From discrete monomeric complexes to hydrogen-bonded dimeric assemblies based on sterically encumbered square planar palladium(ii) ONN-pincers
作者:Okoh Adeyi、Warren B. Cross、Gregory Forrest、Luke Godfrey、Eric G. Hope、Andrew McLeod、Amandeep Singh、Kuldip Singh、Gregory A. Solan、Yining Wang、Luka A. Wright
DOI:10.1039/c3dt50176k
日期:——
The 2-(3-biphenyl-2-ol)-6-iminepyridines, 2-(3-C12H8-2-OH)-6-(CHNAr)C5H3N (Ar = 2,6-i-Pr2C6H3 (L1a-H), 2,4,6-Me3C6H2 (L1b-H)), have been prepared in high yield via sequential Suzuki coupling, deprotection and condensation reactions from 2-methoxybiphenyl-3-ylboronic acid and 2-bromo-6-formylpyridine. Treatment of L1-H with Pd(OAc)2 or (MeCN)2PdCl2 results in deprotonation of L1-H to afford the discrete square planar ONN-chelates, [2-(3-C12H8-2-O)-6-(CHNAr)C5H3N}Pd(OAc)] (Ar = 2,6-i-Pr2C6H3 (1a), 2,4,6-Me3C6H2 (1b)) and [2-(3-C12H8-2-O)-6-(CHNAr)C5H3N}PdCl] (Ar = 2,6-i-Pr2C6H3 (2a), 2,4,6-Me3C6H2 (2b)), in good yield, respectively; conversion of 1 to 2 using aqueous sodium chloride has been demonstrated. Selective reduction of the imino unit in L1-H with LiAlH4 proceeds smoothly to yield the 2-(3-biphenyl-2-ol)-6-(methylamine)pyridines, 2-(3-C12H8-2-OH)-6-(CH2-NHAr)C5H3N (Ar = 2,6-i-Pr2C6H3 (L2a-H), 2,4,6-Me3C6H2 (L2b-H)), which on reaction with Pd(OAc)2 give [2-(3-C12H8-2-O)-6-(CH2-NHAr)C5H3N}Pd(OAc)] (Ar = 2,6-i-Pr2C6H3 (3a), 2,4,6-Me3C6H2 (3b)). Depending on the temperature of the reaction, the oxidised aldimine products 1a or 1b can also be observed as a competitive side-product during the formation of 3a or 3b. Similarly, ketimine-containing, [2-(3-C12H8-2-O)-6-(CMeN(2,6-i-Pr2C6H3))C5H3N}Pd(OAc)] (5), can be detected during the preparation of chiral [2-(3-C12H8-2-O)-6-(CMeH-NH(2,6-i-Pr2C6H3))C5H3N}Pd(OAc)] (4) from 2-(3-C12H8-2-OH)-6-(CH2-NH(2,6-i-Pr2C6H3))C5H3N (L3-H) and Pd(OAc)2. Complexes 3a, 3b and 4 all exist as dimeric species in the solid state in which two anti-aligned square planar monomers are held together by two intermolecular NHamine⋯Ophenolate interactions resulting in palladium–palladium separations of between 3.141–3.284 Å. The structurally related chloride-containing dimeric assemblies, [2-(3-C12H8-2-O)-6-(CH2-NHAr)C5H3N)}PdCl] (Ar = 2,6-i-Pr2C6H3 (6a), 2,4,6-Me3C6H2 (6b)), can also be isolated on treatment of 3 with aqueous sodium chloride or by reaction of L3-H with (MeCN)2PdCl2. Single crystal X-ray diffraction studies have been performed on L1a-H, L3-H, 1a, 1b, 2a, 2b, 3a, 3b, 4, 6a and 6b.
2-(3-联苯-2-醇)-6-亚胺吡啶,2-(3-C12H8-2-OH)-6-(CHNAr)C5H3N (Ar = 2,6-i-Pr2C6H3 (L1a-H) , 2,4,6-Me3C6H2 (L1b-H)), 通过连续的 Suzuki 偶联、脱保护和缩合反应,由 2-甲氧基联苯-3-基硼酸和 2-溴-6-甲酰基吡啶以高产率制备。用 Pd(OAc)2 或 (MeCN)2PdCl2 处理 L1-H 导致 L1-H 去质子化,得到离散的方形平面 ONN-螯合物,[2-(3-C12H8-2-O)-6-( CHNAr)C5H3N}Pd(OAc)] (Ar = 2,6-i-Pr2C6H3 (1a), 2,4,6-Me3C6H2 (1b)) 和 [2-(3-C12H8-2-O)-6 -(CHNAr)C5H3N}PdCl] (Ar = 2,6-i-Pr2C6H3 (2a), 2,4,6-Me3C6H2 (2b)),收率良好;已经证明使用氯化钠水溶液将1转化为2。用 LiAlH4 选择性还原 L1-H 中的亚氨基单元顺利进行,生成 2-(3-联苯-2-醇)-6-(甲胺)吡啶,2-(3-C12H8-2-OH)-6- (CH2-NHAr)C5H3N (Ar = 2,6-i-Pr2C6H3 (L2a-H), 2,4,6-Me3C6H2 (L2b-H)),与 Pd(OAc)2 反应得到 [2- (3-C12H8-2-O)-6-(CH2-NHAr)C5H3N}Pd(OAc)](Ar = 2,6-i-Pr2C6H3 (3a), 2,4,6-Me3C6H2 (3b))。根据反应温度,氧化醛亚胺产物1a或1b也可以在3a或3b形成过程中作为竞争性副产物观察到。同样,含酮亚胺的 [2-(3-C12H8-2-O)-6-(CMeN(2,6-i-Pr2C6H3))C5H3N}Pd(OAc)] (5) 在由2-(3-C12H8)制备手性[2-(3-C12H8-2-O)-6-(CMeH-NH(2,6-i-Pr2C6H3))C5H3N}Pd(OAc)](4) -2-OH)-6-(CH2-NH(2,6-i-Pr2C6H3))C5H3N(L3-H)和Pd(OAc)2。配合物 3a、3b 和 4 均以固态二聚体形式存在,其中两个反向排列的方形平面单体通过两个分子间 NHamine⋯Ophenate 相互作用结合在一起,导致钯-钯分离度在 3.141–3.284 Å 之间。结构相关的含氯二聚体组装体,[2-(3-C12H8-2-O)-6-(CH2-NHAr)C5H3N)}PdCl] (Ar = 2,6-i-Pr2C6H3 (6a), 2 ,4,6-Me 3 C 6 H 2 (6b))也可以通过用氯化钠水溶液处理3或通过L 3 -H与(MeCN) 2 PdCl 2 反应来分离。对 L1a-H、L3-H、1a、1b、2a、2b、3a、3b、4、6a 和 6b 进行了单晶 X 射线衍射研究。