C−C Bond Cleavage of Acetonitrile by a Carbonyl Iron Complex with a Silyl Ligand

Unprecedented iron-assisted room temperature synthesis of AgCN using acetonitrile

A straightforward and convenient approach for producing AgCN at room temperature using acetonitrile as a source has been developed, employing various iron salts. To date, there have been no prior studies documenting the synthesis of AgCN by cleaving the C-CN bond in acetonitrile with the use of iron salts. The resulting highly crystalline material was subjected to characterization through XRD and FT-IR analysis. Additionally, the same process was used for C-CN bond breaking using Ag2S or via the formation of an AgSxOy composite. Consequently, this report is primarily dedicated to exploring the efficacy of different iron salts in breaking the C-CN bond in CH3CN. A theoretical investigation of the proposed experimental scheme has also been performed to confer the feasibility of the reaction.

Direct transformation of nitriles to cyanide using chloride anion as catalyst

A simple method is explored for the scission of C-CN bonds into aldehyde and CN- in air. The transformation was mediated by chloride anions. The cyanide anions were extracted from the reaction solution to form (Et4N)2[Zn(CN)4] and (Et4N)2[Ni(CN)4]. A chloride-induced reaction mechanism is proposed based on experimental studies and DFT calculations. This work might guide the study of halogen catalysts for C-C bond cleavage.

Diiron Aminocarbyne Complexes with NCE− Ligands (E = O, S, Se)

Diiron μ-aminocarbyne complexes [Fe2Cp2(NCMe)(CO)(μ-CO){μ-CN(Me)(R)}]CF3SO3 (R = Xyl, [1aNCMe]CF3SO3; R = Me, [1bNCMe]CF3SO3; R = Cy, [1cNCMe]CF3SO3; R = CH2Ph, [1dNCMe]CF3SO3), freshly prepared from tricarbonyl precursors [1a–d]CF3SO3, reacted with NaOCN (in acetone) and NBu4SCN (in dichloromethane) to give [Fe2Cp2(kN-NCO)(CO)(μ-CO){μ-CN(Me)(R)}] (R = Xyl, 2a; Me, 2b; Cy, 2c) and [Fe2Cp2(kN-NCS)(CO)(μ-CO){μ-CN(Me)(CH2Ph)}], 3 in 67–81% yields via substitution of the acetonitrile ligand. The reaction of [1aNCMe–1cNCMe]CF3SO3 with KSeCN in THF at reflux temperature led to the cyanide complexes [Fe2Cp2(CN)(CO)(μ-CO){μ-CNMe(R)}], 6a–c (45–67%). When the reaction of [1aNCMe]CF3SO3 with KSeCN was performed in acetone at room temperature, subsequent careful chromatography allowed the separation of moderate amounts of [Fe2Cp2(kSe-SeCN)(CO)(μ-CO){μ-CN(Me)(Xyl)}], 4a, and [Fe2Cp2(kN-NCSe)(CO)(μ-CO){μ-CN(Me)(Xyl)}], 5a. All products were fully characterized by elemental analysis, IR, and multinuclear NMR spectroscopy; moreover, the molecular structure of trans-6b was ascertained by single crystal X-ray diffraction. DFT calculations were carried out to shed light on the coordination mode and stability of the {NCSe-} fragment.

Automated Library Generation and Serendipity Quantification Enables Diverse Discovery in Coordination Chemistry

Library generation experiments are a key part of the discovery of new materials, methods, and models in chemistry, but the question of how to generate high quality libraries to enable discovery is nontrivial. Herein, we use coordination chemistry to demonstrate the automation of many of the workflows used for library generation in automated hardware including the Chemputer. First, we explore the target-oriented synthesis of three influential coordination complexes, to validate key synthetic operations in our system; second, the generation of focused libraries in chemical and process space; and third, the development of a new workflow for prospecting library formation. This involved Bayesian optimization using a Gaussian process as surrogate model combined with a metric for novelty (or serendipity) quantification based on mass spectrometry data. In this way, we show directed exploration of a process space toward those areas with rarer observations and build a picture of the diversity in product distributions present across the space. We show that this effectively "engineers" serendipity into our search through the unexpected appearance of acetic anhydride, formed in situ, and solvent degradation products as ligands in an isolable series of three Co(III) anhydride complexes.

Recent advances in C–CN and C–H bond activation of green nitrile (MeCN) for organo-complexation, cyanation and cyanomethylation

The use of green and inexpensive organic nitrile (MeCN) as a cyano and cyano-methyl source for organo-complexation, cyanation, and cyanomethylation is reviewed.

Silylpalladium Cations Enable the Oxidative Addition of C(sp3)-O Bonds

The synthesis and characterization of the room-temperature and solution-stable silylpalladium cations (PCy₃)₂Pd-SiR₃⁺(C₆F₅)₄B^- (SiR₃ = SiMe₂Et, SiHEt₂) and (Xantphos)Pd-SiR₃⁺(BAr^f₄) (SiR₃ = SiMe₂Et, SiHEt₂; Xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene; BAr^f₄ = (3,5-(CF₃)₂C₆H₃)₄B^-) are reported. Spectroscopic and ligand addition experiments suggest that silylpalladium complexes of the type (PCy₃)₂Pd-SiR₃⁺ are three-coordinate and T-shaped. Addition of dialkyl ethers to both the PCy₃ and Xantphos-based silylpalladium cations resulted in the cleavage of C(sp³)-O bonds and the generation of cationic Pd-alkyl complexes. Mechanistically enabling is the ability of silylpalladium cations to behave as sources of both electrophilic silylium ions and nucleophilic L_nPd(0).

Imine hydrosilylation using an iron complex catalyst: A computational study

The reaction mechanism for imine hydrosilylation in the presence of an iron methyl complex and hydrosilane was studied using density functional theory at the M06/6-311G(d,p) level of theory. Benzylidenemethylamine (PhCH = NMe) and trimethylhydrosilane (HSiMe₃ ) were employed as the model imine and hydrosilane, respectively. Hydrosilylation has been experimentally proposed to occur in two stages. In the first stage, the active catalyst (CpFe(CO)SiMe₃ , 1) is formed from the reaction of pre-catalyst, CpFe(CO)₂ Me, and hydrosilane through CO migratory insertion into the FeMe bond and the reaction of the resulting acetyl complex intermediate with hydrosilane. In the second stage, 1 catalyzes the reaction of imine with hydrosilane. Calculations for the first stage showed that the most favorable pathway for CO insertion involved a spin state change, that is, two-state reactivity mechanism through a triplet state intermediate, and the acetyl complex reaction with HSiMe₃ follows a σ-bond metathesis pathway. The calculations also showed that, in the catalytic cycle, the imine coordinates to 1 to form an FeCN three-membered ring intermediate accompanied by silyl group migration. This intermediate then reacts with HSiMe₃ to yield the hydrosilylated product through a σ-bond metathesis and regenerate 1. The rate-determining step in the catalytic cycle was the coordination of HSiMe₃ to the three-membered ring intermediate, with an activation energy of 23.1 kcal/mol. Imine hydrosilylation in the absence of an iron complex through a [2 + 2] cycloaddition mechanism requires much higher activation energies. © 2018 Wiley Periodicals, Inc.

Chemistry of iron nitrate-based precursor solutions for spray-flame synthesis

Understanding the chemistry of precursor solutions for spray-flame synthesis is a key step to developing inexpensive and large scale applications for tailored nanoparticles.

Nickel-catalyzed cyanation of aryl halides and triflates using acetonitrile via C-CN bond cleavage assisted by 1,4-bis(trimethylsilyl)-2,3,5,6-tetramethyl-1,4-dihydropyrazine

A catalyst system of [Ni(MeCN)₆](BF₄)₂, 1,10-phenanthroline, and 1,4-bis(trimethylsilyl)-2,3,5,6-tetramethyl-1,4-dihydropyrazine (Si–Me₄-DHP) assisted cyanation of aryl halides in acetonitrile to give the corresponding aryl nitriles.

We developed a non-toxic cyanation reaction of various aryl halides and triflates in acetonitrile using a catalyst system of [Ni(MeCN)₆](BF₄)₂, 1,10-phenanthroline, and 1,4-bis(trimethylsilyl)-2,3,5,6-tetramethyl-1,4-dihydropyrazine (Si–Me₄-DHP). Si–Me₄-DHP was found to function as a reductant for generating nickel(0) species and a silylation reagent to achieve the catalytic cyanation via C–CN bond cleavage.

The molecular mechanism of palladium-catalysed cyanoesterification of methyl cyanoformate onto norbornene

Potential energy surface mapping was completed for the entire catalytic cycle of palladium-catalysed cyanoesterification onto norbornene (NBE) using density functional theory calculations. We found that after the oxidative addition step of the reagent methyl cyanoformate, the reaction proceeds through an insertion of olefin into a Pd(II)-COOMe bond first. Subsequently, reductive elimination occurs by transferring the cyanide group from the Pd center to NBE. This rearrangement is triggered by the rotation of the ester group into a π-interaction with the Pd(II) centre. The regioselectivity of olefin insertion is controlled by ionic and covalent interactions in the precursor π-complex formation step. Importantly, all of the intermediates and transition states along the exo pathway were found to be more stable than the corresponding structures of the endo pathway without any sign of crossing over between the two surfaces via isomerization. The rate-determining step is the reductive elimination despite the fact that the corresponding activation barrier is reduced by conformational changes via the rotation of a MeOOC-C(NBE) bond.

Sandmeyer cyanation of arenediazonium tetrafluoroborate using acetonitrile as a cyanide source

Palladium-catalyzed cyanation of aryldiazonium tetrafluoroborate using acetonitrile as a non-metallic cyanide source was achieved in the presence of Ag₂O under ambient air, eliminating the involvement of highly toxic CuCN used in the traditional Sandmeyer reaction, in which the CN group comes from metallic cyanides.

The origin of exo-selectivity in methyl cyanoformate addition onto the C=C bond of norbornene in Pd-catalyzed cyanoesterification

A computational investigation has been carried out to elucidate the origin of the exclusive exo-selectivity in the Pd-catalyzed cyanoesterification of strained cyclic olefins, norbornene and norbornadiene. A hybrid density functional was selected for the level of theory with a triple-ζ quality basis set, which was proposed in an earlier study to provide an experimentally sound ground state electronic structure description for palladium(ii) and palladium(iv) complexes from multi-edge X-ray absorption spectroscopic measurements. Given that the product of oxidative addition can be isolated, we focused on the olefin coordination as the earliest possible origin of exo-selectivity. The calculated geometric structure for the trans-Pd(CN)(COOR)(PPh3)2 complex at the BHandHLYP/def2TZVP/PCM(toluene) level is in an excellent agreement with its experimental structure from crystallographic measurements. Upon dissociation of one of its phosphane ligands, the coordinatively unsaturated trans-isomer is only 17 kJ mol(-1) away from the isomerization transition state, leading to the 14-electron cis-isomers that are 17 to 37 kJ mol(-1) lower in energy than the trans-isomers. Regardless of the initial complex for olefin coordination, the exo-isomer for the norbornene complex is at least 8 kJ mol(-1) lower than the corresponding endo-isomer. The origin of this considerable difference in Gibbs free energy can be attributed to the remarkably different steric and agostic hydrogen interactions between the methylene and the ethylene bridges of the norbornene and the adjacent cis-ligands at the Pd(II) center.

Transformations of X (C, O, N)-CN Bonds: Cases of Selective X (C, O, N)-C Activation

Activation of C-C, C-N, and C-O bonds has in recent decades been recognized as a valuable strategic objective. While considerable progress has been achieved, many of the more challenging issues, e.g., regioselective activation of specific C-X (C, O, N) bonds, chemoselective cleavage of C_(sp3)-X bonds, enantioselective activation and even the successful application of solid catalysts in such transformations remain elusive. The research disclosed herein summarize recent advances in C-X bond cleavages, including regioselective processes, although the carbon is activated in the form of a cyano group.

C-C bond cleavage in acetonitrile by copper(II)-bipyridine complexes and in situ formation of cyano-bridged mixed-valent copper complexes

Influencing factors, including organic reductant, counterion of copper(II)-bipyridine complex, reaction solvent, molar ratio of copper(II)-bipyridine complex and organic reductant, reaction time and chelating ligand of copper complex, have been extensively investigated on the reaction of copper(II)-bipyridine complex mediated C-C bond cleavage of acetonitrile. Furthermore, in situ formation of a series of cyano-bridged mixed-valent copper complexes has been described in this paper, where twelve new copper complexes with or without the presence of cyanide anions have been yielded and structurally characterized including two novel one-dimensional (1D) mixed-valent copper coordination polymers. In addition, a trinuclear cyano-bridged mixed-valent copper complex 9, which is believed to be the most stable species in this system, shows effective activity in catalyzing Ullmann C-N cross-coupling reactions.