Calix arene phosphites

Recently van Leeuwen reported the fiigt crystal structure of the diphosphite dicarbonyl rhodium catalyst HRh(CO)2(P P) [258]. Bomer et al. developed a new class of phosphonites which show promising results for the isomerization and subsequent hydroformylation of internal olefins [259]. The number of phosphite ligands based on supramolecular backbones such as calix[4]arenes is growing [260]. They are attractive because of their well defined structure combined with the ability to adopt several discrete conformations. Calix[4]arene diphosphites and calix[6]arene phosphites were first developed by BASF [261]. In... 

Theoretically, calix[4]arene phosphites can exist in six conformations. X-ray structural analyses, NMR spectroscopic studies, and comparison with related monophosphates and monoarsenites showed that, depending on the substituent R, preferentially conformation a or b is adopted (Scheme 2.101) [109]. Both can interconvert simply by rotating the substituted ring from an up to a down position. 

The Maruoka group developed asymmetric MPV allq nylations catalysed by the axially chiral biphenol ligands derived catalyst 46 (Scheme 19.55), and the corresponding alcohols were obtained in 64-96% enantiomeric excess. Very recently, Nandi, Katz and coworkers reported an Al-calix[4]arene-catalyst 47 for the asymmetric MPV reduction (Scheme 19.56). The most enantioselective catalyst consisted of a new axially chiral vaulted-hemispherical calyx[4]arene phosphite ligand, which delivered the chiral alcohols with enantiomeric excesses up to 99%. 

Other [AuCIL] complexes with monophosphines are those derived of o-carborane (427),2506 pyr-anoside group (428),2507 a-dimethylamino(3)ferrocenophan-2-yl,2508 calix[4]arene derived phosphites,25 or aminoxyl radical-substituted phosphines (429),2510 for which ferromagnetic interactions have been observed. 

The smaller p -tert-butyl-calix [4] arenes have a rich coordination chemistry as well (65). Of these, however, only the upper-rim modified calixarenes seem to support metal complexes with confined binding sites (66), except in those cases where the lower-rim substituents form an appended cavity. Thus, Matt and coworkers have reported (67) a pocket-shaped calix[4]arene ligand L2 bearing two lower-rim [([Pg.410]

The reaction of calix[4]arene or its p-t-butyl derivative with tris(dimethylamino)phosphine gives the basket zwitterionic six-coordinate phosphorus derivatives (177 R = H, Bu ) <90JA9422, 91CC562, 93PS(75)253, 94IC2657). The attempted deprotonation at phosphorus with -butyllithium to give the basket aminophosphorane with four basal P—O bonds was unsuccessful (the NH proton was removed), but trifluoroacetic acid or heat yielded the bicyclic phosphite (178 R = H, Bu ). The crystal structures of (177 R = H) and the oxidized form of (178 R = H) were determined. The P—H atom in (177 R = Bu ) is inside the basket. 

Parlevliet has shown that calix[4]arene based monophosphites can exist in different conformations [45]. By using the different conformations as ligands in the rhodium catalyzed hydroformylation of 1-octene he showed that the exact conformation influenced the performance of the catalyst. Some of the conformations behaved more like triphenyl phosphite, whereas others showed catalytic results like bulky monophosphites, giving high rates with moderate selectivity for the linear aldehyde. 

Cobley CJ, Ellis DD, Guy Orpen A, Pringle PG. Rhodium complexes of robust phosphites derived from calix[4]arenes and their apphcation in the hydroformylation of 1-hexene. J Chem Soc Dalton Trans 2000 7 1109-12. 

A remarkable stabilizing effect of rhodium on the hydrolysis rate of a cage monophosphite derived from sulfonated calix[4]arene was observed by Cobley and Pringle [175]. The phosphite has a life in water of only 5 h. However, coordination to Rh enhanced its stability toward hydrolysis to 4 months. Consequently, it survived even the conditions of an aqueous two-phase hydroformylation. 

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