Metal catalyzed, cyanation mechanisms

The reaction took place either via the ArSsl or via the AtSn2 mechanism (see Scheme 14.1, paths h,c), and occurred successfully via the first mechanism when using aryl hahdes or esters with electron-donating substituents. Among halides, both aryl chlorides and fluorides underwent photosubstitution when irradiated in an aqueous MeCN solution of KCN (Scheme 14.10, left part) [59]. It should be noted that, in transition metal-catalyzed reactions, the substitution of a chloro- by a cyano-group occurs only under relatively harsh reaction conditions, whereas such a process does not take place at all with aryl fluorides [57]. In the case of aryl esters the photoinduced cyanation occurred conveniently. As esters are easily... 

Due to their importance for research but also for industrial chemistry, transition metal based catalysts are intensively investigated. Ananikov et al. [684] reviewed various appUcatimis of hybrid ONIOM methods within this field. This review involves reaction mechanisms and enantioselective reactions of transition metal complexes, e.g. Ti-catalyzed cyanation of benzaldehyde [685], Cu-catalyzed cyclopropanation [686], Mn-porphyrin catalyzed epoxidation of alkene [687], and Mo-catalyzed nitrogen activation [688]. These approaches involve QM/QM as well as QM/MM approaches. 

Recently, studies in urea synthesis have focused on transition-metal-catalyzed reactions. Buchwald et al. reported a Pd-catalyzed cross-coupling of aryl chlorides with sodium cyanate, which represented a practical way to synthesize unsymmet-rical ureas [50]. The protocol allows for the synthesis of unsymmetrical N,N -di-and A. A. A -trisubstituted ureas in one pot and is tolerant of a wide range of functional groups (Scheme 5.19). Insight into the mechanism of aryl isocyanate formation was gleaned through studies of the transmetalation and reductive... 

Scheme 11 General reaction mechanism for poly rare earth metal complex-catalyzed asymmetric cyanation and azidation...

---