机理在能量上要优于涉及肟事先去质子化的替代机理。