Rhodium complexes supramolecular

Pyrazine, bridged supramolecular complexes, 46 206-213, 240-243 p-Pyrazine complexes, osmium, 37 307 Pyrazolates, ligand with rhodium complex, 44 278 Pyrazoles... 

The chelating behavior was also evident from H P-NM R experiments. The addition of triphenylphosphine (a) to a catalyst solution of [HRh(CO)2(13 b)] did not affect the complex. Moreover, the addition of 1 equiv. of b to a solution of HRh(CO)2(13) PPhj resulted in the exclusive formation of [HRh(CO)2(13 b)] upon release of free triphenylphosphine. The chelating effect of the supramolecular ligand assembly effectively competes with triphenylphosphine, leading to exclusive formation of the rhodium complex of 13 b. In the complex [HRh(CO)2(13 b) the supramolecular ligand 13 b coordinates in an equatorial-equatorial fashion to the rhodium metal center, whereas the HRh(CO)2(13)PPh3 exists in a mixture of complexes (ee and ea). 

Dessoudeix. M. Urrutigoity. M. Kaick, P. Catalytic activity enhancement of a cyclodextrin/water-soluble-rhodium complex system due to its gradual supramolecular organization in the interphase. Eur. J. Inorg. Chem. 2001. 

Supramolecular chemistry has been a very popular research topic for three decades now. Most applications are foreseen in sensors and opto-electronical devices. Supramolecular catalysis often refers to the combination of a catalyst with a synthetic receptor molecule that preorganizes the substrate-catalyst complex and has also been proposed as an important possible application. The concept, which has proven to be powerful in enzymes, has mainly been demonstrated by chemists that investigated hydrolysis reactions. Zinc and copper in combination with cyclodextrins as the receptor dramatically enhance the rate ofhydrolysis. So far, the ample research devoted to transition metal catalysis has not been extended to supramolecular transition metal catalysis. A rare example of such a supramolecular transition metal catalyst was the results of the joined efforts of the groups of Nolte and Van Leeuwen [SO], They reported a basket-shaped molecule functionalized with a catalytically active rhodium complex that catalyzed hydrogenation reactions according to the principles of enzymes. The system showed substrate selectivity, Michaelis Menten kinetics and rate enhancement by cooperative binding of substrate molecules. The hydroformylation of allyl catachol substrates resulted in a complex mixture of products. 

Switching the roles of the zinc porphyrin template and N-donor adapter provides an alternative mode for the supramolecular construction of biden-tate ligands (Scheme 32). Complex 26 derived from mixing three equivalents of template 24 with two equivalents of monodentate phosphite ligands 23 furnished a rhodium catalyst which displayed good regioselectivity toward... 

Figure 1.13 Generation of rhodium-based supramolecularcatalysts by assembly of pyridine/hydroxypyridine pairs (a) Self-assembly modes of pyridine-based phosphines, (b) Alkene hydroformylation with supramolecular rhodium-diphosphine catalysts (c) CAChe minimized 3D structure ofthe rhodium-diphosphine complex (other ligands from the metal omitted for clarity).

Figure 1.14 Generation of supramolecular catalysts for asymmetric hydrogenation (a) Assembly of heterodimeric chelating ligands, (b) Structure of the optimal rhodium-diphosphonite complex for asymmetric hydrogenation (other ligands from the metal center omitted for clarity), (c) Enantioselective hydrogenation of functionalized alkenes.

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. 

The supramolecular binding motifs described here were also used to attach catalysts to solid (silica) supports (128). The active metal complex could be switched from palladium to rhodium by using a polar solvent that breaks up the binding of the supramolecular motif. Allylic alkylation and hydroformylation catalysis could be carried out by using the same support "receptor" material and different "guest" ligands for the two metals a... 

A host-guest molecular recognition process of L-tryptophan, with the above various triangular, bowl-shaped Cp Rh-nucleobase/nucleoside/nucleotide cyclic trimer molecular receptors, was also detected in a gas phase by electrospray ionization mass spectrometry.In this case, the supramolecular complex formation was found to occur predominately via non-covalent tt-tt interactions non-covalent hydrophobic forces apparently being weak or nonexistent. Trp-Met-Asp-Phe tetrapeptide with the trimeric-rhodium host [Cp Rh(2 -deoxyadenosine)]3[OTf]3 also formed a host-guest complex in water that is detected in the gas phase. 

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