P-heterocyclic ligands

Synthesis of N,P-Heterocyclic Ligands with the P-N = C Structural Moiety via Trapping of Transient Nitrilium Phosphanylid... 

The following bonding picture for 2H-azaphosphirene complexes can be drawn based on the NMR, IR, UV/vis, MS, and X-ray diffraction data [24] The situation of this N,P-heterocyclic ligand should be described as a resonance hybrid of a three-membered ring system with a covalent bonding (XIII) and a... 

Borane complexes of P-heterocycles as versatile precursors for the synthesis of chiral phosphine ligands used for asymmetric catalysis 98S1391. 

Chiral P-heterocycles as P-mono- and P,N-bidentate ligands in the synthesis of coordination compounds and homogeneous asymmetric catalysis 98KK883. 

The rhodium complexes with hydroxyphospholane ligand 125663 or 126660 catalyze the asymmetric hydrogenation of a-acetamidoacrylates with ee values in excess of 98%. System 125 is also very effective in the asymmetric hydrogenation of P-acetamidoacrylates (up to 99.6% ee).664 The planar-chiral heterocyclic ligand 127 complexed with rhodium(I) catalyzes the hydrogenation of a-acetamidoacrylates in excellent yields and ee values from 79-96% under mild conditions.665... 

Abstract In this chapter, selected results obtained so far on Fe(II) spin crossover compounds of 1,2,4-triazole, isoxazole and tetrazole derivatives are summarized and analysed. These materials include the only compounds known to have Fe(II)N6 spin crossover chromophores consisting of six chemically identical heterocyclic ligands. Particular attention is paid to the coordination modes for substituted 1,2,4-triazole derivatives towards Fe(II) resulting in polynuclear and mononuclear compounds exhibiting Fe(II) spin transitions. Furthermore, the physical properties of mononuclear Fe(II) isoxazole and 1-alkyl-tetrazole compounds are discussed in relation to their structures. It will also be shown that the use of a,p- and a,C0-bis(tetrazol-l-yl)alkane type ligands allowed a novel strategy towards obtaining polynuclear Fe(II) spin crossover materials. 

A vast number of derivatives of these general types have been prepared by similar routes for catalytic applications, and at this point we can do no more than provide a series of recent references some have P-donor ligands [24], some have N-heterocyclic carbenes [25], and others have mixed donors [26]. 

A number of P-N ligands has been reported as efficient ligands for the asymmetric hydrosilylation of ketones. We mention the phosphinooxazolines developed by Helmchen, Pfaltz, and Davis, we have seen before and mixed ligands containing planar-chiral heterocycles such as ferrocene [31] (Figure 18.17). For several ketone and silane combinations e.e. s in the high nineties were obtained. 

A,A -Dianionic fused six-membered heterocyclic ligands derived from phenazine and quinoxaline have been found in Ln complexes including [(SmCp )2(p-ri ri -Ci2HgN2)]... 

Different behavior was found for the p-toluenesulfonate and chloride derivatives containing ligands derived from pyrimidine. This could be due to a competitive coordination of these anions against the heterocyclic ligands. For the chloride complexes, a clear resonance broadening is observed at room temperature. Considering the chemical shifts it must be accepted that the free ligand is the dominant species. 

This oxidation state is dominated by amine complexes, and a large variety of complexes with N, 0, S, and P donors. Complexes with N-heterocyclic ligands tend to be strong oxidants. Invariably, Os(III) complexes are low spin and octahedral (2, 5, 6). 

Se = C(C6H4R-p)H ] (R = H, OMe, CF3) with bis( -butylthio)ethyne. The structure of one 2H-selenete complex 132 (R = H) was confirmed by an X-ray structural analysis.247 Based on spectra of these compounds, an equilibrium between the 2H-selenete complexes (132) and their thioselono-carboxylic ester isomers (133) was proposed (Scheme 36). The fraction of 133 in the eqilibrium was estimated to be about 6-10%. Decomplexation of the heterocyclic ligand in 132 (R = H) with [NEt4]Br afforded the first uncoordinated 2//-selenete. In addition, a 3,4-dihydro-l,2-diselenine was obtained.247... 

Hudson, M., Drew, M.G.B., Iveson, P.B., Madic, C., Russell, M.L. 2000. Partitioning-separation of metal ions using heterocyclic ligands. 6th OECD/NEA IEM on An and FP P T. Madrid, Spain, December 11-13. 

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