Chemical Biology & Organic Chemistry, Debye Institute for Nanomaterials Science, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
Dalton Trans. 2010 Jul 21;39(27):6198-216. doi: 10.1039/b925236n. Epub 2010 Jun 2.
The synthesis and catalytic properties of ditopic mono-pincer-mono-porphyrin complexes were investigated. The statistical Adler condensation reaction of 3,5-bis(methoxymethyl)-4-bromo-benzaldehyde, p-tolylaldehyde, and pyrrole, furnished an AB(3)-type tetraphenylporphyrin, containing three meso-p-tolyl groups and one meso-3,5-bis(methoxymethyl)-4-bromophenyl group. This material was converted into the ditopic ligand [2H(Br)], which comprises one porphyrin site and an NCN-pincer type ligand moiety. In order to metalate this compound in a stepwise, site-selective manner, two distinct synthetic routes were followed. Route A relies on the introduction of a metal in the porphyrin cavity followed by pincer metalation and a reversal of this order is employed for route B. For the hetero-bimetallic pincer-porphyrin target compounds, route A invariably proved to be the highest yielding alternative, giving pincer-porphyrin hybrids of general formula [M(1)(M(2)X)] (M(1) = 2H, Mg, Co, Ni, Zn; M(2) = Pd, Br; X = Cl, Br). (195)Pt NMR spectroscopy revealed that the porphyrin metal has a modest influence on the electron density on the NCN-pincer Pt site. When the analogous cationic Pd complexes were used as Lewis acid catalysts for the double Michael addition between methyl vinyl ketone and ethyl alpha-cyanoacetate, it was noted that the catalytic activity did not depend on the central metal for M(1) = 2H, Ni, and Zn. However, when Mg occupied the porphyrin cavity, the rate of the reaction increased by a factor of six. Although a rate enhancement was observed when catalysis was conducted with a mixture of the two constituents of [Mg(PdOH(2))]BF(4) (i.e. MgTTP and [PdOH(2)(NCN)]BF(4)) this could not fully account for the rate enhancement. We believe that the rationale for this behaviour is dual, consisting of "cooperative dual catalysis" and supramolecular aggregation of two or more catalyst-substrate complexes.
研究了双齿单爪单卟啉配合物的合成和催化性能。3,5-双（甲氧基甲基）-4-溴苯甲醛、对甲苯醛和吡咯的统计 Adler 缩合反应提供了一种 AB(3)-型四苯基卟啉，其中含有三个间-对甲苯基和一个间-3,5-双（甲氧基甲基）-4-溴苯基。该材料被转化为双齿配体[2H(Br)]，它包含一个卟啉位和一个 NCN-爪型配体部分。为了以逐步、选择性的方式金属化这种化合物，采用了两种不同的合成路线。路线 A 依赖于在卟啉腔中引入金属，然后进行爪金属化，而路线 B 则采用相反的顺序。对于杂双金属爪卟啉目标化合物，路线 A 总是证明是产率最高的选择，得到的爪卟啉混合体通式为[M(1)(M(2)X)]（M(1) = 2H、Mg、Co、Ni、Zn；M(2) = Pd、Br；X = Cl、Br）。195Pt NMR 光谱表明，卟啉金属对 NCN-爪 Pt 位上的电子密度有适度的影响。当类似的阳离子 Pd 配合物用作甲基乙烯酮和乙基-α-氰基乙酸酯的双迈克尔加成的路易斯酸催化剂时，注意到催化活性不依赖于中心金属，对于 M(1) = 2H、Ni 和 Zn。然而，当 Mg 占据卟啉腔时，反应速率提高了六倍。虽然当用[Mg(PdOH(2))]BF(4)（即 MgTTP 和[PdOH(2)(NCN)]BF(4)）的两种成分的混合物进行催化时观察到了速率增强，但这并不能完全解释速率增强的原因。我们认为这种行为的理由是双重的，包括“协同双催化”和两个或更多催化剂-底物配合物的超分子聚集。
