The Cyanation of Aromatic Halides Catalyzed by Nickel(0) Complexes Generated In Situ. III. Kinetic and Mechanistic Aspects

Abstract

The cyanation of chlorobenzene catalyzed by [Ni(PPh3)n], which was generated in situ from [NiBr2(PPh3)2]–Zn–PPh3 (Ni:Zn:P = 1:3:2 molar ratio), was carried out at 60 °C using KCN or NaCN in hexamethyl phosphoric triamide (HMPA). Kinetic analyses revealed that the reaction rates in the KCN–HMPA system were zero order for both of chlorobenzene and nickel concentrations, and two-thirds order for KCN. The determination of the kinetic order for NaCN was difficult due to its high solubility in HMPA since excess cyanide ion inhibited the reaction. Zinc bromide which was formed with [Ni(PPh3)n] from [NiBr2(PPh3)2]–Zn–PPh3, acted as an important cocatalyst for the successful cyanation by comparison with [Ni(cod)2] (cod = 1,5-cyclooctadiene)–PPh3 system. Based on these experimental results, a reaction mechanism was proposed and discussed.

New Bifunctional Bis(azairidacycle) with Axial Chirality via Double Cyclometalation of 2,2′-Bis(aminomethyl)-1,1′-binaphthyl

“…The cyanation of aryl halides and pseudo-halides with cyanide salts has been disclosed by using Ni or Pd catalysts [ 37 , 38 , 39 , 40 , 41 , 42 , 43 ]. To overcome catalyst deactivation by cyanide anion due to its strong coordination ability, some Cu and Zn cocatalysts have been reported to be effective [ 44 , 45 ].…”

Ex situ generation of stoichiometric HCN and its application in the Pd-catalysed cyanation of aryl bromides: evidence for a transmetallation step between two oxidative addition Pd-complexes

“…2 Conventional means for the instalment of a cyanide group onto an aromatic ring include the Rosenmund-von Braun or Sandmeyer reactions applying stoichiometric CuCN with aryl halides or diazonium salts. 3 Yet, in the last decade, transition metal catalysed cyanations of aromatic halides with metal complexes based on copper, 4 nickel 5 and palladium 6 , 7 have held a key position. In particular, the protocols based on Pd-catalysis through the extensive work by Beller, 7 Grushin 8 and Buchwald 9 are characterised by relatively mild reaction conditions and good functional group tolerance.…”

A Versatile Protocol for Copper‐Catalyzed Cyanation of Aryl and Heteroaryl Bromides with Acetone Cyanohydrin

“…This procedure is complementary to the recently developed cyanation reactions using K 4 [Fe(CN) 6 ]. Advantageously, the method allows a precise control of the critical cyanide concentration in solution by variation of the dosage rate.…”

“…In addition, it is the most toxic of the three metals. [6] Copper-based catalysts show lower activity, but are also lower in price, and have a comparatively lower environmental impact.…”

“…[11] This problem can be circumvented by decreasing the solubility of cyanide in the respective solvent, or by using salts or complexes that deliver CN À slowly, for example, K 4 [Fe(CN) 6 ]. However, for larger scale (> kg-scale) applications it is desirable to control the concentration of CN À even more precisely.…”