Reductive Elimination from Arylpalladium Cyanide Complexes

Abstract

We report the isolation and characterization of arylpalladium cyanide complexes that undergo reductive elimination to form arylnitriles. The rates of reductive elimination from a series of arylpalladium cyanide complexes reveal that the electronic effects on the reductive elimination from arylpalladium cyanide complexes are distinct from those on reductive reductive eliminations from arylpalladium alkoxo, amido, thiolate, and enolate complexes. Arylpalladium cyanide complexes containing aryl ligands with electron-donating substituents undergo faster reductive elimination of aromatic nitriles than complexes containing aryl ligands with electron-withdrawing substituents. In addition, the transition state for the reductive elimination of the aromatic nitrile is much different from that for reductive eliminations that occur from most other arylpalladium complexes. Computational studies indicate that the reductive elimination of an arylnitrile from Pd(II) occurs through a transition state more closely related in structure and electronic distribution to that for the insertion of CO into a palladiumaryl bond.

A General, Practical Palladium‐Catalyzed Cyanation of (Hetero)Aryl Chlorides and Bromides

“…Recently, Hartwig showed that reductive elimination to form ArCN is slower for electron-deficient aryl groups. [25] That a catalyst based on the larger ligand L2 allows for more facile reductive elimination for electron-deficient substrates is in accord with this view. This method exhibits high tolerance for substrates bearing free N–H or O–H groups, such as primary amides ( 1g ), sulfonamides ( 1h ), anilines ( 1j ), and benzylic alcohols ( 1j ), all of which could be converted to the corresponding benzonitrile using less than 1 mol % Pd.…”

Different Performance of Two Isomeric Phosphinobiphenyl Amidosulfonates in Pd-Catalyzed Cyanation of Aryl Bromides

“…The conversions of the latter substrates were not improved even upon extending the reaction time from 2 h to one day with the sole exception of 4-chloro-1-bromobenzene (7g), for which the conversion to 8g increased from less than 5% to 10% (note: the corresponding amides, possibly resulting from hydrolysis of the nitriles, were detected in only negligible amounts). This striking difference noted for the two classes of substrates may reflect changes in the reaction energetics (reductive elimination of ArCN is slower for electron-poor aryl groups [26]) and also a relatively low stability of the formed catalyst. changes in the reaction energetics (reductive elimination of ArCN is slower for electron-poor aryl groups [26]) and also a relatively low stability of the formed catalyst.…”

“…This striking difference noted for the two classes of substrates may reflect changes in the reaction energetics (reductive elimination of ArCN is slower for electron-poor aryl groups [26]) and also a relatively low stability of the formed catalyst. changes in the reaction energetics (reductive elimination of ArCN is slower for electron-poor aryl groups [26]) and also a relatively low stability of the formed catalyst. In summary, the newly synthesized hydrophilic phosphinobiphenyl ligand L2 afforded less stable and less efficient catalysts for the Pd-catalyzed cyanation of aryl bromides with K4[Fe(CN)6] in 1,4-dioxane-water mixtures than its less sterically congested isomer L1.…”

Remote meta‐C–H Cyanation of Arenes Enabled by a Pyrimidine‐Based Auxiliary

“…Notably, silyl-bridged directing groups were used owing to their ease installation/removal and modification. [4,9] Accordingly,w ee xamined fluorinated pyridyl directing groups (as in 3 and 4)and an improved yield relative to the parent pyridyl-based directing group was obtained. Upon transmetalation of the cyanide ion, the palladium metal center is expected to be more electron dense and therefore,t he appropriate pacidic ligand is required to stabilize the short-lived intermediate.…”

“…[2] In this regard, meta-a nd paraselective CÀHb ond activation of aromatic arenes stand as worthy examples. [3][4][5] Recently, meta-C À Ha lkylation and alkenylation have been achieved with the aid of strong coordinating pyrimidine-based template. [3][4][5] Recently, meta-C À Ha lkylation and alkenylation have been achieved with the aid of strong coordinating pyrimidine-based template.…”