Rieke Zinc Research Articles

Reactivity Differences of Rieke Zinc Arise Primarily from Salts in the Supernatant, Not in the Solids.

Contrary to prevailing thought, the salt content of supernatants is found to dictate reactivity differences of different preparation methods of Rieke zinc toward oxidative addition of organohalides. This conclusion is established through combined single-particle microscopy and ensemble spectroscopy experiments, coupled with careful removal or keeping of the supernatants during Rieke zinc preparations. Fluorescence microscopy experiments with single-Rieke-zinc-particle resolution determined the microscale surface reactivity of the Rieke zinc in the absence of supernatants, thus pinpointing its inherent reactivity independent of the convoluting supernatant composition. In parallel experiments, scanning electron microscopy, energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, and inductively coupled plasma-mass spectrometry characterized the zinc metal chemical composition at the bulk and single-particle levels. Proton nuclear magnetic resonance spectroscopy kinetics characterized bench-scale Rieke zinc reactivity in the presence and absence of different supernatants and exogenous salt additives. Together, these experiments show that the differences in reactivity from sodium-reduced vs lithium-reduced Rieke zinc arise from the residual salts in the supernatant rather than the differing salt compositions of the solids. This supernatant salt also determines the structure of the ultimate organozinc product, generating either the diorganozinc or monoorganozinc halide complex. That different organozinc complexes formed upon direct insertion to different preparations of Rieke zinc was not previously reported, despite Rieke zinc's widespread use. These findings impact organozinc-reagent and nanomaterial synthesis by showing that, unexpectedly, desired Rieke zinc reactivity can be achieved through simple addition of soluble salts to solutions that were used to prepare the metals─a substantially easier synthetic manipulation than solid composition and morphology control.

A strongly twisted SiSi bond with resemblance to a buckled dimer in an unexpected isomer of hexasilabenzene.

The reductive debromination of {N(SiMe3)Ph}SiBr31 with Rieke magnesium yields the six-vertex amido-substituted silicon cluster 2 with zwitterionic character that represents an unprecedented isomer of hexasilabenzene. The topology of Si1 and Si2 in 2 has bonding features of a highly twisted disilene and resembles that of a buckled dimer of Si(100)2 × 1 reconstructed surfaces. Cluster 2 forms the adducts 3 and 4 with NHCMe4 and DMAP, respectively. The NHC adduct 4 additionally coordinates to BH3 which affords the saturated cluster BH3NHCMe4Si6{N(SiMe3)Ph}6 (5). Furthermore, 2 undergoes addition with MeI and iodine to form the halogenated silicon clusters 6 and 7, respectively.

Trapping Experiments during Reductive Debrominations of Aminotribromosilanes with Alkenes

AbstractIn‐situ generated amido‐substituted disilynes (SiMe3)2N−Si≡Si−N(SiMe3)2 1 and (SiMe3)DippN−Si≡Si−N(SiMe3)Dipp 2 were observed examined upon the reductive dehalogenation of the tribromosilanes {N(SiMe3)2}SiBr3 3 and {N(SiMe3)Dipp}SiBr3 4 with Rieke magnesium (Mg*). Both disilynes were trapped with ethylene to yield the double [2+1] and [2+2] cycloaddition products 5 and 6, respectively. The transient disilynes 1 and 2 were investigated with DFT calculations that revealed 1 to feature more triple bond character than 2. The in‐situ generated disilyne 2 was further quenched with 1,5‐cyclooctadiene to yield the double [2+2] cycloaddition product 7. In the presence of cyclooctatetraene, the reductive debromination of 4 with Mg* generates the bromo‐substituted silacyclopentene 8. This species was also isolated with 2,3‐dimethyl‐1,3‐butadiene used as trapping reagent as the major product 9, besides the side product 10, that comprises two cyclotrisilene rings linked via a butene unit. The formation of 10 shows that a cyclotrisilene can occur as a side product during the reductive debromination of 4 in the presence of the alkene.

Cycloadditions with a Stable Charge-Separated Cyclobutadiene-Type Amido-Substituted Silicon Ring Compound.

Reductive debromination of {N(SiMe3)2}SiBr3 with Rieke magnesium results in the formation of the five‐vertex silicon cluster with one bromine substituent Si5{N(SiMe3)2}5Br, 1, and the cyclobutadiene analogue 2 in a 1:1 ratio. The latter features a planar four‐membered silicon ring with a charge‐separated electronic situation. Two silicon atoms in 2 are trigonal planar and the other two trigonal pyramidal. In cycloadditions with ethylene, diethylacetylene, 1,5‐cyclooctadiene, and 2,3‐dimethyl‐1,3‐butadiene cyclic unsaturated ring compounds (3–6) were formed at room temperature in quantitative reactions. Two of the products (3 and 6) show photochemical isomerization with LED light (λ=405 nm) to afford saturated ring compounds 4 e and 6′.

High‐Performance Magnesium‐Sulfur Batteries Based on a Sulfurated Poly(acrylonitrile) Cathode, a Borohydride Electrolyte, and a High‐Surface Area Magnesium Anode

AbstractPost‐lithium‐ion battery technology is considered a key element of future energy storage and management. Apart from high gravimetric and volumetric energy densities, economic, ecologic and safety issues become increasingly important. In that regards, both the anode and cathode materials must be easily available, recyclable, non‐toxic and safe, which renders magnesium‐sulfur (Mg−S) batteries a promising choice. Herein, we present Mg−S cells based on a sulfurated poly(acrylonitrile) composite cathode (SPAN), together with a halogen‐free electrolyte containing both Mg[BH4]2 and Li[BH4] in diglyme and a high‐specific surface area magnesium anode based on Rieke magnesium powder. These cells deliver discharge capacities of 1400 and 800 mAh/gsulfur with >99 % Coulombic efficiency at 0.1 C and 0.5 C, respectively, and are stable over at least 300 cycles. Energy densities are 470 and 400 Wh/kgsulfur at 0.1 C and 0.5 C, respectively. Rate tests carried out between 0.1 C and 2 C demonstrate good rate capability of the cells. Detailed mechanistic studies based on X‐ray photoelectron spectroscopy and electric impedance spectroscopy are presented.

Synthesis of Electron-Deficient Heteroaromatic 1,3-Substituted Cyclobutyls via Zinc Insertion/Negishi Coupling Sequence under Batch and Automated Flow Conditions.

Synthesis of 1,3-substituted cyclobutyls enabled by zinc insertion into functionalized iodocyclobutyl derivatives followed by Negishi coupling with halo-heteroaromatics is reported. Two distinct sets of conditions were developed; the first involved a two-step batch protocol using activated Rieke zinc, and the second involved a multistep continuous flow process. Both methods showed complementarity and allowed for rapid access to these medicinally relevant motifs, the possibility of scaling up, and automation for library synthesis.

Synthesis of ester side chain functionalized all-conjugated diblock copolythiophenes via the Rieke method

Ester-functionalized all-conjugated diblock copolythiophenes are synthesized by an optimized Rieke zinc protocol. These light-harvesting semiconducting electron donor polymers are of high interest in the field of organic photovoltaics as both the block architecture and the (functionalized) side chains play a crucial role in determining the bulk heterojunction active layer blend (nano)morphology and thereby the final polymer solar cell efficiency and lifetime.

Facile synthesis of 3-(ω-acetoxyalkyl)thiophenes and derived copolythiophenes using Rieke zinc

An optimized synthetic protocol toward highly reactive Rieke zinc is applied for the preparation of a series of ω-(2,5-dibromothiophene-3-yl)alkyl acetate monomers and statistical copolythiophenes derived thereof, with 10% of ester-functionalized side chains. The obtained conjugated polymers are attractive electron donor materials for organic solar cells, notably to increase the thermodynamic stability of the bulk heterojunction polymer:fullerene active layer blend, and are fully characterized by a combination of spectroscopic, thermal analysis and electrochemical techniques.

Cobalt–Magnesium and Iron–Magnesium Complexes with Weakened Dinitrogen Bridges

The cooperative binding of N2 by late transition metals and main-group metals is a promising strategy for N-N bond weakening and activation. We report the use of activated Rieke magnesium for reduction of iron and cobalt complexes supported by bulky β-diketiminate ligands. Binding of N2 is accompanied by assembly of a linear M-NN-Mg-NN-M (M = Co, Fe) core with N-N bonds that are weakened, as judged by infrared spectroscopy. Both the cobalt and iron complexes require THF solvent, because of Mg-THF binding. The cobalt complex can be isolated as a pure solid, but the iron complex is stable only in solution. These results demonstrate the correlation between the binding mode and N-N weakening in heterobimetallic N2 complexes.

Corrigendum: An Efficient and Reliable Procedure for the Preparation of Highly Reactive Rieke Zinc

For the update by S. Kudret, J. D' Haen, L. Lutsen, D. Vanderzande and W. Maes, in Issue 2-3, 2013, pp 569–575 (DOI:10.1002/adsc.201201077), the name of one of the authors was missing. The full list of authors should read as follows: Suleyman Kudret, Jan D' Haen, Wibren D. Oosterbaan, Laurence Lutsen, Dirk Vanderzande and Wouter Maes* The authors apologize for this oversight.

An Efficient and Reliable Procedure for the Preparation of Highly Reactive Rieke Zinc

AbstractRieke zinc has a wide potential for applications in organic chemistry, notably for the synthesis of highly chemoselective organozinc reagents. However, due to the rather unreliable preparation method, leading to large batch to batch variations, its use has been rather limited. Rieke zinc is commonly prepared by the reduction of zinc chloride with lithium using a stoichiometric amount of naphthalene. In our hands, it was observed that the reaction outcome was highly dependent on the naphthalene source and purity grade. The presence of benzothiophene seems crucial to avoid coagulation of the zinc particles and the amount of benzothiophene has a large effect on the physical properties and the reactivity of the resulting zinc powder. Accordingly, highly reactive Rieke zinc was easily prepared from zinc chloride by adding an optimum amount (3 mol% with regard to ZnCl2) of benzothiophene into the lithium naphthalenide solution (prepared in situ). The Rieke zinc obtained in this way was successfully employed in the so‐called “Rieke method” to prepare regioregular poly(3‐hexylthiophene) (P3HT). The novel approach enables preparation of Rieke zinc in a reproducible manner, which considerably facilitates its use in both small molecule and polymer synthesis.

Polyunsaturated Alkyl Amides from Echinacea: Synthesis of Diynes, Enynes, and Dienes

The synthesis of 20 alkyl amides, including 15 naturally occurring polyunsaturated alkyl amides previously identified from Echinacea spp. (1-13 and 62) or from Achilla sp. (55) and five previously unknown geometric isomers (23, 28, 67, 73, and 80), is described. Importantly, these amides include all of the major alkyl amides present in commercially used Echinacea extracts. The syntheses demonstrate methodology used for constructing alkyl amides containing conjugated diyne and isomerically pure enyne and diene moieties and may be adapted easily for the preparation of other alkyl amides present in Echinacea spp. Terminal-conjugated diynes were prepared by a Cadiot-Chodkiewitz coupling/deprotection sequence utilizing a protected bromoacetylene, and methyl-substituted diynes were made via a base-catalyzed rearrangement of terminal-skipped diynes. Conjugated dienes were prepared conveniently and with high stereoselectivity by the reduction of enynes or diynes with Rieke zinc. With the exception of 1-2 and 11-12, the alkyl amides are synthesized here for the first time, and their NMR data are consistent with that of the reported isolated natural compounds.

ChemInform Abstract: 5‐Bromo‐2‐pyridylzinc Reagent; Direct Preparation and Its Coupling Reactions.

AbstractA practical route for the synthesis of differently 2‐substituted 5‐bromopyridines is developed by generating stable pyridylzinc iodide from 5‐bromo‐2‐iodopyridine and Rieke zinc followed by coupling with activated organic halides.

ChemInform Abstract: 2‐Pyridyl and 3‐Pyridylzinc Bromides: Direct Preparation and Coupling Reaction.

Abstract2‐Pyridyl and 3‐pyridylzinc bromides are readily prepared from the corresponding pyridylbromides and Rieke zinc.

ChemInform Abstract: The Use of Rieke Zinc Metal in the Selective Reduction of Alkynes.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

2-Pyridyl- and 3-Pyridylzincs: Direct Preparation and Coupling Reaction

A convenient synthetic approach to the direct preparation of 2-pyridyl- and 3-pyridyl­zinc bromides has been investigated using Rieke zinc starting from 2- and 3-bromopyridine, respectively. A variety of different electrophiles like acid chlorides or aryl halides have been coupled with the resulting organozinc reagents to give the cross-coupling products in moderate to good yields.

2-Pyridyl and 3-pyridylzinc bromides: direct preparation and coupling reaction

A facile synthetic approach to the direct preparation of 2-pyridyl and 3-pyridylzinc bromides has been demonstrated using Rieke zinc with 2-bromopyridine and 3-bromopyridine, respectively. A variety of different electrophiles have been coupled with the resulting organozinc reagents to give the corresponding cross-coupling products in moderate to good yields.

A Facile Synthetic Approach to the Preparation of 3-Pyridyl Derivatives: Preparations and Coupling Reactions of 3-Pyridylzinc and Its Analogues

A facile synthetic approach to the direct preparation of 3-pyridylzinc bromide has been demonstrated using Rieke zinc with 3-bromopyridine in the presence of a catalytic amount of lithium chloride. A variety of different electrophiles have been coupled to give the corresponding cross-coupling products in moderate to good yields. Also, this methodology has been expanded to the preparation of the corresponding organozinc reagents of 3-bromopyridine analogues.

Synthesis and Reactions of meso-Triphenylporphyrin Grignard Reagent

(5-Bromo-10,15,20-triphenylporphyrinato)nickel(II) reacts with Rieke magnesium in DME to produce the correspondding porphyrin Grignard reagent. Its subsequent reactions with aldehydes and ketones resulted in the formation of desired mesa-alcohol-substituted porphyrins Ni7 and unexpected meso-ketone-substituted porphyrins Ni4, respectively.

Rieke Zinc as a Reducing Agent for Common Organic Functional Groups.

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