1-Ferrocenylmethyl-3-(2,4,6-tri­methyl­benzyl)-1H-imidazolidin-3-ium iodide and trans-bis­(3-benzyl-1-ferrocenylmethyl-1H-imidazolidin-2-yl­idene)diiodidopalladium(II)

Owing to increasing inter­est in the use of N-heterocyclic carbenes (NHCs) based on imidazolidinium ions as ligands in the design of highly efficient transition-metal-based homogeneous catalysts, the characterizations of the 1-ferrocenylmethyl-3-(2,4,6-trimethyl­benzyl)imidazolidin-3-ium iodide salt, [Fe(C₅H₅)(C₁₉H₂₄N₂)]I, (I), and the palladium complex trans-bis­(3-benzyl-1-ferrocenylmethyl-1H-imidazolidin-2-yl­idene)diiodidopalladium(II), [Fe₂Pd(C₅H₅)₂(C₁₆H₁₇N₂)₂I₂], (II), are re­ported. Compound (I) has two iodide anions and two imidazolidinium cations within the asymmetric unit (Z′ = 2). The two cations have distinctly different con­formations, with the ferrocene groups orientated exo and endo with respect to the N-heterocyclic carbene. Weak C—H donor hydrogen bonds to both the iodide anions and the π system of the mesitylene group combine to form two-dimensional layers perpendicular to the crystallographic c direction. Only one of the formally charged imidazolidinium rings forms a near-linear hydrogen bond with an iodide anion. Complex (II) shows square-planar coordination around the Pd^II metal, which is located on an inversion centre (Z′ = 0.5). The ferrocene and benzyl substituents are in a trans–anti arrangement. The Pd—C bond distance between the N-heterocyclic carbene ligands and the metal atom is 2.036 (7) Å. A survey of related structures shows that the lengthening of the N—C bonds and the closure of the N—C—N angle seen here on metal complexation is typical of similar NHCs and their complexes.