Gas-Phase and Computational Study of Identical Nickel- and Palladium-Mediated Organic Transformations Where Mechanisms Proceeding via M(II) or M(IV) Oxidation States Are Determined by Ancillary Ligands

Ligand effect on Ru-centered species toward methane activation

Ligands have been known to profoundly affect the chemical transformations of methane, yet significant challenges remain in shedding light on the underlying mechanisms. Here, we demonstrate that the conversion of methane can be regulated by Ru centered cations with a series of ligands (C, CH, CNH, CHCNH). Gas-phase experiments complemented by theoretical dynamic analysis were performed to explore the essences and principles governing the ligand effect. In contrast to the inert Ru+, [RuC]+, and [RuCNH]+ toward CH4, the dehydrogenation dominates the reaction of ligand-regulated systems [RuCH]+/CH4 and [RuCHCNH]+/CH4. In active cases, CH acts as active sites, and regulates the activation of CH4 assisted by the "seemingly inert" CNH ligand.

Ion mobility mass spectrometry uncovers regioselectivity in the carboxylate-assisted C-H activation of palladium N-heterocyclic carbene complexes

Carboxylate-assisted Pd-catalyzed C-H bond activation constitutes a mild and versatile synthetic tool to efficiently and selectively cleave inert C-H bonds. Herein, we demonstrate a simple method to experimentally evaluate both reactivity and selectivity in such systems using mass spectrometry (MS) methods. The N-heterocyclic carbene (NHC) cations [(NHC)PdX]+, bearing as X- ligand bases commonly used to promote the C-H activation (carboxylates and bicarbonate), are generated in the gas-phase by ESI-MS. Their C-H bond activation at the N-bound groups of the NHC is then studied using Collision Induced Dissociation (CID) experiments. Ion Mobility Spectrometry (IM)-MS is exploited to identify a number of regioisomers associated with the distinctive site selective C-H activations. It is demonstrated that such C-H activation concomitant with acetic acid release occurs from a mixture of activated [(NHC-H)Pd(CH3CO2H)]+ and non-activated [(NHC)Pd(CH3CO2)]+ complexes. The identity of the X-type ligands (X = Cl-, carboxylates and bicarbonate) has a significant impact on the regioisomer branching ratio upon CID conditions. IM-MS in conjunction with a DFT mechanistic study is presented for the acetate-assisted C-H activation of the [(NHC)Pd(CH3CO2)]+ cation featuring butyl and aryl as N-donor groups.

Microscopic Reactivity of Phenylferrate Ions toward Organyl Halides

Despite its practical importance, organoiron chemistry remains poorly understood due to its mechanistic complexity. Here, we focus on the oxidative addition of organyl halides to phenylferrate anions in the gas phase. By mass-selecting individual phenylferrate anions, we can determine the effect of the oxidation state, the ligation, and the nuclearity of the iron complex on its reactions with a series of organyl halides RX. We find that Ph2 Fe(I)- and other low-valent ferrates are more reactive than Ph3 Fe(II)- ; Ph4 Fe(III)- is inert. The coordination of a PPh3 ligand or the presence of a second iron center lower the reactivity. Besides direct cross-coupling reactions resulting in the formation of RPh, we also observe the abstraction of halogen atoms. This reaction channel shows the readiness of organoiron species to undergo radical-type processes. Complementary DFT calculations afford further insight and rationalize the high reactivity of the Ph2 Fe(I)- complex by the exothermicity of the oxidative addition and the low barriers associated with this reaction step. At the same time, they point to the importance of changes of the spin state in the reactions of Ph3 Fe(II)- .

Solvent-Controlled Polymerization of Molecular Strontium Vanadate Monomers into 1D Strontium Vanadium Oxide Chains

We report the polymerization of a solvent-stabilized molecular strontium vanadium oxide monomer into infinite 1D chains. Supramolecular polymerization is triggered by controlled solvent-exchange, which leads to oligomer and polymer formation. Mechanistic insights into the chain formation were obtained by solid-state, solution, and gas-phase studies. The study shows how reactivity control of molecular metal oxides can be used to assemble complex inorganic polymeric structures.

Gas-phase functionalized carbon-carbon coupling reactions catalyzed by Ni (II) complexes

Gas-phase C-C coupling reactions mediated by Ni (II) complexes were studied using a linear quadrupole ion trap mass spectrometer. Ternary nickel cationic carboxylate complexes, [(phen)Ni (OOCR¹ )]⁺ (where phen = 1,10-phenanthroline), were formed by electrospray ionization. Upon collision-induced dissociation (CID), they extrude CO₂ forming the organometallic cation [(phen)Ni(R¹ )]⁺ , which undergoes gas-phase ion-molecule reactions (IMR) with acetate esters CH₃ COOR² to yield the acetate complex [(phen)Ni (OOCCH₃ )]⁺ and a C-C coupling product R¹ -R² . These Ni(II)/phenanthroline-mediated coupling reactions can be performed with a variety of carbon substituents R¹ and R² (sp³ , sp² , or aromatic), some of them functionalized. Reaction rates do not seem to be strongly dependent on the nature of the substituents, as sp³ -sp³ or sp² -sp² coupling reactions proceed rapidly. Experimental results are supported by density functional theory calculations, which provide insights into the energetics associated with the C-C bond coupling step.

Mechanistic understanding of catalysis by combining mass spectrometry and computation

The combination of mass spectrometry and computational chemistry has been proven to be powerful for exploring reaction mechanisms. The former provides information of reaction intermediates, while the latter gives detailed reaction energy profiles.