A reactivity map for oxidative addition enables quantitative predictions for multiple catalytic reaction classes

Making accurate, quantitative predictions of chemical reactivity based on molecular structure is an unsolved problem in chemical synthesis, particularly for complex molecules. We report a generally applicable, mechanistically based structure-reactivity approach to create a quantitative model for the oxidative addition of (hetero)aryl electrophiles to palladium(0), which is a key step in myriad catalytic processes. This model links simple molecular descriptors to relative rates of oxidative addition for 79 substrates, including chloride, bromide and triflate leaving groups. Because oxidative addition often controls the rate and/or selectivity of palladium-catalyzed reactions, this model can be used to make quantitative predictions about catalytic reaction outcomes. Demonstrated applications include a multivariate linear model for the initial rate of Sonogashira coupling reactions, and successful site-selectivity predictions for a series of multihalogenated substrates relevant to the synthesis of pharmaceuticals and natural products

Trichloro(Dinitrogen)platinate(II)

Zeise’s salt, [PtCl3(H2C=CH2)]–, is the oldest known organometallic complex, featuring ethylene strongly bound to a platinum salt. Many derivatives are known, but none involving dinitrogen, and indeed dinitrogen complexes are unknown for both platinum and palladium. Electrospray ionization mass spectrometry of K2[PtCl4] solutions generate strong ions corresponding to [PtCl3(N2)]–, whose identity was confirmed through ion mobility spectroscopy and MS/MS experiments that proved it to be distinct from its isobaric counterparts [PtCl3(C2H4)]– and [PtCl3(CO)]–. Computational analysis established a gas-phase platinum-dinitrogen bond strength of 116 kJ mol-1, substantially weaker than the ethylene and carbon monoxide analogues but stronger than for polar solvents such as water, methanol and dimethylformamide, and strong enough that the calculated N-N bond length of 1.119 Å represents weakening to a degree typical of isolated dinitrogen complexes. </p

An Information-Rich Graphical Representation of Catalytic Cycles

Catalytic reactions are limited in their turnover by certain steps in the cycle. We present a free, open-source, web-based interface to generate visualizations of the rate constants of various steps in the cycle. Population of a web form using known data will generate a highly customizable graphic for annotation by the user to represent their chemistry.</p

Gas-Phase Oxidation of Reactive Organometallic Ions

Analysis of highly reactive compounds at very low concentration in solution using electrospray ionization mass spectrometry requires the use of exhaustively purified solvents. It has generally been assumed that desolvation gas purity needs to be similarly high, and so most chemists working in this space have relied upon high purity gas. However, the increasingly competitiveness of nitrogen generators, which provide gas purity levels that vary inversely with flow rate, prompted an investigation of the effect of gas-phase oxygen on the speciation of ions. For moderately oxygen sensitive species such as phosphines, no gas-phase oxidation was observed. Even the most reactive species studied, the reduced titanium complex [Cp2Ti(NCMe)2]+[ZnCl3]– and the olefin polymerization precatalyst [Cp2Zr(µ-Me)2AlMe2]+ [B(C6F5)4]–, only exhibited detectable oxidation when they were rendered coordinatively unsaturated through in-source fragmentation. Computational chemistry allowed us to find the most plausible pathways for the observed chemistry in the absence of observed intermediates. The results provide insight into the gas-phase oxidation of reactive species and should assure experimentalists that evidence of significant oxidation is likely a solution rather than a gas-phase process, even when relatively low-purity nitrogen is used for desolvation

Continuous Addition Kinetic Elucidation: Catalyst and Reactant Order, Rate Constant, and Poisoning from a Single Experiment

Kinetic analysis of catalytic reactions is a powerful tool for mechanistic elucidation but is often challenging to perform. Establishing order in a catalyst is achieved by running several reactions at different loadings, which is complicated by the challenge of maintaining consistent run-to-run experimental conditions. We present Continuous Addition Kinetic Elucidation (CAKE), which involves steadily injecting catalyst into the reaction, and following reaction progress over time to generate a plot whose shape is dependent only on the order in reactant and in catalyst. Modelling the curve (using a convenient web tool) allows the catalyst and reactant order to be determined, as well as the rate constant and the amount of any catalyst poison present

Mechanistic study of the atomic layer deposition of cobalt: A combined mass spectrometric and computational approach

Cobaltcarbonyl-tert-butylacetylene (CCTBA) is a conventional precursor for the selective atomic layer deposition of Co onto silica surfaces. However, the limited understanding of the deposition mechanism of such cobalt precursors curbs rational improvements on their design for increased efficiency and tuneable selectivity. The impact of using a less reactive internal alkyne to a terminal alkyne was investigated using experimental and computational methods. Electrospray-ionization mass spectrometry was used to monitor the formation of CCTBA analogs and study their gas phase decomposition pathways. Gas phase analysis show that an internal alkyne dissociates at slightly lower energies than a terminal alkyne, suggesting that an internal alkynyl ligand may be more suited to low temperature ALD. Furthermore, the less reactive internal alkyne will result in fewer carbon impurities embedded in surfaces, in particular due to its reduced reactivity with Si-H bonds on the surface of Si wafers. Computational analysis also predicts increased surface binding in the metal centers of the internal alkynyl complex