Selective and adaptable access to N,N-asymmetrically substituted imidazol-2-ylidene bis-NHC ligands: Pd(ii) complexes featuring wide variation in N-alkyl and aryl steric bulkCCDC 913061913064, 913066913068 for 47, 5a, S1 and S2. For crystallographic data in CIF or other electronic format see DOI: 10.1039/c3dt32895c

N , N -Asymmetrically substituted, methylene-linked bis(imidazol-2-ylidene) complexes have been prepared subsequent to a selective synthesis of the bis(imidazolium) salt precursors involving the quarternisation of N -alkyl and -aryl imidazoles with N -halomethyl imidazolium salts. The adaptability of the ligand precursor synthesis is illustrated through access to the N -Me/ N -Mes and N -Mes/ N -2,6-(i-Pr) 2 Ph systems, leading to the Pd( ii ) complexes [{(MeIm)(MesIm)CH 2 }Pd(L) 2 ] n + , L = Cl/I ( n = 0) and NCMe ( n = 2), and [{(MesIm)[2,6-(i-Pr) 2 PhIm]CH 2 }Pd(L) 2 ], L = Cl/I. The dicationic hybrid N , N -alkyl/aryl complex was inactive in the copolymerisation of ethylene/carbon monoxide, displaying reactivity akin to N , N -dialkyl analogues. The first N , N -asymmetrically substituted, methylene-linked bis(imidazol-2-ylidene) complexes are reported. Adaptability of the ligand synthesis is illustrated by steric variations in N -alkyl/ N -aryl and mixed N , N -diaryl systems.