Large effect of a small substitution: competition of dehydration with charge retention and coulomb explosion in gaseous [(bipy(R))Au(mu-O)2Au(bipy(R))]2+ dications

Metalation of a gold(I) metalloligand with P,C-bridging phosphinoferrocenyl groups enables construction of defined multimetallic arrays

The reactions of gold(I) metalloligand [Au2{µ(P,C)-Ph2Pfc}2], where fc stands for ferrocene-1,1ʹ-diyl, with bare or ligand-stabilised group 11 metal ions open an access to diverse oligometallic clusters stabilised by Au-Au, Au-Ag...

Rollover Cyclometalation as a Valuable Tool for Regioselective C-H Bond Activation and Functionalization

Rollover cyclometalation constitutes a particular case of cyclometallation reaction. This reaction occurs when a chelated heterocyclic ligand loses its bidentate coordination mode and undergoes an internal rotation, after which a remote C-H bond is regioselectively activated, affording an uncommon cyclometalated complex, called "rollover cyclometalated complex". The key of the process is the internal rotation of the ligand, which occurs before the C-H bond activation and releases from coordination a donor atom. The new "rollover" ligand has peculiar properties, being a ligand with multiple personalities, no more a spectator in the reactivity of the complex. The main reason of this peculiarity is the presence of an uncoordinated donor atom (the one initially involved in the chelation), able to promote a series of reactions not available for classic cyclometalated complexes. The rollover reaction is highly regioselective, because the activated C-H bond is usually in a symmetric position with respect to the donor atom which detaches from the metal stating the rollover process. Due to this novel behavior, a series of potential applications have appeared in the literature, in fields such as catalysis, organic synthesis, and advanced materials.

A novel approach for rhodium(iii)-catalyzed C-H functionalization of 2,2'-bipyridine derivatives with alkynes: a significant substituent effect

We described a novel approach for the C-H functionalization of 2,2'-bipyridine derivatives with alkynes. DFT calculations and experimental data showed a significant substituent effect at the 6-position of 2,2'-bipyridine, which weakened the adjacent N-Rh bond and provided the possibility of subsequent rollover cyclometalation, C-H activation, and functionalization.

Rh(iii)-Catalyzed switchable C–H functionalization of 2-(1H-pyrazol-1-yl)pyridine with internal alkynes

We reported a Rh(iii)-catalyzed switchable C–H functionalization of 2-(1H-pyrazol-1-yl)pyridine with internal alkynes, which provided diversiform functionalized N,N-bidentate chelating compounds.

Rhodium(III)-Catalyzed Regioselective C3-H Acylmethylation of [2,2'-Bipyridine]-6-carboxamides with Sulfoxonium Ylides

A rhodium(III)-catalyzed C-H acylmethylation of tridentate [2,2'-bipyridine]-6-carboxamides was developed. A variety of [2,2'-bipyridine]-6-carboxamides could be monoalkylated exclusively at the C3 position with sulfoxonium ylides as carbene precursors, giving 3-alkylated products in high yields. This protocol proceeds through a rollover cyclometalation pathway, has a broad range scope of substrates, and exhibits excellent functional group tolerance.

Palladium-Catalyzed Site-Selective C-H Arylation of 2,2'-Bipyridine-6-carboxamides via a Rollover Cyclometalation Pathway

The first example of Pd(II)-catalyzed arylation of 2,2'-bipyridine-6-carboxamides via a rollover cyclometalation pathway is reported. A diverse range of (hetero)aryl iodides could be directly coupled with various 2,2'-bipyridine-6-carboxamides in exclusive site-selectivity, which offers a distinct entry to arylated 2,2'-bipyridine-6-carboxamides. A preliminary mechanistic study supports the Pd(II)-rollover cyclometalation pathway.

Mechanistic Studies on Ruthenium(II)-Catalyzed Base-Free Transfer Hydrogenation Triggered by Roll-Over Cyclometalation

The synthesis of 2-substituted pyridine-pyrimidine ligands and their complexation with arene ruthenium(II) chloride moieties is reported. Depending on the electronic and steric influences of the ligand, the catalysts undergo CH activation by roll-over cyclometalation. This process opens up the route to the catalytic transfer hydrogenation of ketones with isopropanol as the hydrogen source under base-free and mild conditions. Barriers related to the roll-over cyclometalation process can be determined experimentally by collision-induced dissociation ESI mass spectrometry. They are supported by DFT calculations and allow the classification of the ligands according to their electronic and steric properties, which is also in accordance with critical bond parameters derived from X-ray structure data. DFT calculations furthermore reveal that the formation of a ruthenium(II) hydrido species is plausible through β-hydride elimination from isopropanol.

Rhodium-catalyzed selective CH functionalization of NNN tridentate chelating compounds via a rollover pathway

Reported herein is the first example of the Rh(NHC)-catalyzed selective bis C-H alkylation of NNN tridentate chelating compounds in reaction with alkenes. The observed excellent site-selectivity can readily be explained by the postulated rollover pathway in the C-H bond activation step. The reaction is highly facile affording bis-alkylated tridentate products in high yields over a broad range of versatile heteroarene substrates and alkene reactants including ethylene gas, thus enabling its applications to be feasible in coordination and synthetic chemistry.

P,C-bond cleavage in the ligand sphere of a nickel(ii) complex

P,C-bond cleavage at a pyrimidinyl ligand results in a pentacoordinate nickel(ii) complex coordinated by a carbanionic ligand.

The selenite-capped polyoxo-4-aurate(III), [Au(III)4O4(Se(IV)O3)4]4-

The discrete heteropolyaurate [Au(III)(4)O(4)(Se(IV)O(3))(4)](4-) (Au(4)Se(4)) represents only the second member of this class ever reported, and was synthesized via one-pot room temperature condensation in aqueous medium. was structurally characterized in the solid state and in solution by single-crystal XRD, TGA, FT-IR, (77)Se NMR, mass spectrometry and electrochemistry.

Applications of electrospray ionization mass spectrometry in mechanistic studies and catalysis research

Mechanistic studies form the basis for a better understanding of chemical processes, helping researchers develop more sustainable reactions by increasing the yields of the desired products, reducing waste production, and lowering the consumption of resources and energy overall. Conventional methods for the investigation of reaction mechanisms in solution include kinetic studies, isotope labeling, trapping of reactive intermediates, and advanced spectroscopic techniques. Within the past decade, electrospray ionization mass spectrometry (ESI-MS) has provided an additional tool for mechanistic studies because researchers can directly probe liquid samples by mass spectrometry under gentle conditions. Specifically, ESI-MS allows researchers to identify the molecular entities present in solution over the course of a chemical transformation. ESI-MS is particularly useful for investigations of organic reactions or metal catalysis that involve ionic intermediates. Accordingly, researchers are increasingly using ESI-MS in mechanistic studies and catalyst development. However, a further understanding of the ESI process and how it can facilitate mechanistic studies has not accompanied this increased use of the technique. Therefore, at least in part the ESI-MS method not only has offered great promise for the elucidation of reaction mechanisms but also became a black box with the occasional risk of misinterpretation. In this Account, we summarize applications of ESI-MS for synthetic and mechanistic research. Recently researchers have established direct linkages between gas-phase data obtained via ESI-MS and processes occurring in solution, and these results reveal qualitative and quantitative correlations between ESI-MS measurements and solution properties. In this context, time dependences, concentration series, and counterion effects can serve as criteria that allow researchers assess if the gas-phase measurements correlate with the situation in the solution. Furthermore, we report developments that bridge the gap between gas-phase and solution-phase studies. We also describe predictions derived from ESI-MS that have been verified with solution-phase chemistry experiments.

Rh(III)-catalyzed C-H bond activation along with "rollover" for the synthesis of 4-azafluorenes

An intramolecular reaction of 3-alkynyl and 3-alkenyl-2-arylpyridines selectively gave 4-azafluorene compounds in the presence of a catalytic amount of [Cp*RhCl(2)](2) and Cu(OAc)(2). Pyridine-directed C-H bond activation along with "rollover" are likely to be key steps of this transformation.

Aromatic C-H bond activation revealed by infrared multiphoton dissociation spectroscopy

Metal-oxide cations are models of catalyst mediating the C-H bond activation of organic substrates. One of the most powerful reagents suggested in the gas phase is based on CuO(+) . Here, we describe the activation of the aromatic C-H bonds of phenanthroline in its complex with CuO(+) . The reaction sequence starts with a hydrogen atom abstraction by the oxygen atom from the 2-position of the phenanthroline ring, followed by OH migration to the ring. Using infrared multiphoton spectroscopy, it is shown that the reaction can be energetically facilitated by additional coordination of a water ligand to the copper ion. As the reaction is intramolecular, a spectroscopic characterization of the product is mandatory in order to unambiguously address the reaction mechanism.

Complexation between the fungicide tebuconazole and copper(II) probed by electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry (ESI-MS) is used to probe the complex formation between tebuconazole (1) and copper(II) salts, which both are commonly used fungicides in agriculture. Experiments with model solutions containing 1 and CuCl(2) reveal the initial formation of the copper(II) species [(1)CuCl](+) and [(1)(2)CuCl](+) which undergo reduction to the corresponding copper(I) ions [(1)Cu](+) and [(1)(2)Cu](+) under more drastic ionization conditions in the ESI source. In additional experiments, copper/tebuconazole complexes were also detected in samples made from soil solutions of various origin and different amount of mineralization. The direct sampling of such solutions via ESI-MS is thus potentially useful for understanding of the interactions between copper(II) salts and tebuconazole in environmental samples.

Gas-phase fragmentation of deprotonated p-hydroxyphenacyl derivatives

Electrospray ionization of methanolic solutions of p-hydroxyphenacyl derivatives HO-C(6)H(4)-C(O)-CH(2)-X (X = leaving group) provides abundant signals for the deprotonated species which are assigned to the corresponding phenolate anions (-)O-C(6)H(4)-C(O)-CH(2)-X. Upon collisional activation in the gas phase, these anions inter alia undergo loss of a neutral "C(8)H(6)O(2)" species concomitant with formation of the corresponding anions X(-). The energies required for the loss of the neutral roughly correlate with the gas phase acidities of the conjugate acids (HX). Extensive theoretical studies performed for X = CF(3)COO in order to reveal the energetically most favorable pathway for the formation of neutral "C(8)H(6)O(2)" suggest three different routes of similar energy demands, involving a spirocyclopropanone, epoxide formation, and a diradical, respectively.

Intramolecular scrambling of aryl groups in organopalladium complexes [ArPd(PPh3)2]+: from solution to the gas phase, back again, and in-between

Gas-phase experiments are used to probe the intramolecular scrambling of aryl groups between palladium and phosphorus in organopalladium complexes, [ArPd(PPh(3))(2)](+), generated by means of electrospray ionization (ESI). To this aim, ESI mass spectrometry, including tandem mass spectrometric experiments, were carried out on deuterated, non-deuterated, and substituted [ArPd(PPh(3))(2)](+) complexes. The fragment ions obtained from the deuterated parent ions clearly show the occurrence of intramolecular scrambling between the aryl group bound to palladium and the phenyl groups of the phosphine in the gas phase. Fragmentation pathways, supported by a statistical model, are proposed to explain these migrations and the implications for the condensed-phase chemistry are probed experimentally by using ESI mass spectrometry.