Synthesis and crystal structures of palladium(II) complexes of bis-(N-heterocyclic carbenes) on a calix[4]arene platform

A series of calix[4]arene supported N-heterocyclic carbene palladium complexes were successfully prepared and characterised. Their X-ray crystal structures were obtained and are discussed. Notably, the dimeric compound b[5-(3-N-4,5-diphenylimidazol-2-yliden-1-yl)-25,26,27,28-tetrapropyloxy calix[4]arene] palladium(II) dibromide (cone) showed pseudo-polymorphism.