Ylide Ligands

Abstract

The use of ylides of P, N, As or S as ligands toward transition metals is still a very active research area in organometallic chemistry. This fact is mainly due to the nucleophilic character of the ylides and to their particular bonding properties and coordination modes. They can behave as monodentate or bidentate-chelate or bridging-species, they can be used as chiral auxiliary reagents, they are interesting reaction intermediates or useful starting materials in a wide variety of processes, etc. The most interesting bonding properties, structural features and applications of these versatile compounds will be covered in this chapter.

Phosphine-NHC-Phosphonium Ylide Pincer Ligand: Complexation with Pd(II) and Unconventional P-Coordination of the Ylide Moiety

“…With the aim of introducing more diversity in such carbon-based pincer platforms, we report herein the preparation of nonsymmetrical 5,6-NHC core pincer Pd­(II) complexes of type D featuring phosphonium ylide and phosphine donor moieties. In addition, thanks to the possible tuning of the lateral phosphine arm, we were able to prepare and characterize complex E combining the regular C -coordinated phosphonium ylide with a rare P -pallada-substituted ylide moiety …”

NHC Core Phosphonium Ylide-based Palladium(II) Pincer Complexes: The Second Ylide Extremity Makes the Difference

“…From there, considerable efforts have been provided to introduce structural diversity, and carbene ligands have become unavoidable surpassing in some applications their illustrious predecessors based on group 15 elements . Like carbenes, onium ylides and related species, which are charge-neutral in their free state and act as strong σ-donors with weak π-acceptor ability, have experienced a revival of interest confirming their potential as Lewis bases in main group and coordination chemistry . Phosphonium ylides, the most exemplified representatives of this family, differ in the hybridization state of the coordinating atom with respect to N-heterocyclic carbenes (NHCs), Csp 3 type versus Csp 2 type, thus positioning themselves as a complementary class of carbon ligands.…”

A Palladium(II) Complex of a C4 Chelating Bis(NHC) Diphosphonium Bis(ylide) Ligand

“…A plethora of NHC ligands bearing an extra coordinating moiety of different nature (NHC∼X: X = C, N, O, P, S, ...) have also been designed to improve the efficiency and the selectivity of complexation . Phosphonium ylides, which have been used as a complementary class of neutral carbon ligands, different from NHCs in the hybridization state of the coordinating atomC­(sp 3 ) type vs C­(sp 2 ) typehave been also shown to act as Lewis bases in coordination chemistry . On the basis of the preparation of an isostructural series of Rh­(CO) 2 complexes, phosphonium ylides were actually proven to be stronger donor ligands in comparison to NHCs .…”