High-Yield Syntheses of Sterically Demanding Bis(N-heterocyclic carbene) Complexes of Palladium,

The synthesis of bis(N-heterocyclic carbene) chelates of formula (E = spacer linkage; R = alkyl, aryl; X = halide) is presented via improved high-yielding, air-stable procedures (for E = CH 2 ). A detailed study of the intermediates involved in the preparation of (X = Br, I) provide evidence for the difficulty in extending our synthetic procedures to include chelates of different ring sizes and also in preparing the analogous nickel complexes.