A new stable CNHCCHCNHCN-heterocyclic dicarbene ligand: its mono- and dinuclear Ir(i) and Ir(i)–Rh(i) complexesElectronic supplementary information (ESI) available: The formula of ligands and complexes described in this paper, the NMR spectra of compounds 1–11and the CIF files for compounds 6and 9. CCDC reference numbers 706832 and 719957. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/b902733e

The ligand [(1,3-phenylene)bis(methylene)]bis(1-ethyl-imidazol-2-ylidene) (2) (abbreviated as EtCNHCCHCNHCwith CH = central aromatic ring, = CH2spacer) has been synthesised, and isolated, by deprotonation of [(1,3-phenylene)bis(methylene)]bis(1-ethyl-imidazolium) dichloride, Et(CHimid.CHCHimid.)Cl2(1) with LiN(SiMe3)2. This new, remarkably stable NHC dicarbene ligand is quantitatively protonated with HBr to form [(1,3-phenylene)bis(methylene)]bis(1-ethyl-imidazolium) dibromide Et(CHimid.CHCHimid.)Br2(3) and reprotonated slowly enough in MeOH to allow observation of the monoprotonated intermediate 4. Dicarbene 2reacts with S8to give the dithione compound [(1,3-phenylene)bis(methylene)]bis(1-ethyl-imidazol-2-thione) Et[(SC)CH(CS)] (6). Reaction of 2with [IrCl(CO)(PPh3)2] and [Ir(μ-Cl)(cod)]2yielded the mononuclear [Ir(CO)(PPh3)2Et(CHimid.CHCNHC)(PF6)](PF6) (8) and [IrCl(cod)Et(CHimid.CHCNHC)](PF6) (10) complexes, respectively, and the dinuclear complexes [{Ir(CO)(PPh3)2}2Et(μ-CNHCCHCNHC)](PF6)2(7) and [{IrCl(cod)}2Et(μ-CNHCCHCNHC)] (9), respectively, in which 2acts as a bridging, non-pincer type ligand. Only one other Ir(i) complex has been reported before containing a CNHCCHCNHCligand. The structures of 6and 9were determined by X-ray diffraction and depict different conformations of the (1,3-phenylene)bis(methylene) (or xylylene) moiety. The mononuclear Ir complex 9reacted smoothly with [Rh(μ-Cl)(cod)]2and Cs2CO3to generate a rare example of a heteronuclear NHC complex, [IrRhCl2(cod)2Et(μ-CNHCCHCNHC)] (11). [ABSTRACT FROM AUTHOR]