A new family of cationic ligands, N-alkyl/aryl pyridiniophosphines, has been synthesized through a short, scalable, and highly modular route. Evaluation of their electronic properties evidenced weak σ-donor and quite strong π-acceptor character when used as ancillary ligands. These attributes confer a substantially enhanced π-acidity to the Pt^II and Au^I complexes thereof derived and, as result, they depict an improved ability to activate alkynes towards nucleophilic attack. This superior performance has been demonstrated along several mechanistically diverse Pt^II- and Au^I-catalyzed transformations

Mono- and dicationic phosphines have been synthesized through the reaction of chloroimidazolinium or chloroamidinium salts with secondary or primary phosphines respectively. The resulting ligands, which depict a significantly reduced donor ability compared with their neutral analogues, have been used to design Pt(II) and Au(I) complexes that effectively catalyse the hydroarylation of alkynes.

The oxidative addition of bromine to homo-and heterobis(carbene) gold(I) complexes 1−6 containing expanded-ring Nheterocyclic carbene (erNHC) ligands was explored to prepare the first examples of gold(III) erNHC complexes. The use of stoichiometric amounts of bromine consistently gave clean gold-centered oxidations leading to the isolation of monocarbene and mixed carbene complexes of the type [AuBr 3 (erNHC)] (7−9) and trans-[AuBr 2 ( i Pr 2 -bimy)(erNHC)]-BF 4 (13−15), respectively. The use of excess bromine additionally led to ligand brominations in the monocarbene series affording [Au-Br 3 (erNHC Br2 )] complexes (10−12), while in the case of the heterobis-(carbene) series, tribromide complexes of the type trans-[AuBr 2 ( i Pr 2bimy)(erNHC)]Br 3 (16−18) were obtained instead. Comparison of the catalytic activities of all complexes in the hydroamination of alkynes revealed the superior performance of mono-erNHC complexes in all cases.

Rhodium PCcarbeneP pincer complexes 1-L (L = PPh3, PPh2(C6F5), PCy3) readily facilitate deoxygenation of amine and pyridine N-oxides. The resulting complexes exhibit η2-CO coordination of the resulting keto POP pincer ligand. These η2-CO linkages in the metalloepoxide complexes are readily reduced by isopropyl alcohol and various benzylic alcohols. Thus, efficient catalytic deoxygenation of amine and pyridine N-oxides is possible using complexes 1-L and isopropyl alcohol. This represents a pioneering example of PCcarbeneP pincer complexes being used as catalysts for catalytic deoxygenation.