Template-induced formation of heterobidentate ligands and their application in the asymmetric hydroformylation of styrene

Kuil, Mark; Goudriaan, P. Elsbeth; Leeuwen, Piet W. N. M. van; Reek, Joost N. H.

doi:10.1039/b609321c

Cited by 123 publications

(73 citation statements)

References 39 publications

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“…Diisopropylethylamine and triethylamine were distilled from CaH 2 under nitrogen. The following compounds were synthesized according to published procedures: bis-zinc(II) salphen 1, pyridyl phosphite ligands c, 11a-c,15a,33 pyridyl phosphoramidite ligands e, f, and h, 20 and pyridyl phosphite ligand g.…”

Section: Methodsmentioning

confidence: 99%

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Rigid bis-zinc(ii) salphen building blocks for the formation of template-assisted bidentate ligands and their application in catalysis

et al. 2007

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The template-induced formation of chelating bidentate ligands by the selective self-assembly of two monodentate pyridyl phosphorus ligands on a rigid bis-zinc(II) salphen template with two identical binding sites was studied. Using UV-vis, NMR-spectroscopy and X-ray analysis the formed structures were unambiguously proven. The application of these templated bidentate ligands in transition metal catalysis showed, in most cases, typical bidentate character. Compared to previous work based on a more flexible bis-zinc(II) porphyrin template, the current catalytic data suggest that the rigidity of the template is not an important factor for the improvement of the regio-and enantioselectivity under the applied reaction conditions.The most powerful tool in homogeneous transition metal catalysis is ligand design and optimization. Various ligand parameters including steric properties, electronic properties, the bite angle and chirality, have shown to be important.1,2 Systematic variation of these properties is the general strategy for catalyst discovery and optimization. Traditionally, monodentate 3-6 and bidentate ligands 7,8 have been studied as important classes of ligands. For several reactions (hetero)bidentate ligands are superior compared to monodentate ligands, 2,9 but synthetic routes towards these ligands are generally more tedious.An important new strategy comprises a supramolecular approach to form (hetero)bidentate ligands. 10-19In this approach two monodentate ligands are brought together by a self-assembly process using non-covalent interactions such as hydrogen bonds, ionic or dynamic metal-ligand interactions. This class of ligands combines the advantages of synthetic accessibility and the selective formation of (hetero)bidentate ligands. Two monodentate ligands can be assembled by using ligands with complementary binding motifs, 11-14 or alternatively, a template can be used that contains binding sites for the assembly of two monodentate ligands.15 For example, we reported the use of a flexible bis-zinc(II) porphyrin template for the assembly of identical monodentate ligands, which led to chelating bidentate ligands that showed increased (enantio)selectivities in several reactions. tical binding sites (Fig. 1). 20 A more rigid template (i.e. the rigid bis-zinc(II) salphen versus the more flexible bis-zinc(II) porphyrin template used in previous studies) was anticipated to give rise to more selective catalyst systems. For the construction of templated self-assembled bidentate ligands we used two identical monomeric pyridyl phosphorus ligands. Transition metal complexes based on these templated bidentate ligands were explored in various catalytic transformations and they outperformed in most cases their non-templated analogues. Results and discussionWe studied the formation of templated bidentate ligand assemblies using monomeric pyridyl phosphorus ligands a-h in combination with a bis-zinc(II) salphen template 1 (Scheme 1). The bis-zinc(II) salphen building block was synthesized in a straightforward two...

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Section: Methodsmentioning

confidence: 99%

“…1). 20 A more rigid template (i.e. the rigid bis-zinc(II) salphen versus the more flexible bis-zinc(II) porphyrin template used in previous studies) was anticipated to give rise to more selective catalyst systems.…”

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Rigid bis-zinc(ii) salphen building blocks for the formation of template-assisted bidentate ligands and their application in catalysis

et al. 2007

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“…[5f, 6a] This feature has been exploited in various applications to bind ligands at the axial position to afford stable pentacoordinated species. [8] As part of our ongoing studies with the Zn II -centered family of derivatives we were interested in the deformation capability of the salphen ligand upon enforcing the ligation of sterically demanding N-heterocyclic ligands.…”

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Trapping of a Four‐Coordinate Zinc Salphen Complex Inside a Crystal Matrix

Escudero‐Adán

Benet‐Buchholz

Kleij

2009

Chemistry A European J

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A remarkable twosome: Four-coordinate square-planar complexes based on [Zn(salen)] derivatives are conveniently captured inside a crystal matrix using a supramolecular protecting strategy (see figure). The four-coordinate species is accompanied by a five-coordinate complex that binds an axial ligand able to hydrogen bond to an N-heterocycle positioned in the axial region of the coordinative unsaturated derivative. The size of the N-heterocycle is a decisive stabilization parameter.

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“…of base. As previously reported [12][13][14]42,43], the low activity of this ligand can be attributed to the formation of …”

Section: Coordination Chemistry Studiesmentioning

confidence: 54%

“…The assembly in this case, as in many other supramolecular architectures that use Zn II (porphyrins) as synthons, was based on the coordination of the Lewis acidic Zn II with a nitrogen donor ligand. Looking for more rigid structures, bis(Zn II (salphen)) templates (salphen=N,N'-phenylenebis(salicylid eneimine)) based on the same type of interaction were studied [13,14]. In both instances, the strength of the Lewis acid-base interaction, reinforced by two strong rhodium-phosphorus bonds, sufficed to keep the structure intact under catalytic conditions, but certainly stronger interactions were desirable.…”

Section: Introductionmentioning

confidence: 99%

Bidentate ligands templated by a convex trimetallic bis(salphen) platform

Freixa¹,

Ponsico²,

Frischmann³

et al. 2012

Supramolecular Catalysis

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A Zn 3 -bis(salphen) compound was used as a template for the construction of bidentate phosphine ligands by self-assembly with phosphines containing a carboxyl group. The convex shape of the template, exposing the three zinc atoms, ensured the correct orientation of the assembled diphosphine, such that it can coordinate to a single metal atom. The strong zinc-carboxylate bond guaranteed the integrity of the final assembly at the low concentrations (1 mM) used in catalysis. Depending on the substitution pattern of the benzoic acid phosphines, either monometallic chelates or dimeric complexes were formed. Coordination studies were carried out for Pt and Rh. A modest chelate effect in the rhodium catalyzed hydroformylation of 1-octene (l/b=4.7) confirmed the formation of the bidentate assemblies.

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Template-induced formation of heterobidentate ligands and their application in the asymmetric hydroformylation of styrene

Cited by 123 publications

References 39 publications

Rigid bis-zinc(ii) salphen building blocks for the formation of template-assisted bidentate ligands and their application in catalysis

Rigid bis-zinc(ii) salphen building blocks for the formation of template-assisted bidentate ligands and their application in catalysis

Trapping of a Four‐Coordinate Zinc Salphen Complex Inside a Crystal Matrix

Bidentate ligands templated by a convex trimetallic bis(salphen) platform

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