Palladium complexes of N-heterocyclic carbenes displaying an unsymmetrical N -alkylfluorenyl/ N ′-aryl substitution pattern and their behaviour in Suzuki–Miyaura cross coupling

• Published in: Dalton transactions : an international journal of inorganic chemistry 2019, Vol.48 (38), p.14516-14529
• Main Authors: Almallah, Hamzé, Brenner, Eric, Matt, Dominique, Harrowfield, Jack, Jahjah, Mohamad, Hijazi, Akram
• Format: Article
• Language: English
• Subjects: Aromatic compounds; Carbenes; Chemical Sciences; Coordination compounds; Cross coupling; Crystallography; Diffraction patterns; Inorganic chemistry; Ligands; Nanoparticles; NMR; Nuclear magnetic resonance; Occupancy; Palladium; Single crystals; Substitutes
• ISSN: 1477-9226; 1477-9234; 1477-9234
• DOI: 10.1039/C9DT02948F

A series of new Pd–PEPPSI complexes containing imidazolylidene ligands with a mixed 9-alkyl-9-fluorenyl/aryl N , N ′-substitution pattern have been synthesised. Single crystal X-ray diffraction studies were carried out for four complexes, which revealed that the N-heterocyclic carbene ligands display a semi-open, unsymmetrical space occupancy about the metal. Despite their particular unsymmetrical shape, the new complexes were found to perform as well in Suzuki–Miyaura cross coupling (dioxane, 80 °C) as previously reported, highly active analogues bearing two sterically protecting 9-alkylfluorenyl substituents. They were further found to be considerably more active than the standard Pd–PEPPSI complexes [PdCl 2 IMes(pyridine)] and [PdCl 2 IPr(pyridine)]. Surprisingly, unlike the latter, the unsymmetrical complexes of this study were practically inactive in isopropanol at 80 °C. Under these conditions the complexes appear to decompose with formation of non-stabilised nanoparticles.