Coordination Chemistry of Cyclopropenylidene‐Stabilized Phosphenium Cations: Synthesis and Reactivity of Pd and Pt Complexes. Issue 8 (23rd January 2014)

• Record Type: Journal Article
• Authors: Kozma, Ágnes; Deden, Tobias; Carreras, Javier; Wille, Christian; Petuškova, Jekaterina; Rust, Jörg; Alcarazo, Manuel
• Is Part Of: Chemistry. Volume 20:Issue 8(2014)
• Page Start: 2208
• Page End: 2214
• Publication Date: 2014-01-23
• Subjects: Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201303686
• Languages: English
• ISSNs: 0947-6539

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>A straightforward synthesis of cyclopropenylidene‐stabilized phosphenium cations <bold>1 a</bold>–<bold>g</bold> through the reaction of [(<italic>i</italic>Pr<sub>2</sub>N)<sub>2</sub>C<sub>3</sub><sup>+</sup>Cl]BF<sub>4</sub> with secondary phosphines is described. Their donor ability was evaluated by analysis of the CO stretching frequency in Rh complexes [RhCl(CO)L<sub>2</sub>](BF<sub>4</sub>)<sub>2</sub> and electrochemical methods. The cyclopropenium ring induces a phosphite‐type behavior that can be tuned by the other two substituents attached to the phosphorus atom. Despite of the positive charge that they bear, phosphenium cations <bold>1 a</bold>–<bold>g</bold> still act as two‐electron donor ligands, forming adducts with Pd<sup>II</sup> and Pt<sup>II</sup> precursors. Conversely, in the presence of Pd<sup>0</sup> species, an oxidative insertion of the Pd atom into the C<sub>carbene</sub>–phosphorus bond takes place, providing dimeric structures in which each Pd atom is bonded to a cyclopropenyl carbene while two dialkyl/diaryl phosphide ligands serve as bridges between the two Pd centers. The catalytic performance of the resulting library of Pt<sup>II</sup> complexes was tested; all of the cationic phosphines accelerated the prototype 6‐<italic>endo</italic>‐dig cyclization of 2‐ethynyl‐1, 1′‐biphenyl to afford pentahelicene. The best ligand <bold>1 g</bold> was used in the synthesis of two natural products, chrysotoxene and epimedoicarisoside A.</p> </abstract>