Platinum(II)-phosphole complexes: synthesis and evaluation as enyne cycloisomerisation catalysts

Anion Chelation via Double Chalcogen Bonding: The Case of a Bis-telluronium Dication and Its Application in Electrophilic Catalysis via Metal-Chloride Bond Activation

Telluronium cations have long been known to engage their counteranions via secondary interactions. Yet, this property has rarely been exploited for anion binding. Motivated by such an application, we have now synthesized a bis-telluronium dication ([3]²⁺) that was obtained as a tetrafluoroborate salt by reaction of 2,7-di-tert-butyl-9,9-dimethylxanthene-4,5-diboronic acid with phenoxatellurine difluoride and BF₃·OEt₂. As confirmed by the formation of Te-(μ-BF₄)-Te bridges in the structure of [3][BF₄]₂, [3]²⁺ functions as a bidentate Lewis acid toward anions. [3][BF₄]₂ has also been converted into the more exposed [3][BArF₂₄]₂ ([BArF₂₄]^- = [B(3,5-(CF₃)₂C₆H₃)₄]^-). The latter, which readily ionizes Ph₃CCl, displays a chloride anion binding constant that exceeds that of a monofunctional model compound by almost 4 orders of magnitude. The unique properties of this new bis-telluronium dication are further highlighted by its ability to activate Ph₃PAuCl and cis-(Ph₃P)₂PtCl₂, leading to catalytic systems highly active in the cycloisomerization of propargylamide or enyne substrates.

α-Cationic Phospholes: Synthesis and Applications as Ancillary Ligands

A series of structurally differentiated α‐cationic phospholes containing cyclopropenium, imidazolium, and iminium substituents has been synthesized by reaction of chlorophosphole 1 with the corresponding stable carbenes. Evaluation of the donor properties of these compounds reveals that their strong π‐acceptor character is heavily influenced by the nature of the cationic group. The coordination chemistry of these newly prepared ligands towards Au^I centers is also described and their unique electronic properties exploited in catalysis. Interestingly, α‐cationic phosphole containing catalysts were not only able to accelerate model cycloisomerization reactions, but also to efficiently discriminate between concurrent reaction pathways, avoiding the formation of undesired product mixtures.

Enhancing the catalytic properties of well-defined electrophilic platinum complexes

Platinum complexes have been often considered as the least reactive of the group 10 triad metals. Slow kinetics are behind this lack of reactivity but, still, some industrially relevant catalytic process are dominated by platinum compounds and sometimes different selectivities can be found in comparison to Ni or Pd. Nevertheless, during the last years, it has been reported that the catalytic behaviour of well-defined platinum derivatives can be improved through a judicious choice of their electronic and steric properties, leading to highly electrophilic or low-electron count platinum systems. In this feature article, we highlight some catalytic processes in which well-defined electrophilic platinum complexes or coordinatively unsaturated systems play an important role in their catalytic activity.

Platinum-catalysed intermolecular addition of carbonyl compounds to 1,6-enynes: investigation of a new reaction pathway

A novel intermolecular addition of aldehydes to 1,6-enynes via a Pt-carbene intermediate provides the diastereoselective formation of valuable tricyclic compounds.

Phosphole-based ligands in catalysis

This review provides an overview of phosphole-based ligand families (monophospholes, multidentate hybrid phosphole ligands, diphosphole and 2,2′-biphosphole-based ligands) and their potential in metal- and organo-catalyzed reactions (asymmetric reactions included).