Isolation and Structures of Two New Organozinc Anions from Solutions Rich in Halide Ions

Reductive anti-Dizincation of Arylacetylenes

Arylacetylenes undergo anti-1,2-dizincation to afford trans-1,2-dizincioalkenes. The process employs sodium dispersion as a reducing agent and zinc chloride TMEDA complex as a reduction-resistant zinc electrophile. This reductive anti-dizincation contrasts with the conventional additive syn-dimetalation like silylzincation. The resulting dizincated alkenes undergo the cross-coupling to yield multi-substituted alkenes stereoselectively.

Atroposelective NiII -Catalyzed Cross-Coupling Reactions Enable a Deeper Understanding of Negishi Couplings: Isolation and Application of Solid Aryl Higher-Order Zincates

The Negishi cross-coupling reactions involves the application of organozinc reagents and is a highly versatile reaction in synthetic organic chemistry. The transmetallation step plays a pivotal role in the mechanism of these types of cross-coupling reactions. In this study, mechanistic investigations are presented indicating that higher-order zincates are the transmetallating active species in Pd- and Ni-catalyzed Negishi cross-coupling reactions. These findings are supported by halide salt addition experiments and by obtaining a single X-ray crystal structure of the solid monoaryl higher-order zincate [1-NaphthylZnX3 ]2- Mg(THF)2 2+ . The procedure developed in this work was further applied to the synthesis of various monoaryl higher-order zincates, after which their synthetic usefulness in terms of high reactivity towards transmetallation in Negishi cross-couplings, as well as stability, was exemplified in several reactions.

Hydrogen-bonded networks in oxygen-coordinated monoamide complexes of zinc(II)

The preparation of the bulky secondary amide N-(2,6-diisopropylphenyl)-2,2-dimethylpropanamide and the determination of its crystal structure at 173(2) K are reported. The structure displays disorder of the tBu methyl groups due to thermal motion and an infinite N–H····O=C hydrogen-bonded chain described by a [Formula: see text] graph set. Reaction of this amide with ZnCl2 or ZnBr2 in tetrahydrofuran (THF) results in dihalo-(tetrahydrofurano)-(N-(2,6-diisopropylphenyl)–2,2-dimethylpropanamido)-zinc(II) complexes (Cl, Br) for which the crystal structures have also been determined. These complexes, as well as a chloroform solvate of the dichloro-complex, contain N–H····X–Zn hydrogen-bonded chains described by [Formula: see text] graph sets. Evaporative crystallization results in the loss of both chloroform and THF to afford crystals determined to be bis(μ2-chloro)-dichloro-bis(N-(2,6-diisopropylphenyl)-2,2-dimethylpropanamido)-dizinc(II) by single crystal X-ray diffraction. This dimeric complex shows a complex network of N–H····Cl–Zn hydrogen bonds describable by [Formula: see text], [Formula: see text], and [Formula: see text] chains, small [Formula: see text] molecular “squares”, and larger [Formula: see text] rings.

Crystal structure of bis(ethyltriphenylphos-phonium) tetrabromidozincate(II), C40H40Br4P2Zn

C40H40Br4P2Zn, monoclinic, Cc (no. 9), a = 12.2430(6) Å, b = 21.120(1) Å, c = 16.405(1) Å, β = 111.015(2)°, V = 3959.7 Å3, Z = 4, Rgt(F) = 0.0443, wRref(F2) = 0.1070, T = 200 K.

A simple complex on the verge of breakdown: isolation of the elusive cyanoformate ion

Why does cyanide not react destructively with the proximal iron center at the active site of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase, an enzyme central to the biosynthesis of ethylene in plants? It has long been postulated that the cyanoformate anion, [NCCO2](-), forms and then decomposes to carbon dioxide and cyanide during this process. We have now isolated and crystallographically characterized this elusive anion as its tetraphenylphosphonium salt. Theoretical calculations show that cyanoformate has a very weak C-C bond and that it is thermodynamically stable only in low dielectric media. Solution stability studies have substantiated the latter result. We propose that cyanoformate shuttles the potentially toxic cyanide away from the low dielectric active site of ACC oxidase before breaking down in the higher dielectric medium of the cell.

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.