Ligands diphosphonites

The asymmetric hydrogenation of quinoline continues to be of interest. Li et al. reported the asymmetric hydrogenation of a variety of 2-substituted-quinolines to the corresponding tetrahydroquinolines using an Ir-catalyst with a BINOL-derived diphosphonite ligand... 

Subsequently, it was shown that rhodium complexes derived from diphosphi-nites, diphosphonites, and diphosphites - as well as hybrid ligands - are similarly active and selective to diphosphines [46 i],... 

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.

A chiral diphosphonite, derived from BINOL (18) and with an achiral diphenyl ether backbone, is an excellent ligand for the iridium-catalysed asymmetric hydrogenation of quinolines. Enantioselectivities ranging from 90 to 94% were obtained.343... 

PtC=C and Pi C=C-C 13C chemical shifts were reported for (92) and related complexes.428 A typical 195Pt resonance was observed (—2180 ppm) for (93).429 A detailed analysis of and 13C resonances (from 2-D COSY and 13C, HMQC experiments) has been made for (94) and related systems.430 and 31P 1H NMR spectra for cz s-[PtCl L-K3C,P,P ], where L = sterically constrained diphosphonite ligands, gave characteristic Pt-P coupling constants.431 31P NMR spectroscopy was used to differentiate the isomers (95) and (96).432... 

Reetz and Li studied asymmetric hydrogenation of quinolines using iridium complex with a chiral BINOL derived diphosphonite ligand with an achiral diphenyl ether backbone as catalyst, achiral P ligands serving as possible additives (Scheme 10.7) [9]. Under the optimized conditions, 2 substituted and... 

The P-Pt coupling data for the platinum- phosphonite complexes published in the literature have been reviewed by Vlugt et and the 7ppt couplings for two new complexes containing novel, sterically constrained diphosphonite ligands with 2-tert-butyl-phenolate and 2,2 -dioxo-3,3 -di-tert-butyl-5,5 -dimethoxy-1,1 -biphenyl groups have been measured by them. 

Chiral Bidentate and Multidentate Phosphorus Ligands (Diphosphanes and Polyphosphanes, Diphosphites, Diphosphinites, and Diphosphonites). After testing a number of monodentate phosphanes, a real breakthrough came in the area of enantioselective hydrogenation when various types of chiral diphosphanes were applied. The first two diphosphanes employed were DIPAMP and DIOP (see later) introduced by Knowles and Kagan, respectively. Their achievements stimulated research on a variety of bidentate chiral diphosphanes. 

The application of rhodium-diphosphonite catalysts (where diphosphonites are Reetz s ligands with BINOL and ferrocene subvmits) for alkene, ketone, and ketoester hydrogenation resulted in practically enantiospecific reaction (ee higher than 99.5%) (173,223). 

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