Ligands diphosphorus

TMEDA can also participate in the formation of multinuclear zinc telluride complexes with Znio, Zni4, and Zni6 complexes structurally characterized. A comparison was carried out by Pfistner et al. replacing the diamine with a diphosphorus ligand, bis(diphenylphosphino)methane,... 

Diphosphorus ligands stemming from P4 activation are usually quenched in multinuclear complexes, where they generally adopt the side-on coordination mode. As mentioned in the mechanistic section, multinuclear diphosphorus complexes coordinated to 15 VE metal fragments may form via dimerization of reactive P, intermediates and are incorporated into dimetalla-diphosphorus tetrahedranes. However, when P2-complexes are derived from the direct reaction of even-electron metal precursors and P4, it is likely that they form from the... 

Similarly, during the cothermolysis of 66 with [ CpxFe(CO)2 2] [80] or [[Cp Co(CO) 2] [82,99,100], diphosphorus ligands may be installed into a dodecahedron, while P, ligands may be incorporated in a distorted trigonal pyramid. The formation of these heterometal complexes through a synthetic procedure, which leaves out the use of white phosphorus, nicely illustrates the potentiality of P5 complexes to serve as sources of phosphorus units. 

THE SYNTHESIS AND APPLICATION OF ESPHOS a new diphosphorus ligand for THE HYDROFORMYLATION OF VINYL ACETATE... 

Both methodologies have been successfully extended for the preparation of diphosphorus ligands. An important example is ESPHOS (Scheme 3.3), prepared with total stereoselectivity in a 76% yield by Wills and Breeden. ... 

Aminophosphine phosphinite (AMPP) ligands constitute an important class of non-C2 diphosphorus ligands. Some of them are prepared from ephedrine and therefore the Juge-Stephan method constitutes an ideal procedure for the synthesis of P-stereogenic AMPP ligands (Scheme 4.30). ... 

Discovered more than 70 years ago, hydroformylation is nowadays one of the most important reactions in the chemical industry because aldehydes can be transformed to many other products. In the enantioselective version, rhodium/ diphosphorus ligand complexes are the most important catalytic precursors, although cobalt and platinum complexes have also been widely used. For these systems, the active species are pentacoordinated trigonal-bipyramidal rhodium hydride complexes, [HRh(P-P)(CO)2]. In those complexes, the coordination mode of the bidentate ligand (equatorial-equatorial or equatorial-apical) is an important parameter to explain the outcome of the process. The most common substrates of enantioselective hydroformylation are styrenes followed by vinyl acetate and allyl cyanide. With these substrates, mixtures of the branched (b, chiral) and linear (1, not chiral) aldehydes are usually obtained. In addition, some hydrogenation of the double bond is often observed. Therefore, chemo- and regioselectivity are prerequisites to enan-tioselectivity and all of them must be controlled. An additional eomplieation is that chiral aldehydes are prone to racemise in the presenee of rhodium spe-... 

CO can be almost completely expelled, and/or the required vacant coordination sites are blocked (V). As a consequence, the rate of hydroformylation decreases. Complexes with one (II) or two phosphorus ligands (III) are considered to be the most active catalysts in hydroformylation. In contrast, three monodentate and one tridentate, respectively, or even two bidentate diphosphorus ligands on rhodium can be efficient in related reactions, such as decarbonylation (see Chapter 8). 

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