Non-symmetrically substituted di-N-heterocyclic carbene palladium(II) complexes: Synthesis, structure and catalytic activity

Chelating Bis(N‐Heterocyclic Carbene) Palladium‐Catalyzed Reactions

“…The authors further determined that transmetalation was the rate‐determining step, and thus, bulky side arms negatively impacted on the catalytic efficacy of these electron‐rich catalysts. Foley and co‐workers found that bulky substrates hindered the coupling reaction when unsymmetrical Pd–bis(NHC) complexes 56 and 57 were evaluated in the coupling of bulky aryl halides with aryl boronic acids . Again, the negligible impact of the nitrogen substituent on the catalytic performance was reported by Kühn and co‐workers when complexes 58 and 59 were employed as precatalysts in the coupling of phenylboronic acid with bromobenzene (TOF=400–460 h −1 after a reaction time of 24 h), 4‐bromoanisole (TOF=150–160 h −1 ) and 4‐bromoacetophenone (TOF=480–530 h −1 ), respectively …”

“…Foley and co-workers found that bulky substrates hindered the coupling reaction when unsymmetrical Pd-bis(NHC) complexes 56 and 57 were evaluated in the coupling of bulky aryl halides with aryl boronic acids. [39] Again, the negligible impacto ft he nitrogen substituent on the catalytic performance was reported by Kühn and co-workersw hen complexes 58 and 59 were employed as precatalysts in the coupling of phenylboronic acid with bromobenzene (TOF = 400-460h À1 after ar eaction time of 24 h), 4-bromoanisole (TOF = 150-160h À1 )a nd 4-bromoacetophenone (TOF = 480-530h À1 ), respectively. [40] As displayed in Figure 11, cis-chelating Pd-bis(NHC) complexes 60 and 61 with ab iphenyl spacerw ere achieved by Luo and co-workers.…”

An N-heterocyclic carbene-palladium-η3-allyl chloride complex for the Suzuki-Miyaura coupling of aryl halides

“…Nevertheless, the catalyst shows a good substrate scope for aryl bromides with excellent yields, even for deactivated substrates (Entries 3 to 5). Compared with other symmetric [28,29] and non-symmetric catalysts [30,31], complex 2 performs better, working under milder conditions and wider substrate scope.…”

N‐Heterocyclic Carbenes with Neutral Tethers

“…With the unsymmetric bis -carbene palladium(II) complexes coming from Foley ' s research group, we are again on fi rm ground: a square planar metal complex and sterically innocent wingtip groups (methyl, benzyl, p -Bu t -benzyl) let us suspect the preferred formation of a chelate complex and this is indeed what is observed [ 316 ].…”