Abstract
A model palladium‐mediated carbonylation reaction synthesizing N‐benzylbenzamide from iodobenzene and benzylamine was used to investigate the potential of four N‐heterocyclic carbenes (N,N′‐bis(diisopropylphenyl)‐4,5‐dihydroimidazolinium chloride (I), N,N′‐bis(1‐mesityl)‐4,5‐dihydroimidazolinium chloride (II), N,N′‐bis(1‐mesityl)imidazolium chloride (III) and N,N′‐bis(1‐adamantyl)imidazolium chloride (IV)) to act as supporting ligands in combination with Pd~2~(dba)~3~. Their activities were compared with other Pd‐diphosphine complexes after reaction times of 10 and 120 min. Pd~2~(dba)~3~ and III were the best performing after 10 min reaction (20%) and was used to synthesize radiolabelled [^11^C]N‐benzylbenzamide in good radiochemical yield (55%) and excellent radiochemical purity (99%). A Cu(Tp*) complex was used to trap the typically unreactive and insoluble [^11^C]CO which was then released and reacted via the Pd‐mediated carbonylation process. Potentially useful side products [^11^C]N,N′‐dibenzylurea and [^11^C]benzoic acid were also observed. Increased amounts of [^11^C]N,N′‐dibenzylurea were yielded when PdCl~2~ was the Pd precursor. Reduced yields of [^11^C]benzoic acid and therefore improved RCP were seen for III/Pd~2~(dba)~3~ over commonly used dppp/Pd~2~(dba)~3~ making it more favourable in this case. Copyright © 2010 John Wiley & Sons, Ltd.