42860-64-0Relevant academic research and scientific papers
Cyanide Docking and Linkage Isomerism in Models for the Artificial [FeFe]-Hydrogenase Maturation Process
Sil, Debangsu,Martinez, Zachary,Ding, Shengda,Bhuvanesh, Nattamai,Darensbourg, Donald J.,Hall, Michael B.,Darensbourg, Marcetta Y.
supporting information, p. 9904 - 9911 (2018/07/25)
Linkage isomerization of the cyanide on the [2Fe] subsite of the [FeFe]-H2ase active site was reported to occur during the docking of various synthetic diiron complexes onto a carrier protein, apo-HydF, as the initial step for the artificial maturation of the [FeFe]-H2ase enzyme (Berggren et al., Nature, 2013, 499, 66-70). An investigation of our triiron organometallic models (FeFe-CN/NC-Fe′) revealed that, once a Fe-CN-Fe connection is formed, high barriers prevent such cyanide linkage isomerization (Chem. Sci., 2016, 7, 3710-3719). To explore effects of variable oxidation states of the receiver unit, we introduce copper(I/II) fragments, precedented in Holm's models of cytochrome c oxidase to induce cyanide isomerization (Cu-CN/NC-Fe), to the diiron synthetic analogues of [FeFe]-H2ase. For comparison, a zinc variant of the cytochrome c oxidase model is also examined. According to the oxidation state of copper, a cyanide flip was induced during the formation of both Zn-NC-Cu and FeFe-CN-Cu complexes. Density functional theory calculations are used to predict the mechanisms for such linkage isomerization and account for optimal conditions including oxidation states of metals, spin states, and solvation. These results on synthetic paradigms imply a role for oxidation state control of cyanide isomerization during hydrogenase active site assembly.
Mechanisms of catalyst poisoning in palladium-catalyzed cyanation of haloarenes. Remarkably facile C-N bond activation in the [(Ph3P) 4Pd]/[Bu4N]+ CN- system
Erhardt, Stefan,Grushin, Vladimir V.,Kilpatrick, Alison H.,Macgregor, Stuart A.,Marshall, William J.,Roe, D. Christopher
, p. 4828 - 4845 (2008/09/21)
Reaction paths leading to palladium catalyst deactivation during cyanation of haloarenes (eq 1) have been identified and studied. Each key step of the catalytic loop (Scheme 1) can be disrupted by excess cyanide, including ArX oxidative addition, X/CN exchange, and ArCN reductive elimination. The catalytic reaction is terminated via the facile formation of inactive [(CN) 4Pd]2-, [(CN)3PdH]2-, and [(CN) 3PdAr]2-. Moisture is particularly harmful to the catalysis because of facile CN- hydrolysis to HCN that is highly reactive toward Pd(0). Depending on conditions, the reaction of [(Ph 3P)4Pd] with HCN in the presence of extra CN- can give rise to [(CN)4Pd]2- and/or the remarkably stable new hydride [(CN)3PdH]2- (NMR, X-ray). The X/CN exchange and reductive elimination steps are vulnerable to excess CN- because of facile phosphine displacement leading to stable [(CN)3PdAr] 2- that can undergo ArCN reductive elimination only in the absence of extra CN-. When a quaternary ammonium cation such as [Bu 4N]+ is used as a phase-transfer agent for the cyanation reaction, C-N bond cleavage in the cation can occur via two different processes. In the presence of trace water, CN- hydrolysis yields HCN that reacts with Pd(0) to give [(CN)3PdH]2-. This also releases highly active OH- that causes Hofmann elimination of [Bu 4N]+ to give Bu3N, 1-butene, and water. This decomposition mode is therefore catalytic in H2O. Under anhydrous conditions, the formation of a new species, [(CN)3PdBu]2-, is observed, and experimental studies suggest that electron-rich mixed cyano phosphine Pd(0) species are responsible for this unusual reaction. A combination of experimental (kinetics, labeling) and computational studies demonstrate that in this case C-N activation occurs via an SN2-type displacement of amine and rule out alternative 3-center C-N oxidative addition or Hofmann elimination processes.
