Catalysis is immensely important in academia and industry, as emphasized by the Nobel Prize 2021 that was awarded to David MacMillan and Benjamin List for establishing the new field of organocatalysis. Today, the majority of catalytic reactions is still performed using transition metal catalysts. Unfortunately, most are expensive and not environmentally benign. Molecular catalysts immobilized via phosphine linkers on inert solid supports like silica diminish this problem because they can easily be removed from reaction mixtures and recycled. The new tripodal ligands MeOSi(CH2CH2PPh2)3 (1) and EtOSi(CH2CH2PPh2)3 (2) have been synthesized and fully characterized as molecular and surface-bound species. Tripodal phosphines like 1 and 2 display a multitude of interesting and favorable features. (a) They retain metal complexes better than bidentate phosphine ligands, thus reducing leaching of the immobilized catalysts. (b) They enable the efficient and straightforward synthesis of heterodinuclear or trinuclear complexes. (c) Their flexible methylene chains allow the different metals to come into contact, facilitating reactions that are catalyzed in tandem, such as C-C cross-coupling reactions propagated by the Pd/Cu Sonogashira catalyst system. (d) Their heterodinuclear complexes can be transformed into phosphine-shielded dual atom catalysts, trinuclear "drones" like [MeOSi(CH2 CH2PPh2)3 ]2(PdCl2)3 into well-defined Pd 3 clusters. (e) The high mobility of the flexible ligands 1 and 2 in the presence of a solvent allows high-resolution NMR techniques for their characterization even when they are covalently bound to a support surface. In this presentation, points (a) to (e) will be discussed and the structure and dynamics of the Pd component of the Sonogashira catalyst, surface-bound via the flexible tripodal ligands 1 and 2, will be described using 31P HRMAS and 29Si CP/MAS NMR. The NMR results are correlated with the catalytic activity of the different ligand/Pd/Cu systems for the Sonogashira coupling of arylhalides with acetylenes.

Molecular and immobilized Pd complexes with tripodal phosphine ligands

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.