Griffith Gerry A, Al-Khatib Mohamed J, Patel Kalpana, Singh Kuldip, Solan Gregory A
Department of Chemistry, University of Leicester, University Road, Leicester, UKLE1 7RH.
Dalton Trans. 2009 Jan 7(1):185-96. doi: 10.1039/b811309b. Epub 2008 Nov 5.
Two new sterically demanding bis(imino)bipyridine ligands, 6,6'-{(2,6-i-Pr(2)C(6)H(3))N=R}(2)C(10)H(6)N(2) (R = H (L1), Me (L2)), have been prepared in high yield by the condensation reaction of 2,6-diisopropylaniline with 6,6'-(O=R)(2)C(10)H(6)N(2) (R = H, Me). Palladium(0)-mediated cross coupling of 2-(Bu(3)Sn)-6-{C(Me)OCH(2)CH(2)O}C(5)H(3)N with 2-Br-6-{C(Me)OCH(2)CH(2)O}C(5)H(3)N, followed by an acid-mediated deprotection, has been employed as an efficient route to the precursor 6,6'-bis(acetyl)-2,2'-bipyridine. Reaction of aldimino L1 with two equivalents of MX(2) [MX(2) = ZnCl(2), NiCl(2) or (DME)NiBr(2)] in n-BuOH at elevated temperature gives the five-coordinate mononuclear complexes [(L1)MX(2)] (M = Zn, X = Cl 1; M = Ni, X = Cl 2a; M = Ni, X = Br 2b) as the sole products, in which one imine group is bound and the other uncoordinated (endo-exo). In the case of diamagnetic 1, VT (1)H NMR spectroscopy reveals a fast exchange process operating between the two possible forms of the endo-exo isomer which is likely to proceed via an exo-exo intermediate (DeltaH(double dagger)(interconversion) = 35.6 +/- 1.5 kJ mol(-1), DeltaG(double dagger)(298) = 47.4 +/- 3.3 kJ mol(-1)). In contrast, treatment of ketimino L2 with MCl(2) (MCl(2) = ZnCl(2) or NiCl(2)) affords bimetallic [(L2)Zn(2)Cl(4)] (4) and the six-coordinate monometallic species [(L2)NiCl(2)] (5), respectively; in 4, L2 adopts a bis(bidentate) bonding mode (endo-endo) while in 5 it acts as tetradentate ligand (endo-endo). Prolonged standing of 1 in chlorinated solvents results in partial hydrolysis and the formation of the 6-imino-6'-formyl-2,2'-bipyridine zinc complex, [(6-{(2,6-i-Pr(2)C(6)H(3))N=Me)-6'-(CH=)C(10)H(6)N(2))ZnCl(2)] (3) (endo-imine, exo-formyl). Single crystal X-ray structures are reported for L1,1 , 2a, 3, 4 and 5.
通过2,6 - 二异丙基苯胺与6,6'-(O = R)₂C₁₀H₆N₂（R = H，Me）的缩合反应，高产率地制备了两种空间位阻较大的双(亚氨基)联吡啶配体，6,6'-{(2,6 - i - Pr₂C₆H₃)N = R}₂C₁₀H₆N₂（R = H (L1)，Me (L2)）。2-(Bu₃Sn)-6-{C(Me)OCH₂CH₂O}C₅H₃N与2 - Br - 6-{C(Me)OCH₂CH₂O}C₅H₃N在钯(0)介导下进行交叉偶联，随后进行酸介导的脱保护反应，已被用作制备前体6,6'-双(乙酰基)-2,2'-联吡啶的有效途径。醛亚胺L1与两当量的MX₂ [MX₂ = ZnCl₂，NiCl₂或(DME)NiBr₂]在正丁醇中于高温下反应，得到五配位单核配合物[(L1)MX₂]（M = Zn，X = Cl 1；M = Ni，X = Cl 2a；M = Ni，X = Br 2b）作为唯一产物，其中一个亚胺基团配位而另一个未配位（内 - 外）。对于抗磁性的1，变温¹H NMR光谱显示内 - 外异构体的两种可能形式之间存在快速交换过程，该过程可能通过外 - 外中间体进行（互变反应的活化焓ΔH⁺ = 35.6 ± 1.5 kJ mol⁻¹，298 K时的活化自由能ΔG⁺ = 47.4 ± 3.3 kJ mol⁻¹）。相比之下，酮亚胺L2与MCl₂（MCl₂ = ZnCl₂或NiCl₂）反应分别得到双金属配合物[(L2)Zn₂Cl₄]（4）和六配位单金属物种[(L2)NiCl₂]（5）；在4中，L2采用双(双齿)键合模式（内 - 内），而在5中它作为四齿配体（内 - 内）。1在氯化溶剂中长时间放置会导致部分水解并形成6 - 亚氨基 - 6'-甲酰基 - 2,2'-联吡啶锌配合物，[(6 - {(2,6 - i - Pr₂C₆H₃)N = Me}-6'-(CH = )C₁₀H₆N₂)ZnCl₂]（3）（内 - 亚胺，外 - 甲酰基）。报道了L1、1、2a、3、4和5的单晶X射线结构。
