Nonpalindromic Rhodium PCcarbeneP Pincer Complexes Featuring Electron-Deficient Phosphino Substituents

Interest in PCcarbeneP pincer ligands containing a central alkylidene donor has recently grown due to the unique metal-ligand cooperativity offered by such complexes. Despite this, the design of the supporting pincer ligand scaffold in such ligands remains largely unexplored. In particular, there exist no examples of nonpalindromic (or nonsymmetric) PCcarbeneP ligands. This report documents our synthesis and characterization of a series of palindromic and nonpalindromic PCcarbeneP pincer complexes via a proligand dehydration approach. We find that electronic variation of the pincer's diarylphosphino substituents, via incorporation of electron-withdrawing and -donating groups into the aryl substituents, has little effect on the reactivity or bonding of the central rhodium carbene attachment. However, sterically encumbering aryl substituents in the pincer phosphino positions impart selectivity to the complexes, with insertion of phenylacetylene preferred into the less sterically encumbered rhodium-phosphino bond of the pincer ligand. These results present a clear strategy for the diversification of the PCcarbeneP ligand class and future opportunities to impart selectivity on the basis of the steric design of nonpalindromic pincer ligands.

Automated summary

This report discusses the synthesis and characterization of a series of symmetric and asymmetric PCcarbeneP pincer complexes through a proligand dehydration approach. The study found that introducing sterically encumbering aryl substituents at the pincer phosphino positions can impart selectivity to the complexes.