Catalysis by design: wide-bite-angle diphosphines by assembly of ditopic ligands for selective rhodium-catalyzed hydroformylation.
Catalysis by design: wide-bite-angle diphosphines by assembly of ditopic ligands for selective rhodium-catalyzed hydroformylation.
复制标题
DOI：
10.1002/anie.200701255
复制
发表时间：
2007-09
影响因子：
--
通讯作者：
D. Rivillo;H. Gulyás;J. Benet‐Buchholz;Eduardo C. Escudero‐Adán;Z. Freixa;P. V. van Leeuwen
中科院分区：
文献类型：
--
作者：
D. Rivillo;H. Gulyás;J. Benet‐Buchholz;Eduardo C. Escudero‐Adán;Z. Freixa;P. V. van Leeuwen
二膦是均相催化中的强力配体直到十年前，除了极少数例外，这些配体都含有共价键的主链，将两个磷供体连接在一起。最近，双齿二膦通过强[2]或弱[3]氢键相互作用、组装金属相互作用、[4]和离子相互作用组装所有这些方法在超分子化学中都是众所周知的，并且最近被用于有机金属配合物此外，没有预定相互作用的单磷配体系统在许多情况下被证明是非常有效的，混合单磷配体也是如此使用单齿配体及其连接器的模块化方法[4,8,9]可以访问大量新的和潜在选择性催化剂库。许多用双齿磷配体催化剂进行的催化反应对二膦的咬角高度敏感。有铑催化的氢甲酰化反应，镍和钯催化的氢氰化反应，[11]和钯催化的交叉偶联反应[12]，其中使用Xantphos(4,5 -二（二苯基膦）- 9,9 -二甲基-xanthene)，其自然咬角约为1108.[13]，大大提高了速率或选择性在某些情况下，氢键双齿配体系统可能足以给出等于或超过共价键双齿二膦的结果。[2,3]本文重点研究了包含阴离子位和软给体磷原子的模双位配体。前者结合硬金属组装双齿膦配体，而后者结合软金属参与催化我们用这种方法制备了宽咬角二膦配体。双位配体的两个片段与硬金属（可以形成四面体、方平面、八面体或（双）锥体配位球）一起可以产生多种配体，因此需要最少的合成努力。鉴于所涉及的强键，这些分子应该比那些含有较弱氢键或非定向离子相互作用的分子更容易被分子力学设计。为此，我们合成了双位配体1 - 6（方案1）。配体1-3是基于3-二苯基膦-2-羟基-5-甲基苯甲醛13的，Börner和同事报道了它不含5-甲基，[4a， b]使用它（与不对称二胺和Ti (OiPr) 4组装得到Salenophos）进行不对称铑催化的氢甲酰化。合成1-3时，用13处理合适的胺。配体4和6由相应的醛与3-二苯基膦苯胺缩合而成，配体5由3-（二苯基膦）苯甲醛合成。一般来说，希夫碱缩合反应是在有分子筛存在的回流加热甲苯中进行的。通过1-6与[Zn {N (SiMe3) 2} 2]或Ti (OiPr) 4反应制备了组装好的双齿膦配体7-12（见配套资料）。分子模型计算表明，特别是组合10-12可能是有趣的宽咬角配体。一方面，这种方法可以筛选大量的催化剂，但另一方面，必须进行复杂的猜测；事实上，由于结构和反应性的原因，我们将在下面看到，7-9的前景不太好。请注意，8和9与SPANphos是同构的(SPANphos= 4,4,4 ', 4 ' 6,6 ' -六甲基螺- 2,2 ' -bichrom - 8,8…
Diphosphines are powerful ligands in homogeneous catalysis.[1] Until a decade ago, the ligands, with very few exceptions,[2] contained a covalently bonded backbone holding the two phosphorus donors together. More recently, bidentate diphosphines have been assembled by strong [2] or weak [3] hydrogen-bond interactions, assembly metal interactions,[4] and ionic interactions.[5] All of these approaches are wellknown in supramolecular chemistry and have recently been used in organometallic complexes.[6] Also, monophosphorus ligand systems without predetermined interactions turned out to be extremely effective in a number of cases,[7] as did mixed monophosphorus ligands.[8] A modular approach using monodentate ligands and their connectors [4, 8, 9] gives access to large libraries of new and potentially selective catalysts. Many catalytic reactions carried out using catalysts with bidentate phosphorus ligands are highly sensitive to the bite angle of the diphosphine. There are rhodium-catalyzed hydroformylation,[10] nickel-and palladium-catalyzed hydrocyanation,[11] and palladium-catalyzed cross-coupling reactions [12] in which either the rate or the selectivity was considerably improved by the use of, for instance, Xantphos (4, 5-bis (diphenylphosphino)-9, 9-dimethyl-xanthene), which has a natural bite angle of approximately 1108.[13] In some cases, hydrogen-bonded bidentate ligand systems may suffice to give results that equal or surpass those of covalently bonded bidentate diphosphines.[2, 3] Herein, we focus on modular ditopic ligands that contain an anionic site and a soft donor phosphorus atom. The former will be used to bind a hard metal for assembling the bidentate phosphine ligand, while the latter binds a soft metal involved in catalysis.[4] We use this approach to prepare wide-bite-angle diphosphine ligands. The two fragments of the ditopic ligand, together with the hard metal (which can form a tetrahedral, square-planar, octahedral, or (bi) pyramidal coordination sphere) might give rise to a large variety of ligands, thus requiring a minimum of synthetic effort. In view of the strong bonds involved, these molecules should be more amenable to design by molecular mechanics than those containing weaker hydrogen bonds or nondirectional ionic interactions. To this end, we synthesized the ditopic ligands 1–6 (Scheme 1). Ligands 1–3 are based on 3-diphenylphosphino-2-hydroxy-5-methylbenzaldehyde 13, reported without the 5-methyl group by Börner and co-workers,[4a, b] who used it (assembled with an asymmetric diamine and Ti (OiPr) 4 to give Salenophos) for asymmetric rhodium-catalyzed hydroformylation.For the synthesis of 1–3, the appropriate amines were treated with 13. The ditopic ligands 4 and 6 are made by condensation of the corresponding aldehyde and 3-diphenylphosphinoaniline, and 5 is synthesized from 3-(diphenylphosphino) benzaldehyde. In general, the Schiff base condensation reactions were carried out in toluene heated at reflux in the presence of molecular sieves. The assembled bidentate phosphine ligands 7–12 were prepared by reaction of 1–6 with [Zn {N (SiMe3) 2} 2] or Ti (OiPr) 4(see the Supporting Information). Molecular modeling calculations showed that in particular the assemblies 10–12 might be interesting as wide-bite-angle ligands. On the one hand, this approach allows screening of large numbers of catalysts, but on the other hand, sophisticated guesses must be made; indeed, 7–9 are less promising, as we will see below, both for structural and for reactivity reasons. Note that 8 and 9 are isostructural with SPANphos (SPANphos= 4, 4, 4’, 4’6, 6’-hexamethylspiro-2, 2’-bichroman-8, 8 …