Ligands ambiphilic

Gudat D (2003) Zwitterionic Phospholide Derivatives - New Ambiphilic Ligands. 232 175-212... 

In the present volume, our intention was to cover several modern approaches to phosphorus chemistry which were not, or at least not completely, covered in the previous volumes. The selected topics are expected to have broader relevance and to be interesting to a more general readership, since key aspects of phosphorus chemistry are pointed out. Indeed, several fields are investigated coordination chemistry, catalysis, supramolecular chemistry, biochemistry, hybrid organic-inorganic materials, new ambiphilic ligands, and biology. 

Chapter 6, written by D. Gudat, is concerned with zwitterionic phospholide derivatives which can be considered as useful ambiphilic ligands. This review gives an account of the current knowledge on the synthesis, physical properties, and - in particular - chemical behavior of phosphino-substituted phospholide derivatives. 

C. Ambiphilic ligands featuring ortho-phenylene spacers... 

The four coordination modes E-H (Figure 18) have been substantiated spectroscopically and structurally for PBs and related ambiphilic ligands. They differ in the participation of the Lewis acid moiety that may remain... 

The simplest bonding situation conceivable upon coordination of an ambiphilic ligand to a transition metal is that involving the sole coordination of the Lewis base moiety, the Lewis acid fragment remaining pendant. Several examples of such complexes have been described in the recent years, most frequently upon coordination of preformed ambiphilic ligands. 

The ability of ambiphilic ligands to bridge M-X or M-L fragments (coordination mode F resulting from the concomitant coordination of the donor site to the metal and interaction of the Lewis acid with a coligand) has also been demonstrated experimentally. Such bridging coordination remains rare, and most of the known examples involve PB ligands.74... 

The bridging coordination of M-X and M-L fragments by ambiphilic ligands, as described in this section, open interesting perspectives in catalysis. Complex 94 nicely illustrates the possibility to cooperatively activate functionalized 7i-systems by concomitant coordination to a metal center and a Lewis acid. In addition, and in line with what is typically encountered upon activation of metal complexes with Lewis... 

Over the past few years, the coordination of preformed ambiphilic ligands, especially PBs, has been shown to afford straightforward access to complexes featuring metal-Lewis acid interactions. As discussed hereafter, this approach has allowed the significant extension of the scope of M-Z interactions, and to gain better understanding of their bonding situation. 

As discussed in the previous section, the coordination properties of PBs and related ambiphilic ligands have been quite extensively studied over the last decade. Comparatively, the reactivity and catalytic application of the ensuing complexes have only been scarcely explored. The few investigations reported in this area are summarized in this section. They nicely illustrate the various possibilities offered by the presence of the Lewis acid in the coordination sphere of a metal or at proximity. 

A few years later, Landis drew similar conclusions for the l,l -ferro-cenyldiphosphines 53a-c featuring pendant benzoxaborolidine moieties.63 Combined with rhodium precursors, these ambiphilic ligands lead to catalytically active species in hydrogenation and hydroformyla-tion reactions (Tables 7 and 8), but the presence of the Lewis acid moiety has no significant effect on activity and selectivity (compared to ligands 51 and 52). 

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