Towards an Effective Synthesis of Difunctionalized Heptacyclo [6.6.0.0 2,6 .0 3,13 .0 4,11 .0 5,9 .0 10,14 ]tetradecane: Ligand Effects on the Cage Assembly and Selective C−H Arylation Reactions

Carbon-Phosphorus Ligands with Extreme Donating Character

Carbeniophosphines [R2 C+ -PR2 ] and phosphonium ylides [R3 P+ -CR2 - ] are two complementary classes of carbon-phosphorus based ligands defined by their unique donor properties. Indeed, while carbeniophosphines are electron-poor P-ligands due to the positioning of a positive charge near the coordinating P-atom, phosphonium ylides are electron-rich C-ligands due to the presence of a negatively charged coordinating C-atom. Based on this knowledge, this account summarizes our recent contribution on these two classes of carbon-phosphorus ligands, and in particular the strategies developed to lower the donor character of carbeniophosphines and enhance that of phosphonium ylides. This led us to design, at both extremities of the donating scale, extremely electron-poor P-ligands exemplified by imidazoliophosphonites [R2 C+ -P(OR)2 ] and dicarbeniophosphines [(R2 C+ )2 -PR], and extremely electron-rich C-ligands illustrated by pincer architectures exhibiting several phosphonium ylide donor extremities. In the context of carbon-phosphorus analogy, the closely related cases of ligands where the C-atom of a NHC ligand is in close proximity of two positive charges, and that of a phosphonium ylide coordinated through its P-atom are also discussed. An overview of the synthetic methods, coordinating properties, general reactivity and electronic structure of all these C,P-based species is presented here.

Palladium-catalysed Csp3-H functionalisation of unactivated 8-aminoquinoline amides in deep eutectic solvents

The C_sp³-H activation of aliphatic amides is described for the first time in deep eutectic solvents (DESs) without the need for Ag salts. The use of eutectic mixtures improves the yields obtained with volatile organic solvents, and allows for the reuse of the catalyst. Post-synthetic modifications can also be performed in DESs, increasing the sustainability of the process and the value of the products obtained.

α-Cationic Phosphines: from Curiosities to Powerful Ancillary Ligands

The distinguishing feature of α-cationic phosphines is the presence of at least one substituent, normally (hetero)cyclic and positively charged, which is directly attached to the phosphorus atom. As result from this unique substitution pattern, the thus designed ligands depict significantly diminished donor properties if compared with their neutral counterparts. Thus, if in a hypothetical catalytic cycle, the step that determines the rate is facilitated by an increase of the electrophilicity at the metal center; then, the use of α-cationic ancillary phosphines can be highly beneficial. This fact, combined with their easy syntheses and stability, which allows an easy handling, make α-cationic phosphines a useful tool for the synthetic practitioner. Our research on the topic demonstrates that generally a remarkable ligand acceleration effect is observed when α-cationic phosphines are employed in Au(I)- and Pt(II)-promoted cycloisomerizations; moreover, in some cases even otherwise not operative transformations can be promoted. This Account describes how we entered into the topic, our efforts, and those of others to understand the coordination behavior of α-cationic phosphines and further develop their range of applications in catalysis; but it also identifies the drawbacks associated with their use, which limit their range of application.

1 Introduction

2 Polycationic Phosphines: Stronger Acceptors than Phosphites

3 Inconveniences Derived from the Use of (Poly)cationic phosphines

4 A Second Generation of Cationic Ligands: α-Pyridiniophosphines

5 Chiral α-Cationic Phosphines

6 α-Radical Phosphines and (Poly)cationic Phosphine Oxides

7 Conclusions and Outlook