Mechanistic features of the copper-free Sonogashira reaction from ESI-MS.

The mechanism of the Sonogashira reaction in methanol was studied in detail using pressurized sample infusion electrospray ionization mass spectrometry (PSI-ESI-MS). Several key intermediates were identified and their structures were assigned by MS/MS studies. Cationic and anionic charged-tagged substrates were employed to look into the mechanism of this reaction from variety of angles. A reverse kinetic isotope effect was observed in which the reaction rate is accelerated in deuterated solvents (kH/kD = 0.6). The reaction was found to be zero order with respect to the aryl iodide and first order with respect to the phenylacetylene. A Hammett parameter of ρ = 1.4 indicates that the reaction is more favorable for aryl iodides with para EWGs. No evidence of product inhibition, dimerization of palladium catalyst, or agglomeration were observed. However, catalyst decomposition was inferred from a non-zero intercept in the plot of catalyst loading versus reaction rate. Monitoring the reaction by PSI-ESI-(-)MS on neutral and negatively charged substrates at variety of concentrations and conditions did not reveal any detectable anionic palladium complexes. Likewise no evidence of carbopalladation and relevant intermediates in the absence of a base was observed.

A mechanistic investigation of hydrodehalogenation using ESI-MS.

The rate of hydrodehalogenation of aryl iodides with a palladium catalyst in methanol exhibits a strong primary kinetic isotope effect from both CD3OD and CH3OD, suggesting that deprotonation plays a major role in the mechanism.

An Unexpected Pathway for Ligand Substitution in an Aryl Halide Complex of Palladium.

A supposed spectator ligand plays a crucial role in a seemingly simple ligand substitution reaction on palladium. Continuous monitoring by ESI-MS reveals all the details of an initial fast displacement of iodide by an incoming phosphine ligand, and of the recoordination of iodide that prompts the displacement of the bidentate ligand actually being substituted. An apparent double substitution and subsequent isomerization can be readily explained by two fast and one slow ligand substitution reactions.

Synthesis and characterization of a new class of anti-angiogenic agents based on ruthenium clusters.

New triruthenium-carbonyl clusters derivatized with glucose-modified bicyclophosphite ligands have been synthesized. These compounds were found to have cytostatic and cytotoxic activity and depending on the number of bicyclophosphite ligands, and could be tuned for either anti-cancer or specific anti-angiogenic activity. While some compounds had a broad cellular toxicity profile in several cell types others showed endothelial cell specific dose-dependent anti-proliferative and anti-migratory efficacy. A profound inhibition of angiogenesis was also observed in the in vivo chicken chorioallantoic membrane (CAM) model, and consequently, these new compounds have considerable potential in drug design, e.g. for the treatment of cancer.