Assembling the Catalyst Backbone by Using Supramolecular Interactions

Assembling the Catalyst Backbone by Using Supramolecular Interactions 

In this synthetic strategy, supramolecular interactions are used to construct the catalyst backbone. The approach can be used for a wide variety of catalysts, and mechanistic effects include catalytic supramolecular assemblies, self-assembly, metal-mediated catalysis and organocatalysis, and chiral induction. 

The simplest supramolecular bidentate ligand derives from secondary phosphine oxides (SPO). Complexes of transition metals with SPOs have been known for 45 years, and they were introduced as catalysts by van Leeuwen and Roobeek in the early 1980s (66). The complex used first was a platinum hydride containing two SPOs, cormected to one another by a strong hydrogen bond, and a triphenylphosphine to complete the coordination sphere. SPOs have a very strong tendency to occur in pairs connected by hydrogen bonds in many metal complexes they act as bidentate monoanions. 

After Breit and Seiche (67) had reported hydroformylation catalysts containing rhodium and bidentate ligands assembled via hydrogen bonding, Dubrovina and Boerner (68) pointed out that the first use of bidentate ligands obtained via hydrogen bonding in catalysis is represented by the supramolecular work on SPO platinum complexes. 

SCHEME 4 SPO platinum catalysts. Top row stoichiometric hydroformylation with 1 middle row, catalyst 4 and hydrogen bond switching in 6 bottom row heterolytic cleavage of dihydrogen (69-71). (For a color version of this figure, the reader is referred to the Web version of this chapter.) 

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